This invention relates to an imaging element comprising a base polyester layer, an absorbent polyester layer above said base layer, and a glossy polymer layer above said absorbent layer; wherein said element has a 60xc2x0 Gardner gloss greater than 30% wherein said glossy polymer layer has openings comprising between 5.0 and 10.0% of the surface area

The present invention relates generally to an opaque image-recording element and, more particularly, the present invention relates to a recording element for an automated printing assembly such as a computer-driven ink-jet printer having excellent ink-receiving properties and high gloss.
In a typical ink-jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye, and a large amount of solvent in order to prevent clogging of the nozzle. The recording agent can also be a pigment. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol or a polyhydric alcohol or a mixed solvent of water and other water miscible solvents such as a monohydric alcohol or a polyhydric alcohol. The recording elements or media typically comprise a substrate or a support material having on at least one surface thereof an ink-receiving or image-forming layer. The elements include those intended for reflection viewing, which usually have an opaque support, and those intended for viewing by transmitted light, which typically have a transparent support.
While a wide variety of different types of image-recording elements have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have severely limited their commercial usefulness. The requirements for an image-recording medium or element for ink-jet recording are very demanding. For example, the recording element must be capable of absorbing or receiving large amounts of ink applied to the image-forming surface of the element as rapidly as possible in order to produce recorded images having high optical density, good color gamut, and fast dry times.
One example of an opaque image-recording element is described in U.S. Pat No. 5,326,391. It consists of a layer of a microporous material which comprises a matrix consisting essentially of a substantially water-insoluble thermoplastic organic polymer, such as a linear ultra-high molecular weight polyethylene, a large proportion of finely divided water-insoluble filler of which at least about 50 percent by weight is siliceous, and interconnecting pores. The porous nature of the image-recording element disclosed in U.S. Pat. No. 5,326,391 allows inks to penetrate the surface of the element to produce text and/or graphic images. However, the cost of producing these elements is relatively high. Also, the image density has been found to be of poor quality, ie., the images have low optical densities and poor color gamut. U.S. Pat. No. 5,605,750 describes an element which addresses the latter shortcomings of image density and color gamut via the application of an upper image-forming layer. This upper image forming layer is a porous, pseudo-boehmite having an average pore radius of from 10 to 80 xc3x85. Such an element, however, has a high manufacturing cost to form the absorbent layer. This is due to the requirements for a porous substrate such as described in U.S. Pat. No. 5,326,391.
U.S. application Ser. No. 09/472,487, filed Dec. 27, 1999, describes an open celled, voided support made via coextrusion which provides an opaque image-recording element suitable for use in an ink-jet printer, and which is capable of recording images (including color images) having fast dry times, high optical densities and good color gamut, but which is also capable of being manufactured at a relatively low manufacturing cost. However, the support described in said patent application has a matte surface due to the protrusions in the top layer external surface. Said protrusions are created by the void initiating fillers near the surface during the stretching process. It is desirable to obtain a glossy surface for a xe2x80x9cphoto qualityxe2x80x9d ink jet print, while maintaining fast dry time.
There remains a need for an image-receiving member that has rapid absorption of ink and has a glossy surface(60 degree gloss greater than 30%) and which can be manufactured at a relatively low cost.
This invention provides an imaging element comprising a base polyester layer, an absorbent polyester layer above said base layer, and a glossy polymer layer above said absorbent layer; wherein said element has a 60xc2x0 Gardner gloss greater than 30%. In a preferred embodiment the element has an ink absorbency rate resulting in a dry time of less than 10 seconds and a total absorbent capacity of at least 14.0 cm3/m2.
The imaging element of the invention has numerous advantages over the prior practices in the art which have been described in U.S. application Ser. No. 09/472,487, filed Dec. 27, 1999, the entire disclosure of which is incorporated herein by reference. The additional advantage claimed by this invention is that a glossy surface is obtained on an otherwise matte surface. The imaging element of this invention may be made on readily available polyester film formation machines. The imaging element preferably are made in one step with the absorbent layer and the bottom base layer being co-extruded, stretched, and integrally connected during formation. The imaging elements are low in cost, as the one pass formation process leads to low manufacturing cost. The imaging elements have rapid absorption of ink, as well as high absorbent capacity, which allows rapid printing and short dry time. Short dry time is advantageous, as the prints are less likely to smudge and have higher image quality as the inks do not coalesce prior to drying. The imaging elements have the look and feel of paper, which is desirable to the consumer. The imaging element is weather resistant and resistant to curling under differing humidity conditions. The imaging elements further have high resistance to tearing and deformation.
As used herein the terms xe2x80x9ctopxe2x80x9d, xe2x80x9cabovexe2x80x9d, xe2x80x9cupperxe2x80x9d refer to the side or toward the side of the imaging element on which the ink is applied. The terms xe2x80x9clowerxe2x80x9d, xe2x80x9cbelowxe2x80x9d and xe2x80x9cbottomxe2x80x9d refer to the side or toward the side of the imaging element opposite to that to which the ink is applied.
