Polishing pad and wafer polishing method

Abstract

To provide a polishing pad which can polish a polished object with high efficiency, and hardly causes polishing failure in the polished object.SOLUTION: A polishing pad constitutes a polishing surface for polishing a polished object in the presence of a polishing liquid, and has a polishing layer containing a binder resin and innumerable polishing particles. The binder resin is composed of polyvinylidene fluoride. A ratio of initial tensile strength that is tensile strength in an unused state to post-treatment tensile strength that is tensile strength after having been immersed in a strong acid liquid of pH1 from the unused state is 52% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A known wafer polishing apparatus includes a platen and a carrier. The platen has a first fixed surface extending in a direction perpendicular to a first axis and is rotated about the first axis. The carrier has a second fixed surface extending in a direction perpendicular to a second axis parallel to the first axis and facing the first fixed surface, and is rotated about the second axis.

[0003] When using this wafer polishing apparatus to polish flat wafers such as SiC and GaN wafers, a polishing body is used, which has a polishing surface and a fixed surface facing away from the polishing surface and spaced apart in the thickness direction from the polishing surface. The fixed surface of the polishing body is fixed to a first fixing surface of a surface plate, and the flat wafer is fixed to a second fixing surface of a carrier. The surface plate and carrier are then rotated while the polishing body and wafer are brought into contact with each other under a predetermined surface pressure in the presence of a polishing liquid.

[0004] When the polishing body is made of a general nonwoven fabric or hard urethane, a polishing liquid containing abrasive particles is used. Furthermore, as disclosed in Patent Documents 1 to 3, when the polishing body is made of a resin and has a base material with a plurality of pores formed therein and abrasive particles held in the base material or the pores, a polishing liquid containing no abrasive particles can be used. In this way, wafer polishing can be performed. When the polishing liquid contains a chemical such as alkali, the wafer is polished in a CMP (Chemical Mechanical Polishing) process. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4266579 [Patent Document 2] Patent No. 5511266 [Patent Document 3] Patent No. 6636634 Summary of the Invention [Problem to be solved by the invention]

[0006] However, according to the inventors' tests, when the object to be polished is a nitride such as gallium nitride (GaN) or aluminum nitride (AlN), which has high hardness and is chemically stable, conventional polishing pads cannot polish with high polishing efficiency and high surface quality, and there is a risk of polishing defects. Furthermore, when the polishing liquid is strongly acidic, the polishing pad is easily deteriorated, and there is also a risk of polishing defects.

[0007] The present invention has been made in view of the above-mentioned conventional circumstances, and aims to provide a polishing pad that can polish an object to be polished with high efficiency and that is less likely to cause polishing defects on the object to be polished. wafer The problem to be solved is to provide a polishing method. [Means for solving the problem]

[0008] The polishing pad of the present invention constitutes a polishing surface for polishing an object to be polished in the presence of a polishing liquid, and has a polishing layer containing a binder resin and numerous abrasive particles, the binder resin is made of polyvinylidene fluoride, The ratio of the initial tensile strength, which is the tensile strength in an unused state, to the post-treatment tensile strength, which is the tensile strength after immersion in a strong acidic solution of pH 1 from the unused state, is 100.0% and The post-treatment tensile strength was evaluated by immersing the unused polishing pad in the strong acid solution at 25°C for 60 hours; The strong acid solution is prepared by adding nitric acid to a 4% by mass aqueous solution of potassium permanganate to adjust the pH to 1; The object to be polished is a nitride.

[0009] According to the inventors' tests, the polishing pad of the present invention, since the binder resin is made of polyvinylidene fluoride, can polish the object to be polished with high polishing efficiency and high surface quality even if the object is a difficult-to-process material. In addition, this polishing pad has a ratio of initial tensile strength to tensile strength after processing of 100.0% Therefore, even if the polishing liquid is strongly acidic, the polishing pad is unlikely to deteriorate.

