Heterogeneous fluorinated polymer mixture polishing pad

Abstract

A polishing pad suitable for polishing at least one of a semiconductor, optical, magnetic, or electromechanical substrate is provided. The polishing pad includes a polyurea polishing layer and a polyurea matrix. The polyurea matrix has a soft phase and a hard phase. The soft phase is formed from a soft segment and the hard phase is formed from a diisocyanate hard segment and a curing agent. The soft segment is a copolymer of an aliphatic fluorine-free polymer group and a fluorocarbon having a length of at least six carbons. The polyurea matrix is cured by the curing agent and includes gas or liquid filled polymeric microelements. The soft segment forms a fluorine-rich phase that collects adjacent to the polymeric microelements and polishing layer during polishing. The polishing layer remains hydrophilic during polishing under shear conditions.

Description

BACKGROUND

[0001] Chemical mechanical planarization (CMP) is a variant of a polishing process that is widely used to planarize or flatten the build-up layers of integrated circuits to precisely construct multi-layer three-dimensional circuits. The layer to be polished is typically a thin film (less than 10,000 Angstroms) that has been deposited on an underlying substrate. The purpose of CMP is to remove excess material on the wafer surface to produce an extremely flat layer of uniform thickness across the entire wafer area. Controlling the removal rate and removal uniformity is critical.

[0002] CMP uses a liquid containing nano-sized particles, commonly referred to as slurry. This is fed onto the surface of a rotating multi-layer polymeric sheet or pad mounted on a rotating platen. The wafer is mounted into a separate clamp or carrier with a separate rotating device and pressed against the surface of the pad under controlled load. This results in high relative motion rates between the wafer and the polishing pad (i.e., high shear rates at both the substrate and pad surface). The slurry particles trapped at the pad / wafer junction abrade the wafer surface resulting in removal. To control the rate, prevent water slippage and effectively deliver slurry under the wafer, various types of textures are incorporated into the upper surface of the polishing pad. Fine textures are created by lapping the pad with a fine array of diamonds. This is done to control and enhance the removal rate and is commonly referred to as dressing. Larger scale grooves of various patterns and sizes (e.g., XY, circular, radial) are also incorporated for fluid dynamics and slurry delivery regulation.

[0003] It is widely observed that the removal rate during CMP follows the Preston equation, rate = K p *P*V, where P is pressure, V is velocity, and K p is the so-called Preston coefficient. The Preston coefficient is a sum constant that is characteristic of the consumable set used. Several of the most important influences on K p are as follows: (a) pad contact area (primarily from the pad's texture and surface mechanical properties); (b) slurry particle concentration on the surface of the contact area available for work; and (c) reaction rate between surface particles and the surface of the layer to be polished. Influence (a) is largely dependent on the pad's characteristics and the dressing process. Influence (b) is dependent on the pad and slurry, while influence (c) is largely dependent on the slurry characteristics.

[0004] The advent of high capacity multi-layered memory devices such as 3D NAND flash has resulted in the need for further improvement in removal rates. A key part of the 3D NAND fabrication process involves the alternate stacking of multi-layers of Si02 and Si3N4 films in a pyramid shaped staircase fashion. Once completed, the stack is covered with a thick Si02 cap layer which must be planarized before the device structure is completed. This thick film is commonly referred to as the pre-metal dielectric (PMD). The device capacity is proportional to the number of layers in the layered stack. Current commercial devices use 32 and 64 layers and the industry is rapidly moving to 128 layers. The thickness of each oxide / nitride pair in the stack is approximately 125 nm. Therefore, the thickness of the stack increases directly with the number of layers (32 = 4,000 nm, 64 = 8,000 nm, 128 = 16,000 nm). For the PMD step, assuming PMD conformal deposition, the total amount of overburden dielectric to be removed is approximately equal to about 1.5 times the stack thickness.

[0005] The removal rate of conventional dielectric CMP slurries is about 250 nm / min. This results in an undesirably long CMP processing time for the PMD step, which is now the main bottleneck in the 3D NAND fabrication process. Therefore, there has been much work in developing faster CMP processes. Most of the improvements have focused on process conditions (higher P and V), changing pad conditioning processes and improving slurry design, especially Ce02 based slurries. It would constitute a major improvement in CMP technology if an improved pad could be developed that could be paired with existing processes and Ce02 slurries to achieve higher removal rates without any negative consequences.

[0006] The most commonly used top pad layer in dielectric CMP is IC1000 TM Polyurethane polishing pads. This pad has many desirable properties, including its surface charge in water. As shown in the article by Sokolov et al. (J. Colloid Interface Sci, 300(2), p. 475-81, 2006), IC1000 TM The surface charge of the polishing pad becomes increasingly negative. Since the polishing pad is in motion during polishing, the physical properties of the pad asperities under shear are critical.

[0007] The main approaches used in CMP pads to achieve improved rates are as follows: i) optimization of the groove design without changing the top pad layer composition; ii) changing the conditioning process without changing the top pad layer composition; iii) providing the pad with a more desirable conditioning response by changing the conditioning response of the top pad layer; and iv) providing a pad with a top pad layer that has higher hardness or improved elastic properties.

[0008] Hattori et al. (Proc. ISET 07, p. 953-4 (2007)) discloses a plot of zeta potential versus pH for various lanthanide element particle dispersions, including Ce02. The pH of the zero charge or isoelectric point is measured to be about 6.6. Below this pH, the particles have a positive potential; above this pH, the particles have a negative potential. The isoelectric point can shift for different ceria particles or modifications of ceria-containing slurries.

