Polishing pad

Abstract

To provide a polishing pad capable of improving mechanical polishing force.SOLUTION: In the polishing pad according to the present invention, a predetermined number of 100 μm*100 μm square regions SA are extracted in a predetermined procedure in a binarized CT image showing a cross section in a plane direction orthogonal to a thickness direction of a polyurethane resin foam forming a polishing surface. 1 is assigned to white pixels Pa indicating pores and 100 is assigned to black pixels Pb indicating a resin with respect to all pixels constituting each square area SA, the total number of pixels of each square area SA is set to N, the number of white pixels assigned 0 is set to a, the number of black pixels assigned 100 is set to b, and the resin abundance ratio in each square area SA is calculated by (0*a+100*b) / N, when a square region having a resin abundance ratio of 90 or more is defined as an effective resin region, an effective resin ratio calculated by [the number of the effective resin regions] / [the total number of the square regions]*100 is 2% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polishing pad. [Background technology]

[0002] Chemical mechanical polishing (hereinafter referred to as CMP) is performed in the manufacture of semiconductor devices and the like. CMP typically uses a polishing slurry containing abrasive grains and a polishing pad for bringing the abrasive grains into contact with the workpiece. In the field of CMP, there has been active research into improving the polishing rate in order to efficiently manufacture products.

[0003] For example, Patent Document 1 proposes that by uniforming the resin distribution of the polyurethane resin foam that constitutes the polishing pad, the contact point of the polishing surface with the workpiece, such as a silicon wafer, can be made uniform, thereby increasing the polishing speed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-148354 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to achieve the required polishing rate, it is often important for polishing pads used in CMP to be able to improve the mechanical polishing force mediated by abrasive grains. For example, in the CMP of native oxide films that can form on silicon wafers, mechanical polishing force is thought to have a stronger effect than polishing force based on chemical action. Therefore, in such CMP, polishing pads that can exert a strong mechanical polishing force are required.

[0006] In view of the above circumstances, an object of the present invention is to provide a polishing pad capable of improving mechanical polishing power. [Means for solving the problem]

[0007] The polishing pad according to the present invention comprises: The polishing tool has a polyurethane resin foam that forms a polishing surface, In a binarized CT image showing a cross section in a plane direction perpendicular to the thickness direction of the polyurethane resin foam, a measurement region of 1200 μm × 1400 μm is divided into square regions of 100 μm × 100 μm, and for all pixels constituting each square region, white pixels indicating pores are assigned a value of 0, and black pixels indicating resin are assigned a value of 100. The total number of pixels in each square region is defined as N, the number of white pixels assigned a value of 0 is defined as a, and the number of black pixels assigned a value of 100 is defined as b. The resin abundance ratio in each square region is calculated by (0 × a + 100 × b) / N, and the square region where the resin abundance ratio is 90 or more is defined as an effective resin region. The effective resin ratio calculated by [(the number of effective resin regions) / (the total number of square regions)]×100 is 2% or more.

[0008] One aspect of the polishing pad according to the present invention is The effective hardness calculated by [(effective resin ratio) / 100]×(Young's modulus of the polyurethane resin foam) is 3 or more. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a polishing pad capable of improving mechanical polishing power. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 10 is a diagram for explaining a method for calculating a resin abundance ratio by CT. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a polishing pad according to one embodiment of the present invention will be described with reference to the drawings.

[0012] In CMP using the polishing pad of this embodiment, a workpiece is pressed against the polishing pad, which is rotated by a polishing machine platen, while a polishing slurry containing abrasive grains is supplied to the polishing pad. At this time, the abrasive grains come into contact with the workpiece through the polishing pad.

[0013] The polishing pad according to this embodiment includes a polyurethane resin foam. The polyurethane resin foam is formed into a circular sheet shape in a plan view. A first surface of the polyurethane resin foam forms a polishing surface. A second surface of the polyurethane resin foam opposite the polishing surface is a surface fixed to a surface plate of a polishing device. For example, the second surface can be fixed to the surface plate via an adhesive means such as double-sided tape or adhesive. That is, the polishing pad may include double-sided tape or adhesive as an adhesive means laminated on the polyurethane resin foam.

[0014] The polyurethane resin foam has a plurality of pores formed by the resin. Each pore may be spherical. The plurality of pores may include closed pores (closed cells) that are not connected to other pores, or may include interconnected pores (open cells) in which two or more pores are connected.

