JP5087440B2 - Polishing pad, polishing pad manufacturing method, and semiconductor device manufacturing method - 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 method of increasing the amount of slurry retained, there is a method of imparting hydrophilicity to the polishing pad itself and increasing the water absorption rate of the polishing pad. In the following Patent Document 1, a polishing pad having a polishing layer made of a polyurethane resin foam using a hydrophobic isocyanate-terminated prepolymer, a hydrophilic isocyanate-terminated prepolymer, and a chain extender as raw material components is described. According to this configuration, because the hydrophilic property is imparted to the polishing pad itself due to the hydrophilic isocyanate-terminated prepolymer, the slurry holding amount of the polishing pad can be increased. However, if the polishing pad has a polishing layer made of a polyurethane resin foam using a raw material component having more hydrophilic groups in order to further increase the slurry holding amount, the polishing pad swells upon water absorption and polishes over time. In some cases, the characteristics changed.

In the following Patent Document 2, a polishing pad made of a polyurethane resin containing a polyurethane resin copolymerized with a compound having a hydrophilic group and containing a hydrophilic agent is described. However, if a large amount of a hydrophilic agent is used to increase the hydrophilicity of such a polishing pad, the polishing pad may swell during water absorption, and the polishing characteristics may change over time. In addition, with such a polishing pad, it is difficult to suppress swelling during water absorption due to the polymer structure of the polyurethane resin. Patent Document 3 below describes a polishing pad containing a copolymer having at least one hydrophilic repeating unit and at least one hydrophobic repeating unit and having a surface energy of 34 mN / m or less. However, in such a polishing pad, there is a limit to the amount of hydrophilic repeating units that can be introduced into the polishing pad in order to achieve low surface energy. As a result, there is a limit to increasing the water absorption rate of the polishing pad. In addition, with such a polishing pad, it is difficult to suppress swelling during water absorption due to the polymer structure of the polyurethane resin. Therefore, in the conventional polishing pad, there is a limit in increasing the amount of retained slurry by increasing the water absorption rate while suppressing swelling during water absorption.
JP 2005-68175 A Patent No. 3851135 Special table 2007-531275 gazette

  The present invention improves the polishing rate by increasing the water absorption rate while exhibiting stable polishing characteristics by ensuring good dimensional stability at the time of water absorption, and defects in the material to be polished after polishing. An object of the present invention is to provide a polishing pad with reduced generation and a method of manufacturing the polishing pad. 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 described below, and have completed the present invention.

That is, the polishing pad according to the present invention is a polishing pad having a polishing layer made of a polyurethane foam having fine bubbles, wherein the polyurethane foam contains a diisocyanate, a high molecular weight polyol a, and a low molecular weight polyol. A reaction cured product of a polyurethane raw material composition containing an isocyanate-terminated prepolymer A obtained by reacting a product, an isocyanate modified product obtained by adding three or more diisocyanates, and a chain extender, wherein the diisocyanate comprises An aromatic diisocyanate and an alicyclic diisocyanate, and the high molecular weight polyol a is a polyethylene glycol having a number average molecular weight of 600 to 2000, or a polyethylene glycol having a number average molecular weight of 600 to 2000 and a number average molecular weight of 60. Polytetramethylene glycol which is ˜2000, the average hydroxyl value of all polyol components which are raw material components of the isocyanate-terminated prepolymer A is 500 to 590 (mg KOH / g), and ethylene oxide in all the polyol components The content of the unit (—CH ₂ —CH ₂ —O—) is 70 to 100% by weight.

  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 added an isocyanate-terminated prepolymer A and three or more diisocyanates obtained by reacting a prepolymer raw material composition containing diisocyanate, high molecular weight polyol a, and low molecular weight polyol as a raw material for polyurethane foam. By using together with the isocyanate modification product that has been increased in quantity, and by regularly introducing chemical crosslinks into the polymer by reaction with these chain extenders (regularly forming a three-dimensional crosslink structure), moisture absorption Alternatively, it has been found that the cohesive force of the hard segment during water absorption can be increased and the dimensional stability of the polishing layer can be maintained high. In this polyurethane foam, all of the three-dimensional crosslinked structures in the polymer are formed by urea bonds by using together the isocyanate-terminated prepolymer A and a large amount of the isocyanate-modified product and reacting them with a chain extender. Is done. Compared to the case where the three-dimensional crosslinked structure in the polymer is formed by urethane bonds, the polyurethane foam in which the three-dimensional crosslinked structure in the polymer is all formed by urethane bonds, the polishing characteristics of the polishing pad, In-plane uniformity can be improved.

