Abrasive cloth

Abstract

To provide a polishing cloth capable of suppressing variations in fine hardness.SOLUTION: A polishing cloth, which includes a non-woven fabric and a resin impregnated in the non-woven fabric as formation materials forming the polishing cloth, has Asker-C hardness of 80 or more, a quartile range of an average value in a vertical abundance ratio with 100 μm width of the formation materials of 10.5 or less, a compression ratio of 5% or less, a thickness of 0.8 mm or more and 3.0 mm or less, and apparent densities of the formation materials of 0.30 g / cm3 or more and 0.50 g / cm3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Abrasive cloths are used to polish objects such as silicon wafers (see, for example, Patent Document 1). The materials forming the abrasive cloth include a nonwoven fabric and a resin impregnated into the nonwoven fabric.

[0003] It is known that such polishing cloths can cause edge sagging if they are too flexible. Conventionally, edge sagging has been reduced by increasing the amount of resin impregnated into the polishing cloth to make it harder, thereby preventing excessive contact with the edge. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-43811 Summary of the Invention [Problem to be solved by the invention]

[0005] However, increasing the resin content makes it easier for localized unevenness to occur at intervals of approximately 100 to 200 μm across the entire polishing cloth. In particular, unevenness due to vertical entanglement of the nonwoven fabric causes minute variations in hardness, resulting in localized excessive contact and reducing the flatness of the workpiece.

[0006] In view of the above problems, an object of the present invention is to provide a polishing cloth that can suppress minute variations in hardness. [Means for solving the problem]

[0007] The polishing cloth of the present invention is a polishing cloth having a nonwoven fabric and a resin impregnated into the nonwoven fabric as the forming material of the polishing cloth, and has an Asker-C hardness of 80 or more, and the interquartile range of the average value of the longitudinal abundance ratio of the forming material over a width of 100 μm is 10.5 or less.

[0008] This polishing cloth has an Asker-C hardness of 80 or more and an interquartile range of the average value of the longitudinal abundance ratio of the forming material over a 100 μm width of 10.5 or less, which reduces unevenness due to longitudinal entanglement of the nonwoven fabric. As a result, it is possible to suppress minute variations in hardness that cannot be reflected by the Asker-C hardness alone. [Effects of the Invention]

[0009] As described above, the present invention can provide a polishing cloth that can suppress minute variations in hardness. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing the interquartile range of the average value of the longitudinal abundance ratio of the forming material in a width of 100 μm, and the flatness of the workpiece, for the polishing pads of Comparative Example 1 and Examples 1 to 3. [Figure 2] 10 is a graph showing the interquartile range of the average value of the vertical abundance ratio of the forming material in a width of 100 μm, and the flatness of the object to be polished, for the polishing pads of Comparative Example 2 and Examples 4 and 5. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described below.

[0012] The polishing cloth according to this embodiment includes, as the forming materials for forming the polishing cloth, a nonwoven fabric and a resin impregnated into the nonwoven fabric.

[0013] The polishing cloth according to this embodiment has an Asker-C hardness of 80 or more, preferably 85 or more. On the other hand, the Asker-C hardness is preferably 95 or less, from the viewpoint of preventing defects (e.g., scratches) from occurring on the workpiece to be polished. The Asker-C hardness satisfies the above range when two non-overlapping regions (N=2) of one polishing cloth are measured and both regions satisfy the above range.

[0014] The Asker-C hardness is measured using a rubber hardness tester conforming to JIS K 7312 and is commonly used as an index of the hardness of a polishing cloth. The Asker-C hardness is measured on one surface of the polishing cloth, i.e., the polishing surface. The indenter has a diameter of 5.08 mm and a height of 2.54 mm. For example, when the Asker-C hardness is 90, the measurement range is a circle with a diameter of 2.2 mm. Therefore, the Asker-C hardness alone cannot reflect minute variations in hardness that occur at intervals of approximately 100 to 200 μm.

