Polishing generally consists of the controlled wear of an initially rough surface to produce a smooth specular finished surface. This is accomplished by rubbing a polishing pad against the surface of the article to be polished in a repetitive, regular motion while a solution containing a suspension of fine particles, typically a slurry, is present at the interface between the polishing pad and the work piece. Commonly employed pads are made by impregnating non-woven fibers such as polyester with a urethane or are formed from filled cast polyurethanes. The polishing contact area of these pads can be affected by texturing the surface of the pads, grooving the pads, embossing or perforating the pads.

As shown in Cook et al, US Patent 5,489,233 issued Feb. 6,1996, pads having a macrotexture and microtexture can be formed. Such pads can be produced by molding, pressing, embossing, casting, cutting, intering or by photolithographic means.

Typically, polishing pads are made in a batch process where one pad is produced and then another which often results in significant batch to batch variability. This variability in pads is detrimental to semiconductor wafer manufacturing since it leads to polishing process variability and ultimately yield losses. A pad manufacturing process is needed that forms a pad having a uniform surface, and in particular, a continuous process is needed that forms a sheet having a uniform surface. From such a sheet, either individual polishing pads can be cut or the sheet can be left intact to form roll or belt type pads for next generation polishing tools.

The invention relates to polishing pads and a process for making polishing pads by printing.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, according to which: FIG. 1 is a perspective view of gravure printing that can be used to form the polishing pads of this invention.

FIG. 2 is a perspective view of screen printing that can be used to form the polishing pads of this invention.

The invention is directed to polishing pads and a process, preferably a continuous process, for making these polishing pads; wherein the pads have a flexible base substrate; and firmly adhered to the base substrate a hydrophilic polymeric polishing layer having a pattern of polymeric asperities formed by printing. According to one embodiment, printing includes a process of gravure printing. According to another embodiment, printing includes a process of screen printing. An embodiment of a polishing pad without abrasive particles is formed by the process of printing, and perform polishing in combination with particulate containing slurries. Another embodiment of a polishing pad includes abrasive particles that may be incorporated into the pad by the process of printing. The pad with abrasives perform polishing in which the pad is used with a reactive polishing liquid that is without abrasives.

The polishing pad made by the process of this invention has a polishing layer of a hydrophilic polymer having a pattern of polymeric asperities formed by gravure printing or screen printing. The printing process forms a repeatable surface pattern of polymeric asperities that have a controlled particle size, pattern, geometry and height. Prior art methods for forming patterns on polishing pads include molding, sintering, pressing, embossing, casting or cutting. These methods are either not suitable for manufacture of continuous pads or not repeatable with any great accuracy. The use of a printing process, for example, a gravure or screen printing process, provides an accurate repeatable surface area pattern that is applied as a polishing layer of a polishing pad. Gravure printing is best suited for the formation of a polishing layer having a pattern of precise, low-profile polymeric asperities. Screen printing is best suited for the formation of a polishing layer having a pattern of higher aspect polymeric asperities. These polymeric asperities are the numerous peaks of polymeric material which may be of various heights and shapes that form the polishing layer which are applied by the printing process on the flexible substrate.

The shapes, heights and area pattern of the polymeric asperities are repeatably applied with minimized variation, due to the fixed pattern on the surface of the gravure printing roll or the fixed area pattern of a screen used in the screen printing process.

FIG. I discloses a gravure printing apparatus and process for manufacture of a polishing layer onto a flexible substrate on which printing is performed. A rotogravure cylinder 1 is mounted on a typical rotogravure printing machine. The cylinder 1 has an

outer peripheral surface 2 in which the pattern of the polishing layer is etched. The fixed area pattern 3, is etched on the entire surface 2 of the cylinder 1. For simplicity, only a small portion of the pattern is shown. In juxtaposed spaced relationship to cylinder 1 is impression roller 4 which is in intimate contact with cylinder 1 during the printing process.

Cylinder 1 is partially immersed in a tray 7 containing a polymeric material (polymer solution or dispersion or a liquid low molecular weight polymer) 8 and is in frictional engagement with a doctor blade 6, which wipes off the excess polymeric solution or dispersion and returns this excess to the tray 7.

