JP2009123798A - Silicon etchant and etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etchant and an etching method capable of substantially simplifying a work shape confirming operation during an etching process which had to be frequently performed by suppressing the temporal decline of an etching speed when heating is continued, which is peculiar to the etchant containing hydroxylamine, in silicon etching work, especially in the anisotropic etching work of silicon in a manufacturing process of an MEMS component. <P>SOLUTION: The silicon etchant is an alkaline aqueous solution containing hydroxylamine, one or more alkali compounds selected from tetramethylammonium hydroxide, potassium hydroxide and sodium hydroxide, and at least one alkali salt selected from tetramethylammonium hydrochloride, tetramethylammonium nitrate, tetramethylammonium sulfate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium oxalate, tetramethylammonium succinate, potassium chloride, sodium chloride, potassium acetate, and sodium acetate, and anisotropically dissolves single crystal silicon. Also, in the etching method of the silicon, the etachant is used. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a silicon etching process, and more particularly to a silicon etching solution and a silicon etching method used for manufacturing MEMS parts and semiconductor devices.

  In general, when etching a silicon single crystal substrate with a chemical solution, a method of etching with an acid-based etching solution which is a mixed aqueous solution in which components such as hydrofluoric acid and nitric acid are added, or potassium hydroxide (KOH), hydroxide A method of etching with an alkaline etching solution that is an aqueous solution of tetramethylammonium (TMAH) or the like is performed (see Non-Patent Documents 1 and 2).

  When an acid-based etching solution is used, the silicon surface is oxidized by a component having an oxidizing action such as nitric acid to produce silicon oxide, and this silicon oxide is dissolved as silicon fluoride by hydrofluoric acid or the like, so that etching is performed. proceed. A feature of etching with an acid-based etchant is that etching proceeds in the same direction regardless of whether the silicon to be etched is single crystal, polycrystalline, or amorphous. For this reason, when performing pattern etching using a pattern mask or the like, the deeper the etching, the lateral etching equivalent to the depth, that is, the undercut (erosion) under the pattern mask proceeds, It may cause inconvenience.

  On the other hand, when an alkaline etching solution is used, silicon is dissolved as silicic acid ions by hydroxy anions in the solution, and at this time, water is reduced to generate hydrogen. When etching is performed with an alkaline etching solution, unlike an acid etching solution, etching with single crystal silicon proceeds while having anisotropy. This is based on the fact that there is a difference in the dissolution rate of silicon for each crystal plane orientation of silicon, which is also called crystal anisotropic etching. Microscopically, etching progresses while maintaining anisotropy when viewed microscopically, but crystal orientation is randomly distributed, so that isotropic etching progresses macroscopically. Looks like. In amorphous, etching proceeds isotropically both microscopically and macroscopically.

  As an alkaline etching solution, an aqueous solution of sodium hydroxide (NaOH), ammonia, hydrazine, or the like is used in addition to an aqueous solution of KOH and TMAH. In etching of a single crystal silicon substrate using these aqueous solutions, a long processing time of several hours to several tens of hours is often required depending on a target processing shape, temperature conditions for processing, and the like.

In order to shorten the processing time as much as possible, a chemical solution exhibiting a high etching rate has been developed. For example, Patent Document 1 discloses a technique of using an aqueous solution obtained by adding hydroxylamines to TMAH as an etching solution. Patent Document 2 discloses a technique in which an aqueous solution obtained by adding a specific compound such as iron, iron chloride (III), or iron hydroxide (II) to TMAH is used as an etching solution, and the effect of increasing the etching rate is disclosed. It is disclosed that it is particularly preferable to use iron and hydroxylamine in combination. Patent Document 3 discloses a technique using an aqueous solution obtained by adding hydroxylamines to KOH as an etching solution. Further, Patent Document 4 includes (1) an organic alkali compound and (2) at least one selected from hydroxyamines, phosphates, reducing sugars, ascorbic acid, glyoxylic acid, brentzcatechin, and derivatives thereof. The invention relates to an anisotropic etchant composition comprising: (1) hydroxylamine, (2) alkali compound, and (3) hydrochloride, sulfate, nitrate, acetate of the alkali compound, There is no disclosure relating to a silicon etching solution characterized in that it is an aqueous solution containing at least one alkali salt selected from propionate, oxalate, and succinate.
JP 2006-054363 A JP 2006-186329 A JP 2006-351813 A JP2007-214456 Sato, "Silicon Etching Technology", Surface Technology, Vol.51, No.8, 2000, p754-759 Esashi, “2003 Micromachine / MEMS Technology Encyclopedia”, p.109-114

  However, since the hydroxylamine added to accelerate the etching rate in the techniques described in the above-mentioned Patent Documents 1, 2, 3, and 4 is a self-decomposable compound, the concentration is reduced during storage and etching treatment. In particular, by maintaining the etching solution itself in a heated state, the decrease in the concentration becomes more remarkable. Since this decrease in the concentration of hydroxylamine causes a decrease in the etching rate, the etching rate decreases with the passage of time when the temperature is maintained. Therefore, when performing an etching process using an etching solution containing hydroxylamine, it is necessary to perform a complicated operation of confirming the depth of the etching process many times during the etching process.

