JPH06134264A - Turbidity removing device for semiconductor wafer grinding solution - Google Patents

Abstract

PURPOSE:To reduce the replacement of a semiconductor wafer grinding soln. to a large extent, in a device separating and filtering the grinding layer in the grinding soln., by using a porous hollow yarn membrane having specific fractionation capacity as a separation membrane to separate the grinding layer in the grinding soln. with high flux over a long period of time. CONSTITUTION:In a device 13 separating and filtering the grinding layer in a semiconductor wafer grinding soln., a porous hollow yarn membrane 14 with fractionation capacity of 0.05mum or lass is used as a separation membrane. As a result, the grinding layer in the semiconductor grinding soln. can be separated and filtered with high flux over a long period of time and the replacement of the grinding soln. can be reduced to a large extent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for separating and filtering grinding debris in a semiconductor wafer grinding fluid.

[0002]

2. Description of the Related Art Conventionally, a semiconductor wafer is used as a base material of a semiconductor device by processing a single crystal silicon into a disk shape having a mirror surface. In the processes such as ingot cutting (slicing), outer peripheral chamfering grinding (beveling), and surface grinding (lapping) in the manufacture of this semiconductor wafer, a chemical-added grinding fluid is used, but with the passage of time The concentration of grinding debris in the liquid becomes high, and eventually it cannot be used as a grinding liquid and the grinding liquid needs to be replaced.

Hitherto, as a method for removing the grinding dust in the grinding fluid, filtration with diatomaceous earth, filtration with a cartridge filter made of bobbin or non-woven fabric, etc. have been carried out. Was not satisfactory in terms of amount and particle size. Further, although attempts have been made to remove turbidity using various filtration membranes, a reverse osmosis membrane cannot cope with a liquid containing a high concentration of grinding debris and requires a pretreatment step. On the other hand, in the case of the ultrafiltration membrane, the equipment cost for the treatment amount was large for the plate and the tubular membrane, and the pressure filtration using the porous hollow fiber membrane caused clogging in an extremely short time.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a turbidity remover capable of separating and filtering grinding debris in a semiconductor wafer grinding liquid with a high flux for a long period of time and greatly reducing replacement of the grinding liquid. is there.

[0005]

That is, according to the present invention, a porous hollow fiber membrane having a fractionation performance of 0.05 μm or less is used as a separation membrane in an apparatus for separating and filtering grinding dust in a semiconductor wafer grinding liquid. A turbidity eliminator for a semiconductor wafer grinding fluid.

[0006]

The semiconductor wafer grinding liquid turbidity removing device of the present invention comprises:
A porous hollow fiber membrane having a fractionation performance of 0.05 μm or less is used as a separation membrane installed in the separation tank of the apparatus. When a porous hollow fiber membrane having a fractionation performance of 0.05 μm or less is used as the separation membrane, the occurrence of clogging of the pores of the porous hollow fiber membrane due to the grinding dust in the semiconductor wafer grinding fluid is specifically suppressed,
Almost no decrease in flux (volume of filtrate) occurs. The value of the fractionation performance referred to in the present invention is expressed as a value at which the permeation inhibition rate of polystyrene latex particles of that particle size is 90% or more.

Even if a porous hollow fiber membrane having a fractionation performance of about 0.1 μm is used, no problem occurs in terms of the leakage rate of suspended substances (grinding dust). However, when a fractionation performance of more than 0.05 μm is used, the pores are likely to be clogged, and the flux drops early. In the turbidity removing apparatus of the present invention, it is more preferable to use a porous hollow fiber membrane having a fractionation performance in the range of 0.038 to 0.005 μm. It is not preferable to use a material having unnecessarily small fractionation performance, for example, a material having a molecular weight of about 50,000 and a removal rate of 10% or more because the flux becomes too small and the apparatus becomes large.

[0008] The porous hollow fiber membrane is known to be produced by a solvent extraction method and a stretch opening method, depending on the production method. The stretch opening method has a slit-like pore shape. This is preferable as the hollow fiber membrane used in the device of the present invention because it is less likely to cause clogging.

The semiconductor wafer referred to in the semiconductor wafer grinding liquid to be processed by the turbidity removing apparatus of the present invention is not limited to a silicon wafer, but includes a gallium arsenide wafer and the like. The grinding fluid is usually an aqueous solution containing a chemical such as glycol.

In the turbidity removing apparatus of the present invention, a pressure filtration system can be adopted, but it is preferable to employ a total volume filtration system by suction filtration. Since the suction filtration method cannot increase the pressure difference between the membranes so much, the flux is small and the apparatus becomes large as compared with the pressure filtration method. However, no pressure equipment is required, and in particular, since grinding dust does not penetrate into the deep part of the pores of the hollow fiber membrane, the effect that a high flux can be maintained for a long time is exhibited. Further, since the suction pressure is not so high, physically moving the hollow fiber membrane makes it possible to easily separate the suspension adsorbed and attached to the membrane surface from the membrane surface.

