JP2017132013A - Polishing pad - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad capable of suppressing occurrence of scratch, as well as improving a polishing speed.SOLUTION: A polishing pad comprises a polishing layer made of a polyurethane foam containing as raw materials: diphenylmethane diisocyanate-based isocyanate-terminated prepolymer including as raw materials, a diphenylmethane diisocyanate-based compound including at least one type selected from a group of diphenylmethane diisocyanate and modified diphenylmethane diisocyanate, and a surfactant having a hydroxyl group; a toluene diisocyanate-based isocyanate-terminated prepolymer including as raw materials, a toluene diisocyanate and a high-molecular weight polyol; and an active hydrogen-containing compound.SELECTED DRAWING: Figure 1

Description

  The present invention is a polishing for flattening optical materials such as lenses and reflecting mirrors, silicon wafers, glass substrates for hard disks, aluminum substrates, and materials that require high surface flatness such as general metal polishing. Related to pads.

  A typical material that requires high surface flatness is a single crystal silicon disk called a silicon wafer for manufacturing a semiconductor integrated circuit (IC, LSI). Silicon wafers have a highly accurate surface in each process of stacking and forming oxide layers and metal layers in order to form reliable semiconductor junctions of various thin films used for circuit formation in IC, LSI, and other manufacturing processes. It is required to finish flat. In such a polishing finishing process, a polishing pad is generally fixed to a rotatable support disk called a platen, and a workpiece such as a semiconductor wafer is fixed to a polishing head. A polishing operation is performed by generating a relative speed between the platen and the polishing head by both movements, and continuously supplying a polishing slurry containing abrasive grains onto the polishing pad.

  The polishing characteristics of the polishing pad are required to be excellent in the flatness (planarity) and in-plane uniformity of the object to be polished and to have a high polishing rate.

  The polishing rate can be improved by making the polishing layer a foam containing bubbles and increasing the amount of slurry retained (the polishing rate can be increased by making the polishing layer a foam containing bubbles and increasing the amount of slurry retained). For example, the following Patent Document 1).

Japanese Patent No. 3490431 JP 2013-144353 A JP 2006-320981 A

  The polishing rate of the conventional polishing pad is not sufficient. Therefore, it is conceivable to increase the elastic modulus of the polishing layer in order to further improve the polishing rate (for example, Patent Document 2). However, when the elastic modulus of the polishing layer is increased, the polishing rate can be improved, but there is a problem that scratches (scratches) are likely to occur on the surface to be polished of the object to be polished. On the other hand, when the polishing layer is simply made to have a low elastic modulus like the polishing pad described in Patent Document 3, the polishing rate is lowered.

  That is, with the conventional polishing pad, it is difficult to improve the polishing rate while suppressing the generation of scratches.

  An object of this invention is to provide the polishing pad which can improve a grinding | polishing speed, suppressing generation | occurrence | production of a scratch.

  The polishing pad of the present invention is a diphenylmethane diisocyanate-based isocyanate-terminated prepolymer containing, as raw material components, a diphenylmethane diisocyanate-based compound that is at least one selected from the group consisting of diphenylmethane diisocyanate and modified diphenylmethane diisocyanate, and a surfactant having a hydroxyl group, It has a polishing layer made of a polyurethane foam containing a toluene diisocyanate-based isocyanate-terminated prepolymer containing toluene diisocyanate and a high molecular weight polyol as raw material components, and an active hydrogen-containing compound as a raw material component.

  According to the polishing pad of the present invention, the polishing rate can be improved while suppressing the generation of scratches. The reason why the polishing pad of the present invention exhibits such an effect is not clear, but is considered as follows.

  A diphenylmethane diisocyanate-based isocyanate-terminated prepolymer of at least one diphenylmethane diisocyanate-based compound selected from the group consisting of diphenylmethane diisocyanate and modified diphenylmethane diisocyanate and a surfactant having a hydroxyl group, and a toluene diisocyanate-based isocyanate containing toluene diisocyanate as a raw material In a polyurethane foam containing a terminal prepolymer as a raw material, the entire matrix is formed by containing a large amount of diphenylmethane diisocyanate as a constituent unit around bubbles formed by a surfactant that is a constituent unit of a diphenylmethane diisocyanate-based isocyanate terminal prepolymer. Contains a large amount of toluene diisocyanate as a structural unit. The entire matrix containing many toluene diisocyanate-based isocyanate-terminated prepolymers as a structural unit is low in hardness, so that it is difficult to scratch the surface of the material to be polished.However, the polyurethane containing many diphenylmethane diisocyanate-based isocyanate compounds as a structural unit is Since the hardness is higher than that of polyurethane containing a large amount of a toluene diisocyanate-based isocyanate-terminated prepolymer as a structural unit, the periphery of the bubbles has a rigid structure, and the dressing by the dresser is improved, so that the polishing rate is excellent. Therefore, according to the polishing pad of the present invention, it is considered that the polishing rate can be improved while suppressing the generation of scratches.

