Polyolefin resin foam, foam for CMP polishing, and form tape for CMP polishing

Abstract

To provide a polyolefin resin foam, a foam for CMP polishing, and a form tape for CMP polishing, which are able to suppress fluctuations caused by vibration during CMP polishing while realizing conformity to wafer surface irregularities, ensure load uniformity within the wafer surface during CMP polishing, and improve wafer flatness.SOLUTION: A polyolefin resin foam has a 25% compression strength of 1,350 kPa or more, a foaming ratio of 15 times or less, and a thickness of 2.0 mm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyolefin resin foam, a foam for CMP polishing, and a foam tape for CMP polishing. [Background technology]

[0002] In the manufacturing process of semiconductor devices, the surface of a wafer, which includes an insulating film, a conductive film, or the like, is polished and planarized using the chemical mechanical polishing (CMP) method. The CMP apparatus used in the CMP method has a polishing pad with a single or multi-layer structure of two or more layers attached to a surface plate. When the polishing pad has a multi-layer structure, a sub-pad that functions as a cushion layer is attached below the top pad, which the wafer surface is pressed against. A polishing head that holds the wafer is installed above the surface plate with the polishing pad. When polishing a wafer, a slurry containing dispersed ceramics is dropped onto the polishing pad, and the polishing pad moistened with the slurry is pressed against the wafer while the surface plate and polishing head are rotated to polish the film on the wafer.

[0003] To form cutting-edge fine wiring, it is necessary to further improve the flatness of wafers. However, when non-foaming or foaming rubber, or urethane foam, etc., is used as a sub-pad (see, for example, Patent Document 1), the compression load during polishing fluctuates across the wafer surface due to the influence of vibrations caused by the rotational motion during polishing, resulting in variations in the polishing rate across the wafer surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-22886 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, in order to solve the above problems, the present invention aims to provide a polyolefin resin foam, a CMP polishing foam, and a CMP polishing foam tape that can suppress fluctuations due to vibration during CMP polishing while also being able to follow unevenness on the wafer surface, ensure uniformity of the load across the wafer surface during CMP polishing, and improve wafer flatness. [Means for solving the problem]

[0006] The present invention is summarized as follows [1] to [9]. [1] A polyolefin resin foam having a 25% compressive strength of 1,350 kPa or more, an expansion ratio of 15 times or less, and a thickness of 2.0 mm or less. [2] The polyolefin resin foam according to [1], which has a compression set of 10% or more at room temperature. [3] The polyolefin resin foam according to [1] or [2], having an aspect ratio, expressed as the ratio of the average cell diameter in the MD direction to the average cell diameter in the ZD direction (MD / ZD), of 0.8 to 1.9. [4] The polyolefin resin foam according to any one of [1] to [3], which has a degree of crosslinking of 35 to 45% by mass. [5] The polyolefin resin foam according to any one of [1] to [4], wherein the polyolefin resin is a polypropylene resin. [6] The polyolefin resin foam according to any one of [1] to [5], wherein the ratio of the content of the linear low-density polyethylene resin to the content of the polypropylene resin is 0.1 to 0.4. [7] The polyolefin resin foam according to any one of [1] to [6], which has an arithmetic mean height (Sa) of 10 μm or less. [8] A foam for CMP polishing, comprising the polyolefin resin foam according to any one of [1] to [7]. [9] A foam tape for CMP polishing, comprising the polyolefin resin foam according to any one of [1] to [7], and an adhesive layer provided on at least one surface thereof. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a polyolefin resin foam, a CMP polishing foam, and a CMP polishing foam tape that can suppress fluctuations due to vibration during CMP polishing while simultaneously achieving the ability to follow unevenness on the wafer surface, ensure uniformity of the load across the wafer surface during CMP polishing, and improve wafer flatness. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an example of a polishing pad using the polyolefin resin foam of the present invention as a subpad. [Figure 2] FIG. 1 is a schematic diagram showing an example of a CMP polishing apparatus equipped with a polishing pad that uses the polyolefin resin foam of the present invention as a sub-pad. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Polyolefin resin foam] The polyolefin resin foam of the present invention has a 25% compressive strength of 1,350 kPa or more, an expansion ratio of 15 times or less, and a thickness of 2.0 mm or less. The polyolefin resin foam of the present invention will be described in detail below as an embodiment.

