JPH0735638B2 - Manufacturing method of polishing base cloth - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

TECHNICAL FIELD The present invention relates to a method for producing a polishing base cloth for obtaining a polishing substrate used when polishing a semiconductor wafer, glass, metal or the like.

2. Description of the Related Art As a method for obtaining a polishing base cloth, conventionally known is a method in which a nonwoven fabric is impregnated with a polyurethane resin solution, immersed in a water bath or an aqueous dimethylformamide solution to be completely solidified, and then washed and dried. . However, since the product obtained by this method has a porous structure, it is too soft, and when it is used as a polishing base cloth, it has a drawback that it causes edging and a wafer with sharp edges cannot be obtained. Therefore, in order to further strengthen the fiber network structure, the base fabric obtained by the above method is further divided and subjected to high temperature heat treatment excluding both surface layer parts to melt the polyurethane resin having a porous structure. In order to fuse this around the fiber, or to facilitate the fusion and fusion, a polyurethane resin with a different melting point is blended to increase the low melting point component ratio At this time, it has been proposed to obtain a polishing substrate by a method of melting the low melting point resin and fusing the resin around the fibers (see Japanese Patent Laid-Open No. 62-297061).

[Problems to be Solved by the Invention]

The inventors of the present invention repeated the experiment according to the method described in the above publication, and observed with a scanning electron microscope photograph,
It was found that the number of microvoids remaining in the resin portion between the fibers was unexpectedly large. This means that there was a limit to the elimination of microvoids generated as traces of solvent extraction during complete solidification by melting and fusion in the high temperature heat treatment step. Furthermore, regarding high-temperature heat treatment, from the results of physical property measurement, stable structure and physical properties cannot be obtained unless temperature control is performed at a level of ± 2 ° C, and the melting point may vary slightly depending on the production lot of polyurethane resin. It was found that the optimum heat treatment temperature also changed with the change of, which made it more difficult to control. An object of the present invention is to provide a manufacturing method in which it is easy to obtain a good polishing base cloth without generating microvoids even without performing fusion fusion by high temperature heat treatment, and simply dividing this base cloth. By removing both surface layer parts, it is possible to obtain a polishing substrate.

[Means for Solving the Problems]

The present invention, as described above, the reason why the microvoids, which should have disappeared, still remain, are the large amount of microvoids generated by the rapid desolvation by once reaching complete solidification,
Therefore, in view of the fact that microvoids that cannot be completely eliminated even after high temperature heat treatment remain, the present invention has been completed through intensive research. That is, in a method for producing a polishing base cloth by impregnating a synthetic fiber non-woven fabric having a network structure with a dimethylformamide solution of a polyurethane resin, and coagulating this, the coagulation step is divided into two, and the first step is performed at room temperature in water or Immersion in hot water for a short period of time was used to maintain incomplete coagulation, and in the subsequent step, residual dimethylformamide was desolvated in an atmosphere of about 75 ± 5 ° C. to complete coagulation.

[Action]

By dipping a dimethylformamide solution of polyurethane resin impregnated in a synthetic fiber non-woven fabric having a network structure for a short time such as within 1 hour in water at room temperature and within 20 minutes in hot water, 1 part of the solvent is desolvated, Most of the solvent remains. In this way, by keeping the incomplete solidification in the first wet solidification step, it is possible to prevent the generation of microvoids. In the next second dry coagulation step, it is placed in an atmosphere of about 75 ± 5 ° C. and the remaining dimethylformamide is desolvated to complete coagulation. At this time, the reason for setting the atmospheric temperature to 75 ± 5 ° C., which is lower than the boiling point of the solvent, is that when the temperature is within this range, the residual solvent is gently desolvated at a relatively low temperature, so that the occurrence of micro voids is not observed. The polyurethane resin can be fused around the fibers and is effective in forming a structure necessary for preventing clogging of abrasive grains when used as a polishing substrate. If it is above 80 ° C, bumping phenomenon occurs when the heated solvent is desolvated, and the generation of microvoids increases, and if it is below 70 ° C, the heating of the residual solvent is too low and the time required for desolvation becomes long. However, there is a drawback that the polyurethane resin is not uniformly adhered to the polishing base cloth. As described above, as a result of the relatively mild desolvation at the low temperature in the second dry coagulation step, the polyurethane resin is uniformly attached and the formation of microvoids can be completely prevented. The polyurethane resin may be an ester resin or an ether resin. However, from the viewpoint of the physical properties of the obtained polishing substrate, the ether polyurethane resin is preferable.