[0010] The wafer polishing method of the present invention includes a first step of preparing a workpiece to be polished, a polishing pad, and a polishing liquid; a second step of polishing the surface of the object to be polished with the polishing surface of the polishing pad while supplying the polishing liquid between the object to be polished and the polishing pad; the polishing pad has a polishing layer that forms the polishing surface and contains polyvinylidene fluoride and countless abrasive particles; The polishing pad has a ratio of an initial tensile strength, which is a tensile strength in an unused state, to a post-treatment tensile strength, which is a tensile strength after immersion in a strong acidic solution of pH 1 from the unused state. 100.0% and The post-treatment tensile strength was evaluated by immersing the unused polishing pad in the strong acid solution at 25°C for 60 hours; The strong acid solution is prepared by adding nitric acid to a 4% by mass aqueous solution of potassium permanganate to adjust the pH to 1; The object to be polished is a nitride, The second step is characterized in that the polishing surface is pressed against the surface to be polished with a predetermined pressing force, and at least one of the object to be polished and the polishing pad is rotated relative to one another.

[0011] Departure The inventors confirmed the effects of the present invention when the object to be polished was a nitride such as GaN or AlN. , release The inventors confirmed the effectiveness of the present invention when the polishing solution was strongly acidic with a pH of 1. [Effects of the Invention]

[0012] The polishing pad of the present invention can polish an object to be polished with high efficiency and is less likely to cause polishing defects on the object to be polished. wafer The polishing method can polish the object to be polished with high efficiency and is less likely to cause polishing defects on the object to be polished. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic enlarged view of the polishing pad of Example 1. [Figure 2] FIG. 2 is a side view showing the test specimen. DETAILED DESCRIPTION OF THE INVENTION

[0014] The polishing pad of the present invention has an abrasive layer containing a binder resin and numerous abrasive particles. The abrasive layer has a resin matrix with a plurality of pores formed therein, and abrasive particles held in the matrix or the pores. This abrasive layer constitutes the polishing surface.

[0015] The binder resin is polyvinylidene fluoride (PVDF). The abrasive particles may be silica, ceria, alumina, diamond, zirconia, titania, manganese oxide, barium carbonate, chromium oxide, boron carbide, iron oxide, etc. These may be used alone or in combination of two or more.

[0016] The polishing pad of the present invention has a ratio of initial tensile strength, which is the tensile strength in an unused state, to post-treatment tensile strength, which is the tensile strength after immersion in a strong acidic solution of pH 1 from an unused state. 100.0% It is desirable that the ratio of initial tensile strength to post-treatment tensile strength is high. 。

[0017] The post-treatment tensile strength can be evaluated by immersing an unused polishing pad in a strong acid solution at 25° C. for 60 hours. The inventors confirmed the effects of the present invention using this standard.

[0018] The strong acid solution can be prepared by adding nitric acid to a 4 mass % aqueous potassium permanganate solution and adjusting the pH to 1. The inventors confirmed the effects of the present invention using this strong acid solution.

[0019] The polishing pad of the present invention can be manufactured by a manufacturing method comprising the following three steps: In the first step, a paste containing a binder resin made of PVDF, abrasive particles, and a solvent is prepared; in the second step, the paste is molded into a sheet-like compact; and in the third step, the compact is immersed in a replacement liquid, and the solvent in the compact is replaced with the replacement liquid to form countless pores.

[0020] The paste contains a binder resin, numerous abrasive particles, and a solvent. Examples of solvents that can be used include N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, ethyl acetate, and methyl ethyl ketone. These may be used alone or in combination.

[0021] In the second step, it is preferable to cure the molded body until it gels. In this case, the base material becomes mesh-like, and the ratio of the initial tensile strength to the tensile strength after treatment tends to be high. The inventors confirmed this tendency when PVDF was used as the binder resin and N-methyl-2-pyrrolidone was used as the solvent.

[0022] The paste may also contain alkaline fine particles such as sodium carbonate, piperazine, potassium hydroxide, sodium hydroxide, calcium oxide, potassium carbonate, and magnesium oxide. The paste may also contain a water repellent such as a fluorine-based water repellent, a silicon-based water repellent, a hydrocarbon-based water repellent, or a metal compound-based water repellent. Furthermore, the paste may also contain a pigment such as an inorganic pigment such as titanium dioxide, calcium carbonate, or carbon black, or an organic pigment such as an azo pigment or a polycyclic pigment. These may be used alone or in combination of two or more.

