A chemical vapor deposition process for depositing silicon dioxide comprising the steps of heating a substrate upon which deposition is desired to a temperature of from about 325.degree. C. to about 700.degree. C. in a vacuum having a pressure of from about 0.1 to about 1.5 torr, and introducing a silane selected from the group consisting of alkylsilane, arylsilane and araylkylsilane wherein the alkyl-, aryl- or aralkyl- moiety comprises from 2-6 carbons, and oxygen or carbon dioxide into the vacuum.

It is standard practice in the manufacture of many semiconductor devices, and other devices, to provide a thin passive layer or coating of a chemically nonreactive or low reactivity material to protect the semiconductor junctions and layers from degradation by contact with oxygen, fumes in the air, moisture, etc., and from damage by contact during packaging and handling and to stabilize the electrical characteristics of the device.
The production of silicon oxide coatings application to semiconductor devices and to other devices is well known, and there is considerable literature on the subject. The general principles underlying the formation of thin films are described in HANDBOOK OF THIN FILM TECHNOLOGY, Maissell, Leon I. and Glang, Reinhard, editors, McGraw Hill Book Company, New York, 1970, and the general technology for processing silicon-based semiconductor devices in described in SILICON PROCESSING FOR THE VLSI ERA, Wolf, Stanley, and Talbert, Richard N., editors, Lattice Press, Sunset Beach, Calif., 1986, which includes a discussion of thin film technology.
The present invention relates to the manufacture of devices in which thin films of silicon oxides, SiO.sub.2 principally, are deposited on substrates. Economically, the greatest industrial application of this invention is in the manufacture of semiconductor devices; however, the discoveries of this invention are applicable to any thin film deposition of SiO.sub.2 on substrates which are capable of being heated to temperatures in the range of from about 300.degree. C. to about 600.degree. C.
The chemistry of silanes is described by Arkles, B., Peterson, W. R., Jr., KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, 3rd ed. Vol 20, 887-911. Silanes, also referred to as silicon hydrides, are compounds containing a hydrogen-silicon bond. Compounds which include only silicon-carbon bonds, i.e. where all hydrogens have been replaced by alkyl, aryl or aralkyl substituents are also referred to occasionally, and herein, as silanes.
The properties of organosilanes are determined largely by the properties of the silicon atom which is larger than the carbon atom, enabling nucleophilic attack on the silicon to occur more readily than on carbon. Electrophilic attack on hydrogen bonded to silicon is also facilitated by the small steric constraints of hydrogen and the increased bond length for Si--H. In addition to the increased bond length, the Si--H bond energy is considerably lower than C--H and is reflected in the thermal stabilities of such bonds. Organohydrosilanes begin to decompose at 440.degree.-460.degree. C. through homolytic cleavage of the Si--H bond and subsequent radical formation.
Organohydrosilanes undergo a wide variety of chemical conversions. The Si--H bond of organohydrosilanes reacts with elements of most groups of the periodic system. Organosilanes, the simplest of which is methylsilane, are stable to air. The larger-chain alkylsilanes are more stable but ignite spontaneously when vaporized in oxygen under pressure. Phenyl and cyclohexylsilane can be distilled open to the atmosphere. Trialkyl- and triarylsilanes are more stable and have been distilled at as much as 325.degree. C. without decomposition.
Alkylation and arylation of organosilanes occur readily with alkyl and aryl alkalimetal compounds with good yields, especially in tetrahydrofuran and ethyl ether according to the general reaction: EQU R.sub.n SiH.sub.1-n +(4-n)R'M.fwdarw.R.sub.n SiR'.sub.1-n +(4-n)MH
where R and R' are alkyl, aryl or aralkyl and M is Li, Na, or K and n=1 to 4.
The preparation of organosilanes by the direct process was first reported in 1945. By this method, CH.sub.3 SiH(Cl).sub.2, (CH.sub.3).sub.2 SiH(Cl).sub.2, and C.sub.2 H.sub.5 SiH(Cl).sub.2 are prepared and utilized as polymers and reactive intermediates. The synthesis involves the reaction of alkyl halides, e.g., methyl and ethyl chloride, with silicon metal or silicon alloys in a fluidized bed at 250.degree.-600.degree. C. Dialkylamino-substituted silanes have also been obtained by a similar process and similar products are formed by cleavage of disilanes by dialkylamines, e.g. diethylamine cleavage yielding [(C.sub.2 H.sub.5).sub.2 N].sub.2 SiH(Cl). Organosilanes can be synthesized most conveniently in pilot, bench, and lab scale by reduction of organic-substituted halo- and alkoxysilanes with metal hydrides. The versatility of lithium aluminum hydride permits synthesis of alkyl, alkenyl, and arylsilanes--silanes containing functional groups, such as chloro, amino, and alkoxyl in the organic substituents, can also be prepared. Organosilanes are also produced by reaction of organohalosilanes and organoalkoxysilanes with organometallic compounds. Organolithium reagents, e.g., t-butyllithium, have also produced organohydrosilanes on reaction with organo-chlorosilanes and tetrahalosilanes. Disproportionation reactions have also been used to prepare organosilanes. These reactions involve interaction of organosilanes with other silicon compounds containing organic, alkoxy, and halogen groups bound to silicon. Reactions are catalyzed by a variety of materials including alkali metals, alkali metal alcoholates, and Lewis acids, e.g., aluminum, zinc, iron, and boron halides. Organochlorosilanes containing Si--H disproportionate in the presence of aluminum chloride without addition of more organosilane. A wide variety of organosilanes are most commonly prepared through reaction of inorganic and organo-chlorosilanes with Grignard reagents. Organosilanes containing mixed organic groups can be prepared by reaction of organodihalosilanes and diorganohalosilanes or alkoxy derivatives with alkyl or aryl Grignards. Organohydrosilanes can also be prepared by addition of halosilanes and organosilanes containing multiple Si--H bonds to olefins. These reactions are catalyzed by platinum, platinum salts, peroxides, ultraviolet light, or ionizing radiation.
The low pressure chemical vapor deposition (LPCVD) process which will be discussed herein and which is of principle interest in this invention involves the deposition of films from gaseous reagents in the pressure range of from about 100 mtorr to about 1000 mtorr in most instances, with operation being possible up to about 2000 mtorr in some particular examples, the latter pressure being intermediate APCVD and LPCVD operation.
A large variety of "thin films" are used in the fabrication of Very Large Scale Integration (VLSI) devices. These films may be thermally grown or deposited from the vapor phase. They can be metals, semiconductors, or insulators.
Thin films for use in VLSI fabrication must satisfy a large set of rigorous chemical, structural, and electrical requirements. Film composition and thickness must be strictly controlled to facilitate etching of submicron features. Very low densities of both particulate defects and film imperfections, such as pinholes, become critical for the small linewidths, high densities, and large areas necessary for VLSI. These small geometries also create highly rugged topography for overlying films to cover. Therefore, excellent adhesion, low stress, and conformal step coverage are required of a VLSI thin film, and its own surface topography should reduce or even planarize the underlying steps if possible. Finally, non-conducting thin films must have low dielectric constants to reduce parasitic capacitances exacerbated by the scaled down film thicknesses.
Although the properties of a bulk material may be well characterized, the same material in its thin film form may have properties substantially different from those of the bulk. One reason is that thin film properties are strongly influenced by surface properties, while in bulk materials this is not the case. The thin film, by its very definition has a substantially higher surface-to-volume ratio than does a bulk material. The structure of thin films, and their method of preparation also play a vital role in determining the film properties.
The formation of such films is accomplished by a large variety of techniques, but which can conceptually be divided into two groups: (1) film growth by interaction of a vapor-deposited species with the substrate; and (2) film formation by deposition without causing changes to the substrate material. The first category includes thermal oxidation and nitridation of single crystal silicon and polysilicon and the formation of silicides by direct reaction of a deposited metal and the substrate.
The second group includes another three subclasses of deposition: (a) chemical vapor deposition, or CVD, in which solid films are formed on a substrate by the chemical reaction of vapor phase chemicals that contain the required constituents; (b) physical vapor deposition, or PVD, in which the species of the thin film are physically dislodged from a source to form a vapor which is transported across a reduced pressure region to the substrate, where it condenses to form the thin film; and (c) coating of the substrate with a liquid, which is then dried to form the solid thin film. When CVD process are used to form single-crystal thin films, the process is termed epitaxy. The formation of thin films by PVD includes the processes of sputtering and evaporation.
Thin film generally have smaller grain size than do bulk materials. Grain size is a function of the deposition conditions and annealing temperatures. Larger grains are observed for increased film thickness, with the effect increasing with increasing substrate or deposition temperature. The initial deposition temperature plays an important role in determining the final grain size. The dependence on deposition rate is due to the fact that even if clusters have high mobility, at high deposition rate they are quickly buried under subsequent layers. For very high deposition rates, the heat of condensation can raise the substrate temperature, thereby producing increased grain size from thermal effects.
The surface roughness of films occurs as a result of the randomness of the deposition process. Real films almost always show surface roughness, even though this represents a higher energy state than that of a perfectly flat film. Depositions at high temperatures tend to show less surface roughness. This is because increased surface mobility from the higher substrate temperatures can lead to filling of the peaks and valleys. On the other hand, higher temperatures can also lead to the development of crystal facets, which may continue to grow in favored direction, leading the increased surface roughness. At low temperatures the surface roughness as measured by surface area, tends to increase with increased film thickness. Oblique deposition which results in shadowing, also increases surface roughness. Epitaxial and amorphous deposits have shown measured surface area nearly equal to the geometrical area, implying the existence of very flat films. This has been confirmed by Scanning Electron Micrography (SEM) examination of these films. Surface roughness has also been observed to increase as a result of the presence of contamination on the substrate or in the vapor phase during deposition.
The density of a thin film provides information about its physical structure. Density is usually determined by weighing the film and measuring its volume. If a film is porous from the deposition process, it generally has a lower density than bulk material.
The crystallographic structure of thin films depends on the adatom mobility, and can vary from a highly disordered or amorphous-like, state, to a well-ordered state e.g. epitaxial growth on a single crystal substrate. The amorphous structures are frequently observed for the deposited dielectrics such as SiO.sub.2, SiO, and Si.sub.3 N.sub.1, while most metals result in polycrystalline structure. Silicon can be either amorphous, polycrystalline, or single crystal, depending on the deposition parameters and the substrate material.
Some polycrystalline films deposit with a fiber texture or preferred orientation. This texture can be described as having a preponderance of grains with the same orientation in a direction normal to the substrate. Deposition of polycrystalline Si on SiO.sub.2 can occur in this manner. The observed fiber texture in that case has been reported as for poly-Si deposited at 600.degree.-650.degree. C.
Nearly all films are found to be in a state of internal stress, regardless of the means by which they have been produced. The stress may be compressive or tensile. Compressively stressed films would like to expand parallel to the substrate surface, and in the extreme, films in compressive stress will buckle up on the substrate. Films in tensile stress, on the other hand, would like to contract parallel to the substrate, and may crack if their elastic limits are exceeded. In general, the stresses in thin films are in the range of 10.sup.8 -5.times.10.sup.10 dynes/cm.sup.2. Highly stressed films are generally undesirable for VLSI applications for several reasons, including: (a) they are more likely to exhibit poor adhesion; (b) they are more susceptible to corrosion; (c) brittle films, such as inorganic dielectrics, may undergo cracking in tensile stress; and (d) the resistivity of stressed metallic films is higher than that of their annealed counterparts.
The intrinsic stress reflects the film structure in ways not yet completely understood. It has been observed that the intrinsic stress in a film depends on thickness, deposition rate, deposition temperature, ambient pressure, method of film preparation, and type of substrate used, among other parameters.
