Method for forming a micro-porous polishing pad with enhanced effects

Abstract

To provide a fine porous polishing pad capable of further reducing defects caused by the pad and improving polishing speed.SOLUTION: The invention provides a method of forming porous polyurethane polishing pad that includes feeding liquid polyurethane onto a web sheet by using a doctor blade while back tensioning the web. Coagulating the liquid polyurethane onto the web sheet forms a two-layer substrate. The two-layer substrate has a porous matrix, where the porous matrix has large pores extending upward from a base surface and open to an upper surface. Spring-arm sections connect lower and upper sections of the large pores.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a chemical mechanical polishing pad and a method of forming a polishing pad. More specifically, the present invention relates to a microporous chemical mechanical polishing pad and a method of forming a microporous polishing pad.

Background Art

[0002] In the manufacture of integrated circuits and other electronic devices, multiple layers of conductive, semiconductor, and dielectric materials are deposited on and removed from the surface of a semiconductor wafer. Thin layers of conductive, semiconductor, and dielectric materials can be deposited using several deposition techniques. Common deposition techniques in current wafer processing include, among others, sputtering, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), and physical vapor deposition (PVD) also known as electrochemical plating. Common removal techniques include, among others, wet and dry isotropic and anisotropic etching.

[0003] When layers of material are sequentially deposited and removed, the top surface of the wafer becomes non-planar. In subsequent semiconductor processing (such as photolithography), the surface of the wafer needs to be flat, so the wafer needs to be planarized. Planarization helps to remove unwanted surface topography and surface defects (e.g., rough surfaces, agglomerated materials, damage to the crystal lattice, scratches, contaminated layers or materials).

[0004] Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize or polish a workpiece (e.g., a semiconductor wafer). In conventional CMP, a wafer carrier or polishing head was attached to a carrier assembly. The polishing head holds the wafer and positions the wafer to contact the polishing layer of a polishing pad attached to a table or platen within a CMP apparatus. The carrier assembly provides a controllable pressure between the wafer and the polishing pad. At the same time, a polishing medium (e.g., slurry) is dispensed onto the polishing pad and drawn into the gap between the wafer and the polishing layer. To perform polishing, the polishing pad and the wafer typically rotate relative to each other. When the polishing pad rotates under the wafer, the wafer typically sweeps an annular polishing track or polishing region. Here, the surface of the wafer faces directly the polishing layer. The wafer surface is polished and planarized by the chemical and mechanical action of the polishing layer and polishing medium on the surface.

[0005] The CMP process typically occurs in two or three steps on a single polishing tool. The first step planarizes the wafer and removes most of the excess material. After planarization, the next step removes the scratches or chattering marks introduced during the planarization step. The polishing pads used for these applications must be flexible and isotropic so as to polish the substrate without scratching it. Further, these polishing pads and slurries for these steps often require selective removal of materials (e.g., high TEOS to metal removal rate). For the purposes of this specification, TEOS is a decomposition product of tetraethyl orthosilicate. Since TEOS is a harder material than metals such as copper, this has been a difficult problem that manufacturers have been working on for years.

[0006] Over the last several years, semiconductor manufacturers have increasingly migrated to microporous polishing pads (e.g., Politex (trademark) and Optivision (trademark) polyurethane pads for finishing or final polishing operations where a lower defect rate is a more important requirement) (Politex and Optivision are trademarks of DuPont de Nemours, Inc. or one or more of its affiliates). For the purposes of this specification, the term microporous refers to a porous polyurethane polishing pad produced by coagulation from an aqueous solution, a non-aqueous solution, or a combination of an aqueous solution and a non-aqueous solution. The advantage of these polishing pads is that they have few defects and can be removed efficiently. This reduction in defects can lead to a dramatic increase in wafer yield.

[0007] A particularly important polishing application is copper barrier polishing which requires a low defect rate in combination with the ability to remove both copper and TEOS dielectrics simultaneously, and as a result, the TEOS removal rate is higher than the copper removal rate to meet advanced wafer integration designs. Commercially available pads (e.g., Politex polishing pads) do not provide a low enough defect rate for future designs, and the TEOS:Cu selectivity is not high enough either. Another commercially available pad contains a surfactant that produces an excessive amount of foam during polishing that leaches out and interferes with the polishing. Further, the surfactant may contain alkali metals that can contaminate the dielectric and degrade the functional performance of the semiconductor.

[0008] Despite the low TEOS removal rate associated with microporous polishing pads, some advanced polishing applications are migrating to all-microporous pad CMP polishing operations because it may be possible to achieve a lower defect rate with microporous pads compared to another pad type (e.g., IC1000 (trademark) polishing pads). These operations have few defects, but the challenges of further reducing pad-induced defects and increasing the polishing rate remain. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0009] One aspect of the present invention provides a method for forming a porous polyurethane polishing pad that includes: supplying the liquid polyurethane onto the web sheet using a doctor blade while compressing the web and applying a reverse tension to the web sheet so as to prevent the liquid polyurethane from leaking in a direction opposite to the web direction; solidifying the liquid polyurethane on the web sheet to form a two-layer substrate, where the two-layer substrate is a porous body on the web sheet and the porous body has a porous substrate, and the porous substrate has large pores that extend upward from a base surface and open to an upper surface, the large pores are interconnected with tertiary pores, and a portion of the large pores is open to a top polishing surface; pulling the two-layer substrate beyond a touch roll so as to compress the porous body and deform the porous substrate within a shear zone; after passing through the shear zone, at least a portion of the large pores extending to the top polishing surface has a lower section and an upper section with a vertical orientation, where the vertical direction is a direction perpendicular to the web sheet and a spring arm section connects the lower and upper sections, and all of the spring arm sections are in the web direction and have an angle of 15 to 90 degrees from the upward vertical, and the spring arm sections are combined so as to increase the compressibility and contact area of the polishing pad; curing the two-layer substrate so as to cure the porous body and lock the porous body with the spring arm sections that connect the lower section and the upper section; and forming the cured porous body into the polishing pad, where the polishing pad includes the spring arm sections that connect the lower section and the upper section.

