JP7198395B2 - polishing sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polishing sheet suitable for finishing which is used to form a good mirror surface on bare silicon wafers, glass, compound semiconductor substrates, hard disk substrates, and the like.

BACKGROUND ART Conventionally, a polishing method using a polishing sheet has been employed as a means for mirror-finishing bare silicon wafers, glass, compound semiconductor substrates, hard disk substrates, and the like. The polishing sheet is made of non-woven fabric or woven fabric made of synthetic fiber, synthetic rubber, etc. as a base material, and a polyurethane-based solution is applied to the upper surface of the base material. It has a structure having a plurality of openings on the surface and a soft porous layer on the surface layer having a plurality of teardrop-shaped pores inside from the openings. A method of forming the openings by grinding and removing the surface of the skin layer of the soft porous layer having a plurality of teardrop-shaped pores inside is disclosed. (See Patent Document 1.).

In recent years, the quality requirements for such polishing sheets have become more stringent year by year. There was a problem that the edge sagging was large, although it was small. On the other hand, Patent Document 2 also discloses a finishing polishing sheet in which a soft porous layer is formed on a polyester film.

JP-A-11-335979 JP-A-12-101339

SUMMARY OF THE INVENTION In view of the background of the prior art, the object of the present invention is to provide a suitable polishing method for obtaining good substrates with little edge sagging and few defects in silicon bare wafers, glass, compound semiconductor substrates, hard disk substrates, and the like. It is to provide a sheet.

In order to solve the above problems, the present invention discloses the following abrasive sheet.

A polishing sheet having a soft porous layer on the front side and a non-woven fabric on the back side, wherein the soft porous layer has a plurality of openings on the surface and teardrop-shaped pores inside from the openings. The abrasive sheet is characterized in that the compressive elastic modulus of the nonwoven fabric is in the range of 1 to 3 MPa, and the compressive elastic modulus of the abrasive sheet is in the range of 3 MPa to 5 MPa.

One aspect of the present invention is that a polyester film is interposed between the soft porous layer and the nonwoven fabric, the compression modulus of the nonwoven fabric is in the range of 1 to 3 MPa, and the compression modulus of the abrasive sheet is in the range of 3 MPa to 5 MPa. A polishing sheet characterized by:
One aspect of the present invention is a polishing method for polishing a substrate to be polished such as a bare silicon wafer, glass, a compound semiconductor substrate, a hard disk substrate, or the like, using the polishing sheet.

According to the present invention, in the case of reconveyor wafers, glass, compound semiconductor substrates, hard disk substrates, etc., it is possible to obtain a polished surface of higher quality with less edge sagging at the edge and fewer surface defects, for mirror polishing. A suitable abrasive sheet can be obtained.

A polishing sheet and a method for producing the same according to the present invention will be described.

In the present invention, the soft porous layer is a polyurethane resin porous layer having an open surface and a plurality of teardrop-like pores inside, and can be formed by a wet coagulation method for polyurethane resin. It can be produced by applying a polyurethane resin solution obtained by dissolving polyurethane in an organic solvent to the surface of a polyester film of a nonwoven fabric or a laminate of a nonwoven fabric and a polyester film, and coagulating and regenerating the polyurethane resin in an aqueous coagulating liquid. . By grinding the surface of the polyurethane resin porous layer produced by this production method with sandpaper or the like, the pores can form openings on the surface of the layer. The porous layer produced by the wet coagulation method has teardrop-shaped pores extending inward from the opening. A range of ~900 μm is preferred. The opening diameter of the opening is similarly set according to the substrate to be polished and the polishing process, but is preferably in the range of 10 to 150 μm.

The polyurethane resin that can be used for the porous layer of the present invention is a polymer having a urethane bond obtained by polyaddition of a prepolymer having a plurality of terminal active hydrogens, particularly hydroxyl groups, and a compound having a plurality of isocyanate groups. is.

Examples of prepolymers having a plurality of active hydrogens at their terminals include polyester-based, polyether-based, polycarbonate-based and polycaprolactane-based main chain skeletons.

Solvents for the polyurethane solution for forming the first layer include N,N-dimethylformamide (hereinafter "DMF"), N,N-dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, dioxane and N-methylpyrrolidone. is used. DMF is suitable as a solvent for dissolving the polyurethane resin.

The polyurethane solution may suitably contain other resins such as polymers such as polyvinyl chloride, polyester resins, polyethersulfones and polysulfones. The polyurethane solution may also contain, if necessary, carbon, organic pigments, surface active agents that reduce surface tension, and water repellent agents capable of imparting water repellency.