Incidentally, the total volume filtration system referred to herein is a system which, unlike the cross flow system, collects the grinding fluid guided to the separation membrane by filtering it through the total volume separation membrane. That is, it is not always necessary to introduce all of the circulating grinding fluid to the separation tank, but depending on the required concentration level of cutting debris in the grinding fluid in the production process, a part of the circulating fluid (about 5% or more) is usually used. ) Is introduced into the separation tank as a sidestream, and the total amount of the sidestream is filtered, the concentration of cutting chips in the grinding fluid can be controlled.

Further, in the turbidity removing apparatus of the present invention, it is preferable to carry out filtration while moving (swimming) the hollow fiber membrane. As a hollow fiber membrane module suitable for use in such a turbidity eliminator of the present invention, a hollow fiber membrane arranged in a sheet form as shown in FIG. 1 is exemplified. In such a hollow fiber membrane module, the cutting debris is unlikely to be clogged in the gaps between the hollow fiber membranes, and the cutting debris attached to the hollow fiber membrane surface can be easily shaken off.

In the turbidity remover of the present invention, when the hollow fiber membrane is clogged with time and the flux is lowered,
Flux can be easily recovered by performing intermittent backwashing for about one second.

Since the hollow fiber membrane-impermeable grinding debris accumulates in the turbidity remover, the grinding debris accumulated on the bottom of the turbidity eliminator and the grinding debris in the turbidity eliminator are concentrated at an appropriate period. Discard the grinding fluid. Alternatively, a separate sedimentation tank may be provided to precipitate and concentrate the grinding dust, and the grinding dust and the grinding liquid may be discarded. In this way, the amount of waste liquid can be significantly reduced.

[0015]

【Example】

Example and Comparative Example FIG. 2 shows a circulating grinding fluid in a surface grinding process of a silicon wafer.
It processed with the turbidity removal apparatus which consists of the flow shown by. That is, the grinding fluid in the circulation tank 12 was used in the grinding step 11 and returned to the circulation tank as a grinding fluid containing grinding dust. On the other hand, the water supply pump 1 supplies the grinding fluid containing the grinding dust in the circulation tank.
A hollow fiber membrane module (total membrane area 10 m ² ) having a polyethylene porous hollow fiber membrane 14 as a separation membrane is introduced to the separation tank 13 via a suction pump 16 to obtain about 0.2 kg / cm ^2. Suction filtration was performed at a pressure of, and the filtrate was returned to the circulation tank. The hollow fiber membrane module is of the type shown in FIG. 1, and the crank 17 was used to constantly swim the hollow fiber membrane. Further, the liquid containing the concentrated grinding dust at the bottom of the separation tank was introduced into the precipitation tank 19, and the supernatant of the precipitation tank was returned to the separation tank again.

EHF-390A (manufactured by Mitsubishi Rayon Co., Ltd., trade name, fractionation performance 0.03 μm: Example) was used as the hollow fiber membrane, and EHF-410T (Mitsubishi Rayon).
The amount of liquid fed to the circulation tank was measured when a product manufactured by Co., Ltd., trade name, fractionation performance 0.1 μm: Comparative Example) was used, and the results shown in FIG. 3 were obtained. The concentration of grinding debris in the grinding fluid after passing through the separation membrane was 9 ppm in the example and 170 ppm in the comparative example. The concentration of grinding debris in the grinding fluid in the circulation tank during the test was 3000 to 3200 ppm.

[0017]

According to the turbidity remover of the present invention, the concentration of the suspension of the circulating grinding fluid can be maintained at a constant level, and the product yield of semiconductor wafers can be maintained at a high level. Further, since the hollow fiber membrane is not clogged for a long period of time and a high flux can be maintained, the amount of grinding fluid to be discarded can be reduced, and the amount of grinding chemical used can be small.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a hollow fiber membrane module suitable for use in the turbidity removing apparatus of the present invention.

FIG. 2 is a flow sheet of an example of the turbidity removing device of the present invention.

FIG. 3 is a graph showing changes over time in the flux of the return grinding fluid to the circulation tank after passing through the separation membrane in the turbidity removal apparatus of the present invention.

[Explanation of symbols]

 1 Hollow Fiber Membrane 2 Structural Material 3 Potting Material 4 Water Collection Port 11 Grinder 12 Water Storage Tank 13 Separation Tank 14 Hollow Fiber Membrane Module 15 Water Supply Pump 16 Suction Pump 17 Crank 18 Compressor 19 Sedimentation Tank

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yutaka Onuki 3-18-3 Kanda, Chiyoda-ku, Tokyo Koryu Kogyo Co., Ltd. Tokyo Branch

Claims (1)

[Claims] 1. An apparatus for separating and filtering grinding dust in a semiconductor wafer grinding fluid, wherein the separation membrane has a fractionation performance of 0.0.
A turbidity eliminator for a semiconductor wafer grinding liquid, characterized by using a porous hollow fiber membrane having a diameter of 5 μm or less.