  Therefore, an object of the present invention is to reduce the etching rate with time by suppressing the decomposition of hydroxylamine without impairing the feature of high etching rate of the present application using an alkaline aqueous solution containing hydroxylamine. It is an object of the present invention to provide a silicon etching solution and a silicon etching method for suppressing single crystal silicon anisotropically.

As a result of diligent research to solve the above-mentioned problems, the present inventors performed etching with an aqueous solution to which hydroxylamine and an alkali compound and the alkali salt were added, thereby maintaining a high etching rate for silicon. It has been found that the etching rate can be prevented from decreasing due to the decomposition of hydroxylamine, and the present invention has been completed. That is, the present invention relates to a silicon etching solution and an etching method, and is as follows.
1. A silicon etching solution for dissolving single crystal silicon anisotropically, comprising (1) hydroxylamine, (2) an alkali compound, and (3) hydrochloride, sulfate, nitrate, acetate, propionic acid of the alkali compound A silicon etching solution, which is an aqueous solution containing at least one alkali salt selected from salts, oxalates, and succinates.
2. (1) The silicon etching solution according to item 1, wherein the alkali compound is at least one selected from tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide.
3. (3) Alkali salt is tetramethylammonium hydrochloride, tetramethylammonium nitrate, tetramethylammonium sulfate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium oxalate, tetramethylammonium succinate 2. The silicon etching solution according to claim 1, which is at least one selected from potassium chloride, sodium chloride, potassium acetate and sodium acetate.
4). (1) The concentration of hydroxylamine is 1 to 10 wt%, (2) the concentration of alkali compound is 3 to 25 wt%, and (3) the concentration of alkali salt is 3 to 14 wt% Silicon etchant.
5). A silicon etching method for anisotropically dissolving single crystal silicon, wherein (1) the concentration of hydroxylamine is 1 to 10% by weight, (2) the concentration of alkali compound is 3 to 25% by weight, and (3) the An aqueous solution containing 3 to 14% by weight of at least one alkali salt selected from hydrochloride, sulfate, nitrate, acetate, propionate, oxalate, and succinate of an alkali compound is used. A silicon etching method.
6). (2) one or more alkali compounds selected from tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide; and (3) alkali salt is tetramethylammonium hydrochloride, tetramethylammonium nitrate, tetramethylammonium sulfate. And at least one selected from the group consisting of tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium oxalate, tetramethylammonium succinate, potassium chloride, sodium chloride, potassium acetate and sodium acetate The silicon etching method according to Item.

  According to the present invention, while maintaining a high etching rate, which is a feature of an alkaline aqueous solution containing hydroxylamine, it is possible to make single crystal silicon anisotropic so as to suppress degradation of hydroxylamine and suppress a decrease in etching rate. Dissolving silicon etching solution and silicon etching method can be provided. Therefore, there is an effect that it is possible to greatly simplify troublesome operations such as extending the life of the silicon etching solution containing hydroxylamine and frequently checking the processed shape when performing the etching process.

  The alkali compound used in the present invention is preferably tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide, and particularly preferably tetramethylammonium hydroxide and / or potassium hydroxide. The alkali compounds of the present invention may be used alone or in combination of two or more.

  The concentration of the alkali compound can be appropriately determined according to the desired silicon etching rate, and is preferably in the range of 3 to 25% by weight. More preferably, it is 4 to 24% by weight. In a concentration range lower than 3% by weight, a large amount of fine pyramidal protrusions are formed on the surface of the etched surface, which may ultimately have an undesirable effect on the appearance and function of the product. Moreover, in the concentration range higher than 25% by weight, the effect of improving the etching rate obtained by adding hydroxylamine cannot be achieved. The concentration of the alkali compound can be appropriately determined in the range of 3 to 25% by weight.

