A homogeneous non-aqueous compositions containing a fluorinated solvent, ozone, and optionally a co-solvent and the use of these compositions for cleaning and oxidizing substrates is described.

This invention relates to homogeneous non-aqueous compositions containing a fluorinated solvent, ozone, and optionally a co-solvent and the use of these compositions for cleaning and processing semiconductors and integrated circuits including silicon and Ga/As substrates.
The use of microelectronic devices, such as integrated circuits, flat panel displays and micro electromechanical systems, has burgeoned in new business and consumer electronic equipment, such as personal computers, cellular phones, and electronic calendars. Such devices have also become an integral part of more established consumer products such as televisions, stereo components and automobiles.
These devices in turn contain one or more very high quality semiconductor chips made from silicon wafers containing many layers of circuit patterns. Typically nearly 350 processing steps are required to convert a bare silicon wafer surface to a semiconductor chip of sufficient complexity and quality to be used, for example, in high performance logic devices found in today""s personal computers. The most common processing step of semiconductor chip manufacture is wafer cleaning steps, accounting for over 10% of the total processing steps. These cleaning steps are normally one of two types: oxidative and etch. During oxidative cleaning steps, oxidative compositions are used to oxidize the silicon or polysilicon surface, typically by contacting the wafer with aqueous peroxide or ozone. During etch cleaning steps, etching compositions are used to remove native and deposited silicon oxide films and organic contaminants from the silicon or polysilicon surface before gate oxidation or epitaxial deposition, typically by contacting the wafer with aqueous acid. See, for example, L. A. Zazzera and J. F. Moulder, J. Electrochem. Soc., 136, No. 2, 484 (1989). The ultimate performance of the resulting semiconductor chip will depend greatly on how well each cleaning step has been conducted.
Microelectromechanical systems (MEMS) (also called micromachines or micromechanical devices) are small mechanical devices which can be made using traditional integrated circuit manufacturing techniques. Typical devices include motors, gears, accelerometers, pressure sensors, actuators, and mirrors. The manufacture of MEMS results in a chip, or die, which contains the moving pieces of the device made from silicon or polycrystalline silicon (polysilicon) encased in silicon oxide. The die can also contain the circuitry necessary to run the device.
The etch cleaning and drying of MEMS has similar issues to those for semiconductor chip manufacture. Particulate contamination on micromachines can hinder movement of the device and ultimately affect device performance or cause failure. Care is taken to rinse the device with deionized water followed by ethyl alcohol or isopropanol but has similar problems to the IC in that the particles are not easily removed from devices due to the polysilicon surface energy and intricate designs.
In addition to the problem of particulate contamination, drying of MEMS following DI water rinses or alcohol rinses can lead to a phenomenon known as stiction. Stiction can be described as the adhesion of two surfaces due to adhesives forces as well as frictional forces. Polysilicon devices are typically 0.2-4.0 xcexcm, but can range up to hundreds of xcexcm, with lateral dimensions anywhere from 1-500 xcexcm. The high surface area of these structures along with the tight tolerances between structures makes stiction a very troublesome problem. Stiction of microdevices can occur during use of the device, as a result of capillary condensation from exposure to humid air, or as a result of capillary effects during the drying of the device following the release etch process. See, for example, R. Maboudian and R. T. Howe, J. Vac. Sci. Technol. B, 15(1), 1-20 (1997). The high surface tensions of the aqueous or alcoholic rinses can greatly exacerbate the capillary effects and lead to a higher incidence of microstructure stiction following the release-etch and drying steps.
In one aspect, this invention relates to a cleaning composition useful in integrated circuit manufacture, the composition comprising a fluorinated solvent and ozone. The liquid cleaning composition may optionally contain a co-solvent to improve specific cleaning operations. Advantageously, the present invention provides substrate cleaning composition useful for oxidation of a substrate, removal of residues, rinsing and drying, but has an efficient rate of surface oxidation. The present composition may also be rendered non-flammable by appropriate selection of the fluorinated solvent. Substrates useful in the present invention include silicon, germanium, GaAs, InP and other III-V and II-VII compound semiconductors. It will be understood, due to the large number of processing steps involved in integrated circuit manufacture, that the substrate may include layers of silicon, polysilicon, metals and oxides thereof, resists, masks and dielectrics.
In yet another aspect, this invention relates to a cleaning process for substrates comprising contacting a substrate with a liquid cleaning composition comprising a fluorinated solvent and ozone; and then separating the cleaning composition from the processed substrate. The cleaning process makes more efficient use of the available ozone than conventional aqueous processes and achieves an oxidative cleaning rate comparable to that of conventional aqueous oxidative compositions. The present invention also improves safety by avoiding potentially hazardous xe2x80x9cRCAxe2x80x9d solutions that contain strong acids. The process and composition of this invention may also be used in the cleaning and etching of GaAs devices and substrates.
In yet another aspect, this invention relates to a cleaning process for silicon or polysilicon part in MEMS substrates with a homogeneous cleaning composition comprising a fluorinated solvent and ozone. The present invention provides silicon substrate cleaning composition that easily penetrates the intricate microstructures and wets surfaces on MEMS substrates. The cleaning composition is easily removed from MEMS and provides a dry, hydrophilic surface without residual water that would be present from an aqueous cleaning composition. Thus the present invention may avoid a drying step of the prior art, since contact with an aqueous solution is avoided.
In yet another aspect, this invention relates to a cleaning process for silicon or polysilicon part in MEMS chip with a homogeneous cleaning composition comprising a fluorinated solvent and ozone. Advantageously, the present invention provides a cleaning composition useful for oxidizing silicon or polysilicon surface in MEMS. The surface silicon oxide film is rendered hydrophilic thus reducing particle adhesion on the MEMS surfaces. The surface silanol groups present on the silicon oxide films of the treated silicon substrate are also available for reaction with surface modifying agents. The surface silicon oxide film also electrically isolates a silicon or polysilicon part in MEMS.
Compositions of this invention, comprising a fluorinated solvent and ozone are useful in the various cleaning steps of substrates required for subsequent operations. As used herein xe2x80x9ccleaningxe2x80x9d of silicon substrates will refer to any of oxidation of a substrate, removal of residues and/or particulates, rinsing and drying. As used herein xe2x80x9csubstratexe2x80x9d will refer to wafers or chips used in semiconductor manufacture, microelectromechanical devices, as well as glass surfaces. The compositions can effectively remove both inorganic particles, and organic residues, such as oils and greases, oxidize the silicon wafer surface to produce a hydrophilic silicon surface and additionally convert hydrophobic silicon hydrides to hydrophilic silicon oxides. As a result, many of these cleaning steps (e.g., oxidizing, rinsing and drying) can be combined into a single step.
The cleaning composition and method of this invention can improve manufacturing efficiency by lowering defects to increase wafer yield, or by decreasing cleaning times to increase wafer throughput. Further advantages of this invention include: (1) reduced processing time due to fewer chemical processing steps required; (2) reduced flammability of the cleaning compositions (e.g., as compared to compositions containing high levels of isopropyl alcohol); (3) elimination of aqueous rinsing steps that can leave particles on the wafer surface; (4) fewer particles remaining on treated substrates, possibly due to improved wetting of the substrates by the fluorinated solvent; (5) better removal of residues having both inorganic and organic components; (6) comparable oxidation rates relative to aqueous systems compositions and (7) less corrosive relative to prior art aqueous systems.
The improved performance is due in part to the low surface tension and low viscosity of the fluorinated solvents used. These low surface tension contribute to the improved wetting of the surfaces, and the low viscosity contributes to improved separation of the processed silicon substrate from the cleaning composition, better draining of the composition from the surface, and more efficient evaporation of the residue from the surface. The surface tensions of the fluorinated solvents are generally less than 20 dynes/cm and preferably between 10 and 20 dynes/cm when measured at 25xc2x0 C. The viscosity values are generally less than 5, and preferably less than 1 centistokes at 25xc2x0 C.
