Polishing material and method of polishing therewith

TECHNICAL FIELD

[0001] The present invention relates to an abrasive and to a polishing method using the same. More specifically, it relates to an abrasive obtained by curing raw materials containing at least (1) an organic polyisocyanate and at least one member selected from an organic polyol and an organic polyamine as matrix resin raw materials and (2) a particle having a hydroxyl group or colloidal silica and the like as an abrasive particle, by a polymerization reaction and to a polishing method using the same.

BACKGROUND ART

[0002] There has been known CMP (Chemical Mechanical Polishing) method using a nonwoven fabric polishing pad and an abrasive liquid containing free abrasive grains. In recent years, ecological CMP has been desired to reduce the cost of polishing treatment and solve a problem such as the disposal of abrasive liquid waste.

[0003] The above CMP using an abrasive liquid which contains free abrasive grains has a problem that a simple liquid waste disposal method cannot be employed because most of the used free abrasive grains (such as silica or the like) are discharged into liquid waste. In general, consumption of the abrasive grains consumed by wear during polishing is about 3 to 4 wt % of the total, and most of the abrasive grains are wasted without directly contributing to polishing. Therefore, with CMP using an abrasive liquid which contains free abrasive grains, it has been difficult to reduce the cost of processing and take measures for environmental preservation.

[0004] In view of the above situation, studies have been being made on the improvement of CMP using a polishing pad containing abrasive grains without using an abrasive liquid containing free abrasive grains. In this improved CMP, since most abrasive grains (such as silica or the like) are worn away and consumed by contributing to polishing, the amount of abrasive grains to be discharged into abrasive liquid waste can be reduced and therefore the abrasive liquid which has been used for polishing can be recycled by filtration. Since the abrasive grains are not wasted, a great reduction in the running cost of the polishing step can be expected.

[0005] However, as the conventional fixed abrasive grain polishing pad does not exhibit a spontaneous edging function, the polishing efficiency (polishing rate) lowers in a relatively short period of time, thereby making it impossible to carry out long-term continuous polishing. Therefore, abrasive grains must be dressed frequently, thereby causing a reduction in productivity.

[0006] For example, JP 5-8178A discloses a semiconductor wafer polishing cloth which is obtained by impregnating a composite substrate prepared by impregnating a felt-like fibrous sheet with a linear thermoplastic polyurethane resin and solidifying it, with a resin harder than the thermoplastic polyurethane resin and heating and drying the resin. The polishing ability of this polishing cloth is not reduced by loading in a short period of time but its service life is about 60 hours at best.

[0007] JP 8-216034A discloses an abrasive which comprises 60 to 90 wt % of a soft polyurethane resin matrix having a hardness of 50 to 85 and 10 to 40 wt % of at least one type of abrasive grains selected from the group consisting of silica, alumina and silicon carbide and dispersed in the above matrix and which has an expansion ratio of 1.5 to 5.0. Although this abrasive provides excellent surface smoothness to a semiconductor wafer after polishing and can suppress a surface sagging phenomenon, it has a problem that long-term continuous polishing is not possible to conduct therewith.

[0008] Further, JP 11-204467A discloses a semiconductor manufacturing apparatus which comprises a polishing pad for carrying out the mechanical polishing of the surface of a semiconductor substrate having a difference in level on the surface and a device for supplying a solution for carrying out the chemical polishing of the surface of the semiconductor substrate, wherein particles having hardness higher than the semiconductor substrate are contained. This publication discloses that the polishing pad is molded from a mixture of urethane and a silica particle as a raw material. Use of the above apparatus has characteristic features that the speed of polishing an insulating film formed on the substrate and the amount of polishing can be made uniform on the entire surface of the substrate and the supply of an excessive amount of a polishing slurry becomes unnecessary. However, the continuous polishing can not be done still for a long time, and dressing must be carried out regularly.

[0009] In view of the above situation, in order to carry out continuous polishing for a long time, an abrasive liquid containing free abrasive grains had to be used to polish a workpiece to be polished.

[0010] In general, as for requirements for an abrasive for polishing a compound semiconductor wafer or the like, the polished workpiece must have highly accurate surface smoothness, the polishing speed must be high, and a surface sagging phenomenon (which is a phenomenon of the peripheral portion of the polished surface becoming thinner than the central portion) must not occur, in addition to long-term continuous polishing.

[0011] Further, the matrix resin of the abrasive must have high elasticity so that it can fit to the uneven surface of the workpiece to be polished.

DISCLOSURE OF THE INVENTION

[0012] It is therefore an object of the present invention to provide an abrasive which enables long-term continuous polishing, gives high polishing speed and provides the polished workpiece with highly accurate surface smoothness and does not cause a surface sagging phenomenon; and a fixed abrasive grain polishing pad comprising the above abrasive.

[0013] It is another object of the present invention to provide a method of polishing a workpiece to be polished using the above abrasive.

[0014] The inventors of the present invention have conducted studies to solve the above problems and have found that an abrasive which enables long-term continuous polishing, gives high polishing speed and provides the polished workpiece with highly accurate surface smoothness and does not cause a surface sagging phenomenon can be obtained by using a particle having a hydroxyl group or colloidal silica or the like as an abrasive particle in an abrasive obtained by curing raw materials containing at least (1) an organic polyisocyanate and at least one member selected from an organic polyol and an organic polyamine as matrix resin raw materials and (2) an abrasive particle, by a polymerization reaction. The present invention has been accomplished based on this finding.

[0015] That is, according to a first aspect of the present invention, there is provided an abrasive which is obtained by curing raw materials containing at least (1) an organic polyisocyanate (component A) and at least one member selected from an organic polyol (component B) and an organic polyamine (component C) as raw materials of a matrix resin and (2) an abrasive particle (component E), by a polymerization reaction, wherein the particle (component E) is (a) a particle (component E1) having a hydroxyl group in an amount of 0.001 mmol/g or more (measured by neutralization titration, this shall apply hereinafter) and/or (b) at least one member (component E2) selected from fumed silica, colloidal silica, fumed alumina, colloidal alumina, boehmite and bayerite.