The layers of the element of this invention have levels of voiding, thickness, and smoothness adjusted to provide optimum ink absorbency and stiffness. Preferably the layers are co-extruded. The polyester sheet has a voided layer to efficiently absorb the printed inks commonly applied to ink-jet imaging supports without the need of multiple processing steps and multiple coated layers. The polyester base layer of the invention provides stiffness to the imaging element of the invention. It also provides physical integrity to the highly voided absorbing layer. The thickness of the base layer is chosen such that the total imaging element thickness is 50 to 500 xcexcm depending on the required stiffness of the element. However, the thickness of the absorbent polyester layer is adjusted to the total absorbent capacity of the medium. A thickness of at least 28.0 xcexcm is needed to achieve a total preferred absorbency of at least 14 cc/m2. The preferred thickness is between 30 and 60 xcexcm. Preferably the absorbent capacity is between 14 and 30 cc/m2. The rate at which inks are absorbed into the absorbent layer is critical as discussed hereinbefore. The voiding should be such that the voids are interconnected or open-celled. This type of structure enhances the ink absorption rate by enabling capillary action to occur. The element of the described invention has an absorbent layer with an absorbing rate resulting in a dry time of less than 10 seconds. This dry time is measured by printing a color line on the side of the top layer with an ink-jet printer at a laydown of approximately 15 cm3/m2 utilizing typical inks of the following formulation:
This may be accomplished utilizing an HP Photo-Smart ink-jet printer using standard a HP dye-based ink cartridge (HP # C3844A and C3845A) with the printed lines running in the direction of the sheet as it is conveyed through the printer. Dry time is measured by superposing a fresh printing paper on top of the printed line pattern immediately after printing and pressing the papers together with a roller press. If a particular printed line transfers to the surface of the fresh paper, its transferred length L can be used for estimating the dry time tD using a known linear transport speed S for the printer based on the formula       t    D    =      L    S
In a preferred embodiment of the invention, the ink absorbency rate results in a measured dry time of less than 1 second. The thickness of the voided layer should be such as to enable at least 14.0 cm3 of ink to be absorbed per 1 m2. The actual thickness can be determined by using the formula t=14.0/v where v is the void volume fraction defined as the ratio of voided thickness minus unvoided thickness to the voided thickness. The unvoided thickness is defined as the thickness that would be expected had no voiding occurred.
Due to the voiding of the absorbing layer, the surface of the image-recording element described would normally be rough and have a matte appearance. This problem is overcome, however, by the application of a coated polymer layer over the voided layer which results in a smooth layer with pores comprising less than 10% of the surface area, and preferably comprising between 5.0% and 10.0% of the surface area. This layer is aqueous or solvent coated over the cast film prior to stretching. During stretching the microbeads in the voided layer protrude at the surface of the voided layer. The coated layer stretches over these protrusions resulting in a smoother top surface than would occur without the coated layer. At the peak of the protrusions caused by the microbeads, a thinning of the coated layer occurs resulting in occasional rupture of the coated surface-forming pores. These pores, which cover less than 10% of the total coated area, maintain the absorptivity of the voided layer. The smooth surface which covers greater than 90% of the coated area enhances the gloss of the image-recording element. Typically the final thickness of the glossy polymer layer should be less than 0.4 xcexcm in order to achieve the 10% or less pore area to maintain dry time. The thickness is preferably between 0.1 and 0.3 xcexcm. Preferably the imaging element has a 60 degree Gardner gloss greater than 30%, and more preferably between 30% and 50%.
The choice of glossy layer polymer is limited to polymers which adhere to the absorbent layer and have a break elongation at the stretching temperature used which is greater than the stretch ratio used. Examples of such polymers are polyesters, polyvinylalcohols, polyvinylpyrrolidone, and polyurethanes. Preferably the polymer may be an aqueous dispersible polyester or a blend thereof. Polyester ionomers and blends of such with polyvinylpyrrolidone are particularly preferred. One such polyester ionomer is Eastek 1100 from Eastman Chemicals (Knoxville, Tenn.). Eastek 1100 is a water-dispersible polyester ionomer synthesized from addition polymers of isophthalic acid and sodium sulfo-isophthalic acid, along with diethylene glycol and 1,4-cyclohexane dimethanol.
Small particle pigments can also be included in the glossy polymer layer to help aid in gloss. Examples of such pigments are colloidal silica or fumed alumina.
The polyester utilized in the absorbent layer should have a glass transition temperature between about 50xc2x0 C. and 150xc2x0 C., preferably 60-100xc2x0 C., should be stretchable, and have an inherent viscosity of at least 0.50, preferably 0.6 to 0.9 dl/g. Suitable polyesters include those produced from aromatic, aliphatic, or cycloaliphatic dicarboxylic acids of 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24 carbon atoms. Examples of suitable dicarboxylic acids include terephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid, succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic, 1,4-cyclohexane-dicarboxylic, sodiosulfoisophthalic, and mixtures thereof. Examples of suitable glycols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, 1,4-cyclohexane-dimethanol, diethylene glycol, other polyethylene glycols and mixtures thereof. Such polyesters are well known in the art and may be produced by well-known techniques, e.g., those described in U.S. Pat. Nos. 2,465,319 and 2,901,466. Preferred continuous matrix polymers are those having repeat units from terephthalic acid or naphthalene dicarboxylic acid and at least one glycol selected from ethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Poly(ethylene terephthalate), which may be modified by small amounts of other monomers, is especially preferred. Other suitable polyesters include liquid crystal copolyesters formed by the inclusion of a suitable amount of a co-acid component such as stilbene dicarboxylic acid. Examples of such liquid crystal copolyesters are those disclosed in U.S. Pat. Nos. 4,420,607; 4,459,402; and 4,468,510.
The base layer is substantially impermeable. In its preferred embodiment this base layer is comprised of poly(ethylene terephthalate) and its copolymers, which are lowest in cost and readily available.
Suitable particles for the microbeads used for void generation in the absorbent layer during sheet formation are either commercially available inorganic fillers or polymerizable organic materials. The size of the microbeads is preferably in the range of 0.01 to 10 xcexcm, preferably 0.7 to 5.0 xcexcm. Typical inorganic materials are silica, alumina, calcium carbonate, and barium sulfate. Typical polymeric organic materials are polystyrenes, polyamides, fluoro polymers, polycarbonates, or polyolefins. The microbeads are at least partially bordered by voids. The void space in the supports should occupy at least 40%, preferably 50-70%, by volume of the absorbent layer. At this level of voiding the voids have been shown to be interconnected or open-celled. Any less voiding results in a closed cell structure, which does not lend itself to capillary action and thus fast ink absorbency rate is not achievable. Depending on the manner in which the supports are made, the voids may completely encircle the microbeads, e.g., a void may be doughnut-shaped (or flattened doughnut) encircling a microbead, or the voids may only partially surround the microbeads, e.g., a pair of voids may border a microbead on opposite sides.