  Further, the diisocyanate is an aromatic diisocyanate and an alicyclic diisocyanate, the high molecular weight polyol a is a polyethylene glycol having a number average molecular weight of 600 to 2000, or a polyethylene glycol having a number average molecular weight of 600 to 2000 and a number average molecular weight. By using polytetramethylene glycol having a water content of 600 to 2000, a highly water-absorbing polyurethane foam can be obtained. As a result, the retention of the slurry can be improved and the polishing rate can be improved.

  Here, as the aromatic diisocyanate, toluene diisocyanate is particularly preferable. The alicyclic diisocyanate is particularly preferably dicyclohexylmethane diisocyanate or isophorone diisocyanate. As the high molecular weight polyol a, two or more types of polyethylene glycol may be used in combination. When the high molecular weight polyol a is composed of only polyethylene glycol, the water absorption of the polishing pad is further improved. Can do.

Furthermore, the average hydroxyl value of all the polyol components which are the raw material components of the isocyanate-terminated prepolymer A is 500 to 590 (mg KOH / g), and the ethylene oxide unit (—CH ₂ —CH ₂ —O—) in all the polyol components. ) Is 70 to 100% by weight, a highly water-absorbing polyurethane foam can be obtained while ensuring good physical properties such as strength of the polyurethane foam. When the average hydroxyl value of all the polyol components, which are the raw material components of the isocyanate-terminated prepolymer A, is less than 500 (mgKOH / g), the physical properties of the polyurethane resin foam tend to decrease. Since the reactivity with the agent becomes too high, the moldability tends to deteriorate. Moreover, when the content rate of an ethylene oxide unit is less than 70 weight%, since the water absorption of a polishing pad is not enough, it exists in the tendency for a polishing rate to fall. In order to further improve the water absorption of the polishing pad, the content of ethylene oxide units is more preferably 75% by weight or more, and further preferably 80% by weight or more.

  In the above, it is preferable that the isocyanate-modified product that has been multiplied is at least one of isocyanurate-type multimeric hexamethylene diisocyanate and burette-type multimeric hexamethylene diisocyanate. By using these isocyanate modified products, a polyurethane foam can be produced with good handling properties, and the effects of the present invention will be more excellent.

  In the above, it is preferable that the amount of the above-described isocyanate modified product is 5 to 30 parts by weight with respect to 100 parts by weight of the isocyanate-terminated prepolymer A. When the added amount of the isocyanate modification product in a large amount is less than 5 parts by weight, the ratio of chemical crosslinking in the polymer becomes insufficient, so that the cohesive force of the hard segment at the time of moisture absorption or water absorption is insufficient, It tends to be difficult to maintain high dimensional stability. Moreover, it tends to be difficult to obtain a highly water-absorbing polyurethane foam. On the other hand, when it exceeds 30 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, defects tend to occur on the surface of the material to be polished.

  In the above, the polyurethane foam preferably has an average cell diameter of 20 to 70 μm, a water absorption rate of 6.0% or more, and a dimensional change rate at the time of water absorption of 0.8% or less. 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. On the other hand, if the water absorption is less than 6.0%, the polishing pad will not have sufficient water absorption and the polishing rate will decrease, and there will be many defects in the polished material after polishing. In order to further improve the polishing rate of the polishing pad and reduce the occurrence of defects in the polished material after polishing, the water absorption of the polyurethane foam is preferably 8.0% or more, more preferably 10.0% or more preferable. Furthermore, when the dimensional change rate during water absorption exceeds 0.8%, the dimensional change tends to increase when the polishing layer absorbs moisture or absorbs water.

  In the above, the Asker D hardness of the polyurethane foam is preferably 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, defects tend to occur on the surface of the material to be polished.