[0016] In the first aspect of the present invention, it is desired that

[0017] (1) the matrix resin (resin F) should be a resin having at least an urethane bond,

[0018] (2) the matrix resin raw materials should contain an organic polyisocyanate (component A), at least one member selected from an organic polyol (component B) and an organic polyamine (component C), and a foaming agent (component D),

[0019] (3) the matrix resin raw materials should be an organic polyisocyanate (component A), at least one member selected from an organic polyol (component B) and an organic polyamine (component C), and an organic polycarboxylic acid (component J),

[0020] (4) the matrix resin (resin F) should be a resin having at least one of urethane bond, urea bond and amide bond,

[0021] (5) the expansion ratio should be 1.1 to 5,

[0022] (6) the particle (component E) should be colloidal silica,

[0023] (7) the amount of the hydroxyl group in the particle (component E1) should be 0.01 to 6 mmol/g,

[0024] (8) the particle (component E1) should be at least one member selected from diamond, cubic boron nitride, zirconia, ceria, manganese oxide, titanium oxide, calcium carbonate, barium carbonate, magnesium oxide, alumina-silica and silicon carbide all of which are provided with a hydroxyl group,

[0025] (9) the matrix resin (resin F) should be contained in the abrasive in an amount of 60 to 95 wt %,

[0026] (10) the abrasive should be a foamed material obtained by curing raw materials including an organic polyisocyanate compound (component A), at least one member selected from an organic polyol (component B) and an organic polyamine (component C), a foaming agent (component D), a catalyst and a particle (component E), by a polymerization reaction,

[0027] (11) the abrasive should be a foamed material obtained by adding an organic polyisocyanate compound (component A) to a mixture of at least one member selected from an organic polyol (component B) and an organic polyamine (component C), a foaming agent (component D), a catalyst and a particle (component E), mixing them together under stirring, and curing and molding the mixture by a polymerization reaction, and

[0028] (12) the abrasive should be a foamed material obtained by adding a mixture of at least one member selected from an organic polyol (component B) and organic polyamine (component C) and a particle (component E) to a mixture of an organic polyisocyanate compound (component A), a foaming agent (component D) and a catalyst, mixing them together stirring, and curing and molding the mixture by a polymerization reaction.

[0029] According to a second aspect of the present invention, there is provided a fixed abrasive grain polishing pad, which is a fixed abrasive grain polishing pad (polishing pad G) that is composed of an abrasive comprising a matrix resin (resin F) having an urethane bond and obtained by the polymerization reaction of raw materials containing at least an organic polyisocyanate (component A), at least one member selected from an organic polyol (component B) and an organic polyamine (component C) as raw materials of a matrix resin and the above particle (component E) and that is mounted on a polishing table, which is used for polishing a workpiece to be polished by the relative movements of the workpiece and the fixed abrasive grain polishing pad (polishing pad G) while pressing the workpiece between the fixed abrasive grain polishing pad (polishing pad G) and a workpiece holding portion and supplying an abrasive liquid (abrasive liquid H) between the fixed abrasive grain polishing pad (polishing pad G) and the workpiece.

[0030] In the second aspect of the present invention, it is desired that

[0031] (1) the fixed abrasive grain polishing pad (polishing pad G) should have grooves extending radially from the center point toward the circumferential direction, and

[0032] (2) the fixed abrasive grain polishing pad (polishing pad G) should have lattice-like grooves.

[0033] According to a third aspect of the present invention, there is provided a method of polishing a workpiece, comprising mounting the above fixed abrasive grain polishing pad (polishing pad G) composed of the above abrasive on a polishing table, pressing the workpiece between the fixed abrasive grain polishing pad (polishing pad G) and a workpiece holding portion, and polishing the workpiece by the relative movements of the fixed abrasive grain polishing pad (polishing pad G) and the workpiece while supplying an abrasive liquid (abrasive liquid H) between the fixed abrasive grain polishing pad (polishing pad) and the workpiece.

[0034] In the third aspect of the present invention, it is desired that

[0035] (1) the abrasive liquid (abrasive liquid H) should be an alkaline aqueous solution, and

[0036] (2) the above alkaline aqueous solution should have a pH of 10 or higher.

[0037] Even when the workpiece is continuously polished with the abrasive of the present invention for a long time, the polishing function of the abrasive rarely lowers. Further, although the particles (component (E)) blended as the abrasive particles are dispersed in the matrix resin (resin F) after the polymerization reaction and are existent as the abrasive grains (abrasive grains I), the abrasive grains (abrasive grains I) are rarely worn away. Since the amount of the abrasive grains (abrasive grains I) discharged into the abrasive liquid waste is greatly reduced, the abrasive liquid can be recycled by simple filtration means or the like without exerting a bad influence upon the environment.

[0038] The concrete mechanism of the long-term continuous polishing of the workpiece by using the abrasive of the present invention is not made clear but it is assumed that chemical bonding force is developed between the isocyanate group (—CNO) of the organic polyisocyanate (component A) and the hydroxyl group of the particle (component E) when the abrasive of the present invention is cured and molded by a polymerization reaction.

[0039] That is, it is assumed that the hydrogen atom of the hydroxyl group of the particle (component E) acts on the isocyanate group of the organic polyisocyanate (component A) as active hydrogen, the active hydrogen atom is added to the nitrogen atom of the isocyanate group (—CNO), and the oxygen atom of the hydroxyl group devoid of the hydrogen atom is bonded to the carbon atom of the isocyanate group (—CNO) to produce a chemical bond [(matrix resin side) —NH—CO—O— (abrasive grain side)].

[0040] It is presumed that with the consequence of the development of the chemical bond between the matrix resin (resin F) and the abrasive grains (abrasive grains I), the amount of the abrasive grains (abrasive grains I) which fall off in the matrix resin (resin F) is greatly reduced, thereby making long-term continuous polishing possible.

[0041] It is assumed that in the abrasive of the prior art, the hydroxyl group rarely existed or existed in very small quantities in the particle used and hence, abrasive grains were merely held in the matrix resin physically, whereby most of the abrasive grains easily fell off.