[0010] (25% compressive strength) The 25% compressive strength of the polyolefin resin foam of the present invention is 1,350 kPa or more. If the 25% compressive strength of the polyolefin resin foam is less than 1,350 kPa, it becomes impossible to suppress fluctuations due to vibration during CMP polishing, making it difficult to ensure uniformity of the load across the wafer surface during CMP polishing, and it becomes impossible to improve the flatness of the wafer. From this perspective, the 25% compressive strength of the polyolefin resin foam is preferably 1,500 kPa or more, more preferably 1,650 kPa or more, and even more preferably 1,800 kPa or more. The upper limit of the 25% compressive strength range of the polyolefin resin foam of the present invention is not particularly limited, but from the perspective of maintaining conformability to irregularities on the wafer surface, it is, for example, 3,500 kPa. The 25% compressive strength of polyolefin resin foam can be adjusted by the type of resin used, the expansion ratio, and other factors. The 25% compressive strength of the polyolefin resin foam can be measured by the method described in the examples below.

[0011] (Expansion ratio) The polyolefin resin foam of the present invention has an expansion ratio of 15 times or less. If the expansion ratio of the polyolefin resin foam is greater than 15 times, the 25% compressive strength will be small, making it impossible to suppress fluctuations due to vibration during CMP polishing, making it difficult to ensure uniformity of the load across the wafer surface during CMP polishing, and making it impossible to improve wafer flatness. From these perspectives, the expansion ratio of the polyolefin resin foam is preferably 9 times or less, more preferably 6 times or less, and even more preferably 4 times or less. The expansion ratio of the polyolefin resin foam may be 1.2 or more, preferably 1.4 or more, more preferably 1.6 or more, even more preferably 1.8 or more, and even more preferably 2.0 or more. By setting the expansion ratio of the polyolefin resin foam to a certain level or more, the polyolefin resin foam can be given some flexibility and can be made to have the ability to follow the irregularities on the wafer surface. The expansion ratio can be determined by the measurement method described in the Examples below.

[0012] (Thickness) The thickness of the polyolefin resin foam of the present invention is 2.0 mm or less. If the thickness of the polyolefin resin foam is greater than 2.0 mm, the deformation rate of the polyolefin resin foam during CMP polishing increases, making it impossible to suppress fluctuations due to vibration during CMP polishing, making it difficult to ensure uniformity of the load across the wafer surface during CMP polishing, and making it impossible to improve wafer flatness. From this perspective, the thickness of the polyolefin resin foam is preferably 1.7 mm or less, more preferably 1.4 mm or less, and even more preferably 1.0 mm or less. The thickness of the polyolefin resin foam may be 0.2 mm or more, preferably 0.4 mm or more, and more preferably 0.6 mm or more. By setting the thickness of the polyolefin resin foam to a certain level or more, the polyolefin resin foam can be given some flexibility and can be made to have the ability to follow the irregularities on the wafer surface.

[0013] (Compression set) The polyolefin resin foam of the present invention preferably has a compression set at room temperature of 10% or more, more preferably 12% or more, and even more preferably 14% or more. In this specification, "room temperature" refers to a temperature environment of 23°C. When the compression set of the polyolefin resin foam is equal to or greater than the upper limit, repeated compression and release are performed during repeated polishing over a long period of time. In this case, polishing is performed from a compressed state similar to that when the previous wafer was polished after release, thereby suppressing variations in the amount of deformation during compression due to new deformation caused by compression. Therefore, even when polishing is repeated over a long period of time, uniformity of the load is ensured, thereby improving the flatness of the wafer. The polyolefin resin foam preferably has a compression set of 50% or less, more preferably 45% or less, and even more preferably 40% or less at room temperature. When the compression set of the polyolefin resin foam is equal to or less than the lower limit, the polyolefin resin foam is given some flexibility and room for deformation even when repeatedly compressed, and can be made to have the ability to follow the irregularities on the wafer surface. The compression set at room temperature can be measured by the measurement method described in the Examples below.

[0014] (aspect ratio) The polyolefin resin foam of the present invention preferably has a ratio of the average cell diameter in the MD direction to the average cell diameter in the ZD direction (MD / ZD) of 0.8 to 1.9, more preferably 0.9 to 1.8, and even more preferably 1.0 to 1.7. When the MD / ZD ratio is within the above range, the cells do not become too flat, the deformation rate of the polyolefin resin foam during CMP polishing is small, fluctuations due to vibration during CMP polishing can be suppressed, and uniformity of the load across the wafer surface during CMP polishing can be ensured, thereby improving wafer flatness. In the present invention, "MD" means machine direction, which corresponds to the extrusion direction of a sheet forming a polyolefin resin foam, and "ZD" means thickness direction, which corresponds to the direction perpendicular to MD.

[0015] (average bubble diameter) The polyolefin resin foam of the present invention preferably has an average cell diameter in the MD direction of 10 to 500 μm, more preferably 25 to 300 μm, and even more preferably 50 to 250 μm. The polyolefin resin foam of the present invention also has an average cell diameter in the ZD direction of 5 to 200 μm, more preferably 10 to 150 μm, and even more preferably 20 to 100 μm. When the average cell diameter in the MD direction of the polyolefin resin foam is within the above range, the polyolefin resin foam can suppress fluctuations due to vibrations during CMP polishing while also being able to conform to irregularities on the wafer surface. The average cell diameter can be measured according to the method described in the Examples below.