A flexible base substrate sheet 5 that is to be printed passes between the cylinder 1 and impression roller 4 and is maintained in firm intimate contact with cylinder 1 by properly adjusting roller 4. This printing process is advantageous since the depth of the layer of polymeric material and the area pattern of peaks and valleys are continuously applied and repeated with great accuracy, due to the fixed dimensions of the etched pattern on the cylinder l. The intimate contact of the substrate sheet 5 and the cylinder 1 is very important in order to assure the transfer of all available polymeric material to the surface of the substrate being printed. The impression roller 4 must maintain a constant force and pressure on the cylinder 1 with the substrate 5 in order to assure the desired result.

Typically a force of about 150 psi (pounds per square inch) is maintained but depending on the materials used a force in the range of 50-300 psi can be used. After being printed the polymeric material on the substrate sheet is cured, for example, by being passed through a curing zone 13, Fig. 2, that is a heating oven (typically, using temperatures of 75-150°C) but radiation can be used such as UV radiation, to cure the polymeric material printed onto the substrate. The resulting substrate with the cured patterned coating then is wound up and can be cut into individual polishing pads or provides a continuous polishing belt form of polishing pad.

Further details of rotogravure printing and the construction of cylinders used in rotogravure printing are known from Bardin, US Patent 4,197,798, hereby incorporated by reference.

FIG. 2 discloses a screen printing apparatus and process that can be used to form the polishing pads of this invention. Screen printing is performed by dispensing the polymeric material, with or without abrasive particles in suspension, through an open

screen. The fixed area pattern of the screen defines the repeatable area pattern of the polymeric material that is dispensed through the area pattern of the screen. A flexible base sheet substrate 9 is fed from a roll and is in juxtaposed position to a screen template 10 being fed from a roll. A polymeric material (which can be in the form of a solution or dispersion or a liquid low molecular weight polymer) 11 is placed in contact with the template 10 and forced into and through the pattern of the template 10 by doctor blade 12 and into contact with the substrate 9. The template 10, the polymeric material 11 on the substrate 9 are passed through a curing zone 13 which may be an oven (typically, using temperatures of 75-150°C) or for example LTV radiation to cure the polymeric material on the substrate. The template 10 is simply removed after curing and wound up. The resulting substrate with the cured patterned coating 14 then is wound up and can be cut into individual polishing pads or into polishing belts.

Manufacturing of polishing pads by either gravure or screen printing techniques enables a continuous polishing surface with a single continuous region, or a region divided into discrete regions of polishing surface to be defined separated by channels or gaps therebetween. The shape of these discrete regions may be any geometry (circular, square, triangular, polygonal, etc.) but hexagons are preferred because of ease of achieving high- density, regular packing. Typical dimensions of these regions are as follows: Feature Discrete Area Diameter Discrete Area Channel Width Dimension (mm) Thickness (mm) (mm) Range 1-25 0.1-10 0.1-15 Preferred Range 3-15 0.3-3 0.3-3 Most Preferred 5-10 0.5-2 0.5-2 Range These discrete regions are advantageous for the following reasons: After a polishing pad is formed by screen printing, it is necessary to remove moisture from the screened formulation. If there is a continuous coating or layer, unacceptable cracking of the coating or layer occurs. This is eliminated by forming discrete regions.

The channels surrounding the discrete regions facilitate slurry (or reactive liquid) transport across the pad surface and the subsequent removal of polishing debris in the polishing operation.

The flexible base substrates used in this invention can comprise a single layer or multiple layers and can comprise of a combination of layers that are bonded together. The substrate is preferably a flexible web capable of being pulled from a roll or easily wound into a roll. One preferred substrate is a non-corrosive metal, such as aluminum or stainless steel. Other preferred base substrates are plastics, such as engineering plastics, for example a polyamide, polyimide, and/or polyester, particularly"PET"poly (ethylene terephthalate).

The flexible base substrate of the present invention preferably has a thickness of about 0.1-10 millimeters. In a preferred embodiment, the support layer has a thickness of less than 5 millimeters, more preferably less than 2 millimeters. yet more preferably less than lmillimeter.