[0042] Since chemical bonding force develops at the boundary between the matrix resin (resin F) and the abrasive grains (abrasive grains I), not only the abrasive grains (abrasive grains I) existent on the polishing surface of the abrasive but also the entire surface of the abrasive become treated surfaces. Accordingly, it is considered that the polishing rate does not lower even in the case of long-term continuous polishing.

[0043] Owing to these reasons, long-term continuous polishing is made possible even when the spontaneous edging function of the abrasive is not exhibited.

[0044] [First Aspect of the Present Invention]

[0045] The abrasive of the present invention is an abrasive obtained by curing raw materials containing at least an organic polyisocyanate (component A) and at least one member selected from an organic polyol (component B) and an organic polyamine (component C) as matrix resin raw materials and the above particle (component E) as an abrasive particle, by a polymerization reaction, the matrix resin (resin F) having an urethane bond and/or an urea bond.

[0046] The matrix resin raw materials may optionally contain a foaming agent (component D), a catalyst or a foam stabilizer in addition to the organic polyisocyanate (component A), organic polyol (component B) and organic polyamine (component C).

[0047] The particle (component E) used as an abrasive particle material may be a particle having a specific amount of a hydroxyl group, a particle having a hydroxyl group such as colloidal silica or the like which will be described later, or zirconia provided with a hydroxyl group.

[0048] The organic polyisocyanate compound (component A) which is one of the matrix resin raw materials is a compound having two or more isocyanate groups in the molecular, and a polyisocyanate that is generally used to produce a polyurethane resin may be used without restriction.

[0049] Illustrative examples of the organic polyisocyanate compound (component A) include tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), naphthylene diisocyanate (NDI), paraphenylene diisocyanate (PPDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), lysine diisocyanate (LDI), tolysine diisocyanate (TODI), hydrogenated xylylene diisocyanate, modified products of these polyisocyanates and prepolymers obtained by reacting a polyol with polyisocyanate beforehand so that an isocyanate group remains at the terminal.

[0050] The content of the NCO group of the organic polyisocyanate compound (component A) is preferably 20 to 48 wt %, more preferably 20 to 40 wt %, much more preferably 25 to 38 wt %. Within this range, an abrasive having excellent durability and abrasion resistance can be obtained.

[0051] These organic polyisocyanate compounds (component A) may be used alone or in combination of two or more.

[0052] Out of these, tolylene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI) are preferred.

[0053] As the organic polyol (component B) may be used any organic compound having two or more hydroxyl groups in the molecule such as a polyhydric alcohol, polyether-based polyol, polyester polyol or polymer polyols.

[0054] Illustrative examples of the organic polyol (component B) include polyhydric alcohols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1, 4-bis (hydroxymethyl)cyclohexane, bisphenol A, hydrogenated bisphenol A, hydroxypivalylhydroxypivalate, trimethylolethane, trimethylolpropane, 2,2,4-trimethyl-1,3-pentanediol, glycerine and hexanetriol; polyether glycols such as polyoxyethylene glycol, polyoxypropylene glycol, polyoxyethylene, polyoxypropylene and polyoxytetramethylene glycol; modified polyether polyols obtained by the ring-opening polymerization of the above polyhydric alcohol and ethylene oxide, propylene oxide, tetrahydrofuran, ethyl glycidyl ether, propyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether or allyl glycidyl ether; polyester polyols obtained by the cocondensation of at least one of the above polyhydric alcohols and a polycarboxylic acid such as succinic acid, maleic acid, adipic acid, glutaric acid, pimellic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthailc acid or terephthalic acid; lactone-based polyester polyols obtained by the polycondensation reaction of at least one of the above polyhydric alcohols and a lactone such as ε-caprolactone, δ-valerolactone or 3-methyl-δ-valerolactone; epoxy-modified polyester polyols obtained by using at least one epoxy compound such as bisphenol A epoxy compound, hydrogenated bisphenol A epoxy compound, glycidyl ether of monohydric and/or polyhydric alcohol(s) or glycidyl ester of a monobasic acid and/or polybasic acid at the time of synthesizing a polyester polyol; polyester polyamide polyol, polycarbonate polyol, polybutadiene polyol, polypentadiene polyol, castor oil, castor oil derivatives, hydrogenated castor oil, hydrogenated castor oil derivatives and hydroxyl group-containing acryl copolymers.

[0055] The above organic polyol (component B) has a hydroxyl value of preferably 100 to 1,800, particularly preferably 200 to 1,200.

[0056] The above organic polyols (component B) may be used alone or in combination of two or more.

[0057] The blend ratio of the organic polyisocyanate compound (component A) to the organic polyol (component B) is 0.8 to 1.2, preferably 1 to 1.2 in terms of functional group ratio ([active hydrogen-containing compound]/[isocyanate]).

[0058] In the present invention, the organic polyamine (component C) may be used in place of part or all of the organic polyol (component B). The polyamine which can be used is a known diamine, triamine or a mixture thereof which is generally used to produce a polyurethane resin. Typical examples thereof include 1,2-ethylenediamine, bis-(3-aminopropyl)-amine, hydrazine, hydrazine-2-ethanol, bis-(2-methylaminoethyl)-methylamine, 1,4-diaminocyclohexane, 3-amino-1-methylaminopropane, N-methyl-bis-(3-aminopropyl)-amine, tetraethylenediamine, hexamethylenediamine, 1-aminoethyl-1,2-ethylenediamine, bis-(N,N′-aminoethyl)-1,2-ethylenediamine, diethylenetriamine, tetraethylenepentamine, pentaethylenehexamine, phenylenediamine, toluylenediamine, 2,4,6-triaminotoluene trihydrochloride, 1,3,6-triaminonaphthalene, isophoronediamine, xylylenediamine, 4,4′-diaminodiphenylmethane, hydrogenated 4,4′-diaminodiphenylmethane and derivatives of these polyamine monomers.