Schematic configuration diagram showing an example of a polishing apparatus used in CMP polishing

<Polishing pad>
The polishing pad of this embodiment is a diphenylmethane diisocyanate-based isocyanate-terminated prepolymer containing, as raw material components, at least one diphenylmethane diisocyanate-based compound selected from the group consisting of diphenylmethane diisocyanate and modified diphenylmethane diisocyanate and a surfactant having a hydroxyl group. And a polishing layer made of a polyurethane foam containing a toluene diisocyanate-based isocyanate-terminated prepolymer containing toluene diisocyanate and high molecular weight polyol as raw material components, and an active hydrogen-containing compound as a raw material component.

[Diphenylmethane diisocyanate-based isocyanate-terminated prepolymer]
The polyurethane foam includes diphenylmethane diisocyanate containing, as raw material components, at least one diphenylmethane diisocyanate compound selected from the group consisting of diphenylmethane diisocyanate and modified diphenylmethane diisocyanate and a surfactant having a hydroxyl group from the viewpoint of improving the polishing rate. A diisocyanate-terminated prepolymer is included as a raw material component (hereinafter, diphenylmethane diisocyanate is also referred to as MDI, and MDI and modified MDI are also referred to as MDI compounds. In addition, diphenylmethane diisocyanate-based isocyanate-terminated prepolymer is also referred to as MDI-based prepolymer) . Since the MDI prepolymer contains a surfactant having a hydroxyl group as a raw material component, it acts as a surfactant.

[MDI compounds]
The MDI compound is at least one selected from the group consisting of MDI and modified MDI. The MDI compounds include 2,2′-MDI, 2,4′-MDI, 4,4′-MDI, polymeric MDI, uretonimine modified MDI, urethane modified MDI, isocyanurate modified MDI, acylurea diisocyanate, and carbodiimide. Examples thereof include at least one selected from the group consisting of modified MDI (for example, trade name Millionate MTL, manufactured by Nippon Polyurethane Industry). Among these, 4,4′-MDI is preferable from the viewpoint of suppressing generation of scratches and improving the polishing rate, and carbodiimide-modified 4,4′-MDI is more preferable.

[Surfactant having a hydroxyl group]
The surfactant having a hydroxyl group is preferably a silicone surfactant having a hydroxyl group from the viewpoint of producing a polyurethane foam having uniform cells. Examples of the silicone surfactant having a hydroxyl group include SZ1718 (manufactured by Toray Dow Corning), L5420 (manufactured by Toray Dow Corning), SRX295 (manufactured by Toray Dow Corning), Tegostarb B8465 (manufactured by Evonik Japan), and the like. .

  The hydroxyl value of the surfactant having a hydroxyl group is preferably 30 to 300 mgKOH / g, more preferably 80 to 200 mgKOH / g, from the viewpoint of improving the polishing rate.

  The MDI prepolymer can be obtained by reacting the MDI compound with the surfactant having a hydroxyl group. In the MDI-based prepolymer, it is preferable to react only the MDI-based compound and the surfactant having a hydroxyl group, but a known compound can be reacted within a range that does not impair the effects of the present embodiment. . However, the amount of the MDI compound contained as a structural unit in the MDI prepolymer is preferably 60 to 90 mol% in the structural unit of the MDI prepolymer from the viewpoint of improving the polishing rate. In addition, the amount of the surfactant having a hydroxyl group contained as a structural unit in the MDI prepolymer is a structural unit of the MDI prepolymer from the viewpoint of efficiently forming bubbles when producing a polyurethane foam. 10-40 mol% is preferable.

  The NDI weight% of the MDI prepolymer is preferably 2 to 23% by weight, and more preferably 4 to 10% by weight. If the NCO weight% of the MDI-based prepolymer is too high, there will be no effect on scratches. If it is too low, the polishing rate will be low and the flatness will be poor.

In the MDI prepolymer, the equivalent ratio (NCO / H ^* ) of isocyanate group (NCO) to active hydrogen (H ^* ) in the raw material is usually 1.2 to 8, preferably 1.5 to 3. It can be produced by heating reaction.

[Toluene diisocyanate-based isocyanate-terminated prepolymer]
The polyurethane foam contains, as a raw material component, a toluene diisocyanate-based isocyanate-terminated prepolymer containing toluene diisocyanate and a high molecular weight polyol as raw material components from the viewpoint of suppressing the occurrence of scratches (hereinafter, toluene diisocyanate is also referred to as TDI, and toluene diisocyanate). Systemic isocyanate-terminated prepolymers are also referred to as TDI based prepolymers).

