JP4128607B2 - Polishing pad - Google Patents

Description

  The present invention stabilizes flattening processing of 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 processing, In addition, the present invention relates to a polishing pad that can be performed with high polishing efficiency. The polishing pad of the present invention is particularly suitable for a step of planarizing a silicon wafer and a device having an oxide layer, a metal layer, etc. formed thereon, before further laminating and forming these oxide layers and metal layers. Used for.

  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 flatness and in-plane uniformity of the object to be polished can be improved to some extent by increasing the elastic modulus of the polishing layer. The polishing rate can be improved by using a foam containing bubbles and increasing the amount of slurry retained.

  As a polishing pad that satisfies the above characteristics, polishing pads made of polyurethane foam have been proposed (Patent Documents 1 and 2). The polyurethane foam is produced by reacting an isocyanate-terminated prepolymer with a chain extender (curing agent). As the polymer polyol component of the isocyanate prepolymer, hydrolysis resistance, elastic properties, abrasion resistance From the viewpoint of properties, polyether (polytetramethylene glycol having a number average molecular weight of 500 to 1600) and polycarbonate are used as suitable materials.

  However, in the polishing layer, the cohesive force of the hard segment is reduced during moisture absorption or water absorption, and the dimensional stability of the polishing layer is likely to be reduced. In a severe case, the polishing pad is warped or wavy, which causes a problem that the polishing characteristics such as flattening characteristics and in-plane uniformity gradually change.

  Patent Document 3 discloses a polishing pad polymer composition having a volume swelling rate of 20% or less when immersed in water at a temperature of 23 ° C. for 72 hours for the purpose of improving the retention of the slurry. Yes. However, the polishing pad polymer composition uses a thermoplastic polymer as the polishing pad polymer, and it is difficult to maintain high dimensional stability of the polishing pad during moisture absorption or water absorption.

JP 2000-17252 A Japanese Patent No. 3359629 JP 2001-47355 A

  An object of this invention is to provide the polishing pad which can maintain high dimensional stability at the time of moisture absorption or water absorption, and its manufacturing method. Moreover, it aims at providing the manufacturing method of the semiconductor device using this polishing pad.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by the polishing pad shown below, and have completed the present invention.

That is, the present invention provides a polishing pad having a polishing layer comprising a polyurethane foam having fine bubbles, wherein the polyurethane foam is
Diisocyanate, high molecular weight polyols, and low molecular weight polyol including prepolymer raw material composition and the reaction was obtained that isocyanate-terminated prepolymers obtained, isocyanate modified body obtained by a large amount by the three or more diisocyanate is added, and a chain extender It is related with the polishing pad characterized by being the reaction hardening body of the polyurethane raw material composition containing an agent.

  Since the conventional polishing layer is a polyurethane foam having a hard segment formed only by physical crosslinking, it is considered that the cohesive force of the hard segment easily decreases during moisture absorption or water absorption. Therefore, it is considered that the dimensional change increases due to elongation, warpage, etc., as the polishing layer absorbs moisture or absorbs water.

The present inventors, as a raw material of polyurethane foam, a diisocyanate, a high molecular weight polyol, and an isocyanate-terminated prepolymer of low molecular weight polyols that are obtained by reacting including prepolymer raw material composition, three or more diisocyanates By using together with the isocyanate-modified product that has been increased in quantity by addition, and partially introducing chemical crosslinks into the polymer by reaction with these and chain extenders (partially forming a three-dimensional cross-linked structure), It has been found that the cohesive force of the hard segment during moisture absorption or water absorption can be increased and the dimensional stability of the polishing layer can be maintained high. Moreover, regular chemical crosslinking can be introduced into the polymer by reacting the isocyanate-modified product directly with the chain extender without introducing it into the isocyanate-terminated prepolymer. Thereby, the dimensional change in the entire surface of the polishing layer can be made uniform, and variations in polishing characteristics can be suppressed.

The high molecular weight polyol is a polyether polyol having a number average molecular weight of 500 to 5000, and the diisocyanate is preferably toluene diisocyanate and dicyclohexylmethane diisocyanate. The isocyanate-modified product is preferably an isocyanurate type and / or burette type multimerized hexamethylene diisocyanate. By using these, a polyurethane foam can be produced with good handling properties, and the effects of the present invention are more excellent.

