JPS6058797B2 - Etching solution continuous purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, in the process of etching silicone substrates in semiconductor manufacturing processes, contamination of suspended particles during silicone etching has become a problem.

In particular, in recent years, as integrated circuits have become smaller, the degree of their influence has become greater. Usually, the etching solution is
Drugs whose main ingredients are inorganic acids such as hydrofluoric acid, sulfuric acid, phosphoric acid, and hydrochloric acid and ammonium fluoride are used. Therefore, the purification of these agents during the etching process is disadvantageous due to the chemical deterioration of commonly used membrane filters.

Furthermore, recently, as a continuous purification device during etching,
Filters made of fluorine-based polymer membranes folded into pleated shapes are on the market. Since this filter is fluorine-based, it has good chemical resistance, but because it performs filtration using a total filtration method, it quickly becomes clogged, reducing the filtration rate and making it impossible to maintain its effectiveness over a long period of time. Based on the above, the present inventors conducted intensive research on a continuous purification treatment method in the etching process of a silicone base material, and as a result, they arrived at the present invention.

That is, in the process of etching a silicone base material with an etching solution mainly composed of an inorganic acid such as hydrofluoric acid, a part of the etching solution during etching is passed through a hollow fiber filter, and the etching solution is etched. This is a continuous etching solution purification method characterized in that the concentrated residual solution containing the separated fine particles is returned to the processing step and is combined with the etching solution passed through the filter and subjected to continuous circulation filtration.

The hollow fiber filter referred to here is a general filter in which a certain number of hollow fibers are housed in a housing (case), and adhesive is embedded between the hollow fibers and the housing at both ends of the housing. It is a hollow fiber filter.

According to the method of the present invention, the etching solution containing suspended fine particles existing or mixed in the etching treatment tank, specifically, dead bacteria, dust, organic matter, etc., is continuously circulated and filtered through a hollow fiber filter, and the fine particles are removed by the filter. Since the cleaned etching solution is returned to the etching tank, the etching solution in the etching tank is constantly cleaned.

on the other hand,? As the filtration progresses, the number of fine particles in the concentrate increases, but if the number of particles increases too much, the filtration rate decreases, so some of the concentrate is discharged at a stage when the filtration rate does not decrease too much. In the present invention, it is essential to combine the concentrated solution containing fine particles separated by the hollow thread filter with the etching solution passed through the filter and pass it through the filter again for continuous circulation filtration. If 6 filtration is performed using the conventional general filtration method without continuous circulation filtration, a large number of particles will be present or mixed in the etching treatment tank, and the filter will not be removed quickly due to the nature of the particles. It becomes clogged, the filtration rate decreases, and it cannot be maintained immediately.
The hollow fiber filter applicable to the present invention is as described above. However, in order to fully provide this function, the linear velocity of the inside of the hollow fiber is 0.1 to 5.0w1. It is preferable to pass the etching solution through the etching solution at /Sec and circulate it through the etching solution. Circulating filtration of etching solution through a hollow fiber filter by passing it from the outside to the inside of the hollow fiber is also effective.

Also, at appropriate time intervals, pass through the inside of the hollow fiber at high linear speed to scrape off the dirt layer all at once, or remove the dirt layer from the outside surface.
It is also preferable to perform cleaning treatment by passing a liquid through the surface. In particular, hollow fiber membranes are most suitable for the above treatment, which is why they maximize the effects of the present invention. The average pore diameter of the hollow fiber filter in the present invention is preferably 0.01 to 5μ, and 0.01 to 5μ.
．． 07 to 3μ is more preferred, and 0.1 to 0.8μ is most preferred.

Moreover, the porosity is preferably 15 to 90%. If the pore size of the membrane is too small or the porosity is too small, the filtration rate will not be sufficient.

In addition, the membrane area needs to be as small as possible, and the above range is preferable in order to increase the offshore velocity.On the other hand, if the pore size is large, the particle capture efficiency will be poor, and the porosity may be too large. If there is, the mechanical strength of the filter will be weakened.

The material of the polyolefin continuous porous membrane includes polyethylene, polypropylene, polydifluoroethylene, a mixture of two or more thereof, or a copolymer consisting of a mixture of two or more of ethylene, propylene, butene, hexene, and tetrafluoroethylene. etc. apply.

Furthermore, since the above-mentioned porous membrane is actually hydrophobic in nature, it must be soaked with a surfactant or an organic solvent such as isopropanol, methanol, ethanol, ketone, or ester before passing the liquid through it. It will be used later.

Also suitable as a hollow fiber filter material is a membrane whose surface has been permanently rendered hydrophilic by sulfonation.