[TDI]
The TDI is at least one selected from the group consisting of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate.

  The TDI prepolymer may contain an isocyanate component other than TDI as a raw material component as long as the effects of the present embodiment are not impaired. As isocyanate components other than the TDI, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, aromatic diisocyanates such as p-xylylene diisocyanate and m-xylylene diisocyanate, aliphatic diisocyanates such as ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate and 1,6-hexamethylene diisocyanate, 1,4- Such as cyclohexane diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, etc. Cyclic diisocyanates, Desmodur -N (Bayer) and Duranate ™ (Asahi Kasei Kogyo) a polyfunctional polyisocyanate compound of three or more functional groups is a diisocyanate adduct compounds such like. However, from the viewpoint of expression of the effect of the present embodiment, the content of the TDI is preferably 50 mol% or more and more preferably 70 mol% or more in the isocyanate component contained as a raw material component in the TDI prepolymer. preferable.

[High molecular weight polyol]
As said high molecular weight polyol, what is normally used in the technical field of a polyurethane can be used. Examples include polyether polyols typified by polytetramethylene ether glycol, polyethylene glycol, etc., polyester polyols typified by polybutylene adipate, polycaprolactone polyols, reactants of polyester glycols such as polycaprolactone and alkylene carbonate, etc. Polyester polycarbonate polyol, Polyester polyol obtained by reacting ethylene carbonate with polyhydric alcohol and then reacting the resulting reaction mixture with organic dicarboxylic acid, Polycarbonate polyol obtained by transesterification of polyhydroxyl compound and aryl carbonate Etc. These may be used alone or in combination of two or more.

  The number average molecular weight of these high molecular weight polyols is not particularly limited, but is preferably about 500 to 5000 from the viewpoint of the elastic properties of the resulting polyurethane resin. When the number average molecular weight is less than 500, the polyurethane resin obtained by using the polyurethane resin does not have sufficient elastic properties and tends to be a brittle polymer, the polishing pad made of this polyurethane resin becomes too hard, May cause scratches. Moreover, since it becomes easy to wear, it is not preferable from the viewpoint of the life of the polishing pad. On the other hand, when the number average molecular weight exceeds 5000, a polishing pad made of a polyurethane resin obtained using the number average molecular weight becomes soft, and it is difficult to obtain a sufficiently satisfactory planarity, which is not preferable.

  In addition to the high molecular weight polyol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2, 3-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, 1,4-bis (2-hydroxy Ethoxy) benzene, trimethylolpropane, glycerin, 1,2,6-hexanetriol, pentaerythritol, tetramethylolcyclohexane, methylglucoside, sorbitol, mannitol, dulcitol, sucrose, 2,2,6,6-tetrakis (hydroxymethyl) ) Cyclohexanol, diethanolamine, N- methyldiethanolamine, and can be used in combination a low molecular weight polyol component such as triethanolamine. Moreover, low molecular weight polyamine components such as ethylenediamine, tolylenediamine, diphenylmethanediamine, and diethylenetriamine can be used in combination. Also, alcohol amines such as monoethanolamine, 2- (2-aminoethylamino) ethanol, and monopropanolamine can be used in combination. These low molecular weight polyols and low molecular weight polyamines may be used alone or in combination of two or more. The blending amount of the low molecular weight polyol, the low molecular weight polyamine or the like is not particularly limited, and is appropriately determined depending on the properties required for the polishing pad (polishing layer) to be produced, and is 20 to 70 mol% of the total polyol component. Is preferred.

  The TDI prepolymer can be obtained by reacting the TDI and the high molecular weight polyol. In the TDI prepolymer, it is preferable to react only the TDI and the high molecular weight polyol, but a known compound can be reacted within a range that does not impair the effect of the present embodiment. However, the amount of TDI contained as a structural unit in the TDI prepolymer is preferably 30 to 65 mol% and more preferably 45 to 60 mol% in the structural unit of the TDI prepolymer from the viewpoint of suppressing scratches. . In addition, the amount of the high molecular weight polyol contained as a structural unit in the TDI prepolymer is preferably 35 to 70 mol%, and preferably 40 to 55 mol% in the structural unit of the TDI prepolymer, from the viewpoint of suppressing scratches. Is more preferable.

  The NDI wt% of the TDI prepolymer is preferably 4.5 to 8.5 wt%, more preferably 6.5 to 8.2 wt% from the viewpoint of suppressing the occurrence of scratches and improving the polishing rate.

In the TDI prepolymer, the equivalent ratio (NCO / H ^* ) of isocyanate group (NCO) to active hydrogen (H ^* ) in the raw material is usually 1.2 to 8, preferably 1.5 to 3. It can be produced by heating reaction.