The compositions of this invention are preferably non-flammable, which is defined herein as having a flash point of greater than about 140xc2x0 F. (about 60xc2x0 C.) when tested according to ASTM D3278-89. Because the compositions may be used in the cleaning and processing of electronic devices, it is preferred that all components of the composition be highly pure and have low concentrations of particulates, metals and non-volatile residues. In particular, the fluorinated solvents used in the composition and process of the invention should have less than 3 particles (of greater than 5.0 micron diameter) /ml, less that 5000 parts per trillion of metals and less than 250 parts per trillion of non-volatile residues.
The ozone is generally added to the fluorinated solvent immediately prior to use by any conventional technique, such as sparging or gas injection. The dissolved ozone concentration in the fluorinated solvent is typically higher than the dissolved ozone concentration in conventional aqueous compositions prepared at the same temperature, pressure and concentration of gaseous ozone being injected.
Ozone is generated using commercially available ozone generators. The ozone generators typically use an electrostatic or (corona discharge) in an air or oxygen atmosphere. The ozone thus generated is bubbled through the fluorinated solvent. The temperature, pressure and concentration of gaseous ozone being injected will determine the concentration of dissolved ozone in the fluorinated solvent.
The concentration of ozone in the fluorinated solvents may be measured by any conventional technique including titrimetry, direct and colorimetric spectrometry, amperometry, by the oxidation-reduction potential, chemiluminescence, calorimetry, thermal conductivity and isothermal pressure change on decomposition. One convenient method is to extract the ozone/fluorinated solvent with aqueous KI. The liberated iodine is then measured spectrometrically or may be titrated with standard sodium thiosulfate solution.
The co-solvent, if used, is selected to enhance the cleaning or rinsing performance of the cleaning composition. The co-solvent should be essentially non-reactive with the ozone and not substantially reduce the solubility of the ozone in the fluorinated solvent. Useful co-solvents include ethers, esters, polyethers, carboxylic acids, tertiary alcohols, hydrofluorocarbons, hydrochlorocarbons, ketones and aliphatic hydrocarbon
Representative examples of co-solvents which can be used in the cleaning composition include acetic acid, carbonic acid, formic acid, t-butyl alcohol, methyl t-butyl ether, methyl t-amyl ether, 1,2-dimethoxyethane, cyclohexane, 2,2,4-trimethylpentane, n-decane, acetone, methylcyclopentane, decalin, 2-butanone, methyl isobutyl ketone, methylene chloride, chlorocyclohexane, and 1-chlorobutane.
By substantially non-reactive it is meant that the co-solvent does not react with the ozone at an appreciable rate, or that the rate of oxidation of a silicon substrate is not significantly retarded. For this reason, co-solvents having carbon-carbon unsaturation are generally unsuitable for use. The co-solvent should be relatively volatile to facilitate evaporation from a silicon surface, with those having a b.p. of 120xc2x0 C. or less being preferred, and is preferably substantially free of other contaminants such as metals, particulates and non-volatile residues in order to effectively clean the silicon surface at the maximum rate during the manufacturing process. Generally the co-solvent may comprise 30 wt. % or less of the composition.
Fluorinated solvents useful in compositions of this invention should be chosen such that a composition can be formulated which contains up to saturation quantities, general up to about 0.1% by weight of ozone and up to about 30% by weight of optional co-solvent. It is preferred that the concentration of ozone is 10 to 500 ppm.
For rapid evaporation during the drying step, the fluorinated solvent should have a boiling point of less than about 120xc2x0 C. at atmospheric pressure. It is believed that the very low surface energy of the fluorinated solvents renders the composition much more effective as a cleaning composition: the low surface energy fluorinated solvents effectively wet the silicon surface much more readily than the conventional aqueous compositions of the prior art. Useful fluorinated solvents include hydrofluoroethers (HFEs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), hydrohalofluoroethers (HHFEs) and hydrochlorofluorocarbons (HCFCs).
The fluorinated solvent of the present invention comprises a nonionic, fluorinated hydrocarbon that may be linear, branched, or cyclic, and optionally may contain one or more additional catenary heteroatoms, such as nitrogen or oxygen. The solvent may be selected from the group consisting of fully- and partially-fluorinated alkanes, amines, and ethers. Preferably, the fluorinated solvent is partially fluorinated and is non-functional, i.e. lacking functional groups that are polymerizable, reactive toward acids, bases, oxidizing agents, reducing agents or nucleophiles.
Preferably, the number of fluorine atoms exceeds the number of hydrogen atoms in the fluorinated solvent. To be non-flammable, the relationship between the number of fluorine, hydrogen, and carbon atoms can preferably be related in that the number of fluorine atoms is equal to or exceeds the sum of the number of number of hydrogen atoms and carbon-carbon bonds:
#F atomsxe2x89xa7(#H atoms+#Cxe2x80x94C bonds).
One class of compounds useful as fluorinated solvent comprises perfluorocarbons (PFCs) in which all carbon-bound hydrogen is replaced by fluorine atoms. Such compounds are known to be inert and exhibit high thermal and chemical stability. Such PFCs may include perfluoroalkanes, perfluoroamines and, perfluoroethers, which may be linear or branched, and cyclic or acyclic. Examples of PFCs include perfluoroalkanes having the general formula CnF2n+2, perfluoroethers and polyethers having the general formula CnF2n+2Om and perfluoroamines having the general formula CnF2n+3N, where n is an integer of 3 to 20 and m is 1 to 5.
Useful fluorinated solvents typically contain from 3 to 20 carbon atoms and may optionally contain one or more catenary heteroatoms, such as divalent oxygen or trivalent nitrogen atoms. The term xe2x80x9cperfluorocarbonxe2x80x9d or xe2x80x9cPFCxe2x80x9d as used herein includes organic compounds in which all (or essentially all) of the hydrogen atoms are replaced with fluorine atoms. Representative perfluorocarbons include cyclic and non-cyclic perfluoroalkanes, perfluoroamines, perfluoroethers, perfluorocycloamines, and any mixtures thereof. Specific representative perfluorocarbons include the following: perfluoropentane, perfluorohexane, perfluoroheptane, perfluorooctane, perfluoromethylcyclohexane, perfluorotributyl amine, perfluorotriamyl amine, perfluoro-N-methylmorpholine, perfluoro-N-ethylmorpholine, perfluoroisopropyl morpholine, perfluoro-N-methyl pyrrolidine, perfluoro-1,2-bis(trifluoromethyl)hexafluorocyclobutane, perfluoro-2-butyltetrahydrofuran, perfluorotriethylamine, perfluorodibutyl ether, and mixtures of these and other perfluorinated liquids.
Commercially available PFCs that can be used in this invention include: FLUORINERT FC-43(trademark)-Electronic Fluid, FLUORINERT FC-72(trademark) Electronic Fluid, FLUORINERT FC-77(trademark) Electronic Fluid, FLUORINERT FC-84(trademark) Electronic Fluid, FLUORINERT FC-87(trademark) Electronic Fluid, Performance Fluid PF-5060(trademark), Performance Fluid PF-5070(trademark), and Performance Fluid PF-5052(trademark). Some of these liquids are described in FLUORINERT(trademark) Electronic Fluids, product bulletin 98-0211-6086(212)NPI, issued February 1991, available from 3M Co., St. Paul, Minn. Other commercially available perfluorinated liquids that are considered useful in the present invention include perfluorinated liquids sold as GALDEN(trademark) LS fluids available from Ausimont Inc., Italy, KRYTOX(trademark) and VERTREL(trademark) fluids available from DuPont and FLUTEC(trademark) PP fluids available from BNFL Fluorochemicals Ltd.
Perfluorocarbons are known and can be made by techniques such as direct fluorination, electrochemical fluorination, addition polymerization of fluorine-containing monomers and the oxidative polymerization of fluorine containing monomers. See, for example, Chemistry of Organic Fluorine Compounds II, M. Hudlicky and A. Pavlath, Eds., ACS Monograph 187, American Chemical Society, Washington, D.C., 1995, pp. 95-120.
