Polishing pad and wafer polishing method

Abstract

To provide a polishing pad and a method for polishing a wafer that are capable of polishing an oxide semiconductor wafer with high efficiency and high surface quality.SOLUTION: A polishing pad according to the present invention includes a matrix 13 containing a binder resin and having a plurality of pores 15a, 15b formed therein, and abrasive particles 11 held within the matrix 13 or the pores 15a, 15b. The binder resin is a thermoplastic fluoropolymer, and the abrasive particles 11 are diamond, the polishing pad having a density of 0.9 to 1.3 g / cm3, a durometer hardness (D) of 25 to 50, and a compressive modulus of elasticity of 1640 to 3250 MPa.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a polishing pad and a method for polishing a wafer. [Background technology]

[0002] Patent Documents 1 to 4 disclose conventional polishing pads. The polishing pads in Patent Documents 1 to 3 are made by impregnating a nonwoven fabric with a paste and then removing the solvent from the paste. The paste in Patent Document 1 consists of urethane, a solvent such as dimethylformamide, abrasive particles such as SiO2, and alkaline fine particles such as sodium carbonate. The paste in Patent Document 2 consists of an ether-based urethane and a solvent such as N,N-dimethylformamide. The paste in Patent Document 3 consists of urethane, a solvent, and a water repellent. By removing the solvent by drying or the like, the urethane is solidified while bonded to the nonwoven fabric. The polishing pad in Patent Document 4 is made using a paste made by mixing a binder resin, abrasive particles, and a solvent.

[0003] The polishing pad of Patent Document 1 is used to polish the outer peripheral edge of a disk-shaped wafer made of silicon or the like used in manufacturing semiconductor devices. Specifically, the wafer is held on a rotating table that can rotate around its center of rotation. The central axis of the wafer is positioned at the center of rotation of the rotating table. Meanwhile, a polishing pad is mounted on the upper end of a spindle so that the outer peripheral edge of the polishing pad abuts against the outer peripheral edge of the wafer. A polishing liquid is then supplied between the outer peripheral edge of the wafer and the outer peripheral edge of the polishing pad, and the rotating table and spindle are rotated while a predetermined load is applied. This allows the outer peripheral edge of the wafer to be polished. This makes it possible to suppress the occurrence of defects in semiconductor devices due to the outer peripheral edge of the wafer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-46838 [Patent Document 2] Japanese Patent Application Publication No. 2019-118981 [Patent Document 3] Japanese Patent Application Publication No. 2020-49639 [Patent Document 4] Patent No. 5511266 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is a demand for a polishing pad that can be used when the wafer is an oxide semiconductor such as gallium oxide (Ga2O3).

[0006] The present invention has been made in consideration of the above-mentioned conventional situation, and has as its object to provide a polishing pad and a wafer polishing method that can polish oxide semiconductor wafers with high efficiency and high surface quality. [Means for solving the problem]

[0007] The polishing pad of the present invention has a flat polishing surface, and is used to polish the upper or lower surface of a wafer, a base material containing a binder resin and having a plurality of pores formed therein; and abrasive particles held in the base material or the pores; the wafer is an oxide semiconductor; the binder resin is a thermoplastic fluoropolymer, the abrasive particles are diamond; Density 0.9~1.3g / cm 3 and Durometer hardness (D) is 25 to 50, It is characterized by a compressive elastic modulus of 1640 to 3250 MPa.

[0008] The method for polishing a wafer of the present invention includes a first step of preparing a wafer, a polishing pad, and a polishing liquid; a second step of polishing the wafer with the polishing pad while supplying the polishing liquid between the wafer and the polishing pad; the wafer is an oxide semiconductor; The polishing pad is composed of a polishing body including a base material containing a binder resin and having a plurality of pores formed therein, and abrasive particles held in the base material or the pores, the polishing liquid is a manganese-based slurry, the binder resin is a thermoplastic fluoropolymer, the abrasive particles are diamond; Density 0.9~1.3g / cm 3 and Durometer hardness (D) is 25 to 50, It is characterized by a compressive elastic modulus of 1640 to 3250 MPa.

[0009] The polishing pad of the present invention has a polishing surface composed of an abrasive body containing a base material and abrasive particles. The base material contains a binder resin and has a plurality of pores formed therein. The abrasive particles are held within the base material or the pores. Therefore, when a wafer is polished with the polishing pad of the present invention according to the wafer polishing method of the present invention, the pad exhibits excellent followability when pressed against the wafer, and good polishing can be achieved.