[0059] The organic polyamine (component C) has an amine value of preferably 56 to 560 (mgKOH/g), particularly preferably 80 to 400 (mgKOH/g). Within this range, an abrasive having excellent durability and polishing properties can be obtained.

[0060] Further, in the present invention, an organic polycarboxylic acid (component J) may be used in place of the above organic polyol (component B) and/or organic polyamine (component C). In this case, the matrix resin (resin F) becomes a resin having at least one of urethane bond, urea bond and amide bond.

[0061] Examples of the organic polycarboxylic acid (component J) include aromatic carboxylic acids such as phthalic acid and aliphatic carboxylic acids such as adipic acid. Preferably, they function as a stabilizer for a curing catalyst and have not odor.

[0062] The foaming agent (component D) which can be used for a reaction between the organic polyisocyanate compound (component A) and at least one member selected from the organic polyol (component B) and the organic polyamine (component C) is a mixture of one or two or more member of water, trichloromonofluoromethane, dichlorodifluoromethane, methylene chloride, trichlorofluoroethane and trichloroethane.

[0063] The expansion ratio at the time when the matrix resin (resin F) is molded is preferably 1.1 to 5.

[0064] The term “expansion ratio” as used herein is represented by D1/D2 wherein D1 is a bulk density calculated from the weight and volume of a non-foamed cured product produced without mixing a foaming agent (component D) with raw materials containing the matrix resin raw materials and an abrasive particle (component E) and D2 is a bulk density calculated from the weight and volume of a foamed cured product produced by mixing a foaming agent (component D) with raw materials containing the same abrasive particle (component E).

[0065] Although an abrasive having an expansion ratio higher than 5.0 provides a high polishing speed because its bubble structure is rough, it roughens the surface of a workpiece to be polished such as a wafer and reduces the surface smoothness of the workpiece after polishing.

[0066] On the other hand, an abrasive having an expansion ratio lower than 1.1 enhances the surface smoothness of a wafer or the like because its bubble structure is dense but it provides a low polishing speed and reduces productivity at the time of polishing.

[0067] The catalyst which can be used for the reaction between the organic polyisocyanate compound (component A) and the organic polyol (component B) or the like is not particularly limited, and an amine-based catalyst or organic metal-based catalyst may be used. Examples of the amine-based catalyst include triethylenediamine, triethylamine, tripropylamine, triisopropanolamine, tributylamine, trioctylamine, N-methylmorpholine and N-ethylmorpholine. Examples of the organic metal-based catalyst include tin octylate, tin laurate and dibutyltin dilaurate. Out of these, amine-based catalysts are preferred.

[0068] The amount of the catalyst is not particularly limited but generally about 0.01 to 0.5 part by weight based on 100 parts by weight of the total of the organic polyisocyanate compound (component A) and the organic polyol (component B).

[0069] As the foam stabilizer may be used a conventionally known organosilicone-based surfactant. Examples of the organosilicone-based surfactant include L-520, L-532, L-540, L-544, L-3550, L-5740S, L-5740M and L-6202 of Nippon Unicar Co., Ltd.; SH-190, SH-192, SH-193, SH-194, SRX-294 and SRX-298 of Toray Silicone Co., Ltd.; and F-114, F-121, F-122, F-230, F-258, F-260B, F-317, F-341, F-601 and F-606 of Shin-Etsu Silicon Co., Ltd.

[0070] Optionally, a flame retardant, a dehydrator and a weathering agent may be further added to the raw material composition.

[0071] Examples of the flame retardant include aluminum hydroxide, phosphates, melamine, red phosphorus and expanded graphite. Examples of the dehydrator include calcium silicate, calcium carbonate, magnesium sulfate and synthetic zeolite. Examples of the weathering agent include ultraviolet light absorbers, optical stabilizers and antioxidants which are generally used for polyurethane resins.

[0072] In the present invention, as the abrasive particle (component E) may be used (a) a particle having a hydroxyl group in an amount of 0.001 mmol/g (component E1) and/or (b) at least one member (component E2) selected from fumed silica, colloidal silica, fumed alumina, colloidal alumina, boehmite and bayerite.

[0073] When the above particle (component E1) is used as the abrasive particle, the amount of the hydroxyl group of the particle having a hydroxyl group (component E1) is 0.001 mmol/g or more when measured by the following neutralization titration. When the amount of the hydroxyl group is 0.001 mmol/g or more, chemical bonding force can be developed between the matrix resin (resin F) and the abrasive grains (abrasive grains I) after the curing of the matrix resin (resin F), which is the effect of the present invention.

[0074] The amount of the hydroxyl group is preferably 0.01 mmol/g or more, particularly preferably 0.05 mmol/g or more.

[0075] Although there is no upper limit to the amount of the hydroxyl group of the particle (component E1), when it is too large, the particle (component E1) is apt to be covered with the matrix resin and hence, an effect obtained by increasing the amount of the hydroxyl group cannot be expected. The amount of the hydroxyl group of the particle (component E1) is preferably 20 mmol/g or less, more preferably 10 mmol/g or less, particularly preferably 6 mmol/g or less.

[0076] The method of measuring the amount of the hydroxyl group contained in the abrasive particle (component E) is as follows. That is, 2.00 g of the sample particle is weighed (W g) and put in a 100 ml Erlenmeyer flask, 80 ml of a 0.05 N aqueous solution of NaOH is added to this flask, and the flask is tightly sealed with a rubber cap and left as it is under stirring for 12 hours. Thereafter, the particle and the solution are separated from one another by a centrifugal separator, and 10 ml of the solution is put into a pipette from this solution, and titrated with a 0.05 N aqueous solution of HCl for neutralization. The amount of the HCl aqueous solution required for neutralization is represented by A ml. The same operation is carried out without adding the particle and the amount of an HCl aqueous solution required for neutralization is represented by B ml. The amount (X mmol/g) of the OH group per unit weight of the particle is calculated from the following equation.