Perfluorocarbons, since they lack chlorine atoms, are not ozone-depleting agents, but these compounds may exhibit a global warming potential (GWP) due to their long atmospheric lifetimes. It is preferred that the fluorinated solvent be partially or incompletely fluorinated, i.e. contain at least one aliphatic or aromatic hydrogen atom in the molecule. These compounds generally are very thermally and chemically stable, yet are much more environmentally acceptable in that they degrade in the atmosphere and thus have a low global warming potential, in addition to a zero ozone depletion potential, and better solvency properties.
Partially fluorinated solvents suitable for use typically contain from 3 to 20 carbon atoms and may optionally contain one or more catenary heteroatoms, such as divalent oxygen or trivalent nitrogen atoms. Useful partially fluorinated liquids include cyclic and non-cyclic fluorinated alkanes, amines, ethers, and any mixture or mixtures thereof. Preferably, the number of fluorine atoms exceeds the number of hydrogen atoms and more preferably the number of fluorine atoms is equal to or exceeds the sum of the number of hydrogen atoms and carbon-carbon bonds. Although not preferred, due to environmental concerns, the partially fluorinated liquids optionally may contain one or more chlorine atoms provided that where such chlorine atoms are present there are at least two hydrogen atoms on the geminal or adjacent carbon atom(s).
One class of useful fluorinated solvents are hydrofluorocarbons; i.e. compounds having only carbon, hydrogen and fluorine, and optionally catenary divalent oxygen and/or trivalent nitrogen. Such compounds are nonionic, may be linear or branched, cyclic or acyclic. Such compounds are of the formula CnHmF2n+2xe2x88x92m, where n is from about 3 to 20 inclusive, m is at least one, and where one or more non-adjacent xe2x80x94CF2xe2x80x94 groups may be replaced with catenary oxygen or trivalent nitrogen atoms. Preferably the number of fluorine atoms is equal to or greater than the number of hydrogen atoms, and more preferably the number of fluorine atoms is equal to or exceeds the sum of the combined number of hydrogen atoms and carbon-carbon bonds of fluorine atoms.
A preferred class of fluorinated solvents particularly useful to form the stable composition of the invention comprises hydrofluoroethers of the general formula:
(R1xe2x80x94O)nxe2x80x94R2xe2x80x83xe2x80x83(I)
where, in reference to Formula I, n is a number from 1 to 3 inclusive and R1 and R2 are the same or are different from one another and are selected from the group consisting of alkyl, aryl, and alkylaryl groups and their derivatives. At least one of R1 and R2 contains at least one fluorine atom, and at least one of R1 and R2 contains at least one hydrogen atom. R1 and R2 may also be linear, branched, cyclic or acyclic and optionally, one or both of R1 and R2 may contain one or more catenary heteroatoms, such as trivalent nitrogen or divalent oxygen. Preferably the number of fluorine atoms is equal to or greater than the number of hydrogen atoms, and more preferably the number of fluorine atoms is equal to or exceeds the sum of the number of hydrogen atoms and carbon-carbon bonds. Although not preferred, due to environmental concerns, R1 or R2 or both of them optionally may contain one or more chlorine atoms provided that where such chlorine atoms are present there are at least two hydrogen atoms on the R1 or R2 group on which they are present.
More preferably, the compositions of the present invention are prepared with hydrofluoroethers of the formula:
Rfxe2x80x94Oxe2x80x94Rxe2x80x83xe2x80x83(II)
where, in reference to Formula II above, Rf and R are as defined for R1 and R2 of Formula I, except that Rf contains at least one fluorine atom, and R contains no fluorine atoms. Such ethers may be described as segregated ethers in that the fluorinated carbons are segregated from the non-fluorinated carbons by the ether oxygen atom. More preferably, R is an acyclic branched or straight chain alkyl group, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, i-butyl, or t-butyl, and Rf is preferably a fluorinated derivative of a cyclic or acyclic, branched or straight chain alkyl group having from 3 to about 14 carbon atoms, such as n-C4F9xe2x80x94, i-C4F9xe2x80x94, i-C3F7, (n-C3F7)CFxe2x80x94 or cyclo-C6F11xe2x80x94, Rf may optionally contain one or more catenary heteroatoms, such as trivalent nitrogen or divalent oxygen atoms.
In a preferred embodiment, R1 and R2, or Rf and R, are chosen so that the compound has at least three carbon atoms, and the total number of hydrogen atoms in the compound is at most equal to the number of fluorine atoms. In the most preferred embodiment, R1 and R2 or Rf and R are chosen so that the compound has at least three carbon atoms, and more preferably number of fluorine atoms is equal to or exceeds the sum of the number of combined hydrogen atoms and carbon-carbon bonds.
Representative hydrofluoroethers described by Formula II useful in the present invention include, but are not limited to, the following compounds:
wherein cyclic structures designated with an interior xe2x80x9cFxe2x80x9d are perfluorinated.
Particularly preferred segregated hydrofluoroethers of Formula II include n-C3F7OCH3, (CF3)2CFOCH3, n-C4F9OCH3, (CF3)2CFCF2OCH3, n-C3F7OC2H5, n-C4F9OC2H5, (CF3)2CFCF2OC2H5, (CF3)3COCH3, (CF3) 3COC2H5, and mixtures thereof. Segregated hydrofluoroethers are available as 3M(trademark) NOVEC(trademark) HFE-7100 and HFE-7200 Engineered Fluids from Minnesota Mining and Manufacturing Company, St. Paul, Minn.
A number of synthetic routes to hydrofluoroethers are known. These methods may be broadly divided into two groups; methods of fluorinating an ether compound, and methods where the ether linkage is formed within a compound by reaction with a fluorine-containing precursor. The former methods include: (1) direct fluorination of an ether compound; and (2) electrochemical fluorination of an ether compound. The latter methods include: (3) the addition reaction of an alcohol to a fluorinated olefin; (4) alkylation of a partially fluorinated alcohol; and (5) non-catalytic alkylation of a fluorinated carbonyl compound with a suitable alkylating agent. Japanese Patent No. JP 6-293686 provides a partial summary description of these varied methods.
The segregated hydrofluoroethers (alkoxy-substituted perfluorocompounds) suitable for use in the process of the invention can be prepared by alkylation of perfluorinated alkoxides prepared by the reaction of the corresponding perfluorinated acyl fluoride or perfluorinated ketone with an anhydrous alkali metal fluoride (e.g., potassium fluoride or cesium fluoride) or anhydrous silver fluoride in an anhydrous polar, aprotic solvent. (See, e.g., the preparative methods described in French Patent Publication No. 2,287,432, German Patent Publication No. 1,294,949, and U.S. Pat. No. 5,750,797 (Flynn et al.). Alternatively, a fluorinated tertiary alcohol can be allowed to react with a base, e.g., potassium hydroxide or sodium hydride, to produce a perfluorinated tertiary alkoxide which can then be alkylated by reaction with alkylating agent.
Suitable alkylating agents for use in the preparation include dialkyl sulfates (e.g., dimethyl sulfate), alkyl halides (e.g., methyl iodide), alkyl p-toluenesulfonates (e.g., methyl p-toluenesulfonate), alkyl perfluoroalkanesulfonates (e.g., methyl perfluoromethanesulfonate), and the like. Suitable polar, aprotic solvents include acyclic ethers such as diethyl ether, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether; carboxylic acid esters such as methyl formate, ethyl formate, methyl acetate, diethyl carbonate, propylene carbonate, and ethylene carbonate; alkyl nitriles such as acetonitrile; alkyl amides such as N,N-dimethylformamide, N,N-diethylformamide, and N-methylpyrrolidone; alkyl sulfoxides such as dimethyl sulfoxide; alkyl sulfones such as dimethylsulfone, tetramethylene sulfone, and other sulfolanes; oxazolidones such as N-methyl-2-oxazolidone; and mixtures thereof.
As yet another alternative, the fluorinated ethers may be prepared by reacting a fluorinated carbonyl compound, such as a ketone or acid fluoride, with an alkylating agent in the presence of a Lewis acid catalyst as described in WO 99/47480 (Lamanna et al.).