During stretching the voids assume characteristic shapes from the balanced biaxial orientation of paperlike films to the uniaxial orientation of microvoided/satinlike fibers. Balanced microvoids are largely circular in the plane of orientation, while fiber microvoids are elongated in the direction of the fiber axis. The size of the microvoids and the ultimate physical properties depend upon the degree and balance of the orientation, temperature and rate of stretching, crystallization kinetics, the size distribution of the microbeads, and the like.
The film supports according to this invention are preferably prepared by:
(a) forming a mixture of molten continuous matrix polymer and microbeads uniformly dispersed throughout the matrix polymer
(b) forming a two-layered sheet from the mixture by co-extrusion of material in (a) with a base polyester layer and casting said sheet on a chill roll,
(c) coating a glossy polymer layer on said cast coextruded sheet over the layer containing microbeads and drying
(d) orienting the cast sheet by stretching to form voids in the layer containing microbeads at least partially bordering the microbeads on sides thereof in the direction, or directions of orientation.
The mixture may be formed by forming a melt of the matrix polymer and mixing therein the microbeads. When using microbeads of the cross-linked polymer, it may be in the form of solid or semisolid microbeads. Due to the incompatibility between the matrix polymer and cross-linked polymer, there is no attraction or adhesion between them, and they become uniformly dispersed in the matrix polymer upon mixing.
After the microbeads are uniformly dispersed in the polymer matrix the resin is used to form a layered film structure by the co-extrusion process. Any one of the known techniques for coextruding cast polymer sheets can be employed. Such forming methods are well known in the art. Typical coextrusion technology is taught in W. J. Schrenk and T. Alfrey, Jr, xe2x80x9cCoextruded Multilayer Polymer Films and Sheets,xe2x80x9d Chapter 15, Polymer Blends, p. 129-165, 1978, Academic Press; and D. Djorjevic, xe2x80x9cCoextrusion,xe2x80x9d Vol. 6, No. 2, 1992, Rapra Review Reports.
Coating of the glossy layer can be achieved by any of the known coating methods in the art. The polymer coating formulation can be dispersed as finely divided particles in an aqueous-dispersion medium which is then used as a coating liquid for the formation of the gloss layer. The polymer of the present invention may be prepared by emulsion polymerization, that is, obtained as an aqueous dispersion of particulate emulsion polymerizate, a so-called latex. In addition, the polymer may be an aqueous-dispersible polymer, such as an aqueous-dispersible polyester. The polymer may also be aqueous soluble, such as poly(vinyl alcohol), or the like. A part of the water may be replaced by a water-miscible organic solvent (e.g., methanol or acetone). A coating aide is typically added to aide in wetting the polyester support.
Aqueous compositions containing the present polymers used in the glossy layer are preferably used in such a manner that the polymer prepared as an aqueous dispersion according to the aforementioned alternate methods is diluted, if necessary, with water or a water-miscible organic solvent so that the solids concentration in the diluted dispersion of said polymer may become 1-20 weight %. The mode of using the present composition may vary depending on the purpose for which said composition is used and on the coating technique employed therefor. The aqueous compositions may contain a variety of additives besides the above-mentioned polymer. For instance, the aqueous compositions may comprise, in order to improve dispersibility of polymer particles or coatability of the composition at the time of coating, anionic surface active agents such as alkali metal or ammonium salts of alcohol sulfuric acid of 8 to 18 carbon atoms; ethanolamine lauryl sulfate; ethylaminolauryl sulfate; alkali metal and ammonium salts of paraffin oil; alkali metal salts of aromatic sulfonic acid such as dodecane-1-sulfonic acid, octadiene-1-sulfonic acid or the like; alkali metal salts such as sodium isopropylbenzene-sulfate, sodium isobutylnaphthalenesulfate or the like; and alkali metal or ammonium salts of esters of sulfonated dicarboxylic acid such as sodium dioctylsulfosuccinate, disodium dioctadecylsulfosuccinate or the like; nonionic surface active agents such as saponin, sorbitan alkyl esters, polyethyl oxides, polyoxyethylene alkyl ethers or the like; cationic surface active agents such as octadecyl ammonium chloride, trimethyldosecyl ammonium chloride or the like; and high molecular surface active agents other than those above mentioned such as polyvinyl alcohol, partially saponified vinyl acetates, maleic acid containing copolymers, gelatin or the like. Further, additives which may be incorporated into the present aqueous composition include inorganic pigments such as titanium oxide, silicon oxide, colloidal silica, zinc oxide, aluminum oxide, etc., matting agents comprising particles of polymers such as polymethyl methacrylate, etc., antistatic agents comprising inorganic salts or copolymers and, according to the purpose for which the present aqueous composition is used, dyes or pigments for coloring purposes and alkali or acid for adjusting a pH value of the present polymer-containing composition.
It is also possible to use coalescing aides, more preferably phenolic or naphtholic type compounds (in which one or more hydroxy groups are substituted onto an aromatic ring), for example, phenol, resorcinol, orcinol, catechol, pyrogallol, 2-4-dinitrophenol, 2,4,6-dinitrophenol, 4-chlororesorcinol, 2-4-dihydroxy toluene, 1,3-naphthalenediol, the sodium salt of 1-naphthol-4-sulfonic acid, o-fluorophenol, m-fluorophenol, p-fluorophenol, o-cresol, p-hydroxybenzotrifluoride, gallic acid, 1-naphthol, chlorophenol, hexyl resorcinol, chloromethylphenol, o-hydroxybenzotrifluoride, m-hydroxybenzotrifluoride, and the like, and mixtures thereof. Chloromethylphenol is especially preferred for use with glycidyl-functional homopolymers. Other coalescing agents include acrylic acid, benzyl alcohol, trichloroacetic acid, chloral hydrate, ethylene carbonate, and combinations of the foregoing. Typically, the concentration of the coalescing aide is about 5-30%, by weight of solids, preferably 10-20% in the glossing layer.
The aqueous polymeric composition of the present invention is usually coated and dried on the cast coextruded sheet at a coverage of approximately 0.3-3 g of polymer solids per m2 of support and, in this case, the conventional coating technique is applicable, for example, dip coating, roll coating, spray coating, or the like. Subsequent drying is then done to evaporate off the carrier and leave a continuous polymer layer on the cast sheet.