As these materials, in addition to polyethylene, polypropylene, and polybutene, copolymers containing one or more of ethylene, propylene, and butene as components can be used. The hollow fiber filter made of the continuous polyphilic membrane as described above preferably has an inner diameter of 0.05 to 5 TWLφ.

If the inner diameter is smaller than 0.05T0tφ, filtration will not be performed satisfactorily, and if the inner diameter is larger than 5W$L, the compactness of the filter will not be sufficient. In addition, the thickness of the hollow fiber is 0.03 to 2
TrOn is preferred.

If the thickness of the hollow fiber is less than 0.03W0n, the strength will not be sufficient, and if it is more than 2W1, the offshore speed will decrease, which is not preferable. Example 1 A mixture containing 1 part by weight of dioctyl phthalate, 3 parts by weight of silicic anhydride, and 3 parts by weight of polyethylene was extruded into a hollow fiber, and then dioctyl phthalate was mixed with 1,1,1-trichloroethane (manufactured by Asahi Tau, trade name; After that, silicic anhydride was extracted with a 40% caustic soda solution, and the inner diameter was 1.0W! A continuous porous hollow fiber filter was constructed from a membrane having flφ, thickness of 0.2WUrL1, pore diameter of 0.15μ, porosity of 65%, and membrane area of 0.5bo.

The filter was pre-soaked with methanol and then soaked in water to substantially remove the methanol.

On the other hand, for comparison, a porous membrane with a thickness of 0.2WL1 pore diameter of 0.15μ and a porosity of 65% was obtained by extruding it into a film using the method described above and extracting it in the same manner, and a pleated filter with a membrane area of 0.5d was obtained. Got ready. These two types of filters
It was attached to another tank attached to the etching treatment tank, and the etching solution was passed through the filter continuously through a pump.

At this time, the sample filter was passed through the inside of the hollow fiber at a linear velocity of 0.5 m/sec, a portion of the filter was removed as a permeate liquid, and transferred to the original etching treatment tank, and the remaining liquid was discharged as a concentrated liquid. Is it circulated together with the liquid extracted from the treatment tank? I soaked the liquid. On the other hand, the filter of the comparative example was completely filtered so that the initial filtration amount was equal to that of the example filter, and the offshore filtrate was returned to the original treatment tank.

The initial number of suspended fine particles of 0.2μ or more in the etching treatment tank was 5×1ω particles/Cc. When silicone wafers were photo-etched for about 1 turbidity and the overspeeds were measured immediately before and after the start of processing in Examples and Comparative Examples, the following results were obtained.

As shown above, the Example filter achieves the effect of removing particulates without substantially reducing the p overrate even after one cycle has passed, whereas the Comparative Example's effect is less than half. As a result, the number of fine particles in the etching tank is increasing.

Example 2 The following wall diameter 0.6 was prepared using a method similar to Example 1.
A polypropylene continuous porous hollow fiber having Tnmφ and thickness of 0.15 was obtained.

Furthermore, the above filter was stretched to obtain the filter shown below.

Separately, the hole diameter is 10A, the inner diameter is 1.5mm in order, and the thickness is 0.3mIn.
A polysulfone-based ultra-P filtration membrane with a porosity of 60% was selected as Filter C, and separately attached to the apparatus shown in Example 1, and the membrane area necessary to obtain the required initial filtration rate of 5e/gourd was measured. did.

As mentioned above, filters B and C have lower porosity and smaller pore size than filters A, A'', and B'' due to their low porosity or small pore size.
This requires a membrane area that is more than ten times larger, and actually incorporating this filter and processing it inside the clean pliers would require a considerably larger membrane area and pump.

Furthermore, economically, it has been found that both filters B and C require more than ten times the processing cost as compared to filters A, A'', and B''. Example 3 According to Example 1, average pore diameter 0.80μ, porosity 60%
, inner diameter 1.4wLφ, thickness 0.2Tnm ethylene●
Tetrafluoroethylene copolymer hollow fiber porous filter D was obtained.

The above filter was stretched and had an average pore diameter of 8.0 μ, a porosity of 95%, an inner diameter of 0.9 bleached φ, and a thickness of 0.05 TnI! L
A filter E was obtained. Next, the two types of film coolers are individually attached to the concentration circulation tank attached to the etching processing tank, a part of the etching solution is passed through the filter, and a part of it is extracted as a p filtrate and returned to the processing tank, and then suspended. The residual liquid containing turbid particles was discharged into a concentration circulation tank, and the concentrated liquid was passed through a circulation tank together with a portion of the etching liquid. Etching solution: 15% hydrofluoric acid, 15% ammonium fluoride
% as the main component, and was subjected to silicone wafer photo-etching treatment in a processing tank. Two weeks after the start of the experiment, the condition of the phlegm was as shown below. The linear velocity at the filter inlet is 1.0rrL/Sec, and the inlet pressure is 1.
．． It was 5k9/CTl.

