JPH01146666A - Abrasive cloth for fine polishing - Google Patents

Abstract

PURPOSE:To enable an abrasive cloth to obtain an excellent polishing characteristic by forming the abrasive cloth by a foam body with specific expansion ratios and specific average cell sizes. CONSTITUTION:An abrasive cloth for fine polishing is formed by a polyolefine resin foam body of cell-construction whose expansion ratios range from 1.5-30 and an average cell size in the section of the foam body is less than 300mum, preferably 1-90mum. When the expansion ratio is below 1.5, the abrasive cloth is hard, scratches caused by grits are not sufficiently smoothed out, and the surface being worked is subjected to damages, orange-peel, etc. On the other hand, when the expansion ratio exceeds 30, the abrasive cloth becomes too soft, an elastic deformation constant of the abrasive cloth becomes large, and flatness of the surface to be worked is reduced. Further, when an average cell size is larger than 300mum, the surface smoothness of the abrasive cloth becomes worse, surface defects such as scratches, orange-peels, etc. are easy to occur.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a polishing cloth, which is used for precision polishing of silicon single crystal wafers, compound semiconductor wafers, aluminum disk substrates, cathode ray tubes, optical lenses, optical crystals, etc. The present invention relates to a polishing cloth made of a polyolefin resin foam having excellent polishing properties, especially for mirror finishing.

[Conventional technology]

In recent years, in silicon wafer substrates, which make up the majority of IC substrates, in addition to shrinking circuit line widths and increasing densities due to the increase in the degree of integration of integrated circuits, the diameter of the wafers has also increased, and the demand for mirror-finishing precision of silicon wafers has increased. is becoming increasingly severe.

In addition, compound semiconductors such as GaAs have the disadvantage of being easily damaged during processing compared to silicon semiconductors, and since they are used in a wide variety of ways, it is necessary to process them for mirror finishing.
This requires even more care and ingenuity than silicon substrates.

These strict requirements for processed products (wafers, etc.)
Naturally, some of these changes have arisen as demands on tools have become more sophisticated (polishing tools consist of a supporting/driving device, a polishing cloth (in the polisher), and an abrasive agent, each of which has been improved to meet new demands. Polishing cloths, especially polishing cloths for mirror finishing, have been replaced by polishing cloths made of a polyester base fabric laminated with a polyurethane foam layer, in place of conventional pitch and wax polishers.

[Problem that the invention seeks to solve]

Polishing cloth, which is made by impregnating or laminating a polyurethane foam layer on a polyester base fabric, has problems with the uniformity and flatness of the polished surface due to variations in the density of the base fabric layer, and variations in the size and density of the bubbles in the foam layer. There were problems such as the surface polishing layer being thin and having poor durability, frequent replacement work, and poor work efficiency.

Furthermore, regarding the structure of the conventionally used polyurethane foam layer, there is no strict regulation of its suitability based on the cell diameter in the cross section of the foam that serves as the polishing surface, and for other resin foams, the suitability of the polishing cloth is not determined. There were no cases that were fully evaluated.

[Means for solving problems]

As a result of intensive research to solve the above problems, the present inventors found that the foaming ratio is 1.5 to 30 times and the average cell diameter is 30 times.
It has been discovered that a foam with a diameter of 0 μm or less exhibits unprecedented polishing properties, leading to the completion of the present invention.

That is, the present invention relates to a polishing cloth for precision polishing made of a polyolefin resin foam having a cell structure in which the expansion ratio is 1.5 times or more and 30 times or less, and the average cell diameter in the cross section of the foam is 300 μm or less. It is.

The foam of the present invention has an expansion ratio of 1.5 times or more and 30 times or less. If the foaming ratio is less than 1.5 times, it is hard and does not sufficiently alleviate the scratching action of abrasive grains, which is the mission of an abrasive cloth, and causes processing damage and defects such as orange peel on the processed surface, which is undesirable. In addition, a highly foamed material that exceeds 30 times becomes too soft and has a large elastic deformation constant (amount of deformation under a constant load) as a polishing cloth, which reduces the flatness of the machined surface and makes it difficult to Since the processing pressure cannot be maintained, the processing speed is also significantly reduced, which is undesirable.