[0010] Another aspect of the present invention provides a method for forming a porous polyurethane polishing pad, including: while compressing the web to apply reverse tension to the web sheet so as to prevent the liquid polyurethane from leaking in a direction opposite to the web direction, supplying the liquid polyurethane onto the web sheet using a doctor blade; solidifying the liquid polyurethane on the web sheet so as to form a two-layer substrate, where the two-layer substrate is a porous body on the web sheet and the porous body has a porous substrate, and here, the porous substrate has large pores extending upward from a base surface and opening at an upper surface, the large pores are interconnected with tertiary pores, and a part of the large pores is open to a top polishing surface; pulling the two-layer substrate beyond a touch roll so as to compress the porous body and deform the porous substrate within a shear zone to pull the porous body; after passing through the shear zone, at least a part of the large pores extending to the top polishing surface has a lower section and an upper section with a vertical orientation, where the vertical direction is a direction perpendicular to the web sheet, and a spring arm section connects the lower and upper sections, the spring arm sections are all in the web direction and have an angle of 15 to 90 degrees from the upward vertical, and here, the spring arm sections are combined so as to increase the compressibility and contact area of the polishing pad, form medium pores with a vertical orientation adjacent to the spring arm sections of the large pores, and form small pores between the medium pores; curing the two-layer substrate so as to cure the porous body and lock the porous body with the spring arm sections connecting the lower and upper sections; and forming the cured porous body into the polishing pad, where the polishing pad includes the spring arm sections connecting the lower section and the upper section.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 3A

Figure 3B

Figure 4

Figure 4A

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0012] The polishing pad of the present invention is useful for polishing at least one of a magnetic substrate, an optical substrate, and a semiconductor substrate. In particular, the polyurethane pad is useful for polishing semiconductor wafers. In particular, for this pad, a very low defect rate is important compared to the planarization ability, and for example, it is useful for polishing advanced applications (such as copper-barrier applications) that require simultaneous removal of multiple materials such as copper, barrier metals, and dielectric materials (including but not limited to TEOS, low-k and ultra-low-k dielectrics). For the purposes of this specification, "polyurethane" is a product derived from bifunctional or polyfunctional isocyanates (such as polyether ureas, polyisocyanurates, polyurethanes, polyureas, polyurethane ureas, their copolymers, and their mixtures).

[0013] The porous polyurethane polishing pad includes a porous substrate having large pores that extend upward from a base surface and open to an upper surface, i.e., a polishing surface. The large pores interconnect with the tertiary pores. Although it is possible for all pores to open at the top surface, usually only a portion of the large pores open to the top polishing surface. At least a portion of the large pores extends to the top polishing surface and has a lower section and an upper section with a vertical orientation. As used herein, vertical refers to a direction perpendicular to the base surface and toward the upper surface. Usually, the average diameter of the lower section of the large pores is larger than the average diameter of the upper section of the large pores.

[0014] The spring arm sections connect the lower section and the upper section. All of the spring arm sections extend in the same horizontal direction as measured from the vertical direction. Although it is possible to bend the spring arms in multiple directions, usually when the web is pulled with a shear force, spring arm sections that all extend in the same direction are created. As a result, the intermediate section, i.e., the spring arm section, usually has an average diameter smaller than the average diameter of the lower section of the large pores. In the case of long intermediate arm sections, i.e., spring arm sections, they usually have an average diameter smaller than the average diameter of the lower section and the upper section of the large pores.

[0015] These spring arm sections are combined to increase the compressibility of the polishing pad and the contact area of the top polishing surface during polishing. Advantageously, the spring arm sections create a horizontal overlap between most of the lower section and the upper section of the large pores. This shift of the large pores facilitates the compression of the entire polishing pad. Most advantageously, the spring arm sections create a horizontal separation gap between most of the lower section and the upper section of the large pores. The longer the spring arms, the greater this effect and the higher the compressibility of the polishing pad. Increasing the compression ratio can improve the conformity of the polishing pad on the wafer, increase the contact area, and increase the polishing rate. Advantageously, the spring arm sections have an angle between 15 and 90 degrees as measured from the upward vertical direction.

[0016] In addition to the large pores, medium pores begin adjacent to the spring arm section of the large pores, and these medium pores have a vertical orientation. The medium pores typically begin from horizontal and upper adjacent positions of the spring arm section. Similarly, small pores begin between and interconnect with the medium pores. As suggested, the large pores are the largest and typically have a vertical height that is about twice the vertical height of the medium pores. The large pores with spring arms or connection sections advantageously occupy less than 50 percent of the total of the large pores plus the medium and small pores. The combination of all large, medium, and small pores improves the compressibility of the polishing pad.

