JP2002217163A - Dissolving method of silicon layer formed on silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dissolving method of a silicon layer formed on a silicon wafer. SOLUTION: It is possible to dissolve selectively only the silicon layer formed on the silicon wafer by using an aqueous solution of tetraalkyl ammonium hydrooxide and to reuse the silicon wafer. By analyzing a slight amount of metal constituent contained in the meltage, it is possible to analyze the slight amount of metal contained in only the silicon layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dissolving a silicon layer formed on a silicon wafer.

[0002]

2. Description of the Related Art Single crystal silicon wafers are manufactured by semiconductors.
Used on a silicon wafer substrate.
Polycrystalline or amorphous silicon layer or silicon oxide
(SiO _Two) Layer and the like. these
Hydrofluoric acid (HF) or a method for dissolving the thin film layer of
Is a mixture of hydrofluoric acid (HF) mixed with nitric acid, hydrogen peroxide, etc.
Acid is used. Mixed acid such as hydrofluoric acid (HF) and nitric acid
Represents a silicon layer and silicon oxide (SiO_Two)
Processing, as the surface of the silicon wafer becomes rough
It is difficult to reuse the later silicon wafer.
In addition, since each thin film layer cannot be separated and dissolved,
It is also difficult to analyze trace components of metals.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for dissolving a silicon layer which can selectively dissolve a silicon layer formed on a silicon wafer. It is another object of the present invention to provide a method for dissolving a silicon layer that can reuse a silicon wafer after dissolving. Still another object of the present invention is to provide a method for dissolving a silicon layer capable of obtaining a sample for analyzing a trace metal contained in the silicon layer.

[0004]

SUMMARY OF THE INVENTION The present invention is a method for dissolving a silicon layer and a method for analyzing trace metals in a silicon layer. (1) A method for dissolving a silicon layer, comprising dissolving a silicon layer formed on a silicon wafer with an aqueous solution of tetraalkylammonium hydroxide. (2) The method according to (1) above, wherein the silicon layer formed on the silicon wafer is dissolved with an aqueous solution of tetraalkylammonium hydroxide to obtain a reusable silicon wafer. (3) The method according to the above (1) or (2), wherein the aqueous solution of the tetraalkylammonium hydroxide in which the silicon layer is dissolved is used as a sample for analyzing a trace metal component in the silicon layer. (4) The above (1) to (3), wherein the aqueous solution of the tetraalkylammonium hydroxide contains ammonia.
The method according to any of the above. (5) The method according to the above (4), wherein the aqueous solution of the tetraalkylammonium hydroxide contains 0.5 to 5 mol / l of ammonia. (6) After dissolving a silicon layer formed on a silicon wafer with an aqueous solution of tetraalkylammonium hydroxide, nitric acid is added to the aqueous solution.
Or the method according to any one of (5) to (5). (7) The method according to the above (6), wherein nitric acid is added to the aqueous solution of the tetraalkylammonium hydroxide so that the nitric acid concentration becomes 0.5 to 5 mol / l. (8) The method according to any one of the above (1) to (7), wherein the tetraalkylammonium hydroxide is tetramethylammonium hydroxide. (9) The method according to any of (1) to (8) above, wherein the concentration of the tetraalkylammonium hydroxide in the aqueous solution of the tetraalkylammonium hydroxide is 0.05 to 2.5 mol / l. (10) The method according to any one of the above (1) to (9), wherein the temperature of the aqueous solution of the tetraalkylammonium hydroxide is 15 to 50 ° C. (11) The method according to any one of (1) to (10), wherein the silicon layer is polycrystalline or amorphous.

[0005] The silicon wafer that is the object of the present invention is:
There is no particular limitation as long as it has a silicon layer. In the present invention, it is particularly preferable to apply the present invention to a silicon wafer having a polycrystalline (polysilicon) or amorphous silicon layer. As a specific example of the silicon wafer, there is a silicon wafer having a silicon oxide (SiO ₂ ) layer and a silicon layer on one or both sides of the silicon wafer.
In this case, usually, a silicon wafer / silicon oxide (SiO 2)
₂ ) It has a laminated structure in the order of layer / silicon layer. Such a silicon oxide (SiO ₂ ) layer usually has a thickness of 0.0
The thickness is about 01 to 1.0 micron (μm), and the thickness of the silicon layer is about 0.01 to 1.0 micron (μm).

In any case, the present invention is characterized in that the silicon layer (polycrystalline or amorphous) is dissolved in an aqueous solution of tetraalkylammonium hydroxide.

In the present invention, the aqueous solution of alkyl ammonium hydroxide used for dissolution can be used as a sample for analyzing trace metals contained in the silicone layer. In this case, it is possible to analyze a trace metal contained only in the silicon layer.