At low substrate temperatures, metal films tend to exhibit tensile stress. This decreases with increasing substrate temperature, often in a linear manner, finally going through zero or even becoming compressive. The changeover to compressive stress occurs at lower temperatures for lower melting point metals.
The effect of deposition rate on film stress is ambiguous. The film stress starts out tensile, decreases as the power increases, and finally becomes compressive with further power increase. Several models relating to the origins of intrinsic stress have been proposed. These invoke the following stress-causing mechanisms: (a) lattice mismatch between the substrate and the film; (b) rapid film growth which locks in defects; and (c) incorporation of impurities into the film.
A Chemical Vapor Deposition (CVD) process can be summarized as consisting of the following sequence of steps: (a) a given composition and flow rate of reactant gases and diluent inert gases is introduced into a reaction chamber; (b) the gas species move to the substrate; (c) the reactants are adsorbed on the substrate; (d) the adatoms undergo migration and film-forming chemical reactions, and (e) the gaseous by-products of the reaction are desorbed and removed from the reaction chamber. Energy to drive the reactions can be supplied by several methods, e.g. thermal, photons, or electrons, with thermal energy being the most commonly used.
In practice, the chemical reactions of the reactant gases leading to the formation of a solid material may take place not only on or very close to the wafer surface, a heterogeneous reaction, but also in the gas phase, a homogeneous reaction. Heterogeneous reactions are much more desirable, as such reactions occur selectively only on heated surfaces, and produce good quality films. Homogeneous reactions, on the other hand, are undersirable, as they form gas phase clusters of the depositing material, which can result in poorly adhering, low density films, or defects in the depositing film. In addition, such reactions also consume reactants and can cause decreases in deposition rates. Thus, one important characteristic of a chemical reaction for CVD application is the degree to which heterogeneous reactions are favored over gas phase reactions.
Since the aforementioned steps of a CVD process are sequential, the one which occurs at the slowest rate will determine the rate of deposition. The steps can be grouped into (1) gas-phase processes, and (2) surface processes. The gas phase phenomenon of interest is the rate at which gases impinge on the substrate. This is modeled by the rate at which gases cross the boundary layer that separates the bulk regions of flowing gas and substrate surface. Such transport processes occur by gas-phase diffusion, which is proportional to the diffusivity of the gas, D, and concentration gradient across the boundary layer. The rate of mass transport is only relatively weakly influenced by temperature.
Several surface processes can be important once the gases arrive at the hot substrate surface, but the surface reaction, in general, can be modeled by a thermally activated phenomenon which proceeds at a rate which is a function of the frequency factor, the activation energy, and the temperature. The surface reaction rate increases with increasing temperature. For a given surface reaction, the temperature may rise high enough so that the reaction rate exceeds the rate at which reactant species arrive at the surface. In such cases, the reaction cannot proceed any more rapidly than the rate at which reactant gases are supplied to the substrate by mass transport, no matter how high the temperature is increased. This situation is referred to as a mass-transport limited deposition process.
On the other hand, at lower temperatures, the surface reaction rate is reduced, and eventually the arrival rate of reactants exceeds the rate at which they are consumed by the surface reaction process. Under such conditions the deposition rate is reaction rate limited. Thus, at high temperatures, the deposition is usually mass-transport limited, while at lower temperatures it is surface-reaction rate-limited. In actual processes the temperature at which the deposition condition moves from one of these growth regimes to the other is dependent on the activation energy of the reaction, and the gas flow conditions in the reactor. Thus, it is impossible to extrapolate with any certainty or accuracy date or process conditions or results from one pressure regime or temperature regime to another.
In processes that are run under reaction rate-limited conditions, the temperature of the process is an important parameter. That is, uniform deposition rates throughout a reactor require conditions that maintain a constant reaction rate. This in turn implies that a constant temperature must also exist everywhere at all wafer surfaces. On the other hand, under such conditions the rate at which reactant species arrive at the surface is not as important, since their concentration does not limit the growth rate. Thus, it is not as critical that a reactor be designed to supply an equal flux of reactants to all locations of a wafer surface. It will be seen that in low-pressure CVD (LPCVD) reactors, wafers can be stacked vertically and at very close spacing because such systems operate in a reaction rate limited mode. The reason for this is as follows:
Under the low pressure of an LPCVD reactor .about.1 torr the diffusivity of the gas species is increased by a factor of 1000 over that at atmospheric pressure, and this is only partially offset by the fact that the boundary layer, the distance across which the reactants must diffuse, increases by less than the square root of the pressure. The net effect is that there is more than an order of magnitude increase in the transport of reactants to and by-products away from the substrate surface, and the rate-limiting step is thus the surface reaction.
In deposition processes that are mass-transport limited, however, the temperature control is not nearly as critical. As mentioned earlier, the mass transport process which limits the growth rate is only weakly dependent on temperature. On the other hand, it is very important that the same concentration of reactants be present in the bulk gas regions adjacent to all locations of a wafer, as the arrival rate is directly proportional to the concentration in the bulk gas. Thus, to insure films of uniform thickness across a wafer, reactors which are operated in the mass transport limited regime must be designed so that all locations of wafer surfaces and all wafers in a run are supplied with an equal flux of reactant species. Atmospheric pressure reactors that deposit SiO.sub.2 at .about.400.degree. C. operate in the mass-transport limited regime. The most widely used APCVD reactor designs provide a uniform supply of reactants by horizontally positioning the wafers and moving them under a gas stream.
CVD systems usually contain the following components: (a) gas sources; (b) gas feed lines; (c) mass-flow controllers for metering the gases into the system; (d) a reaction chamber or reactor; (e) a method for heating the wafers onto which the film is to be deposited, and in some types of systems, for adding additional energy by other means; and (f) temperature sensors. LPCVD and PECVD systems also contain pumps for establishing the reduced pressure and exhausting the gases from the chamber.
The design and operation of CVD reactors depends on a variety of factors, and hence they can be categorized in several ways. The first distinction between reactor types is whether they are hot-wall or cold-wall reactors, and this is dependent on the method used to heat the wafers. The next criterion used to distinguish reactor types is their pressure regime of operation atmospheric pressure or reduced pressure reactors. Finally, the reduced pressure group is split into: (a) low-pressure reactors the so called low-pressure CVD, or LPCVD reactors, in which the energy input is entirely thermal; and (b) those in which energy is partially supplied by a plasma as well known as plasma-enhanced CVD, or PECVD reactors. Each of the reactor types in the two pressure regimes are further divided into sub-groups, defined by reactor configuration and method of heating.
Table 1 summarizes the characteristics and applications of the various CVD reactor designs.
TABLE I __________________________________________________________________________ Characteristics and Applications of CVD Reactors Process Advantages Disadvantages Applications __________________________________________________________________________ APCVD Simple Reactor, Poor Step Cover- Low Temperature Low Tem- Fast Deposition, age, Particle Oxides, both doped and perature Deposition, Low Contamination undoped Temperature LPCVD Excellent Purity High Temperature High Temperature and Uniformity, Low Deposition Oxides, both doped Conformal Step Rate and undoped, Silicon Coverage, Large Nitride, Poly-Si, W, Wafer Capacity WSI.sub.2 PECVD Low Temperature, Chemical, e.g. H.sub.2 Low Temperature Fast Deposition, and Particulate Insulators over Metals, Good Step Cover- Contamination Passivation - Nitride age __________________________________________________________________________
Low pressure chemical vapor deposition (LPCVD) in some cases is able to overcome the uniformity, step coverage, and particulate contamination limitations of early APCVD systems. By operating at medium vacuum, 0.25-2.0 torr, and higher temperatures, 550.degree.-600.degree. C., LPCVD reactors typically deposit films in the reaction rate limited regime. At reduced pressure the diffusivity of the reactant gas molecules is sufficiently increased so that mass-transfer to the substrate no longer limits the growth rate. The surface reaction rate is very sensitive to temperature, but precise temperature control is relatively easy to achieve. The elimination of mass-transfer constraints on reactor design allows the reactor to be optimized for high wafer capacity. Low pressure operation also decreases gas phase reactions, making LPCVD films less subject to particulate contamination. LPCVD is used for depositing many types of films, including poly-Si, Si.sub.3 N.sub.4, SiO.sub.2, PSG, BPSG, and W.
The two main disadvantages of LPCVD are the relatively low deposition rates, and the relatively high operating temperatures. Attempting to increase deposition rates by increasing the reactant partial pressures, tends to initiate gas phase reactions. Attempting to operate at lower temperatures, results in unacceptably slow film deposition. One of the features of the present invention is the discovery that by using selected deposition source reagents, rather than methyl-containing reagents and the like which have been traditional, greatly increased deposition rates can be accomplished without the deleterious reactions and poor results which have plagued the industry for so many years.
LPCVD reactors are designed in two primary configurations: (a) horizontal tube reactors; and (b) vertical flow isothermal reactors.
Horizontal tube, hot wall reactors are the most widely used LPCVD reactors in VLSI processing. They are employed for depositing poly-Si, silicon nitride, and undoped and doped SiO.sub.2 films. They find such broad applicability primarily because of their superior economy, throughput, uniformity, and ability to accommodate large diameter, e.g. 150 mm wafers. Their main disadvantages are susceptibility to particulate contamination and low deposition rates.
The vertical flow isothermal LPCVD reactor further extends the distributed gas feed technique, so that each wafer receives an identical supply of fresh reactants. Wafers are again stacked side by side, but are placed in perforated-quartz cages. The cages are positioned beneath long, perforated, quartz reaction-gas injector tubes, one tube for each reactant gas. Gas flows vertically from the injector tubes, through the cage perforations, past the wafers, parallel to the wafer surface and into exhaust slots below the cage. The size, number, and location of cage perforations are used to control the flow of reactant gases to the wafer surfaces. By properly optimizing cage perforation design, each wafer can be supplied with identical quantities of fresh reactants from the vertically adjacent injector tubes. Thus, this design can avoid the wafer-to-wafer reactant depletion effects of the end-feed tube reactors, requires no temperature ramping, produces highly uniform depositions, and reportedly achieves low particulate contamination.
The third and last of the major CVD deposition methods is categorized not only by pressure regime, but also by its method of energy input. Rather than relying solely on thermal energy to initiate and sustain chemical reactions, plasma enhanced CVD, or PECVD uses an rf-induced glow discharge to transfer energy into the reactant gases, allowing the substrate to remain at a lower temperature than in APCVD or LPCVD processes. Lower substrate temperature is the major advantage of PECVD, and in fact, PECVD provides a method of depositing films on substrates that do not have the thermal stability to accept coating by other methods, the most important being the formation of silicon nitride and SiO.sub.2 over metals. In addition, PECVD can enhance the deposition rate when compared to thermal reactions alone, and produce films of unique compositions and properties. Desirable properties such as good adhesion, low pinhole density, good step coverage, adequate electrical properties, and compatibility with fine-line pattern transfer processes, have led to application of these films in VLSI.
The plasma, also referred to as a glow discharge, which is defined as a partially ionized gas containing an equal number of positive and negative charges, as well as some other number of non-ionized gas particles is generated by the application of a radio frequency field to a low pressure gas, thereby creating free electrons within the discharge region. The electrons gain sufficient energy from the electric field so that when they collide with gas molecules, gas-phase dissociation and ionization of the reactant gases, e.g. silane and nitrogen or oxygen-containing species then occurs.