[0017] The polishing pad advantageously also has a compression ratio measured by a uniaxial compression tester having a Keyence laser thickness measuring instrument configured as follows.

Table 1

[0018] The polishing pad advantageously has a compression ratio of at least 5% in the above test. Most advantageously, the polishing pad has a compression ratio of 5 - 10% in the above test.

[0019] Advantageously, the polishing pad has an embossed surface that forms grooves extending to the perimeter of the polishing pad. Typically, the embossing is in an X-Y square grid pattern. However, the embossing can be in any known pattern (e.g., circular, or circular and radial).

[0020] Referring to FIG. 1, a polyurethane-water-dimethylformamide (“DMF”) coating mixture 10 coats the felt roll 12 by controlling the backing blade 14 and the knife or doctor blade 16. The porous polishing layer is fixed to a polymeric film substrate or formed on a woven or non-woven substrate so as to form a polishing pad. When depositing the porous polishing layer on a polymeric substrate (e.g., a non-porous poly(ethylene terephthalate) film or sheet), it is often advantageous to use a binder (e.g., a proprietary urethane, or an acrylic adhesive) to enhance adhesion to the film or sheet. These films or sheets can be porous, but advantageously, these films or sheets are non-porous. The advantage of a non-porous film or sheet is to facilitate a uniform thickness or flatness, increase the overall rigidity of the polishing pad, decrease the overall compressibility, and eliminate the slurry suction effect during polishing.

[0021] The felt roll 12, the backing blade 14, and the doctor blade 16 with sidewalls (not shown) together form a trough 18 that holds the coating mixture 10. The backing blade 14 presses the felt roll 12 against the backup roll 20 to prevent the coating mixture 10 from flowing out of the rear of the trough 18. The backup roll 20 rotates clockwise during operation of the coating line.

[0022] By moving the back blade 14 closer to or farther from the backup roll 20, the width of the gap 22 is determined. The smaller the gap 22, the greater the reverse tension of the felt roll 12. The dotted arrow 22A indicates the change in the width of the gap 22. This is achieved by moving the back blade 14 towards the backup roll 20 to decrease (-) the gap and increase the tension, or away from the backup roll 20 to increase (+) the gap and decrease the tension. The tension vector A indicates the direction of the reverse tension of the felt roll 12. The height of the doctor blade 16 determines the thickness of the coating 24 on the felt roll 12. Since the doctor blade 16 controls the thickness of the liquid coating mixture 10, it gives the felt roll 12 a reverse tension close to or equal to zero.

[0023] A tension roller (not shown) pulls the felt roll 12 having the coating 24 into the water bath 26. The tension vector B indicates the direction of the tension pulling both the felt roll 12 and the coating 24 through the water bath 26. As soon as it is immersed in the water bath 26, DMF diffuses out of the coating mixture 10 and is replaced by water with a lower concentration of DMF. This rapid diffusion creates pores in the coating 24. Moving the touch roll 28 up and down facilitates the adjustment of the tension and compression of the felt roll 12 having the coating 24. Since the coating mixture 10 is a liquid-solid mixture, there is no reverse tension in the coating 24 between the doctor blade 16 and the touch roll 28. Tension in the coating 24 exists only after the coating 24 has passed through the touch roll 28. The touch roll 28 rotates counterclockwise during the operation of the coating line. When the large pores 30 move and engage with the touch roll 28, the tension and compression forces combine to deform the pores 30. Increasing the line speed shortens the time for the substrate surrounding the pores to align and harden. The substrate should have sufficient strength to retain its shape but insufficient strength to elastically deform and recover. This partial hardening before curing in the oven facilitates the formation of the deformed pores 30.

[0024] Referring to FIG. 2, the combination of the reverse tension on the felt roll 12 and the tensile tension of the coated portion 24 after the felt roll 12 and the touch roll 28 acts to create a shear zone illustrated by dotted lines with respect to the lower shear zone boundary 32 and the upper shear zone boundary 34. Arrow C indicates the direction of rotation of the touch roll 28. In the shear zone 33, between the dotted lines 32 and 34, the large pores 30 change from the vertical pores to the large vertical pores 40 having the curved portion of the spring arm section 42 (FIG. 3A). Arrow D gives the direction of the felt roll 12 at the touch roll 28. At the touch roll 28, the tension vectors A and B pull in the opposite direction through the lower shear zone boundary 32 to the upper shear zone boundary 34 or the upper end of the shear zone 33. The shear zone 33 defined between the lower boundary 32 and the upper boundary 34 gradually deforms the large pores 30. The pore 30A shows the first bend of the intermediate section. The pore 30B has a clearer bend in the central part. The pore 30C has a clearly defined bend with the central part moderately narrowed. The pore 30D has a substantially final bend with the central part having a substantially final narrowness. The pore 40 represents the final large pore including the spring arm section. These spring arm sections facilitate the high compressibility and compatibility of the final polishing pad.