After dissolving and removing the silicon layer,
Further, if necessary, the silicon oxide (SiO ₂ ) layer may be dissolved with hydrofluoric acid (including a case where nitric acid, hydrogen peroxide, or the like is mixed with hydrofluoric acid). Thus, the silicon layer and the silicon oxide (SiO ₂ ) layer can be separately dissolved and removed. In this case, when dissolving the silicon oxide layer using the above-mentioned hydrofluoric acid, a trace metal contained in the silicon oxide (SiO ₂ ) layer may be analyzed.

Further, a silicon layer or a silicon oxide (SiO ₂ ) layer is dissolved and removed, and a silicon wafer is
It can be reused by forming a silicon oxide layer and a silicon layer again.

The tetraalkylammonium hydroxide used in the present invention can be exemplified by tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, etc. Among them, tetramethylammonium hydroxide is particularly preferred. It is.

The tetraalkylammonium hydroxide is usually used in an aqueous solution, and its concentration is usually 0.05 to 2.5 mol / l, preferably 0.2 to 2 mol / l.

The temperature of the aqueous solution of tetraalkylammonium hydroxide at the time of dissolving the silicon layer should be determined in a preferable range depending on the composition of the silicon layer, the crystal structure (size of crystal grains, amorphous state, etc.), its thickness, etc. Can be. Usually, it is desired to be about 15 to 50 ° C, preferably about 20 to 40 ° C. The dissolution can be performed, for example, by immersing the silicon layer in an aqueous solution of tetraalkylammonium hydroxide. The time required for dissolution is usually preferably about 0.5 to 15 minutes.

It is desirable that the aqueous solution of the tetraalkylammonium hydroxide contains ammonia. The concentration of ammonia in the aqueous solution is usually about 0.
Desirably, it is 5 to 5 mol / l, preferably about 0.5 to 3 mol / l. Therefore, it is possible to prepare a solution by mixing an aqueous ammonia solution with an aqueous tetraalkylammonium hydroxide solution. If it contains ammonia like this,
The dissolving power of the tetraalkylammonium hydroxide in the silicon layer can be increased. Further, it is possible to prevent the chemicals from remaining on the silicon wafer when washing with water after dissolving the silicon layer, and it becomes easy to wash the surface of the silicon wafer.

When the metal analysis in the solution is performed after the dissolution of the silicon layer, when the aqueous solution of the tetraalkylammonium hydroxide contains ammonia, after dissolution of the silicon layer, the pH may be adjusted to be acidic by adding nitric acid. desirable. The concentration of nitric acid in the aqueous solution is usually about 0.5
To 5 mol / l, preferably 0.5 to 3 mol / l. When nitric acid is added as described above, the metal in the solution in which the silicon layer is dissolved is prevented from being precipitated as a hydroxide, and the analysis accuracy of the trace metal component is improved.

[0015]

According to the present invention, only the silicon layer formed on the silicon wafer can be selectively dissolved by using an aqueous solution of tetraalkylammonium hydroxide. When the silicon layer is removed by the dissolving method of the present invention, the silicon wafer from which the silicon layer has been removed can be reused. Further, if the silicone layer is dissolved by the dissolution method of the present invention, the solution can be used as a sample for analyzing trace metal components contained in the silicon layer formed on the silicon wafer,
In this case, it is possible to analyze a trace metal contained only in the silicon layer.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 Silicon wafer / silicon oxide film (thickness: 0.05 μm)
/ Polysilicon film (thickness 0.2 μm) / Si (natural) oxide film, after removing the outermost surface layer (natural oxide film) with a hydrofluoric acid (HF) solution, tetramethylammonium hydroxide The polysilicon film was completely removed using a solution obtained by mixing an aqueous solution and aqueous ammonia, and washed with pure water. The conditions used are as follows. Concentration of aqueous solution Tetramethylammonium hydroxide: 0.5
Mol / l Ammonia: 1.2 mol / l Temperature of aqueous solution: 30 ° C (heating) Immersion time: 5 minutes

As a result, it was possible to regenerate a silicon wafer / silicon oxide (thickness: 0.05 μm) having a smooth surface.

Example 2 Silicon wafer / silicon oxide film (0.1 μm thick) /
In a multilayer structure composed of a polysilicon film (thickness 0.2 μm) / silicon nitride film (thickness 0.1 μm), the outermost surface layer (silicon nitride film) is dissolved in a hydrofluoric acid (HF) solution.
After recovery, the polysilicon film is completely dissolved using a solution (aqueous solution) in which tetramethylammonium hydroxide and ammonia water are mixed, and a nitric acid aqueous solution (a nitric acid concentration of 1.5 mol / liter) is added to the solution. It was collected after adding the same amount. Further, the lower Si oxide film was dissolved and recovered with a hydrofluoric acid (HF) solution. The metal concentration in each layer was separately quantified by analyzing the metal concentration in the dissolved and recovered liquid of each layer by ICP mass spectrometry, graphite furnace atomic absorption spectrometry, ICP emission spectrometry, or the like. The conditions used are as follows. Concentration of aqueous solution: same as in Example 1 Temperature of aqueous solution: 20 ° C (room temperature)

As a result, the trace metal component contained only in the polysilicon layer and the trace metal component contained only in the Si oxide film could be accurately analyzed using the solution.