X
=[(B−A)×0.05×8]/W

[0077] The measurement value of the amount of the hydroxyl group is the measurement value of the amount of the hydroxyl group existent relatively near the surface of the particle (component E). In the present invention, since the hydroxyl group existent relatively near the surface of the particle (component E) makes it possible to actually develop chemical bonding force between the matrix resin (resin F) and the particle, the above measurement method is employed and its measurement value is taken as the amount of the hydroxyl group of the particle (component E) for convenience.

[0078] Illustrative examples of the particle having a hydroxyl group (component E1) include all particles used in known inorganic abrasive grains, such as silica, alumina or the like. Further, examples of the particle provided with a hydroxyl group (component E1) include metal oxides such as titanium oxide provided with a hydroxyl group by a hydration reaction. Further, there are methods of producing a composite particle by applying mechanical energy to a plurality of different raw material particles to cause a mechanochemical reaction (inserting a hydroxyl group by conjugating a particle having a hydroxyl group with a particle not having a hydroxyl group). Thus, the hydroxyl group can be provided by various methods depending on the type of the particle.

[0079] Examples of the above particle include diamond, cubic boron nitride, zirconia, ceria, manganese oxide, titanium oxide, calcium carbonate, barium carbonate, magnesium oxide, alumina-silica and silicon carbide all of which are provided with a hydroxyl group.

[0080] As the abrasive particle (component E2) may be used at least one member selected from fumed silica, colloidal silica, fumed alumina, colloidal alumina, boehmite and bayerite.

[0081] Since these abrasive particles (component E2) generally have a hydroxyl group on the surface, they may be used alone or in combination without taking into consideration the amount of the hydroxyl group, unlike the above particle (component E1). Out of these, colloidal silica is preferred.

[0082] When fumed silica and fumed alumina have a large number of Si—Cl bonds on the surface, they are preferably heated at about 200 to 800° C. in the presence of water to convert these Si—Cl bonds into Si—OH bonds before use.

[0083] The method of producing the above colloidal silica is not particularly limited. For example, colloidal silica produced by known production methods disclosed by JP 4-2602A, JP 4-231319A, JP 5-97422A, JP 2003-89786A and JP 2003-100678A may be used.

[0084] The above colloidal silica and fumed silica have a large number of hydroxyl groups in the form of Si—OH (silanol group) on the surface (terminal groups of the structure), which is advantageous when they are chemically bonded to the matrix resin (resin F).

[0085] Preferably, these abrasive particles (component E) are uniform in diameter and have a small diameter in order to prevent the surface of the workpiece from being scratched by abrasion grains and to prevent a change in composition caused by precipitation during storage. The particle diameter of the abrasive particle (component E) can be observed through a scanning electron microscope. The particle diameter is preferably in the range of 0.005 to 50 μm. When the particle diameter is smaller than 0.005 μm, it is difficult to obtain the high polishing speed, while when the particle diameter is larger than 50 μm, the surface of the workpiece is liable to be scratched disadvantageously.

[0086] The abrasive of the present invention desirably contains 60 to 95 wt % of the matrix resin (resin F).

[0087] When the content of the matrix resin (resin F) in the abrasive is higher than 95 wt % (i.e., the content of the abrasive particle is lower than 5 wt %), the polishing speed becomes low and high productivity cannot be maintained. When the content is lower than 60 wt % (i.e., the content of the abrasive particle is higher than 40 wt %), the fluidity of a liquid polyurethane resin as a matrix greatly lowers at the time of producing an abrasive, thereby making molding difficult.

[0088] The abrasive of the present invention is obtained by the polymerization reaction of raw materials containing an organic polyisocyanate (component A), at least one member selected from an organic polyol (component B) and an organic polyamine (component C) (in some case, an organic polycarboxylic acid is added as required) as matrix resin raw materials and an abrasive particle (component E).

[0089] As described above, a catalyst, a foaming agent (component D) and a foam stabilizer may be optionally blended.

[0090] A mixture of the above raw materials can be cured and molded by a polymerization reaction in accordance with a reaction injection method or casting method.

[0091] [Second Aspect of the Present Invention]

[0092] The fixed abrasive grain polishing pad (polishing pad G) composed of the above abrasive is mounted on the polishing table, and the workpiece is pressed against the surface of the fixed abrasive grain polishing pad (polishing pad G) and polished by the relative movements of the fixed abrasive grain polishing pad (polishing pad G) and the workpiece.

[0093] When an abrasive liquid is used, grooves are desirably provided in the fixed abrasive grain polishing pad (polishing pad G) radially from the center point toward the circumferential direction or in a lattice form to uniformly spread the abrasive liquid all over the surface of the fixed abrasive grain polishing pad (polishing pad G).

[0094] [Third Aspect of the Present Invention]

[0095] The third aspect of the present invention is a method of polishing a workpiece, comprising mounting the above fixed abrasive grain polishing pad (polishing pad G) composed of the abrasive on a polishing table, pressing a workpiece between the fixed abrasive grain polishing pad (polishing pad G) and a workpiece holding portion, and polishing the workpiece by the relative movements of the fixed abrasive grain polishing pad (polishing pad G) and the workpiece while supplying the abrasive liquid (abrasive liquid H) between the fixed abrasive grain polishing pad (polishing pad G) and the workpiece.

[0096] The above polishing method makes possible chemical mechanical polishing, provides a high polishing speed and makes it possible to obtain a workpiece having highly accurate surface smoothness when an alkali aqueous solution is used as the abrasive liquid (abrasive liquid H).

[0097] The above abrasive liquid (abrasive liquid H) is an aqueous solution of sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like and preferably has a pH of 10 or higher to obtain a chemical polishing function.

[0098] By employing the polishing method of the present invention, a reduction in polishing rate can be suppressed even when polishing is continuously carried out for a long time.

[0099] Since an alkaline aqueous solution is used as the abrasive liquid (abrasive liquid H) and the amount of abrasive grains (abrasive grains I) falling off from the abrasive is extremely small, the abrasive liquid (abrasive liquid H) can be recycled merely by filtering it with a simple regenerating apparatus.