[0025] Referring to FIGS. 3, 3A, and 3B, the large pore 30 includes a main section 50 having a teardrop shape, an intermediate section 52 having a tapered neck shape, and an upper section 54 having a vertical orientation and a slight taper. Arrow sections 50A, 52A, and 54A define the heights of the main section 50, the intermediate section 52, and the upper section 54, respectively. Normally, the shear zone boundaries 32 and 34 extend from the upper part of the main section 50 through the intermediate section 52 to the lower part of the upper section 54. During deformation, the upper part of the main section 50 deforms in the direction of being pulled. The intermediate section 52 deforms in multiple directions and laterally. The pore is stretched and narrowed for the first bend from the vertical direction to the partially horizontal - partially vertical direction, and then bent upward to return from the partially horizontal - partially vertical direction to the vertical direction. When the pore is stretched and narrowed, the cross-sectional area or the average diameter decreases. This narrow region that extends at least partially horizontally is known as the spring arm section 60. Arrow 60A defines the height and length of the spring arm section 60. Arrow 60B extends from the vertical bisector Line of the main section 50 to the vertical bisector Line of the upper section 54 and defines the offset of the upper section. Advantageously, the spring arm section 60 has an angle of 15 degrees to 90 degrees from the vertical. Most advantageously, the spring arm section 60 has an angle of 25 degrees to 80 degrees from the vertical.

[0026] Referring to FIG. 3A, when the shear zone 33 is large, the upper section 54 shifts horizontally by a distance sufficient to create a horizontal gap 60B for the spring arm section 60 that extends beyond the lower section 50 of the large pore. Referring to FIG. 3B, when the shear zone 33 is small, the upper section 54 shifts horizontally by a distance insufficient to create a horizontal gap 60B for the spring arm section 60 that extends beyond the lower section 50 of the large pore 40. In this case, there is a horizontal overlap between the upper section of the spring arm section 60 and the outermost portion of the lower section 50 of the large pore 40. The force of the shear zone 33 combined with the yield strength of the polymer matrix control controls the final length 60A of the spring arm section.

[0027] Referring to FIG. 4, the coated felt substrate 12 includes a plurality of large pores 40 including the spring arm section 60. The plurality of spring arm sections are combined to increase the compressibility and contact area during polishing. A series of large secondary pores 70 begin at a position adjacent to the spring arm section 60. Similarly, a set of upper secondary pores 72 begin at approximately the midpoint of the secondary pores 70. Typically, the large pores 40 have the largest size. The secondary pores 70 tend to be smaller than the large pores 40 but larger than the upper secondary pores 72. The large pores 40, secondary pores 70, and upper secondary pores 72 all extend to the skin layer 76 at the top surface. A large number of micropores 78 exist just below the surface immediately below the skin layer 76.

[0028] After DMF removal, oven drying cures the thermoplastic polyurethane. Optionally, the high-pressure washing and drying steps further clean the substrate. After drying, referring to FIG. 4A, the buffing process removes the skin layer 76 and the fine pores 78, and opens the large pores 40, secondary pores 70, and upper secondary pores 72 to a controlled depth. This enables a consistent pore count and open pore area at the top surface. It is advantageous to use a stable abrasive that does not fall off and does not penetrate the porous substrate during buffing. Typically, diamond abrasives produce the most consistent texture and have the lowest likelihood of breaking during buffing. After buffing, the substrate has a normal "tooth" (i.e., pore) height of 10 - 30 mils (0.25 - 0.76 mm) and an overall thickness of 30 - 60 mils (0.76 - 1.52 mm). The average large pore diameter ranges from 5 - 85 μm. Typical density values are from 0.2 to 0.5 g / cm 3 3. The cross-sectional pore area is typically 10 - 30 percent, the surface roughness Ra is less than 14, and Rp is less than 40. The hardness of the polishing pad is preferably 40 - 74 on the Asker C scale.

[0029] In an alternative embodiment, a non-porous film serves as the base substrate. The most prominent drawback of the film is the possibility of air bubbles being trapped between the polishing pad and the platen of the polishing tool when the non-porous film or porous substrate is used as the base substrate in combination with an adhesive film. These air bubbles distort the polishing pad and cause defects during polishing. The patterned release liner facilitates the removal of air and removes air bubbles under these circumstances. This results in a major problem of increased polishing non-uniformity, increased defects, increased pad wear, and shortened pad life. When felt is used as the base substrate, these problems are eliminated because air permeates the felt and air bubbles cannot be trapped. Second, when the polishing layer is applied to the film, the adhesion of the polishing layer to the film depends on the strength of the adhesive bond. Under some aggressive polishing conditions, this bond can fail, resulting in catastrophic failure. When felt is used, the polishing layer actually penetrates to a specific depth within the felt, forming a strong, mechanically interlocked boundary layer. A woven structure is acceptable, but a non-woven structure can provide additional surface area for strong bonding to the porous polymer substrate. An excellent example of a suitable non-woven structure is a polyester felt impregnated with polyurethane to hold the fibers together. The thickness of a typical polyester felt roll is 0.5 to 1.5 mm.