[0010] The polishing pad of the present invention uses a thermoplastic fluoropolymer binder resin and diamond abrasive grains, and has a specific density, durometer hardness (D), and compressive modulus. Test results by the inventors have shown that these properties enable the polishing of oxide semiconductor wafers with high efficiency and high surface quality while shortening processing time. [Effects of the Invention]

[0011] By using the polishing pad of the present invention, it is possible to polish a wafer made of an oxide semiconductor with high efficiency and high surface quality. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an SEM photograph of the polishing pad of Example 1 at 500x magnification. [Figure 2]FIG. 2 is an SEM photograph of the polishing pad of Example 1 at 2000 magnifications. [Figure 3] FIG. 3 is an SEM photograph of the polishing pad of Example 1 at 5000 magnifications. [Figure 4] FIG. 4 is a 500x SEM photograph of the polishing pad of Example 1 showing some large pores. [Figure 5] FIG. 5 is a 500x SEM photograph of the polishing pad of Example 1 showing other large pores. [Figure 6] FIG. 6 is a schematic enlarged cross-sectional view of the polishing pads of Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0013] The polishing pad of the present invention has a flat polishing surface. The polishing pad includes a base material containing a binder resin and having a plurality of pores formed therein, and abrasive particles held within the base material or the pores. This polishing pad is an abrasive-containing type polishing pad, also known as an LHA (Loosely Held Abrasive) pad.

[0014] Wafers made of oxide semiconductors such as gallium oxide (Ga2O3) can be polished. The inventors confirmed the effectiveness of the present invention using gallium oxide. They speculate that wafers made of sapphire (Al2O3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), etc. can also be polished.

[0015] When polishing an oxide semiconductor wafer, it is preferable to use a manganese-based slurry containing abrasive particles as the polishing liquid, because the manganese-based slurry contains manganese oxide (manganese oxide and potassium permanganate), alumina, and silica, and therefore has the property of weakening the oxide bonds of the oxide semiconductor through chemical action.

[0016] Thermoplastic fluoropolymers are used as binder resins. The LHA pad can use, as binder resins, polyethersulfone resins, rigid polyurethane foams, epoxy resins, fluorine-based synthetic resins such as polyvinyl fluoride, vinyl fluoride-hexafluoropropylene copolymers, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymers, polyethylene resins, polymethyl methacrylate, etc. However, according to the inventors' test results, thermoplastic fluoropolymers are preferred for the polishing pad of the present invention in terms of chemical resistance, flexibility, etc. The inventors have confirmed the effectiveness of the present invention by using gallium oxide for the wafer and polyvinylidene fluoride as the binder resin.

[0017] Diamond is used as the abrasive particles. Although the LHA pad can use silica, ceria, alumina, zirconia, titania, manganese oxide, barium carbonate, chromium oxide, boron carbide, iron oxide, etc., according to the inventors' test results, diamond is preferred for the polishing pad of the present invention because of its high Knoop hardness and excellent polishing durability.

[0018] According to the test results of the inventors, the polishing pad of the present invention has a density of 0.9 to 1.2 g / cm 3 The durometer hardness (D) is preferably 26 to 47, and the compressive modulus is preferably 1645.1 to 3241.7 MPa. According to the inventor's estimation, the density is preferably 0.9 to 1.3 g / cm 3 If the durometer hardness (D) is 25 to 50 and the compressive modulus is 1640 to 3250 MPa, similar effects can be expected.

[0019] According to the results of the inventors' tests, it is particularly preferable for the polishing body to contain silica particles held within the matrix or pores. Silica particles are softer than the diamond abrasive particles and provide a flexible support for the diamond.

[0020] It is particularly preferable that the pores consist of fine pores forming a three-dimensional network structure and large pores having a larger volume than the fine pores and communicating with the fine pores while opening onto the polishing surface. The large pores suppress the processing resistance during polishing of the wafer and reduce scratches on the wafer.

[0021] According to the test results of the inventors, it is preferable that the fine pores are 46.8 to 57.7% by volume and the large pores are 0 to 13.8% by volume.

[0022] (Examples and Comparative Examples) Examples 1 to 6 embodying the present invention and Comparative Examples 1 to 3 will be described below.

[0023] First, the following binder resin, abrasive particles, and solvent were prepared. (binder resin) PVDF (Polyvinylidene Fluoride) (abrasive particles) Diamond (average particle size: 5 μm) (solvent) NMP (N-methyl-2-pyrrolidone) (filler) Silica particles (average particle size: 200 nm) (pore-forming agent) Granulated sugar (average particle size 200 μm)

[0024] The binder resin, abrasive particles, solvent, filler, and pore-forming agent were mixed in the mass percentages shown in Table 1 to form pastes. Each of the resulting pastes was used to obtain a sheet-shaped molded body using a T-die. The solvent was removed from each molded body, and the binder resin was solidified.