[0023] The polishing liquid may be pure water, oil-based, or may contain an acidic or alkaline chemical. The polishing liquid may also contain abrasive particles.

[0024] (Examples and Comparative Examples) Example 1 embodying the present invention and Comparative Examples 1 and 2 will be described below.

[0025] The polishing pads of Example 1 and Comparative Example 1 were manufactured by the following steps 1 to 3. First, in the first step, the following binder resin, solvent, and abrasive particles were prepared. (binder resin) PVDF (Polyvinylidene Fluoride) PES (Polyethersulfone) (solvent) N-Methyl-2-pyrrolidone (abrasive particles) Silica (SiO2) (average particle size: 0.3 μm)

[0026] As shown in Table 1, the binder resin in Example 1 was PVDF, and the binder resin in Comparative Example 1 was PES. In Example 1, 15% by mass of binder resin, 15% by mass of abrasive particles, and 70% by mass of solvent were mixed to form a paste. In Comparative Example 1, 25% by mass of binder resin, 25% by mass of abrasive particles, and 50% by mass of solvent were mixed to form a paste.

[0027] [Table 1]

[0028] In the second step, the paste obtained in the first step is molded into a sheet-like compact using a molding device such as a T-die. This molding method is not limited to this as long as it can achieve a uniform thickness to a certain extent. In this second step, the compact is cured until it gels.

[0029] In the third step, the compacts were immersed in the replacement liquid. After a predetermined time, they were removed from the replacement liquid and dried. During this time, the inventors observed that the solvent in each compact was replaced with the replacement liquid, resulting in the formation of fine pores.

[0030] After a predetermined time had passed, the compact was removed from the replacement liquid. All of the solvent in the compact was replaced by the replacement liquid, solidifying it into a solidified body. The solidified body was dried and ground to a predetermined thickness to obtain polishing pads (diameter 30 cm) of Example 1 and Comparative Example 1.

[0031] Each of the polishing pads of Example 1 and Comparative Example 1 has a base material made of resin with a plurality of pores formed therein, and abrasive particles held in the base material or the pores. In particular, the polishing pad of Example 1 has a mesh-like base material 1, and abrasive particles 5 are held in the pores 3 between the base material 1, as shown in Figure 1.

[0032] The polishing pad of Comparative Example 2 is a hard pad used for loose abrasive polishing. This polishing pad is a known pad made of nonwoven fabric (Nitta Haas, product number SUBA600) and does not contain abrasive grains.

[0033] (test) A wafer polishing machine (Engis EJW-380), polishing pads of Example 1 and Comparative Examples 1 and 2, and a GaN bare wafer (2 inch) were prepared, and the GaN bare wafer was polished under the following conditions. Polishing fluid flow rate: 10 mL / min Load: 85kPa Rotation speed of the surface plate: 60 rpm Carrier rotation speed: 60 rpm Processing time: 60 minutes Polishing liquid: In Example 1 and Comparative Example 1, a polishing liquid (25°C) was used in which nitric acid was added to a 4 mass% aqueous solution of potassium permanganate to adjust the pH to 1. In Comparative Example 2, 5 mass% of silica (average particle size: 0.3 μm) was added as abrasive particles to the polishing liquid to prepare a polishing liquid (25°C).

[0034] The GaN bare wafer was polished by the polishing surface of each polishing pad by rotating the surface plate and the carrier while supplying a polishing liquid between the GaN bare wafer and each polishing pad.

[0035] The polishing rate (nm / hour) was measured using Keyence's "SI-FR80R," the surface roughness Sa (nm) after polishing was measured using Nikon's "BW-D501," and the presence or absence of scratches was measured using Lessertec's "OPTELICS HYBRID."