[0030] The polishing pad of the present invention is suitable for polishing or planarizing at least one of a semiconductor substrate, an optical substrate, and a magnetic substrate by using a polishing liquid and relative movement between the polishing pad and at least one of the semiconductor substrate, the optical substrate, and the magnetic substrate. The polishing layer has a continuous bubble polymer matrix. At least a part of the continuous bubble structure is open to the polishing surface. The large pores extend to the polishing surface having a vertical orientation. These large pores contained within the solidified polymer matrix form a "kebab" layer up to a specific "kebab" height. The height of the vertical pores is the same as the height of the "kebab" layer. The orientation of the vertical pores is formed during the solidification process. For the purposes of this patent application, the vertical or up-down direction is perpendicular to the polishing surface. The average diameter of the vertical pores increases with the distance from the polishing surface or the distance below the polishing surface. The polishing layer typically has a thickness of 20 to 200 mils (0.5 to 5 mm), preferably 30 to 80 mils (0.76 to 2.0 mm). A continuous bubble polymer matrix having vertical pores and open channels interconnecting the vertical pores. Preferably, the continuous bubble polymer matrix has interconnected pores having a diameter sufficient to allow fluid transport. These interconnected pores have an average diameter much smaller than the average diameter of the vertical pores. The pore morphology is characterized by open primary pores at the top with a size of about 40 μm and interconnected micropores with a size of about 2 μm within the polyurethane layer.

[0031] The plurality of grooves in the polishing layer facilitate the distribution of slurry and the removal of polishing debris. Preferably, the plurality of grooves form an orthogonal grid pattern. Usually, these grooves form an X-Y coordinate grid pattern on the polishing layer. These grooves have an average width measured adjacent to the polishing surface. The plurality of grooves have a debris removal residence time such that a point on at least one of a semiconductor substrate, an optical substrate, and a magnetic substrate rotating at a constant speed passes through the width of the plurality of grooves. The plurality of protruding land regions within the plurality of grooves are preferably supported by a tapered support structure that extends outwardly and downwardly from the top or plane of the polishing surface of the plurality of protruding land regions. Preferably, at an inclination of 30 to 60 degrees measured from the plane of the polishing surface, and most preferably, the plurality of land regions have a frustum or non-pointed top that forms the polishing surface from a polymer matrix containing vertical pores. Usually, the protruding land regions have a shape selected from hemispherical, truncated pyramid-shaped, truncated trapezoidal, and combinations thereof, and are provided with a plurality of grooves extending linearly between the protruding land regions. The plurality of grooves have an average depth greater than the average height of the vertical pores. Further, the vertical pores have an average diameter that increases the depth of at least one below the polishing surface.

[0032] Melting and solidifying the thermoplastic polyurethane at the bottom of the inclined sidewalls closes most of the large and small pores and forms the groove channels. Preferably, the plastic deformation of the sidewalls and the melting and solidifying process form a grid of interconnected grooves. The bottom surface of the groove channels has few or no open pores. This facilitates the smooth removal of debris and secures the microporous polishing pad within the open pore tapered pillow structure. Preferably, the grooves form a series of pillow structures formed from a porous matrix containing large and small pores. Preferably, the small pores have a diameter sufficient to allow the flow of deionized water between the vertical pores.

[0033] The substrate is important for forming a proper foundation. The substrate can be a polymer film or sheet. However, woven or non-woven fibers provide an optimal base material for the micro-porous polishing pad. For the purposes of this specification, micro-porous is a breathable synthetic leather formed from the aqueous replacement of an organic solvent. Non-woven felt provides an excellent base material for most applications. Usually, these base materials are occupied by polyester fibers (e.g., polyethylene terephthalate fibers, or other polymer fibers formed by mixing, carding, and needle punching).

[0034] For consistent properties, it is important that the felt has a consistent thickness, density, and compressibility. Forming the felt from consistent fibers with consistent physical properties results in a base substrate with consistent compressibility. To enhance consistency, shrinkable fibers and non-shrinkable fibers can be mixed, and the felt can be passed through a warm water bath to control the density of the felt. This has the advantage that the final felt density can be finely adjusted using the bath temperature and residence time. After forming the felt, it is sent to a polymer impregnation bath (e.g., an aqueous polyurethane solution), and the fibers are coated. After coating the fibers, curing the felt in an oven increases its rigidity and elasticity.

[0035] The post-coating curing and subsequent buffing process control the thickness of the felt. To finely adjust the thickness, the buff can first be applied with coarse abrasive grains and then the felt can be finished with fine abrasive grains. After buffing the felt, it is preferable to wash and dry the felt to remove the sand and debris picked up during the buffing process. After drying, dimethylformamide (DMF) is then confined to the back side to prepare the felt for the waterproofing process. For example, perfluorocarboxylic acid and its precursors (e.g., the AGC Chemicals' textile repellent AG-E092) can waterproof the upper surface of the felt. After waterproofing, the felt needs to be dried, and an optional burning process can remove the ends of the fibers protruding from the top layer of the felt. Next, the waterproof felt is prepared for coating and coagulation.

[0036] A mixture of anionic and nonionic surfactants preferably forms pores during solidification, contributing to improved hard-segment / soft-segment formation and optimal physical properties. For anionic surfactants, the surface-active part of the molecule bears a negative charge. Examples of anionic surfactants include, but are not limited to, carboxylates, sulfonates, sulfate esters, phosphates and polyphosphate esters, and fluorinated anions. More specific examples include, but are not limited to, dioctyl sodium sulfosuccinate, sodium alkylbenzene sulfonate, and salts of polyoxyethylenated fatty alcohol carboxylates. In the case of nonionic surfactants, the surface-active part has no apparent ionic charge. Examples of nonionic surfactants include, but are not limited to, polyoxyethylene (POE) alkylphenol, POE linear alcohol, POE polyoxypropylene glycol, POE mercaptan, long-chain carboxylic acid esters, alkanolamine alkanolamides, tertiary acetylenic glycols, POE silicones, N-alkylpyrrolidone, and alkyl polyglycosides. More specific examples include, but are not limited to, monoglycerides of long-chain fatty acids, polyoxoethylenated alkylphenols, polyoxyethylenated alcohols, and polyoxyethylene cetyl stearyl ether. For a more complete description of anionic and nonionic surfactants, see, for example, Chapter 1 of "Surfactants and Interfacial Phenomena" by Milton J. Rosen, 3rd Edition, Wiley-Interscience, 2004.