[0009] With the development of 3D NAND, there is an increasing demand for polishing pads with improved ceria polishing rates. SUMMARY

[0010] An embodiment of the present invention provides a polishing pad suitable for polishing at least one of a semiconductor, optical, magnetic, or electromechanical substrate, comprising: a polyurea polishing layer, the polyurea polishing layer comprising a polyurea matrix, the polyurea matrix having a soft phase and a hard phase, the soft phase being formed from a soft segment, and the hard phase being formed from a diisocyanate hard segment and a curing agent, the soft segment being a copolymer of an aliphatic fluorine-free polymer group and a fluorocarbon having a length of at least six carbons, the polyurea matrix being cured by the curing agent and comprising gas or liquid filled polymeric microelements, the soft segment forming a fluorine-rich phase that concentrates adjacent to the polymeric microelements and polishing layer during polishing, wherein the polishing layer remains hydrophilic during polishing under shear conditions.

[0011] Another embodiment of the present invention provides a polishing pad suitable for polishing at least one of a semiconductor, optical, magnetic, or electromechanical substrate, comprising: a polyurea polishing layer, the polyurea polishing layer comprising a polyurea matrix, the polyurea matrix having a soft phase and a hard phase, the soft phase being formed from a soft segment, and the hard phase being formed from a diisocyanate hard segment and a curing agent and wherein the hard phase is precipitated in the soft phase, the soft segment being a copolymer of an aliphatic fluorine-free polymer group and a fluorocarbon having a length of at least six carbons, the polyurea matrix being cured by the curing agent and comprising gas or liquid filled polymeric microelements, the soft segment forming a fluorine-rich phase that concentrates adjacent to the polymeric microelements and polishing layer during polishing, wherein the polishing layer remains hydrophilic during polishing under shear conditions. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a schematic representation of the SIMS TOF assembly of the fluorine-rich region of the polishing pad of the present invention, converted to a black and white scale, where the solid black region represents the background without the polishing pad.

[0013] Figure 2is a cross-sectional SEM of a used polishing pad showing collapse of polymer microelements adjacent to the polishing surface without being pierced by the diamond dresser.

[0014] Figure 3 is a higher magnification cross-sectional SEM of a used polishing pad showing collapse of polymer microelements adjacent to the polishing surface without being pierced by the diamond dresser.

[0015] Figure 4 is a cross-sectional SEM of a used polishing pad showing formation of small teeth-like polishing surface.

[0016] Figure 5 shows comparative ceria slurry polishing tests of pads of the invention versus pads made from a base formulation that does not contain fluorinated polymer.

[0017] Figure 6 shows comparative silica slurry polishing tests of pads of the invention versus pads made from a base formulation that does not contain fluorinated polymer. DETAILED DESCRIPTION

[0018] The polishing pads of the present invention are suitable for polishing at least one of a semiconductor, optical, magnetic or electromechanical substrate. The key element of the present invention is the modification of the top pad surface properties to force the ceria slurry or other particles above their isoelectric point to polish with the upper surface or polishing layer. In particular, the present invention improves the effectiveness or efficiency of the ceria slurry particles on the upper surface, increasing the polishing rate. The surprising and novel effect of the pads of the present invention is that the addition of a fluorine-containing copolymer to the soft segment of the polyurethane block copolymer at a relatively low concentration (about 1-20 wt% of the total soft segment concentration) results in an increased removal rate. For the purposes of this application, all amounts are in weight percent unless specifically indicated otherwise. Preferably, the concentration of fluorinated species is 8 to 30 wt% of the total fluorinated species plus the content of the aliphatic non-fluorinated polymer groups in the soft segment. Furthermore, the polishing pads must be used with a polishing pad that is hydrophilic during polishing to achieve improved performance. Obtaining a polishing pad that is hydrophilic during polishing helps to achieve a thin and effective pad-wafer gap for effective polishing. Additionally, the unexpected effect of adding the fluorine-containing copolymer is a reduction in the electronegativity or zeta potential of the pad, making the pad surface very hydrophilic during polishing.

[0019] In view of the above, the surprising discovery of the present invention is that by selectively adding a small percentage of fluorinated polymer segments to the soft segment of the polyurethane block copolymer, one can achieve an increase in the zeta potential in water and an increase in the removal rate of slurries with cationic particles (such as CeO2) in a very low surface energy pad. More specifically, as shown in the examples below, the addition of a fluorinated copolymer to the soft segment of the polyurethane block copolymer results in a reduction in the zeta potential of the pad and an increase in the removal rate of ceria slurry. Figure 1As shown, the addition of the fluorinated soft segment component resulted in significant phase separation, forming fluorine-rich regions (dark gray) and fluorine-lean regions (light gray and white). Figure 1 Fluorine-rich regions of higher and lower fluorine concentration around the polymer microelements are shown. However, the fluorine-rich regions, pixelated in dark gray, are almost exclusively concentrated adjacent to the chloro-containing polymer microspheres, pixelated in black. This migration of the fluorine-rich phase toward the microelements forms the heterogeneous mixture microstructure of the present invention. The thickness of the fluorine-rich phase adjacent to the microspheres is less than fifty percent of the average diameter of the polymer microelements. Also unexpected is the aggregation of the fluorine-rich soft phase at the polished surface. This soft phase appears to smear and cover much of the polished surface. The majority of the polyurea, pixelated in light gray and white, illustrates the polyurea matrix containing the fluorocarbon-containing compound.

[0020] In the block polyurethane copolymer, the rigid hard segment provides stiffness and has a high glass transition temperature (Tg). The soft segment is generally more flexible at room temperature and has a low Tg. Phase separation occurs due to immiscibility between the hard segment and the soft segment. In addition, biuret crosslinking groups connect some of the soft segment to the hard segment. The biuret has the formula R2NC(O)NR’C(O)NHR”, where R2 is the soft segment, R’ includes an aromatic ring, and R” includes an aromatic ring.