[0025] [Table 1]

[0026] In this way, the polishing pads of Examples 1 to 6 were obtained. Each polishing pad was disk-shaped with a diameter of 300 mm and a thickness of 3.0 mm.

[0027] An SEM photograph of the polishing pad of Example 1 at 500x magnification is shown in Figure 1, an SEM photograph at 2000x magnification is shown in Figure 2, and an SEM photograph at 5000x magnification is shown in Figure 3. An SEM photograph of one large pore in the polishing pad of Example 1 at 500x magnification is shown in Figure 4, and an SEM photograph of another large pore at 500x magnification is shown in Figure 5.

[0028] As shown in Figures 1 and 2, the polishing pads of Examples 1 to 6 have a base material 13 and abrasive particles 11, as also shown in Figure 6. The base material 13 is made of a binder resin and has a plurality of pores 15a, 15b formed therein. The abrasive particles 11 are held within the base material 13 or the pores 15a. Each polishing pad also contains filler 12 held within the base material 13 or the pores 15a. As shown in Figures 3 and 4, the pores 15a, 15b of each polishing pad are composed of pores 15a forming a three-dimensional network structure and large pores 15b that are larger in volume than the pores 15a and that open to the polishing surface and communicate with the pores 15a.

[0029] The physical properties of the polishing pads of Examples 1 to 6 thus obtained were durometer hardness (D), density (g / cm 3 The results are shown in Table 2.

[0030] [Table 2]

[0031] The binder resin content (vol %), abrasive particle content (vol %), filler content (vol %), and pore content (vol %) were also measured. The results are shown in Table 3.

[0032] [Table 3]

[0033] The breakdown of the pore content, i.e., the volume percent of fine pores and the volume percent of large pores, was also measured. The results are shown in Table 4.

[0034] [Table 4]

[0035] (test) An unpolished wafer made of gallium oxide (β-Ga2O3) was prepared. The wafer was a disk with a diameter of 2 inches. A polishing machine (Engis' "EJW-400IFN") was also prepared.

[0036] Then, 200 wafers were polished under the following conditions using the polishing pads of Examples 1 to 6 or the polishing pads of Comparative Examples 1 to 4. The polishing pads of Comparative Examples 1 and 2 were commercially available hard urethane pads (hardness D: 60), and the polishing pads of Comparative Examples 3 and 4 were commercially available nonwoven fabric pads (hardness D: 30). Pressure: 40.6kPa Rotation speed: 60 / 60 (rpm) Polishing liquid flow rate: 10mL / min Polishing time: 60 minutes

[0037] For the polishing pads of Examples 1 to 6 and Comparative Examples 1 and 3, a manganese-based slurry having the following composition was used as the polishing liquid. Abrasive grains: alumina (4.10% by mass), silica (0.59% by mass), manganese oxide (0.03% by mass) Solution: Pure water (95.00% by mass), potassium permanganate (0.28% by mass)

[0038] For the polishing pads of Comparative Examples 2 and 4, a polishing liquid containing abrasive particles made of diamond was used.

[0039] The removal rate (nm / h) and the surface roughness Sa (nm) of the polished wafer were evaluated. The removal rate was calculated from the mass difference before and after polishing. The surface roughness Sa was measured using a white light interference microscope.

[0040] The polishing rate was rated as follows: ⊚ if 5000 nm / h or more, ◯ if 3000 nm / h or more and less than 5000 nm / h, △ if 2000 nm / h or more and less than 3000 nm / h, and × if less than 2000 nm / h.

[0041] The surface roughness Sa was evaluated as follows: less than 2.0 nm, ⊚; 2.0 nm or more but less than 3.0 nm, ◯; 3.0 nm or more but less than 4.0 nm, △; and 4.0 nm or more, ×.

[0042] Overall, if either the polishing rate or the surface roughness Sa was × or △, it was marked ×, if both were ○ or above it was marked ○, and if either one of them was ◎, it was marked ◎. The results are shown in Table 5.

[0043] [Table 5]

[0044] From Table 5, the polishing pads of Examples 1 to 3 were overall awarded an excellent rating, and the polishing pads of Examples 4 to 6 were awarded an excellent rating. In contrast, the polishing pads of Comparative Examples 1 to 4 were inferior in polishing rate and surface roughness Sa. This is presumably due to the following reasons.