It is important that the cast, laminated sheet be subsequently oriented by stretching in at least one direction. Methods of unilaterally or bilaterally orienting sheet or film material are well known in the art. Basically, such methods comprise stretching the sheet or film at least in the machine or longitudinal direction, after it is cast on a chill roll, by an amount of about 1.5-4.5 times its original dimension. Such sheet or film may also be stretched in the transverse or cross-machine direction by apparatus and methods well known in the art, in amounts of generally 1.5-4.5 times the original dimension. Stretching to these ratios is necessary to sufficiently void the top layer and to achieve desired levels of thickness uniformity and mechanical performance. Such apparatus and methods are well known in the art and are described, for example, in U.S. Pat. No. 3,903,234. The final dry coverage of the polymer gloss layer after stretching ranges from 30 mg/m2 to 300 mg/m2 based on the weight of the polymer. When the amount is less than the above, the gloss promoting effect is small.
The element as heretofore described can be coated on the top layer with an ink receiving layer commonly used which contains mordanting agents to hold the ink dyes close to the top surface of the support. Said ink receiving layer may also contain UV absorbers and the like. Such layers are generally very thin and do not significantly reduce the absorbency rates of the support under said receiving layer. Preferably the ink receiving layer would comprise silica particles in a polyvinyl alcohol matrix. One preferred ink jet receiving layer is described in U.S. application Ser. No. 09/650,069 filed Aug. 29, 2000.
Ink jet inks used to image the recording elements of the present invention are well known in the art. The ink compositions used in ink jet printing may be dye or pigment based and typically are liquid compositions comprising aqueous, non-aqueous, or mixed solvents, as well as other additives such as humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. The dyes used in such compositions are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, U.S. Pat. Nos. 4,381,946; 4,239,543; and 4,781,758, the disclosures of which are hereby incorporated by reference.
The following examples illustrate the practice of this invention. They are not intended to be exhaustive of all possible variations of the invention. Parts and percentages are by weight unless otherwise indicated.

Gloss coating on permeable surface imaging support


Various techniques for holding open an SSSV using expansion technology are disclosed. A sleeve is delivered to the SSSV and expanded mechanically or hydraulically to deposit the deformed sleeve in position over a flapper or against a flow tube holding the flapper in the open position.

The field of this invention is mechanisms that can hold open a subsurface safety valve (SSSV) that has malfunctioned so that another valve can be installed to take its place.
SSSVs are normally closed valves that are used primarily in offshore and gas wells to prevent uncontrollable flow of fluid to the surface, in the event the surface safety equipment fails to properly operate. If the SSSV malfunctions or for any other reason requires replacement with a backup SSSV, the well operator will normally want the old SSSV locked in the open position so it does not interfere with well operations after the old SSV has been taken out of service. Typically, to avoid undue complication in the design and operation of an SSSV, the lock open assembly is not installed with the SSSV but is subsequently run in when needed on an accessory tool known as a flapper lock open (FLO) tool.
One known design of an FLO tool is U.S. Pat. No. 4,577,694, which illustrates the use of a scroll of wound spring steel that is allowed to spring out after being delivered to the SSSV to keep the flapper from rotating back to a closed position. The downside of this design and several others is that flow through the locked open SSSV could and did, at times, dislodge the lock open device, allowing the flapper to close off the well. In this particular patent, the ring of steel was coiled, like a watch spring and held at opposite ends until properly positioned. When the delivery tool released the ring, it sprang outwardly to contact the flapper. This tool was complicated and required stocking of various sizes of rings as well as an installation method that involved two wireline trips with jar down/jar up activation.
Another technique, shown in U.S. Pat. No. 5,574,889 required that the flow tube be engaged and forcibly moved down to get the flapper into the open position. After that one or more indentations were made in the flow tube, which could engage a shoulder and prevent the flow tube from returning to the flapper-closed position. This device had several disadvantages. The flow tube was permanently damaged. The tool required enough force to overcome bias on the flow tube to push it into the flapper open position. Finally, part of the procedure required pumping fluid under pressure into the well, which could adversely affect subsequent production.
Another technique, shown in U.S. Pat. No. 5,564,675, the flow tube is forcibly engaged and pushed so far down that the actuating piston comes out of its seal bore in a manner as to wedge the flow tube in the flapper open position. This design has similar disadvantages as U.S. Pat. No. 5,574,889 and a further disadvantage that flow communication to the control system occurs due to operation of this lock open device.
Another technique illustrated in U.S. Pat. No. 6,059,041, forces the flow tube down and releases an expandable tube to hold the flapper open. Similar, disadvantages as the previous two techniques are realized in this design.
Other art in the area of lock open devices for SSSVs includes U.S. Pat. Nos. 3,786,866; 4,344,602; 4,967,845; 4,624,315 and 4,457,379. Of more general interest are U.S. Pat. Nos. 5,040,283(using a shape memory metal for downhole patches); 4,846,281; 4,760,879; 4,729,432; 4,566,541 and 4,213,508.
One of the objectives of the present invention is to deliver and set a hold open device in an SSSV in a manner that it will not become dislodged. The technique to accomplish this objective comprises using an expansion of a tubular member so as to deform it into position where it will prevent a flow tube from returning to the flapper closed position or to actually use the expanded structure directly against the flapper when it is held open by the flow tube. Those skilled in the art will have a clearer understanding of the various embodiments for accomplishing the objective of holding an SSSV in an open position from the detailed description of the preferred embodiment and the claims, which appear below.
Various techniques for holding open an SSSV using expansion technology are disclosed. A sleeve is delivered to the SSSV and expanded mechanically or hydraulically to deposit the deformed sleeve in position over a flapper or against a flow tube holding the flapper in the open position.


A multilayer copper structure has been provided for improving the adhesion of copper to a diffusion barrier material, such as TiN, in an integrated circuit substrate. The multilayer copper structure comprises a thin high-resistive copper layer to provide improved adhesion to the underlying diffusion barrier layer, and a low-resistive copper layer to carry the electrical current with minimum electrical resistance. The invention also provides a method to form the multilayer copper structure.