The foam of the present invention has an average cell diameter of 300 μm or less. If the average cell diameter is larger than 300 μm, the surface smoothness of the polishing cloth will deteriorate, and defects such as localization of abrasive grains, scratches on the machined surface, orange beer, etc. will easily occur, and the coefficient of friction and wear as a polishing cloth will deteriorate. The coefficients become unbalanced,
Excessive temperature rise of the workpiece and shortened polishing cloth life may occur.
Undesirable.

The polyolefin resin of the present invention is, for example, one or a mixture of two or more selected from polyethylene, polypropylene, poly-4-methyl-1-pentene, ionomer resin, and the like. Further, the resin may be copolymerized, if necessary.

The foam of the present invention may be either a non-crosslinked foam or a crosslinked foam, but a crosslinked foam is preferred in terms of durability during polishing. The crosslinking step at that time may be performed before or simultaneously with the foaming step.

Among the foams of the present invention, the expansion ratio is 1.5 times or more and 15 times or less, and the average cell diameter in the cross section of the foam is 1 μm or more and 9
If the diameter is 0 μm or less, the polishing properties are well balanced (,
Particularly preferred.

The foam of the present invention is produced by uniformly mixing a chemical foaming agent, a physical foaming agent, or an inert gas with a resin and foaming it. For example, a method of foaming using a chlorogenated hydrocarbon such as dichlorodifluoromethane, trichlorofluoromethane, dichlorofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, etc., or a hydrocarbon such as butane or pentane is preferable. As the foaming method, extrusion foaming method, in-mold foaming method, normal pressure foaming method, etc. may be used.Also, thermoplastic resin is molded into a sheet or film shape, and then ionizing radiation, such as γ rays, electron beams, etc. A method of crosslinking and producing a foam by irradiation can also be used.

Furthermore, methods for producing foams from polymer solutions by gel-liquid phase separation (e.g., J. CELLULARPL
ASTICS, Vol. 23, p. 55) are also used.

The polishing cloth for precision polishing of the present invention is produced by processing the foam into a desired shape by cutting, slicing, tearing, grinding, etc.
In addition, it is used with the cell cross section of the foam exposed on the surface. Its shape is appropriately selected depending on the shape of the object to be polished, the purpose of polishing, the polishing method, etc., but generally, in the case of surface polishing, a sheet-like one is used. It is important to precisely control the smoothness of the surface of these polishing cloths, as it affects the surface roughness, waviness, etc. of the polishing cloth. The difference between the peak and the valley between the intestines) is 50μ or less per 2III11 of its length,
Preferably, those having a diameter of 25 μm or less are used.

The polishing cloth for precision polishing of the present invention can have a surface with a width of 0.1 to 2IIIm and a depth of 0.1m depending on the polishing method, whether the surface remains the uniform cross-section of the cell structure of the above-mentioned foam, or depending on the polishing method.
A material in which grooves of ~2III1 are regularly formed at intervals of 1 to 50111 m in a lattice, diamond, or satin pattern is used.

The polishing cloth for precision polishing of the present invention may use the above-mentioned foam alone, and depending on the purpose, it may have a foam with a different expansion ratio or a reinforcing material made of another material, a Kutsusilane layer, or a stiffening material on the back or front surface. A polishing cloth having a surface hardness of 90 to 30 (JIS A method) is generally used, and may be used by bonding the application layer.

The polishing cloth for precision polishing of the present invention, unlike conventionally known foam polishing cloths, has a uniform cell structure in its cross section and is very homogeneous without large void-like cells. This is thought to have an effect on polishing properties such as surface roughness and waviness.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples, and various characteristic values in the present invention were determined by the following methods.