[Active hydrogen-containing compounds]
Examples of the active hydrogen-containing compound include those usually used in the technical field of polyurethane, such as a high molecular weight polyol, a low molecular weight polyol, a low molecular weight polyamine, an alcohol amine, and a chain extender. However, the surfactant having a hydroxyl group is not included in the active hydrogen-containing compound.

  Examples of the high molecular weight polyol which is the active hydrogen-containing compound include the same high molecular weight polyols used as a raw material for the TDI prepolymer.

  Examples of the low molecular weight polyol that is the active hydrogen-containing compound include those similar to the low molecular weight polyol used as a raw material for the TDI prepolymer.

  Examples of the low molecular weight polyamine that is the active hydrogen-containing compound include the same as the low molecular weight polyamine used as a raw material for the TDI prepolymer.

  Examples of the alcohol amine that is the active hydrogen-containing compound include the same alcohol amine used as a raw material of the TDI prepolymer.

  The chain extender is an organic compound having at least two active hydrogen groups, and examples of the active hydrogen group include a hydroxyl group, a primary or secondary amino group, and a thiol group (SH). Specifically, 4,4′-methylenebis (o-chloroaniline) (MOCA), 2,6-dichloro-p-phenylenediamine, 4,4′-methylenebis (2,3-dichloroaniline), 3,5 -Bis (methylthio) -2,4-toluenediamine, 3,5-bis (methylthio) -2,6-toluenediamine, 3,5-diethyltoluene-2,4-diamine, 3,5-diethyltoluene-2 , 6-diamine, trimethylene glycol-di-p-aminobenzoate, 1,2-bis (2-aminophenylthio) ethane, 4,4′-diamino-3,3′-diethyl-5,5′-dimethyl Diphenylmethane, N, N′-di-sec-butyl-4,4′-diaminodiphenylmethane, 3,3′-diethyl-4,4′-diaminodiphenylmethane, m-xyl Polyamines exemplified by diamine, N, N′-di-sec-butyl-p-phenylenediamine, m-phenylenediamine, and p-xylylenediamine, or the low molecular weight polyols and low molecular weight polyamines described above. Can be mentioned. These may be used alone or in combination of two or more.

  The ratio of the MDI-based prepolymer, the TDI-based prepolymer, and the active hydrogen-containing compound can be variously changed according to the respective molecular weights, desired physical properties of the polishing pad, and the like. The amount of the MDI-based isocyanate-terminated prepolymer added is preferably 1 to 10 parts by weight and more preferably 3 to 7 parts by weight with respect to 100 parts by weight of the TDI prepolymer. If the amount of the MDI-based isocyanate-terminated prepolymer is small, polishing performance cannot be obtained, and if it is large, the rigidity of the urethane foam increases and scratches are likely to occur. In order to obtain a polishing pad having desired polishing characteristics, the isocyanate group number (NCO Index) of the isocyanate compound relative to the number of active hydrogen groups (hydroxyl group, amino group) of the active hydrogen-containing compound is 0.9 to 1. Is preferably 10.10, more preferably 0.9 to 1.0. When the number of isocyanate groups is outside the above range, curing failure occurs and the required specific gravity and hardness cannot be obtained, and the polishing characteristics tend to deteriorate.

[Production of polyurethane foam]
The polyurethane foam can be produced by applying a known urethanization technique such as a melting method or a solution method, but is preferably produced by a melting method in consideration of cost, working environment and the like.

  The polyurethane resin is produced by a prepolymer method. The polyurethane resin obtained by the prepolymer method is suitable because of its excellent physical properties.

  As the TDI prepolymer, those having a number average molecular weight of about 300 to 5,000 are preferable because they have excellent processability and physical characteristics.

  The polyurethane resin is produced by reaction-curing a polyurethane composition containing the MDI prepolymer, the TDI prepolymer, and the active hydrogen-containing compound.

  As long as the effect of the polishing pad is not impaired, a stabilizer such as an antioxidant, a lubricant, a pigment, a filler, an antistatic agent, and other additives may be contained. Moreover, you may mix | blend suitably the surfactant of the state which is not made to react other than the MDI type isocyanate which acts as surfactant. The surfactant may or may not have a hydroxyl group.

  The production of the polyurethane foam may be a batch system in which each component is weighed and put into a container and stirred, or each component is continuously fed to a stirrer and stirred, and a mixed solution is sent out to form a molded product. May be a continuous production method.

  Also, the MDI prepolymer and the TDI prepolymer are placed in a reaction vessel, and then an active hydrogen-containing compound is added, stirred, and then poured into a casting mold of a predetermined size to produce a polyurethane resin block. The polishing layer may be produced by slicing using a slicer, or may be produced by processing into a thin sheet at the above-described casting stage.