The polishing layer of the polishing pad of this invention comprises a hydrophilic polymeric material that optionally may be filled with abrasive particles. The polishing layer preferably has: (i) a density greater than 0. 5g/cm3 ; (ii). a critical surface tension greater than or equal to 34 milliNewtons per meter; (iii) a tensile modulus of 0.02 to 5.00 GigaPascals; (iv) a ratio of tensile modulus at 30°C to tensile modulus at 60° C of 1.0 to 2.5; (v) a hardness of 25 to 80 Shore D; (vi) a yield stress of 300-6000 psi (2.1-41.4 MegaPascal); (vii) a tensile strength of 1000 to 15,000 psi (7-105 MegaPascal); and (viii) an elongation to break up to 500%. In a preferred embodiment, the polishing layer further comprises a plurality of soft domains and hard domains.

Preferred hydrophilic polymeric materials used to provide a polishing layer having a critical surface tension greater than or equal to 34 milliNewtons per meter, more preferably greater than or equal to 37 and most preferably greater than or equal to 40 milliNewtons per meter are shown below in comparison other conventional polymers.

Critical surface tension defines the wettability of a solid surface by noting the lowest surface tension a liquid can have and still exhibit a contact angle greater than zero degrees on that solid. Thus, polymers with higher critical surface tensions are more readily wet and are therefore more hydrophilic.

Polymer Critical Surface Tension (mN/m) Polytetrafluoroethylene 19 Polydimethylsiloxane 24 Silicone Rubber 24 Polybutadiene 31 Polyethylene 31 Polystyrene 33 Polypropylene 34 Polyester 39-42 Polyacrylamide 35-40 Polyvinyl alcohol 37 Polymethyl methacrylate 39 Polyvinyl chloride 39 Polysulfone 41 Nylon 6 42 Polyurethane 45 Polycarbonate 45 In one preferred embodiment, the polishing layer of the pad is derived from one of the following: 1. an acrylated urethane; 2. an acrylated epoxy; 3. an ethylenically unsaturated organic compound having a carboxyl, benzyl, or amide functionality; 4. an aminoplast derivative having a pendant unsaturated carbonyl group; 5. an isocyanurate derivative having at least one pendant acrylate group; 6. a vinyl ether, 7. a urethane 8. a polyacrylamide 9. an ethylene/ester copolymer or an acid derivative thereof;

10. a polyvinyl alcohol; 11. a polymethyl methacrylate; 12. a polysulfone ; 13. an polyamide ; 14. a polycarbonate; 15. a polyvinyl chloride; 16. an epoxy ; 17. a copolymer of the above; or 18. a combination of any of the above.

In another preferred embodiment of this invention, the polishing layer material comprises: (1) a plurality of rigid domains which resists plastic flow during polishing; and (2) a plurality of less rigid domains which are less resistant to plastic flow during polishing. This combination of properties provides a dual mechanism which has been found to be particularly advantageous in the polishing of silicon dioxide and metal. The hard domains tend to cause the protrusion to rigorously engage the polishing interface, whereas the soft domains tend to enhance polishing interaction between the protrusion and the substrate surface being polished.

The rigid phase size in any dimension (height, width or length) is preferably less than 100 microns, more preferably less than 50 microns, yet more preferably less than 25 microns and most preferably less than 10 microns. Similarly the non-rigid phase is also preferably less than 100 microns, more preferably less than 50 microns, more preferably less than 25 microns and most preferably less than 10 microns. Preferred dual phase materials include polyurethane polymers having a soft segment (which provides the non- rigid phase) and a hard segment (which provides the rigid phase). The domains are produced during the forming of the polishing layer by a phase separation, due to incompatibility between the two (hard and soft) polymer segments.

Other polymers having hard and soft segments could also be appropriate, including ethylene copolymers, copolyester, block copolymers, polysulfones copolymers and acrylic copolymers. Hard and soft domains within the pad material can also be created: (1) by hard and soft segments along a polymer backbone; (2) by crystalline regions and non- crystalline regions within the pad material; (3) by alloying a hard polymer with a soft

polymer; or (4) by combining a polymer with an organic or inorganic filler. Useful compositions include copolymers, polymer blends interpenetrating polymer networks and the like.

In a another embodiment of this invention, thin polishing layers less than 200 microns, more preferably less than 100 microns and yet more preferably less than 50 microns and comprise a random surface texture comprising pores and/or micro-voids of varying sizes and dimensions can be formed.