[0036] 2 were cut out from the polishing pads of Example 1 and Comparative Examples 1 and 2 before and after the polishing test. The dimensions a to d shown in the figure of each test piece 15 are as follows: a=15(mm) b=20(mm) c=60(mm) d=10(mm) Thickness = 2.5 (mm)

[0037] The tensile strength (maximum yield load / cross-sectional area) (MPa) of each test piece was measured under the following conditions. Testing machine: Universal testing machine (Instron 5569) Test conditions: JIS K6550 compliant

[0038] The ratio (%) of the initial tensile strength, which is the tensile strength before use, to the post-treatment tensile strength, which is the tensile strength after the polishing test, was then calculated. In other words, the strong acid solution was a polishing solution.

[0039] In addition, the polishing pad was visually inspected after the polishing test, and the degree of resin deterioration was evaluated by marking it as "x" if resin deterioration was observed and marking it as "o" if no resin deterioration was observed.

[0040] Table 2 shows the polishing rate, surface roughness Sa, presence or absence of scratches, tensile strength ratio, and degree of deterioration.

[0041] [Table 2]

[0042] From Table 2, it can be seen that the polishing pads of Example 1 and Comparative Example 1 can polish GaN bare wafers with high efficiency and high surface quality. Furthermore, the polishing pad of Example 1 is resistant to deterioration even when the polishing solution is strongly acidic. The polishing pad of Example 1 has a binder resin made of polyvinylidene fluoride, and the ratio of the initial tensile strength to the tensile strength after treatment is 100.0% This is because, it is understood that the polishing pad of Example 1 is less likely to cause polishing defects on bare GaN wafers.

[0043] Although the present invention has been described above in accordance with Example 1, it goes without saying that the present invention is not limited to the above Example 1 and can be modified and applied as appropriate within the scope of the spirit of the present invention.

[0044] For example, in Example 1, a bare GaN wafer was polished, but the polishing pad and wafer polishing method of the present invention can also be applied to polishing wafers made of AlN or AlGaN, or other nitrides such as Si3N4.

[0045] Furthermore, the polishing pad and wafer polishing method of the present invention can be applied to polishing uneven parts of the workpiece, such as the outer peripheral edge of a wafer, due to the high acid resistance of the polishing pad of the present invention. [Industrial Applicability]

[0046] The present invention can be used in semiconductor device manufacturing equipment. [Explanation of symbols]

[0047] 1...Base material 3...Stoma 5...Abrasive particles

Claims

1. A polishing pad having a polishing layer containing a binder resin and numerous abrasive particles, which constitutes a polishing surface for polishing an object to be polished in the presence of a polishing liquid, the binder resin is made of polyvinylidene fluoride, the ratio of the initial tensile strength, which is the tensile strength in an unused state, to the post-treatment tensile strength, which is the tensile strength after immersion in a strong acidic solution of pH 1 from the unused state, is 100.0%; The post-treatment tensile strength was evaluated by immersing the unused polishing pad in the strong acid solution at 25° C. for 60 hours. The strong acid solution is prepared by adding nitric acid to a 4% by mass aqueous solution of potassium permanganate to adjust the pH to 1; A polishing pad characterized in that the object to be polished is a nitride.

2. 2. The polishing pad of claim 1, wherein the nitride is GaN.

3. A first step of preparing an object to be polished, a polishing pad, and a polishing liquid; a second step of polishing the surface of the object to be polished with the polishing surface of the polishing pad while supplying the polishing liquid between the object to be polished and the polishing pad, the polishing pad has a polishing layer that forms the polishing surface and contains polyvinylidene fluoride and countless abrasive particles; The polishing pad has a ratio of an initial tensile strength, which is a tensile strength in an unused state, to a post-treatment tensile strength, which is a tensile strength after immersion in a strong acidic solution of pH 1 from the unused state, of 100.0%; The post-treatment tensile strength was evaluated by immersing the unused polishing pad in the strong acid solution at 25° C. for 60 hours. The strong acid solution is prepared by adding nitric acid to a 4% by mass aqueous solution of potassium permanganate to adjust the pH to 1; The object to be polished is a nitride, A wafer polishing method, characterized in that in the second step, the polishing surface is pressed against the surface to be polished with a predetermined pressing force, and at least one of the object to be polished and the polishing pad is rotated relatively.

4. 4. The wafer polishing method according to claim 3, wherein the nitride is GaN.

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