[0016] (Crosslinking degree (gel fraction)) The polyolefin resin foam of the present invention may be crosslinked, and the degree of crosslinking (gel fraction) of the polyolefin resin foam is preferably 25 to 65 mass%, more preferably 30 to 60 mass%, and even more preferably 35 to 55 mass%. When the degree of crosslinking (gel fraction) is within the above range, it becomes easier to achieve an appropriate 25% compressive strength. The degree of crosslinking can be measured by the following method. A test piece of approximately 100 mg is taken from the polyolefin resin foam, and the weight A (mg) of the test piece is precisely weighed. Next, the test piece is immersed in 30 cm of xylene at 120°C. 3 After immersion for 24 hours, the insoluble matter on the wire mesh is filtered through a 200-mesh mesh, dried in a vacuum, and the weight B (mg) of the insoluble matter is precisely weighed. The degree of crosslinking (mass%) is calculated from the obtained value using the following formula: Degree of crosslinking (mass%) = (B / A) × 100

[0017] (Arithmetic mean height (Sa)) The arithmetic mean height (Sa) of the surface of the polyolefin resin foam of the present invention is preferably 10 μm or less, more preferably 10 to 8 μm. When the arithmetic mean height (Sa) is within the above range, the surface of the polyolefin resin foam has smoothness, which ensures uniformity of the load across the wafer surface during CMP polishing, thereby improving the flatness of the wafer. The arithmetic mean height (Sa) can be measured using a commercially available surface texture measuring device, and specifically, can be measured by the method described in the examples.

[0018] <Polyolefin resin> The polyolefin resin foam of the present invention is produced by foaming a foamable composition containing at least a polyolefin resin. The use of a polyolefin resin can ensure the desired 25% compressive strength of the polyolefin resin foam. Examples of polyolefin resins include polypropylene resin, polyethylene resin, etc. As the polyolefin resin, it is preferable to use polypropylene resin from the viewpoint of ensuring that the polyolefin resin foam has the desired 25% compressive strength, and it is more preferable to use a combination of polypropylene resin and polyethylene resin from the viewpoint of ensuring conformability to the irregularities on the wafer surface.

[0019] <Polypropylene resin> The polypropylene resin may be a homopolypropylene, which is a homopolymer of propylene, or a copolymer of propylene and a small amount of an α-olefin other than propylene, with propylene as the main component (preferably 75% by mass or more, more preferably 90% by mass or more of all monomers). Examples of copolymers of propylene and an α-olefin other than propylene include block copolymers, random copolymers, and random block copolymers, with random copolymers (ie, random polypropylene) being preferred among these. Examples of α-olefins other than propylene include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Among these, α-olefins having about 4 to 10 carbon atoms are preferred. In the copolymer, these α-olefins may be used alone or in combination of two or more. The polypropylene resins may be used alone or in combination of two or more kinds.

[0020] <Polyethylene resin> As polyethylene resin, low-density polyethylene resin (0.93 g / cm 3 hereinafter referred to as LDPE), medium density polyethylene resin (0.930 g / cm 3 Larger than 0.942g / cm 3 less than MDPE), high density polyethylene resin (0.942g / cm 3 A specific example of a suitable low-density polyethylene resin is linear low-density polyethylene (LLDPE). From the viewpoint of imparting flexibility, the polyethylene resin is preferably a linear low-density polyethylene resin. The density of the linear low-density polyethylene resin is preferably 0.90 g / cm. 3 More preferably, it is 0.91 g / cm or more. 3 More than 0.93g / cm 3 The following is the result.

[0021] The polyethylene resin may be an ethylene homopolymer, or may be a copolymer of ethylene and a small amount of an α-olefin other than ethylene, with ethylene as the main component (preferably 75% by mass or more, more preferably 90% by mass or more of all monomers). In particular, the linear low-density polyethylene resin is preferably a copolymer of ethylene and a small amount of an α-olefin other than ethylene, with ethylene as the main component. The α-olefin other than ethylene preferably has 3 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, and specific examples include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, and 1-octene. In the copolymer, these α-olefins may be used alone or in combination of two or more. The polyethylene resin may be used alone or in combination of two or more kinds.

[0022] The polyolefin resin may be a polypropylene resin, a polyethylene resin, or a mixture thereof, polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, or a chromium oxide compound. Among these, the use of a polyethylene resin, particularly a linear low-density polyethylene, obtained with a metallocene compound polymerization catalyst makes it easier to obtain a polyolefin resin foam with appropriate flexibility.