The addition amount of the isocyanate-modified product is preferably 5 to 40 parts by weight with respect to 100 parts by weight of the isocyanate-terminated prepolymer. When the amount of the isocyanate-modified product added is less than 5 parts by weight, the ratio of chemical cross-linking in the polymer becomes insufficient, so the cohesive strength of the hard segments at the time of moisture absorption or water absorption is insufficient, and the dimensional stability of the polishing layer Tends to be difficult to maintain high. On the other hand, when the amount exceeds 40 parts by weight, the ratio of chemical crosslinking in the polymer becomes excessive, and the hardness of the polishing layer becomes too high, so that the in-plane uniformity of the material to be polished tends to decrease. In addition, scratches are likely to occur on the surface of the material to be polished.

  The polyurethane foam preferably has an average cell diameter of 20 to 70 μm and a dimensional change rate of 0.8% or less upon water absorption. When the average cell diameter deviates from the above range, the polishing rate tends to decrease or the planarity (flatness) of the polished material after polishing tends to decrease. When the dimensional change rate at the time of water absorption exceeds 0.8%, the dimensional change tends to increase when the polishing layer absorbs moisture or absorbs water.

  The polyurethane foam preferably has an Asker D hardness of 45 to 65 degrees. When Asker D hardness is less than 45 degrees, the flatness of the material to be polished tends to decrease. On the other hand, when it is larger than 65 degrees, the flatness is good, but the in-plane uniformity of the material to be polished tends to be lowered. In addition, scratches are likely to occur on the surface of the material to be polished.

  The polyurethane foam preferably contains 0.05 to 10% by weight of a silicon-based nonionic surfactant. When the amount of the silicon-based nonionic surfactant is less than 0.05% by weight, a fine-bubble foam tends to be not obtained. On the other hand, when it exceeds 10% by weight, a polyurethane foam having a high hardness tends to be difficult to obtain due to the plasticizing effect of the surfactant.

The present invention also relates to a method for producing a polishing pad comprising the step (1) of mixing a first component containing an isocyanate-terminated prepolymer and a second component containing a chain extender to produce a polyurethane foam by curing.
In the step (1), an isocyanate-terminated prepolymer obtained by reacting a prepolymer raw material composition containing a diisocyanate, a high molecular weight polyol, and a low molecular weight polyol , and an isocyanate increased in number by adding three or more diisocyanates. A silicon-based nonionic surfactant is added to the first component including the modified body so as to be 0.05 to 10% by weight in the polyurethane foam, and the first component is stirred with a non-reactive gas and the non-reactive gas is added. It is a step of preparing a polyurethane foam by preparing a bubble dispersion in which reactive gas is dispersed as fine bubbles, and then mixing and curing a second component containing a chain extender in the bubble dispersion. And a method of manufacturing a polishing pad.

  Furthermore, the present invention relates to a semiconductor device manufacturing method including a step of polishing a surface of a semiconductor wafer using the polishing pad.

  The polishing pad of the present invention has a polishing layer made of a polyurethane foam having fine bubbles. The polishing pad of the present invention may be only the polishing layer or a laminate of the polishing layer and another layer (for example, a cushion layer).

  Polyurethane resin is a particularly preferable material for forming the polishing layer because it has excellent wear resistance and a polymer having desired physical properties can be easily obtained by variously changing the raw material composition.

The polyurethane resin, a diisocyanate, a high molecular weight polyol and low molecular weight polyol is that isocyanate-terminated prepolymer obtained by reacting including prepolymer raw material composition, a large amount of the isocyanate-modified by more than two diisocyanate added And a reaction cured product of a polyurethane raw material composition containing a chain extender.

As the diisocyanate , a known compound in the field of polyurethane can be used without particular limitation. For example, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene Aromatic diisocyanates such as diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 1,6-hexamethylene diisocyanate 1,4-cyclohexane diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, isophorone diisocyanate, norborna And alicyclic diisocyanates such as diisocyanates. These may be used alone or in combination of two or more. Of these, it is preferable to use toluene diisocyanate and dicyclohexylmethane diisocyanate in combination.

On the other hand, the isocyanate-modified product in the present invention is a compound or a mixture thereof which has been multiplied by adding three or more diisocyanates. Examples of the modified isocyanate include 1) trimethylolpropane adduct type, 2) burette type, and 3) isocyanurate type, with isocyanurate type and burette type being particularly preferable.

In the present invention, aliphatic diisocyanate is preferably used as the diisocyanate forming the isocyanate-modified product, and 1,6-hexamethylene diisocyanate is particularly preferably used. The isocyanate-modified product may be modified by urethane modification, allophanate modification, burette modification or the like.