BRIEF DESCRIPTION OF DRAWINGS

[0100]
FIG. 1 is a perspective view showing the outline of a polishing apparatus using an abrasive according to a first embodiment as a fixed abrasive grain polishing pad;

[0101]
FIG. 2 is a perspective view showing the constitution of a fixed abrasive grain polishing pad according to a second embodiment; and

[0102]
FIG. 3 is a graph showing the relationship between polishing time and polishing efficiency in Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0103] (First Embodiment)

[0104] The abrasive of the present invention can be manufactured as follows.

[0105] A mixture of the above-described organic polyisocyanate compound (component A), organic polyol (component B), foaming agent (component D), catalyst and foam stabilizer and the particle (component E) is stirred to disperse the particle (component E) into the raw material liquid composition uniformly.

[0106] In this case, it is particularly preferred that the organic polyisocyanate compound (component A) be added to a mixture of the organic polyol having an average molecular weight of 250 to 4,000 (component B), foaming agent (component D), catalyst, foam stabilizer and particle (component E), and stirred and mixed together.

[0107] It is also preferred that the raw materials (excluding the particle (component E) and the organic polyol (component B) be blended together in predetermined amounts to prepare a liquid composition and that a mixed solution prepared by fully mixing and stirring together the chemically stable organic polyol (component B) and the particle (component E) be added to the above composition.

[0108] The raw material composition is then put into a mold having predetermined size and shape, and heated for a predetermined period of time. The raw material composition is foamed and cured at the same time. After curing, the foamed abrasive is taken out from the mold to obtain the abrasive of the present invention.

[0109] When a reaction injection molding method is employed, a mixture of the raw materials is injected into the mold from a resin gate and cured in the mold by heating for a relatively short period of time to obtain a molded product.

[0110] The Shore D surface hardness specified in JIS K6253-1997/IS07619 of 20 to 85 at a temperature range of 20 to 150° C. is suitable to the abrasive. When the Shore D hardness is lower than 20, the polishing rate worsens and when it is higher than 85, scratching is liable to occur (due to roughness).

[0111] (Second Embodiment)

[0112] As shown in FIG. 2, grooves 16a or 16b are formed on the surface of the fixed abrasive grain polishing pad 16 according to the second embodiment. These grooves are formed in order to spread the abrasive liquid over the whole surface (the center portion in particular) of the fixed abrasive grain polishing pad efficiently and uniformly. This makes it possible to flatten the surface of a wafer, improve the polishing rate and prevent thermal expansion caused by a local temperature rise. For example, radial grooves as shown in FIG. 2(A) and lattice type grooves as shown in FIG. 2(B) can be formed.

[0113] To form the radial grooves 16a in the fixed abrasive grain polishing pad 16 as shown in FIG. 2(A), the fixed abrasive grain polishing pad 16 is preferably divided into 16 to 32 sections radially starting from the center point (at a center angle of 22.5 to 11.250). Preferably, the width of each groove is, for example, about 1 to 2 mm and the depth of each groove is, for example, about 1 to 2 mm. It is preferred that grooves should not be formed in a predetermined range (for example, 100 mm or less from the center) from the center to prevent the excessive concentration of the grooves 16a around the center of the fixed abrasive grain polishing pad 16.

[0114] To form the lattice-like grooves 16b in the fixed abrasive grain polishing pad 16 as shown in FIG. 2(B), the grooves are preferably formed at intervals of, for example, 15 to 30 mm.

[0115] In the above embodiment, the formation of radial or lattice type grooves in the fixed abrasive grain polishing pad is exemplified, but the present invention is not limited to these examples. Hexagonal, wavy grooves and the like may be suitably formed. While the sectional form of each groove has been described as square (rectangular), it may be circular, V-shaped or U-shaped.

[0116] (Third Embodiment)

[0117] A preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, constituent elements having substantially the same functions are given the same reference symbols to avoid the repetitions of their descriptions.

[0118] With reference to FIG. 1, the constitution of a polishing apparatus comprising a fixed abrasive grain polishing pad according to the third embodiment will be first described. FIG. 1 is a perspective view showing the constitution of the polishing apparatus comprising a fixed abrasive grain polishing pad according to this embodiment.

[0119] As shown in FIG. 1, the polishing apparatus 10 using a fixed abrasive grain polishing pad related to this embodiment is constituted by a polishing table 14 which can be rotated by a motor 12, a fixed abrasive grain polishing pad 16 mounted on the polishing table 14, a substrate holding portion 20 for pressing the surface to be polished of the held substrate 30 against the fixed abrasive grain polishing pad 16, a substrate holding portion drive means 18 for rotating and driving under pressure the substrate holder portion 20 and an abrasive liquid supply port 24 for supplying an abrasive liquid 25 to the polishing table 14.

[0120] The polishing table 14 is a substantially disk-like table formed from stainless steel or ceramic and has a smooth horizontal top surface. This polishing table 14 rotates at a predetermined speed (for example, 40 rpm) in a direction shown by a bold arrow in FIG. 1 when, for example, the drive force of the motor 12 provided in the apparatus below the table is transmitted via a spindle 26 and a transmission (not shown).

[0121] The fixed abrasive grain polishing pad 16 is stuck on the polishing table 14 in such a manner that it becomes as flat as possible, and rotationally moved relative to the substrate 30 as the polishing table 14 is rotated, whereby the polishing surface of the substrate 30 is polished by the aid of the abrasive liquid 25 supplied from the abrasive liquid supply port 24. A detailed description of the fixed abrasive grain polishing pad 16 will be given hereinafter.

[0122] The substrate holding portion drive means 18 rotates the substrate holding portion 20 while applying pressure to the portion through a rod 28, and is, for example, composed of a motor, cylinder and the like (not shown). That is, the substrate holding portion 20 holding the substrate 30 can be pressed against the fixed abrasive grain polishing pad 16 in a vertical direction for example, by the cylinder as a pressurizing unit and at the same time, is rotated in a direction shown by a thin arrow in FIG. 1 by the motor as a rotary unit. The substrate holding portion drive means 18 may be so constituted that the substrate holding portion 20 can be swung in any substantially horizontal direction.