[0015] When a cross section parallel to the surface direction of the polyurethane resin foam is observed, the polyurethane resin foam has a predetermined amount or more of regions with a high resin occupancy ratio. Such a polyurethane resin foam can be said to have many resin walls (thick resin walls) that extend widely in the surface direction, which can generate a large stress that resists the pressing force of the workpiece to be polished, thereby improving mechanical polishing power. Furthermore, such a polyurethane resin foam can be said to have many resin surfaces with large areas on the polishing surface, which can hold many abrasive grains, thereby improving mechanical polishing power. The resin occupancy ratio in any cross section of a polyurethane resin foam produced by the manufacturing method described below can be understood to reflect the resin occupancy ratio in other cross sections and on the polishing surface. In other words, the resin occupancy ratio in any cross section can be understood to be reflected throughout the thickness direction of the polyurethane resin foam.

[0016] The proportion of the resin in the planar direction of the polyurethane resin foam can be quantified by cross-sectional observation using CT. The method for this quantification will be described in detail below.

[0017] First, a CT scan of the polyurethane resin foam is performed using a three-dimensional measuring X-ray CT device (TDM1000H-1, manufactured by Yamato Scientific Co., Ltd.) under the following conditions. (CT scan conditions) Views per rotation: 1500 Frames / Views: 10 X-ray tube voltage: 28~33kV Magnification axis position: 7.416 mm Reconstruction pixel size X: 0.003880 mm Reconstruction pixel size Y: 0.003880 mm Reconstruction pixel size Z: 0.003880 mm

[0018] Next, image processing is performed using image processing software (VGStudio Max 2.1, manufactured by Japan Visual Science Volume Graphics Co., Ltd.). Specifically, 12 cross-sectional images of a 2000 μm × 2000 μm field of view parallel to the surface direction of the polyurethane resin foam are obtained at 100 μm intervals in the thickness direction. In addition, the contrast of each cross-sectional image is adjusted to classify pore areas from areas other than pores (areas where polyurethane resin is present).

[0019] Next, each cross-sectional image was processed using ImageJ (Rasband, WS, US National Institutes of Health, Bethesda, Maryland, USA). Specifically, the pixel type of the cross-sectional image was first converted from RGB color to 8-bit (grayscale, gradation 0-255). Next, a binarization process was performed, where the gradation range of 0-128 was designated as a white region where pores existed, and the gradation range of 129-255 was designated as a black region where polyurethane resin existed. The binarized image size was reduced to 12 pixels horizontally and 14 pixels vertically. Note that 1 pixel x 1 pixel of this reduced image corresponds to a size of 100 μm x 100 μm.

[0020] Next, the abundance ratio of polyurethane resin is measured for the reduced image using ImageJ. More specifically, as shown in FIG. 1, a measurement area MA, which is a region of interest, is selected in the reduced image CI. The measurement area MA is 312 pixels (=1201.2 μm) horizontally and 364 pixels (=1401.4 μm) vertically from the (132, 22) position, with a size of 1200 μm × 1400 μm (1680000 μm). 2 Next, the measurement area MA is divided into 100 μm × 100 μm square areas SA. This results in 168 (1,680,000 μm 2 / 10000μm 2) square area SA is extracted. Next, for all pixels (dimensions of one pixel: 3.88 μm × 3.88 μm) in each square area SA, 0 is assigned to white pixels Pa and 100 is assigned to black pixels Pb. Next, the total number of pixels in each square area SA is N, the number of white pixels assigned 0 is a, and the number of black pixels assigned 100 is b, and the resin abundance ratio in the square area SA is calculated using the following (Equation 1). Resin abundance ratio=(0×a+100×b) / N (Formula 1) This resin abundance ratio is calculated for all square regions (168 square regions), and square regions with a resin abundance ratio of 90 or more are defined as effective resin regions. Note that, because the above series of image analyses is performed on 12 cross-sectional images, a total of 2016 (12 (images) × 168) square regions are extracted from one measurement target, a polyurethane resin foam.