[0015] As a result of intensive research, the inventors have found that the average value of the longitudinal abundance ratio obtained by image analysis in the thickness direction of the polishing pad is proportional to the hardness. Based on this finding, they have found that by narrowing the measurement range to a width of 100 μm and specifying the longitudinal abundance ratio within a predetermined range, it is possible to suppress minute variations in hardness.

[0016] That is, in the polishing cloth according to this embodiment, the interquartile range of the average value of the longitudinal abundance ratio of the forming material in a 100 μm width is 10.5 or less. The interquartile range of the average value of the longitudinal abundance ratio is preferably 10.0 or less, and more preferably 9.0 or less. The case where the interquartile range of the average value of the longitudinal abundance ratio satisfies the above range means that when measurements are taken in two non-overlapping regions (N=2) for one polishing cloth, the above range is satisfied in both regions.

[0017] The interquartile range of the average value of the vertical abundance ratio of the forming material in a width of 100 μm can be determined as follows.

[0018] First, a measurement area is photographed in a 2000 μm × 2000 μm field of view on a slice plane (cross section) perpendicular to the surface of the abrasive cloth, and multiple small areas of 100 μm × 100 μm are extracted from the measurement area. For example, for a 1.3 mm thick abrasive cloth, 144 small areas of 100 μm × 100 μm are extracted from a measurement area of ​​1200 μm (parallel to the surface of the abrasive cloth) × 1200 μm (perpendicular to the surface of the abrasive cloth, i.e., in the thickness direction of the abrasive cloth). At this time, the measurement area in the thickness direction depends on the thickness of the abrasive cloth.

[0019] The arithmetic mean of the abundance ratios of the vertical rows aligned from the front to the back of the polishing cloth was taken as the "average value of the vertical abundance ratio in a 100 μm width." In this measurement, 17 images of the cross section of the polishing cloth were taken at 100 μm intervals in one measurement, and the "average value of the vertical abundance ratio in a 100 μm width" was the average value of the vertical abundance ratios for 12 rows x 17 images = 204 rows, and measurements were taken in two non-overlapping areas (N = 2) for one polishing cloth.

[0020] The abundance ratio of the forming material in each 100 μm x 100 μm small region means the proportion of the area in which the forming material is present when the total area of ​​each 100 μm x 100 μm small region is taken as 100%.

[0021] In the measurement, the polishing cloth is photographed by CT-scan. Specifically, a slice plane (cross section) perpendicular to the surface of the polishing cloth is photographed every 100 μm, and two measurement areas are photographed in a 2000 μm × 2000 μm field of view (the two measurement areas do not overlap), and in each measurement area, multiple small areas of 100 μm × 100 μm are extracted, and the image of each small area of ​​100 μm × 100 μm is subjected to a binarization process to classify it into voids and areas other than voids (areas where the forming material exists), thereby measuring the presence ratio (area ratio).

[0022] The CT device can be a three-dimensional measurement X-ray CT device (TDM1000H-1) manufactured by Yamato Scientific Co., Ltd. The CT image processing software can be VGStudio Max 2.1 manufactured by Japan Visual Science Volume Graphics Co., Ltd. Furthermore, the image analysis software used to calculate the abundance ratio (area ratio) of the forming material can be ImageJ (Rasband, WS, US National Institutes of Health, Bethesda, Maryland, USA).

[0023] For example, the abundance ratio (area ratio) of the forming material is measured under the following conditions.

[0024] In the measurement, the measurement area of ​​the polishing pad is continuously measured with the following field of view size. Field of view size (length x width x height): 2,000 μm x 2,000 μm x full thickness

[0025] The measurement conditions are as follows: Views per rotation: 1500 Frames / Views: 10 X-ray tube voltage (KV): 28,000 Enlargement axis position (mm): 7.416 Reconstruction pixel size X (mm): 0.003880 Reconstruction pixel size Y (mm): 0.003880 Reconstruction pixel size Z (mm): 0.003880

[0026] The binarization process for classifying each measurement region into voids and non-void portions (portions where the forming material is present) is as follows.