【Example】

Physical properties were measured according to the following methods. (1) Density (g / cm ³ ) Except for the edge of the sample of 50 mm, three 100 × 100 mm sample pieces were prepared, and g / cm ³ was determined from the average value of the measured weights. (2) Compressibility, compressive elastic modulus (%) 3 pieces of 2 × 2 cm test piece were sampled, and the thickness after applying 100g for 30 seconds using YSS type Shopper type thickness meter manufactured by Yasuda Seiki The t ₀ is measured, and then the thickness t ₁ after standing for 5 minutes at 900 g is measured. Next, except 900g, leave it for 5 minutes without weighting, then again 100g, 30
The thickness t ₂ after pressurizing for ₂ seconds was measured and calculated from the following formula. Compression rate = (t ₀ −t ₁ / t ₀ ) × 100 Compression modulus = (t ₂ −t ₁ / t ₀ −t ₁ ) × 100 (3) Hardness durometer Type A (The Shore Instrument & Mfg.C
o.), 2 x 2 cm sample pieces are stacked on each other so that the thickness is 4.5 mm or more. Place the sample on the table and drop the pressure needle from 25 mm above to measure 3 points of the sample. Then, the average value was obtained. (4) Water vapor transmission rate (mg / cm ² / hr) It was measured based on JIS K-6549. A beeswax: paraffin ratio of 60:40 was used as a wax sealant. (5) Taber abrasion (mg / 1000 times) A Taber abrasion tester manufactured by Toyo Sokki was used. Leave the sample piece in a standard condition (room temperature 20 ± 2 ° C, humidity 65 ± 2%), completely remove adhering fibers etc. before measurement, and then measure the weight (Amg) of the specimen with an analytical balance. , Load 500g, wear wheel H-22, set the sample on the abrasion tester set to 1000 rotations, operate, and after completion, measure the weight (Bmg) of the sample from which abrasion debris was removed and repeat twice. The result of the test is calculated by the following formula and expressed as the average value. Taber abrasion = AB <Example 1> The non-woven fabric used was a web of polyester fibers having a denier of 3 mm and a cut length of 51 mm, laminated with 700 needle punches per cm ^2, and having a thickness of 4.2 mm. It has a basis weight of 860 g / m ² . An ether-based polyurethane resin solution (trade name: Sampren; Sanyo Kasei Co., Ltd., average molecular weight 20)
00, resin concentration 20%, dimethylformamide 80%), squeezed with a roll press machine with a clearance of 3.5 mm and a pressure of 3 kg / cm ² for uniform impregnation. Dip this resin-impregnated base cloth in water at room temperature (20 ° C) for 50 minutes,
Then, it was taken out from the water bath, squeezed with a roll press, and immediately dried with a dryer at 75 ± 5 ° C. for 2 hours. The resin adhesion rate of this polishing base cloth was 38%. Divide the obtained polishing base cloth into two pieces with a thickness of 2.1 mm, remove 0.8 mm of the skin layer from each, and have a thickness of 1.3 mm and a resin adhesion rate of 35
% Of two polishing substrates (Reference 1) were obtained. The scanning electron micrograph of this product is shown in Fig. 1.
No microvoids were seen. The results of measuring the physical properties of the polishing substrate are shown in Table 1. <Example 2> In Example 1, the resin-impregnated base fabric has a clearance of 3.5 mm and a pressure of 3 k.
It was squeezed with a roll press machine of g / cm ² . In Example 2, it was squeezed by a roll press machine having a clearance of 2.7 mm and a pressure of 3 kg / cm ² .
Except for this difference, the conditions were the same as in Example 1. The resin adhesion rate of this polishing base cloth was 27%. Two polishing substrates (Data 2) were prepared from the obtained polishing base cloth (resin adhesion rate of the polishing substrate was 25%), and the physical property measurement results of the polishing substrate are shown in Table 1. <Example 3> In Example 3, the roll was pressed with a roll press having a clearance of 4.1 mm and a pressure of 3 kg / cm ² . Except for this difference, the conditions were the same as in Example 1. The resin adhesion rate of this polishing base cloth was 48%. Two polishing substrates (Data 3) were prepared from the obtained polishing base fabric (resin adhesion rate of the polishing substrate was 44%), and the results of measuring the physical properties of the polishing substrate are shown in Table 1. <Example 4> In Example 1, the resin-impregnated base fabric was immersed in water at room temperature for 50 minutes, but in Example 4, it was immersed in hot water at 40 ° C for 15 minutes. Except for this difference, the other conditions were the same as in Example 1. A polishing substrate was made from the obtained polishing base fabric, and a scanning electron micrograph and measurement of physical properties were performed. The results were almost the same as in Example 1. <Comparative example> The non-woven fabric used is a 3 denier, 51 mm cut length polyester fiber web laminated and 700 needle punched per cm ² , with a thickness of 4.2 mm and a basis weight of 610 g / m ² . Is. Ester polyurethane resin solution (trade name: Crisbon; dimethyl formamide solution with average molecular weight 2000, resin concentration 20%, manufactured by Dainippon Ink and Chemicals, Inc.) and ether type polyurethane resin solution (trade name: Samprene; Sanyo Kasei Co., Ltd. stock) Company-made average molecular weight 2000 resin concentration 20% dimethylformamide solution) 70:30 weight ratio
It was dipped in a mixed polyurethane resin solution having a solid content concentration of 20% mixed in. Next, it was squeezed with a roll press having a clearance of 3.5 mm and a pressure of 3 kg / cm ² to uniformly impregnate it, and this resin-impregnated base fabric was immersed in water at room temperature (20 ° C.) for 48 hours to completely solidify the polyurethane resin. Then, it was taken out from the water bath, washed with water and squeezed three times, and then dried in a dryer at 130 ° C. for 2 hours. The resin adhesion rate of this polishing base cloth was 60%. Divide the obtained polishing base cloth into two pieces with a thickness of 2.1 mm, remove 0.8 mm of the skin layer from each, and have a thickness of 1.3 mm and a resin adhesion rate of 55
% Of two polishing substrates were obtained. Each of the obtained polishing substrates was heat-treated for 5 minutes in a dryer set at 190 ° C. to obtain a polishing substrate. The scanning electron micrograph of this product is shown in Fig. 2.
It can be clearly seen that microvoids remain. The results of measuring the physical properties of the polishing substrate are shown in Table 1. From the viewpoint of the resin adhesion rate of the polishing substrate, the resin adhesion amount of the polishing substrate is 25 to 40%, preferably 30%.
It can be said that a range of up to 40% is suitable as a polishing substrate. <Application example> The polishing substrate from the polishing base cloth obtained by the manufacturing method of Example 1 and the comparative example was coated on both sides of the surface plate (diameter 812 mmφ) of a single-side polishing machine (model 32SPAW) manufactured by Speed Huam Co., Ltd. Stick with tape and use colloidal silica-based abrasive grains to rotate a silicon wafer (125 mmφ) at a rotation speed of 87 RPM and a pressure of 50.
Polishing was performed at 0 g / cm ² for 20 minutes in one cycle. As a result, the polishing substrate according to Example 1 withstood 80 hours of use, whereas the polishing substrate of Comparative Example withstood only 50 hours. Further, the flatness of the polished surface was better with the substrate for polishing according to Example 1 than with the substrate for polishing of the comparative example, and the surface roughness was less.