The combination of a thin base layer and a thin polishing layer can provide ultra high performance polishing, due to a more precise and predictable polishing interaction when a rigid support presses the thin polishing pad against (and the pad is moved in relation to) a substrate to be polished. This polishing pad can be manufactured to very tight tolerances and (together with the rigid support) can provide predictable compressibility and planarization length."Planarization length"is intended to mean the span across the surface of a polishing pad which lies substantially in a single plane and remains in a single plane during polishing, such that as tall peaks are polished, peaks of lesser height do not polish unless or until the taller peak is diminished to the height of the shorter peak.

The polishing pads formed according to this invention have a polishing layer that is substantially free of macro-defects."Macro-defects"are intended to mean burrs or other protrusions from the polishing surface of the pad which have a dimension (either width, height or length) of greater than 25 microns. Macro-defects should not be confused with "micro-asperities."Micro-asperities are intended to mean burrs or other protrusions from the polishing surface of the pad which have a dimension (either width, height or length) of less than 10 microns. It has been surprisingly discovered that micro-asperities are generally advantageous in ultra precision polishing, particularly in the manufacture of semi-conductor devices, and in a preferred embodiment, the polishing layer provides a large number of micro-asperities at the polishing interface.

To obtain adequate adhesion of the hydrophilic polymer polishing layer to the flexible base substrate, the substrate may require a primer or an adhesion promoter.

Conventional polishing compositions or slurries used with the polishing pads of this invention to polish dielectric metal composites, semiconductors or integrated circuits

generally contain finely divided abrasive particles in an aqueous slurry or dispersion. The part or substrate that is to be polished is bathed or rinsed in the composition while the polishing pad is pressed against the substrate and the pad and substrate are moved relative to each other. The abrasive particles are pressed against the substrate under a load and the lateral motion of the pad causes the abrasive particles to move across the surface of the substrate resulting in wear and volumetric removal of the surface of the substrate. The rate of removal is determined by the amount of pressure applied, the velocity of the polishing pad and the chemical activity of the abrasive particles.

Polishing rates can be increased by adding components to the polishing composition which by themselves are corrosive to the substrate. When used together with abrasive particles, substantially higher polishing rates can be achieved. This process is termed chemical-mechanical polishing (CMP) and is a preferred technique used to polish semiconductors and semiconductor devices, particularly integrated circuits. Additives can be introduced to the polishing compositions to accelerate the dissolution of a metal component of the substrate such as a dielectric/metal composite structure, for example an integrated circuit. The purpose of this is to preferentially remove the metal portion of the circuit so that the resulting surface becomes coplanar with an insulating or dielectric feature, typically composed of silicon dioxide. This process is termed planarization.

Oxidizing agents, such as hydrogen peroxide, also can be added to the polishing compositions used for CMP to convert a metal surface into an oxide that then is subject to CMP.

Typical polishing compositions used for CMP of semiconductors, integrated circuits wafers and the like are disclosed in Brancaleoni et al, US Patent 5,264,010 issued Nov. 23,1993; Cook et al, US Patent 5,382,272 issued Jan. 17,1995; Brancaleoni et al, US Patent 5,476,606 issued Dec. 19,1995 and Wang et al, US Patent 5,693,239 issued Dec. 2,1997. While these are excellent polishing compositions, it would be desirable to have a composition that would remove an extremely thin layer without scratching of the surface and can be used for polishing substrates for semiconductor devices that require high planarization.

These conventional polishing compositions typically are slurries and the abrasive particles therein have a surface area of about 40-430 m2/g, and mean aggregate size of

less than 500 nm and a force sufficient to repel and overcome van der Walls forces between the particles. The surface area of the particles is measured by the nitrogen adsorption method of S. Brunaure, P. H. Emmet, and 1. Teller, J. Am. Chemical Society, Vol. 60, page 309 (1938). The particles may comprise between 0.5%-55% by weight of the slurry depending on the degree of abrasion required.

The abrasive particles can be primary particles having a mean size range of 25-500 nm or a mixture of primary particles and agglomerated smaller particles having a mean size range of 25-500 nm. In a preferred embodiment of the method of this invention, the abrasive particles have a mean size ranging of 25 and 500 nm. Typically useful abrasive particles are alumina, ceria, diamond, silica, titania and the like. These particles and agglomerates can be encapsulated and suspended satisfactorily so that, while maintaining the hardness, the possibility of scratches to the surface being polished is minimal.