■Cell diameter The cell referred to here consists of a bubble and a cell membrane (wall) surrounding it. It was calculated from the number of cells that cross the area.

■Foaming ratio Calculated using the following formula.

(2) A cross section of the cell structure foam was observed using an electron microscope or an optical microscope, and the distribution of cell sizes within the cross section and the presence or absence of voids were observed and evaluated. A uniform structure is one in which the cells are uniform in size and have no large void-like pores.

0 Surface Smoothness Regarding the cross section of the polishing cloth, the surface layer was observed under magnification, and the unevenness of the external tangent line of the surface (difference between peaks and valleys between unit lengths) was observed.
was measured at 211II11 intervals, and the average value was used for evaluation.

■ A chemical-resistant polishing cloth or its foam layer was subjected to a 90-hour immersion test in a Br-methanol solution at a concentration of 0.1 to 5% and a temperature range of 25 to 60°C. change,
Changes in tensile strength and cell structure were measured and observed, and those with no observed change were evaluated as good.

■ As a pre-processing for polishing properties, a GaAs single crystal wafer lapped using alumina abrasive grains with an average particle size of 5μ The appearance and roughness of the wafer surface were evaluated. In addition, the surface condition of the polishing cloth after polishing was observed under magnification, and changes in the cell structure were evaluated.

During polishing, as the polishing process progresses, the surface to be polished and the polished surface are slightly separated from each other on a surface plate to which a polishing cloth is attached, and both surfaces are continuously brought into a contact state and a non-contact state. Alternatively, fix the wafer on a polishing jig that alternately changes the Br to 0.
．． While supplying a 25% methanol solution (a mixed solvent of 80% methanol and 20% ethylene glycol), both surfaces were moved in a direction in which they were intended to come into sliding contact with each other, and polishing was performed.

The appearance, roughness, etc. of the wafer surface were determined according to the method described in the SEMI standard.

Example 1 Polypropylene resin (manufactured by Asahi Kasei Kogyo ■, PP-M2S
O4) was supplied to an extrusion molding device and extruded to a thickness of 1 m.
The II+ sheet was placed in an autoclave, dichlorodifluoromethane was press-injected, and the mixture was soaked at 80° C. for 1 hour to obtain a foamable sheet. This foam sheet is 4.0 Kg/c
It was heated with iG steam for 15 seconds to obtain a foam sheet with an expansion ratio of 8 times and a wall thickness of 2 mm. This foam was sliced on both sides to a thickness of 1 mm using a slicer (Hessy 320-D, manufactured by Fortuner AG, West Germany), and the foam sheet had an average cell diameter of 35 μm on the sliced surface. The sliced sheet was punched out into a circular shape with a diameter of 300 mm to obtain an abrasive cloth, and its abrasive properties were examined using the method described above. The results are shown in Table 1, and the foamed sheet had high polishing ability without impairing the quality of the polished surface of GaAs wafers.

Example 2 4-Methyl-1-pentene resin (manufactured by Mitsui Petrochemical Industries Ltd., DX-845) was melted in Durene at 180°C to prepare a 5% by weight polymer solution, and then gradually heated to 140°C. It was cooled to precipitate a foam. Next, the solvent Durene was removed under reduced pressure at 50°C to obtain the desired foam. The average cell diameter of this foam was 10 μm, and the expansion ratio was 15 times. When the polishing cloth performance of the foam was examined in the same manner as in Example 1, the results were as shown in Table 1, and it was found to have high polishing ability.

Example 3 9 parts by weight of azobisformamide were uniformly kneaded into low density polyethylene (Mr 1.7), extruded into a sheet, irradiated with electron beam to crosslink to a gel content of 70%, and heated to 200°C. The foamed polyethylene crosslinked foam sheet was sliced in the same manner as in Example 1 to prepare an abrasive cloth.