  Examples of the method for producing the polyurethane foam include a method of adding hollow beads, a mechanical foaming method (including a mechanical floss method), and a chemical foaming method. In addition, although each method may be used together, the mechanical foaming method is preferable.

[Production example of polyurethane foam by mechanical foaming method]
An example of a method for producing the polyurethane foam by a mechanical foaming method will be described below. The manufacturing method of this polyurethane foam has the following processes.
1) Foaming step for producing a bubble dispersion liquid The first component containing the MDI prepolymer and the TDI prepolymer is stirred in the presence of a nonreactive gas to disperse the nonreactive gas as fine bubbles. Use bubble dispersion. When the prepolymer is solid at normal temperature, it is preheated to an appropriate temperature and melted before use.
2) Active hydrogen-containing compound mixing step A second component containing an active hydrogen-containing compound is added to the bubble dispersion and mixed and stirred to obtain a foaming reaction liquid.
3) Casting step The foaming reaction solution is poured into a mold.
4) Curing process The foaming reaction liquid poured into the mold is heated and reacted and cured.

  As the non-reactive gas used to form the fine bubbles, non-flammable gases are preferable, and specific examples include nitrogen, oxygen, carbon dioxide, rare gases such as helium and argon, and mixed gases thereof. In view of cost, it is most preferable to use air that has been dried to remove moisture.

  As a stirrer for dispersing non-reactive gas in the form of fine bubbles and dispersing in the first component, a known stirrer can be used without any particular limitation. Specifically, a homogenizer, a dissolver, a two-axis planetary mixer (planetator) Lee mixer) and the like. The shape of the stirring blade of the stirring device is not particularly limited, but it is preferable to use a whipper type stirring blade because fine bubbles can be obtained. In order to obtain the target polyurethane foam, the rotational speed of the stirring blade is preferably 500 to 2000 rpm, more preferably 800 to 1500 rpm. The stirring time is appropriately adjusted according to the target density.

  In addition, it is also a preferable aspect to use a different stirring apparatus for the stirring which produces a bubble dispersion liquid in a foaming process, and the stirring which adds and mixes an active hydrogen containing compound in a mixing process. In particular, the stirring in the mixing step may not be stirring that forms bubbles, and it is preferable to use a stirring device that does not involve large bubbles. As such an agitator, a planetary mixer is suitable. There is no problem even if the same stirring device is used as the stirring device for the foaming step and the mixing step, and it is also preferable to adjust the stirring conditions such as adjusting the rotation speed of the stirring blade as necessary. .

  In the production method of polyurethane foam, heating and post-curing the foam that has reacted until the foaming reaction liquid is poured into the mold and no longer flows is effective in improving the physical properties of the foam and is extremely suitable. It is. The foam reaction solution may be poured into the mold and immediately put into a heating oven for post cure, and heat is not immediately transferred to the reaction components under such conditions, so the bubble size does not increase. . The curing reaction is preferably performed at normal pressure because the bubble shape is stable.

  In addition, you may use the catalyst which accelerates | stimulates well-known polyurethane reactions, such as a tertiary amine type | system | group. The type and amount of the catalyst are selected in consideration of the flow time for pouring into a mold having a predetermined shape after the mixing step.

  It is preferable that the average cell diameter of a polyurethane foam is 20-70 micrometers, More preferably, it is 30-60 micrometers.

  The Asker D hardness of the polyurethane foam is preferably 30 to 48 degrees, and more preferably 35 to 45 degrees. When the Asker D hardness is less than 30 degrees, the polishing rate tends to decrease or the surface smoothness of the polished material after polishing tends to deteriorate. On the other hand, when it is larger than 48 degrees, scratches are likely to occur on the surface of the material to be polished.

  The specific gravity of the polyurethane foam is preferably 0.7 to 0.85, more preferably 0.73 to 0.80. When the specific gravity is less than 0.7, the durability of the polishing layer tends to decrease. On the other hand, when it is larger than 0.85, the abrasive retention of bubbles is deteriorated and the polishing rate tends to decrease.

  The polishing surface of the polishing pad (polishing layer) of the present embodiment that comes into contact with the material to be polished preferably has a concavo-convex structure for holding and renewing the slurry. The polishing layer made of foam has many openings on the polishing surface and has the function of holding and updating the slurry. By forming a concavo-convex structure on the polishing surface, the slurry can be held and updated more efficiently. It can be performed well, and destruction of the material to be polished due to adsorption with the material to be polished can be prevented. The concavo-convex structure is not particularly limited as long as it is a shape that holds and renews the slurry. For example, an XY lattice groove, a concentric circular groove, a through hole, a non-penetrating hole, a polygonal column, a cylinder, a spiral groove, Examples include eccentric circular grooves, radial grooves, and combinations of these grooves. In addition, these uneven structures are generally regular, but in order to make the slurry retention and renewability desirable, the groove pitch, groove width, groove depth, etc. should be changed for each range. Is also possible.