[0023] <Content of each resin> When a polypropylene resin is used as the polyolefin resin, the content of the polypropylene resin relative to the total amount of resin contained in the polyolefin resin foam is, for example, 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more. In the polyolefin resin foam, the polypropylene resin may be used alone as a resin component, and the content of the polypropylene resin may be 100% by mass or less, but is preferably 90% by mass or less, and more preferably 85% by mass or less. The polypropylene resin preferably contains homopolypropylene to harden the foam and suppress fluctuations due to vibration during CMP polishing, and it is also preferable to use a combination of homopolypropylene and random polypropylene. When used in combination, the ratio of the homopolypropylene content to the random polypropylene content is preferably 0.3 to 0.9, more preferably 0.4 to 0.8, and even more preferably 0.5 to 0.7, by mass.

[0024] When a polyethylene resin is used as the polyolefin resin, the amount of the polyethylene resin relative to the total amount of resin contained in the polyolefin resin foam is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. The foam does not necessarily contain polyethylene resin, and the content of the polyethylene resin may be 0% by mass or more, but is preferably 10% by mass or more, and more preferably 15% by mass or more. Furthermore, when a linear low-density polyethylene resin is used as the polyethylene resin, the ratio of the content of the linear low-density polyethylene resin to the content of the polypropylene resin is preferably 0.1 to 0.4, more preferably 0.15 to 0.35, and even more preferably 0.2 to 0.3.

[0025] <Resins other than polyolefin-based resins> The polyolefin resin foam may use a resin other than polypropylene resin or polyethylene resin as the polyolefin resin, for example, various ethylene propylene thermoplastic elastomers such as EPDM, etc. Furthermore, the olefin resin may be used in combination with a resin other than the olefin resin, and examples of the resin other than the polyolefin resin include a styrene thermoplastic elastomer and a rubber component. When a polyolefin-based resin foam contains resins other than polypropylene resin and polyethylene resin (other resins), the proportion of the other resins relative to the total amount of resin in the polyolefin-based resin foam is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 0% by mass.

[0026] <Foaming agent> The polyolefin resin foam of the present invention may be obtained by foaming a polyolefin resin composition (hereinafter, simply referred to as "resin composition") containing a polyolefin resin and a foaming agent. The resin composition may contain additives, which will be described later, as appropriate, in addition to the polyolefin resin and the foaming agent. The foaming agent is preferably a foaming agent that foams the resin composition by generating gas upon heating, and specifically, a thermal decomposition type foaming agent is preferred. Examples of the thermal decomposition type foaming agent include organic foaming agents and inorganic foaming agents. Examples of the organic foaming agent include azo compounds such as azodicarbonamide, azodicarboxylic acid metal salts (e.g., barium azodicarboxylate), and azobisisobutyronitrile, nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, hydrazine derivatives such as hydrazodicarbonamide, 4,4'-oxybis(benzenesulfonylhydrazide), and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonylsemicarbazide. Examples of inorganic foaming agents include ammonium carbonate, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, and anhydrous monosodium citrate. Among these, from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety, azo compounds are preferred, and azodicarbonamide is more preferred. The foaming agents may be used alone or in combination of two or more.

[0027] The amount of the foaming agent in the resin composition is preferably 0.5 to 5 parts by mass, more preferably 1.0 to 4 parts by mass, and even more preferably 1.5 to 3 parts by mass, relative to 100 parts by mass of the polyolefin resin. By setting the amount of the foaming agent within the above range, excessive foaming is prevented, and a polyolefin resin foam with a desired expansion ratio can be obtained.

[0028] <Additives> The polyolefin resin foam may contain, for example, a cross-linking aid as an additive. A polyfunctional monomer can be used as the cross-linking aid. Adding the cross-linking aid to the polyolefin resin reduces the amount of ionizing radiation irradiated during cross-linking, thereby preventing scission and degradation of resin molecules due to irradiation with ionizing radiation. Specific examples of the crosslinking aid include compounds having three functional groups in one molecule, such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, trimellitic acid triallyl ester, 1,2,4-benzenetricarboxylic acid triallyl ester, and triallyl isocyanurate; compounds having two functional groups in one molecule, such as 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, and divinylbenzene; diallyl phthalate, diallyl terephthalate, diallyl isophthalate, ethylvinylbenzene, neopentyl glycol dimethacrylate, lauryl methacrylate, and stearyl methacrylate. These crosslinking aids may be used alone or in combination of two or more.

[0029] The amount of the crosslinking aid is preferably 0.5 to 10 parts by mass, more preferably 1.0 to 8 parts by mass, and even more preferably 1.5 to 5 parts by mass, relative to 100 parts by mass of the polyolefin resin. By setting the amount of the crosslinking aid within the above range, it becomes easy to control the degree of crosslinking, and it becomes possible to stably obtain the desired degree of crosslinking.