The results of examining the polishing properties of this polishing cloth are shown in Table 1.

Example 4 Ionomer resin (Himilan [F] 1601)
100M parts and 0.5 parts by weight of talc were supplied to an extrusion foaming device, and 32 parts by weight of dichlorodifluoromethane was press-fitted.
The mixture was uniformly mixed under high temperature and high pressure, cooled to 119° C., and extruded into the atmosphere through a nozzle equipped with a circular die to obtain a foamed sheet.

The obtained foam had a foaming ratio of 28 times and an average cell diameter of 90μ.
m, the cell membrane was an open-celled body with fine pores of 1 to 10 μm.

This foam sheet was sliced in the same manner as in Example 1,
The polishing properties were investigated. The results are shown in Table 1.

Example 5 In Example 1, a foamable sheet impregnated with dichlorodifluoromethane was heated for 15 seconds with steam at 3.8 Kg/cIAG to obtain a foaming ratio of 4 times and an average cell diameter of 33 μm.
A foam sheet was obtained.

This foam sheet was sliced in the same manner as in Example 1, and its polishing properties were examined. The results are shown in Table 1.

Example 6 Ultra-high molecular weight polyethylene (molecular weight approximately 3 million) was dissolved in tetralin at 150°C to form a 9% by weight solution. Next, it is cooled at a rate of 10°C/min to precipitate the polymer.
After gelation, the tetralin was removed under reduced pressure to obtain a foam. The average cell diameter of this foam was 1 μm, and the expansion ratio was about 8 times. The obtained foam was sliced in the same manner as in Example 1, and its polishing properties were evaluated. Results first
Shown in the table.

Example 7 A foaming ratio of 8 times and an average cell diameter of 90 μm obtained in the same manner as in Example 3 except that the amount of chemical blowing agent was changed to 4 M parts.
A polishing cloth was prepared in the same manner as in Example 1 using the crosslinked polyethylene foam sheet, and its polishing properties were evaluated. The results are shown in Table 1.

Comparative Example 1 Expanded polyethylene foam, expansion ratio 8 times, average cell diameter 40
A 0 μm board (manufactured by Asahi Kasei Corporation, Santic Foam) was sliced in the same manner as in Example 1 and evaluated as an abrasive cloth. Although the chemical resistance was good, the surface roughness and waviness of the wafer were large, and the polishing performance was poor.

Comparative Example 2 A commercially available polyethylene crosslinked foam sheet with an expansion ratio of 33 times and an average cell diameter of 90 μm (manufactured by Vercules, Minicell L-
200) was sliced in the same manner as in Example 1 and evaluated as an abrasive cloth. The surface roughness and waviness were large (and the cell structure was also significantly deformed after polishing.

Comparative Example 3 Polishing properties were evaluated using a commercially available polyurethane polishing cloth. The polishing cloth has a structure in which a polyurethane foam layer is laminated on a polyester base cloth, and the polyurethane foam layer has one layer in the thickness direction.
There are eggplant-shaped pores with a size of 00 to 200 μm,
The 10 to 30 μm surface layer has a fine cell structure with a cell diameter of about 30 μm, and the cell structure in the thickness direction is uneven, and the surface has large irregularities that seem to be caused by the base fabric, resulting in poor smoothness. Moreover, the chemical resistance was poor.

The polishing properties were extremely poor in surface roughness, and were so poor that defects on the wafer surface could be visually identified.

(Margin below)

Claims (2)

[Claims] (1) A polishing cloth for precision polishing made of a polyolefin resin foam having a cell structure with an expansion ratio of 1.5 times or more and 30 times or less and an average cell diameter in the cross section of the foam of 300 μm or less. (2) Claim 1 comprising a polyolefin resin foam having a cell structure in which the expansion ratio is 1.5 times or more and 15 times or less, and the average cell diameter in the cross section of the foam is 1 μm or more and 90 μm or less. Abrasive cloth for precision polishing.