[0037] Examples The following examples illustrate the present invention with a focus on polyurethane formulation, coagulation control, and polishing performance.

[0038] Materials

[0039] In the examples, Component A represents CRISVON (trademark) 8166NC of DIC and methylene diphenyl diisocyanate (MDI) for generating a "hard section" in thermoplastic polyurethane. In particular, the polyurethane is a polyester-type low-elasticity polyurethane, which is processed in a coagulation process to form an upper porous layer as a polishing layer. The analysis specifications of Component A are as follows. Non-volatile solid weight %: 29.0 - 31.0%. Viscosity at 25°C: 60,000 - 80,000 MPa·s; 300% modulus of elasticity - 17 MPa; tensile strength - 55 MPa; elongation up to at least 500% break and melting point of 195°C.

[0040] The chemical composition of Component A was determined by proton and carbon-13 NMR and was as follows: [Table 2]

[0041] The first surfactant was sodium dioctyl sulfosuccinate (DSS) "RESAMINE CUT-30" purchased from Dainichiseika. The second surfactant was polyoxyethylene alkyl ether (EOPO) "PL-220" purchased from Kao Chemical.

[0042] Component A: Polyurethane Component B: Dioctyl sodium sulfosuccinate surfactant Component C: Polyoxyalkylene alkyl ether surfactant Component D: Dimethylformamide (DMF)

[0043] The formulations used various combinations of Components A - D formed by various coagulation processes: [Table 3]

[0044] The control of pore growth and the final pore morphology was achieved by using surfactant components B and C at various concentrations. The coating solution was a mixture of components A, B, C, and D used for coating, and water was added for the subsequent DMF substitution coagulation process.

[0045] The coagulation film of the polyurethane formulation was prepared by a laboratory drawdown test to investigate the surfactant ratio for producing a porous material. An impregnated nonwoven polyester felt was used as the substrate. The polyurethane was diluted to the designed solid content % with DMF, mixed with the surfactant, degassed, equilibrated to the designed temperature, and then drawn down. Coagulation was carried out in a DMF / water bath, followed by washing and drying.

Table 4

[0046] Two surfactants controlled the coagulation mechanism and enabled primary pore growth. The DSS surfactant promoted the growth of primary pores deep at the bottom of the coated layer. The height of the "barbs" of the primary pores became deeper as the concentration of the DSS surfactant increased.

[0047] The combination of DSS and EOPO surfactants regulated the coagulation of polyurethane, and instead of a pure teardrop shape without a cylindrical section, increased primary pores with a cylindrical upper section were formed. An EOPO surfactant concentration exceeding 2.0 phr hindered the growth of primary pores, leaving only a uniform layer of micropores. This was probably due to the affinity of EOPO for the soft segments of the polyurethane chains, promoting the solvation of the polyurethane and reducing the degree of phase separation.

[0048] The best ratio of DSS / EOPO surfactants was 4:1 phr / phr. Example 2 : Candidate formulation: Component A Polymer concentration: 20 wt%, 22 wt% in DMF Surfactant: DSS and EOPO Concentration of surfactant mixture: DSS concentration = 4.0 phr EOPO concentration = 1.0 phr Coating thickness: 65 mils (1.65 mm), 90 mils (2.23 mm) DMF concentration: 7 wt% Coagulation bath temperature: 25℃、30℃、35℃ Sample size: 12 drawdown Method: Laboratory drawdown test, standard conditions Results: The coagulation temperature affected the pore morphology and the growth of the "barbs" (i.e., pores). The solid content concentration affected the pore morphology, especially the shape of the teardrops. The growth of the pores could reach the bottom of the drawdown with a thicker coating, but better control of the pore morphology was needed. Example 3 : Candidate formulation: Component A Polymer concentration: 20 wt% in DMF Surfactant: DSS and EOPO Concentration of surfactant mixture: DSS concentration = 4.0 phr EOPO concentration = 1.0 phr Coating thickness: 65 mils (1.65 mm) DMF concentration: 0 wt%, 7 wt%, 14 wt% Coagulation bath temperature: 20℃、30℃、40℃ Sample size: 9 drawdowns Method: Laboratory drawdown test, standard conditions Result: The coagulation temperature had a great influence on the pore morphology and the growth of "hairs". Increasing the DMF concentration hindered the formation of primary pores. The main process conditions in coagulation control and pore morphology were determined as follows. Coagulation bath temperature Polymer solids % DMF / water concentration Coating thickness Example 4 : Candidate formulation: Component A Polymer concentration: 20 wt% in DMF Surfactant: DSS and EOPO Concentration of surfactant mixture: DSS concentration = 3.2, 4.0, 4.8 phr EOPO concentration = 0.8, 1.0, 1.2 phr Coating thickness: 65 mils (1.65 mm) DMF concentration: 7 wt% Coagulation bath temperature: 25℃ Method: Laboratory drawdown test, standard conditions Sample size: 11 drawdowns

Table 5

[0049] Table 5 summarizes the ratio of surfactants for Example 4. Table 6 provides the results for the polishing pads manufactured under the conditions of Table 5. The data were summarized as follows based on SEM analysis.