  In the above, it is preferable that the polyurethane foam 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.

Another method for producing a polishing pad according to the present invention comprises: a first component containing an isocyanate modified prepolymerized by addition of an isocyanate-terminated prepolymer and three or more diisocyanates; and a second component containing a chain extender. In the method for producing a polishing pad comprising the step (1) of mixing and curing to produce a polyurethane foam, the step (1) comprises the first component containing the isocyanate-terminated prepolymer and the isocyanate modified product that has been multimerized. In addition, a silicon-based nonionic surfactant is added to the polyurethane foam so as to be 0.05 to 10% by weight, and the first component is stirred with a non-reactive gas to form the non-reactive gas as fine bubbles. After preparing a dispersed cell dispersion, a second component containing a chain extender is mixed with the cell dispersion and cured to produce a polyurethane foam. The isocyanate-terminated prepolymer is an isocyanate-terminated prepolymer obtained by reacting a prepolymer raw material composition containing diisocyanate, high molecular weight polyol a, and low molecular weight polyol, wherein the diisocyanate is aromatic. A diisocyanate and an alicyclic diisocyanate, and the high molecular weight polyol a is a polyethylene glycol having a number average molecular weight of 600 to 2000, or a polyethylene glycol having a number average molecular weight of 600 to 2000 and a number average molecular weight of 600 to 2000. It is an isocyanate-terminated prepolymer A that is polytetramethylene glycol, and the average hydroxyl value of all polyol components that are raw material components of the isocyanate-terminated prepolymer A is 500 to 590 (mg KOH / g). Ri, and the content of ethylene oxide units in the total polyol component _{(-CH 2} -CH ₂ -O-) is characterized in that 70 to 100 wt%.

  Another semiconductor device manufacturing method according to the present invention includes a step of polishing a surface of a semiconductor wafer using the polishing pad described above.

  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.

  Such a polyurethane resin is an isocyanate-modified prepolymer A obtained by reacting a prepolymer raw material composition containing a diisocyanate, a high molecular weight polyol a, and a low molecular weight polyol, and having been increased in quantity by adding three or more diisocyanates. Body, as well as chain extenders.

  As diisocyanate, aromatic diisocyanate and alicyclic diisocyanate are used in combination. Examples of the aromatic diisocyanate include 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 diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate and the like can be mentioned. These may be used alone or in combination of two or more. Among these, toluene diisocyanate is particularly preferable. Examples of the alicyclic diisocyanate include 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and norbornane diisocyanate. These may be used alone or in combination of two or more. Among these, dicyclohexylmethane diisocyanate or isophorone diisocyanate is particularly preferable. In addition, a diisocyanate known in the field of polyurethane may be used in combination as long as the effects of the present invention are not impaired. Examples of such diisocyanates include aliphatic diisocyanates such as ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 1,6-hexamethylene diisocyanate.

  On the other hand, examples of the isocyanate modified product that has been multiplied by adding three or more diisocyanates in the present invention include 1) trimethylolpropane adduct type, 2) burette type, and 3) isocyanurate type. In particular, the isocyanurate type and the burette type are preferable. These isocyanate-modified products may be used alone or in combination of two or more.

  In the present invention, aliphatic diisocyanate is preferably used as diisocyanate forming an isocyanate-modified product which has been increased by adding three or more diisocyanates, and 1,6-hexamethylene diisocyanate is particularly preferably used. Further, the above-mentioned increased amount of the isocyanate-modified product may be modified by urethane modification, allophanate modification, burette modification or the like.

  The number average molecular weight of the high molecular weight polyol a is 600 to 2000, preferably 600 to 1000 from the viewpoint of the viscoelastic properties of the resulting polyurethane resin. When the number average molecular weight is less than 600, a polyurethane resin using the number average molecular weight does not have sufficient elastic properties and becomes a brittle polymer. For this reason, a polishing pad manufactured from this polyurethane resin becomes too hard, causing defects 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 2000, a polyurethane resin using the number average molecular weight becomes too soft, and a polishing pad produced from this polyurethane resin tends to have poor planarization characteristics.