【The invention's effect】

As described above, the method of the present invention divides the solidification step into two parts, incomplete solidification at the first stage, complete solidification by relatively low temperature drying treatment at the next stage, and formation of microvoids. It is possible to obtain a polishing base cloth that does not look at the conventional high temperature heat treatment step,
Further, it is a very simple and easy manufacturing method that does not require strict temperature control in the same process, and is very effective in terms of thermal economy. The polishing substrate prepared by using the polishing base fabric obtained by the present invention has a low compressibility, a high compression elastic modulus, a low Taber abrasion, and the desirable physical properties as a polishing substrate, and has a useful life. Is also long.

[Brief description of drawings]

1 is a scanning electron micrograph showing the state of fibers in the surface state of the polishing substrate obtained in Example 1 of the present invention, and FIG. 2 is the polishing substrate obtained in the comparative example ( 400 times).

Claims (1)

[Claims] 1. A synthetic fiber non-woven fabric having a mesh structure is impregnated with a dimethylformamide solution of a polyurethane resin,
In the method for producing a polishing base cloth for solidifying this, the solidifying step is performed by first dipping in water at room temperature or hot water for a short time to incompletely solidify, and then removing remaining dimethylformamide. A second step of desolvating in an atmosphere of 75 ± 5 ° C. to complete solidification, the method for producing a polishing base cloth.