Example 3 Silicon wafer / silicon oxide film (thickness: 0.05 μm)
/ Polysilicon film (thickness 0.08μm) / Si (natural)
After removing the outermost layer (natural oxide film) with a hydrofluoric acid (HF) solution in a multi-layer structure film composed of an oxide film, half of the polysilicon film (film) Thickness ratio) and washed with pure water. In order to examine the effect of dissolution, a portion of the polysilicon film from the outer peripheral portion to a width of about 5 mm was left around the silicon wafer. The conditions of the reagent used are as follows. Concentration of aqueous solution Tetramethylammonium hydroxide: 0.5
Mol / l Ammonia: 1.2 mol / l Aqueous solution temperature: 20 ° C (heating) Immersion time: 5 minutes

As a result, except for a portion having a width of about 5 mm from the outer peripheral portion of the silicon wafer, the polysilicon film is dissolved at 100% (area ratio), and the silicon wafer / silicon oxide film (thickness 0.05) μm / poly Silicon film (film thickness 0.04
μm) as a smooth multi-layered silicon wafer, and it was confirmed that the intended thickness (polysilicon film) of the intended portion (area) could be dissolved. The film thickness was determined by observing a cross section of the silicon wafer with a scanning electron microscope.

Comparative Example 1 In a silicon wafer having a multilayer structure film having the same structure as in Example 3, the outermost surface layer (natural oxide film) was made of hydrofluoric acid (H).
F) After the removal with the solution, the polysilicon film was removed using a mixed acid of hydrofluoric acid and nitric acid, and washed with pure water. The conditions of the reagents used are as follows. Concentration of mixed acid Hydrofluoric acid: 5 mol / l Nitric acid: 1.5 mol / l Temperature of mixed acid: 20 ° C Immersion time: 1 hour

In order to investigate the effect of the dissolution, the polysilicon film was to be left around the silicon wafer from the outer peripheral portion to a width of about 5 mm. However, the wettability of the mixed acid to the polysilicon film was poor and the It was difficult to dissolve the exposed portion, and only 70% (area ratio) of the polysilicon film was dissolved except for a portion having a width of about 5 mm from the outer peripheral portion of the silicon wafer. Furthermore, the solubility in the film thickness direction cannot be controlled, and a part of the polysilicon film (with respect to the film thickness direction) is dissolved in some places. To the direction)
In some places, the silicon wafer itself was dissolved, and in other places the silicon wafer itself was dissolved, and a silicon wafer having a smooth surface could not be obtained. Thus, it was found that when the mixed acid was used, it was difficult to dissolve the intended portion (area) of the polysilicon film, and it was not possible to dissolve the polysilicon film by the intended thickness.

Continuing from the front page (72) Inventor Tetsuya Miyazaki 1-2-1, Waki-cho, Kuga-gun, Yamaguchi Prefecture F-term in Mitsui Chemical Analysis Center Co., Ltd. 4G072 AA01 BB10 BB12 BB13 EE07 FF09 GG03 HH01 LL14 UU01 4M106 AA01 BA12 CB01 DH01 5F043 AA02 BB03 BB04 GG10

Claims (11)

[Claims] 1. A method for dissolving a silicon layer, comprising dissolving a silicon layer formed on a silicon wafer with an aqueous solution of tetraalkylammonium hydroxide. 2. The method according to claim 1, wherein the silicon layer formed on the silicon wafer is dissolved with an aqueous solution of tetraalkylammonium hydroxide to obtain a reusable silicon wafer. 3. The method according to claim 1, wherein an aqueous solution of a tetraalkylammonium hydroxide in which a silicon layer is dissolved is used as a sample for analyzing a trace metal component in the silicon layer. 4. An aqueous solution of a tetraalkylammonium hydroxide containing ammonia.
The method according to any of the above. 5. The method according to claim 4, wherein the aqueous solution of the tetraalkylammonium hydroxide contains 0.5 to 5 mol / l of ammonia. 6. The method according to claim 1, wherein after dissolving the silicon layer formed on the silicon wafer with an aqueous solution of tetraalkylammonium hydroxide, nitric acid is added to the aqueous solution. 7. The method according to claim 6, wherein nitric acid is added to the aqueous solution of the tetraalkylammonium hydroxide such that the nitric acid concentration becomes 0.5 to 5 mol / l. 8. The method according to claim 1, wherein the tetraalkylammonium hydroxide is tetramethylammonium hydroxide. 9. The concentration of the tetraalkylammonium hydroxide in the aqueous solution of the tetraalkylammonium hydroxide is 0.05 to 2.5 mol / mol.
9. The method according to claim 1, wherein the amount is liter. 10. The method according to claim 1, wherein the temperature of the aqueous solution of the tetraalkylammonium hydroxide is 15 to 50 ° C. 11. The method according to claim 1, wherein the silicon layer is polycrystalline or amorphous.