It is preferred that the particles in the slurry not settle and not be agglomerated.

However, it is understood that depending on the percentage of primary particles and agglomerated particles, the particles in the slurry may settle and require redispersion by mechanical means such as mixing.

Oxidizers can be added to these slurries in amounts of about 0.01-10.0% by weight, based on the weight of the slurry. A wide variety of oxidizers can be used such as oxidizing metal salts, oxidizing metal complexes, iron salts such as nitrates, sulfates, potassium fern'cyanide and the like, aluminum salts, sodium salts, potassium salts, ammonium salts, quaternary ammonium salts, phosphonium salts, peroxides, chlorates, perchlorates, iodates, periodates, permanganates, persulfates and mixtures thereof. These oxidizers also can be added to polishing compositions of this invention wherein colloidal sulfur is the primary polishing constituent and other abrasives are not present.

Organic additives can be used in the slurries in concentrations of about 0.01-10% by weight, based on the weight of the slurry. These additives function as an encapsulating, suspending means for the particles, which are present, so that the possibility of scratches is minimal in spite of the hardness of the small particles. Alternatively, these additives may improve the surface quality by adsorbing on the polished surface as well as protecting the oxide surface and associated barrier layer during polishing. These organic additives may also be incorporated to improve the global wafer uniformity of the surface of the

semiconductor being polished. Preferred additives contain carboxy or amino groups and are organic liquids such as polyvinyl pyrrolidone, phthalates like ammonium hydrogen phthalate and potassium phthalate and phosphates like acetodiphosphonic acid.

Typically, organic acids can be added. These acids are defined as having functional groups having a dissociable proton. These include, but are not limited to carboxylate, hydroxyl, sulfonic and phosphonic groups. Carboxylate and hydroxyl groups are preferred since these present the widest variety of effective organic acids. Useful acids include citric acid, lactic acid, malic acid and tartaric acid.

These organic additives also can be used in polishing compositions in which colloidal silica is the primary polishing constituent.

In order to further stabilize the slurry against settling, flocculation and agglomeration a variety of additives such as surfactants, polymeric stabilizers, or other surface active dispersing agents may be used.

Physical, chemical and mechanical parameters all play a role in polishing a surface.

Polishing pressure is an external magnitude with which the polishing can be controlled and optimized. Relatively low polishing pressure yields an optimal result, although it is not required, because the particles may be prevented from being pressed through the encapsulating layer, created by the organic additives, during polishing.

The following examples illustrate the invention. All numbers and percentages are on a weight basis unless otherwise specified.

EXAMPLES Example 1: This example demonstrates the ability to achieve good polishing performance with a pad made using a gravure printing process.

Using the gravure printing process shown in FIG. 1, a sheet of 2 millimeter thick polyethylene terephthalate (PET) film, precoated with an adhesion promoting coating was printed with a polishing pattern. An aqueous based latex urethane (W242 from Witco) containing 2 weight % (40 vol. %) of polymeric microballons (Expancel) was charged into tray 7. A rotogravure cylinder 1 etched with a polishing pattern designed for a polishing pad was used to apply the polishing layer. The roll pressure used on the impression roll 4 was 150 psi. The polishing layer was cured to form a sheet having a polishing layer

having uniform pattern of polymeric asperities. The sheet was die cut into 28 inch diameter pad. A pressure sensitive adhesive was applied to the back of the pad and attached to a polishing machine described below.

The pad was used to polish TEOS oxide films deposited on silicon wafers.

Polishing was performed on a Strasbaugh 6DS-SP using a down-force of 9 psi, platen speed of 20 rpm and a carrier speed of 15 rpm. The slurry was ILD1300 from Rodel, used at a flow rate of 125 mil/min. No pad conditioning was done either during polishing or between wafers. Wafers that were polished had excellent planarization, good surface appearance and excellent removal rate of material.

Example 2: This example demonstrates the ability to achieve good polishing performance with a pad made by a screen printing process. The abrasive is incorporated into the pad and the pad is used with a particulate-free reactive liquid to polish tungsten.