The energetic particles used to strike target materials to be sputtered in VLSI sputter deposition systems are generated by glow-discharges. A glow-discharge is a self-sustaining type of plasma.
The energetic species are then adsorbed on the film surface. The radicals tend to have high sticking coefficients, and also appear to migrate easily along the surface after adsorption. These two factors can lead to excellent film conformality. Upon being adsorbed on the substrate, they are subjected to ion and electron bombardment, rearrangements, reactions with other adsorbed species, new bond formations and film formation and growth. Adatom rearrangement includes the diffusion of the adsorbed atoms onto stable sites and concurrent desorption of reaction products. Desorption rates are dependent on substrate temperature, and higher temperatures produce films with fewer entrapped by-products. Gas-phase nucleation should be avoided to reduce particulate contamination.
The fact that the radicals formed in the plasma discharge are highly reactive presents some options, as well as some problems, to the process engineer. PECVD films, in general, are not stoichiometric because the deposition reactions are so varied and complicated. Moreover, by-products and incidental species are incorporated into the resultant films, especially hydrogen, nitrogen, and oxygen, in addition to the desired products. Excessive incorporation of these contaminants may lead to outgassing and concomitant bubbling, cracking, or peeling during later thermal cycling, and to threshold shifts in MOS circuits.
A plasma process requires control and optimization of several deposition parameters besides those of an LPCVD process, including rf power density, frequency, and duty cycle. The deposition process is dependent in a very complex and interdependent way on these parameters, as well as on the usual parameters of gas composition, flow rates, temperature, and pressure. Furthermore, as with LPCVD, the PECVD method is surface reaction limited, and adequate substrate temperature control is thus necessary to ensure film thickness uniformity.
Chemical vapor deposited (CVD) SiO.sub.2 films, and their binary and ternary silicates, find wide use in VLSI processing. These materials are used as insulation between polysilicon and metal layers, between metal layers in multilevel metal systems, as getters, as diffusion sources, as diffusion and implantation masks, as capping layers to prevent outdiffusion, and as final passivation layers. In general, the deposited oxide films must exhibit uniform thickness and composition, low particulate and chemical contamination, good adhesion to the substrate, low stress to prevent cracking, good integrity for high dielectric breakdown, conformal step coverage for multilayer systems, low pinhole density, and high throughput for manufacturing.
CVD silicon dioxide is an amorphous structure of SiO.sub.4 tetrahedra with an empirical formula SiO.sub.2. Depending on the deposition conditions, as summarized in Table 2, CVD silicon dioxide may have lower density and slightly different stoichiometry from thermal silicon dioxide, causing changes in mechanical and electrical film properties, such as index of refraction, etch rate, stress, dielectric constant and high electric-field breakdown strength. Deposition at high temperatures, or use of a separate high temperature post-deposition anneal step, referred to as densification can make the properties of CVD films approach those of thermal oxide.
TABLE 2 __________________________________________________________________________ Properties of CVD and Thermal Silicon Film Type Thermal PECVD APCVD SiCl.sub.2 H.sub.2 + N.sub.2 O TEOS __________________________________________________________________________ Deposition 800-1200 200 450 900 700 Temp. (.degree.C.) Step Cover Conformal Good Poor Conformal Conformal age Stress (.times. 10.sup.9 3C 3C-3T 3T 3T 1C-2T dynes/cm.sup.2) Dielectric 6-10 8 10 10 3-6 Strength (10.sup.6 V/cm) Etch Rate 400 60 30 30 (.ANG./min): (100;1, H.sub.2 O:HF) __________________________________________________________________________
Deviation of the CVD silicon dioxide film's refractive index, n, from that of the thermal SiO.sub.2 value of 1.46 is often used as an indicator of film quality. A value of n greater than 1.46 indicates a silicon rich film, while smaller values indicate a low density, porous film. CVD SiO.sub.2 is deposited with or without dopants, and each type has unique properties and applications.
There are various reactions that can be used to prepare CVD SiO.sub.2. The choice of reaction is dependent on the temperature requirements of the system, as well as the equipment available for the process. The deposition variables that are important for CVD SiO.sub.2 include: temperature, pressure, reactant concentrations and their ratios, presence of dopant gases, system configuration, total gas flow, and wafer spacing. There are three temperature ranges in which SiO.sub.2 is formed by CVD, each with its own chemical reactions and reactor configurations. There are: (1) low temperature deposition, 300.degree.-450.degree. C.; (2) medium temperature deposition, 650.degree.-750.degree. C.; and (3) high temperature deposition, .about.900.degree. C.
The low temperature deposition of SiO.sub.2 utilizes a reaction of silane and oxygen to form undoped SiO.sub.2 films. The depositions are carried out in APCVD reactors, primarily of the continuous belt type, in distributed feed LPCVD reactors, or in PECVD reactors. The depletion effect precludes the use of conventional LPCVD for the SiH.sub.4 +O.sub.2 reaction. The addition of PH.sub.3 to the gas flow forms P.sub.2 O.sub.5, which is incorporated into the SiO.sub.2 film to produce a phosphosilicate glass (PSG). The reactions are given by: EQU SiH.sub.4 +O.sub.2 .fwdarw.SiO.sub.2 +2H.sub.2 EQU 4PH.sub.3 +5O.sub.2 .fwdarw.2P.sub.2 O.sub.5 +6H.sub.2
The reaction between silane and excess oxygen forms SiO.sub.2 by heterogeneous surface reaction. Homogeneous gas-phase nucleation also occurs, leading to small SiO.sub.2 particles that form a white powder on the reaction chamber walls, and which may potentially cause particulate contamination in the deposited films.
The deposition rate increases slowly with increased temperature between 310.degree. and 450.degree. C. An apparent activation energy of less than 0.4 eV has been measured which is indicative of a surface adsorption or gas phase diffusion deposition process. The deposition rate can be increased at constant temperature, up to a limit by increasing the O.sub.2 :SiH.sub.4 ratio. Continued increase in the ratio eventually results in a decrease in deposition rate, as a result of O.sub.2 being adsorbed on the substrate, thus inhibiting the SiH.sub.4 decomposition.
Silicon dioxide films deposited at low temperatures exhibit lower densities than thermal SiO.sub.2, and have an index of refraction of .about.1.44. They also exhibit substantially higher etch rates in buffered hydrofluoric acid, HF solutions that thermal SiO.sub.2. Subsequent heating of such films to temperatures between 700.degree.-1,000.degree. C. causes densification. That is, this step causes the density of the material to increase from 2.1 g/cm.sup.3 to 2.2 g/cm.sup.3, the film thickness to decrease, and the etch rate in HF to decrease.
SiO.sub.2 can also be deposited by a plasma enhanced reaction between SiH.sub.4 and N.sub.2 O, nitrous oxide or O.sub.2 at temperatures between 200.degree.-400.degree. C. ##STR1##
Nitrogen and/or hydrogen is often incorporated in PECVD SiO.sub.2. A low ratio of N.sub.2 O/SiH.sub.4 will increase the index of refraction, due to large amounts of nitrogen incorporated in the film and the formation of silicon rich films. Nearly stoichiometric, n=1.46, plasma oxide films can be achieved by reacting SiH.sub.4 and O.sub.2 mixtures. The buffered HF etch rate is a sensitive measure of the film's stoichiometry and density. Lower deposition temperatures and higher N.sub.2 O/SiH.sub.4 ratios lead to less dense films and faster etch rates. As with nitride films, PECVD oxides also contain 2-10 at % H.sub.2 in the form of Si--H, Si--O--H, and H--O--H. The hydrogen concentration is a strong function of the deposition parameters. Low deposition temperatures, high rf power, and high carrier-gas flow rates are required to prevent gas phase nucleation and its attendant particulate problems.
Plasma oxide films are generally deposited in compressive stress, with values ranging between 1.times.10.sup.8 -4.times.10.sup.9 dynes/cm.sup.2, depending on deposition temperature and rate. Dielectric strengths of 4-8.times.10.sup.6 V/cm, and dielectric constants ranging from 4-5 have been obtained. Low pinhole counts have been obtained with PECVD oxides, as have very conformal coatings. Adhesion to metal is also reported to be excellent.
In the medium temperature range, SiO.sub.2 is deposited in LPCVD reactors by decomposing tetraethosiloxane, Si(OC.sub.2 H.sub.5).sub.4, also known as tetraethyl orthosilicate, or TEOS. The deposition rate for TEOS shows an exponential increase with temperature in the range of 650.degree.-800.degree. C. with an apparent activation energy of 1.9 eV. This pronounced temperature dependence can lead to thickness control problems. The deposition rate is also dependent on the TEOS partial pressure. It is linearly dependent at low partial pressures, and tends to level off as the adsorbed TEOS saturates the surface. TEOS films generally show excellent conformality.
At high temperatures, near 900.degree. C., SiO.sub.2 is formed by an LPCVD process in which dichlorosilane and nitrous oxide are reacted. The reaction is given by: EQU SiH.sub.2 CL.sub.2 +2N.sub.2 O.fwdarw.SiO.sub.2 +2N.sub.2 +2HCl.
Such depositions produce films having excellent uniformity, and with properties close to those of thermal SiO.sub.2. High-temperature LPCVD is sometimes used to deposit SiO.sub.2 over poly-Si.
Many treatises, texts and a massive volume of technical journal literature describe in more detail the background of the technology in which this invention lies; see, for example, Thomas, HANDBOOK OF TRANSISTORS, SEMICONDUCTORS, INSTRUMENTS AND MICROELECTRONICS, Prentice Hall, Englewood Cliffs, N.J. 1968 and the extensive publications of the J. C. Schumacher Company, e.g. Tetraethyl Orthosilicate (TEOS), Product Data Sheet No. 6; Tetraethyl Orthosilicate for Semiconductor High Temperature Silicon Dioxide Depositions, Product Application Note No. 8; TEOS and Liquid Dopant Sources for CVD SiO.sub.2, PSG, and BPSG, Product Application Note No. 15; Adams and Capio, The Deposition of Silicon Dioxide Films at Reduced Pressure, Technical Article Reprint No. 5.
Thus, the deposition of doped and undoped silicon oxide films is an important process in semiconductor device fabrication. The decomposition process commonly utilizes toxic and pyrophoric gases. The use of safer liquid sources is the goal of many investigators. F. S. Becker and D. Pawlik, ECS 85-2 (85)380, ECS 86-8 p 148 "A New LPCVD Borophosphosilicate Glass Process Based on the Doped Deposition of TEOS-Oxide". G. Smolinsky and T. P. H. F. Wendling, JECS 132(85)950 "Measurement of the Temperature Dependent stress of Silicon Oxide Films Prepared by a Variety of CVD Methods". G. Smolinsky and R. E. Dean "LPCVD of Silicon Oxide Films in the Temperature Range of 410.degree. to 600.degree. C. from Diacetoxyditertiarybutoxysilane". F. S. Becker, D. Pawlik, H. Schaefer, and G. Staudigl, JVST B4(86)232 "Process and Film Characterization of Low Pressure TEOS-Borophosphosilicate Glass". D. S. Williams and E. A. Dein "LPCVD of Borophosphosilicate Glass from Organic Reactants". The thermal decomposition of tetraethoxysilane (TEOS) has been used for over twenty years to obtain undoped silicon dioxide films in the temperature range from 600.degree. to 800.degree. C., A. Hochberg and D. O'Meara "LPCVD of Silicon Dioxide Films from Tetraethoxysilane".
The deposition of silicon dioxide films has been disclosed in copending U.S. patent application Ser. No. 07/036,979, filed Apr. 10, 1987, to which reference is made for further background as to the state of the art, and U.S. Pat. No. 4,168,330 to Kaganowicz also discloses the use of some siloxanes in the deposition of silicon oxides by glow discharge at low temperatures.
Alkylsilanes have also been considered as source reagents for the production of silicon dioxide films on semiconductor devices, but only in high temperature reactions typically above 800.degree. C. in most instances. East German Patent No. 90,185 discloses the coating of silicon substrates at about 1,000.degree. C. with silicon nitride or silicon oxide, the latter according to the reaction: EQU Si(CH.sub.3).sub.4 +2H.sub.2 O.fwdarw.SiO.sub.2 +4CH.sub.4 ;
H. Fischer discloses the production of silicon oxynitride films by the APCVD process, reacting tetramethylsilane, ammonia and oxygen at 800.degree. C. to 1,000.degree. C., Z. phys. Chemie. Leipzig 252 (1973) 3/4, S. 213-234; and Y. Avigal, I. Beinglass and M. Schieber disclose APCVD process production of SiO.sub.2 films by the oxidation of tripropylsilane vapors at 650.degree. C., J. Electrochem. Soc. V. 121, N. 8, pp. 1103-7 and Israeli Patent No. 42,249. The skill and tradition of the art has been to the effect that satisfactory SiO.sub.2 films could be obtained from alkoxy and alkylsilanes only at temperatures of from about 800.degree. C. to 1,100.degree. C., Avigal et al departing only slightly in studying the oxidation of a particular species, tripropylsilane, at about 650.degree. C. in an APCVD process with low deposition rates, but concluded that a temperature of about 850.degree. C. was optimum.
It has now been discovered that methylsilanes are distinctly inferior to ethyl-, propyl-, butyl-, etc., alkylsilanes in LPCVD processes and that very high quality silicon dioxide films can be deposited at hitherto unattainable deposition rates in an LPCVD process at low temperatures using 2-carbon or greater alkylsilanes.