[0021] The polishing pad has a polyurea polishing layer. The polyurea polishing layer includes a polyurea matrix that includes a soft phase and a hard phase. The soft phase is formed from a soft segment having two or more aliphatic non-fluoropolymer groups and at least one fluorinated species having two terminal groups. Typically, the fluorinated species has a length of at least six carbon atoms. Preferably, the fluorinated species has a length of at least eight carbon atoms. Most preferably, the fluorinated species has a length of at least ten carbon atoms. The aliphatic non-fluoropolymer groups are bonded to the two terminal groups of the at least one fluorinated species through a nitrogen-containing linkage. Examples of the nitrogen-containing linkage include urea groups and polyurethane groups. The aliphatic non-fluoropolymer groups have one end attached to the at least one fluorinated species through the nitrogen-containing linkage. Typically, the aliphatic non-fluoropolymer groups have a number average molecular weight of between 200 and 7500. For purposes of clarity, the aliphatic non-fluoropolymer groups are terminated before the isocyanate end groups (such as toluene diisocyanate) and do not include the isocyanate end groups, the nitrogen-containing linkage, or the amine curing agent. Most preferably, the aliphatic non-fluoropolymer groups have a number average molecular weight of between 250 and 5000 as measured after reaction with the amine curing agent. The isocyanate groups cap the reactive end of the aliphatic non-fluoropolymer groups. The soft segment forms the soft phase in the polyurea matrix. Most preferably, the aliphatic non-fluoropolymer groups are polytetramethylene ether connected to the fluorinated species. The fluorinated species can contain at least one of a fluorinated ether. Preferably, the fluorinated species contains a fluorinated oxirane, a fluorinated oxy methylene, and an oxirane. Most preferably, the fluorinated ether groups such as the fluorinated oxirane and the fluorinated oxy methylene to oxirane atomic ratio is less than 3.

[0022] The hard phase is formed from diisocyanate containing hard segments that do not contain fluorine groups and an amine containing curing agent. The hard segments contain urea groups formed from the isocyanate groups at the outer ends of the capped aliphatic fluorine free polymer groups reacting with the amine containing curing agent. Preferably, the hard segments precipitate as a hard phase in a soft phase. This morphology provides a fluorine rich phase for enhanced ceria interaction and a hard phase for stiffening the soft phase to improve polish roughness integrity and thereby increase pad life and stability when polishing multiple wafers. Preferably, the hard segments and soft segments form a prepolymer which is then reacted with an amine containing curing agent to form a polyurea matrix. The presence of the fluoride moiety in the soft segments increases the soft segment glass transition temperature or Tg of the soft phase. This unexpected increase in glass transition temperature improves the thermal stability of the polymer. At the uppermost surface of the polymer in air, an enrichment of the fluorinated soft segment component occurs during polishing. This in situ and continuously generated fluorine rich phase at the surface further enhances the beneficial effects of the small amount of fluorinated polymer. At fairly low concentrations of fluorinated soft segments (e.g., less than 20 wt% of the total soft segment content), the amount of fluorinated material is insufficient to prevent the dipole rearrangement of water molecules when the polymer is subsequently exposed to water, especially under shear. This results in complex wetting behavior when the droplet is subjected to shear. Specifically, it is believed that the water surface rearrangement results in an increased interaction of water with the hydrophilic portion of the polymer. This results in a decrease in the receding contact angle of the droplet and a corresponding increase in surface energy during polishing. As a result, the polishing pad of the present invention can be even more hydrophilic under shear than its non-fluorine containing analog.

[0023] It is generally accepted that fluorinated polymers such as polytetrafluoroethylene (PTFE) have a high negative zeta potential in water, typically greater than -20 mV, and are highly resistant to surface wetting by aqueous solutions in the absence of a suitable wetting agent. [For the purposes of this specification, zeta potential is a general term that refers to the potential adjacent to a charged surface. Zeta potential measurements can vary greatly depending on the equipment, equipment settings, and a variety of other factors.] However, the explanation for the high negative zeta potential of PTFE is simple, i.e., due to the high degree of orientation of water dipoles at the polymer surface and the low surface polarity.

[0024] For the polishing pads of the present invention, the liquid / solid contact angle dynamic method represents the best technique for measuring contact angles. This is because polishing is a dynamic process in which water is subjected to shear forces between a wafer rotating at one speed and a larger diameter polishing pad rotating at another speed. The difference in diameter results in the surfaces moving in the same, opposite, partially same, and partially opposite directions. Due to the difference in speed, all of the polishing fluid between the wafer and the polishing pad is subjected to a range of shear forces. For a moving droplet, the advancing contact angle represents the degree of liquid / solid cohesion, while the receding contact angle represents the degree of liquid / solid adhesion. Typically, the advancing contact angle is significantly higher than the receding angle. The degree of difference between the two is referred to as the contact angle hysteresis. The contact hysteresis in surface wetting can be affected by a number of factors. The primary influences are caused by surface roughness (e.g., lotus effect), contaminants, surface inhomogeneity, the degree of solvent / surface interaction (including hydrogen bonding and direct reaction), and shear rate. Regardless of other factors, due to the contact hysteresis, the surface energy of the solid directly increases with increasing shear rate. In the case of a set of materials with identical surfaces, an increase in contact hysteresis is a direct measure of an increase in solvent / surface attraction (i.e., for water, a more hydrophilic surface) and correlates with wettability as measured by differences in surface polarization. Importantly, the polishing pads of the present invention are hydrophilic as measured by an increase in receding contact angle as in polishing under shear conditions. In particular, the polishing layer is hydrophilic during polishing under shear conditions as shown by receding angle testing with deionized water and diiodomethane.

[0025] A CMP polishing pad according to the present invention can be made by a method comprising: providing an isocyanate-terminated polyurethane prepolymer; separately providing a curative component; and combining the isocyanate-terminated polyurethane prepolymer with the curative component to form a combination; reacting the combination to form a product; forming a polishing layer from the product, such as by skiving the product to form a polishing layer of a desired thickness and such as by machining it, and forming a chemical mechanical polishing pad having the polishing layer.