Table 6

[0050] Pore formation was observed to have pore morphology within ±1.5 sigma variation. The ratio of surfactants had a significant effect on the height of the "hairs" compared to other parameters. For the substrates in Table 6, the pore structures of Samples 1, 5, and 8 with a concentration of 4 to 1 by weight percent of DSS to EOPO provided the best pore morphology.

[0051] Example 5 Film Tensile Properties

Table 7

[0052] The above data show excellent toughness and breaking energy of the porous substrate. Note: The above properties are representative of film substrates tested in accordance with (ASTM D886).

[0053] Polishing Protocol

[0054] Pad polishing performance was determined on 300 mm blanket wafers attached to an Applied Material Reflexion® LK 300 mm CMP polishing tool. The polishing removal rate experiments were conducted on a copper wafer of a Novellus 300 mm sheet 20K Cu electronic plate, on a TEOS wafer of a Novellus 300 mm blanket 20k tetraethyl orthosilicate (TEOS) sheet wafer, on a tantalum (Ta) wafer of a Sematech 300 mm sheet 1K tantalum, on a Black Diamond™ and Coral™ low-k dielectric wafer of a CNSE 300 mm sheet 5K BD (k = 3.0), and on a BD2S wafer of a SVTC 300 mm sheet 5K BD2 (k = 2.7).

[0055] All polishing experiments were carried out using the ACuPLANE® LK393c4 Cu barrier slurry from Rohm and Haas Electronic Materials CMP Inc. All wafers were polished under standard conditions of a low pressure of 12.4 kPa (1.8 psi), a flow rate of 300 mL / min of the chemical mechanical polishing composition, a table rotation speed of 93 rpm, and a carrier rotation speed of 87 rpm, usually for 60 seconds. A 3M-A82 diamond pad conditioner commercially available from 3M was used to condition the polishing pad. The specifications of the 3M-A82 disk are listed in Table 8. The polishing pad was conditioned by a conditioner that turned on the high pressure cleaning (HPR) of the conditioner, at a platen speed of 73 rpm / a conditioner speed of 111 rpm, and used a downward force of 2.0 pounds (0.9 kg) for 10 minutes. During polishing, the pad was fully conditioned by a conditioner that turned on the high pressure cleaning (HPR), at a platen speed of 73 rpm and a conditioner speed of 111 rpm, and used a downward force of 2.0 pounds (0.9 kg) for only 3.2 seconds.

[0056] The TEOS removal rate was determined by measuring the film thickness before and after polishing using a KLA-Tencor SPECTRAFX200 measurement tool. The removal rates of copper (Cu) and tantalum (Ta) were determined using a KLA-Tencor RS100C measurement tool. The defect map scan was performed using a KLA-Tencor SP2 measurement tool, and the defect review was performed using a KLA-Tencor eDR-5210 measurement tool.

Table 8

[0057] Polishing Examples Examples of four pads and their respective characterizations are summarized below. All pads were manufactured with the same polyurethane / surfactant formulation with different process parameters for Sample 1.

Table 9

[0058] All of the above pads had the pore structures of FIGS. 3A, 4, and 5. In particular, the primary pores had a spring arm shape that promoted the compressibility of the pads. The above data shows that increasing the line speed increases the compression rate of the polishing pad. As the compression rate increases, the contact area during polishing increases. This increased contact area enabled the pad to operate in a softer structure that was less likely to generate defects.

[0059] Example 6 Polishing Performance

[0060] The results of the removal rate and defects are summarized in the following table.

[0061] Example 7: Polishing Performance of Pads 1, 4 (different batches):

Table 10

Table 11

[0062] The above table shows the excellent polishing stability of 500 wafers when polishing copper, TEOS, and tantalum substrates. Example 7 Removal Rate [Table 12] [Table 13]

[0063] Regarding the copper removal rate, the pads of Examples 1-4A and 1-4B showed copper rates of 694 and 680 A / min, respectively, which were approximately 12% and 14% lower than that of the commercially available pad A. The TEOS removal rates of 1-4A and 1-4B were 1416 and 1414 A / min, which were the same as those of the commercially available pads A and B. The similar removal rates among the commercially available pad A, pad B, and the pads of Examples 1-4A and 1-4B suggest that good contact area or wear, and the affinity among the pad, abrasive, and wafer facilitate effective oxide and copper removal. Example 8 Defect Performance [Table 14] [Table 15] [Table 16] [Table 17]

[0064] The polishing pads 1-4A and 1-4B showed far fewer total defects than commercially available pads A and B. The total number of defects averaged 73, 146, 19, and 37 respectively, and the scratch and chattering marks averaged 35, 10, 4, and 1 respectively for pads A, B, 1-4A, and 1-4B. This showed a measurable and dramatic reduction in polishing defects. The high compressibility pads manufactured at the highest line speed tended to have the fewest total defects.

