JP2010147304A - Method of regenerating etchant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of regenerating an etchant targeting an etchant of silicon nitride and/or silicon nitride oxide containing sulfuric acid, extremely easily removing a silicon compound produced in the etchant, suitable for an industrial process, reducing regeneration process expense of the etchant, and capable of reducing waste liquid. <P>SOLUTION: Silicon nitride and/or silicon nitride oxide is etched by an etchant containing sulfuric acid, fluoride and water, and thereafter the etchant is heated and/or depressurized to remove a silicon compound produced by the etching. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for regenerating an etching solution containing sulfuric acid, fluoride and water used for etching silicon nitride or silicon nitride oxide. More specifically, the present invention relates to a method for regenerating the etching solution used for etching silicon nitride or silicon nitride oxide used for insulating films such as semiconductor devices and flat panel displays.

  Silicon nitride and silicon nitride oxide are very important compounds as ceramic materials and semiconductor materials.

  Semiconductor manufacturing processes include processes that require selective etching of only silicon nitride or silicon nitride oxide without damaging the silicon oxide. Currently, high-purity phosphoric acid is mainly used in this process. However, high-purity phosphoric acid is expensive because the supply amount of raw material yellow phosphorus is limited, and there is a problem in using it in a large amount.

  On the other hand, as an etching method that does not use phosphoric acid at all, an etching method using an etching solution in which a fluorine compound such as hydrogen fluoride or ammonium fluoride is added to sulfuric acid has been proposed (see, for example, Patent Document 1). Although this is a useful method that does not use expensive phosphoric acid, it is not preferable to dispose of it as it is, even if it is inexpensive sulfuric acid, from the viewpoint of resource saving and waste disposal.

  By the way, in the etching process in the mass production line of various substrates, etc., in order to keep the etching solution in the etching tank clean, the etching solution is circulated and continuously etched while removing foreign matters such as dust in the etching solution. Is going to. This also applies to the etching of silicon nitride and silicon nitride oxide. The etching solution (for example, phosphoric acid aqueous solution) is filtered and circulated, and the silicon compound deposited in the etching solution is filtered and purified together with other foreign substances. Etching is performed (see, for example, Patent Document 2).

  However, in the method described in Patent Document 1, the concentration of the silicon compound in the etching solution is increased by repeatedly using the same etching solution and performing the etching treatment, so that the silicon compound is on the device or in the semiconductor in the etching solution. There is a problem that the yield of the product decreases due to deposition on the wafer.

  Therefore, it has been studied to regenerate the etching solution used for etching. For example, a method of adding hydrofluoric acid to phosphoric acid and removing silicon dissolved in phosphoric acid (see, for example, Patent Document 3 and Patent Document 4) has been proposed.

  However, in the above-described method for regenerating an etching solution, hydrofluoric acid to be used is a substance that affects the etching selectivity of silicon nitride and silicon nitride oxide as well as the silicon compound. The concentration of hydroacid must be measured with high accuracy, and the end point of the etching solution regeneration process (concentration of hydrofluoric acid that does not affect the etching, etc.) must be confirmed and managed. This end point management is performed, for example, by sampling a part of the etching solution, but is complicated in maintaining continuous etching and causes an increase in cost.

JP 2002-246378 A Japanese Patent Publication No. 03-20895 Japanese Patent Application Laid-Open No. 07-86260 Japanese Patent Laid-Open No. 09-45660

  The present invention has been made in view of the background art described above, and an object of the present invention is to remove a silicon compound generated in the etching solution, which is an etching solution of silicon nitride and / or silicon nitride oxide containing sulfuric acid. The present invention is to provide a method for regenerating an etching solution that is extremely easy, suitable for an industrial process, can reduce the cost of regenerating the etching solution, and can reduce waste solution.

  As a result of intensive studies on a method for regenerating an etching solution containing silicon nitride and / or silicon nitride oxide containing sulfuric acid, the present inventors reused the etching solution containing sulfuric acid by heating and / or reducing the pressure of the etching solution. The present inventors have found that the silicon compound can be reduced to a level that can be achieved, and have completed the present invention.

  That is, the present invention is an etching solution regeneration method as described below.

  [1] Etching in which silicon nitride and / or silicon nitride oxide is etched with an etching solution containing sulfuric acid, fluoride and water, and then this etching solution is heated and / or decompressed to remove the silicon compound produced by the etching. Liquid regeneration method.