[0026] The pads of the present invention are polyurea block copolymers containing both hard and soft segments. The isocyanate-terminated polyurethane prepolymer used in the formation of the polishing layer of the chemical mechanical polishing pad of the present invention preferably comprises: the reaction product of ingredients including: a polyfunctional isocyanate and a prepolymer mixture containing two or more components, one of which is fluorinated.

[0027] Preferably, the isocyanate is a diisocyanate. More preferably, the polyfunctional isocyanate is a diisocyanate selected from the group consisting of 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; 4,4' diphenylmethane diisocyanate; naphthalene- 1,5-diisocyanate; toluidine diisocyanate; p-phenylene diisocyanate; xylylene diisocyanate; isophorone diisocyanate; hexamethylene diisocyanate; 4,4'-dicyclohexylmethane diisocyanate; cyclohexane diisocyanate; and mixtures thereof. Most preferably, the diisocyanate is toluene diisocyanate.

[0028] Optionally, the aliphatic fluorine-free polymeric group reacts from the group consisting of diols, polyols, polyol diols, copolymers thereof, and mixtures thereof. For example, the aliphatic fluorine-free polymeric group can be reacted with a diisocyanate and then a fluorinated species is attached to the diisocyanate. In particular, the prepolymer polyol can be selected from the group consisting of polyether polyols (e.g. poly(oxytetramethylene)diol, poly(oxypropylene)diol, poly(oxyethylene)diol); polycarbonate polyols; polyester polyols; polycaprolactone polyols; mixtures thereof; and mixtures thereof with one or more low molecular weight polyols selected from the group consisting of ethylene glycol; 1,2-propanediol; 1,3 propanediol; 1,2- butanediol; 1,3-butanediol; 2-methyl 1,3-propanediol; 1,4-butanediol; neopentyl glycol; 1,5-pentanediol; 3-methyl-1,5-pentanediol; 1,6-hexanediol; diethylene glycol; dipropylene glycol; and tripropylene glycol. Still more preferably, the prepolymer polyol is selected from the group consisting of at least one of polytetramethylene ether glycol (PTMEG); polypropylene ether glycol (PPG), and polyethylene ether glycol (PEG); optionally, mixed with at least one low molecular weight polyol selected from the group consisting of ethylene glycol; 1,2-propanediol; 1,3-propanediol; 1,2-butanediol; 1,3-butanediol; 2-methyl-1,3-propanediol; 1,4-butanediol; neopentyl glycol; 1,5-pentanediol; 3-methyl-1,5-pentanediol; 1,6-hexanediol; diethylene glycol; dipropylene glycol; and tripropylene glycol. Most preferably, the prepolymer polyol is primarily (i.e. > 90 wt%) polytetramethylene ether. The fluorinated polyol can be formed by the displacement addition from any of the unfluorinated polyols referenced above. This results in minimal changes in the final mechanical properties.

[0029] Preferably, the isocyanate-terminated polyurethane prepolymer has an unreacted isocyanate (NCO) concentration of 8.5 to 9.5 wt%. Examples of commercially available isocyanate-terminated polyurethane prepolymers include Imuthane TMPrepolymers (available from COIM USA, Inc., such as PET-80A, PET-85A, PET-90A, PET-93A, PET-95A, PET-60D, PET-70D, PET-75D); Adiprene TM Prepolymers (available from Chemtura, such as LF 800A, LF 900A, LF 910A, LF-930A, LF-931A, LF 939A, LF 950A, LF 952A, LF 600D, LF 601D, LF 650D, LF 667, LF 700D, LF 750D, LF 751D, LF 752D, LF 753D, and L325); Andur TM Prepolymers (available from Anderson Development Company, such as 70APLF, 80APLF, 85APLF, 90APLF, 95APLF, 60DPLF, 70APLF, 75APLF).

[0030] Preferably, the isocyanate-terminated polyurethane prepolymer is a low free isocyanate-terminated polyurethane prepolymer having a free toluene diisocyanate (TDI) monomer content of less than 0.1 wt%.

[0031] The curative component used in the formation of the polishing layer of the CMP polishing pad of the present application optionally contains a polyol curative or a polyfunctional aromatic amine curative, such as a difunctional curative. Examples of commercially available polyol curatives include Specflex TM Polyols, Voranol TM Polyols and Voralux TM Polyols (available from Dow Chemical Company). These polyfunctional curatives all contain at least three hydroxyl groups to increase crosslinking of the polymer.

[0032] Preferably, the difunctional curing agent is selected from diols and diamines. More preferably, the difunctional curing agent used is a diamine selected from the group consisting of primary amines and secondary amines. Still more preferably, the difunctional curing agent used is selected from the group consisting of: diethyltoluene diamine (DETDA); 3,5-dimethylthio-2,4-toluene diamine and its isomers; 3,5-diethyltoluene-2,4-diamine and its isomers (e.g., 3,5-diethyltoluene-2,6-diamine); 4,4'-bis-(sec-butylamino)diphenylmethane; 1,4-bis-(sec-butylamino)-benzene; 4,4'-methylene-bis-(2-chloroaniline); 4,4'-methylene-bis-(3-chloro-2,6-diethyl aniline) (MCDEA); polytetramethylene oxide-di-p-aminobenzoate; N,N-dialkyldiaminodiphenylmethane; p,p'- methylenedianiline (MDA); m-phenylenediamine (MPDA); 4,4'-phenylene-bis(2-chloroaniline) (MBOCA); 4,4'-methylene-bis-(2,6-diethyl aniline) (MDEA); 4,4'-methylene-bis-(2,3-dichloroaniline) (MDCA); 4,4'-diamino-3,3'-diethyl-5,5'-dimethyl diphenylmethane; 2,2',3,3-tetrachlorodiaminodiphenylmethane; trimethylene glycol di-p-aminobenzoate; and mixtures thereof. Most preferably, the diamine curing agent used is selected from the group consisting of: 4,4'-methylene-bis(2-chloroaniline) (MBOCA); 4,4'-methylene-bis-(3-chloro 2,6-diethyl aniline) (MCDEA); and isomers thereof.