  The concentration of hydroxylamine used in the present invention can be appropriately determined according to the desired silicon etching rate, and is preferably in the range of 1 to 10% by weight. More preferably, it is 2-10 weight%, More preferably, it is 3-10 weight%. If the concentration is lower than 1% by weight, the effect of improving the silicon etching rate by adding hydroxylamine may not be clearly obtained. If it is 1% by weight or more, the effect of improving the etching rate by adding hydroxylamine can be clearly obtained, and when the hydroxylamine concentration is increased, the etching rate tends to be improved accordingly. . However, even if the concentration exceeds 10% by weight and the concentration of hydroxylamine is increased, the effect of further improving the etching rate is hardly seen. The alkali compound and hydroxylamine concentrations may be adjusted in consideration of the desired etching rate.

  Alkali salts used in the present invention are tetramethylammonium hydrochloride, tetramethylammonium sulfate, tetramethylammonium nitrate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium oxalate, tetramethylammonium succinate Potassium chloride, potassium sulfate, potassium nitrate, potassium acetate, potassium propionate, potassium oxalate, potassium succinate, sodium chloride, sodium sulfate, sodium nitrate, sodium acetate, sodium propionate, sodium oxalate, sodium succinate, In particular, alkali salts include tetramethylammonium hydrochloride, tetramethylammonium nitrate, tetramethylammonium sulfate, tetramethylammonium acetate, La tetramethylammonium propionate, tetramethylammonium oxalate, tetramethylammonium succinate, potassium chloride, sodium chloride, potassium acetate, sodium acetate is preferred. The alkali salts of the present invention may be used alone or in combination of two or more.

  The concentration of the alkali salt used in the present invention may be appropriately selected in order to ensure the silicon etching rate and the stability of the etching solution, but is used at 3 to 14% by weight. If the concentration is lower than 3% by weight, the stability of hydroxylamine by the addition of salt and the effect of suppressing the decrease in the etching rate associated therewith may not be obtained. If it is 3% by weight or more, the effect of stabilizing the silicon etching rate can be obtained, and as the alkali salt concentration is increased, the decrease in the etching rate tends to be suppressed. However, when the alkali salt concentration is increased beyond 14% by weight, the effect on the stability of hydroxylamine is hardly observed. The salt concentration may be adjusted within a concentration range of 3 to 14% by weight so as to ensure the stability of the etching solution.

  In addition, a surfactant may be added to the etching solution of the present invention in order to improve wettability. For example, any of cationic, nonionic and anionic surfactants may be used. Furthermore, general additives, such as a coloring agent, can also be added. The etching solution of the invention must be alkaline, and the pH is preferably 10 or more, more preferably pH 11 or more.

  In the silicon etching method of the present invention, the object is usually immersed in a heated etching solution, taken out after a lapse of a predetermined time, and the etching solution adhering to the object is washed away with water or the like and then attached. The method of drying and removing the water which has been carried out is performed. The working temperature of the etching solution is preferably 40 ° C. or higher and lower than the boiling point, more preferably 50 ° C. to 90 ° C., particularly preferably 70 ° C. to 90 ° C. When the temperature of the etching solution is lower than 40 ° C., the etching rate is lowered, so that the production efficiency is remarkably lowered. When the temperature is raised to the boiling point, the liquid composition changes remarkably and it is difficult to keep the etching conditions constant. Although the etching rate is increased by increasing the temperature of the etching solution, an optimum processing temperature may be determined as appropriate in consideration of minimizing the temporal variation in the performance of the etching solution.

  An object to be etched in the present invention is a substrate or polyhedral block containing single crystal silicon, and single crystal silicon exists in the entire region or a partial region of the substrate or block. Note that single crystal silicon may be a single layer or a stacked state of multiple layers. Those that are ion-doped in the entire region or a partial region of these substrates and blocks are also objects to be etched. Further, the present invention also applies to a case where a material such as a silicon oxide film, a silicon nitride film, a silicon organic film, or a metal film such as an aluminum film, a chromium film, or a gold film is present on the surface of the etching object or inside the object. It is included in the object of the etching process.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not restrict | limited to these Examples at all. The etching object used for the evaluation is a single crystal silicon (100) (sometimes simply referred to as silicon (100)) wafer. One side of the silicon (100) wafer is covered with a protective film made of a silicon thermal oxide film, and a part of the silicon thermal oxide film is removed by dry etching on the other side. However, it has a pattern shape in which the silicon surface is exposed. The silicon (100) wafer was immersed in a 1% hydrofluoric acid aqueous solution for 7 minutes at room temperature immediately before etching, and then rinsed with ultrapure water and dried. By this hydrofluoric acid aqueous solution treatment, the treatment was carried out after removing the silicon natural oxide film formed on the surface of the exposed portion of the patterned silicon surface.