[0027] In the binarization process, the image processing software VGStudio Max is used to adjust the contrast of the image of the measurement area in order to classify it into voids and areas other than voids (areas where the forming material is present). The contrast adjustment is performed in ramp mode.

[0028] The contrast is adjusted so that the difference between the voids and the areas other than the voids (areas where the forming material is present) becomes clear.

[0029] In VGStudio Max, contrast adjustment is referred to as "opacity adjustment." Specifically, in the VGStudio Max opacity adjustment screen, the lower limit of the gray value is set to the peak, and then the upper limit of the gray value is set to the range of "peak value + 100 ± 5." Note that the light transmittance differs depending on the material, so the contrast adjustment range is not necessarily limited to this.

[0030] After adjusting the contrast of the 2D image, an image of the slice cross section, which is the measurement area, is acquired. Note that the viewing angle must be set to be large relative to the measurement area, so when saving the cross section as an image, the surface of the polishing cloth should be positioned at the top of the image.

[0031] Next, the abundance ratio of the forming material is measured for the image of the measurement area obtained above using the image processing software ImageJ.

[0032] The measurement range in ImageJ is 1200 μm × the thickness of the polishing cloth. For example, for a 1.0 mm thick polishing cloth, the upper left corner of the image data is set to (x,y) = (0 pix,0 pix), and the measurement range is extracted from the (120,10) position, measuring 312 pixels (= 1201.2 μm) horizontally and 234 pixels (= 900.9 μm) vertically. The image type is then converted from RGB color to 8-bit, and the image is binarized. Under these binarization conditions, the area with a gradation range of "129" to "255" corresponds to the area where the forming material is present. The image data is then reduced to 12 pixels horizontally and 9 pixels vertically. Each pixel of this reduced image corresponds to a 100 μm × 100 μm surface. This operation is performed every 100 μm on 17 images perpendicular to the polishing surface. In the binarization process in ImageJ, the areas with a gradation range of "129" to "255" are considered to be areas other than voids (areas where forming material exists).

[0033] The compressibility of the polishing cloth according to this embodiment is preferably 5% or less, and more preferably 3.5% or less. The compressibility satisfies the above range when the compressibility is measured in two non-overlapping regions (N=2) of one polishing cloth and both regions satisfy the above range.

[0034] The compressibility can be determined by the following method: using a compression elasticity tester (indenter area: 50 mm) according to JIS L1096:2010. 2 ) and applied a pressure of 300gf / cm 2 The thickness T1 of the polishing cloth was measured after it was pressed in the thickness direction with a pressure of 1800 gf / cm 2 After pressing the polishing pad in the thickness direction at a pressure of 1000 kJ / cm2 and holding the pressure for 60 seconds, the thickness T2 of the polishing pad is measured, and the compressibility can be calculated using the following formula. Compression ratio = (T1-T2)×100 / T1

[0035] The thickness of the polishing cloth according to this embodiment is preferably 0.8 mm or more and 3.0 mm or less, more preferably 1.0 mm or more and 2.0 mm or less. Having a thickness of 0.8 mm or more, the polishing cloth has the advantage of easily mitigating the adverse effects on polishing performance due to the state of the polishing machine surface plate. This also has the advantage of, for example, making it easier to stably flatten the workpiece. On the other hand, having a thickness of 3.0 mm or less, the polishing cloth has the advantage of reducing the amount of deformation of the polishing cloth during polishing, thereby reducing the occurrence of edge sagging of the workpiece. The thickness satisfies the above range when measured in two non-overlapping regions (N=2) on one polishing cloth, and both regions satisfy the above range.