[0021] The polyurethane resin foam of the present embodiment has an effective resin ratio calculated by the following (Equation 2) of 2% or more. Effective resin ratio (%)=[(number of effective resin regions) / (total number of square regions)]×100 (Equation 2)

[0022] In summary, the polyurethane resin foam has an effective resin ratio of 2% or more, which is determined by the following procedure. (Step 1) Twelve cross-sectional images of a 2000 μm×2000 μm field of view parallel to the surface direction of the polyurethane resin foam are obtained at intervals of 100 μm in the thickness direction. (Step 2) Each cross-sectional image is binarized. (Step 3) For each binarized cross-sectional image, a rectangular measurement area of ​​1200 μm × 1400 μm is set. (Step 4) Divide each measurement area into square areas of 100 μm x 100 μm, and extract a total of 2016 square areas. (Step 5) For all pixels in each square area, assign a value of 0 to white pixels and a value of 100 to black pixels. (Step 6) Let the total number of pixels in each square region be N, the number of white pixels assigned with 0 be a, and the number of black pixels assigned with 100 be b. Calculate the resin abundance ratio in each square region using the above (Equation 1). (Step 7) Calculate the effective resin ratio using the above (Equation 2).

[0023] The effective resin ratio of 2% or more specifies that the cross section of the polyurethane resin foam in the planar direction and the polishing surface contain many regions with a high resin occupancy ratio, which contributes to improving the mechanical polishing power of the polishing pad as described above. The effective resin ratio is preferably 3% or more, and more preferably 3.0% or more. The effective resin ratio may be 10% or less, 8% or less, 7% or less, or 6% or less.

[0024] The polyurethane resin foam preferably has a Young's modulus of 40 to 250 MPa. The Young's modulus is measured using a dumbbell-shaped No. 1 test piece as specified in JIS K6251. A tensile tester is used to measure the Young's modulus, and the test piece is pulled in the longitudinal direction at a tensile speed of 100 mm / min to obtain multiple test force measurements and strain measurements corresponding to each test force value. Next, the measured values ​​are plotted on a coordinate system where the X axis represents the test force and the Y axis represents the strain, to create a graph. An approximate line is determined by the least squares method within the test force range of 0.5 N to 15 N on the graph. The slope of the approximate line is then taken as the Young's modulus (MPa) of the polyurethane resin foam.

[0025] As described above, the polyurethane resin foam has many resin walls with large cross-sectional areas (thick walls), and is also considered to have many resin surfaces with large areas on the polishing surface, so the hardness of the polyurethane resin foam can effectively contribute to improving the mechanical polishing power. From this perspective, the polyurethane resin foam preferably has an effective hardness calculated by the following (Equation 3) of 2 or more, more preferably 3 or more. The effective hardness may be 7 or less, 6 or less, or 5 or less. Effective hardness=[(effective resin ratio) / 100]×(Young's modulus) (Equation 3)

[0026] The apparent density of the polyurethane resin foam is 0.2 g / cm 3 More than 0.8g / cm 3 It is preferable that the concentration is 0.3 g / cm or less. 3 More than 0.7g / cm 3 More preferably, it is 0.3 g / cm or less. 3 More than 0.5g / cm 3 It is more preferable that the apparent density is not more than 1000 kJ / cm.sup.2. The apparent density can be measured by the method described in JIS K7222.

[0027] The object to be polished by CMP using the polishing pad according to this embodiment is preferably a silicon wafer, which may produce an oxide film. Other suitable objects include those having a polishing surface made of silicon nitride, and insulating films made of silicon oxide (SiO2) or silicon nitride (SiN) in semiconductor devices.

[0028] The polyurethane resin contained in the polyurethane resin foam according to this embodiment can be the same as that used in general polishing pads. Typically, the polyurethane resin contains a polyisocyanate compound (e.g., a prepolymer having isocyanate groups at both ends of the molecular chain) and a curing agent. That is, the polyurethane resin foam according to this embodiment can be obtained by preparing a liquid mixture containing the polyisocyanate compound and the curing agent, and then curing the mixture.

[0029] Examples of the polyisocyanate compound include urethane prepolymers containing, as constituent units, one or more polyols and one or more polyisocyanates, and having an isocyanate group at the terminal.

[0030] The polyol may be a polyol polymer such as a polyether polyol, a polyester polyol, a polyester polycarbonate polyol, or a polycarbonate polyol.

[0031] Examples of the polyether polyol include polytetramethylene ether glycol (PTMG), polypropylene glycol (PPG), polyethylene glycol (PEG), and ethylene oxide-added polypropylene polyol.