  The method for producing the concavo-convex structure is not particularly limited. For example, a method of machine cutting using a jig such as a tool of a predetermined size, pouring a resin into a mold having a predetermined surface shape, and curing. Using a press plate having a predetermined surface shape, a method of producing a resin by pressing, a method of producing using photolithography, a method of producing using a printing technique, a carbon dioxide laser, etc. Examples include a manufacturing method using laser light.

  The thickness of the polishing layer is not particularly limited, but is usually about 0.8 to 4 mm, and preferably 1.2 to 2.5 mm. As a method for producing the polishing layer having the above thickness, a method in which the block of the fine foam is made to have a predetermined thickness using a band saw type or canna type slicer, a resin is poured into a mold having a cavity having a predetermined thickness, and curing is performed. And a method using a coating technique or a sheet forming technique.

  Further, the thickness variation of the polishing layer is preferably 100 μm or less. When the thickness variation exceeds 100 μm, the polishing layer has a large waviness, and there are portions where the contact state with the material to be polished is different, which adversely affects the polishing characteristics. In order to eliminate the thickness variation of the polishing layer, in general, the surface of the polishing layer is dressed with a dresser in which diamond abrasive grains are electrodeposited and fused in the initial stage of polishing. As a result, the dressing time becomes longer and the production efficiency is lowered.

  Examples of a method for suppressing the variation in the thickness of the polishing layer include a method of buffing the surface of the polishing sheet sliced to a predetermined thickness. Moreover, when buffing, it is preferable to carry out stepwise with abrasives having different particle sizes.

  The polishing pad of this embodiment may be a laminate of the polishing layer and a cushion sheet.

  The cushion sheet (cushion layer) supplements the characteristics of the polishing layer. The cushion sheet is necessary for achieving both planarity and uniformity in a trade-off relationship in CMP. Planarity refers to the flatness of a pattern portion when a material having fine irregularities generated during pattern formation is polished, and uniformity refers to the uniformity of the entire material to be polished. The planarity is improved by the characteristics of the polishing layer, and the uniformity is improved by the characteristics of the cushion sheet. In the polishing pad of this embodiment, it is preferable to use a cushion sheet that is softer than the polishing layer.

  Examples of the cushion sheet include fiber nonwoven fabrics such as polyester nonwoven fabric, nylon nonwoven fabric, and acrylic nonwoven fabric, resin-impregnated nonwoven fabrics such as polyester nonwoven fabric impregnated with polyurethane, polymer resin foams such as polyurethane foam and polyethylene foam, butadiene rubber, and isoprene. Examples thereof include rubber resins such as rubber and photosensitive resins.

  Examples of means for attaching the polishing layer and the cushion sheet include a method of pressing the polishing layer and the cushion sheet with a double-sided tape.

  The double-sided tape has a general configuration in which adhesive layers are provided on both sides of a substrate such as a nonwoven fabric or a film. In consideration of preventing the penetration of the slurry into the cushion sheet, it is preferable to use a film for the substrate. Examples of the composition of the adhesive layer include rubber adhesives and acrylic adhesives. Considering the content of metal ions, an acrylic adhesive is preferable because the metal ion content is low. In addition, since the composition of the polishing layer and the cushion sheet may be different, the composition of each adhesive layer of the double-sided tape can be made different so that the adhesive force of each layer can be optimized.

  The polishing pad of this embodiment may be provided with a double-sided tape on the surface to be bonded to the platen. As the double-sided tape, a tape having a general configuration in which an adhesive layer is provided on both surfaces of a base material can be used as described above. As a base material, a nonwoven fabric, a film, etc. are mentioned, for example. In consideration of peeling from the platen after use of the polishing pad, it is preferable to use a film for the substrate. Examples of the composition of the adhesive layer include rubber adhesives and acrylic adhesives. Considering the content of metal ions, an acrylic adhesive is preferable because the metal ion content is low.