  [2] The composition of the etching solution after etching, wherein the ratio of fluoride to silicon compound is more than 4 in terms of the molar ratio of fluorine to silicon (F / Si). Etching solution regeneration method.

  [3] The method for regenerating an etching solution according to the above [1] or [2], wherein the fluoride is at least one selected from the group consisting of hydrofluoric acid and ammonium fluoride.

  [4] The above-mentioned [1] to [3], wherein the concentration of fluoride in the etching solution is 1 ppm by weight to 0.1% by weight with respect to the entire etching solution. Of regenerating an etching solution.

  [5] The method for regenerating an etching solution according to any one of [1] to [4], wherein the concentration of water in the etching solution is 1 to 70% by weight with respect to the etching solution. .

  [6] The method for regenerating an etching solution according to any one of the above [1] to [5], wherein the heating temperature is in the range of 100 to 200 ° C.

  [7] The method for regenerating an etching solution according to any one of the above [1] to [6], wherein the pressure during decompression is in the range of 1 to 90 kPa.

  [8] The above-mentioned [1], wherein the etching solution after etching is heated and / or decompressed so that the concentration of the silicon compound in the etching solution is 50 ppm by weight or less with respect to the etching solution. ] The reproduction | regeneration method of the etching liquid in any one of [7].

  According to the method for regenerating an etching solution of the present invention, since the silicon compound in the etching solution can be removed by a simple method of heating and / or decompression, the industrial value is extremely high. That is, the etching solution regenerated by the method of the present invention can be reused not only as an etching solution but also as sulfuric acid, so that waste liquid can be reduced.

  The present invention is described in further detail below.

  In the method of the present invention, after etching silicon nitride and / or silicon nitride oxide with an etching solution containing sulfuric acid, fluoride and water, the etching solution is heated and / or decompressed to remove the silicon compound produced by the etching. Remove.

  The etching solution used in the method of the present invention contains sulfuric acid, fluoride and water.

  As a fluoride used for etching liquid, fluoride salts, such as hydrofluoric acid, ammonium fluoride, sodium fluoride, potassium fluoride, are mentioned as a suitable thing, for example. Among these, hydrofluoric acid and ammonium fluoride which do not contain a metal component are particularly preferably used for manufacturing electronic devices such as semiconductors. Moreover, there is no restriction | limiting in particular about the sulfuric acid and water which are used for etching liquid, What is generally distribute | circulating can be used. For electronic materials, sulfuric acid and water with a small amount of metal are circulated, and it is particularly preferable to use these.

  The composition of the etching solution used in the method of the present invention includes sulfuric acid, 1 wt ppm to 0.1 wt% fluoride with respect to the entire etching solution, and 1 to 70 wt% water with respect to the entire etching solution. It is preferable to contain, and the composition which contains a sulfuric acid, 5-500 weight ppm fluoride with respect to the whole etching liquid, and 1 to 50 weight% of water with respect to the whole etching liquid is further more preferable.

  In the composition containing less than 1 ppm by weight of fluoride with respect to the entire etching solution and less than 1% by weight of water with respect to the entire etching solution, the etching rate may be unsatisfactory. Moreover, when hydrofluoric acid exceeding 0.1 weight% with respect to the whole etching liquid is added, there exists a possibility of corroding materials other than silicon nitride.

  On the other hand, when water containing more than 70% by weight with respect to the entire etching solution is contained, the temperature of the etching solution is excessively lowered, and in this case as well, there is a possibility that the etching rate becomes so slow that it is not industrial. Moreover, even if the water concentration is less than 1% by weight or more than 70% by weight, the removal rate of the silicon compound may be slow.

  In the method of the present invention, the temperature at which silicon nitride and / or silicon nitride oxide is etched is usually in the range of 120 to 180 ° C, preferably in the range of 130 to 170 ° C. At temperatures above 180 ° C, semiconductor materials other than silicon nitride and silicon nitride oxide are likely to be damaged, and at temperatures below 120 ° C, silicon nitride and silicon nitride oxide are etched at an industrially satisfactory rate. Is difficult.