The demand for progressively smaller, less expensive, and more powerful electronic products creates the need for smaller geometry integrated circuits (ICs), and large substrates. It also creates a demand for a denser packaging of circuits onto IC substrates. The desire for smaller geometry IC circuits requires that the dimensions of the interconnection between components and dielectric layers be as small as possible. Therefore, recent research continues developing methods of reducing the cross section area of via interconnects and connecting lines. The conductivity of the interconnects is reduced as the surface area of the interconnect is reduced, and the resulting increase in interconnect resistivity has become an obstacle in IC design. Conductors having high resistivity create conduction paths with high impedance and large propagation delays. These problems result in unreliable signal timing, unreliable voltage levels, and lengthy signal delays between components in the IC. Propagation discontinuities also result from intersecting conduction surfaces that are poorly connected, or from joining conductors having highly different resistivity characteristics.
There is a need for interconnects and vias that have low resistivity, and the ability to withstand volatile process environments. Aluminum and tungsten metals are often used in the production of integrated circuits for making-interconnections or vias between electrically active areas. These metals are popular because there is much knowledge, experience and expertise due to the long term usage in production environment.
Copper is a natural choice to replace aluminum in the effort to reduce the size of lines and vias in an electrical circuit. The conductivity of copper is approximately twice that of aluminum and over three times that of tungsten. As a result, the same current can be carried through a copper line having half the width of an aluminum line.
The electromigration characteristics of copper are also much superior to those of aluminum. Copper is approximately ten times more resistance to electromigration than aluminum. As a result, a copper line, even one having a much smaller cross-section than an aluminum line, is better able to maintain electrical integrity.
However, there have been problems associated with the use of copper in IC processing. Copper poisons the active area of silicon devices, creating unpredictable responses. Copper also diffuses easily through many materials used in IC processes and, therefore, care must be taken to keep copper from migrating.
Various means have been suggested to deal with the problem of copper diffusion into integrated circuit materials. Several materials, including metals and metal alloys, have been suggested for use as barriers to prevent copper diffusion. The typical conductive diffusion barrier materials are TiN, TaN and WN. Addition of silicon into these materials to create TiSiN, TaSiN, WSiN, could improve the diffusion barrier properties. For non-conductive diffusion barrier, silicon nitride has been the best material so far. However, adhesion of copper to these diffusion barrier materials has been, and continues to be, an IC process problem.
The conventional process of sputtering, used in the deposition of aluminum, will not work well when the geometry of the selected IC features becomes small. Therefore new deposition processes have been used to deposit diffusion barrier and copper lines and interconnects in an integrated circuit. It is impractical to sputter metal, either aluminum or copper, to fill small diameter vias, since the gap filling capability is poor. One of the techniques to deposit copper that provides excellent gap fill capability is the chemical vapor deposition (CVD) technique.
In a typical copper CVD process, copper is combined with a ligand, or a organic compound, to make the copper volatile. That is, copper becomes an element in a compound, called a precursor, that is vaporized into a gas. Selected surfaces of an integrated circuit, such as that of diffusion barrier materials, are exposed to the copper precursor in an elevated temperature environment. When the copper precursor decomposes, copper is left behind on the selected surfaces and the remaining gases (by-products) are exhausted away. Several copper precursors are available for use with the CVD process. It is generally accepted that the configuration of the copper precursors, at least partially, affects the ability of the copper residue to adhere itself to the selected surfaces. Although certain precursors may improve the copper adhesion process, variations in the diffusion barrier surfaces to which the copper is applied, and variations in the copper precursors themselves, often result in unsatisfactory adhesion of copper to a selected surface.
Similarly, diffusion barrier materials could be deposited by the chemical vapor deposition technique. For example, in the case of TiN CVD deposition, a precursor that contains Ti and optionally nitrogen, is used. The precursor decomposes at the selected surfaces, and the decomposed elements react together to form a TiN layer on these selected surfaces. Precursor by-products (products formed as the precursor decomposes that do not participate in the reactions) and reaction by-products (products formed from the reaction that do not deposit on the selected surfaces) are often volatile and are exhausted away.
Another deposition technology similar to the CVD technique is atomic layer deposition (ALD). In ALD various gases are injected into the chamber for as short as 100–500 milliseconds in alternating sequences. For example, a first gas is delivered into the chamber for about 500 milliseconds and the substrate is heated, then the first gas (heat optional) is turned off. The residue from the first gas is then evacuated. Another gas is delivered into the chamber for another 500 milliseconds (heat optional). The residue from this gas is also evacuated before the next gas is delivered for about 500 milliseconds (and optionally heated). This sequence is done until all gases have been cycled through the chamber, each gas sequence typically forms a monolayer which is highly conformal. ALD technology thus pulses gas injection and heating sequences that are between 100 and 500 milliseconds. This approach has a high dissociation energy requirement to break the bonds in the various precursor gases such as silane and oxygen and thus requires the substrate to be heated to a high temperature, for example in the order of 600–800 degree Celsius for silane and oxygen processes.
ALD also uses radical generators, such as plasma generators, to increase the reactivity of the second gas and effect the reaction between the first and the second gases at the substrate. U.S. Pat. No. 5,916,365 to Sherman entitled "Sequential chemical vapor deposition" provides for sequential chemical vapor deposition by employing a reactor operated at low pressure, a pump to remove excess reactants, and a line to introduce gas into the reactor through a valve. Sherman exposes the part to be coated to a gaseous first reactant, including a non-semiconductor element of the thin film to be formed, wherein the first reactant adsorbs on the part. The Sherman process produces sub-monolayer per gas injection due to adsorption. The first reactant forms a monolayer on the part to be coated (after multiple cycles), while the second reactant passes through a radical generator which partially decomposes or activates the second reactant into a gaseous radical before it impinges on the monolayer. This second reactant does not necessarily form a monolayer but is available to react with the deposited monolayer. A pump removes the excess second reactant and reaction products completing the process cycle. The process cycle can be repeated to grow the desired thickness of film.