[0065] An enhanced scanning recipe was created to increase resolution and differentiate performance. The results are summarized in the graph on the right, showing total defect counts of 241, 736, 34, and 85, and scratch and chattering marks of 126, 360, 5, and 9 respectively for pads A, B, 1-4A, and 1-4B. The polishing pads 1-4A and 1-4B had an average reduction in scratches and chattering of over 99% compared to commercially available pad B and over 95% compared to commercially available pad A. The high compressibility pads manufactured at the highest line speed had the fewest chattering mark defects. Example 9 Pad Analysis after Polishing

[0066] To evaluate pad wear, SEM analysis was performed on the pad surface after polishing. The sampling areas included the center, middle, and edge of the pad. In the case of polishing pads 1-4A and 1-4B, all primary pores remained open and there were no fragments. No significant hanging materials were seen from pad break-in, conditioning, or wafer polishing. Furthermore, there was no significant difference in the surface pore morphology from the center, middle, or edge of the pad. This suggests that consistent wear occurred throughout the pad. Additionally, high-resolution SEM images (magnifications 500x and 1000x) showed a distinct secondary pore structure. The smaller micropores remained open after polishing and no accumulation of fragments was observed. This indicated an effective slurry flow through the porous structure. There was no difference between the center, middle, or edge of the pad.

[0067] The uniform distribution of primary pores and interconnected micropores represents one reason for the excellent performance of the pad that, in combination with excellent defect performance, provides a satisfactory removal rate. The present invention has demonstrated a new highly compressible structure that provides excellent polishing performance. In particular, it has shown an ultra-low defect rate, good removal rates for copper, TEOS, and barrier metals, and a long pad life. In particular, the pad is polished at excellent copper and TEOS rates while maintaining stability for multiple wafers. Further, the pad has significantly fewer scratch and chattering defects than conventional polishing pads. The use of the manufacturing process was a determining factor in the final primary and secondary pore structures. Further, the manufacturing process provided a robust and reproducible pad pore morphology and polishing performance.

Claims

1. A method of forming a porous polyurethane polishing pad, comprising: feeding the liquid polyurethane onto the web sheet using a doctor blade while compressing the web to apply a reverse tension to the web sheet so as to prevent the liquid polyurethane from leaking in a direction opposite to the direction of the web; coagulating the liquid polyurethane on the web sheet to form a two-layer substrate, wherein the two-layer substrate is a porous body on the web sheet, the porous body having a porous substrate, the porous substrate having large pores extending upward from a base surface and opening at an upper surface, the large pores being interconnected with micropores, a portion of the large pores opening to a top polishing surface, pulling the two-layer substrate beyond a touch roll so as to pull the porous body to compress the porous body and deform the porous substrate within a shear zone, after passing through the shear zone, at least a portion of the large pores extending to the top polishing surface having a lower section and an upper section with a vertical orientation, the lower section having a teardrop shape and a vertical bisector defined, the vertical direction being a direction perpendicular to the web sheet, and a spring arm section connecting the lower and upper sections, the spring arm section having a spring arm shape in which all the spring arm sections are in the web direction and have an angle of 15 to 90 degrees from the upward vertical, the spring arm sections being joined so as to increase the compressibility and contact area of the polishing pad and offset the lower and upper sections horizontally, curing the two-layer substrate so as to cure the porous body and lock the porous body with the spring arm section connecting the lower and upper sections, and forming the cured porous body into the polishing pad, the polishing pad including the spring arm section connecting the lower and upper sections, comprising the above method.

2. A method of forming a porous polyurethane polishing pad, comprising: While preventing the liquid polyurethane from leaking in a direction opposite to the direction of the web, the liquid polyurethane is supplied onto the web sheet using a doctor blade while compressing the web to apply reverse tension to the web sheet. Coagulating the liquid polyurethane on the web sheet to form a two-layer substrate. The two-layer substrate is a porous body on the web sheet. The porous body has a porous substrate. The porous substrate has large pores that extend upward from the base surface and open at the upper surface. The large pores are interconnected with fine pores. A part of the large pores is open to the top polished surface. Pulling the two-layer substrate beyond a touch roll so as to pull the porous body formed to compress the porous body and deform the porous substrate within a shear zone. After passing through the shear zone, at least a part of the large pores extending to the top polished surface has a lower section and an upper section with a vertical orientation. The lower section has a teardrop shape and a vertical bisector is defined. The vertical direction is a direction perpendicular to the web sheet. The spring arm section connects the lower and upper sections. The spring arm section has a spring arm shape in which all the spring arm sections are in the web direction and have an angle of 15 to 90 degrees from the upward vertical. The spring arm sections are combined so as to increase the compressibility and contact area of the polishing pad and offset the lower and upper sections in the horizontal direction. Forming medium pores with a vertical orientation adjacent to the spring arm section of the large pores and forming small pores between the medium pores. Curing the two-layer substrate so as to cure the porous body and lock the porous body with the spring arm section connecting the lower and upper sections. Forming the cured porous body on the polishing pad. The polishing pad includes the spring arm section connecting the lower section and the upper section. Including The above method. **Claim 3**: The method according to claim 1 or 2, wherein the back blade presses the web against the rotating roll so as to apply reverse tension to the web, and the knife blade adjusts the thickness of the porous body without applying significant reverse tension to the porous body.

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