[0123] The substrate holding portion (also called “polishing head or carrier”) 20 has a substantially columnar shape as a whole and is rotatably installed above the polishing table 14. The substrate holding portion 20 is connected to the holding portion drive means 18 via the rod 28 and has a ring (retainer ring) for preventing a horizontal slide of the substrate 30 on the under surface.

[0124] At the time of regular polishing, the substrate holding portion 20 presses the surface to be polished of the substrate 30 against the fixed abrasive grain polishing pad 16 while rotating in a state of holding the substrate 30. The substrate 30 which is thus pressed against the fixed abrasive grain polishing pad 16 is rubbed bi-directionally with the fixed abrasive grain polishing pad 16 which rotates in the opposite direction, so that its entire polishing surface is uniformly polished.

[0125] The abrasive liquid supply nozzle 24 supplies the abrasive liquid 25 to the rotating fixed abrasive grain polishing pad 16 at the time of polishing the substrate 30. The abrasive liquid 25 is a solution containing a chemically reactive substance, and enters the gap between the substrate 30 and the fixed abrasive grain polishing pad 16 during polishing to smooth the polishing surface of the substrate 30 with high accuracy while it chemically reacts with the surface to be polished.

[0126] In the polishing apparatus of this embodiment, the substrate holding portion (polishing head) 20, the polishing table 14 and the abrasive liquid supply nozzle 24 are each provided with a temperature regulator (not shown) and the temperature of each of the above units is suitably adjusted to a preferred value to carry out polishing in a more preferred manner.

[0127] The abrasive liquid is preferably an alkaline aqueous solution having a pH of 10 or higher. When an abrasive liquid having a pH lower than 10 is used as shown in Example 2, the polishing rate greatly lowers.

[0128] As the alkaline solution is thus used as the abrasive liquid in this embodiment, it can be recycled merely by filtering with a simple regeneration apparatus. For example, when an alkaline solution prepared from sodium hydroxide or potassium hydroxide is used, a neutralizing apparatus is used to carry out the disposal of liquid waste more easily. Since the recycling of the abrasive liquid is easily realized as described above, it can contribute to environmental preservation. The abrasive liquid (alkaline solution) of this embodiment can be prepared from, for example, sodium hydroxide, potassium hydroxide, amine, ammonia and the like. Preferably, the abrasive liquid is prepared at a temperature range of 20 to 150° C. and used for polishing at a temperature range of 20 to 150° C.

EXAMPLES

[0129] The polishing rate and the like of a workpiece to be polished (silicon wafer) were evaluated by preparing various polyurethane polishing pads and using various abrasive liquids based on the above embodiments, and will be specifically described hereinbelow.

Example 1 and Comparative Examples 1 and 2

[0130] A polyurethane polishing pad of the present invention was used in Example 1, a polyurethane polishing pad containing alumina abrasive grains was used in Comparative Example 1, and a conventional commercially available fixed abrasive grain polishing pad was used in Comparative Example 2 as the fixed abrasive grain polishing pad.

[0131] The polishing particle used in Example 1 was colloidal silica (manufactured by Fuso Chemical Co., Ltd., under the trade name of Quartron SP-4B), and the polishing particle used in Comparative Example 1 was alumina (manufactured by Fujimi Incorporated, under the trade name of WA#3000). The commercially available fixed abrasive grain polishing pad of Comparative Example 2 was manufactured by Noritake Co., Ltd., (trade name: FARD pad).

[0132] The raw material compositions and physical properties of the polishing pads in Example 1 and Comparative Example 1 are shown in Table 1.

1TABLE 1Ex. 1Comp. Ex. 1Raw materialOrganic polyol A48.548.5composition ofOrganic polyol B31.531.5matrix resinOrganic polyisocyanate38.538.3(parts byWater0.20.2weight)Catalyst0.70.7Silicone foam stabilizer0.50.5AbrasiveColloidal silica88.70particleAlumina088.7(parts byweight)PhysicalContent of abrasive grain3030properties ofAverage molecular weigh15001500polishing padof polyolExpansion ratio (times)22Hardness at 20° C. (Shore4039D)Ex.: Example, Comp. Ex.: Comparative Example

[0133] As shown in Table 1, the polyether polyol having a molecular weight of 250 to 5,000 and 2 to 3 functional groups (manufactured by Sanyo Kasei Co., Ltd., under the trade name of Sanix), polyisocyanate (content of NCO group: 31 wt %, manufactured by Dow Polyurethane Systems Co., Ltd., under the trade name of PAPI 135), water, amine-based catalyst (manufactured by Tosoh Corporation, under the trade name of TOYOCAT-ET), silicone foam stabilizer (manufactured by Nippon Unicar co., Ltd., under the trade name of L-5309) and the above abrasive particle material were mixed together in a ratio (parts by weight) shown in Table 1 to prepare a liquid mixture. This liquid mixture was injected into a mold and left at 20 to 30° C. for 24 hours to be foamed and cured in order to produce a polyurethane polishing pad.

[0134] This polyurethane polishing pad was stuck on the table of a polishing machine by an adhesive tape, and the surface of the polyurethane polishing pad was corrected with a correction ring having diamond electrodeposited to obtain a 9 mm-thick polyurethane polishing pad having foamed structure exposed on its surface.

[0135] The polishing pad used in Comparative Example 1 was obtained in the same manner as in Example 1 except that alumina was used in place of colloidal silica in Example 1.

[0136] As shown in FIG. 1, the workpiece (silicon wafer) to be polished was pressed against the polyurethane polishing pad and polished by the relative movements of the polyurethane polishing pad and the workpiece (silicon wafer) while supplying the abrasive liquid between the polyurethane polishing pad and the workpiece.

[0137] The polishing conditions are given below.

[0138] Polishing pressure: 300 g/cm2

[0139] Revolution of table: 40 rpm.

[0140] The hardness of the polyurethane polishing pad was measured with a Shore D hardness meter specified in JIS K6253-1997/IS07619. The expansion ratio was represented by D1/D2 wherein D, is the density of a non-foamed cured product and D2 is the density of the polyurethane polishing pad produced in Example 1.