[0033] The polishing layer of the chemical mechanical polishing pad of the present application can further comprise a plurality of microelements. Preferably, the microelements are uniformly dispersed throughout the polishing layer. Preferably, the microelements are selected from the group consisting of entrapped gas bubbles, hollow core polymeric materials, liquid-filled hollow core polymeric materials, water-soluble materials, and insoluble phase materials (e.g., mineral oil). More preferably, the plurality of microelements are selected from the group consisting of entrapped gas bubbles and hollow core polymeric materials uniformly dispersed throughout the polishing layer. Preferably, the plurality of microelements have a weight average diameter of less than 150 μm (more preferably equal to or less than 50 μm; most preferably 10 to 50 μm). Preferably, the plurality of microelements are polymeric microspheres having a shell wall of polyacrylonitrile or vinylidene chloride-polyacrylonitrile copolymer (e.g., Expancel® microspheres from Akzo Nobel). Preferably, the plurality of microelements are incorporated into the polishing layer at a porosity of 0 to 50 vol. % (preferably a porosity of 10 to 35 vol. %). The vol. % porosity is determined by dividing the difference between the specific gravity of the unfilled polishing layer and the specific gravity of the polishing layer containing the microelements by the specific gravity of the unfilled polishing layer. TM microspheres. Preferably, the plurality of microelements are incorporated into the polishing layer at a porosity of 0 to 50 vol. % (preferably a porosity of 10 to 35 vol. %). The vol. % porosity is determined by dividing the difference between the specific gravity of the unfilled polishing layer and the specific gravity of the polishing layer containing the microelements by the specific gravity of the unfilled polishing layer.

[0034] With reference toFigure 2 The polymer microelements in the transition region adjacent to the polishing layer decrease in thickness as they approach the polishing layer. Below the transition region, the polymer microelements remain intact and do not break apart like the spherical microelements. These polymer microspheres are closed cell or non- reticulated. But as polymer microspheres near the polishing surface, they break apart and compress into smaller non-spherical microelements. The force behind this consolidation of the polymer microspheres appears to be the associated compression of the polishing head and conditioner before the microspheres are penetrated by the diamond or another abrasive. However, most conditioner disks rely on diamonds mounted on or otherwise secured to a metal plate. It can be seen from the surface texture adjacent to the compressed or broken microspheres that the microspheres were not broken by diamond conditioning. Thus, the cause of the polymer microsphere breakage is unrelated to diamond puncture caused by diamond conditioning. In particular, Figure 3 The compressed microspheres are shown at higher magnification. As the polishing pad is worn by polishing, the microspheres adjacent to the polishing layer compress to a thickness that is less than their original diameter. Typically, this thickness is less than fifty percent of the original diameter; and it can be less than thirty percent of the original diameter. Another surprising feature of the present invention is that the compression of the polishing pad during polishing forms interconnecting adjacent channels and the polymer microspheres break apart at the polishing layer. This is a local phenomenon that occurs only near the polishing surface. The remaining microspheres remain closed cell or intact until the pad is worn enough to bring the microspheres near the polishing surface. This appears to release fluid from the interior of the microspheres and allow additional compression of the microspheres before they are punctured by the diamond conditioner.

[0035] The polishing layer of the CMP polishing pad of the present invention can be provided in a porous and non-porous (i.e., unfilled) configuration. Preferably, the polishing layer of the chemical mechanical polishing pad of the present invention exhibits a density of 0.4 to 1.15 g / cm3 3 ; more preferably, 0.70 to 1.0 g / cm3 3 ; measured according to ASTM D1622 (2014).

[0036] Preferably, the polishing layer of the chemical mechanical polishing pad of the present invention exhibits a Shore D hardness of 28 to 75 as measured according to ASTM D2240 (2015).

[0037] Preferably, the average thickness of the polishing layer is 20 to 150 mils (0.05 to 0.4 cm). More preferably, the average thickness of the polishing layer is 30 to 125 mils (0.08 to 0.3 cm). Still more preferably, the average thickness of the polishing layer is 40 to 120 mils (0.1 to 0.3 cm); most preferably, 50 to 100 mils (0.13 to 0.25 cm).

[0038] Preferably, the CMP polishing pad of the present application is adapted to interface with a platen of a polishing machine. Preferably, the CMP polishing pad is adapted to be secured to a platen of a polishing machine. Preferably, at least one of a pressure sensitive adhesive and a vacuum can be used to secure the CMP polishing pad to the platen.

[0039] The CMP polishing pad of the present application optionally further comprises at least one additional layer interfaced with the polishing layer. Preferably, the CMP polishing pad optionally further comprises a compressible base layer adhered to the polishing layer. The compressible base layer preferably improves the conformability of the polishing layer to the surface of the substrate being polished.

[0040] The final form of the CMP polishing pad of the present application also includes one or more dimensional textures incorporated on its upper surface. These can be classified as macro-textures or micro-textures according to their size. Macro-textures of the conventional type used for CMP control fluid dynamic response and slurry transport, and include but are not limited to grooves of many configurations and designs, such as annular, bias radial, and hatching. These can be formed as uniform sheets by machining processes, or can be formed directly on the pad surface by net-shaping processes. Micro-textures of the common type are finer scale features that create a large number of surface asperities that are points of contact with the substrate wafer undergoing polishing. Common types of micro-textures include but are not limited to those formed by lapping with an array of hard particles such as diamond before, during, or after use, commonly referred to as pad conditioning, and those formed during the pad manufacturing process.