Useful non-segregated hydrofluoroethers include alpha-, beta- and omega-substituted hydrofluoroalkyl ethers such as those described in U.S. Pat. No. 5,658,962 (Moore et al.), incorporated herein by reference, which can be described by the general structure shown in Formula III:
Xxe2x80x94[Rfxe2x80x2xe2x80x94O]yRxe2x80x3Hxe2x80x83xe2x80x83(III)
wherein:
X is either F, H, or a perfluoroalkyl group containing from 1 to 3 carbon atoms; each Rfxe2x80x2 is independently selected from the group consisting of xe2x80x94CF2xe2x80x94, xe2x80x94C2F4xe2x80x94, and xe2x80x94C3F6xe2x80x94;
Rxe2x80x3 is a divalent organic radical having from 1 to about 3 carbon atoms, and is preferably perfluorinated; and
y is an integer from 1 to 7, preferably from 1 to 3;
wherein when X is F, Rxe2x80x3 contains at least one F atom, and wherein the sum of the number of carbon atoms in the Rfxe2x80x2 group(s) and the number of carbon atoms in the Rxe2x80x3 group is between 4 and about 8.
Representative compounds described by Formula III useful in the present invention include, but are not limited to, the following compounds:
Preferred non-flammable, non-segregated hydrofluoroethers include C4F9OC2F4H, C6F13OCF2H, HC3F6OC3F6H, C3F7OCH2F, HCF2OCF2OCF2H, HCF2OCF2CF2OCF2H, HC3F6OCH3, HCF2OCF2OC2F4OCF2H, and mixtures thereof. Non-segregated hydrofluoroethers specialty liquids are available from Ausimont Corp., Milano, Italy, under the GALDEN H(trademark).
Useful fluorinated solvents also include hydrofluorocarbons (HFCs) having a 3- to 8-carbon backbone. The carbon backbone can be straight, branched, cyclic, or mixtures of these. Useful HFCs include compounds having more than approximately 5 molar percent fluorine substitution, or less than about 95 molar percent fluorine substitution, based on the total number of hydrogen and fluorine atoms bonded to carbon, but having essentially no substitution with other atoms (e.g., chlorine. Useful HFCs can be selected from:
(1) Compounds of Formula IV
CnHmF2n+2xe2x88x92m,xe2x80x83xe2x80x83(IV)
wherein n is at least 3, and m is at least one.
Representative compounds of Formula IV include CF3CH2CF2H, CF2HCF2CH2F, CH2FCF2CFH2, CF2HCH2CF2H, CF2HCFHCF2H, CF3CFHCF3, and CF3CH2CF3; CHF2(CF2)2CF2H, CF3CF2CH2CH2F, CF3CH2CF2CH2F, CH3CHFCF2CF3, CF3CH2CH2CF3, CH2FCF2CF2CH2F, CF3CH2CF2CH3, CHF2CH(CF3)CF3, and CHF(CF3)CF2CF3; CF3CH2CHFCF2CF3, CF3CHFCH2CF2CF3, CF3CH2CF2CH2CF3, CF3CHFCHFCF2CF3, CF3CH2CH2CF2CF3, CH3CHFCF2CF2CF3, CF3CF2CF2CH2CH3, CH3CF2CF2CF2CF3, CF3CH2CHFCH2CF3, CH2FCF2CF2CF2CF3, CHF2CF2CF2CF2CF3, CH3CF(CHFCHF2)CF3, CH3CH(CF2CF3)CF3, CHF2CH(CHF2)CF2CF3, CHF2CF(CHF2)CF2CF3, and CHF2CF2CF(CF3)2; CHF2(CF2)4CF2H, (CF3CH2)2CHCF3, CH3CHFCF2CHFCHFCF3, HCF2CHFCF2CF2CHFCF2H, H2CFCF2CF2CF2CF2CF2H, CHF2CF2CF2CF2CF2CHF2, CH3CF(CF2H)CHFCHFCF3, CH3CF(CF3)CHFCHFCF3, CH3CF(CF3)CF2CF2CF3, CHF2CF2CH(CF3)CF2CF3, and CHF2CF2CF(CF3)CF2CF3; CH3CHFCH2CF2CHFCF2CF3, CH3(CF2)5CH3, CH3CH2(CF2)4CF3, CF3CH2CH2(CF2)3CF3, CH2FCF2CHF(CF2)3CF3, CF3CF2CF2CHFCHFCF2CF3, CF3CF2CF2CHFCF2CF2CF3, CH3CH(CF3)CF2CF2CF2CH3, CH3CF(CF3)CH2CFHCF2CF3, CH3CF(CF2CF3)CHFCF2CF3, CH3CH2CH(CF3)CF2CF2CF3, CHF2CF(CF3)(CF2)3CH2F, CH3CF2C(CF3)2CF2CH3, CHF2CF(CF3)(CF2)3CF3; CH3CH2CH2CH2CF2CF2CF2CF3, CH3(CF2)6CH3, CHF2CF(CF3)(CF 2)4CHF2, CHF2CF(CF3)(CF2)4CHF2, CH3CH2CH(CF3)CF2CF2CF2CF3, CH3CF(CF2CF3)CHFCF2CF2CF3, CH3CH2CH2CHFC(CF3)2CF3, CH3C(CF3)2CF2CF2CF2CH3, CH3CH2CH2CF(CF3)CF(CF3)2 and CH2FCF2CF2CHF(CF2)3CF3.
Preferred HFCs include CF3CFHCFHCF2CF3, C5F11H, C6F13H, CF3CH2CF2H, CF3CF2CH2CH2F, CHF2CF2CF2CHF2, 1,2-dihydroperfluorocyclopentane and 1,1,2-trihydroperfluorocyclopentane. Useful HFCs include HFCs available under the VERTREL(trademark), available from E. I. duPont de Nemours and Co. (e.g., CF3CHFCHFCF2CF3); under the ZEORORA-H(trademark), available from Nippon Zeon Co. Ltd., Tokyo, Japan; and under the HFC designation from AlliedSignal Chemicals, Buffalo, N.Y.
Useful fluorinated solvents also include hydrohalofluoroethers (HHFEs). For the present invention, HHFEs are defined as ether compounds containing fluorine, non-fluorine halogen (i.e., chlorine, bromine, and/or iodine) and hydrogen atoms. An important subclass of HHFEs is perfluoroalkylhaloethers (PFAHEs). PFAHEs are defined as segregated ether compounds having a perfluoroalkyl group and a haloalkyl group, wherein at least one of the halogen atoms of the haloalkyl group is chlorine, bromine, or iodine. Useful PFAHEs include those described by the general structure shown in Formula V:
Rfxe2x80x94Oxe2x80x94CaHbFcXdxe2x80x83xe2x80x83(V)
wherein Rf is a perfluoroalkyl group preferably having at least about 3 carbon atoms, most preferably from 3 to 6 carbon atoms, and optionally containing a catenary heteroatom such as nitrogen or oxygen; X is a halogen atom selected from the group consisting of bromine, iodine, and chlorine; xe2x80x9caxe2x80x9d preferably is from about 1 to 6; xe2x80x9cbxe2x80x9d is at least 1; xe2x80x9ccxe2x80x9d can range from 0 to about 2; xe2x80x9cdxe2x80x9d is at least 1; and b+c+d is equal to 2a+1. Such PFAHEs are described in PCT Publication No. WO 99/14175, which is incorporated herein by reference. Useful PFAHEs include cxe2x80x94C6F11xe2x80x94OCH2Cl, (CF3)2CFOCHCl2, (CF3)2CFOCH2Cl, CF3CF2CF2OCH2Cl, CF3CF2CF2OCHCl2, (CF3)2CFCF2OCHCl2, (CF3)2CFCF2OCH2Cl, CF3CF2CF2CH2OCHCl2, CF3CF2CF2CF2OCH2Cl, (CF3)2CFCF2OCHClCH3, CF3CF2CF2CF2OCHClCH3, (CF3)2CFCF(C2F5)OCH2Cl, (CF3)2CFCF2OCH2Br, and CF3CF2CF2OCH2I.