  In the method of the present invention, the etching solution after etching silicon nitride and / or silicon nitride oxide is regenerated by heating and / or reducing pressure. When the silicon compound is removed only by heating under atmospheric pressure, the heat treatment is usually performed at a temperature of 100 to 200 ° C, preferably 100 to 180 ° C. At temperatures below 100 ° C., the removal of silicon compounds is not industrially slow, and at temperatures above 200 ° C. it is energetically disadvantageous. When removing the silicon compound, the removal is facilitated by reducing the pressure. This effect is exhibited if the pressure is lowered even a little below atmospheric pressure, but the effect is further increased if the pressure is in the range of 1 to 90 kPa. If the pressure exceeds 90 kPa, the effect of reducing the pressure is small, and if it is less than 1 kPa, it is disadvantageous in terms of energy.

  In the method of the present invention, the etching solution after etching silicon nitride and / or silicon nitride oxide contains a silicon compound in addition to sulfuric acid, fluoride, and water. In the etching solution regenerated by the method of the present invention, the ratio of the fluoride to the silicon compound in the composition of the etching solution after the etching is desirably more than 4 in terms of the molar ratio of fluorine to silicon (F / Si).

  In general, silicon compounds react with fluoride ions to form volatile silicon fluoride or hexafluorosilicic acid, but in the presence of strong acids such as sulfuric acid and water used in the method of the present invention, silicon fluoride. And hexafluorosilicic acid decomposes into non-volatile silicon dioxide insoluble in the etching solution. Here, in the above etching solution, if the ratio of fluoride to silicon compound exceeds 4 in terms of the molar ratio of fluorine to silicon, formation of silicon dioxide is hindered and a volatile silicon compound is formed. In addition, the silicon compound can be easily removed by reducing the pressure. These reactions are equilibrium reactions, and the higher the fluorine concentration, the more volatile silicon compounds become, and the more easily the silicon compounds are removed. On the other hand, the higher the silicon concentration, the more likely they become silicon dioxide and precipitate.

  In the method of the present invention, etching of silicon nitride and / or silicon nitride oxide is usually performed by bringing the object to be processed into contact with the etching solution in an etching tank storing the etching solution.

  In the method of the present invention, the heating and / or decompression of the etching solution may be carried out in the etching bath, or the etching solution containing a silicon compound is extracted from the etching bath and carried out in another bath. good. At that time, when a method such as stirring, gas bubbling, ultrasonic irradiation or the like is used in combination, the removal of the silicon compound is further promoted.

  In the method of the present invention, it is desirable to remove the silicon compound so that the concentration of the silicon compound contained in the etching solution is 50 ppm by weight or less with respect to the entire etching solution. When the silicon compound is present in excess of 50 ppm by weight, the silicon compound may be decomposed into silicon dioxide insoluble in sulfuric acid and deposited on an etching device, an etching apparatus, or an electronic device such as a wafer.

  The etching solution regenerated in the method of the present invention is not only a silicon compound but also fluorine is removed at the same time, and since the purity is high, it can be used as an etching solution without further purification, analysis, etc. It can also be used by mixing with unused sulfuric acid or etching solution. Further, since it can be reused as sulfuric acid, there is an advantage that waste liquid can be reduced.

  The present invention will be described in more detail with reference to the following examples, but the present invention should not be construed as being limited thereto. In order to simplify the title, the following abbreviations were used.

SiN: silicon nitride,
SiO: silicon oxide,
HF: hydrofluoric acid,
SiF: hexafluorosilicic acid,
Si: silicon,
F: Fluorine,
F / Si: molar ratio of fluorine and silicon.

Example 1.
[Preparation of Etching Solution A]
Concentrated sulfuric acid was added to deionized water to prepare 66 wt% sulfuric acid water. This is designated etching solution A.

[Preparation of Etching Solution B]
Concentrated sulfuric acid, SiF, and HF were added to deionized water to prepare sulfuric acid water containing 200 wt ppm HF, 80 wt ppm SiF, and 34 wt% water. This is designated etching solution B.

[SiN etching]
100 g of the etching solution A and 100 g of the etching solution B were put in a Teflon (registered trademark) container and heated until the temperature of the etching solution reached 160 ° C. The etching solution A was supplied at 100 g / hour and the etching solution B was supplied at 100 g / hour continuously from the bottom of a Teflon (registered trademark) container. On the other hand, the etching solution was removed from the upper part of the container so that the level of the etching solution was constant.