[0041] As can be seen from Figure 4 During the diamond conditioning process, a sharkskin-like denticulate polishing surface can be formed. This micro-texture is extremely fine, and can further help to increase the polishing removal rate. This effect is particularly pronounced when polishing with cationic particles such as ceria particles.

[0042] An important step in the substrate polishing operation is determining the endpoint of the process. One common in-situ method for endpoint detection involves providing a polishing pad with a window that is transparent to a selected wavelength of light. During polishing, a light beam is directed through the window to the substrate surface where it is reflected and passes back through the window to a detector (e.g., a spectrophotometer). Based on the returned signal, the characteristics of the substrate surface (e.g., film thickness thereon) can be determined for endpoint detection purposes. To facilitate such light-based endpoint methods, the chemical mechanical polishing pads of the present invention optionally further comprise an endpoint detection window. Preferably, the endpoint detection window is selected from the group consisting of an integrated window incorporated into the polishing layer; and an insert endpoint detection window block incorporated into the chemical mechanical polishing pad. For unfilled pads of the present invention having sufficient transmissivity, the upper pad layer itself can serve as the window aperture. Since the pads of the present invention exhibit phase separation, more transparent regions of the top pad material can also be created by locally increasing the cooling rate during manufacture to locally suppress phase separation, thereby creating more transparent regions suitable for use as endpoint windows.

[0043] As described in the Background section of the present invention, CMP polishing pads are used in conjunction with polishing slurries. The CMP polishing pads of the present invention are designed for use with slurries having a pH below the isoelectric point pH of the particles used. For example, Ce02has an isoelectric point pH of about 6.6. Below this pH, the particle surface has a net positive charge. Above this pH, the particle has a net negative charge. Since the pads of the present invention exhibit a high negative charge at this pH, a rate increase is achieved when the particles are below the isoelectric point.

[0044] The CMP pads of the present invention can be manufactured by a variety of methods compatible with the thermoset polyurethane. These methods include mixing the ingredients described above and casting into a mold, annealing, and then cutting into pieces of the desired thickness. Alternatively, they can be manufactured in a more precise net shape form. According to the preferred method of the present invention, it comprises: 1. thermoset injection molding (commonly referred to as "reaction injection molding" or "RIM"); 2. thermoplastic or thermoset injection blow molding; 3. compression molding; or 4. any similar type of method in which a flowable material is positioned and solidified to produce at least a portion of the macro- or micro-texture of the pad. In the preferred molded embodiment of the present invention: 1. the flowable material is forced into or onto a structure or substrate; 2. the structure or substrate imparts a surface texture to the material as it solidifies, and 3. the structure or substrate is then separated from the solidified material.

[0045] Some embodiments of the present invention will be described in detail in the following examples.

[0046] Example

[0047] The pad samples used in the examples were prepared as follows:

[0048] Material

[0049] PTMEG is a blend of various PTMEGs from Invista, with molecular weights ranging from 250 to 2000. 4,4'-Dicyclohexylmethane diisocyanate / toluene diisocyanate (“H…”) 12 MDI / TDI”)PTMEG is an Adiprene from Lanxess with 8.95 to 9.25 wt% NCO. TM L325 prepolymer. TDI is from Dow Chemical Company using Voranate. TM Obtained from T-80. The polymer microspheres are Expansion. TM The microspheres are made of vinylidene chloride-polyacrylonitrile copolymer with an average particle size of approximately 20 μm. The fluorinated polymer is an ethoxylated perfluoroether. The fluorinated polymer has a linear structure of ethylene oxide-fluorinated ethylene oxide-fluorinated oxymethylene groups terminated in ethylene oxide. The "R" atomic ratio of the fluorinated ether to ethylene oxide is 1.9 or 5.3.

[0050] Synthesis of prepolymers

[0051] Prepolymers ranging from approximately 200 to 1000 grams were synthesized in batches. Ethoxylated perfluoroethers were added by replacing a portion of the PTME2000 component in the prepolymer to produce varying levels of fluorinated polytetramethyl ether. TDI and H were added to the mixture before being added. 12 MDI was mixed at a weight ratio of 80:20. Sufficient isocyanate mixture was then added to the mixture to achieve the desired NCO wt%. The entire mixture was mixed again and then placed in a preheated oven at 65°C for 4 hours before use. All samples were tested on the day of synthesis.

[0052] Pad production

[0053] The synthesized prepolymer and 4,4'-dicyclohexylmethane diisocyanate / toluene diisocyanate (“H”) were then combined. 12 MDI / TDI” polytetramethylene ether was heated to 65°C. MBOCA was pre-weighed and melted in an oven at 110°C. After a 4-hour reaction time, or once heated, polymer microspheres were added to the prepolymer and degassed using a vacuum. All filled samples contained a sufficient distribution of polymer microspheres to achieve the desired specific gravity or final density. After degassed, and once both components had reached a certain temperature, MBOCA was added to the prepolymer and mixed. After mixing, the sample was poured onto a hot plate and heated using Teflon. TMThe coated rods were stretched, with the rods spaced at 175 mils (4.4 mm). The plates were then transferred to an oven and heated to 104°C and held at that temperature for 16 hours. The knife coated films were then de-molded and punched into 22" (55.9 cm) and used to make laminated pads for polishing. All pads were 20" (50.8 cm) in diameter with 80 mil (2.0 mm) top pads, 1010 round grooves with 20 mil, 30 mil, and 120 mil (0.51 mm, 0.76 mm, and 3.05 mm) width, depth, and pitch, respectively, pressure sensitive adhesive film for subpads, Suba IV TM Polyurethane impregnated polyester felt subpad and pressure sensitive platen adhesive. Plates from each material set were also made into plates for property testing, with and without polymeric microsphere filler for property testing.