Useful fluorinated solvents also include HCFCs. For the present invention, HCFCs are compounds containing a carbon backbone substituted with carbon-bound fluorine, chlorine, and hydrogen atoms. HCFCs useful as heat transfer fluids include CF3CHCl2, CH3CCl2F, CF3CF2CHCl2 and CClF2CF2CHClF. However, in the long term, HCFCs production may be banned due to ozone layer degradation.
Concentrations of ozone and fluorinated solvent components in the compositions of this invention can vary, depending upon the requirement of the silicon substrate, such as amount of surface oxidation required or amount of particulate and/or residue removal. In a cleaning composition useful concentration ranges are up to the saturation limit of ozone in a particular fluorinated solvent, and generally about 10 to 500 ppm ozone, about 0 to about 5% alcohol, and about 95 to about 99.99% fluorinated solvent. Preferably the concentration of ozone is about 50 to 250 ppm.
Ozone may be prepared by any procedure known to the art. Typically the ozone is prepared by passing oxygen or an oxygen containing gas such as air though a high voltage, alternating current electric discharge. The gaseous effluent, containing ozone is passed through a volume of fluorinated solvent, into which the ozone dissolves. Generation of ozone is more thoroughly described in Kirk-Othmer Encyclopedia of Chemical Technology, vol. 17, pp. 953-994, John Wiley and Sons (4th Edition, 1996)
In the method of the invention, a substrate is contacted with a composition comprising a fluorinated solvent and ozone and optionally co-solvent, for a time sufficient to clean the surface of the substrate. The cleaning method may be used to oxidize the surface to replace the hydrophobic silane (Sixe2x80x94H) groups with hydrophilic silanol (Sixe2x80x94OH) groups, remove particulates or residues, rinse and dry the surface or a combination of these. The method preferably comprises the additional step of separating the cleaned substrate from the cleaning composition.
The cleaning composition is used in the liquid state and any of the known techniques for xe2x80x9ccontactingxe2x80x9d a substrate can be utilized. For example, a liquid cleaning composition can be sprayed, brushed or poured onto the substrate, or the substrate can be immersed in a liquid composition. Elevated temperatures, ultrasonic energy, and/or agitation can be used to facilitate the cleaning. Various different solvent cleaning techniques are described by B. N. Ellis in Cleaning and Contamination of Electronics Components and Assemblies, Electrochemical Publications Limited, Ayr, Scotland, pages 182-94 (1986).
After contacting, the substrate may be removed from the cleaning composition. Normally draining is sufficient to remove substantially all of the cleaning composition from the surface of the substrate. This may be enhanced by the application of heat, agitation, air jets, or spinning of the substrates (i.e. centrifugal removal processes) to effect more complete removal, as desired. Additionally the cleaning process may further comprise a rinsing step to ensure complete removal of the cleaning composition. The substrate may be rinse in any solvent known to be useful in the cleaning of substrates. Although alcohols are known in the art, their use represents a potential fire hazard. It is preferred to rinse in a fluorinated solvent (such as those previously described), which may be the same of different then that used in the cleaning composition.
Normally after extended use, replacement, renewal or purification of the composition is required. Such techniques including filtration to remove particulates, extraction to remove soluble residues or salts, decantation and distillation to recover the fluorinated solvent may be used. It will be noted that as a silicon surface is cleaned, the compositions begin to become contaminated. Removal of particulates and residues from the substrate lead to a build up of these materials in the composition. In particular the process may produce both water and various silanols. As the concentration of water increases, it will eventually phase separate from the composition as a less dense, water-rich phase. This may be easily separated from the cleaning composition by techniques known in the art, such as decantation or use of a weir. The cleaning composition may then be recycled. It is generally not necessary or desirable to recover any co-solvent from the spent cleaning composition, as these materials are present in small amounts and not readily recovered. It is more desirable to recover the fluorinated solvent and to add or charge ozone to it.

Fluorinated solvent compositions containing ozone


The present invention provides plating solutions, particularly copper plating solutions, designed to provide uniform coatings on substrates and to provide substantially defect free filling of small features formed on substrates with none or low supporting electrolyte, i.e., which include no acid, low acid, no base, or no conducting salts, and/or high metal ion, e.g., copper, concentration. Defect free filling of features is enhanced by a plating solution containing blends of polyethers (xe2x80x9ccarrierxe2x80x9d) and organic divalent sulfur compounds (xe2x80x9cacceleratorxe2x80x9d), wherein the concentration of the carrier ranges from about 0.1 ppm to about 2500 ppm of the plating solution, and the concentration of the accelerator ranges from about 0.05 ppm to about 1000 ppm of the plating solution. The plating solution is further improved by adding an organic nitrogen compound at a concentration from about 0.01 ppm to about 1000 ppm to improve the filling of vias on a resistive substrate. The organic nitrogen is preferably a substituted thiadiazole, which is used at concentrations from 0.1 ppm to about 50 ppm of the plating solution, or a quartenary nitrogen compound, which is used at concentrations from about 0.01 ppm to about 500 ppm.

1. Field of the Invention
The present invention relates to new formulations of metal plating solutions designed to provide uniform coatings on substrates and to provide defect free filling of small features, e.g., micron scale features and smaller, formed on substrates with metals.
2. Background of the Related Art
Electrodeposition of metals has recently been identified as a promising deposition technique in the manufacture of integrated circuits and flat panel displays. As a result, much effort is being focused in this area to design hardware and chemistry to achieve high quality films on substrates which are uniform across the area of the substrate and which can fill or conform to very small features.
Typically, the chemistry, i.e., the chemical formulations and conditions, used in conventional plating cells is designed to provide acceptable plating results when used in many different cell designs, on different plated parts and in numerous different applications. Cells which are not specifically designed to provide highly uniform current density (and the deposit thickness distribution) on specific plated parts require high conductivity solutions to be utilized to provide high xe2x80x98throwing powerxe2x80x99 (also referred to as high Wagner number) so that good coverage is achieved on all surfaces of the plated object. Typically, a supporting electrolyte, such as an acid or a base, or occasionally a conducting salt, is added to the plating solution to provide the high ionic conductivity to the plating solution necessary to achieve high xe2x80x98throwing powerxe2x80x99. The supporting electrolyte does not participate in the electrode reactions, but is required in order to provide conformal coverage of the plated material over the surface of the object because it reduces the resistivity within the electrolyte, the higher resistivity that otherwise occurs being the cause of the non-uniformity in the current density. Even the addition of a small amount, e.g., 0.2 Molar, of an acid or a base will typically increase the electrolyte conductivity quite significantly (e.g., almost double the conductivity).
However, on objects such as semiconductor substrates that are resistive, e.g., metal seeded wafers, high conductivity of the plating solution negatively affects the uniformity of the deposited film. This is commonly referred to as the terminal effect and is described in a paper by Oscar Lanzi and Uziel Landau, xe2x80x9cTerminal Effect at a Resistive Electrode Under Tafel Kineticsxe2x80x9d, J. Electrochem. Soc. Vol. 137, No. 4 pp. 1139-1143, April 1990, which is incorporated herein by reference. This effect is due to the fact that the current is fed from contacts along the circumference of the part and must distribute itself across a resistive substrate. If the electrolyte conductivity is high, such as in the case where excess supporting electrolyte is present, it will be preferential for the current to pass into the solution within a narrow region close to the contact points rather than distribute itself evenly across the resistive surface, i.e., it will follow the most conductive path from terminal to solution. As a result, the deposit will be thicker close to the contact points. Therefore, a uniform deposition profile over the surface area of a resistive substrate is difficult to achieve.