[0036] The polishing cloth according to this embodiment preferably has a compressibility of 5% or less and a thickness of 0.8 mm to 3.0 mm, which can further suppress minute variations in hardness.

[0037] The polishing cloth according to this embodiment preferably has an apparent density of the material of the polishing cloth of 0.30 g / cm 3 More than 0.50g / cm 3 or less, more preferably 0.40 g / cm 3 More than 0.50g / cm 3 The apparent density of the forming material is 0.30 g / cm or less. 3 More than 0.50g / cm 3 By satisfying the above condition, minute variations in hardness can be further suppressed. The apparent density can be measured based on JIS K7222:2005. The apparent density satisfies the above range when it is measured in two non-overlapping regions (N=2) on one polishing cloth, and both regions satisfy the above range.

[0038] Examples of fibers that make up the nonwoven fabric include polyester fibers and nylon fibers.

[0039] The nonwoven fabric preferably has a basis weight of 200 g / m 2 More than 600g / m2 The nonwoven fabric has a basis weight of 200 g / m or less. 2 By setting the nonwoven fabric weight to 200 g / m or more, the hardness is easily increased, which has the advantage that the edge sagging of the workpiece is less likely to occur. 2 More than 600g / m 2 By satisfying this condition, the polishing surface is likely to have an appropriate proportion of voids, which has the advantage of making it easier to suppress fluctuations in polishing performance due to clogging of the voids with polishing debris and the like.

[0040] Examples of the resin include urethane resin.

[0041] Examples of the object to be polished with the polishing cloth according to this embodiment include a silicon wafer.

[0042] The polishing cloth according to this embodiment is configured as described above. Next, a method for manufacturing the polishing cloth according to this embodiment will be described.

[0043] The method for manufacturing the polishing cloth according to this embodiment will be described below by taking as an example a method in which a two-stage impregnation process is performed in which a nonwoven fabric is wet-impregnated with a urethane resin and then dry-impregnated with the urethane resin.

[0044] In the wet impregnation, a urethane resin is dissolved in a water-soluble organic solvent to obtain a first impregnation liquid. Examples of the water-soluble organic solvent include dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and dimethylacetamide. The first impregnation liquid may contain a filler, such as carbon black. The first impregnation liquid may also contain a dispersion stabilizer, such as a surfactant.

[0045] Next, the nonwoven fabric is immersed in the first impregnation liquid, and then the nonwoven fabric is immersed in water. As a result, the water-soluble organic solvent in the first impregnation liquid attached to the nonwoven fabric is replaced with water, the urethane resin coagulates, and the urethane resin adheres to the surface of the nonwoven fabric.

[0046] In the dry impregnation, a prepolymer having an isocyanate group as a terminal group, a curing agent which is an organic compound having active hydrogen, and an organic solvent are mixed to obtain a second impregnation liquid. Examples of the organic solvent include methyl ethyl ketone, acetone, alcohol, and ethyl acetate.

[0047] The wet-impregnated nonwoven fabric is then immersed in a second impregnation liquid, and the nonwoven fabric immersed in the second impregnation liquid is heated in a drying oven, which evaporates the organic solvent and causes a curing reaction between the prepolymer and the curing agent to form a urethane resin, resulting in additional urethane resin adhering to the surface of the nonwoven fabric.

[0048] The polishing cloth according to this embodiment has the above-described structure and therefore has the following advantages.

[0049] That is, the polishing cloth according to this embodiment is a polishing cloth having a nonwoven fabric and a resin impregnated into the nonwoven fabric as the forming material of the polishing cloth, and has an Asker-C hardness of 80 or more, and the interquartile range of the average value of the longitudinal abundance ratio of the forming material over a width of 100 μm is 10.5 or less.

[0050] This polishing cloth has an Asker-C hardness of 80 or more and an interquartile range of the average value of the longitudinal abundance ratio of the forming material over a 100 μm width of 10.5 or less, which reduces unevenness due to longitudinal entanglement of the nonwoven fabric. As a result, it is possible to suppress minute variations in hardness that cannot be reflected by the Asker-C hardness alone.