[0030] The polyolefin resin foam may contain, as an additive, for example, an antioxidant, such as phenol-based antioxidants (e.g., tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane and 2,6-di-t-butyl-p-cresol), sulfur-based antioxidants (e.g., dilaurylthiodipropionate), phosphorus-based antioxidants, and amine-based antioxidants. The amount of the antioxidant to be blended is, for example, 0.01 to 5 parts by mass per 100 parts by mass of the polyolefin resin.

[0031] <Other additives> The foam may further contain additives other than the crosslinking aid and the antioxidant, and may also contain additives commonly used in foams, such as a decomposition temperature regulator, a heat stabilizer, a colorant, an antistatic agent, and a filler.

[0032] <Method of manufacturing foam> The polyolefin resin foam of the present invention can be obtained by foaming a resin composition containing a polyolefin resin and a foaming agent. If necessary, the foaming may be performed after crosslinking. A method for producing the polyolefin resin foam will be described in detail below.

[0033] A method for producing a polyolefin resin foam according to a preferred embodiment of the present invention includes the following steps 1 and 2. Step 1: A polyolefin resin, a foaming agent, and additives that are blended as needed are mixed to obtain a resin composition, and the obtained resin composition is molded into a sheet. Step 2: The sheet-shaped resin composition obtained in step 1 is foamed to obtain a foam.

[0034] (Process 1) Step 1 is not particularly limited, but may be carried out using, for example, an extruder. When using an extruder, a polyolefin resin, a foaming agent, and additives that are blended as needed are fed into the extruder, and these components are melt-kneaded and extruded from the extruder to obtain a sheet-shaped resin composition. However, melt-kneading may be performed using a mixing device other than an extruder. Furthermore, molding of the resin composition may be performed by a method other than extrusion molding, and the resin composition may be formed into a sheet by press molding or the like. The temperature during melt-kneading may be such that the foaming agent does not foam and the components can be mixed together. For example, when the foaming agent is a thermally decomposable foaming agent, the temperature should be lower than the decomposition temperature of the thermally decomposable foaming agent.

[0035] When the resin composition obtained in step 1 is crosslinked, examples of the crosslinking method include a method of irradiating the resin composition with ionizing radiation such as electron beams, α-rays, β-rays, and γ-rays, and a method of blending an organic peroxide into the resin composition in advance and heating the resin composition to decompose the organic peroxide, and these methods may be used in combination. Among these, the method of irradiating with ionizing radiation is preferred. The irradiation dose of ionizing radiation is preferably 0.5 to 20 Mrad, more preferably 1.0 to 12 Mrad.

[0036] Examples of organic peroxides used for crosslinking include 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane and 1,1-bis(t-butylperoxy)cyclohexane. These may be used alone or in combination of two or more. The amount of organic peroxide added is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the polyolefin resin. When the amount of organic peroxide added is within the above range, crosslinking of the resin composition proceeds easily, and the amount of decomposition residue of the organic peroxide in the resulting foam can be suppressed. The organic peroxide may be mixed with the polyolefin resin in step 1, like other additives.

[0037] (Process 2) Step 2 is not particularly limited as long as it can foam the sheet-shaped resin composition, but it is preferable to foam the resin composition by heating it. The method for heating the resin composition is not particularly limited, and examples thereof include a method for heating the resin composition with hot air, a method for heating with infrared rays, a method for heating in a salt bath, a method for heating in an oil bath, and the like, and these may be used in combination. The heating temperature during foaming in step 2 is not particularly limited, but when a thermally decomposable foaming agent is used, the temperature should be equal to or higher than the decomposition temperature of the thermally decomposable foaming agent, for example, 200 to 300°C, preferably 220 to 280°C.

[0038] The polyolefin resin foam may or may not be stretched in step 2. The stretching may be carried out after the resin composition is foamed to obtain the polyolefin resin foam, or may be carried out while the resin composition is being foamed.

[0039] The polyolefin-based resin foam thus obtained may be further cut by a known method to appropriately adjust the contour shape and mold it into a sub-pad for a polishing pad. Furthermore, the obtained polyolefin resin foam can be sliced ​​to produce a foam having the desired thickness, but in order to adjust it so that the arithmetic mean height (Sa) of the surface is satisfied, it is preferable to leave the skin layer unsliced. The method for producing a polyolefin resin foam described above is just one example, and the polyolefin resin foam of the present invention may be produced by a method other than the method described above.

[0040] <Application> The polyolefin resin foam of the present invention can be used, for example, as a foam for CMP polishing. Specifically, the polyolefin resin foam of the present invention can be used as a sub-pad provided under a top pad of a polishing pad having a multi-layer structure used in CMP polishing.