Another problem encountered with conventional plating solutions is that the deposition process on small features is controlled by mass transport (diffusion) of the reactants to the feature and by the kinetics of the electrolytic reaction instead of by the magnitude of the electric field as is common on large features. In other words, the replenishment rate at which plating ions are provided to the surface of the object can limit the plating rate, irrespective of voltage. Essentially, if the voltage dictates a plating rate that exceeds the local ion replenishment rate, the replenishment rate dictates the plating rate. Hence, highly conductive electrolyte solutions that provide conventional xe2x80x9cthrowing powerxe2x80x9d have little significance in obtaining good coverage and fill within very small features. In order to obtain good quality deposition, one must have high mass-transport rates and low depletion of the reactant concentration near or within the small features. However, in the presence of excess acid or base supporting electrolyte, (even a relatively small excess) the transport rates are diminished by approximately one half (or the concentration depletion is about doubled for the same current density). This will cause a reduction in the quality of the deposit and may lead to fill defects, particularly on small features.
It has been learned that diffusion is of significant importance in conformal plating and filling of small features. Diffusion of the metal ion to be plated is directly related to the concentration of the plated metal ion in the solution. A higher metal ion concentration results in a higher rate of diffusion of the metal into small features and in a higher metal ion concentration within the depletion layer (boundary layer) at the cathode surface, hence faster and better quality deposition may be achieved. In conventional plating applications, the maximum concentration of the metal ion achievable is typically limited by the solubility of its salt. If the supporting electrolyte, e.g., acid, base, or salt, contain a co-ion which provides a limited solubility product with the plated metal ion, the addition of a supporting electrolyte will limit the maximum achievable concentration of the metal ion. This phenomenon is called the common ion effect. For example, in copper plating applications, when it is desired to keep the concentration of copper ions very high, the addition of sulfuric acid will actually diminish the maximum possible concentration of copper ions. The common ion effect essentially requires that in a concentrated copper sulfate electrolyte, as the sulfuric acid (H2SO4) concentration increases (which gives rise to H+ cations and HSO4xe2x88x92 and SO4xe2x88x92 anion), the concentration of the copper (II) cations decreases due to the greater concentration of the other anions. Consequently, conventional plating solutions, which typically contain excess sulfuric acid, are limited in their maximal copper concentration and, hence, their ability to fill small features at high rates and without defects is limited.
Therefore, there is a need for new formulations of metal plating solutions designed particularly to provide good quality plating of small features, e.g., micron scale and smaller features, on substrates and to provide uniform coating and defect-free fill of such small features.
The present invention provides plating solutions having novel blends of specific additives that enhance defect-free fill of small features. The plating solutions promote uniform metal deposition within the features and can provide highly reflective metal surfaces without polishing. The plating solutions typically contain little or no supporting electrolyte (i.e., which include no acid, low acid, no base, or no conducting salts) and/or high metal ion concentration (e.g., copper). The additives that enhance uniform deposition include a polyether (xe2x80x9ccarrierxe2x80x9d), such as a polyalkylene glycol, wherein the concentration of the carrier ranges from about 0.1 ppm to about 2500 ppm of the plating solution. The additives further include an organic divalent sulfur compound (xe2x80x9cacceleratorxe2x80x9d), wherein the concentration of the accelerator ranges from about 0.05 ppm to about 1000 ppm of the plating solution. The plating solution may further include halide ions at a concentration from about 5 ppm to about 400 ppm. The plating solutions may also contain additives which enhance the plated film quality and performance by serving, inter alia, as brighteners, levelers, surfactants, grain refiners, and stress reducers. An organic nitrogen compound is preferably added to the compositions at a concentration from about 0.01 ppm to about 1000 ppm to improve the filling of vias on a resistive substrate. Most preferably a substituted thiadiazole such as 2-amino-5-methyl-1,3,4-thiadiazole or 2-amino-5-ethyl-1,3,4-thiadiazole is added to solutions that contain the polyether and the divalent sulfur compound.
The present invention generally relates to electroplating solutions having low conductivity, particularly those solutions containing no supporting electrolyte or low concentration of supporting electrolyte, i.e., essentially no acid or low acid concentration (preferably less than 0.1 molar acid solution, and where applicable, no or low base), essentially no conducting salts and high metal concentration to achieve good deposit uniformity across a resistive substrate and to provide good fill within very small features such as micron and sub-micron sized features and smaller. The invention provides plating solutions having high concentrations of metal ions and low concentrations of additives that provide uniform plating of the metal ions over the substrate and provide void free deposition within small features.
The additives to the plating solution preferably include blends of a polyether (xe2x80x9ccarrierxe2x80x9d), an organic divalent sulfur compound (xe2x80x9cacceleratorxe2x80x9d), and a nitrogen compound as described in more detail below.
The concentration of the carrier ranges from about 0.1 ppm to about 2500 ppm of the plating solution. Preferably the plating solution contains a polyalkylene glycol at a concentration of from about 0.5 ppm to about 2000 ppm. The polyalkylene glycols have a molecular weight from about 60 to about 100,000. A preferred polyalkylene glycol is UCON(copyright) 75-1400 polyalkylene glycol at a concentration from about 5 ppm to about 500 ppm.
The concentration of the xe2x80x9cacceleratorxe2x80x9d ranges from about 0.05 ppm to about 1000 ppm of the plating solution. Preferably the plating solution comprises from about 0.1 ppm to about 60 ppm of an accelerator having the structure R1xe2x80x94(S)nxe2x80x94R2, wherein R1 and R2 are the same or different organic groups, and n is the number of sulfur atoms between 1 and 6. Typically, R1 and R2 are the same or different alkyl groups terminated with an acid or a salt, such as a sulfonic acid or a sulfonate, a phosphoric acid or a phosphate, a nitric acid or a nitrate, or a sulfuric acid or a sulfate. A preferred divalent sulfur compound is the disodium salt of 3,3-dithiobis-1-propanesulfonic acid.
Other additives are included, and may improve brightening and other properties of the resultant metal plated on substrates when used in electroplating solutions with no or low supporting electrolyte, e.g., no or low acid. Filling of submicron features is enhanced by addition of soluble organic compounds containing nitrogen and sulfur bound to the same carbon atom by single or double bonds. Preferred additives are from about 0.1 ppm to about 1000 ppm of a nitrogen containing organic compound comprising a ring structure containing from 4 to 10 nitrogen, carbon, or sulfur atoms that form the ring, or from about 0.01 to about 500 ppm of a quartenary nitrogen compound or a nitrogen compound that forms a quartenary nitrogen compound in the plating solution. The preferred additives are from about 0.1 ppm to about 50 ppm of a substituted thiodiazole having the cyclic structure:
wherein X1 and Y2 can be the same or different groups, including amines, hydrogen, alkyl groups with 1 to 6 carbon atoms, ethyl-thio groups, hydroxyl or sulfonate groups. The preferred additives are 2-amino-5-methyl-1,3,4-thiadiazole, 2-amino-5-ethyl-1,3,4-thiadiazole, 2-amino-5-isopropyl-1,3,4-thiadiazole, and 2-amino-5-propyl-1,3,4-thiadiazole. The 5-methyl and 5-ethyl compounds have demonstrated improved filling of apertures on resistive substrates at reasonably high (40 to 60 mA/cm2) current density. The substituted thiadiazole is most preferably used at concentrations from about 0.5 ppm to about 5 ppm of the plating solution. The plating compositions alternatively can include a quartenary nitrogen compound selected from alkylated polyimines, phenazine dyes, triazoles, tetrazoles, or mixtures thereof.
The plating solutions of the invention also preferably contain halide ions, such as chloride ions, bromide, fluoride, iodide, typically in amounts from 0 to about 0.2 g/L, preferably from about 5 ppm to about 400 ppm. However, this invention also contemplates the use of copper plating solutions without chloride or other halide ions.
The invention is described below in reference to plating of copper on substrates in the electronic industry. However, it is to be understood that the electroplating solutions, particularly those having low or complete absence of supporting electrolyte, can be used to deposit other metals on resistive substrates and has application in any field where plating can be used to advantage.
In one embodiment of the invention, aqueous copper plating solutions are employed which are comprised of copper sulfate, preferably from about 200 to about 350 grams per liter (g/l) of copper sulfate pentahydrate in water (H2O), and essentially no added sulfuric acid, or very low acid, less than 0.1 M. The copper concentration may be from about 0.1 to about 1.2 Molar, and is preferably greater than about 0.8 Molar. In addition to copper sulfate, the invention contemplates copper salts other than copper sulfate, such as copper fluoborate, copper gluconate, copper sulfamate, copper sulfonate, copper pyrophosphate, copper chloride, copper cyanide, copper citrate, and the like, all without (or with little) supporting electrolyte. Some of these copper salts offer higher solubility than copper sulfate, and therefore may be advantageous.