There are other applications using plasma in ALD process. U.S. Pat. No. 6,200,893 to Sneh entitled "Radical-assisted sequential CVD" discusses a method for CVD deposition on a substrate wherein radical species are used in alternate steps to depositions from a molecular precursor to treat the material deposited from the molecular precursor and to prepare the substrate surface with a reactive chemical in preparation for the next molecular precursor step. By repetitive cycles a composite integrated film is produced. In a preferred embodiment the depositions from the molecular precursor are metals, and the radicals in the alternate steps are used to remove the ligands left from the metal precursor reactions, and to oxidize or nitride the metal surface in subsequent layers.
In one embodiment taught by Sneh, a metal is deposited on a substrate surface in a deposition chamber by (a) depositing a monolayer of metal on the substrate surface by flowing a molecular precursor gas or vapor bearing the metal over a surface of the substrate, the surface saturated by a first reactive species with which the precursor will react by depositing the metal and forming reaction product, leaving a metal surface covered with ligands from the metal precursor and therefore not further reactive with the precursor; (b) terminating flow of the precursor gas or vapor; (c) purging the precursor with an inert gas; (d) flowing at least one radical species into the chamber and over the surface, the radical species is highly reactive with the surface ligands of the metal precursor layer and eliminates the ligands as reaction product, and saturates the surface, providing the first reactive species; and (e) repeating the steps in order until a metallic film of desired thickness results.
In another Sneh aspect, a metal nitride is deposited on a substrate surface in a deposition chamber by (a) depositing a monolayer of metal on the substrate surface by flowing a metal precursor gas or vapor bearing the metal over a surface of the substrate, the surface saturated by a first reactive species with which the precursor will react by depositing the metal and forming reaction product, leaving a metal surface covered with ligands from the metal precursor and therefore not further reactive with the precursor; (b) terminating flow of the precursor gas or vapor; (c) purging the precursor with inert gas; (d) flowing a first radical species into the chamber and over the surface, the atomic species highly reactive with the surface ligands of the metal precursor layer and eliminating the ligands as reaction product and also saturating the surface; (e) flowing radical nitrogen into the chamber to combine with the metal monolayer deposited in step (a), forming a nitride of the metal; (f) flowing a third radical species into the chamber terminating the surface with the first reactive species in preparation for a next metal deposition step; and (g) repeating the steps in order until a composite film of desired thickness results.
The Sneh embodiments thus deposit monolayers, one at a time. This process is relatively time-consuming when a thick film is desired.
Another application of sequential deposition is nanolayer thick film deposition (NLD) which is disclosed in U.S. patent application Ser. No. 09/954,244 filed on Sep. 10, 2001 to Tue Nguyen et al. NLD is a process of depositing a thin film by chemical vapor deposition, including the steps of evacuating a chamber of gases, exposing a workpiece to a gaseous first reactant, wherein the first reactant deposits on the workpiece to form the thin film, then evacuating the chamber of gases, and exposing the workpiece, coated with the first reactant, to a gaseous second reactant under plasma, wherein the thin film deposited by the first reactant is treated to form the same materials or a different material.
In comparison with CVD, atomic layer deposition (ALD or ALCVD) is a modified CVD process that is temperature sensitive and flux independent. ALD is based on self-limiting surface reaction. ALD provides uniform deposition over complex topography and is temperature independent since the gases are adsorbed onto the surface at lower temperatures than that of CVD because it is in the adsorption regime.
As discussed in Sherman and Sneh, the ALD process includes cycles of flowing gas reactant into the chamber, adsorbing one sub-monolayer onto the wafer surface, purging the gas reactant, flowing a second gas reactant into the chamber, and reacting the second gas reactant with the first gas reactant to form a monolayer on the wafer substrate. Thick film is achieved by deposition of multiple cycles.
It has become standard practice in the semiconductor industry to apply CVD copper immediately after the deposition of the diffusion barrier material to the integrated circuit to improve the adhesion and to reduce the contact resistance. Typically, the processes are performed in a single chamber or an interconnected cluster chamber. It has generally been thought that the copper layer has the best chance of adhering to the diffusion barrier material when the diffusion barrier material surface is clean and free of contaminants. Hence, the diffusion barrier surface is often kept under vacuum, or in a controlled environment, and the copper is deposited on the diffusion barrier as quickly as possible. However, even when copper is immediately applied to the diffusion barrier surface, copper adhesion to the diffusion barrier remains a problem.
The problem is compounded because good diffusion barrier materials adhere poorly to most materials. In addition, copper also has a low adhesion property to many materials. Therefore adhesion of direct CVD copper to a diffusion barrier surface is even more difficult.
To improve the adhesion property of copper to a diffusion barrier, it is imperative to change the interfacial property between the copper and the diffusion barrier. U.S. Pat. No. 5,909,637, to Charneski, et al., entitled "Copper adhesion to a diffusion barrier surface and method for same", proposed a method to use reactive gas species to clean the surface of the diffusion barrier to improve the adhesion to the subsequently deposited copper layer. This method has very limited success and often does not provide enough adhesion to be practical. U.S. Pat. No. 5,913,144, to Nguyen, et al., entitled "Oxidized diffusion barrier surface for the adherence of copper and method for same", further proposed a method to use reactive oxygen species to oxidize the diffusion barrier surface to improve the adhesion to the subsequently deposited copper layer. This method works well to improve the adhesion property, but by oxidizing the barrier material and producing a non conductive layer, even a very thin layer, significantly increases the contact resistance of the integrate circuit. A co-pending application Ser. No. 10/292,929 filed Nov. 13, 2002, now U.S. Pat. No. 6,670,266 to Nguyen, et al. entitled "Multilayer diffusion barrier structure for improving adhesion property" disclosed a method to partially incorporate oxygen into the thin diffusion barrier surface to improve the adhesion of copper to the diffusion barrier without the formation of a non conductive oxide layer.
However, the thickness of the diffusion barrier is much thinner than the thickness of the copper layer because much of the conductive area needs to be devoted to copper in order to improve the conductivity. Therefore modifying the copper layer to improve adhesion to the diffusion barrier is much simpler than modifying the diffusion barrier.