  Examples of the high molecular weight polyol include polyether polyols typified by polytetramethylene ether glycol, polyester polyols typified by polybutylene adipate, polycaprolactone polyol, and a reaction product of a polyester glycol such as polycaprolactone and alkylene carbonate. Polyester polycarbonate polyol, polyester polycarbonate polyol obtained by reacting ethylene carbonate with polyhydric alcohol and then reacting the resulting reaction mixture with organic dicarboxylic acid, and polycarbonate polyol obtained by transesterification reaction between polyhydroxyl compound and aryl carbonate Etc. These may be used alone or in combination of two or more.

  The number average molecular weight of the high molecular weight polyol is not particularly limited, but is preferably 500 to 5000, more preferably 1000 to 2000, from the viewpoint of the elastic properties of the resulting polyurethane resin. When the number average molecular weight is less than 500, a polyurethane resin using the number average molecular weight does not have sufficient elastic properties and becomes a brittle polymer. Therefore, the polishing pad manufactured from this polyurethane resin becomes too hard and causes scratches on the wafer surface. Moreover, since it becomes easy to wear, it is not preferable from the viewpoint of the pad life. On the other hand, when the number average molecular weight exceeds 5,000, the polyurethane resin using the number average molecular weight becomes too soft, and the polishing pad produced from this polyurethane resin tends to have poor planarization characteristics.

  Examples of the low molecular weight polyol include 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-hydroxyethoxy) 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 triethanolamine, and the like. These may be used alone or in combination of two or more.

  Moreover, low molecular weight polyamines, such as ethylenediamine, tolylenediamine, diphenylmethanediamine, and diethylenetriamine, can also be used together as a raw material component of the isocyanate-terminated prepolymer. Also, alcohol amines such as monoethanolamine, 2- (2-aminoethylamino) ethanol, and monopropanolamine can be used in combination. These 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 characteristics required for the polishing pad (polishing layer) to be produced. It is preferable that it is 20-70 mol% of a group containing compound.

  When a polyurethane foam is produced by a prepolymer method, a chain extender is used for curing the 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, polytetramethylene oxide-di-p-aminobenzoate, 4,4′-diamino-3,3 ′, 5,5′-tetraethyldiphenylmethane, 4, 4'-diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane, 4,4'-diamino-3,3 ', 5,5'-tetra Sopropyldiphenylmethane, 1,2-bis (2-aminophenylthio) ethane, 4,4′-diamino-3,3′-diethyl-5,5′-dimethyldiphenylmethane, N, N′-di-sec-butyl -4,4'-diaminodiphenylmethane, 3,3'-diethyl-4,4'-diaminodiphenylmethane, m-xylylenediamine, N, N'-di-sec-butyl-p-phenylenediamine, m-phenylenediamine And polyamines exemplified by p-xylylenediamine and the like, or the above-mentioned low molecular weight polyols and low molecular weight polyamines. These may be used alone or in combination of two or more.

The ratio of the isocyanate-terminated prepolymer, isocyanate-modified product , and chain extender in the present invention can be variously changed depending on the molecular weight of each, the desired physical properties of the polishing pad, and the like. The addition amount of the isocyanate-modified product is preferably 5 to 40 parts by weight, more preferably 10 to 20 parts by weight with respect to 100 parts by weight of the isocyanate-terminated prepolymer. In order to obtain a polishing pad having desired polishing characteristics, the number of isocyanate groups in the isocyanate component relative to the number of active hydrogen groups (hydroxyl groups, amino groups) in the chain extender is preferably 0.80 to 1.20. More preferably, it is 0.99 to 1.15. 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 be deteriorated.

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

  As the isocyanate-terminated prepolymer, a polymer having a molecular weight of about 800 to 5000 is preferable because it has excellent processability and physical characteristics.

In the production of the polyurethane foam, a first component containing an isocyanate-terminated prepolymer and an isocyanate-modified product and a second component containing a chain extender are mixed and cured.

  Examples of the method for producing the polyurethane foam include a method of adding hollow beads, a mechanical foaming method, a chemical foaming method, and the like. Each method may be used in combination, but a mechanical foaming method using a silicon-based nonionic surfactant that is a copolymer of polyalkylsiloxane and polyether is particularly preferable. Examples of the silicon nonionic surfactant include SH-192, L-5340 (manufactured by Toray Dow Corning Silicon) and the like as suitable compounds.