Method for etching single crystal silicon (100) wafer and method for calculating etching rate The etching solutions shown in the following examples and comparative examples are placed in a PTFE container, and the container is immersed in a hot water bath to etch the temperature of the etching solution. Was heated to 80 ° C. After the temperature of the etching solution reached 80 ° C., the single crystal silicon (100) wafer was immersed in the etching solution for 10 minutes for etching treatment, and then the wafer was taken out and rinsed and dried with ultrapure water. . In the etched wafer, the pattern portion is recessed from the surroundings as the silicon is etched, and the difference in height between the etched portion and the unetched portion is measured to measure the silicon in 10 minutes. The etching depth of the (100) plane was determined. A value obtained by dividing the etching depth by 10 was calculated as an etching rate (unit: μm / min) of the silicon (100) surface.

Heat aging test method and rate of decrease in etching rate After measuring the etching rate of the silicon (100) surface, the etching solution was kept at 80 ° C. for 8 hours, and then the heating was stopped to bring it to room temperature. And left for 16 hours. 8 + 16 = After 80 hours of heating at 80 ° C. and standing at room temperature for 5 hours (= heat aging treatment), the etching rate of the silicon (100) surface at 80 ° C. is measured again and heated. Compare the etching rate before and after aging treatment. The difference between the etching rates before and after the heat aging treatment is divided by the etching rate before the heat aging treatment, and a value multiplied by 100 is called the etching rate reduction rate.

  In addition, the heat aging treatment performed in Examples 1 to 7 and Comparative Examples 1 and 2 lowers the silicon (100) etching rate by intentionally decomposing hydroxylamine in the etching solution, and the stability of the chemical solution. This is just an example of the process performed to evaluate the process, and the higher the heating temperature and the longer the heating time, the more prominent the decomposition of hydroxylamine and the lower the etching rate. Needless to say. Here, it is only necessary to compare and confirm the degree of decrease in the etching rate of the silicon (100) surface for each etching solution, and thus the heat aging treatment is merely performed under the above conditions.

Example 1
An aqueous solution containing 5.2% by weight of tetramethylammonium hydroxide (TMAH), 10% by weight of hydroxylamine, and 7.1% by weight of tetramethylammonium hydrochloride was prepared as an etching solution, and a predetermined etching process was performed. went. As a result, the etching rate of the silicon (100) surface was 1.62 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.53 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.62−1.53) /1.62} × 100 = 5.6%.

Example 2
An aqueous solution containing 5.2% by weight of TMAH, 10% by weight of hydroxylamine, and 8.8% by weight of tetramethylammonium nitrate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 1.35 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.16 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.35-1.16) /1.35} × 100 = 14.1%.

Comparative Example 1
An aqueous solution containing 5.2% by weight of TMAH and 10% by weight of hydroxylamine was prepared as an etchant and subjected to a predetermined etching treatment. As a result, the etching rate of the silicon (100) surface was 1.46 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.02 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.46-1.02) /1.46} × 100 = 30.1%.

Example 3
An aqueous solution containing 6.5% by weight of TMAH, 10% by weight of hydroxylamine, and 6.3% by weight of tetramethylammonium acetate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 1.43 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.33 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.43-1.33) /1.43} × 100 = 7.0%.

Example 4
An aqueous solution containing 6.5% by weight of TMAH, 10% by weight of hydroxylamine, and 7.0% by weight of tetramethylammonium propionate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 1.50 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.35 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.50-1.35) /1.50} × 100 = 10.0%.

Example 5
An aqueous solution containing 6.5% by weight of TMAH, 10% by weight of hydroxylamine, and 3.8% by weight of tetramethylammonium oxalate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 1.60 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.31 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.60-1.31) /1.60} × 100 = 18.0%.

Example 6
An aqueous solution containing 6.5% by weight of TMAH, 10% by weight of hydroxylamine, and 4.5% by weight of tetramethylammonium succinate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 1.53 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.30 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.53-1.30) /1.53} × 100 = 15.0%.

Example 7
An aqueous solution containing 6.5% by weight of TMAH, 10% by weight of hydroxylamine, and 5.6% by weight of tetramethylammonium sulfate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 1.60 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 1.29 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(1.60-1.29) /1.60} × 100 = 19.4%.

Comparative Example 2
An aqueous solution containing 6.5% by weight of TMAH and 10% by weight of hydroxylamine was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 1.54 μm / min.
It was 1.07 micrometer / min when the etching rate of the silicon | silicone (100) surface after a heat aging test was measured.
From this result, the etching rate reduction rate by the heat aging test is {(1.54-1.07) /1.54} × 100 = 30.5%.

