JP2001351906A - Method of etching silicon substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon substrate, having a smooth etched surface with a small undercut through anisotropic etching using an alkaline aqueous solution. SOLUTION: At least one of polyethylene glycol and polypropylene glycol and one of 3-oxy 2-methyl anthraquinone, hydroquinone, and catechol disulfonic acid are added to an alkaline aqueous solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for etching a silicon substrate. More specifically, the present invention relates to an anisotropic etching method for processing a micromachining precision member using a silicon substrate.

[0002]

2. Description of the Related Art When etching a silicon substrate, a mixed solution of hydrofluoric acid and nitric acid is used for isotropic etching, and hydroxide is used for anisotropic etching depending on the crystal orientation of a silicon single crystal substrate. An alkaline aqueous solution such as tetramethylamine, potassium hydroxide or hydrazine is used. 2. Description of the Related Art Anisotropic etching using an alkaline aqueous solution is performed for processing micromachining precision members such as a semiconductor pressure sensor and a recording head for an inkjet printer using a silicon substrate.

[0003]

However, in hydrofluoric-nitric acid etching, which has an isotropic etching rate regardless of the crystal orientation of the silicon single crystal substrate, the undercut is large relative to the etching depth. However, there is a problem that the shape is far away from the shape.
Also, in anisotropic etching using an alkaline aqueous solution, when processing a member having a large etching depth such as a semiconductor pressure sensor or a recording head for an ink jet printer, desired performance is obtained due to large roughness and undercut of the etching surface. There was a problem that it could not be obtained.

In order to solve these problems, an etching solution in which an alcohol such as isopropyl alcohol is added to an alkaline aqueous solution has been developed. When the etching depth is about 50 μm, both the roughness of the etched surface and the undercut do not cause any problem. However, when the etching depth is large due to micromachining such as a semiconductor pressure sensor and a recording head for an ink jet printer, the solution of the problem has not reached a satisfactory level. Also, alcohol is not used much at present because alcohol is easily volatilized and the characteristics of the etchant are unstable.

An object of the present invention is to provide an etching method for obtaining a smooth etching surface with a small undercut by solving the above problems in anisotropic etching of a silicon substrate.

[0006]

SUMMARY OF THE INVENTION Therefore, in order to achieve the above object, the present invention provides an etching method for anisotropically etching a silicon substrate with an alkaline aqueous solution such as tetramethylamine hydroxide, potassium hydroxide or sodium hydroxide. At least one of polyethylene glycol and polypropylene glycol and at least one of 3-oxy-2-methylanthraquinone, hydroquinone and catechol disulfonic acid are added to the aqueous solution.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the etching solution having the above-mentioned structure, polyethylene glycol and polypropylene glycol are adsorbed on the uneven portion of the undercut surface generated at the time of anisotropic etching to form hydroxyl ions having an etching action. Inhibiting the contact has the effect of suppressing the progress of the undercut. The average molecular weight of the polyethylene glycol is 200 to 600, and the average molecular weight of the polypropylene glycol is 400 to 1
000. In the etching solution having the above structure, it is preferable that the addition amount of polyethylene glycol is 0.1% to 10%, and the addition amount of polypropylene glycol is 0.1% to 10%.

Further, in the etching solution having the above structure, 3
-Oxy-2-methylanthraquinone reacts with hydrogen generated during anisotropic etching, adheres to the etched surface, inhibits the progress of the etching reaction, and removes hydrogen bubbles that cause roughness. This has the effect of suppressing the roughness of the etched surface. It is preferable that the amount of 3-oxy-2-methylanthraquinone to be added is 1% to 10% in the etching solution having the above configuration.

Another cause of the roughness is that oxygen in the air that is in contact with the etching solution enters the solution and reacts with silicon on the etching surface to partially form silicon oxide. The slow progress may cause a local difference in the etching rate. In the etching solution having the above structure, hydroquinone has an effect of suppressing roughness of an etching surface by reacting with oxygen in the etching solution to remove oxygen in the solution. In the etching solution having the above structure, the amount of hydroquinone added is preferably 1% to 10%.