[0051] The polishing cloth according to the present invention is not limited to the above-described embodiment. Furthermore, the polishing cloth according to the present invention is not limited by the above-described effects. Various modifications can be made to the polishing cloth according to the present invention without departing from the spirit and scope of the present invention. [Example]

[0052] Next, the present invention will be described more specifically with reference to examples and comparative examples.

[0053] Polishing cloths were prepared as examples whose physical properties are shown in Tables 1 and 2. Also, polishing cloths (commercially available products) were prepared as comparative examples whose physical properties are shown in Tables 1 and 2. The Asker-C hardness, compressibility, apparent density of the forming material, average value of the longitudinal abundance ratio of the forming material in a 100 μm width, and interquartile range of the average value were measured by the methods described above.

[0054] The flatness of the polishing cloths having a thickness of 1.2 to 1.3 mm and the polishing cloths having a thickness of 0.9 to 1.1 mm was evaluated under the following conditions.

[0055] Polishing cloth with a thickness of 1.2 to 1.3 mm: Comparative Example 1, Examples 1 to 3 The GBIR was measured from the wafer shape when the wafer was polished using the polishing cloth. The polishing was performed by setting the polishing cloth in the double-sided polisher and then performing a dressing treatment before polishing. The GBIR and ESFQR of the wafer were calculated based on the GBIR / ESFQR values ​​that were most improved within the gap range of 0 to 3 μm. The results are shown in Table 1 and Figure 1.

[0056] The polishing conditions are as follows: Polishing machine: Speed ​​FAM 20B Dresser: Speed ​​FAM genuine dresser #100 / #120 Gap setting: 0 to 3 μm Grinding load: 1500 kg Rotation speed: 10 rpm Wafer: 12 inch P-wafer Polishing solution: Solution with solid content (115°C) 36.6%, average particle size 108 nm, pH = 11.3.

[0057] Polishing pads with a thickness of 0.9 to 1.1 mm: Comparative Example 2, Examples 4 and 5 For polishing, the polishing cloth was set in the single-sided polishing machine, and then dressed before polishing. However, since single-sided polishing is significantly affected by the shape before polishing, the difference between the shape before and after polishing was analyzed and flatness was evaluated in the form of differential GBIR. Furthermore, because differential GBIR is a parameter that correlates well with the polishing rate, shape comparisons were made in the form of differential GBIR / polishing rate. The results are shown in Table 2 and Figure 2.

[0058] The polishing conditions are as follows: Polishing machine:Poli762 Dresser: Kinik Dresser #150 Polishing pressure: 300gf / cm 2 Rotation speed Head / Platen: 40 / 43 rpm Wafer: 8" (P-) Polishing fluid: NP6610 (manufactured by Nitta DuPont Co., Ltd.) Add 7.14% to DIW (pure water) Polishing fluid flow rate: 600 mL / min

[0059] [Table 1]

[0060] [Table 2]

[0061] As shown in Tables 1 and 2 and FIGS. 1 and 2, the polishing cloths of the examples that satisfy all of the constituent requirements of the present invention suppress minute variations in hardness, and as a result, the flatness of the wafer is good.

Claims

1. A polishing cloth comprising a nonwoven fabric and a resin impregnated in the nonwoven fabric as a forming material for forming the polishing cloth, Asker-C hardness is 80 or more, A polishing cloth in which the interquartile range of the average value of the longitudinal abundance ratio of the forming material in a width of 100 μm is 10.5 or less.

2. 2. The polishing cloth according to claim 1, wherein the compressibility is 5% or less and the thickness is 0.8 mm or more and 3.0 mm or less.

3. The apparent density of the forming material is 0.30 g / cm ３ 0.50g / cm or more ３ 3. The polishing cloth according to claim 1, wherein:

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