Deposition of silicon oxide films using alkylsilane liquid sources


Stable facsimile communications and reduced deterioration in image quality are achieved, when standard facsimile apparatuses communicate using a communication network composed a subnetwork with relatively good transmission quality such as a wire system and a subnetwork with relatively bad transmission quality such a mobile system subnetwork, both subnetworks being interspersed between the facsimile apparatuses, by inserting a pair of FAX signal converting apparatuses into the communication channel between the facsimile apparatuses for error control responsive to the quality of the channel in use.

1. Field of the Invention
The present invention relates to facsimile communications between standard facsimile apparatuses, and more particularly to facsimile communications through a communication network composed of networks with good transmission quality, such as a wire system subnetwork, and of subnetworks with relatively bad transmission quality, such as an open-wire carrier circuit and a mobile system network, the foregoing subnetworks of good and bad quality being interspersed in the communication network between the facsimile apparatuses.
Communications between facsimile apparatuses are primarily achieved conventionally through a wire system network, such as a public data network (PDN), an integrated services digital network (ISDN), a public switched data network (PSDN) or a facsimile communication network (FICS), with equipment for use in the above networks. International standards for example the CCITT Recommendations, facsimile communications through a wire system network in particular. Standard facsimile systems, enjoying wide application over domestic and overseas areas, adopt the international standards or at least a standards based thereupon. However such standards are designed for a wire system network with relatively good transmission quality, without having any protection against the occurrence of noises and broken lines, e.g., a powerful error correcting function.
Automobile telephones and other mobile networks suffer from a variety of disturbances because of their inclusion of mobile radio channels. These disturbances include internal noises emitted from radio transmitter-receiver units (TRU), urban noises such as multipath phasing and shadowing which occur during propagation of electric waves and the effect on control signals and voice channels of the hand-off procedure peculiar to a cellular system, which would severely reduce the quality of a network with regard to facsimile communications. The use of conventional standard facsimile devices therefore results in deteriorated image quality or frequent interruptions of communications, as reported in "Experimental Facsimile Signal Transmission in Mobile Communication channels", Omori and Kinoshita, No. 2432, the Unified Meeting of the Society of the Electro Communication, 1984.