  The semiconductor device is manufactured through a step of polishing the surface of the semiconductor wafer using the polishing pad. A semiconductor wafer is generally a laminate of a wiring metal and an oxide film on a silicon wafer. The method and apparatus for polishing the semiconductor wafer are not particularly limited. For example, as shown in FIG. 1, a polishing surface plate 2 that supports a polishing pad (polishing layer) 1 and a support table (polishing head) that supports the semiconductor wafer 4. 5 and a polishing apparatus equipped with a backing material for uniformly pressing the wafer and a supply mechanism of the abrasive 3. The polishing pad 1 is attached to the polishing surface plate 2 by attaching it with a double-sided tape, for example. The polishing surface plate 2 and the support base 5 are disposed so that the polishing pad 1 and the semiconductor wafer 4 supported on each of the polishing surface plate 2 and the support table 5 face each other, and are provided with rotating shafts 6 and 7 respectively. Further, a pressurizing mechanism for pressing the semiconductor wafer 4 against the polishing pad 1 is provided on the support base 5 side. In polishing, the semiconductor wafer 4 is pressed against the polishing pad 1 while rotating the polishing surface plate 2 and the support base 5, and polishing is performed while supplying slurry. The flow rate of the slurry, the polishing load, the polishing platen rotation speed, and the wafer rotation speed are not particularly limited and are appropriately adjusted.

  As a result, the protruding portion of the surface of the semiconductor wafer 4 is removed and polished flat. Thereafter, a semiconductor device is manufactured by dicing, bonding, packaging, or the like. The semiconductor device is used for an arithmetic processing device, a memory, and the like.

<Measurement and evaluation method>
[Measurement of specific gravity]
This was performed according to JIS Z8807-1976. The produced polyurethane foam sheet was cut into a 4 cm x 8.5 cm strip (thickness: arbitrary) and used as a specific gravity measurement sample. I put it. The specific gravity was measured using a hydrometer (manufactured by Sartorius).

[D hardness measurement]
This was performed in accordance with JIS K6253-1997. The produced polyurethane foam sheet was cut into a size of 2 cm × 2 cm (thickness: arbitrary) and used as a sample for hardness measurement, and was allowed to stand for 16 hours in an environment of temperature 23 ° C. ± 2 ° C. and humidity 50% ± 5%. . At the time of measurement, the samples were overlapped to a thickness of 6 mm or more. The hardness was measured using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., Asker D type hardness meter).

[Polishing rate and scratch]
[Polishing conditions]
The polishing pad was attached to a polishing apparatus (manufactured by MAT, model number: ARW-8C1A), and the oxide film wafer was polished. The polishing conditions are as follows.
Polishing pressure: 4.5 psi
Retainer pressure: 5.0 psi
Polishing head rotation speed: 90 rpm
Platen rotation speed: 93rpm
Slurry: SS25 (manufactured by Cabot) was diluted twice with ultrapure water, the slurry flow rate was 120 ml / min, and the polishing time was 1 min.
Dressing condition: The dresser used was DK45 manufactured by Saesol, and was polished while applying an in-situ dressing process at a load of 4.8 lbf and a rotation speed of 63 rpm.
As a polishing operation, after attaching the polishing pad to the apparatus surface plate, the pad surface was dressed for 30 minutes under the above-mentioned dresser conditions while flowing ultrapure water. Then, after eight dummy wafers were flowed, one polishing rate monitor wafer and one scratch monitor wafer were polished.

[Evaluation of polishing rate]
The polishing rate was calculated from the polishing amount at this time by polishing a wafer obtained by forming a 10,000-mm tungsten film on an 8-inch silicon wafer for 60 seconds. An optical interference film thickness measuring device (manufactured by Nanometrics, device name: Nanospec) was used for measuring the thickness of the oxide film.

[Scratch evaluation]
The scratch was evaluated by measuring the number of streaks of 0.19 μm or more on the polished wafer using a defect evaluation apparatus (Surfscan SP1) manufactured by KLA Tencor.

<Prepolymer preparation>
[Preparation of MDI Prepolymer]
Put 35.7 parts by weight of MDI isocyanate (Tosoh product name: Millionate MTL) and 64.3 parts by weight of silicone surfactant (Evonik Japan product name: Degostarb B8465 OHV: 110 mg KOH / g) in a container and continue at 70 ° C for 6 hours. Reaction was performed to obtain an MDI-based prepolymer. The NCO weight percent was 5.4%.

[Preparation of TDI prepolymer]
In a container, toluene diisocyanate (Mitsui Chemicals product name: Cosmonate T80) 27.2 parts by weight, isophorone diisocyanate (Evonik Japan product name: VEST ANAT IPDI) 6.1 parts by weight, polytetramethylene ether glycol having an average molecular weight of 1000 (Mitsubishi Chemical product name: (PTMG1000) 64.4 parts by weight and 1,4 butanediol (manufactured by Nacalai Tesque) 2.3 parts by weight were added and reacted at 70 ° C. for 4 hours to obtain a TDI prepolymer. The NCO weight% was 7.9%.