The nonwoven fabric of the present invention preferably has a compression modulus in the range of 1.0 to 3.0 MPa. Furthermore, 1.3 to 2.8 MPa is preferable. If the compressive elastic modulus is less than 1.0 MPa, the edge sag of the substrate to be polished increases, which is not preferable. If the compression elastic modulus exceeds 3.0 MPa, probably reflecting the influence of deterioration of the followability of the polishing sheet, fine defects increase and it is difficult to obtain the quality of the substrate to be polished, which is not preferable.

The compression elastic modulus of the abrasive sheet of the present invention is preferably in the range of 3 MPa to 5 MPa. If the compressive elastic modulus is less than 3 MPa, the edge sag of the substrate to be polished becomes large, which is not preferable. If the compression elastic modulus exceeds 5 MPa, it is not preferable because fine defects increase and it is difficult to obtain the quality of the substrate to be polished, probably reflecting the influence of deterioration of the followability of the polishing sheet.

As the nonwoven fabric of the present invention, an ultrafine fiber nonwoven fabric having a fiber diameter of about several μm is preferable in terms of uniform followability in the plane and low and stable edge sagging at the edge.

The thickness of the polyester film of the present invention is preferably 75 µm or more and 250 µm or less. If the thickness is less than 75 μm, the edge sag of the substrate to be polished becomes large, which is not preferable. If the thickness exceeds 250 μm, it is not preferable because fine defects increase and it is difficult to obtain the quality of the substrate to be polished, probably reflecting the influence of deterioration of the followability of the nonwoven fabric.

An adhesive is used to bond the polyester film of the present invention and the nonwoven fabric. Examples of this adhesive include acrylic resin adhesives, α-olefin adhesives, urethane resin adhesives, and hot melt adhesives made of thermoplastic resins. Urethane resin adhesives and hot melt adhesives are preferred. It is preferably used in that it can be adhered in a short time. As for the urethane resin-based adhesive, a method of dissolving the adhesive in various organic solvents and dry-coating with a laminator can be given as a suitable example.

As hot melt adhesives, Hitachi Kasei Polymer Co., Ltd.'s "Hibon" (registered trademark) series, Mitsui Takeda Chemicals Co., Ltd.'s "Takemelt" (registered trademark) MA series, Toa Gosei Co., Ltd.'s "Aron Melt" ( R series, Nitta Gelatin Co., Ltd. "Nittite" (registered trademark) ARX series, and Konishi Co., Ltd. "Bond" (registered trademark) KUM series.

The thickness of the adhesive is preferably 30 to 150 μm, more preferably 40 to 100 μm, in terms of maintaining a high adhesive strength.

As a manufacturing method for obtaining a nonwoven fabric having a compression modulus in the range of 1 to 3 MPa according to the present invention, a method of compressing the nonwoven fabric between two heated rolls ensures uniformity in the width direction after compression and compression modulus. is preferable in that it is easy to adjust the A temperature range of 130° C. to 190° C. for the hot roll is preferred because it is relatively easy to compress and the shape is retained after compression. In order to keep the nonwoven fabric of the present invention within an appropriate range of compression elastic modulus, the thickness of the nonwoven fabric before compression and the gap between the two hot rolls are adjusted. If the surface of the non-woven fabric is too compacted, the coating liquid that forms the soft porous layer will not penetrate the interior of the non-woven fabric well, and peeling will easily occur at the interface between the soft porous layer obtained by wet coagulation and the non-woven fabric. In that case, the surface of the compressed nonwoven fabric is coated with the same resin as the soft porous layer and dried to form a primer layer, and then the soft porous layer is formed. A polishing sheet having sufficient peel strength can be produced by applying the liquid and wet coagulating it. A method of manufacturing a polishing sheet in which a polyester film is interposed between a soft porous layer and a nonwoven fabric having a compressive modulus of elasticity in the range of 1 to 3 MPa is to bond the polyester film and nonwoven fabric with an adhesive in advance, and then form the laminated sheet. After compressing between two heated hot rolls to make the compression elastic modulus within the range of the present invention, a coating liquid that forms a soft porous layer is applied to the surface of the polyester film and wet solidified to the surface of the polyester film. Forms a soft porous layer. As another manufacturing method, a soft porous layer is formed on the nonwoven fabric by wet coagulation, and before opening the surface of the soft porous layer with a buff, the laminated sheet of the soft porous layer and the nonwoven fabric is compressed between two heated rolls. The abrasive sheet of the present invention can also be produced by processing the nonwoven fabric so that the compression modulus of the nonwoven fabric falls within a predetermined range, and then buffing the surface of the soft porous layer to open the surface. Equipment for applying the coating liquid for forming the soft porous layer includes roll coaters, knife coaters, knife over roll coaters and die coaters. A solvent that has affinity with DMF but does not dissolve the resin of the first layer is used in the coagulation bath for forming the soft porous layer after the coating liquid is applied. Generally, water or a mixed solution of water and DMF is used.