Etching solution initial suspended fine particle concentration Initial bottom overrate (e/Min-d) 1010 P overrate after 2 weeks (e/Min-i) 8.58.8 Suspended fine particle concentration after 2 weeks (min/Cc) 150900 Above As shown, Filter E does not have sufficient particulate capture efficiency.

Example 4 The membrane surface of Filter D of Example 3 was substantially sulfonated with fuming sulfuric acid in a state containing silicic anhydride to produce a hydrophilic polyolefin with a sulfonic group content of 0.45 meq/g polymer. A porous membrane was obtained.

This microporous membrane had substantially good wettability with the etching solution, and when the percolation performance was evaluated according to Example 3, the results shown below were obtained.

Initial etching information fine particle concentration (a). 2μ or more) 2×103 pieces/
Cc initial filtration rate 10e/Wft-
B. Concentration of fine particles in the etching tank after one month (4). 2μ or more)
After 18 months/Ccl? overspeed
9.0'/Wr! nd Example 5 An etching solution was filtered using the following hollow fiber filter (membrane area: 0.5 rrt).

Filter F: Obtained by extruding a mixture consisting of 6% by weight of chlorotrifluoroethylene oligomer, % by volume of silicic anhydride B, and 27% by volume of polymer fluorochlorinated ethylene, and extracting the chlorotrifluoroethylene oligomer and silicic anhydride. .

Inner diameter 0.6T! r! ILφ, thickness 0.1TIr! It is composed of poly(3-monofluorochloroethylene) hollow fibers with a porosity of 45% and an average pore diameter of 0.01μ. Ilter G: A mixture consisting of 61% by volume of dioctyl sebacate, 1% by volume of silicic anhydride, and 2% by volume of polyethylene was extruded into a hollow fiber, and dioctyl sebacate and silicic anhydride were extracted.

Inner diameter 0.6WRφ, thickness 0. I5w! n1 porosity 59%
, is composed of polyethylene hollow fibers with an average pore diameter of 0.07μ. Ilter H: Dioctyl phthalate 60% by volume
, an inner diameter of 0.6T1rInφ obtained by extruding a mixture consisting of silicic anhydride B volume % and polyvinylidene fluoride 2 mol% into a hollow fiber, and extracting dioctyl phthalate and silicic anhydride.
It is composed of polyvinylidene fluoride hollow fibers having a thickness of 0.2Tfn1, a porosity of 68%, and an average pore diameter of 3μ.

The above hollow fiber filter was subjected to continuous circulation filtration of the etching solution under the same conditions as in Example 1, and the filtration rate and the particulate concentration of the etching solution after one full hour were measured, and the following results were obtained.

Claims (1)

[Claims] 1. In the process of etching a silicone base material with an etching solution mainly composed of an inorganic acid such as hydrofluoric acid, a part of the etching solution during etching is filtered through a hollow fiber filter, and the filter is etched. A method for continuous purification of an etching solution, characterized in that the concentrated residual solution containing the separated fine particles is returned to the processing step and is combined with the etching solution passed through the filter for continuous circulation filtration. 2. The purification method according to claim 1, wherein the hollow fiber filter is made of polyethylene, polypropylene, ethylene-tetrafluoroethylene copolymer, or difluoroethylene polymer. 3. A patent in which the hollow fiber filter is a hollow fiber porous membrane made of a homopolymer of ethylene or butene, or a copolymer containing one or more of them, and the membrane surface is made hydrophilic by sulfonation. A purification method according to claim 1. 4. The hollow fiber filter has an average pore diameter of 0.01 to 5μ,
Polyolefin continuous porous membrane with porosity of 15 to 90%, inner diameter of 0.05 to 5 mmφ, thickness of 0.03 to 2 mm
The purification method according to claim 1, 2, or 3, which is constituted by hollow fibers. 5. The purification method according to claim 1, wherein the etching solution contains as a main component a chemical selected from inorganic acids such as hydrofluoric acid, sulfuric acid, phosphoric acid, and hydrochloric acid, and ammonium fluoride. 6 Linear speed of hollow fiber inside of hollow fiber filter is 0.1 to 5.
．． 2. The purification method according to claim 1, wherein the etching solution is circulated and filtered at a rate of 0 m/sec.