[0045] That is, as shown in FIG. 6, in the polishing pads of Examples 1 to 6, the pores 15 are composed of small pores 15a and large pores 15b. The small pores 15a have a three-dimensional network structure. The large pores 15b have a larger volume than the small pores 15a and are open to the polishing surface 2 while communicating with the small pores 15a. The diamond abrasive particles 11 are contained within the small pores 15a of the base material 13 and are fixed to the base material 13 by point or surface contact. If an excessively large load is concentrated on a certain abrasive particle 11 during polishing, that abrasive particle 11 falls off the base material 13 and polishes while maintaining local freedom within the small pores 15a. At this time, the filler 12 flexibly supports the abrasive particles 11 within the small pores 15a, preventing excessive load concentration on the abrasive particles 11. This prevents deep scratches from occurring on the wafer.

[0046] Furthermore, it is presumed that the polishing pads of Examples 1 to 6 have large pores 15b, which improve flexibility and allow them to deform easily during processing, polishing while following the wafer. Thus, in the polishing pads of Examples 1 to 6, large pores 15b suppress the processing resistance during wafer polishing, reducing chipping of the wafer.

[0047] In particular, the polishing pads of Examples 1 to 6 have specific densities, durometer hardness (D), and compressive modulus while using polyvinylidene fluoride as the binder resin and diamond as the polishing grains 11. These characteristics enable shortening of processing time while polishing gallium oxide wafers with high efficiency and high surface quality.

[0048] In addition, this polishing method uses a manganese-based slurry as the polishing liquid. Therefore, it is thought that the polishing pads of Comparative Examples 1 to 4 intensively polish chemically unstable areas due to manganese oxide. In contrast, in the polishing pads of Examples 1 to 6, it is thought that the diamond abrasive particles come into mild contact with the wafer due to the binder resin, removing irregularities and scratches on the wafer surface, even though the deep polishing marks caused by manganese oxide are present.

[0049] The present invention has been described above in accordance with Examples 1 to 6, but it goes without saying that the present invention is not limited to the above Examples 1 to 6 and can be modified and applied as appropriate within the scope of the invention.

[0050] For example, in Examples 1 to 6, gallium oxide was polished, but the polishing pad and wafer polishing method of the present invention can also be applied to polishing wafers made of sapphire, lithium niobate, lithium tantalate, or the like. [Industrial Applicability]

[0051] The present invention can be used in semiconductor device manufacturing equipment and the like. [Explanation of symbols]

[0052] 15a, 15b...pores (15a...small pores, 15b...large pores) 13...Base material 11...Abrasive particles 12...Silica particles (filler)

Claims

1. A polishing pad having a flat polishing surface, which polishes the upper or lower surface of a wafer with the polishing surface in the presence of a polishing liquid, a base material containing a binder resin and having a plurality of pores formed therein; and abrasive particles held in the base material or the pores; the wafer is an oxide semiconductor; the binder resin is a thermoplastic fluoropolymer, the abrasive particles are diamond; Density 0.9 to 1.3 g / cm 3 and Durometer hardness (D) is 25 to 50, A polishing pad characterized in that the compressive elastic modulus is 1640 to 3250 MPa.

2. the wafer is made of gallium oxide; 2. The polishing pad according to claim 1, wherein the binder resin is made of polyvinylidene fluoride.

3. 3. The polishing pad according to claim 1, wherein the polishing body contains silica particles held within the matrix or the pores.

4. 2. The polishing pad according to claim 1, wherein the pores are composed of fine pores forming a three-dimensional network structure and large pores having a larger volume than the fine pores, opening onto the polishing surface and communicating with the fine pores.

5. The pores are 46.8 to 57.7% by volume; 5. The polishing pad according to claim 4, wherein the large pores are 0 to 13.8% by volume.

6. A first step of preparing a wafer, a polishing pad, and a polishing liquid; a second step of polishing the wafer with the polishing pad while supplying the polishing liquid between the wafer and the polishing pad; the wafer is an oxide semiconductor; The polishing pad is composed of a polishing body including a base material containing a binder resin and having a plurality of pores formed therein, and abrasive particles held in the base material or the pores, the polishing liquid is a manganese-based slurry, the binder resin is a thermoplastic fluoropolymer, the abrasive particles are diamond; Density 0.9 to 1.3 g / cm 3 and Durometer hardness (D) is 25 to 50, A method for polishing a wafer, characterized in that the compressive elastic modulus is 1640 to 3250 MPa.

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