[0054] The reference table for the samples referenced in the following examples is given in Table 1. Fluorinated polymer content in the comparative is expressed as a percentage replacement of PTMEG content, the comparative being a mixture of polyether-based toluene diisocyanate capped liquid prepolymers (NCO 8.9 to 9.3 wt%) cured with 4,4'-methylene-bis(2-chloroaniline) in stoichiometry of 105% NCO to amine cured. For the purposes of this specification, stoichiometry indicates the molecular ratio of NCO to amine.

[0055] Table 1

[0056] Sample Ethoxylated perfluoroether (Wt. %) A 0 1 6 2 12 3 18 4 24

[0057] Example 1

[0058] Samples of polyurea formulations with varying degrees of fluorinated substitution were prepared. Comparative A is the non-fluorinated parent material; while samples 1 and 2 were produced with 6 wt% and 12 wt% of the polytetramethylene ether component replaced with fluorinated species. The plate samples produced without filler showed a significant decrease in transparency at both levels of fluorinated polymer content, indicating a higher degree of phase separation. In addition, FTIR analysis indicated the presence of biuret, with a peak at 1535 cm -1

[0059] The material properties of the three materials are summarized in Table 2. The differences in performance at replacement levels of 12 wt% or less are relatively small. However, at higher replacement levels, the pads become increasingly brittle. The functional limit of elongation and toughness reduction without undesirable effects on the polishing process is estimated to occur at about 20 wt% replacement.

[0060] Table 2

[0061]

[0062] ​Note: The perfluoroether / ethylene oxide atomic ratio for samples 1-4 is approximately 1.9.

[0063] Example 2

[0064] The useful range of pads were tested for surface properties relative to the fluorine-free parent. The properties measured were both static and dynamic contact angle measurements to derive surface energy. Both sets of measurements used plate samples to ensure that measurements were made on a smooth, as-cast surface. This avoids measurement errors caused by surface roughness. This is most critical for surface energy measurements.

[0065] Surface energy measurements were made by the sessile drop method using a commercial apparatus manufactured by Kruss. Measurements were made using deionized water and diiodomethane ("methylene iodide"). Surface energy values were derived from the measured average contact angles using the two component Fowkes method. Both static and dynamic measurements were made to derive the surface energy for equilibrium, advancing, and receding.

[0066] Dynamic contact angle

[0067] Table 3

[0068]

[0069] Assuming a contact angle of 0 (completely wetted by diiodomethane), the comparative pad control pad becomes hydrophilic under dynamic conditions. Surprisingly, the data show that samples 2 and 3, which have a high amount of fluorinated polymer and high electronegativity, are also hydrophilic under dynamic conditions. This test verifies that the polishing pads are hydrophilic during polishing.

[0070] Example 3

[0071] A second mixture of polyether-based toluene diisocyanate capped liquid prepolymers having 8.9 to 9.3 wt% NCO cured with 4,4'-methylene-bis(2-chloroaniline) at a stoichiometry of 105% NCO to curing amine ("Comparative Sample B") having different specific gravities of the pads of the present invention were used to polish TEOS wafers using two slurries.

[0072] The first slurry was a commercially available ceria slurry (Asahi CES333F) prepared using the manufacturer's instructions. The pH during use was 5.5. Based on the data provided earlier, a pH well below the isoelectric point pH of the ceria particles used was employed. The second slurry was also a commercially available silica slurry (Cabot SS25) prepared using the manufacturer's instructions. The pH during use was 10.5. Based on the data provided earlier, a pH well above the isoelectric point pH of the silica particles used was employed.

[0073] Each pad was used to polish wafers over a range of applied pressures using the same conditions to allow for estimation of differences in Preston's coefficient as measured by the slope of the pressure versus rate response. The polishing conditions used for each test were a platen speed of 93 rpm, a wafer carrier speed of 87 rpm, and a slurry flow rate of 200 ml / min. The polishing equipment used was a Mirra Mesa® tool from Applied Materials. TM Tool.

[0074] As shown in Tables 4 and Figure 5 the polishing rate of the inventive pads was observed to increase significantly over the entire range of down pressure when polished with cationic ceria particles. Depending on the down pressure, the inventive pads provided a 20% to 30% increase in removal rate. The slope of the pressure / rate response is a measure of the contribution of the Preston's coefficient of the pad, and this slope was at least 60% higher than that of the parent pad.

[0075]

[0076] In contrast, as shown in Tables 5 and Figure 6 the rate of both fluorine-containing samples was lower over the entire range of down pressure when anionic silica particles were employed. In addition, the slope of the pressure / rate response is a measure of the difference in the contribution of the Preston's coefficient of the pad, and this slope was approximately 10% higher than that of the parent pad.

[0077]

[0078] For both polishing experiments shown above, total defects after polishing were measured at 3 psi (20.7 kPa). The ceria polish was measured after application of HF, and the silica polish used EKC 5650 cleaning solution. The results are shown in Table 6. The fluorinated formulations showed reduced total defects when polished with ceria, while the opposite effect was observed when colloidal silica was used.

[0079] Table 6

[0080] Sample Slurry Total defects after polishing (#) B Asahi CES333 635 2 Asahi CES333 470 B SS25 16012 2 SS25 22017

[0081] Note: Total defects vary greatly due to polishing process, slurry, measurement technique and setup. DuPont TM EKC PCMP 5650 TM cleaning chemistry (1 :90 dilution) Lam Ontrak Synergy TM cleaner Polished wafers after cleaning for total defects. KLA / TENCOR The cleaned wafers were measured on a Sp2 non-patterned wafer defect detection system (using a defect size of >0.16um). KLA / TENCOR The defect data was analyzed using software.