[0032] Examples of the polyester polyol include polyethylene adipate glycol, polybutylene adipate glycol, polycaprolactone polyol, and polyhexamethylene adipate glycol.

[0033] Examples of the polyester polycarbonate polyol include a reaction product of a polyester glycol such as polycaprolactone polyol with an alkylene carbonate, and also include a reaction product obtained by reacting ethylene carbonate with a polyhydric alcohol, and then further reacting the reaction product with an organic dicarboxylic acid.

[0034] Examples of the polycarbonate polyol include reaction products of diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene ether glycol with phosgene, diallyl carbonate (e.g., diphenyl carbonate), or cyclic carbonate (e.g., propylene carbonate).

[0035] The polyol may be an aromatic polyol such as 1,4-benzenedimethanol or 1,4-bis(2-hydroxyethoxy)benzene; an aliphatic polyol such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, or 2-methyl-1,8-octanediol; an alicyclic polyol such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, or hydrated bisphenol A; or a polyfunctional polyol such as glycerin, trimethylolpropane, tributyrolpropane, pentaerythritol, or sorbitol.

[0036] The polyisocyanate may be an aromatic diisocyanate, an aliphatic isocyanate, an alicyclic isocyanate, or the like.

[0037] Examples of the aromatic isocyanate include tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, etc. Furthermore, examples of the aromatic isocyanate include diphenylmethane diisocyanate (MDI) and modified products of diphenylmethane diisocyanate (MDI).

[0038] Examples of modified diphenylmethane diisocyanate (MDI) include carbodiimide-modified, urethane-modified, allophanate-modified, urea-modified, biuret-modified, isocyanurate-modified, and oxazolidone-modified products.

[0039] Examples of the aliphatic diisocyanate include ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate (HDI).

[0040] Examples of the alicyclic diisocyanate include 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, and methylenebis(4,1-cyclohexylene) diisocyanate.

[0041] Examples of the cured product include the polyols, polyamines, and mixtures thereof.

[0042] Examples of the polyamine include 4,4'-methylenebis(2-chloroaniline) (MOCA), 4,4'-methylenedianiline, trimethylenebis(4-aminobenzoate), 2-methyl-4,6-bis(methylthio)benzene-1,3-diamine, 2-methyl-4,6-bis(methylthio)-1,5-benzenediamine, 2,6-dichloro-p-phenylenediamine, 4,4'-methylenebis(2,3-dichloroaniline), Examples include 3,5-bis(methylthio)-2,4-toluenediamine, 3,5-bis(methylthio)-2,6-toluenediamine, 3,5-diethyltoluene-2,4-diamine, 3,5-diethyltoluene-2,6-diamine, trimethylene glycol-di-p-aminobenzoate, 1,2-bis(2-aminophenylthio)ethane, and 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane.

[0043] Next, a method for manufacturing a polishing pad according to this embodiment will be described.

[0044] The production method according to this embodiment includes a mixing step in which shear force is applied to a curable urethane composition containing a foaming agent. Examples of means for applying shear force include an open-type mixer equipped with a mixing tank and an agitator blade that applies shear force to the curable urethane composition filled in the mixing tank, or a closed-type mixer equipped with a mixing head having a rotor inside. In the mixing step, the effective resin ratio of the polyurethane resin foam can be adjusted by adjusting the rotation speed of the agitator blade or the rotor. For example, if the effective resin ratio is lower than desired when a curable urethane composition of a certain composition is used, the effective resin ratio can be increased by reducing the rotation speed of the agitator blade or the rotor so that the uniformity of the blowing agent in the curable urethane composition of that composition becomes uneven (misdistributed).

[0045] The curable urethane composition includes, for example, the prepolymer, the curing agent, the foaming agent, and a catalyst. The curable urethane composition may also include other additives.

[0046] The foaming agent may be, for example, one or more of water, a chemical foaming agent that decomposes when heated to generate gas, a low-boiling hydrocarbon having a boiling point of −5 to 70° C., a halogenated hydrocarbon, or liquefied carbon dioxide.

[0047] The catalyst is preferably a tertiary amine compound such as triethylamine, dimethylcyclohexylamine, bis[(2-dimethylamino)ethyl]ether, 1,4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, or diethylbenzylamine.