<Example 1>
5 parts by weight of an MDI prepolymer was blended in a polymerization vessel with 100 parts by weight of a TDI prepolymer heated to 60 ° C. Then, it stirred violently for 4 minutes so that a bubble might be taken in in a reaction system with the rotation speed of 900 rpm using the stirring blade. Thereafter, 24.6 parts by weight of MOCA (Ihara Chemical Co., Ltd., Cuamine MT) whose temperature was adjusted to 120 ° C. was added and stirred for 1 minute. Then, it was poured into an open mold (casting container). When the fluidity of this mixed solution disappeared, it was put in an oven and post-cured at 100 ° C. for 16 hours to obtain a polyurethane resin foam block.

  The polyurethane resin foam block heated to about 80 ° C. was sliced using a slicer (manufactured by Amitech, VGW-125) to obtain a polyurethane resin foam sheet. Next, using a buffing machine (manufactured by Amitech Co., Ltd.), it is sequentially cut with # 120, # 240 and # 400 sand peppers, and the surface of the sheet is buffed until the thickness becomes 2 mm. And it was set as the sheet | seat which prepared the thickness precision. The buffed sheet is punched out with a diameter of 508 mm, and a concentric circle having a groove width of 0.40 mm, a groove pitch of 3.1 mm, and a groove depth of 0.8 mm on the surface using a groove processing machine (manufactured by Techno). Groove processing was performed to produce a polishing layer. A double tack tape (Sekisui Chemical Co., Ltd. product name: 5882W) was attached to the surface of the polishing layer opposite to the grooved surface using a laminator. Further, the surface of the cushion layer (Toray Industries, polyethylene foam, Torepefu, thickness 1.27 mm) subjected to corona treatment was buffed and bonded to the double tack tape using a laminator. Further, a surface plate tape (442M made by 3M) was bonded to the other side of the cushion layer using a laminator to prepare a polishing pad. The polishing layer had a density of 0.77 and a D hardness of 43 (60 sec value).

<Example 2>
In Example 1, a polishing pad was prepared in the same manner as in Example 1, except that 100 parts by weight of TDI prepolymer was mixed with 2 parts by weight of MDI prepolymer and 24.3 parts by weight of MOCA was mixed. The polishing layer had a density of 0.79 and a D hardness of 44 (60 sec value).

<Example 3>
In Example 1, a polishing pad was produced in the same manner as in Example 1 except that 100 parts by weight of TDI prepolymer was mixed with 9 parts by weight of MDI prepolymer and 25.3 parts by weight of MOCA was mixed. The polishing layer had a density of 0.77 and a D hardness of 44 (60 sec value).

<Example 4>
Example 1 Example 1 except that 5 parts by weight of MDI-based prepolymer was added to 100 parts by weight of TDI-based prepolymer, and 3 parts by weight of surfactant B8465 (Evonik Japan product name: Degostarb B8465) was added. A polishing pad was prepared in the same manner as described above. The density of the polishing layer was 0.78, and the D hardness was 42 (60 sec value).

<Comparative Example 1>
In Example 1, a polishing pad was prepared in the same manner as in Example 1 except that 3 parts by weight of surfactant B8465 was added and 23.8 parts by weight of MOCA was mixed without adding an MDI-based prepolymer. did. The density of the polishing layer was 0.68, and the D hardness was 28.

  The evaluation results of Examples 1 to 4 and Comparative Example 1 are shown in Table 1 below.

In Examples 1 to 4 in which the MDI prepolymerized surfactant was blended, the polishing rate was high and the number of defects was small compared to Comparative Example 1 in which the surfactant was not blended.

Claims (6)

  A diphenylmethane diisocyanate-based isocyanate-terminated prepolymer, a toluene diisocyanate and a high-molecular-weight polyol, each containing at least one diphenylmethane diisocyanate compound selected from the group consisting of diphenylmethane diisocyanate and modified diphenylmethane diisocyanate and a surfactant having a hydroxyl group as raw material components; A polishing pad having a polishing layer made of a polyurethane foam containing a toluene diisocyanate-based isocyanate-terminated prepolymer as a raw material component and an active hydrogen-containing compound as a raw material component.   The polishing pad according to claim 1, wherein the NCO wt% of the diphenylmethane diisocyanate-based isocyanate-terminated prepolymer is 2 to 23 wt%.   The polishing pad according to claim 1 or 2, wherein the content of the diphenylmethane diisocyanate-based isocyanate-terminated prepolymer is 1 to 10 parts by weight with respect to 100 parts by weight of the toluene diisocyanate-based isocyanate-terminated prepolymer.   The polishing pad according to any one of claims 1 to 3, wherein the toluene diisocyanate-based isocyanate-terminated prepolymer has an NCO wt% of 4.5 to 8.5 wt%.   The polishing pad according to claim 1, wherein the active hydrogen-containing compound is 4,4′-methylenebis (o-chloroaniline). A method for manufacturing a semiconductor device, comprising a step of polishing a surface of a semiconductor wafer using the polishing pad according to claim 1.

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