  The low molecular weight polyol is an essential raw material for the isocyanate-terminated prepolymer A. 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, as a raw material of the isocyanate terminal prepolymer A, low molecular weight polyamines 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 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, but all active hydrogen which is a raw material of the isocyanate-terminated prepolymer A It is preferable that it is 10-25 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 low molecular weight polyols and low molecular weight polyamines mentioned above. These may be used alone or in combination of two or more.

  In the present invention, the ratio of the isocyanate-terminated prepolymer A, the isocyanate-modified product increased by adding three or more diisocyanates, and the chain extender can be variously changed depending on the respective molecular weights, desired physical properties of the polishing pad, and the like. It is preferable that the addition amount of the multimeric isocyanate modified product is 5 to 30 parts by weight, and more preferably 10 to 25 parts by weight with respect to 100 parts by weight of the isocyanate-terminated prepolymer A. In addition, in order to obtain a polishing pad having desired polishing characteristics, the equivalent ratio of the number of isocyanate groups of the prepolymer and the amount of the isocyanate modified product to the number of active hydrogen groups of the chain extender (NCOindex in the urethane raw material composition) is: 0.8 to 1.2, more preferably 0.99 to 1.15. When the NCOindex in the urethane raw material composition is out of the above range, curing failure occurs and the required specific gravity and hardness cannot be obtained, and the polishing characteristics tend to deteriorate.

  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, those having a molecular weight of about 800 to 5000 are preferable because of excellent processability and physical characteristics.

  The polyurethane foam is produced by mixing and curing the first component containing the isocyanate-terminated prepolymer A and the amount of the isocyanate modified product and the second component containing the chain extender.

  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 process for producing a cell dispersion liquid A silicon-based nonionic surfactant is added to a polyurethane foam as a first component containing an isocyanate-modified product that has been multimerized by adding an isocyanate-terminated prepolymer A and three or more diisocyanates. It adds so that it may become 0.05 to 10 weight%, it stirs in presence of non-reactive gas, a non-reactive gas is disperse | distributed as a fine bubble, and it is set as a bubble dispersion liquid. 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.

  It is preferable that the average cell diameter of the polyurethane foam in this invention is 20-70 micrometers, More preferably, it is 30-60 micrometers. Moreover, it is preferable that a water absorption is 6.0% or more, More preferably, it is 8.0% or more, More preferably, it is 10.0% or more. Moreover, it is preferable that the dimensional change rate at the time of water absorption is 0.8% or less, More preferably, it is 0.6% or less. In addition, the measuring method of a dimensional change rate is based on description of an Example.

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

  The polishing surface of the polishing pad (polishing layer) of the present invention that comes into contact with the material to be polished 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 1.5 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.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this 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 hydroxyl value)
The average hydroxyl value (mgKOH / g) is calculated from the hydroxyl value of each polyol used and the molar ratio of each hydroxyl value to the polyol used.
Hydroxyl value (mgKOH / g) = (f × [KOH] × 1000) / Mw
f: number of hydroxyl groups [KOH]: molecular weight of KOH Mw: molecular weight of polyol (number average molecular weight)
For example, the calculation method of the average hydroxyl value at the time of using 3 types of polyol (a, b, c) is shown.
[Average hydroxyl value (mgKOH / g)] = (Va × Ma + Vb × Mb + Vc × Mc) / (Ma + Mb + Mc)
Va: hydroxyl value of polyol a Vb: hydroxyl value of polyol b Vc: hydroxyl value of polyol c Ma: molar ratio of polyol a Mb: molar ratio of polyol b Mc: molar ratio of polyol c

(Measurement of average bubble diameter)
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.

(Measurement of specific gravity)
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).