Method of and apparatus for facsimile communications


This technology relates to smoothly performing a test on a memory circuit having a high memory capacity while reducing the size of a test circuit. A test circuit according to the present invention includes a test execution unit configured to perform a test on a target test memory circuit, an internal storage unit configured to store data for the test execution unit, and a conversion setting unit configured to set a part of or the entire storage space of the target test memory circuit as an external storage unit for storing the data for the test execution unit.

1. Field
Exemplary embodiments of the present invention relate to a test circuit, a memory system, and the test method of the memory system.
2. Description of the Related Art
As the size of a semiconductor chip is reduced, demands for a technique for reducing the size of the semiconductor chip or a semiconductor package have increased. The technique for reducing the size of the semiconductor chip or the semiconductor package commonly includes a system on chip (hereinafter referred to as an SOC) technique for making several individual semiconductor devices into one semiconductor chip and a system in package (hereinafter referred to as an SIP) technique for packaging several semiconductor chips into one semiconductor package. Above techniques are also used when fabricating memory chips or memory packages.
For an efficient test on a plurality of memory circuits included in a memory chip or a memory package, there is a recent proposal for a method of including a built-in self test (BIST) circuit (hereinafter referred to as a test circuit) for testing a plurality of memory circuits, together with the plurality of memory circuits, in the memory chip or the memory package when fabricating the memory chip or the memory package by using the SOC or SIP technique.
In case of a memory chip or a memory package that includes a test circuit, test equipment externally connected to the memory chip or the memory package and a large number of ports for coupling memory circuits within the memory chip or the memory package are not necessary and the memory chip or the memory package may be rapidly tested because a test algorithm for testing the memory circuits may be embodied in the memory chip or the memory package.
FIG. 1 shows a known memory system that includes a test circuit (shows a memory chip or a memory package that includes heterogeneous or homogeneous memory circuits).
As shown in FIG. 1, the memory system includes first to third memory circuits 110, 120, and 130 having different capacities, a test circuit 140 for testing the first to third memory circuits 110, 120, and 130, and a bus BUS for transferring signals between different elements included in the memory system. It is hereinafter assumed that the first to third memory circuits 110, 120, and 130 are heterogeneous or homogeneous. However, they have different densities and different memory capacities. The first memory circuit 110 has the lowest memory capacity, and the third memory circuit 130 has the highest memory capacity.
The known memory system is described below with reference to FIG. 1.
When a test is started, the test circuit 140 tests the first to third memory circuits 110, 120, and 130. For example, when the first memory circuit 110 is tested, the test circuit 140 supplies commands (including a read command and a write command), an address, and data that has a test pattern (hereinafter referred to as test execution information) for the test to the first memory circuit 110 through the bus BUS. The test circuit 140 receives and analyzes the output of the first memory circuit 110 through the bus BUS, and generates information indicating whether a failure has occurred in the first memory circuit 140 and indicating a fail address (hereinafter referred to as test result information) based on a result of the analysis. Here, the test circuit 140 may perform the test by using test execution information stored in a storage unit (not shown in FIG. 1) (hereinafter referred to as an embedded storage unit) embedded in the test circuit 140 and store test result information in the embedded storage unit.
In general, when a memory circuit that has a higher memory capacity is tested, the size of test execution information or test result information is increased. For this reason, the embedded storage unit of the test circuit 140 is designed to have a memory capacity so that a memory circuit that has the highest memory capacity among memory circuits to be tested by the test circuit 140 (hereinafter referred to as target test memory circuits) may be smoothly tested. For example, in case of the memory system of FIG. 1, the embedded storage unit of the test circuit 140 is designed to have a memory capacity enough to smoothly test the third memory circuit 130 not the first memory circuit 110 or the second memory circuit 120.
However, if the memory capacity of the embedded storage unit of the test circuit 140 is designed based on a memory circuit that has the highest memory capacity among target test memory circuits, the memory capacity and the area of the test circuit 140 are increased. As a result, the size of the memory system is increased.

Test circuit, memory system, and test method of memory system


The invention is directed to a shaving head for dry shaving apparatus, comprising a shaving head frame arranged on the shaver housing so as to be removable therefrom and a circumferentially closed, box-shaped exchangeable frame of a material of limited elasticity which is insertable into the shaving head frame, the exchangeable frame having a shaving foil mounted therein in arched form which is in cooperative relation with a reciprocating lower cutter assembly of suitable configuration which is urged against the foil by spring means, with corresponding holding and guiding means being provided on the exchangeable frame as well as on the shaving head frame to guide the exchangeable from in the shaving head frame in vertical direction.

Shaving heads constructed in this manner and known, for example, from U.S. Pat. No. 4,271,590 have the advantage that for cleaning purposes and for the replacement of damaged or worn down shaving foils they can be easily disassembled and refitted, also by laymen and inexperienced users, without exposing the delicate shaving foil to the risk of damage. The manufacture of the exchangeable frame and the mounting of the shaving foil thereon can be accomplished in an injection-molding process, thus eliminating the need for additional operation cycles.
To enable the shaving foil to yield under shaving pressure in cooperation with the lower cutter also when it is mounted in an exchangeable frame, so that relative contact between foil and cutter is maintained and damage to the shaving foil due to buckling and flexing is avoided, a variety of attempts have been made which, however, have been unsatisfactory so far and, as a result, were not adopted in series production, in contrast to the yielding mounting of the shaving foil in the shaving head frame directly.
Accordingly, the arrangement of torsion springs as an integral part of the exchangeable frame appears at first advantageous because it, too, dispenses with the need for an additional operation, however, it has been established that this type of spring suspension can only be implemented with relatively stiff springs because of the necessary thickness of the material, and that the damping of vibrations incited by the working motion of the lower cutter is insufficient (U.S. Pat. No. 4,271,590, Japanese Utility Pat. Application No. 49-2702). In addition, the exchangeable frame disclosed in the last-mentioned reference cannot be removed from the shaving head frame by simple means.
On the basis of this state of the art, it is an object of the present invention to ensure in a shaving head of the type initially referred to that the shaving foil is in a position to readily follow the yielding motion of the lower cutter under shaving pressure, while remaining locked against entrainment by the working motion of the lower cutter, and to ensure ready removal of the shaving foil together with the exchangeable frame at any time.


By reacting polyamines with cyclic carbonates, di-poly-(hydroxyalkyl urethanes) are produced. These diols and polyols are particularly useful for the synthesis of polyurethanes by reaction with diisocyanates or polyisocyanates.

This invention relates to the formation of hydroxyl functional monomers in general, and in particular to the formation of hydroxyl functional monomers useful in the synthesis of polyurethanes.
Synthesis of polyurethanes by reacting isocyanates and alcohols is well known to the art. Typically, long or medium chain diols or polyols are used to provide the "soft" segments of segmented polyurethanes. These polyols generally consist of hydroxyl terminated polyethers or polyesters. Reaction of these polyols with polyisocyanates produces polyether or polyester urethanes, respectively. Short chain polyols are often reacted with polyisocyanates to form the "hard" segments of segmented polyurethanes.
Unfortunately, commercial availability of polyols appropriate for use in the synthesis of polyurethanes is sometimes limited. However, certain polyamines having backbones appropriate for polymer synthesis are more readily available. They may be reacted with polyisocyanates, to form polyureas. However, reactions between polyamines and polyisocyanates are often too fast to allow for commercially feasible production. Moreover, polyureas generally have limited thermal processability.

Method for producing polyurethanes from poly-(hydroxyalkyl urethanes)


An electric distance meter is downsized by using a condensing optical member having a small outer diameter (effective diameter) as a condensing optical member in a light-receiving optical system, reducing a focal length of the condensing optical member without reducing a spread angle to a light-receiving optical fiber and reducing a diameter of the light-receiving optical fiber. An optical distance meter emits outgoing light from a light source to an object, and receives reflection light R from the object by a light receiver, so as to perform distance measurement. The optical distance meter includes an emitting optical system which irradiates the object by the emission light via an objective lens and a light-receiving optical system which guides the reflection light via the objective lens to the light receiver, and a cone prism which changes a cross-section shape of a light beam without generating a transmission deflection angle is provided.

An electric distance measuring method, which measures a distance based on outgoing light toward an object and reflection light of the outgoing light by the object received by a light receiver, is known in surveying with public works, for example. In an electric distance meter which performs such a method, the same objective lens is used in the outgoing optical path to the object and the reflection optical path from the object (for example, refer to Japanese Unexamined Patent Application Publication No. 2004-69611). In such an electric distance meter, in the optical path passing through the objective lens facing the object, the central area including the optical axis is used as the outgoing optical path and the circumferential area thereof is used as the reflection optical path.
However, in the above electric distance meter, the reflection optical path is set in the circumferential area, so that it is necessary for the reflection light via the reflection optical path not to have a light beam in the central portion. A condensing lens (condensing optical member) for receiving reflection light by a light receiver is generally used in an electric distance meter. Accordingly, it is necessary to use a condensing lens having a large diameter (effective diameter) relative to a large-outer diameter reflection light without having a light beam in the central portion, so that it becomes difficult to downsize the electric distance meter.
Moreover, the electric distance meter can be downsized by reducing the distance between the condensing lens and the light receiver. In this case, in order to reduce the distance between the condensing lens and the light receiver, i.e., in order to reduce the focal length of the condensing lens, it is necessary to use a condensing lens having a large NA (numerical aperture stop). However, if a diameter (effective diameter) of a lens is large, it is difficult to set a large NA compared to a small diameter (effective diameter) lens, and it is difficult to reduce the focal length of the condensing lens.
It is, therefore, an object of the present invention to provide a downsized electric distance meter by using a condensing optical member having a small outer diameter (effective diameter) as a condensing optical member in a light receiving optical system of reflection light from an object, and by reducing a focal length of the condensing optical member without reducing a spread angle to a light-receiving optical fiber, so as to reduce a diameter of the light-receiving optical fiber.