  In addition, you may add stabilizers, such as antioxidant, a lubricant, a pigment, a filler, an antistatic agent, and another additive as needed.

An example of a method for producing a fine cell type polyurethane foam constituting the polishing pad (polishing layer) will be described below. The manufacturing method of this polyurethane foam has the following processes.
1) Foaming step for producing a cell dispersion liquid A silicone-based nonionic surfactant is added to the first component containing an isocyanate-terminated prepolymer and an isocyanate-modified product so as to be 0.05 to 10% by weight in the polyurethane foam. The mixture is stirred in the presence of a non-reactive gas to disperse the non-reactive gas as fine bubbles to obtain a bubble dispersion. When the prepolymer is solid at normal temperature, it is preheated to an appropriate temperature and melted before use.
2) Curing Agent (Chain Extender) Mixing Step A second component containing a chain extender is added to the above cell dispersion, mixed and stirred to obtain a foaming reaction solution.
3) Casting process The above foaming reaction liquid 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 the stirring device for dispersing the non-reactive gas in the form of fine bubbles and dispersing in the first component containing the silicon-based nonionic surfactant, a known stirring device can be used without particular limitation. Specifically, a homogenizer, a dissolver, A two-axis planetary mixer (planetary mixer) is exemplified. 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 addition, it is also a preferable aspect to use a different stirring apparatus for the stirring which produces a cell dispersion in a foaming process, and the stirring which adds and mixes the chain extender 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 the polyurethane foam, a known catalyst that promotes polyurethane reaction such as tertiary amine may be used. The type and addition 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.

  Polyurethane foam can be produced by weighing each component, putting it in a container and stirring it, or by continuously supplying each component and non-reactive gas to the stirrer and stirring to disperse the bubbles. It may be a continuous production method in which a liquid is fed to produce a molded product.

  Also, put the prepolymer that is the raw material of the polyurethane foam into the reaction vessel, and then add the chain extender, and after stirring, cast it into a casting mold of a predetermined size to make the block into a bowl shape or a band saw shape In the method of slicing using the above slicer, or in the casting step described above, a thin sheet may be formed. Alternatively, a raw material resin may be dissolved and extruded from a T-die to directly obtain a sheet-like polyurethane foam.

  The average cell diameter of the polyurethane foam is preferably 20 to 70 μm, more preferably 30 to 60 μm. Further, the polyurethane foam preferably has a dimensional change rate at the time of water absorption of 0.8% or less, more preferably 0.5% or less. In addition, the measuring method of a dimensional change rate is based on description of an Example.

  The polyurethane foam preferably has an Asker D hardness of 45 to 65 degrees, more preferably 55 to 65 degrees.

  The polishing surface that contacts the material to be polished of the polishing pad (polishing layer) of the present invention has a concavo-convex structure for holding and updating 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 1.5 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.

  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 the present invention 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 the present invention, it is preferable to use a cushion sheet that is softer than the polishing layer.

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

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

[Measurement and evaluation methods]
(Measurement of number average molecular weight)
The number average molecular weight was measured by GPC (gel permeation chromatography) and converted by standard polystyrene.
GPC device: manufactured by Shimadzu Corporation, LC-10A
Column: Polymer Laboratories, (PLgel, 5 μm, 500 mm), (PLgel, 5 μm, 100 mm), and (PLgel, 5 μm, 50 mm) connected to three columns, flow rate: 1.0 ml / min
Concentration: 1.0 g / l
Injection volume: 40 μl
Column temperature: 40 ° C
Eluent: Tetrahydrofuran

(Average bubble diameter measurement)
The produced polyurethane foam was cut as thin as possible to a thickness of 1 mm or less in parallel with a microtome cutter, and used as a sample for measuring the average cell diameter. The sample was fixed on a slide glass and observed at 100 times using SEM (S-3500N, Hitachi Science Systems, Ltd.). Using the image analysis software (WinRoof, Mitani Shoji Co., Ltd.) for the obtained image, the total bubble diameter in an arbitrary range was measured, and the average bubble diameter was calculated.

(Specific gravity measurement)
This was performed according to JIS Z8807-1976. The produced polyurethane foam was cut into a 4 cm x 8.5 cm strip (thickness: arbitrary) and used as a sample for measuring the specific gravity, and allowed to stand for 16 hours in an environment of a temperature of 23 ° C ± 2 ° C and a humidity of 50% ± 5%. did. The specific gravity was measured using a hydrometer (manufactured by Sartorius).