[0141] The polishing rate was calculated from a change in thickness obtained by measuring a weight change per minute during polishing. The surface roughness was measured with a surface roughness meter (manufactured by Kosaka Laboratory Ltd., under the trade name of Surfcoder SE 3500 K).

[0142] As for the evaluation of liquid waste, the liquid waste was filtered with a qualitative filter having a retained particle diameter of 1 μm to observe the state of the filtered liquid waste. The filtered liquid waste was put into a test tube having a diameter of 10 mm and evaluated as satisfactory when characters on newspaper could be read from the opposite side and unsatisfactory when they could not be read.

[0143] The evaluation results are shown in FIG. 3 and Table 2.

2TABLE 2Ex. 1Comp. Ex. 1Comp. Ex. 2polishing3338010possible timePolishing ratePolishing ratePolishing ratePolishing rateremains almostlowers eachgreatly lowersunchanged eventime polishingeach timeafter 333is carriedpolishing ishours ofout.carried out.continuousPolishingPolishingpolishing.becomesbecomesimpossibleimpossibleafter 80 hoursafter 10 hoursof continuousof continuouspolishing.polishing.State ofNo abrasiveAbrasiveAbrasiveabrasivegrains fallgrains fallgrains fallgrainsoff.off.off.Ex.: Example, Comp. Ex.: Comparative Example

[0144] As shown in FIG. 3 and Table 2, in the case of the polyurethane polishing pad containing silica abrasive grains of the present invention, even after 333 hours of continuous polishing, the polishing rate was constant. It could not be confirmed whether abrasive grains fell off at the time of polishing. Since the polishing time of one silicon wafer is generally 10 minutes, when continuous polishing is carried out for 333 hours, about 2,000 silicon wafers can be polished continuously.

[0145] The evaluation result of the liquid waste was satisfactory.

[0146] In the case of the polyurethane polishing pad containing alumina abrasive grains of Comparative Example 1, the polishing rate lowered with the passage of the polishing time, and polishing became impossible after 80 hours. The first silicon wafer could be polished normally but the polishing rate of the second silicon extremely lowered.

[0147] In the case of the conventional fixed abrasive grain polishing pad of Comparative Example 2, instantaneous with start of polishing, the polishing rate sharply dropped and polishing became impossible after 10 hours. The first silicon wafer could be polished normally but the polishing rate of the second silicon wafer was almost null.

[0148] When a fixed abrasive grain polishing pad produced by using colloidal silica as an abrasive particle material and urethane as a matrix resin was used in the above Example 1, it was confirmed that the polishing rate was maintained at a constant level even after 333 hours of continuous polishing. When it is taken into consideration that dressing is necessary after 10 minutes of polishing in the method using the conventional fixed abrasive grain polishing pad, it is understood that the continuous polishing time is sharply improved. Further, the thickness of the fixed abrasive grain polishing pad was not reduced and the abrasive grains did not fall off at all. Therefore, since only silicon as the material of the workpiece to be polished and the alkaline solution were discharged into the liquid waste after polishing, the disposal of the liquid waste could be carried out easily without exerting any bad influence upon the environment.

Example 2

[0149] A glycerin-based polyether polyol having a molecular weight of 600 (manufactured by Sanyo Kasei Co., Ltd., under the trade name of GP-600) as polyol A, glycerin-based polyether polyol having a molecular weight of 3,000 (manufactured by Sanyo Kasei Co., Ltd., under the trade name of GP-3000) as polyol B, and organic polyisocyanate (manufactured by Dow Polyurethane Systems Co., Ltd., under the trade name of PARI 135) were used, and catalyst (manufactured by Tosoh Corporation, under the trade name of TOYOCAT-ET), foam stabilizer (manufactured by Nippon Unicar Co., Ltd., under the trade name of L-5309) and the same colloidal silica as in Example 1 as an abrasive particle were used. These were mixed together in a ratio shown in Table 3 and cured at normal temperature by a casting method to obtain an abrasive. The expansion ratio, hardness and roughness of the obtained abrasive are shown in Table 3.

[0150] The workpiece (silicon wafer) to be polished was polished by the aid of an abrasive liquid having a pH of 9.5 to 13.5 under the following conditions. The results are shown in Table 3.

[0151] The polishing conditions were given below.

[0152] Polishing pressure: 300 g/cm2

[0153] Revolution of table: 40 rpm.

3TABLE 3Example No.Ex. 2Raw materialOrganic polyol A71.6composition ofOrganic polyol B8.4matrix resin (partsOrganic polyisocyanate52.5by weight)Water0.2Catalyst0.7Silicone foam stabilizer0.5Abrasive particlecolloidal silica90.1(parts by weight)Physical propertiesContent of abrasive grains30of polishing padExpansion ratio (times)2Hardness at 20° C. (Shore D)70Roughness (Ry) [nm]30polishingpH of abrasive liquidratePolishing rate9.50.01100.110.50.15110.211.50.3120.412.50.45130.4713.50.48

[0154] It is understood from Table 3 that the pH of the abrasive liquid is preferably 10 or higher. When an abrasive liquid having a pH lower than 10 is used, the polishing rate greatly lowers.

[0155] The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. It is obvious to those skilled in the art that changes and modifications will occur without departing from the scope of the technical idea set forth in the appended claims and it is to be understood as a matter of course that they are included in the technical scope of the present invention.

INDUSTRIAL FEASIBILITY

[0156] Since chemical bonding exists between the matrix resin and the abrasive grains in the abrasive of the present invention, bonding force between the matrix resin and the abrasive grains greatly improves and as a result, the abrasive grains rarely fall off from the matrix resin. This makes possible long-term continuous polishing without obtaining the spontaneous edging function of the abrasive. Even when polishing is continuously carried out for a long time, the abrasive grains are hardly wasted and contained in liquid waste (abrasive liquid). Therefore, the abrasive liquid can be easily recycled by simple filtration means without exerting a bad influence upon the environment.

Polishing material and method of polishing therewith

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