A resilient band holds a pick for a stringed musical instrument securely in contact with a thumb or finger of the instrumentalist. In one aspect this device appears as a ring that has been slit along its center line over a portion of its circumference, the slit then being separated to produce a Y-shape. The two arms and leg of the Y provide the pick with a three-point support that maintains stability of the pick against a finger in both strumming and plucking modes over a wide range of attack angles. The resiliency of the band serves to adapt to various fingers as well as to a variety of conventional picks according to the preferences of the user, including flat picks, thumb picks, and finger picks. Methods of manufacture are described.

Among players of stringed instruments who use a pick rather than a finger or fingernail, most prefer to use some form of conventional pick. Such picks, or plectrums, are generally made from small thin pieces of plastic or similar material having a rounded triangular shape. A user of a pick most often holds it between a thumb and the opposing index finger. The more pointed end of the pick extends beyond the finger and thumb to contact and excite the strings in either a plucking or strumming manner. If the user is not careful to maintain a relatively constant force to grip the pick between the thumb and finger, the pick may rotate away from proper playing position or be dropped completely. The force required by the user can be fatiguing over long periods of play. In U.S. Pat. No. 6,346,662 Sielaff has shown an ergonomically shaped pick that generally conforms to the shape of the thumb and index finger that grasp it. This was one attempt to reduce the required force and delay the onset of fatigue during a play session.
One primitive solution that has been used to reduce the stress between the thumb and index finger is to fasten the pick to the thumb with a common rubber band. While this may be acceptable in some cases, more often than not at least one of two problems arise: either the pick twists or rotates with respect to the thumb because the rubber band is too loose; or circulation of blood to the finger tip is reduced resulting in a loss of sensitivity, if not pain, from a rubber band that is too tight.
A different approach has been to incorporate some form of a specially designed pick mechanism into a structure that is fitted to a thumb or other finger. Such devices generally take the form of a thimble or a ring. One of the earlier examples of this format was Formey's 1904 U.S. Pat. No. 756,348 for an annular band with an integrated, substantially semicircular, loop having an abrupt projection, which extended beyond the finger tip, for picking. Some devices of this type offer great stability to the pick mechanism by requiring that they be sized to fit a particular thumb or finger of each individual user. One shortcoming that arises once such a device has been fitted is that it often becomes uncomfortably warm due to heat accumulated over a prolonged session of play.
Picking devices that are either conformable or adjustable to an individual's finger have been shown in a variety of formats. Strong provided in his U.S. Pat. No. 4,015,502 an adjustable strap connected to a wire frame that doubled as a pick. A device which allowed a pick element to slide along a finger-engaging wire band was described by Beall in U.S. Pat. No. 4,497,237. McVicker was granted U.S. Pat. No. 4,625,615 for a Thumb Pick made from a single flat piece of flexible material having two parallel slits forming three straps which engaged a thumb. A fingernail shaped pick body having an annular band at its rear and a criss-crossing strip nearer its tip was secured to a finger in the device that was patented by Crafton in U.S. Pat. No. 4,741,239. Miller showed in U.S. Pat. No. 6,335,477 how to form a specially shaped resilient band to serve as a pick that could be wrapped around any finger or thumb.
The object of all of these devices has been to provide a means of fastening a specially designed pick to a thumb or finger. In many cases the pick has been an integral part of the fastening mechanism itself. U.S. Pat. No. 5,864,075 granted to Mapson showed both finger and thumb picks, each being formed as a single unit with wings that wrapped around the finger or thumb. However, Mapson extended his design to describe a form that provided a swivel fastener that could accept a special compatible pick. Recently, Atkin has shown in U.S. Pat. No. 6,797,871 a thumb sleeve that will accept, either interiorly or exteriorly, an attachable and releasable pick by means of a hook and loop fastener. Again, these devices all require a pick that has been fitted with some sort of special adapter.
The Pick Harness described by Brundage in U.S. Pat. No. 4,102,234 departs from other designs by providing a means of securely holding a conventional pick. Brundage shows a flexible strap that encircles the thumb and has three triangularly-related slits that accept the apices of the conventional pick with provision for the pointed end of the pick to protrude through one of the slits into a playing position.


A sensor element is formed by cutting a laminated body and heating with the cutting taking place in a state where a difference in resistance on sides of a cutting component is as small as possible. That is, a uniform cutting is where resistance added to both sides of the cutting component is substantially the same. When uniform cutting cannot be performed, a nonuniform cutting in a state where resistance added to both sides of the cutting component is different is performed. Consequently, a surface perpendicular to a longitudinal direction of the sensor element is trapezoidal.

1. Field of the Invention
The present invention relates to a sensor element manufactured by cutting out a laminated body formed by laminating ceramics green sheets, and a manufacturing method thereof.
2. Description of the Background Art
Conventionally, various measuring devices have been used for determining a concentration of a desired gas component in a measurement gas. A known device of measuring a NOx concentration in a measurement gas such as a combustion gas, for example, is a sensor having a Pt-containing electrode and a Rh-containing electrode formed on an oxygen ion conductive solid electrolyte, such as zirconia (ZrO2) (see Japanese Patent Application Laid-Open No. 8-271476, for example).
A sensor element of a gas sensor as recited in Japanese Patent Application Laid-Open No. 8-271476 is manufactured as follows: forming circuit patterns (hereinafter also referred to as merely a "pattern") for a plurality of the sensor elements (e.g., several to several tens of the sensor elements) on each of a plurality of ceramics green sheets (hereinafter also referred to as merely a "green sheet") including zirconia which is an oxygen ion conductive solid electrolyte as a ceramics component, laminating those green sheets and integrating them to obtain a laminated body, then cutting the laminated body to obtain a plurality of cutting elements (chips), and burning those cutting elements. The manufactured sensor element is stored in a ceramics housing and held by a plate spring which also functions as a contact point to an external connection electrode provided on a surface of the sensor element.
In the gas sensor manufactured by the above described method, breaks and cracks are often generated in a side end portion of a longitudinal direction of the sensor element by an end portion of the sensor element making a contact with a housing, causing yield deterioration of manufacturing the gas sensor. Specifically, it has been a problem that such breaks and cracks are notably generated in a side where a heater of the sensor element is provided. The inventors of the present invention has confirmed that this is because that the sensor element does not have outline dimension in accordance with a predetermined design.

Method of cutting out chips for a plurality of sensor elements from laminated body, method of manufacturing sensor element, and sensor element


The invention relates to an agrochemical composition containing a compound of formula (1), a glutamic acid compound, and a source of magnesium and/or a source of iron. The composition applied e.g. foliarly has demonstrated synergistic benefits that improve crop yields and quality characteristics.

Applications of plant nutrients are regularly made with aim to improve plant's yield and quality. Great efforts are made to concentrate compositions in terms of nutrients without fully understanding nutrient interactions and uptake efficiency by plants. In most instances fertiliser compositions are diluted in water and sprayed on plant's foliage or applied to the soil with the hope that they will be available for uptake by the plants. The mechanisms of nutrient uptake by plants is still under research and very little is known as to how the plant regulates nutrient absorption throughout its lifecycle with temporal variation of nutrient interactions at the different growth and development stages.
Plant nutrition alone can only achieve what is potential by the plant (not considering other contributing parameters such as crop protection and abiotic stresses) and most crop nutrition formulations are not providing nutrients adequately as they are typically applied on a hit-and-miss basis without understanding or affecting the plant nutrient absorption mechanisms. Therefore, the potential of the plant to produce is not achieved or improved.
Cytokinins have been shown to have effects on many physiological and developmental processes, including leaf senescence, nutrient mobilization, apical dominance, the formation and activity of shoot apical meristems, floral development, the breaking of bud dormancy, and seed germination. Cytokinins also appear to mediate many aspects of light-regulated development, including chloroplast differentiation, the development of autotrophic metabolism, and leaf and cotyledon expansion.
Cytokinins work typically in the presence of auxins and the most common first cytokinins are known as zeatin (natural) and kinetin (synthetic) regulating cell activities within the plant. Some synthetic compounds can mimic or antagonize cytokinin action. Cytokinins are defined as compounds that have biological activities which include the ability to do the following, i. induce cell division in callus cells in the presence of an auxin, ii. promote bud or root formation from callus cultures when in the appropriate molar ratios to auxin, iii. delay senescence of leaves and iv. promote expansion of dicot cotyledons.
Nearly all compounds active as cytokinins are N6-substituted amino-purines, such as benzyladenine (BA).