[0041] As shown in FIG. 1, a polishing pad 1 using the polyolefin resin foam of the present invention as a subpad comprises two layers: a top pad 10 and a subpad 11. The top pad 10 is pressed against an object to be polished during CMP polishing, and functions to polish the object. The subpad 11 functions as a cushion layer for uniformly pressing the top pad 10 against the polishing surface of the object to be polished during CMP polishing. The polishing pad 1 further comprises a first adhesive layer 20 that bonds the top pad 10 and the subpad 11 together, and a second adhesive layer 21 that bonds the subpad 11 and the surface plate 30 together. The top pad 10 may be made of any abrasive material that can uniformly polish the surface of the wafer to be polished, such as hard urethane, suede, or nonwoven fabric impregnated with urethane. The polyolefin resin foam of the present invention may be used as the subpad 11. Use of the polyolefin resin foam of the present invention prevents fluctuations in the compressive load during polishing within the surface of the wafer being polished, which is the object to be polished, due to the influence of vibrations caused by rotational motion during polishing, and suppresses variations in the polishing rate within the wafer surface.

[0042] As shown in Fig. 2, the CMP polishing apparatus has a polishing head 40 disposed above a platen 30 on which a polishing pad 1 is placed. The polishing head 40 is capable of holding a wafer 50 and is provided with a pressure mechanism (not shown) such as a multi-zone pressure chamber that can press the wafer 50 against the polishing pad 1 (top pad 10) at a predetermined pressure. The polishing head 40 is rotatably supported by a rotation shaft 41. The rotation shaft 41 of the polishing head 40 is disposed parallel to the rotation shaft 31 of the platen 30. Furthermore, the polishing head 40 is supported above the platen 30 so as to be able to reciprocate between the radial center and the radial outer side. Furthermore, above the surface plate 30, there are provided a slurry pipe 60 for supplying slurry onto the polishing pad 1, and a cleaning pipe 61 for supplying ultrapure water onto the polishing pad 1 for cleaning or the like.

[0043] Next, an outline of CMP polishing of a wafer using the CMP polishing apparatus shown in FIG. 2 will be explained. Next, the polishing head 40 holding the wafer 50 to be polished is placed on the polishing pad 1 (top pad 10), and the platen 30 and polishing head 40 are rotated while slurry is supplied from the slurry pipe 60. This causes the polishing pad 1 (top pad 10) and the wafer 50 to rub against each other via the abrasive grains of the slurry, generating heat. As a result, the temperature at the interface between the wafer 50 and the polishing pad 1 (top pad 10) rises, and chemical mechanical polishing progresses. When the chemical reaction begins, the heat generated by the chemical reaction is also added, accelerating the rate of temperature rise. Eventually, a steady state is reached, and polishing at a constant rate begins. When polishing is completed, the polishing head 40 is raised upward and ultrapure water is supplied from the cleaning pipe 61 to the polishing pad 1 (top pad 10) to remove polishing residues remaining on the surface of the wafer 50 on the polishing pad 1 (top pad 10).

[0044] In the above-described polishing pad 1, the polyolefin resin foam of the present invention as the sub-pad 11 is configured to have the first adhesive layer 20 and the second adhesive layer 21 separately provided thereon, but the polyolefin resin foam may also be used as a CMP polishing foam tape having an adhesive layer provided on at least one surface thereof. A CMP polishing foam tape having an adhesive layer provided on at least one surface of the polyolefin resin foam can be easily adhered to the top pad 10 or the surface plate 30, which are the objects to be adhered. The adhesive layers used for the first adhesive layer 20 and the second adhesive layer 21 are not particularly limited as long as they can adhere to the top pad 10 or the surface plate 30 to be adhered. For example, they may be composed of a single adhesive layer made of an adhesive, or may be a double-sided adhesive tape having a substrate and adhesive layers provided on both sides of the substrate. The adhesive may be an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, or the like. The adhesive used for the first adhesive layer 20 may be an adhesive that is resistant to the slurry used in CMP polishing, and preferably a rubber adhesive. The adhesive used for the second adhesive layer 21 may preferably be an acrylic adhesive. [Example]

[0045] The present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way.

[0046] The methods for measuring the various physical properties and evaluating the foams are as follows.

[0047] <25% compressive strength> The 25% compressive strength of the foam in each of the examples and comparative examples was measured at 23°C in accordance with JIS K6767.

[0048] <Expansion ratio> The expansion ratio is the ratio of the specific volume (unit: cm) of the resin composition before expansion to the foam after expansion. 3 / g) was measured and calculated by (specific volume of foam) / (specific volume of resin composition before foaming).

[0049] <Thickness> The thickness of the foam in each example and comparative example was measured using a dial gauge.