It would be advantageous to develop a copper structure having improved adhesion of CVD copper to a diffusion barrier material surface.
It would be advantageous to employ a method of improving the adhesion of CVD copper to a diffusion barrier material surface without modifying the diffusion barrier structure.
It would be advantageous to employ a method of improving the adhesion of CVD copper to a diffusion barrier material surface that can be optimized with respect to the contact resistance.
Accordingly, a structure and method of improving the adhesion of copper to the diffusion barrier surface are provided. The structure is a multilayer copper structure, comprising layers of:                a) a thin high-resistive copper layer, whereby this layer serves to improve the adhesion of copper to the underlying diffusion barrier layer; and        b) a low-resistive copper layer, in which the resistivity of the low resistive layer is lower than the resistivity of the high resistive layer, whereby this layer serves to carry the electrical current with minimum electrical resistance.
The presence of oxygen tends to promote the adhesion of copper to a certain diffusion barrier materials. TiN, for example, exhibits much improved adhesion to copper when being oxidized. The resistivity of TiN is around 100–1000 μΩ-cm, depending on the deposition technique. After being oxidized, the film becomes non conductive, thus it is not suitable for conductive diffusion barrier. Providing a thin oxide to use tunneling phenomenon for conduction, a method proposed in U.S. Pat. No. 5,913,144 to Nguyen, et al., would not be a reliable method since the resistance based on the tunneling current is exponentially proportional to the thickness of the oxide film. Oxy-nitriding the TiN film, a method proposed in a co-pending patent application Ser. No. 10/292,929, filed Nov. 13, 2002, now U.S. Pat. No. 6,670,266 to Nguyen, et al., entitled "Multilayered diffusion barrier structure for improving adhesion property", would be a preferred method since the amount of oxygen incorporating into the TiN film could be adjusted to optimizing the adhesion and the film resistance. However the difficulty with oxy-nitriding the diffusion barrier is the thickness and the high resistivity of the TiN film. Therefore the current invention discloses a structure to improve the adhesion. The deposited copper film comprises two layers, a high resistive copper layer to serve as an adhesion layer, and a low resistive copper layer in which the resistivity of the low resistive layer is lower than the resistivity of the high resistive layer, whereby this layer serves to carry the electrical current with minimum electrical resistance.
The thickness of the high resistive copper layer in the multilayered copper can be less than 5 nm. The thickness of this layer is optimization between the desired adhesion and the overall resistivity. Since the high resistive copper layer typically has lower resistivity than the diffusion barrier, the thickness can be high without affecting the overall resistivity significantly.
The increase in resistivity of the high-resistive copper layer can be due to the presence of excess oxygen. The oxygen incorporated in the copper layer in the form of impurities or in the form of copper oxides, thus raising the resistivity. The presence of oxygen in the high-resistive copper layer promotes the bonding with the selected underlying diffusion barrier such as TiN. In some aspects of the invention, the multilayered copper structure further comprises a diffusion barrier structure. With the enhanced adhesion feature of the multilayered copper structure, the diffusion barrier structure could just be a simple diffusion barrier layer. To further improve the adhesion, the diffusion barrier could be a multilayered diffusion barrier structure, like the one disclosed in a co-pending patent application Ser. No. 10/292,929, filed Nov. 13, 2002, now U.S. Pat. No. 6,670,266 to Nguyen, et al., entitled "Multilayered diffusion barrier structure for improving adhesion property".
The current invention also provides a method to form the multilayered copper structure to improve the adhesion to an underlying diffusion barrier structure. The method comprises the steps of:                a) depositing a thin high-resistive copper layer, whereby this high-resistive layer serves to improve the adhesion of copper to the underlying diffusion barrier layer;        b) treating the thin high-resitive copper layer to reduce the resistance of the thin high-resistive copper layer, whereby the treatment step improves the conductivity of the high-resistive copper layer without destroying the adhesion property; and        c) depositing a low-resistive copper layer, in which the resistivity of the low-resistive layer is lower than the resistivity of the treated high-resistive layer, whereby this layer serves to carry the electrical current with minimum electrical resistance.
The high-resistive copper layer is needed for adhesion purpose, but the high resistance of this layer is a side effect. The high resistance of the copper layer is normally achieved by the introduction of oxygen to form copper oxide. But copper oxide is not an electrically conductive material, therefore if the high-resistive layer is composed of 100% copper oxide, it would be non-conducting and the circuit would be broken. The amount of oxygen incorporated would be small so that the high-resistive copper layer is still conducting. In other words, the high-resistive copper layer would be composed mainly of copper with only a small fraction of copper oxide to improve adhesion and have high conductance.
To improve the conductance without sacrify the adhesion, a treatment step is performed following the formation of the high-resistive copper layer. The purpose of the treatment step is to reduce the resistance of the high-resistive copper layer without destroying the adhesion. There is no need to reduce the resistance to that of copper metal level, because that would damage the adhesion. The amount of resistance reduction can be controlled so that there is a balance between resistivity and adhesion.
There are various ways to reduce copper oxide to copper metal. The basic technique is by oxygen gettering. A special purpose chemical is introduced to get oxygen from the copper oxide layer, meaning reacting with copper oxide to form copper metal and some by-products. One method uses plasma hydrogen. Energetic hydrogen will react with copper oxide to take oxygen away from copper oxide. Another method uses an organic compound such as a composition of alcohols, aldehydes and formic acid. The organic compound will react with copper oxide to reduce it to copper metal with volatile by-products to be exhausted away. Still another method uses special metals. Special metals with lower heat of formation than that of copper oxide will take oxygen from copper oxide. This special metal will need to have the oxide phase conductive so that the total resistivity of the high-resistive layer is reduced. Examples of metals that have its oxide phase conducting are iridium, indium tin, tin. Selecting the special metals needs to take into consideration the possibility of the alloying property of copper with this special metal. Still another method is the alloying property of copper oxide to form high temperature superconducting material. Materials such as La, Sr, Nd, Ce, Y, Ba, Pb, Tl, and Ca can combine with copper and oxygen in certain compositions to form superconducting material. At the current progress, the temperature for superconducting is still lower than room temperature. However, its resistivity is much less than nonconducting materials.