[0082] Example 4

[0083] Two versions of the above molecule were used, n value of 1.5 (fluorinated species, MW of approximately 1800 g / mol) and n > 4 (fluorinated species, MW of approximately 2000 g / mol). The larger n value will result in increased compatibility of the fluorinated segment used in the soft segment urea. To evaluate the impact on polishing, a control prepolymer was prepared from the following polyurea formulation.

[0084]

[0085] PTME = polytetramethylene ether (molecular weight)

[0086] A comparative prepolymer was prepared using ethoxylated perfluoroether in place of some of the PTMEG 2000 component as shown below:

[0087]

[0088] PTME = polytetramethylene ether (molecular weight)

[0089] The prepolymers with a perfluoroether / ethylene oxide atom ratio of 1.9 had higher compatibility and could be used to make prepolymers that were viable at both concentrations, while the perfluoroether / ethylene oxide atom ratio of 5.3 was only viable at the lower concentration due to excessive phase separation resulting in increased prepolymer viscosity and solidification. Solidification of the prepolymers made them unsuitable for casting with a curative into a polyurea polishing pad.

[0090] Pads were cast from the viable formulations using MBOCA as the curative (105% stoichiometry). The removal rate results as a function of downforce are shown below. As can be seen from the graph, the fluorinated prepolymers samples all increased the removal rate over the unfluorinated control, however, sample 5 had a further increase in removal rate over samples 6 and 8 due to the increased compatibility and higher achievable concentration of the ethoxylated perfluoroether.

[0091] The estimated perfluoroether / oxirane atomic ratio for the 3-oxirane fluorinated polymers of samples 7 and 8 was determined to be 5.3. For about 8, the perfluoroether / oxirane atomic ratio for samples 5 and 6 was about 1.9. To improve castability and soft segment separation, the perfluoroether / oxirane atomic ratio is preferably less than 4. More preferably, this ratio is less than 3, and most preferably, it is less than 2.5. Alternatively, surfactants can improve the solubility of high perfluoroether / oxirane atomic ratio formulations. However, these formulations do not always provide additional removal rate increases as the fluorinated polymer is increased.

[0092] Table 9 below provides the ceria polishing rates when using the ceria slurry of Example 3 and the prepolymers cast into pads as described above.

[0093] Table 9

[0094]

[0095] As can be seen from Table 9, the fluorinated polymer additives provided increased removal rates at higher down pressures when using the modified ceria slurry Hitachi HS-08005A diluted 1 :9 at pH 8.35.

[0096] Sample 7 prepolymers can be prepared by adding 0.5 wt% of Merpol A alcohol phosphate surfactant to the mixture prior to the reaction for the total prepolymers. This allows it to be used for cast pad samples. However, no further improvement was observed by increasing the atomic ratio R to 5.3 by using a surfactant, as opposed to the atomic ratio R of 1.9 observed by comparing it to sample 5 described above.

[0097] Table 10

[0098]

[0099] Note: The polishing data for Table 10 is from the same ceria modified slurry used in Table 9.

[0100] The polyurea-terminated fluorinated polymers of the present invention provide a surprising increase in dielectric removal rates when polishing using ceria-containing slurries at acidic pH levels or modified ceria-containing alkaline slurries. In addition, the fluorine-rich phase is concentrated around the microspheres, forming a heterogeneous mixture microstructure. Further, the fluorine-rich phase is concentrated near the surface to increase the polishing rate. Finally, the microspheres near the surface can be compressed and flattened to form a polished layer with small dentil-like microtexture.

Claims

1. A polishing pad suitable for polishing at least one of a semiconductor, optical, magnetic or electromechanical substrate comprising: a polyurea polishing layer comprising a polyurea matrix having a soft phase and a hard phase, the soft phase being formed from soft segments and the hard phase being formed from diisocyanate hard segments and a curing agent, the soft segments being copolymers of an aliphatic fluorine-free polymer group and a fluorocarbon having a length of at least six carbons, the polyurea matrix being cured by the curing agent and comprising gas or liquid filled polymer microelements, the soft segments forming a fluorine-rich phase that concentrates adjacent to the polymer microelements and polishing layer during polishing, wherein the polishing layer remains hydrophilic during polishing under shear conditions.

2. The polishing pad of claim 1, wherein, the thickness of the fluorine-rich phase adjacent to the polymer microelements is less than fifty percent of the average diameter of the polymer microelements.

3. The polishing pad of claim 1, wherein, the polymer microelements fracture under compression adjacent to the polishing surface independent of diamond conditioning.

4. The polishing pad of claim 1, wherein, the polishing layer can form a surface containing small dentil structures during polishing.

5. A polishing pad suitable for polishing at least one of a semiconductor, optical, magnetic or electromechanical substrate comprising: a polyurea polishing layer comprising a polyurea matrix having a soft phase and a hard phase, the soft phase being formed from soft segments and the hard phase being formed from diisocyanate hard segments and a curing agent and wherein the hard phase is precipitated in the soft phase, the soft segments being copolymers of an aliphatic fluorine-free polymer group and a fluorocarbon having a length of at least six carbons, the polyurea matrix being cured by the curing agent and comprising gas or liquid filled polymer microelements, the soft segments forming a fluorine-rich phase that concentrates adjacent to the polymer microelements and polishing layer during polishing, wherein the polishing layer remains hydrophilic during polishing under shear conditions.

6. The polishing pad of claim 5, wherein, the thickness of the fluorine-rich phase adjacent to the polymer microelements is less than fifty percent of the average diameter of the polymer microelements.

7. The polishing pad of claim 5, wherein, the polymer microelements fracture under compression adjacent to the polishing surface independent of diamond conditioning.

8. The polishing pad of claim 5, wherein, the polishing layer can form a surface containing small dentil structures during polishing.

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