[0050] <Average bubble diameter> The foams in each Example and Comparative Example were cut into 50 mm squares, immersed in liquid nitrogen for 1 minute, and then cut in the thickness direction along the MD, and a 200x magnification photograph was taken using a digital microscope (Keyence Corporation, product name VHX-900). For the foams in the photographed images, the MD cell diameters of 50 bubbles present on the cut surface in the MD were measured, and the average value was taken as the average cell diameter in the MD.

[0051] <Compression set> The thickness of the center of the foam in each of the examples and comparative examples was measured at room temperature (23° C.) (t0). The foam in each example and comparative example was placed on a compression plate (a smooth stainless steel plate), and spacers having a height (t1) when the foam was compressed to 25% were placed on both sides of the foam. Another compression plate was then placed on top of the foam, with the foam and spacers sandwiched between the two compression plates. The foam sandwiched between two compression plates was placed in a compression device (compression set tester, manufactured by M&K Corporation). The compression device was then used to compress the foam until the spacer came into contact with the upper and lower compression plates. This resulted in a 25% compression of the foam. The spacer, which does not compress, prevented the foam from being compressed beyond 25%. The compression device compressing the foam was placed in a thermostatic chamber adjusted to room temperature. This time was the test start time. 22 hours after the start of the test, the compression device was removed from the thermostatic chamber, and the foam was removed from the compression device. The foam removed from the chamber was left to stand in a standard test chamber under room temperature and 1 atm standard atmospheric pressure for 24 hours, after which the thickness of the center of the foam was measured (t2). The compression set (Cs) was then calculated using the following formula (1): Cs=(t2-t0) / (t1-t0)×100 (1)

[0052] <Aspect ratio> A foam sample was prepared for measurement by cutting it into a 50 mm square. After immersing it in liquid nitrogen for 1 minute, it was cut into thickness directions along the MD and TD with a razor blade. This cross section was photographed at 200x magnification using a digital microscope (Keyence Corporation, "VHX-900"), and the bubble diameters of all bubbles present on a 2 mm-long cut surface in both the MD and ZD directions were measured. This procedure was repeated five times. The average values ​​of all bubbles were then calculated as the average bubble diameters in the MD and ZD directions. Then, the ratio of the average cell diameter in the MD direction to the average cell diameter in the ZD direction (MD / ZD) was calculated from the calculated average cell diameters in the MD and ZD directions.

[0053] <Degree of cross-linking (gel fraction)> The degree of crosslinking (gel fraction) of the foam was measured by the method described in the specification.

[0054] <Arithmetic mean height (Sa)> Surface quality analysis was performed using a laser microscope (Keyence Corporation, VK-X150) in accordance with ISO 25178. Specifically, the surface profile of a two-dimensional area of ​​1,000 μm × 1,000 μm was measured using a laser method at a lens magnification of 10x. Measurements were taken at three locations on the same foam sample, and the average of these measurements was taken as the arithmetic mean height (Sa).

[0055] <Deformation stability evaluation> The foam obtained in each Example and Comparative Example was cut into a 25 mm square to prepare a foam sample for measurement. A load of 1,000 kPa was applied to the sample in the thickness direction, and the thickness of the foam sample after the load was applied was measured. The amount of deformation in the sample thickness and the deformation rate of the sample thickness before and after the load were calculated. The deformation stability was evaluated according to the following evaluation criteria. ○: The deformation rate of the sample thickness is less than 1% ×: The deformation rate of the sample thickness is 1% or more

[0056] <Pressure-sensitive paper evaluation> The foams obtained in each example and comparative example were cut into cylindrical shapes with a diameter of 10 mm to prepare foam samples for measurement. The foam samples were placed on pressure-sensitive paper (Fujifilm's Prescale for ultra-low pressure, model number LLLW), and a load of 4,000 N was applied in the thickness direction of the foam sample. The color change of the pressure-sensitive paper after the load was applied was measured and evaluated according to the following criteria. The pressure-sensitive paper was originally white, and the areas where pressure was applied turned red. 〇: White is 5% or less ×: White is over 5%

[0057] <Repeated compression evaluation> The foam obtained in each Example and Comparative Example was cut into 25 mm squares to prepare foam samples for measurement. A load of 40 kPa was applied to the sample five times in the thickness direction, and the thickness of the foam sample after the fifth load application was measured to calculate the amount of deformation in the sample thickness and the deformation rate of the sample thickness before and after the load application. The repeated compressibility was evaluated according to the following evaluation criteria. ○: The deformation rate of the sample thickness is 1% or less ×: The deformation rate of the sample thickness is 1% or more

[0058] <Raw materials used> The materials used in the examples and comparative examples are as follows.