As a method for buffing the surface of the first layer, sandpaper may be wound around a rotating roll, and the surface of the first layer may be ground by bringing the surface of the rotating sandpaper into contact with the surface. As a method for managing an appropriate amount of grinding, it is possible to appropriately perform by monitoring the resistance value of the shaft of the rotating roll around which the sandpaper is wound.

Defects can be further reduced by applying a hydrophilic resin to the surface of the soft porous layer of the polishing cloth of the present invention to make the surface hydrophilic. Polyvinyl alcohol is preferable as a hydrophilic resin because it has little effect on the slurry. Specific examples of the polyvinyl alcohol include Gosenol N-300 and NL- 05, A-300, AL-06R, GH-23, GH-22, GH-20, GH-20R, GH-17R, GM-14R, GM-14L, GL-05, GL-03, KH-20, KH-17, KL-05, KL-03, KP-08R, NK-05R, EG-05, EG-40, Gohsenex Z-100, Z-200, Z-205, Z-210, Z-220, Z-300, Z-320, Z-410, K-434, L-3266, GKS-50, T-320H, T-330, T-350, LW-100, LW-200, WO-320N, G polymer AZF8035W, OKS-6026, OKS-1011, OKS-8049, OKS-1028, OKS-1027, OKS-1109, OKS-1081, OKS-1083, OKS-8041, OKS-8105, OKS-8089, OKS-8096 etc.

It is preferable to select appropriately according to the slurry to be used. Then, by polishing the substrate to be polished with the polishing sheet of the present invention or with the polishing sheet obtained by the method of manufacturing the polishing sheet of the present invention, a substrate with less edge sagging and fewer surface defects is completed. can do.

The following examples further illustrate details of the present invention. However, the present invention should not be construed as being limited by this example. Polishing evaluation and each measurement were performed as follows.

[Measurement of compression modulus]
Measurement was performed under the following conditions using an automated compression tester (KESFB3-AUTO-A) manufactured by Kato Tech. Calculated from the strain rate of 16 gf/cm ² (0.00157 MPa) and 40 gf/cm ² (0.00392 MPa) when pressurized from 0 gf/cm ² to 50 gf/cm ² using this machine (measured 5 times average value).

・ Strain rate: (initial thickness - thickness at predetermined pressure) / initial thickness ・ Compressive elastic modulus: (0.00392 - 0.00157) / (strain rate _{40 gf/cm2} - strain rate _{16 gf/cm2} )
[MPa]
・Indenter area: 1.0 cm ²
・Indenter speed: 0.02mm/sec
・Upper limit load: 50 gf/cm.

[Polishing evaluation]
Using a polishing machine (model: SPP600) manufactured by Okamoto Machine Tool Works, an edged wafer was first polished with SUBA800, and an 8-inch silicon bare wafer was used. were prepared and evaluated under the following conditions.
・Platen rotation: 46 rpm
・Wafer head rotation: 49 rpm
・Head load: 200 g/cm ²
・ Slurry volume: 700 ml / min (slurry: colloidal silica slurry abrasive grain concentration 1%)
- Polishing time: 15 minutes.

- After polishing 100 dummy wafers, the 8-inch silicon bare wafer was polished.

[Defects on Silicon Wafer]
The surface of the silicon wafer polished under the above polishing conditions was analyzed with SURFSCAN SP-3 manufactured by KLA-Tencor to determine the number of defects of 0.026 μm.

[Edge sagging of silicon wafer edges]
Under the above polishing conditions, edge sagging of 2 mm perimeter of the edge portion was measured with ZYGO NewView7300.

Examples and comparative examples are described below. Table 1 shows the composition of the polishing sheet, and Table 2 shows the polishing properties of the resulting polishing sheet.

[Example 1]
A non-woven fabric using fiber cotton with a fiber diameter of 14 μm was compressed with a hot roll at 160° C. to obtain a product with a compressive elastic modulus of 2.1 MPa (thickness: 0.9 mm). A 10% by weight solution of polyester polyurethane in dimethylformamide was applied and dried to form a polyester polyurethane primer layer.