The conventional copper plating electrolyte includes a relatively high sulfuric acid concentration (from about 45 g of H2SO4 per L of H2O (0.45 M) to about 110 g/L (1.12 M)) which is added to the solution to provide high conductivity to the electrolyte. The high conductivity is necessary to reduce the non-uniformity in the deposit thickness caused by the cell configuration and the differently shaped parts encountered in conventional electroplating cells. However, the present invention is directed primarily towards applications where the cell configuration has been specifically designed to provide a relatively uniform deposit thickness distribution on given parts. However, the substrate is resistive and imparts thickness non-uniformity to the deposited layer. Thus, among the causes of non-uniform plating, the resistive substrate effect may dominate and a highly conductive electrolyte, containing, e.g., high H2SO4 concentrations, is unnecessary. In fact, a highly conductive electrolyte (e.g., generated by a high sulfuric acid concentration) is detrimental to uniform plating because the resistive substrate effects are amplified by a highly conductive electrolyte. This is the consequence of the fact that the degree of uniformity of the current distribution, and the corresponding deposit thickness, is dependent on the ratio of the resistance to current flow within the electrolyte to the resistance of the substrate. The higher this ratio is, the lesser is the terminal effect and the more uniform is the deposit thickness distribution. Therefore, when uniformity is a primary concern, it is desirable to have a high resistance within the electrolyte. Since the electrolyte resistance is given by 1/xcexaxcfx80r2, it is advantageous to have as low a conductivity, xcexa, as possible, and also a large gap, 1, between the anode and the cathode. Also, clearly, as the substrate radius, r, becomes larger, such as when scaling up from 200 mm wafers to 300 mm wafers, the terminal effect will be much more severe (e.g., by a factor of 2.25). By eliminating the acid, the conductivity of the copper plating electrolyte typically drops from about 0.5 S/cm (0.5 ohmxe2x88x921 cmxe2x88x921) to about {fraction (1/10)} of this value, i.e., to about 0.05 S/cm, making the electrolyte ten times more resistive.
Also, a lower supporting electrolyte concentration (e.g., sulfuric acid concentration in copper plating) often permits the use of a higher metal ion (e.g., copper sulfate) concentration due to elimination of the common ion effect as explained above. Furthermore, in systems where a soluble copper anode is used, a lower added acid concentration (or preferably no acid added at all) minimizes harmful corrosion and material stability problems. Additionally, a pure or relatively pure copper anode can be used in this arrangement. Because some copper dissolution typically occurs in an acidic environment in the presence of dissolved oxygen, copper anodes that are being used in conventional copper plating typically contain phosphorous. The phosphorous forms a film on the anode that protects it from excessive dissolution, but phosphorous traces will be found in the plating solution and also may be incorporated as a contaminant in the deposit. In applications using plating solutions with no acidic supporting electrolytes as described herein, the phosphorous content in the anode may, if needed, be reduced or eliminated. Also, for environmental considerations and ease of handling the solution, a non acidic or low acid electrolyte is preferred.
Another method for enhancing thickness uniformity includes applying a periodic current reversal. For this reversal process, it may be advantageous to have a more resistive solution (i.e., no supporting electrolyte) since this serves to focus the dissolution current at the extended features that one would want to preferentially dissolve.
In some specific applications, it may be beneficial to introduce small amounts of acid, base or salts into the plating solution. Examples of such benefits may be some specific adsorption of ions that may improve specific deposits, complexation, pH adjustment, solubility enhancement or reduction and the like. Also, addition of a small amount of acid (e.g. sulfuric acid) will prevent the formation of copper oxides on the surfaces. The invention also contemplates the addition of such acids, bases or salts into the electrolyte in amounts up to about 0.4 M.
A plating solution having a high copper concentration (i.e.,  greater than 0.4M) is beneficial to overcome mass transport limitations that are encountered when plating small features. In particular, because micron scale features with high aspect ratios typically allow only minimal or no electrolyte flow therein, the ionic transport relies solely on diffusion to deposit metal into these small features. A high copper concentration, preferably about 0.8 molar (M) or greater, in the electrolyte enhances the diffusion process and reduces or eliminates the mass transport limitations. The metal concentration required for the plating process depends on factors such as temperature and the acid concentration of the electrolyte.
The plating solutions of the present invention are typically used at current densities ranging from about 10 mA/cm2 to about 80 mA/cm2. Current densities as high as 100 mA/cm2 and as low as 5 mA/cm2 can also be employed under appropriate conditions. In plating conditions where a pulsed current or periodic reverse current is used, current densities in the range of about 5 mA/cm2 to about 400 mA/cm2 can be used periodically.
The operating temperatures of the plating solutions may range from about 0xc2x0 C. to about 95xc2x0 C. Preferably, the solutions range in temperature from about 15xc2x0 C. to about 60xc2x0 C.
The copper plating solutions of the invention preferably contain chloride ions, typically in amounts from about 30 ppm to about 120 ppm, most preferably from about 40 ppm to about 80 ppm. However, this invention also contemplates the use of copper plating solutions without chloride or other halide ions.
The copper plating solutions of the invention are suppressed by the polyalkylene glycol xe2x80x9ccarriersxe2x80x9d. An example of a preferred carrier that is commercially available is UCON Lubricant 75-H-1400 polyalkylene glycol available from Union Carbide Corp. of Danbury, Conn. This carrier has a general formula of:
H(OCH2CH2)x(OCH2CH(CH3))yOH
wherein x and y provide an approximate weight average molecular weight of 2500. The specific gravity is 1.095 at 20xc2x0 C.
Copper plating solutions containing polyalkylene glycols are accelerated by organic divalent sulfur compounds having the structure R1xe2x80x94(S)nxe2x80x94R2, wherein R1 and R2 are the same or different organic groups, and n is the number of sulfur atoms between 1 and 6. Preferably R1and R2 are the same or different alkyl groups having from 1 to 8 carbon atoms, and are terminated with an acid or a salt, such as a sulfonic acid or a sulfonate. Commercially available organic divalent sulfur compounds include xe2x80x98SPSxe2x80x99 which is the disodium salt of 3,3-dithiobis-1-propanesulfonic acid, available from Raschig Corp. of Richmond, Va. The commercial disodium salt comprises at least 80% of the SPS, and the remaining components include monosodium salts of 3-mercapto-1-propanesolfonic acid or 3-hydroxy-1-propanesulfonic acid. The commercial SPS may also contain the disodium salt of 3,3-thiobis-1-propanesulfonic acid.
In addition to the constituents described above, the copper plating solutions may contain various additives that are introduced typically in small (ppm range) amounts. The additives typically improve the thickness distribution (levelers), the reflectivity of the plated film (brighteners), its grain size (grain refiners), stress (stress reducers), adhesion and wetting of the part by the plating solution (wetting agents), and other process and film properties.
The additional additives typically constitute small amounts (ppm level) from one or more of the following groups of chemicals:
1. Organic nitrogen compounds and their corresponding salts and polyelectrolyte derivatives thereof.
2. Polar heterocycles
A preferred additive is 2-amino-5-methyl-1,3,4-thiadiazole, which is available from Aldrich, and is used at concentrations from 0.1 ppm to about 50 ppm of the plating solution, preferably from about 0.5 ppm to about 5 ppm. The additive enhances the surface brightness of the deposited metal and improves filling of sub-micron features with copper.
Further understanding of the present invention will be had with reference to the following examples which are set forth herein for purposes of illustration but not limitation.