All the naturally occurring cytokinins are aminopurine derivatives. There are also synthetic cytokinin compounds that have not been identified in plants, such as thidiazuron, which is used commercially as a defoliant and an herbicide. It is also known that some molecules act as cytokinin antagonists. These molecules are able to block the action of cytokinins, and their effects may be overcome by the addition of more cytokinin.
Cytokinins can stimulate or inhibit a variety of physiological, metabolic, biochemical, and developmental processes when they are applied to higher plants, and it is increasingly clear that endogenous cytokinins play an important role in the regulation of these events in the intact plant. Cytokinins are also responsible for delaying senescence in leaves and alter the source-sink relationship of nutrients.
Mg2+ is essential for plant growth and the amounts of Mg2+ vary in different parts of the plant. Excess Mg2+ may be stored in vascular cells and in times of starvation Mg2+ is redistributed typically from older to newer leaves. When Mg2+ is taken up into plants via the roots which carry a great number of negative charges (key to the uptake of cations by root cells), due to the Mg2+ binding relatively weakly to these charges, it can be displaced by other cations, impeding uptake and causing deficiency in the plant. Within individual plant cells the Mg2+ requirements are largely the same as for all cellular life; Mg2+ is used to stabilise membranes, is vital to the utilisation of ATP, is extensively involved in the nucleic acid biochemistry, and is a cofactor for many enzymes (including the ribosome). Also, Mg2+ is the coordinating ion in the chlorophyll molecule. It is the intracellular compartmentalisation of Mg2+ in plant cells that leads to additional complexity. Four compartments within the plant cell have reported interactions with Mg2+. Initially Mg2+ will enter the cell into the cytoplasm (by an as yet unidentified system), but free Mg2+ concentrations in this compartment are tightly regulated at relatively low levels and so any excess Mg2+ is either quickly exported or stored in the second intracellular compartment, the vacuole.
When a Mg2+ ion has been absorbed by a cell requiring it for metabolic processes, it is generally assumed that the ion stays in that cell for as long as the cell is active. In vascular cells this is not always the case; in times of plenty Mg2+ is stored in the vacuole, takes no part in the day-to-day metabolic processes of the cell, and is released at need. But for most cells it is death by senescence or injury that releases Mg2+ and many of the other ionic constituents, recycling them into healthy parts of the plant. Additionally, when Mg2+ in the environment is limiting, some species are able to mobilise Mg2+ from older tissues. These processes involve the release of Mg2+ from its bound and stored states and its transport back into the vascular tissue, where it can be distributed to the rest of the plant. In times of growth and development Mg2+ is also remobilised within the plant as source and sink relationships change. Mg2+ is the coordinating metal ion in the chlorophyll molecule and in plants where the ion is in high supply about 6% of the total Mg2+ is bound to chlorophyll. Thylakoid stacking is stabilised by Mg2+ and is important for the efficiency of photosynthesis.
It is an object of the present invention to provide an improved agrochemical composition.
It is an object of the present invention to provide agrochemical compositions that increase crop yield and/or crop quality characteristics.
It is an object of the present invention to improve plant physiology.
It is an object of the present invention to provide agrochemical compositions that increase chlorophyll levels in plants.
It is a further object of the invention to provide agrochemical compositions that increase the photosynthetic rate in plants.
It is a further object of the invention to provide agrochemical compositions that increase foliar absorption of plant nutrients such as magnesium and/or iron.
It is yet a further object of the invention to provide agrochemical compositions that balance the phytohormonal activity of plants which optimise crop physiological characteristics.

Agrochemical composition comprising a N,N#-disubstituted (thio)urea for the improvement of crop productivity


This invention speeds up the execution of instructions in an information processing system by tightly coupling two or more processors to a random access storage mechanism in such a manner that no arbitration is required and no processor is forced to wait while another processor accesses the storage mechanism. This is accomplished by coupling the processors to the storage mechanism in a time multiplexed manner which enables each processor to have a periodic regularly occurring turn at accessing the storage mechanism.

A measure of the power of a digital processor is the number of instructions it can execute per second. The greater the number, the greater is the computational power of the processor. To increase the power of a processor, it is therefore necessary to increase the speed at which it executes instructions. Various methods have been heretofore proposed for doing this. These include the use of instruction decode overlap, the use of multiple processors, and the use of so-called pipelining techniques. These methods are more commonly associated with large-scale processors as opposed to smaller processors like microprocessors.
Assume, for example, that it is desired to design a digital information processing system which uses an existing commercially available microprocessor as the primary processing engine. How would one speed up the execution of instructions in such a system? The parameters and operating characteristics of the microprocessor have already been defined. Is there anything that can be done? One solution would be to employ two or more microprocessors which operate in a parallel manner to simultaneously execute instructions for different ones of the program tasks. In such case, the various microprocessors would need to be able to access the instructions and data contained in the same system storage unit. Unfortunately, this leads to contention problems and requires the use of an arbitration mechanism for deciding which one of the microprocessors is to be given access to the storage unit when two or more of them desire such access at the same time. When such contention occurs, the microprocessor performing one of the program tasks is required to sit and wait and hold up further processing until the other microprocessor completes its accessing of the storage unit. This waiting tends to slow things down. Also, in some applications, particularly real time type applications where program tasks must be performed within a fixed time window, this waiting to obtain access to the storage unit is unacceptable.

Time multiplexed system for tightly coupling pipelined processors to separate shared instruction and data storage units

International Business Machines Corporation


The invention relates to an archery device having a part or component is injection molded; the part is injection molded metal, ceramic, or composite material. A sight pin for a bow sight is a part that is especially suited for being injection mold. Injection molding of metal, ceramic or composite sight pins allows for various cross-sectional shapes and areas for the pin along its length. The injection molded sight pin can be a vertically extending pin or a horizontally positioned pin, and multiple pins may be configured for viewing in a straight line.

Many bow sight designs and configurations are known. Bow sights generally have multiple sight points used when shooting at targets positioned at different distances from the archer.
A common sight point is a two-dimensional dot, such as painted on the end of a pin. The end of a fiber optic or other light gathering fiber is another common sight point. When a fiber end is used as the sight point, the fiber optic may or may not be supported, for example by a pin.
Many bow sights include multiple sight points attached to horizontal pins; examples of such bow sights are shown, for example, in U.S. Pat. Nos. 5,103,568 (Canoy); 5,676,122 (Wiseby et al.); and 5,685,081 (Winegar). A more recent development has been a bow sight with vertical pins. An example of a bow sight having multiple vertical pins and a fiber optic sight point at the end of the pins is shown, for example, in U.S. Pat. No. 6,418,633 (Rager). A number of U.S. patents disclose bow sights having various other arrangements of sight points. See, for example, U.S. Pat. Nos. 3,234,651 (Rivers); 4,120,096 (Keller); 5,086,567 (Tutsch); and 5,131,153 (Seales).
The pins, which are sufficiently rigid and strong to support the sight points, are usually either plastic or metal. Plastic has generally been preferred due its ease of processability; pins of various shapes and sizes can be easily produced, such as by extrusion or molding. Metal pins are preferable due to their strength, however, it has generally been difficult to produce acceptable pins, as the metal is generally machined or cast to form the pin structure.
Improvements in bow sights and their parts, particularly in the pins, are desired.

This patent is subject to a terminal disclaimer.

Bow sight with injection molded metal sight pins, and methods


A transmitter module includes a processor configured to receive input data, and determine input values corresponding to the input data; a digital-to-analog converter configured to receive the input values from the processor, and generate first and second voltage signals based on the input values; a laser configured to output light; a Mach-Zehnder modulator configured to receive the light from the laser and the first and second voltage signals from the digital-to-analog converter, and modulate the light based on the first and second voltage signals to generate a modulated optical signal that includes distortion; and a filter configured to receive the modulated optical signal from the modulator, process the modulated optical signal to reduce or eliminate the distortion and produce an output optical signal, and output the output optical signal.

Wavelength division multiplexed (WDM) optical communication systems (referred to as "WDM systems") are systems in which multiple optical signals, each having a different wavelength, are combined into a single optical fiber using an optical multiplexer circuit (referred to as a "multiplexer"). Such systems may include a transmitter circuit, such as a transmitter (Tx) photonic integrated circuit (PIC) having a transmitter component to provide a laser associated with each wavelength, a modulator configured to modulate the output of the laser, and a multiplexer to combine each of the modulated outputs (e.g., to form a combined output or WDM signal).
A WDM system may also include a receiver circuit having a receiver (Rx) PIC and an optical demultiplexer circuit (referred to as a "demultiplexer") configured to receive the combined output and demultiplex the combined output into individual optical signals. Additionally, the receiver circuit may include receiver components to convert the optical signals into electrical signals, and output the data carried by those electrical signals.
A PIC is a device that integrates multiple photonic functions on a single integrated device. PICs may be fabricated in a manner similar to electronic integrated circuits but, depending on the type of PIC, may be fabricated using one or more of a variety of types of materials, including silica on silicon, silicon on insulator, or various polymers and semiconductor materials which are used to make semiconductor lasers, such as GaAs and InP.
The transmitter (Tx) and receiver (Rx) PICs, in an optical communication system, may support communications over a number of wavelength channels. For example, a pair of Tx/Rx PICs may support ten channels, each spaced by, for example, 200 GHz. The set of channels supported by the Tx and Rx PICs can be referred to as the channel "grid" for the PICs. Channel grids for Tx/Rx PICs may be aligned to standardized frequencies, such as those published by the Telecommunication Standardization Sector (ITU-T). The set of channels supported by the Tx and Rx PICs may be referred to as the ITU frequency grid for the Tx/Rx PICs. The spacing, between the channels, may be less than 200 GHz, in order to tightly pack the channels together to form a super-channel.


In a client apparatus, when a request to install a program stored in a server is received, a dependence display creating unit acquires server program information including information indicating the program stored in the server and information indicating the dependence between the program and other programs, and acquires apparatus program information including information indicating a program installed in the client apparatus. The dependence display creating unit creates a display screen on the basis of the information indicating the dependence in the server program information such that the dependence between a program which is designated to be installed and other programs is clear. In addition, the dependence display creating unit displays information indicating an installed program among the programs to be installed, on the basis of the apparatus program information.