(Measurement of hardness)
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

(Measurement of 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 water absorption was calculated by substituting the weight before and after immersion into the following formula.
Water absorption (%) = [(weight after immersion−weight before immersion) / weight before immersion] × 100

(Cut rate)
Measuring device: MAT-BC15 manufactured by MAT Co., Ltd.
Measurement condition:
(Evaluation sample): φ380 mm, thickness 1.25 mmt, a double-sided tape laminated on the back, and bonded to the platen of a polishing machine.
(Dress conditions): Dresser: Mitsubishi Materials Subbot type, forced drive rotation speed 115 rpm, platen rotation speed 70 rpm, dress load 7 lb (7 pounds), water absorption 200 ml / min, dressing time 1.5 hours
1) After the dressing is completed, the pad is cut into a strip having a width of 10 mm and a length of 380 mm, and the double-sided tape on the back surface is peeled off.
2) The thickness of the polishing layer after dressing is measured with a micrometer at intervals of 20 mm from the center of the pad, and the difference from the undressed center portion is obtained, and the amount of wear at each position is obtained (9 points on one side, total 18 Point measurement).
3) The average value of the wear amount of 18 samples was obtained, and the wear amount per minute was calculated by dividing by the measurement time (the following formula). The results are shown in Table 2.
(Cut rate (μm / min)) = (average value of wear amount of 18 samples) / (1.5 × 60)

(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. The polishing rate was calculated from the time obtained by polishing 0.5 μm of a 1-μm thermal oxide film formed on an 8-inch silicon wafer. Table 4 shows the polishing rates for the 100th, 300th and 500th wafers. 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 4 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 4 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

(Evaluation of number of defects)
After completion of the polishing property evaluation test, the wafer was washed, and the total number of defects (number of defects) at EE 5 mm was measured with Surfscan SP1 TBI manufactured by KLA Tencor. Table 4 shows the number of defects in the 100th, 300th, and 500th wafers.

Example 1
In a container, 1238 parts by weight of toluene diisocyanate (mixture of 2,4-isomer / 2,6-isomer = 80/20), 279 parts by weight of isophorone diisocyanate, 1414 parts by weight of polyethylene glycol having a number average molecular weight of 1000, polyethylene having a number average molecular weight of 600 457 parts by weight of glycol and 213 parts by weight of diethylene glycol were added and reacted at 80 ° C. for 3 hours to obtain an isocyanate-terminated prepolymer A (1).
100 parts by weight of the above prepolymer A (1), a multimerized 1,6-hexamethylene diisocyanate (Sumidule N-manufactured by Sumika Bayer Urethane Co., Ltd.), which is an isocyanate modified product multimerized by adding three or more diisocyanates. 3300, isocyanurate type) 10 parts by weight, and silicon nonionic surfactant (manufactured by Toray Dow Corning Silicon, L5340) 3.3 parts by weight are added to the polymerization vessel and mixed, adjusted to 70 ° C. and degassed under reduced pressure. did. 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, 34.7 parts by weight (NCOindex: 1.1) of 4,4′-methylenebis (o-chloroaniline) previously melted at 120 ° C. was added. 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 blending of isocyanate-terminated prepolymer A (1), the average hydroxyl value of all polyol components that are the raw material components of isocyanate-terminated prepolymer A (1), the content of ethylene oxide units in all polyol components, NCO%, and NCOindex Is shown in Table 1. Table 2 shows the composition of the polyurethane raw material composition.

  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.

Examples 2-4, Comparative Examples 1-3
Isocyanate-terminated prepolymers A (2) to (4) (Examples 2 to 4) or isocyanate-terminated prepolymers A (5) to (7) (Comparative Examples 1 to 3) prepared by blending shown in Table 1. A polishing pad was prepared in the same manner as in Example 1 except that it was used and mixed with an isocyanate modified product that was multiplied by adding 3 or more diisocyanates in the formulation shown in Table 2. Table 1 shows the average hydroxyl value of all polyol components, which are the raw material components of isocyanate-terminated prepolymers A (2) to (7), the content of ethylene oxide units in all polyol components, NCO%, and NCOindex. Table 2 shows the composition of the polyurethane raw material composition and the type of the isocyanate modification used. The evaluation results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 3 and Table 4.

  From the results of Tables 3 and 4, it can be seen that the polishing pads of Examples 1 to 4 have a low dimensional change rate upon water absorption and excellent dimensional stability, and thus exhibit stable polishing characteristics. Moreover, since the polishing pad of Examples 1-4 shows a high water absorption rate, it turns out that the polishing rate is improved and the occurrence of defects in the polished material after polishing is reduced.