In some aspects of the invention, the increase in resistivity of the high-resistive copper layer is due to the presence of oxygen.
To be effective in treating the high-resistive copper layer, the layer lo might have to be thin enough. Therefore the current invention also disclose a method where the formation of the high-temperature copper layer and the treatment of this layer are repeated many times until achieving a desired thickness before depositing the low-resistive copper layer. The desired thickness can be directly related to the adhesion property.
In some aspects of the invention, the total thickness of the treated high-resistive copper layer in the multilayered copper is less than 5 nm. In some aspects of the invention, the resistivity of the high-resistive copper layer is between 10 to 500 μΩ-cm, and the resistivity of the treated high-resistive copper layer is between 3 to 400 μΩ-cm.
To be effective in treating the high-resistive copper layer, the layer might have to be thin. Therefore the thickness of the high-resistive copper layer can be less than a monolayer, which is roughly about 0.5 nm. The formation of less-than-a-monolayer thickness can be performed by an ALD method. In ALD method, a copper carrying precursor can be adsorbed on the surface of a workpiece to form a copper layer. The resistivity of this layer depends on the precursor. The resistivity of this layer can also be modified by adding an oxygen carrying precursor.
The thin high-resistive copper layer can be deposited by the chemical vapor deposition technique. Copper CVD deposition uses liquid precursors such as Cu-hfac-L, in which hfac is hexafluoroacetylacetonate, and L is a ligand that permits the copper precursor to deposit pure copper. Typical L is trimethylvinylsilane (tmvs), alpha methyl styrene, and 3-hexene, dimethyl cyclooctadiene. For lowest resistivity, copper-hfac-tmvs requires an additional small amount of water as disclosed in U.S. Pat. No. 5,744,192, to Nguyen, et al. entitled "Method of using water vapor to increase the conductivity of copper deposited with Cu(hfac)tmvs". As the water amount increases, the film resistivity increases. For Cu(hfac)tmvs blend, a mixture of Cu(hfac)tmvs and other ingredients including water, the optimum copper film will require different amounts of water since there is already some water incorporated in the copper precursor. With different precursors and process conditions, controlling the resistivity level in the copper layer is a simple and straightforward matter by changing the amount of impurity such as oxygen. The current invention provides a thin high-resistive copper layer with a resistivity between 10 to 500 μΩ-cm. In one aspect of the invention, the modification of resistivity is achieved by exposing the precursor to a plasma source, where the exposure serves to break up the precursors for easier incorporation of impurities into the high-resistive copper layer. The modification of resistivity can be achieved by an oxygen-containing precursor. The oxygen-containing precursor serves to incorporate oxygen into the deposited copper layer to achieve the resistivity between 2 to 500 μΩ-cm. The oxygen-containing precursor is a precursor comprising an oxygen species such as O2, N2O, NO2, water vapor, alcohol vapor, OH ligand, and chemicals containing OH ligand, chemicals releasing OH ligand upon annealing.
In other aspects of the invention, the resistivity of the low-resistive copper layer is less than 3 μΩ-cm.
The current invention also provides a method to deposit the low-resistive copper film by the electrochemical deposition technique or by the chemical vapor deposition technique. The electrochemical deposition technique needs a copper seed layer to deposit and have good purity film. The current invention also provides a method to deposit the low-resistive copper film by the chemical vapor deposition technique and then by the electrochemical deposition technique.
The invention also provides a further step, preceding step a) to deposit an underlying diffusion barrier structure on a substrate, whereby the diffusion barrier structure serves to block the diffusion of copper to the substrate.
The diffusion barrier could be a single layer diffusion barrier, or a multilayered diffusion barrier structure, as disclosed by co-pending patent application Ser. No. 10/292,929 filed Nov. 13, 2002, now U.S. Pat. No. 6,670,266 to Nguyen, et al., entitled "Multilayered diffusion barrier structure for improving adhesion property".
The chemical vapor deposition technique uses a combination of process precursors and process conditions with the process precursors comprising a liquid copper precursor and an oxygen-contained precursor, whereby the liquid copper precursor serves to deposit a copper layer, and the oxygen-contained precursor serves to modifying the copper layer's resistivity by incorporating oxygen into the deposited copper layer.
The thin high-resistive film by chemical deposition technique has a high ratio of the oxygen-contained precursor, such as water or alcohol, to the copper precursor, such as Cu(hfac)tmvs. The high ratio can be accomplished by a high flow of oxygen-containing precursor, or alternatively, a low flow of copper precursor. Low flow of copper precursor has the additional benefit of allowing time for the copper to react with the diffusion barrier, similar to the method disclosed in U.S. Pat. No. 5,948,467, to Nguyen, et al., entitled "Enhanced CVD copper adhesion by two-step deposition process". This invention differs from U.S. Pat. No. 5,948,467 to Nguyen, et al., because of the presence of the oxygen-contained precursor. The major adhesion promoter in this invention is oxygen, not the reaction time. The low-resistive film by chemical deposition technique has a low ratio of the oxygen-contained precursor to the copper precursor. The low ratio can be accomplished by a low flow of the oxygen-contained precursor, or alternately, a high flow of the copper precursor. In the case of a copper precursor blend, meaning a copper precursor with oxygen-contained additive such as water, Hhfac dihydrate, the oxygen-contained precursor is no longer necessary, thus there is no flow of the oxygen-containing precursor.
The flow of the oxygen-contained precursor, such as water vapor, is between 1–100 cm3/minute. The copper precursor is typically a liquid, and the unit is ml of liquid. The liquid copper precursor is converted to gas phase by passing through a vaporizer. The oxygen-containing precursor though it could be in a liquid form such as water or alcohol, is much more desirable to be in a gaseous form for the reaction. The liquid oxygen-containing precursor, such as water, is bubbled with an inert gas, and the inert gas carries the dissolved liquid to the reaction chamber. The flow unit of the oxygen-containing precursor is cm3 of inert gas with some amount of liquid oxygen-contained precursor dissolved within.

Multilayer copper structure for improving adhesion property