[0059] (resin) Homopolypropylene (Prime Polymer, product name "J106G", MFR = 15g / 10min (230℃)) Random polypropylene (manufactured by Sumitomo Chemical Co., Ltd., product name "AD571", MFR = 0.5 g / 10 min (230 °C)) Random polypropylene: (Prime Polypro, product name "E222", density 0.90 g / cm 3 , MFR=1.5g / 10min (230℃) Linear low-density polyethylene (LLDPE) (Prime Polymer Co., Ltd., product name "Ultzex ​​1020L", density 0.91 g / cm 3 , MFR=2.0g / 10min (190℃) Low-density polyethylene (LDPE) (Sumitomo Chemical, product name "G215", density 0.92 g / cm 3 , MFR=1.4g / 10min (190℃) Low-density polyethylene (LDPE) (Sumitomo Chemical, product name "G201", density 0.919 g / cm 3 , MFR=2.0g / 10min (190℃)

[0060] (foaming agent) Azodicarbonamide (thermal decomposition type foaming agent, manufactured by Otsuka Chemical Co., Ltd., trade name "SOL", decomposition temperature: 197°C, average particle size: 3.2 μm)

[0061] (Crosslinking aid) 1,9-nonanediol dimethacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name "Light Ester 1.9-ND", viscosity 8 mPa·s (25°C))

[0062] (antioxidant) Phenolic antioxidant (manufactured by BASF Japan, trade name "Irganox 1010", tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane)

[0063] [Example 1] 30 parts by mass of homopolypropylene (J106G), 50 parts by mass of random polypropylene (AD571), 20 parts by mass of LLDPE (Ultzex ​​1020L), 4 parts by mass of cross-linking aid, 2.3 parts by mass of foaming agent, and 1 part by mass of antioxidant were kneaded in a plastomill, and then heat-pressed to obtain a 0.7 mm-thick sheet-shaped resin composition. Next, both sides of the sheet-like resin composition were irradiated with an electron beam at an acceleration voltage of 800 kV and 2.5 Mrad to crosslink the resin composition, and then heated in a hot air oven set at 270°C for 3 minutes to foam the resin composition, yielding a foam. The evaluation results of the obtained foam are shown in Table 1.

[0064] [Example 2-4] The same procedure as in Example 1 was carried out except that the formulation of the foaming agent was changed and the expansion ratio was changed as shown in Table 1.

[0065] [Comparative Example 1-3] The same procedure as in Example 1 was carried out except that the formulation of the foaming agent was changed and the expansion ratio was changed as shown in Table 1.

[0066] [Table 1]

[0067] The foam of the example has a specific compressive strength and expansion ratio, and when used as a sub-pad of a CMP polishing pad, it suppresses fluctuations due to vibration during CMP polishing while achieving conformability to irregularities on the wafer surface, ensuring uniformity of the load across the wafer surface during CMP polishing and improving wafer flatness. On the other hand, when the foam of the comparative example is used as a sub-pad of a CMP polishing pad, it is difficult to suppress fluctuations due to vibration during CMP polishing, and conformability to irregularities on the wafer surface is insufficient, resulting in failure to achieve uniformity of the load across the wafer surface during CMP polishing, and the edge portion of the wafer becomes thicker than the center. [Explanation of symbols]

[0068] 1...Polishing pad 10...Top pad 11...Subpad 20…First adhesive layer 21…Second adhesive layer 30...Surface plate 31...Rotation axis 40...Polishing head 41...Rotation axis 50...wafer 60...Slurry piping 61...Cleaning piping

Claims

1. A polyolefin resin foam having a 25% compressive strength of 1,350 kPa or more, an expansion ratio of 15 times or less, and a thickness of 2.0 mm or less.

2. The polyolefin resin foam according to claim 1, which has a compression set of 10% or more at room temperature.

3. 2. The polyolefin resin foam according to claim 1, wherein the aspect ratio, expressed as the ratio of the average cell diameter in the MD direction to the average cell diameter in the ZD direction (MD / ZD), is 0.8 to 1.

9.

4. The polyolefin resin foam according to claim 1, having a degree of crosslinking of 35 to 45% by mass.

5. The polyolefin resin foam according to claim 1 , wherein the polyolefin resin is a polypropylene resin.

6. 2. The polyolefin resin foam according to claim 1, wherein the ratio of the content of the linear low-density polyethylene resin to the content of the polypropylene resin is 0.1 to 0.

4.

7. The polyolefin resin foam according to claim 1, having an arithmetic mean height (Sa) of 10 μm or less.

8. A CMP polishing foam comprising the polyolefin resin foam according to any one of claims 1 to 7.

9. A foam tape for CMP polishing, comprising the polyolefin resin foam according to any one of claims 1 to 7, and an adhesive layer provided on at least one surface thereof.

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