  On the other hand, the polishing pad of Comparative Example 1 deteriorates the dimensional change rate at the time of water absorption, and the polishing characteristics are not stable. Further, it can be seen that since the water absorption is low, the polishing rate is low, and many defects occur in the polished material after polishing. In addition, the polishing pad of Comparative Example 2 has a significantly deteriorated dimensional change rate upon water absorption, and the polishing characteristics are not stable. Furthermore, it can be seen that the polishing pad of Comparative Example 3 has a low water absorption rate and thus has a low polishing rate, and many defects occur in the polished material after polishing.

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 (8)

In a polishing pad having a polishing layer made of a polyurethane foam having fine bubbles, the polyurethane foam is:
Isocyanate-terminated prepolymer A obtained by reacting a prepolymer raw material composition containing diisocyanate, high-molecular-weight polyol a, and low-molecular-weight polyol, isocyanate-modified product multimerized by addition of three or more diisocyanates, and chain extension It is a reaction cured body of a polyurethane raw material composition containing an agent,
The diisocyanate is an aromatic diisocyanate and an alicyclic diisocyanate,
The high molecular weight polyol a is polyethylene glycol having a number average molecular weight of 600 to 2000, or polyethylene glycol having a number average molecular weight of 600 to 2000 and polytetramethylene glycol having a number average molecular weight of 600 to 2000.
The average hydroxyl value of all polyol components which are raw material components of the isocyanate-terminated prepolymer A is 500 to 590 (mg KOH / g), and the ethylene oxide units (—CH ₂ —CH ₂ —O—) in the all polyol components are used. ) Is 70 to 100% by weight.   2. The polishing pad according to claim 1, wherein the amount of the isocyanate-modified product which has been increased is at least one of an isocyanurate-type increased amount of hexamethylene diisocyanate and a burette-type increased amount of hexamethylene diisocyanate.   3. The polishing pad according to claim 1, wherein an amount of the isocyanate modified product added in a large amount is 5 to 30 parts by weight with respect to 100 parts by weight of the isocyanate-terminated prepolymer A. 4.   The average cell diameter of the polyurethane foam is 20 to 70 µm, the water absorption is 6.0% or more, and the dimensional change rate at the time of water absorption is 0.8% or less. Polishing pad.   The polishing pad according to any one of claims 1 to 4, 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 5, wherein the polyurethane foam contains 0.05 to 10% by weight of a silicon-based nonionic surfactant. A step of mixing a first component containing an isocyanate-modified product and a second component containing a chain extender, which are obtained by adding an isocyanate-terminated prepolymer and three or more diisocyanates, and curing the mixture to produce a polyurethane foam. In the manufacturing method of the polishing pad containing (1),
In the step (1), a silicon-based nonionic surfactant is added to the first component containing the isocyanate-terminated prepolymer and the amount of the isocyanate-modified product so as to be 0.05 to 10% by weight in the polyurethane foam. Further, after the first component is stirred with a non-reactive gas to prepare a bubble dispersion in which the non-reactive gas is dispersed as fine bubbles, a second component containing a chain extender is added to the bubble dispersion. Mixing and curing to produce a polyurethane foam,
The isocyanate-terminated prepolymer is
An isocyanate-terminated prepolymer obtained by reacting a prepolymer raw material composition containing a diisocyanate, a high molecular weight polyol a, and a low molecular weight polyol, wherein the diisocyanate is an aromatic diisocyanate and an alicyclic diisocyanate, and the high molecular weight In the isocyanate-terminated prepolymer A, the polyol a is a polyethylene glycol having a number average molecular weight of 600 to 2000, or a polyethylene glycol having a number average molecular weight of 600 to 2000 and a polytetramethylene glycol having a number average molecular weight of 600 to 2000. Yes,
The average hydroxyl value of all polyol components which are raw material components of the isocyanate-terminated prepolymer A is 500 to 590 (mg KOH / g), and the ethylene oxide units (—CH ₂ —CH ₂ —O—) in the all polyol components are used. ) Content of 70 to 100% by weight.   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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