[0048] Examples of the additive include a foam stabilizer such as a silicone surfactant, a fluorine-based surfactant, or an ionic surfactant. To increase the effective resin ratio, the content of the foam stabilizer in the curable urethane composition may be reduced. In other words, to obtain a polyurethane resin foam having a high effective resin ratio, the content of the foam stabilizer in the polyurethane resin foam may be less than 0.1% by mass, less than 0.05% by mass, or less than 0.01% by mass. Alternatively, the polyurethane resin foam may be substantially free of a foam stabilizer.

[0049] The mixture obtained in the mixing step is filled into a mold, cured, and molded into a cylindrical molded body. A general molding method can be used here. Then, a sheet-like polyurethane resin foam having a predetermined thickness is cut out from the molded body.

[0050] As described above, one embodiment has been shown as an example, but the polishing pad according to the present invention is not limited to the configuration of the above embodiment. Furthermore, the polishing pad according to the present invention is not limited by the above-described effects. The polishing pad according to the present invention can be modified in various ways without departing from the spirit and scope of the present invention. [Example]

[0051] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0052] (Raw materials used) Prepolymer A: A PTMG-containing prepolymer obtained by reacting polytetramethylene ether glycol (PTMG) with tolylene diisocyanate (TDI). Prepolymer B: A PPG-containing prepolymer obtained by reacting polypropylene glycol (PPG) with tolylene diisocyanate (TDI) Hardener: 4,4'-methylenebis(2-chloroaniline) (MOCA) Foaming agent: Water Catalyst: Tertiary amine compound (Tosoh Corporation, Toyocat L-33) Foam stabilizer: Silicone surfactant

[0053] Example 1 The raw materials shown in Table 1 below were mixed using a closed-type mixer equipped with a mixing head having a rotor, with the rotor rotation speed set to 2000 rpm. The mixture was filled into a mold and then cured to produce a polyurethane resin foam. The effective resin ratio and Young's modulus of the obtained polyurethane resin foam were measured by the above-mentioned measurement methods.

[0054] (Comparative Example 1) A polyurethane resin foam was produced in the same manner as in Example 1 except that the rotation speed of the rotor was set to 4000 rpm, and the effective resin ratio and Young's modulus were measured.

[0055] Example 2 A polyurethane resin foam was produced in the same manner as in Example 1, except that the formulation shown in Table 1 was used and the rotor rotation speed was set to 2500 rpm, and the effective resin ratio and Young's modulus were measured.

[0056] (Comparative Example 2) A polyurethane resin foam was produced in the same manner as in Example 1 except that an open mixer equipped with a mixing vessel and stirring blades was used and a foam stabilizer was added, and the effective resin ratio and Young's modulus were measured.

[0057] (Evaluation method) Using polishing pads made from each polyurethane resin foam, silicon wafers with oxide films formed thereon are polished under the polishing conditions shown in Table 2 below. Whether the mechanical polishing power has been improved is evaluated based on the polishing rate. The results are shown in Table 1.

[0058] A comparison of Example 1 and Comparative Example 1, which have similar Young's modulus and apparent density, suggests that Example 1, which has a higher effective resin ratio, has a higher polishing rate and therefore a higher mechanical polishing power. A similar tendency is also observed when comparing Example 2 and Comparative Example 2, which have similar Young's modulus and apparent density.

[0059] [Table 1]

[0060] [Table 2] [Explanation of symbols]

[0061] CI: reduced image, MA: measurement area, SA: square area, Pa: white pixels, Pb: black pixels

Claims

1. The polishing tool has a polyurethane resin foam that forms a polishing surface, In a binarized CT image showing a cross section in a plane direction perpendicular to the thickness direction of the polyurethane resin foam, a measurement region of 1200 μm × 1400 μm is divided into square regions of 100 μm × 100 μm, and for all pixels constituting each square region, white pixels indicating pores are assigned the number 0 and black pixels indicating resin are assigned the number 100. The total number of pixels in each square region is N, the number of white pixels assigned the number 0 is a, and the number of black pixels assigned the number 100 is b. The resin abundance ratio in each square region is calculated by (0 × a + 100 × b) / N, and the square region with a resin abundance ratio of 90 or more is defined as an effective resin region. A polishing pad having an effective resin ratio calculated by [(the number of effective resin regions) / (the total number of square regions)]×100 of 2% or more.

2. 2. The polishing pad according to claim 1, wherein the effective hardness calculated by [(the effective resin ratio) / 100] x (Young's modulus of the polyurethane resin foam) is 3 or more.

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