Referring to the screen printing process shown in Figure 2, a sheet of 0-0.15 mm thick polyethylene terephthalate (PET) film 9 precoated with an adhesion promoting coating was used as a substrate and was screen printed with a filled latex formulation 11.

The filled latex formulation consisted of a mixture of an aqueous based latex (Vinyl Acetate-Ethylene emulsion, A-460, from Air Products) and an abrasive filler of 0.25 micron alumina. The filler loading was 75% based on dry weight of total formulation and total percent solids was 70%. A stainless steel stencil 10 was placed in intimate contact with the PET film. The stencil had a 79% open area, comprising hexagonal openings of 6 mm hole diameter separated by 35mil wide ribs. The filled latex formulation was applied over the stencil using a doctor blade 12. This forced the latex formulation material through the stencil onto the PET film. The resulting layer which is the polishing layer, consists of discrete hexagonal regions, and was cured at 60°C in an oven to form a polishing layer of 1 mm uniform thickness and having uniform distribution of asperities. A pressure sensitive adhesive was subsequently applied to the back of the PET film and the resultant polishing pad was used to polish a tungsten film as described below.

A polishing pad was cut from the above prepared coated PET film and attached to the polishing platen of a 12"Leco AP-300 polishing machine, using a down force of 7 psi, platen speed of 56 rpm and a carrier speed of 150 rpm. The pad was used in conjunction

with a particulate-free reactive liquid based on potassium iodate as the oxidizing component (MSW2000B from Rodel Inc.), used at a delivery rate of 20 ml/min. Pad concurrent conditioning was done using a 3"100-grit TBW diamond disc which rotated at 48 rpm. A tungsten film was polished with the pad and a stable 7 grams/min. removal rate of tungsten was achieved.

In this example, the screen printing process demonstrated the following major advantages over pads made according to a conventional process: (1) at high filler loading, 75% and above, surface cracking on drying in a oven was eliminated and, (2) the printing process automatically created channels for liquid distribution across the pad surface. In conventional pad manufacturing, the above are normally created in subsequent, separate manufacturing steps.

Nothing from the above discussion is intended to be a limitation of any kind with respect to the present invention. For example, optionally, additional fillers such as polymeric micro-balloons may be added to the latex formulation to control rheology and/or polishing performance, polymer coated alumina aggregates can be used as the abrasive and the stencil can be of aluminum or plastic.

Example 3: Using the screen printing process described in Example 2, a polishing pad was produced containing 72.5% by weight of abrasive particle agglomerates, where the abrasive particle agglomerates comprise alumina particles held together by a polymeric binder. The resulting 24 inch diameter pad was used to polish tungsten wafers using a Strasbaugh 6DS- SP machine, The reactive liquid was MSW2000BTM from Rodel Inc. and was delivered at a rate of 150 ml/min. Platen speed was 80 rpm, carrier speed was 83 rpm with a down force of 7 psi. Pad concurrent conditioning was done using a 100-grit RESI disk at 7 psi. A tungsten removal rate of 1000 to 2000A was achieved.

Example 4: Another screen printed polishing pad, similar to the one described in Example 3, was used to polish copper wafers using a Westech 372U polisher. The reactive liquid used was an experimental hydrogen peroxide based formulation (HR32-1) from Rodel Inc. at a delivery rate of 150 ml/min. The pad was pre-conditioned using a 100-grit TBW diamond disk.

Platen speed was 80 rpm and carrier speed was 83 rpm with a 4 psi down force. A copper removal rate of 6000 to 7000A was achieved using post conditioning between wafers.

Example 5: A screen printed polishing pad, similar to the one described in example 2, was laminated to different sub-pads (SubaIV and DPM1OOO, both from Rodel Inc.), and evaluated for copper polishing using the Westech 372U polisher. The reactive liquid and polishing conditions were the same as those used in Example 4. It was found that the compressibility of the sub-pad significantly affected the copper removal rate, such that the more compressible the sub-pad the higher the copper removal rate. No sub-pad, SubaIV, and DPM1OOO gave removal rates of 3000 to 5000A, 8000 to 9000A, and 12,000 to 14, 000A respectively. These removal rates were achieved without post conditioning between wafers.