  From Examples 1 to 7 and Comparative Examples 1 and 2, by adding 3 to 14% by weight of tetramethylammonium salt in an aqueous solution containing the alkali compounds TMAH and hydroxylamine, the silicon (100 It can be seen that the rate of decrease in the etching rate of the surface is suppressed.

Example 8
An aqueous solution containing 20% by weight of KOH, 10% by weight of hydroxylamine, and 9.5% by weight of potassium chloride was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 4.36 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 3.54 μm / min.
From this result, the rate of decrease in the etching rate by the heat aging test is {(4.36-3.54) /4.36} × 100 = 18.8%.

Example 9
An aqueous solution containing 20% by weight of KOH, 10% by weight of hydroxylamine, and 12.6% by weight of potassium acetate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 4.52 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 3.84 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(4.52-3.84) /4.52} × 100 = 15.0%.

Comparative Example 3
An aqueous solution containing 20% by weight of KOH and 10% by weight of hydroxylamine was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 3.98 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 2.61 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(3.98-2.61) /3.98} × 100 = 34.4%.

  From Examples 8 and 9 and Comparative Example 3, etching of the silicon (100) surface by the heat aging test was performed by adding 3 to 14% by weight of potassium salt in an aqueous solution containing KOH and hydroxylamine which are alkali compounds. It can be seen that the rate of speed reduction is suppressed.

Example 10
An aqueous solution containing 14.4% by weight NaOH, 10% by weight hydroxylamine, and 9.1% by weight sodium chloride was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 3.62 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 2.96 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(3.62−2.96) /3.62} × 100 = 18.2%.

Example 11
An aqueous solution containing 14.4% by weight NaOH, 10% by weight hydroxylamine, and 12.8% by weight sodium acetate was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 3.75 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 3.19 μm / min.
From this result, the etching rate reduction rate by the heat aging test is {(3.75-3.19) /3.75} × 100 = 14.9%.

Comparative Example 4
An aqueous solution containing 14.4% by weight NaOH and 10% by weight hydroxylamine was prepared as an etchant and subjected to a predetermined etching process. As a result, the etching rate of the silicon (100) surface was 3.81 μm / min.
When the etching rate of the silicon (100) surface after the heat aging test was measured, it was 2.62 μm / min.
From this result, the rate of decrease in the etching rate by the heat aging test is {(3.81−2.62) /3.81} × 100 = 31.2%.

  From Examples 10 and 11 and Comparative Example 4, etching of the silicon (100) surface by the heat aging test was performed by adding 3 to 14% by weight of a sodium salt in an aqueous solution containing NaOH and hydroxylamine as alkali compounds. It can be seen that the rate of speed reduction is suppressed.

  The results of Examples and Comparative Examples are shown in Table 1.

Claims (6)

  A silicon etching solution for dissolving single crystal silicon anisotropically, comprising (1) hydroxylamine, (2) an alkali compound, and (3) hydrochloride, sulfate, nitrate, acetate, propionic acid of the alkali compound A silicon etching solution, which is an aqueous solution containing at least one alkali salt selected from salts, oxalates, and succinates.   (1) The silicon etching solution according to claim 1, wherein the alkali compound is at least one selected from tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide.   (3) Alkali salt is tetramethylammonium hydrochloride, tetramethylammonium nitrate, tetramethylammonium sulfate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium oxalate, tetramethylammonium succinate 2. The silicon etching solution according to claim 1, which is at least one selected from potassium chloride, sodium chloride, potassium acetate and sodium acetate.   The concentration of (1) hydroxylamine is 1 to 10% by weight, (2) the concentration of alkali compound is 3 to 25% by weight, and (3) the concentration of alkali salt is 3 to 14% by weight. Silicon etchant.   A silicon etching method for anisotropically dissolving single crystal silicon, wherein (1) the concentration of hydroxylamine is 1 to 10% by weight, (2) the concentration of alkali compound is 3 to 25% by weight, and (3) the An aqueous solution containing 3 to 14% by weight of at least one alkali salt selected from hydrochloride, sulfate, nitrate, acetate, propionate, oxalate, and succinate of an alkali compound is used. A silicon etching method.   (2) one or more alkali compounds selected from tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide; and (3) alkali salt is tetramethylammonium hydrochloride, tetramethylammonium nitrate, tetramethylammonium sulfate. And at least one selected from tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium oxalate, tetramethylammonium succinate, potassium chloride, sodium chloride, potassium acetate and sodium acetate. 6. The silicon etching method according to 5.