Electrodeposition chemistry for filling of apertures with reflective metal


The invention relates to a device for delaying the pylorus passage of orally administered medicament forms. Said device comprises a component which expands upon contact with the gastric juice and a polymer coat which is permeable to liquids but not to gases. The device can contain an active substance whose release into the gastric juice is mainly controlled by the medicament form into which it is incorporated. Unlike conventional medicament forms with delayed pylorus passage, the release of the active substance does not so much depend on the kind and structure of the polymer coat but is mainly determined by the incorporated medicament form. The inventive device can be easily rolled or folded and can be filled into capsules.

This application is a 371 of PCT/EP99/08043 filed Oct. 23, 1999.
The present invention describes a device for delaying the pyloric passage of orally assimilable pharmaceutical forms having a component which is expandable on contact with gastric juice and a polymer coat which is permeable to liquids but gas-tight. The device can contain an active compound which is mainly released into the gastric juice in a controlled manner by the incorporated pharmaceutical form. Compared with conventional pharmaceutical forms having a delayed pyloric passage, the release of active compound is less dependent on the nature and composition of the polymer coat and is mainly determined by the incorporated form. The device according to the invention can be easily rolled or folded and can be filled into capsules.
U.S. Pat. No. 4,207,890 describes a device for the controlled release of active compounds, which due to its expansion undergoes local retention in the stomach and thereby has a prolonged residence time in the stomach. The device has (a) a polymer coat which is present in collapsed form before administration. The polymer coat itself has no openings and consists of a material which is virtually unhydratable, but is permeable to body fluids. The device additionally has (b) an element which controls the release of active compound. According to claim 2, this element can be the polymer coat itself. As a further element (c), the device has a component which is expandable in contact with body fluids.
The driving principle of the retentive action is osmosis, the element (c) being an osmotically active substance which drives water through the polymer coat (a) and thereby causes the formation of a solution in the device. The device will thus contain an aqueous solution in the expanded state and on account of the concentration conditions will make possible a diffusion of active compound from the device, but will correspond approximately to the chyme in its apparent density. The device will thus float or sink in the chyme. The retentive principle is exclusively the size of the device. A possible deflation mechanism is not described, thus removal of the device from the stomach and disposal after active compound administration is not elucidated.
A modification of the principle of retention is shown in EP 0 307 904 A1 and U.S. Pat. No. 4,996,058. Expandable components indicated are substances which, under admission of acid, form gaseous components such as carbon dioxide or nitrogen which inflate the polymer coat (a) and thus form a device which can be floated on the chyme. The principle of retention (see U.S. Pat. No. 4,996,058 column 3, lines 6 to 7) is floating on the chyme and thus the device is protected from emptying of the stomach through the pylorus. These devices have crucial disadvantages. In both cases, the control of the release of active compound essentially takes place through the polymer coat. At the same time, the inflation kinetics of the device are essentially limited by the polymer coat, as water and hydronium ions must diffuse through the polymer coat, but on the other hand active compound molecules must diffuse out in the opposite direction. The diffusion constant in the polymer coat is a crucial parameter. In the case of damage to the relatively thin and thus sensitive polymer coat by mechanical or chemical action, there is the danger of a sudden release of the active compound in the sense of dose-dumping. The extent of the expanding amount of gas produced depends, inter alia, strongly on the acidity of the environment and thus, however, on the composition of the chyme and the secretion of gastric acid. In the case of a strongly acidic environment and thus high gas production, the mechanical stress on the devices must not reach the bursting limit, on the other hand, in the case of a less acidic environment, an adequate production of gas must be achieved. This dilemma leads to highly variable states of the devices as a result of circadian variations in the gastric acidity.
The invention is therefore based on the object of making available a gastroretentive system which avoids these disadvantages of the systems known in the prior art.
According to the invention, these problems are solved by a gastroretentive device which contains the following elements:
(a) a polymer coat of microporous membrane or partially microporous membrane or a combination of both with another nonporous film-like polymer. The production of the pores can be carried out according to the invention by any desired process, e.g. by stretching of films, by use of multiphase systems and evaporation of a part of the system, by controlled polymerization, e.g. in the form of ionomers, by mechanical processes such as needling, by thermal processes such as lasers, or by irradiation with ionizing radiation and subsequent etching etc. Materials which can be used according to the invention for the microporous membrane are: polyurethanes, polypropylene, polyvinyl alcohol, polyvinyl acetate, polyacrylic acid and derivatives, polymethylmethacrylic acid and derivatives, polycarbonates, polyvinylidene difluoride, polytetrafluoroethylene and any other desired polymers which can be provided with pores of suitable size. According to the invention, the size of these pores is between 0.1 and 20 xcexcm, preferably between 0.3 and 10 xcexcm and particularly preferably between 0.5 and 1 xcexcm. If appropriate, in order to make the pores better wettable, the membranes according to the invention can be impregnated with wetting agents or other hydrophilic components.
(b) an expandable component which produces a gas such as, for example, carbon dioxide or nitrogen on contact with gastric juice, in particular under the action of acid. Examples of these used according to the invention are, for example, carbonates and hydrogencarbonates of the alkali metals and alkaline earth metals, the ammonium cations or sodium azide or mixtures thereof. These expandable components can be optionally modified for the modification of the gas production kinetics, e.g. by coating with or embedding in lipophilic components such as waxes or fats or suitable coatings such as polymethacrylates or polymethylmethacrylates and derivatives or similar substances known to the person skilled in the art. According to the invention, the expandable component can also be foam-forming, e.g. as a result of the incorporation into polyvinyl alcohol, or in the form of a semisolid, ointment-like preparation, in order to control the deflation kinetics.
(c) a component containing the active compound such as, for example, multiparticulate preparations, tablets, capsules or semisolid, ointment-like preparations, or foams. Possible active compounds are fundamentally all substances having a physiological action, in particular pharmaceuticals for human or veterinary medicine, preferably those which are absorbed by the gastric mucosa or act on the surface of the gastric mucosa. Such pharmaceutical active compounds are known to the person skilled in the art. The components (b) and (c) can also be present in a joint preparation.
The device can be filled into a container made of physiologically acceptable material, for example into a hard gelatin capsule, in order to facilitate administration and handling.
The inflated form of the device is preferably that of an inflated triangle in order to have a planar structure of maximum bulk. Due to the planarity, in the state floating on the chyme, two preferred positions are stable which both allow passage of the chyme past the gastroretentive device such that the chyme cannot force the inflated form through the pylorus. Among the planar forms, the form of a triangle is a good compromise of bulkiness and stiffness of the structure in the inflated state and is therefore proposed for the retentive device. In the stomach, the bulky structure wedges between the stomach walls and allows the chyme to escape through the pylorus. The wedging in the lumen only has to withstand the flow resistance in the chyme. The more spherical the device, the more likely a bulb-like sealing of the stomach exit is conceivable, with the result that the emptying pressure forces the device through the pylorus. According to the invention, however, quadrangular and polygonal structures and also those having rounded corners can also be used.
As a result of the use of the microporous or porous polymer coat, according to the invention a number of problems can be solved. Owing to the surface tension of liquid, in particular aqueous systems, a certain pressure is necessary for the emptying of a liquid-filled pore, which essentially depends on pore diameter, surface tension and interfacial tension and the contact angle. By a suitable choice of the pore diameter, a defined pressure can be set for a given system, below which the pores cannot be emptied. The membrane is thus gas-tight. Liquids, however, can easily flow through the membrane; the flow is specified by the pore number and the dimensions of the pores and also the viscosity of the medium. By using microporous membranes of defined pore size, it is thus possible according to the invention to produce a device which is highly permeable to liquids, but impermeable to gases below a defined pressure. The internal pressure of the device is thereby limited to a prespecified value. On exceeding the pressure limit, the membrane becomes permeable and prevents, as a nondestructive safety device, mechanical stress on the device above the permissible bursting pressure. Thus it is possible with the device according to the invention to achieve an almost constant internal pressure over the period of use of the device. The period of use of the device is controllable by the nature and amount of the expandable component. By means of capillarity, particles lying on the inside of the membrane are wetted and release the active compound through the microporous membrane with only a small delay.
The systems according to the invention can be employed in human and veterinary medicine.

Expandable gastroretentive therapeutical system with prolonged stomach retention time