(Hardness measurement)
This was performed in accordance with JIS K6253-1997. A sample obtained by cutting the produced polyurethane foam into a size of 2 cm × 2 cm (thickness: arbitrary) was used as a sample for hardness measurement and 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).

(Measurement of dimensional change rate during water absorption)
This was performed according to JIS K7312. A sample obtained by cutting the produced polyurethane foam into a size of width 20 mm × length 50 mm × thickness 1.27 mm was used as a sample. The sample was immersed in distilled water at 25 ° C. for 48 hours, and the dimensional change rate was calculated by substituting the length before and after the immersion into the following formula.
Dimensional change rate (%) = [(length after immersion−length before immersion) / length before immersion] × 100

(Evaluation of polishing characteristics)
Using SPP600S (manufactured by Okamoto Machine Tool Co., Ltd.) as a polishing apparatus, polishing characteristics were evaluated using the prepared polishing pad. An interference type film thickness measuring device (manufactured by Otsuka Electronics Co., Ltd.) was used for measuring the thickness of the oxide film. As polishing conditions, silica slurry (SS12, manufactured by Cabot Corporation) was added as a slurry at a flow rate of 150 ml / min. The polishing load was 350 g / cm ² , the polishing platen rotation number was 35 rpm, and the wafer rotation number was 30 rpm.

  In the evaluation of the planarization characteristics, after depositing a thermal oxide film of 0.5 μm on an 8-inch silicon wafer and performing predetermined patterning, an oxide film of 1 μm is deposited by p-TEOS, and an initial step of 0.5 μm is formed. A wafer with a pattern was prepared, and this wafer was polished under the above conditions.

  The amount of scraping was measured as the flattening characteristic. In a pattern in which lines with a width of 270 μm are arranged in a space of 30 μm and a pattern in which lines with a width of 30 μm are arranged in a space of 270 μm, the cutting of the space of 270 μm when the level difference of the upper part of the above two types of patterns is 2000 mm or less The amount was measured. If the amount of shaving is small, the amount of shaving that is not desired to be shaved is small and the flatness is high. Table 1 shows the amount of wear on the 100th, 300th and 500th wafers.

In-plane uniformity is evaluated by polishing for 2 minutes under the above polishing conditions using a 1-μm thick thermal oxide film deposited on an 8-inch silicon wafer, and polishing at 25 specific positions on the wafer as shown in FIG. The maximum polishing rate and the minimum polishing rate were obtained from the measured film thickness before and after, and the values were calculated by substituting them into the following formula. Table 1 shows the in-plane uniformity of the 100th, 300th and 500th wafers. Note that the smaller the in-plane uniformity value, the higher the uniformity of the wafer surface.
In-plane uniformity (%) = {(maximum polishing rate−minimum polishing rate) / (maximum polishing rate + minimum polishing rate)} × 100

Example 1
In a container, 1229 parts by weight of toluene diisocyanate (mixture of 2,4-isomer / 2,6-isomer = 80/20), 272 parts by weight of 4,4′-dicyclohexylmethane diisocyanate, polytetramethylene ether glycol 1901 having a number average molecular weight of 1018 Part by weight and 198 parts by weight of diethylene glycol were added and reacted at 70 ° C. for 4 hours to obtain an isocyanate-terminated prepolymer.
100 parts by weight of the prepolymer, 20 parts by weight of multimerized 1,6-hexamethylene diisocyanate (manufactured by Sumika Bayer Urethane Co., Ltd., Sumidur N-3300, isocyanurate type), and silicon-based nonionic surfactant (Toray Dow Corning Silicon) Manufactured, SH-192) 3 parts by weight was added to the polymerization vessel, mixed, adjusted to 80 ° C. and degassed under reduced pressure. Then, it stirred vigorously for about 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. Thereto was added 39 parts by weight of 4,4′-methylenebis (o-chloroaniline) previously melted at 120 ° C. The mixed liquid was stirred for about 70 seconds, and then poured into a pan-shaped open mold (casting container). When the fluidity of the mixed solution disappeared, it was put in an oven and post-cured at 100 ° C. for 16 hours to obtain a polyurethane foam block. The polyurethane foam block heated to about 80 ° C. was sliced using a slicer (AGW Tech, VGW-125) to obtain a polyurethane foam sheet. Next, using a buffing machine (Amitech Co., Ltd.), the surface of the sheet was buffed to a thickness of 1.27 mm to obtain a sheet with an adjusted thickness accuracy. The buffed sheet is punched out with a diameter of 61 cm, and a concentric circle having a groove width of 0.25 mm, a groove pitch of 1.50 mm, and a groove depth of 0.40 mm on the surface using a groove processing machine (manufactured by Techno). Groove processing was performed to obtain a polishing sheet (polishing layer). A double-sided tape (manufactured by Sekisui Chemical Co., Ltd., double tack tape) was applied to the surface of the polishing sheet opposite to the grooved surface using a laminator. Furthermore, the surface of the cushion sheet (Toray Industries, Inc., polyethylene foam, Torepef, thickness 0.8 mm) subjected to corona treatment was buffed and bonded to the double-sided tape using a laminator. Further, a double-sided tape was attached to the other surface of the cushion sheet using a laminator to prepare a polishing pad.