1. Field of the Invention
The present invention relates to a program management system that manages programs, a program management method, a client, and a program.
2. Description of the Related Art
In recent years, an information processing apparatus has been proposed which has a network communication function, downloads from a program from a server through a network, and installs the program. In addition, a multi-function machine has been developed which has a printing function, a copy function, a facsimile function, and a network communication function, downloads a program from a server through a network, and installs the program. In this way, new functions can be added to the multi-function machine.
However, for example, in many cases, a plurality of programs cooperates with each other to achieve a certain function of the multi-function machine. There is dependence between the plurality of programs which cooperate with each other to achieve a certain function.
When a function is added to the multi-function machine, all of the programs which are dependent on each other need to be installed in the multi-function machine in order to achieve the function. In addition, when the function added to the multi-function machine is removed, the programs which are dependent on each other are uninstalled from the multi-function machine in order to remove the function.
Japanese Patent Application Laid-open No. 2006-261970 discloses a structure in which, when the configuration of a multi-function machine is changed, the information of the plug-in programs installed in the multi-function machine is transmitted to a server that manages the plug-in information of each multi-function machine connected to the network and the multi-function machine requests the server to determine whether to apply the plug-in program.
However, in the system according to the related art, it is difficult for the user to check the dependence between the programs, which is information required to add a function to the multi-function machine or remove the function added to the multi-function machine. This causes a problem in the management of a function adding program in the multi-function machine.
According to the structure disclosed in Japanese Patent Application Laid-open No. 2006-261970, the information of the plug-in programs is exchanged between the server and the multi-function machine through the network and the multi-function machine presents information indicating whether the plug-in programs are applicable. However, in the structure disclosed in Japanese Patent Application Laid-open No. 2006-261970, the problem that it is difficult for the user to clearly check the dependence between the programs is not solved.

Program management system, program management method, client, and computer program product


A method for detecting the physical stoppage of an internal combustion engine including a crankshaft that drives a toothed wheel having a plurality of teeth, each tooth corresponding to different angular positions of the crankshaft, a sensor positioned next to the toothed wheel generates a signal characteristic of the passage of a tooth. The method detects a tooth from the signal generated by the sensor, identifies the tooth detected, triggers a timeout, and detects stoppage of the engine if the passage of a tooth adjacent to the tooth detected has not been detected before the end of the timeout. The value of the timeout is dependent on the tooth identified, and including: determining crankshaft angular position depending on the tooth identified, the value of the timeout dependent on the angular position of the crankshaft, determining the preferential stopping positions of the crankshaft and assigning a first timeout value for the preferential stopping positions and assigning at least a second value for the other positions of the crankshaft. The first timeout value being less than the second timeout value.

The starting of an internal combustion engine is conventionally facilitated by a starter, which comprises a shaft provided with a pinion that allows the engine to begin to turn over by engaging with a pinion borne thereby.
During a, possibly brief, stoppage of the engine, it is necessary to determine that the engine is completely stopped before it can be restarted. This is because if the engine is not completely stopped when the starter is actuated, the engaging of the pinions may damage the engine and the starter.
In order to determine a stopped status of the engine, it is known practice to make use of the data acquired by an engine crankshaft rotation sensor, as for example in the document JP2009138662, incorporated herein by reference. This sensor is positioned next to a toothed wheel secured to the crankshaft, and detects the teeth of the toothed wheel as they file past when the latter is rotationally driven, typically by detecting the rising or falling front of each tooth.
Engine stoppage is detected after a timeout of 300 ms, starting from the last tooth detected. If a new tooth is detected before the timeout elapses, the timeout is interrupted and the engine is considered to be in motion.
This solution has a major drawback. It entails systematically waiting for the end of the timeout, namely 300 ms, in order to detect an engine stoppage, and therefore to authorize the restarting of the engine. However, it is desirable to be able to restart the engine as soon as possible, for example in vehicles equipped with "stop and start" devices or similar for automatically restarting the engine of a vehicle, for example in circumstances in which the driver is said to have changed his mind (for example in the case of arriving at a red light which turns to green just at the moment of stopping).

Method for detecting physical stoppage of an engine


A cable connector having a generally tubular shape with a frontal portion and a rear portion is provided. The frontal portion is on a plane perpendicular to an axis with an undivided annular structure having an outer semi-conic wing that secures the cable connector to a knock-out opening prior to a cable insertion therein and an inner receptacle structure for receiving a cable in a direction that is parallel to the axis. A rear grasping portion separated into a pivoting rigid latch segment with a tightening handle for clasping against a fixed slot segment with a releasing handle for grasping the inserted cable is also provided.

Connectors providing strain relief to cables or wires in a junction box are known. Examples are shown in U.S. Pat. No. 4,892,979 to Rossow, U.S. Pat. No. 3,889,909 to Koscik, and U.S. Pat. No. 3,788,582 to Swanquist. However, these devices are designed to provide strain relief of the cable, and do not necessarily provide an environmental protection from dust and debris for the junction box itself.
The Rossow '979 reference, in particular, discloses two embodiments designed to provide functionality for adding additional wires to an existing connector assembly. In one embodiment, a cable is fastened to the bottom of a ring member having upper annular ridges provided at a distance away from the cable. This allows additional cables or wires to be added into the ring at a later time. However, this design leaves a gap between the cables and the upper annular ridges.
The other embodiment of the Rossow '979 reference discloses a break-away wedging member which partially encloses the opening. However, the wedging member does not effectively protect the inner junction box at the end of the opening. As the breakaway leaves the corners at the ends open, dusts, debris and other particulates may enter the junction box. In addition, both embodiments require assembly of the frontal portion before being inserted into the junction box, making its usage awkward and difficult. Furthermore, even the fastening serrated wrap member needs to be navigated through a tiny hole on the other side and does not allow a necessary simple clasping solution out in the field.
Likewise, the device of the Koscik '909 reference does not provide any protection for the gap between the ring and the cable. The Swanquist '582 reference requires a specific dimension cable for insertion into the rectangular passage, after which the electrician would rotate a cam portion to secure the cable to the connector and anchor the connector body to the box.
There is a need for a cable connector which can be fabricated unitarily in a cost-effective economical manufacturing process. It would also be preferable for such cable connector construction to allow easy insertion into a junction box knock-out opening without requiring any pre-assembly inconvenience either prior to installation or at the time of manufacture. Further, a need exists for a cable connector which can accommodate different dimension cables in a simple to use, remove and reuse convenient fastening mechanism. In addition, a cable connector which provides environmental protection for the inside of the junction box is also preferred.


The present invention pertains to a ladder top for a stepladder. The top comprises a plane having a front and a rear. The plane has a bin with a curved front side adjacent the front of the plane for holding small electrical parts. The plane has at least one screwdriver hole for holding the screwdriver. The plane has a hammer/drill holster slot. The plane has a pliers slot. The plane has a wire strippers slot and a channel locks slots. A method for using a ladder top for a stepladder.

For years, stepladders have been designed for the general construction and painting professionals needs. The new electrician's ladder is designed for the specific needs of the electrician. New features have been added to aid in the installation of conduit, running wires, and tool storage. Specifically, the top has been redesigned to greatly benefit the electrician while on the ladder.


Methods, systems, and computer program products for performing prepaid account balance screening are disclosed. According to one aspect, the subject matter described herein includes a method for performing prepaid account balance screening. The method includes receiving, at a network entity for processing network signaling messages, a signaling message containing information that identifies a prepaid subscriber, the message being sent from a message source and intended for a message destination. It is determined whether the prepaid subscriber's account balance satisfies a threshold requirement, using prepaid account balance screening data and the information in the signaling message that identifies the prepaid subscriber, where the prepaid account balance screening data is a subset of available prepaid subscriber account information stored in a prepaid subscriber database separate from the prepaid account balance screening data. In response to determining that the prepaid subscriber's account balance does not satisfy the threshold requirement, a screening action is performed. In one example, the screening action shields the prepaid subscriber database from signaling message traffic associated with the prepaid subscriber's account.

With the increasing popularity of prepaid network services, such as prepaid mobile plans, in which a user of a mobile phone purchases a number of cell-phone minutes in advance, the network infrastructure required to support prepaid services must be enhanced to handle the increased traffic and processing requirements.
FIG. 1 is a block diagram illustrating a conventional system for telecommunications in which a large number of subscribers are prepaid subscribers. When a mobile subscriber makes a call, the call enters the core telecommunication network via a mobile switching center (MSC 100). If the mobile subscriber is a prepaid subscriber, MSC 100 must confirm that the subscriber's prepaid account has a sufficient balance before allowing the subscriber to access the network. To do this, MSC 100 typically queries a service control point (SCP) designated for handling prepaid queries and which may include the prepaid database itself. Such an SCP is herein referred to as a prepaid SCP, or PPSCP. In FIG. 1, MSC 100 sends a query to one of a bank of PPSCPs 102 through a signal transfer point (STP 104).
For example, MSC 100 may send an initial detection point (IDP) query to STP 104 (FIG. 1, message 1). STP 104 may forward the IDP query to the bank of PPSCPs 102 (FIG. 1, message 2), which may respond to the query with either a CONNECT message if the prepaid subscriber has a sufficient account balance or a CONTINUE message if the prepaid subscriber has an insufficient account balance (FIG. 1, message 3). STP 104 may then forward the response to MSC 100 (FIG. 1, message 4). MSC 100 may either allow or deny the prepaid subscriber access to the network, based on whether the response received from STP 104 was a CONNECT or CONTINUE message, respectively.
As the number of prepaid subscribers increases, the number of SCPs in the bank of PPSCPs 102 may increase, with a corresponding increase in the number of connections to the bank of PPSCPs 102. An increase in SCPs and connections required may drive up the costs of the system, not only in physical hardware but also in resources required to administer and maintain the additional nodes. In addition, the increase in traffic due to the increased number of queries to the prepaid database may cause overall network performance to suffer. For example, excessive network traffic caused by prepaid database queries may limit or impair the function of other nodes on the network, such as home location registers (HLRs), E.164 number mapping (ENUM) servers, home subscriber servers (HSSs), and the like.
Thus, there exists a need to minimize the number of PPSCPs required, and/or minimize the number of signaling links connecting the PPSCPs with the network or with each other. There also exists a need to reduce prepaid query traffic and the corresponding effect on network performance. Accordingly, there exists a need for methods, systems, and computer program products for performing prepaid account balance screening.