100 parts by mass of a dimethylformamide solution of a polyester-based polyurethane having a solid content concentration of 30%, 60 parts by mass of a dimethylformamide solvent, 1.5 parts by mass of a foaming aid, and 10 parts by mass of a dimethylformamide solution containing 20% carbon black as a pigment. A coating solution for forming a soft porous layer is prepared by dispersing each part, the coating solution is applied to the surface of the primer layer of the nonwoven fabric, and the nonwoven fabric is immersed in a coagulation bath of a 10% aqueous solution of dimethylformamide, It was wet coagulated, washed with water to remove dimethylformamide, and dried to form a soft porous layer having a thickness of 550 µm. The surface was ground with sandpaper to obtain a polishing sheet.

The compression elastic modulus of the resulting abrasive sheet was 4.1 MPa. Observation of the cross section revealed that a large number of tear-shaped pores were formed in the soft porous layer, and pores having an average diameter of 40 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. As shown in Table 2, the number of defects and edge sagging of the edge portion were good.

[Example 2]
A non-woven fabric using fiber cotton with a fiber diameter of 14 μm was compressed with a hot roll at 160° C. to obtain a compressive elastic modulus of 1.1 MPa (thickness: 1.2 mm). A 10% by weight solution of polyester polyurethane in dimethylformamide was applied and dried to form a polyester polyurethane primer layer.

Under the same conditions as in Example 1, a soft porous layer of 400 μm was formed. The surface was ground with sandpaper to obtain a polishing sheet.

The compressive elastic modulus of the resulting polishing sheet was 3.1 MPa. Observation of the cross section revealed that a large number of tear-like pores were formed in the soft porous layer, and pores having an average diameter of 30 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. As shown in Table 2, the number of defects and edge sagging of the edge portion were good.

[Example 3]
A non-woven fabric using fiber cotton with a fiber diameter of 14 μm was compressed with a hot roll at 160° C. to obtain a compressive elastic modulus of 2.9 MPa (thickness: 0.7 mm). A 10% by weight solution of polyester polyurethane in dimethylformamide was applied and dried to form a polyester polyurethane primer layer.

Under the same conditions as in Example 1, a soft porous layer of 450 μm was formed. The surface was ground with sandpaper to obtain a polishing sheet.

The compression elastic modulus of the obtained polishing sheet was 4.9 MPa. Observation of the cross section revealed that a large number of tear-shaped pores were formed in the soft porous layer, and pores having an average diameter of 50 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. As shown in Table 2, the number of defects and edge sagging of the edge portion were good.

[Comparative Example 1]
Instead of the nonwoven fabric used in Example 1, the fiber diameter was the same, the density was changed, the compression elastic modulus was changed to 0.9 MPa (thickness: 1.0 mm), and under the same conditions as in Example 1, a soft porous layer was formed to a thickness of 600 μm. The surface was ground with sandpaper to obtain a polishing sheet.

The compressive elastic modulus of the resulting polishing sheet was 3.2 MPa. Observation of the cross section revealed that a large number of tear-like pores were formed in the soft porous layer, and pores having an average diameter of 30 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. Regarding the number of defects and edge sagging of the edge portion, as shown in Table 2, the edge sagging was poor.

[Comparative Example 2]
Instead of the nonwoven fabric used in Example 1, the fiber diameter is the same, compression is performed with a hot roll to create a compression elastic modulus of 3.3 MPa (thickness: 0.6 mm), and under the same conditions as in Example 1 , a soft porous layer of 700 μm was formed. The surface was ground with sandpaper to obtain a polishing sheet.

The compression elastic modulus of the obtained polishing sheet was 4.7 MPa. Observation of the cross section revealed that a large number of teardrop-shaped pores were formed in the soft porous layer, and pores having an average diameter of 60 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. As for the number of defects and the sagging of the edge portion, as shown in Table 2, the number of defects was large and the film was unsatisfactory.
[Comparative Example 3]
A non-woven fabric using fiber cotton with a fiber diameter of 14 μm was compressed with a hot roll at 160° C. to obtain a compressive elastic modulus of 1.1 MPa (thickness: 1.2 mm). A 10% by weight solution of polyester polyurethane in dimethylformamide was applied and dried to form a polyester polyurethane primer layer.