Example 2
A polishing pad was prepared in the same manner as in Example 1 except that 20 parts by weight of a large amount of 1,6-hexamethylene diisocyanate (manufactured by Sumika Bayer Urethane Co., Ltd., Sumidur N-3200, burette type) was used as the isocyanate-modified product. Produced.

Example 3
A polishing pad was produced in the same manner as in Example 1 except that the amount of Sumidur N-3300 added in Example 1 was changed from 20 parts by weight to 10 parts by weight.

Comparative Example 1
In Example 1, a polishing pad was produced in the same manner as in Example 1 except that Sumidur N-3300 was not added.

  As is apparent from the results in Table 1, it can be seen that the polishing pad of the present invention has high dimensional stability during moisture absorption or water absorption, and suppresses variations in planarization characteristics and in-plane uniformity characteristics.

Schematic configuration diagram showing an example of a polishing apparatus used in CMP polishing Schematic showing 25 film thickness measurement positions on wafer

Explanation of symbols

1: Polishing pad (polishing layer)
2: Polishing surface plate 3: Abrasive (slurry)
4: Material to be polished (semiconductor wafer)
5: Support base (polishing head)
6, 7: Rotating shaft

Claims (9)

In a polishing pad having a polishing layer made of a polyurethane foam having fine bubbles, the polyurethane foam is:
Diisocyanate, high molecular weight polyols, and low molecular weight polyol including prepolymer raw material composition and the reaction was obtained that isocyanate-terminated prepolymers obtained, isocyanate modified body obtained by a large amount by the three or more diisocyanate is added, and a chain extender A polishing pad, which is a reaction cured product of a polyurethane raw material composition containing an agent. The polishing pad according to claim 1, wherein the high molecular weight polyol is a polyether polyol having a number average molecular weight of 500 to 5,000, and the diisocyanate is toluene diisocyanate and dicyclohexylmethane diisocyanate. Isocyanate-modified body, isocyanurate type and / or polishing pad of claim 1 or 2, wherein the f hexamethylene diisocyanate modified product of biuret type. The polishing pad according to any one of claims 1 to 3, wherein the amount of the isocyanate-modified product added is 5 to 40 parts by weight with respect to 100 parts by weight of the isocyanate-terminated prepolymer. The polishing pad according to any one of claims 1 to 4, wherein the polyurethane foam has an average cell diameter of 20 to 70 µm and a dimensional change rate at the time of water absorption of 0.8% or less. The polishing pad according to any one of claims 1 to 5, wherein the polyurethane foam has an Asker D hardness of 45 to 65 degrees. The polishing pad according to any one of claims 1 to 6, wherein the polyurethane foam contains 0.05 to 10% by weight of a silicon-based nonionic surfactant. In the method for producing a polishing pad comprising the step (1) of mixing a first component comprising an isocyanate-terminated prepolymer and a second component comprising a chain extender and curing to produce a polyurethane foam,
In the step (1), an isocyanate-terminated prepolymer obtained by reacting a prepolymer raw material composition containing a diisocyanate, a high molecular weight polyol, and a low molecular weight polyol , and an isocyanate increased in number by adding three or more diisocyanates. A silicon-based nonionic surfactant is added to the first component including the modified body so as to be 0.05 to 10% by weight in the polyurethane foam, and the first component is stirred with a non-reactive gas and the non-reactive gas is added. It is a step of preparing a polyurethane foam by preparing a bubble dispersion in which reactive gas is dispersed as fine bubbles, and then mixing and curing a second component containing a chain extender in the bubble dispersion. A method for producing a polishing pad. 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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