  In a Teflon (registered trademark) container containing an etching solution, a silicon wafer (15 mm square) having a SiN film formed to a thickness of 300 nm by a CVD method and a silicon wafer (15 mm) having a thermal oxide film formed to a thickness of 1000 nm are formed. Corner square) was immersed for 10 minutes. The wafer was taken out, washed with water, and dried, and the film thickness of SiN and the thermal oxide film was measured with an optical interference film thickness meter. The etching rate of SiN and SiO was calculated from the change in the film thickness. As a result, the SiN etching rate was 4.1 nm / min, and the SiO etching rate was 0.024 nm / min.

[Regeneration of etchant]
The etching solution was extracted from the upper part of the container, and the Si concentration was measured by the ICP-AES method, and the F concentration was measured by the colorimetric method (JIS K 0102-34.1). F was 40.0 ppm by weight [F / Si = 10.7 (molar ratio)]. This etchant is designated as a regeneration etchant C.

  After the regeneration etching solution C was heated at 160 ° C. for 1 hour, the Si concentration and the F concentration were measured in the same manner as described above. As a result, Si decreased to 0.8 ppm by weight and F decreased to 3.5 ppm.

  Water was added to the etching solution so that the water content was 34% by weight. Etching of SiN was performed in the same manner as [SiN etching] except that this was used in place of the etching solution A (sulfuric acid). As a result, the SiN etching rate was 4.1 nm / min, the SiO etching rate was 0.024 nm / min, and the etching rate was not different from that when the etching solution A prepared from concentrated sulfuric acid was used.

Comparative example.
Water was added to the regenerating etchant C that was neither heated nor depressurized so that the water content was 34% by weight. Etching of SiN was performed in the same manner as in Preparation Example 3 except that this was used as the etching solution A (sulfuric acid solution). As a result, the SiN etching rate was 4.8 nm / min, the SiO etching rate was 0.011 nm / min, and the etching rate was changed.

  Further, when the same operation was repeated, silicon dioxide was deposited on the silicon wafer on which the thermal oxide film was formed.

Example 2
After etching SiN, 200 g of an etching solution containing 15.5 wt ppm of Si, 66 wt% of sulfuric acid and 66 wt ppm of HF [the balance is water, F / Si = 6.0 (molar ratio)] is Teflon (registered trademark). ) And heated at 150 ° C. for 1 hour. When this liquid was analyzed in the same manner as in Example 1, Si was reduced to 1.5 ppm by weight, and F was reduced to 2.3 ppm.

Example 3 FIG.
After etching SiN, 200 g of an etching solution containing 20 wt ppm of Si, 66 wt% of sulfuric acid and 66 wt ppm of HF [the balance is water, F / Si = 4.6 (molar ratio)] manufactured by Teflon (registered trademark) And decompressed at 80 ° C. and 85 kPa for 1 hour. When this liquid was analyzed in the same manner as in Example 1, Si was reduced to 0.3 ppm by weight, and F was reduced to 1.0 ppm.

Claims (8)

Etching silicon nitride and / or silicon nitride oxide with an etching solution containing sulfuric acid, fluoride and water, and then heating and / or depressurizing the etching solution to remove the silicon compound produced by the etching. Method. The composition of the etching solution after etching is characterized in that the ratio of fluoride to silicon compound exceeds 4 in terms of the molar ratio of fluorine to silicon (F / Si). Method. The method for regenerating an etching solution according to claim 1, wherein the fluoride is at least one selected from the group consisting of hydrofluoric acid and ammonium fluoride. The regeneration of the etching solution according to any one of claims 1 to 3, wherein the concentration of the fluoride in the etching solution is 1 ppm by weight to 0.1% by weight with respect to the etching solution. Method. The method for regenerating an etching solution according to any one of claims 1 to 4, wherein the concentration of water in the etching solution is 1 to 70% by weight with respect to the etching solution. The method for regenerating an etching solution according to any one of claims 1 to 5, wherein the heating temperature is in the range of 100 to 200 ° C. The method for regenerating an etching solution according to any one of claims 1 to 6, wherein the pressure during decompression is in the range of 1 to 90 kPa. The etching solution after etching is heated and / or decompressed so that the concentration of the silicon compound in the etching solution is 50 ppm by weight or less with respect to the etching solution. 8. The method for regenerating an etching solution according to any one of 7 above.