100 parts by weight of a dimethylformamide solution of a polyester-based polyurethane having a solid content concentration of 20%, 60 parts by weight of a dimethylformamide solvent, 1.5 parts by weight of a foaming aid, and 10 parts by weight of a dimethylformamide solution containing 15% carbon black as a pigment. A coating solution for forming a soft porous layer is prepared by dispersing each part, the coating solution is applied to the surface of the primer layer of the nonwoven fabric, and the nonwoven fabric is immersed in a coagulation bath of a 10% aqueous solution of dimethylformamide, It was wet coagulated, washed with water to remove dimethylformamide, and dried to form a soft porous layer having a thickness of 620 μm. The surface was ground with sandpaper to obtain a polishing sheet.

The compressive elastic modulus of the resulting abrasive sheet was 2.8 MPa. Observation of the cross section revealed that a large number of tear-shaped pores were formed in the soft porous layer, and pores having an average diameter of 50 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. Regarding the number of defects and edge sagging of the edge portion, as shown in Table 2, the edge sagging was poor.
[Comparative Example 4]
A non-woven fabric using fiber cotton with a fiber diameter of 14 μm was compressed with a hot roll at 160° C. to obtain a compressive elastic modulus of 2.7 MPa (thickness: 1.2 mm). A 10% by weight solution of polyester polyurethane in dimethylformamide was applied and dried to form a polyester polyurethane primer layer.

100 parts by mass of a dimethylformamide solution of a polyester-based polyurethane having a solid content concentration of 40%, 60 parts by mass of a dimethylformamide solvent, 1.5 parts by mass of a foaming aid, and 10 parts by mass of a dimethylformamide solution containing 25% carbon black as a pigment. A coating solution for forming a soft porous layer is prepared by dispersing each part, the coating solution is applied to the surface of the primer layer of the nonwoven fabric, and the nonwoven fabric is immersed in a coagulation bath of a 10% aqueous solution of dimethylformamide, Wet coagulation was performed, washed with water to remove dimethylformamide, and dried to form a soft porous layer having a thickness of 700 μm. The surface was ground with sandpaper to obtain a polishing sheet.

The compression elastic modulus of the obtained polishing sheet was 5.2 MPa. Observation of the cross section revealed that a large number of tear-shaped pores were formed in the soft porous layer, and pores having an average diameter of 20 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. As shown in Table 2, the number of defects and the edge sagging of the edge portion were many defects and were unsatisfactory.

[Example 4]
Instead of the nonwoven fabric in Example 2, a nonwoven fabric made of ultrafine fibers with a fiber diameter of 4 μm was compressed with a hot roll, and a compressive elastic modulus of 2.1 MPa (thickness: 0.8 mm) was used. A polishing sheet was prepared in the same manner as above.

The compression elastic modulus of the obtained polishing sheet was 3.9 MPa. Observation of the cross section revealed that a large number of tear-like pores were formed in the soft porous layer, and pores having an average diameter of 30 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. As shown in Table 2, the number of defects and edge sagging of the edge portion were good.

[Example 5]
A polyester film having a thickness of 100 µm was adhered to a nonwoven fabric made of ultrafine fibers having a fiber diameter of 4 µm with an adhesive to prepare a laminated sheet, which was then compressed with a hot roll having a roll temperature of 160°C to obtain a compressive elastic modulus of 1.9 MPa and a thickness of 0.9 MPa. 8 mm) was used to form a soft porous layer on the surface of the polyester film in the same manner as in Example 2 to prepare a polishing sheet.

The compression elastic modulus of the obtained polishing sheet was 3.8 MPa. Observation of the cross section revealed that a large number of tear-shaped pores were formed in the soft porous layer, and pores having an average diameter of 40 μm were formed in the surface layer of the pores. A silicon wafer was polished using the obtained polishing sheet and polishing apparatus. There was no peeling with the polishing sheet, and the polishing was completed without problems. As shown in Table 2, the number of defects and edge sagging of the edge portion were good.

Claims (3)

A polishing sheet having a soft porous layer on the front side and a non-woven fabric on the back side, wherein the soft porous layer has a plurality of openings on the surface and teardrop-shaped pores inside from the openings. A polishing sheet characterized in that the nonwoven fabric has a compression modulus of elasticity in the range of 1 to 3 MPa, and the compression modulus of the polishing sheet is in the range of 3 MPa to 5 MPa. 2. The abrasive sheet according to claim 1, wherein a polyester film is interposed between the soft porous layer and the nonwoven fabric. A polishing method comprising polishing a substrate to be polished with the polishing sheet according to any one of claims 1 and 2.