[0010] In addition, since the progress of etching in the etching liquid is delayed due to the metal ions in the etching solution and the dissolved silicon itself adhering or adhering partially to the etching surface, a local difference in the etching rate occurs, resulting in roughening. May cause. Catechol disulfonic acid binds to these metal ions and the dissolved silicon itself by forming a complex or chelate, and has an effect of suppressing the roughness of the etched surface by adhering or adsorbing to the etched surface. Catechol disulfonic acid is preferably added in an amount of 0.1% to 5%.

As the kind of the alkaline aqueous solution, alkaline compounds such as tetramethylamine hydroxide, potassium hydroxide and sodium hydroxide can be used alone or in combination.

[0012]

(Example 1) A silicon oxide film having a thickness of 1 μm was formed by thermal oxidation on a silicon substrate having a thickness of 600 μm and a (100) plane orientation. By photolithography using buffered hydrofluoric acid, the side is 2 m along the <100> direction.
A m-square square silicon oxide mask pattern was formed. Then, tetramethylamine hydroxide 20%, average molecular weight 4
In an etching solution having a composition of 2% polyethylene glycol, 2% 3-oxy-2-methylanthraquinone, 2% hydroquinone, and 74% deionized water, the silicon substrate was subjected to etching using the etching apparatus shown in FIG. ° C
Etching was performed for 3 hours.

FIG. 2 is a schematic diagram showing the result of observing the silicon substrate etched by the etching method of the present invention with an optical microscope. Five silicon substrates were processed for each etching, and the processing was performed a total of 20 times. Table 1 shows the etching depth, undercut constant, and etched surface appearance at the time of the second treatment, and the etched surface appearance at the time of the twentieth treatment. As shown in Table 1, a silicon substrate having a smooth etching surface and a small undercut was obtained.

The etching depth was measured using a stylus type roughness meter. The undercut width was measured using an optical microscope. The undercut constant is expressed by the following equation, where D is the etching depth and W is the undercut width.

Undercut constant = W / D The appearance of the etched surface was observed using an optical microscope.

(Example 2) A mask pattern of silicon oxide was formed on a silicon substrate by the same method as in the first example. Subsequently, 30% of potassium hydroxide, 2% of polypropylene glycol having an average molecular weight of 600, and 3-oxy2
The above silicon substrate was etched at 80 ° C. × 3 hours in an etching solution having a composition of 2% of methyl anthraquinone, 2% of catechol disulfonic acid, and 64% of deionized water using the etching apparatus shown in FIG. Five silicon substrates were processed for each etching, and the processing was performed a total of 20 times. Table 1 shows the etching depth, undercut constant, and etched surface appearance at the time of the second treatment, and the etched surface appearance at the time of the twentieth treatment. As shown in Table 1,
A silicon substrate having a smooth etched surface and a small undercut was obtained. Even after the twentieth treatment, the etched surface has no roughness, and the surface is a mirror surface, and the stability of the etching solution is excellent.

Comparative Example 1 A mask pattern of silicon oxide was formed on a silicon substrate in the same manner as in Example 1. Next, the silicon substrate was etched at 80 ° C. for 3 hours in an etching solution having a composition of 30% potassium hydroxide, 15% isopropyl alcohol, and 55% deionized water using the etching apparatus shown in FIG. Processing 5 silicon substrates per etching,
A total of 20 treatments were performed. Etching depth, undercut constant and etched surface appearance during the second treatment, 2
Table 1 shows the appearance of the etched surface at the time of the 0th treatment. FIG.
Fig. 3 shows a schematic view of the surface of a silicon substrate observed by an optical microscope after etching.

In this comparative example, which is a conventional etching method, as shown in FIG. 3, a micro pyramid is observed on the etching surface, and the surface is rough. Also, as shown in Table 1, the undercut is large.

[0019]

[Table 1]

[0020]

As described above, according to the present invention,
In a method of etching a silicon substrate with an alkaline aqueous solution, at least one of polyethylene glycol and polypropylene glycol, and 3-oxy2
By adding at least one of -methylanthraquinone, hydroquinone and catechol disulfonic acid, the etching surface becomes smooth without roughness and the undercut is reduced. As a result, even a silicon member requiring a large etching depth can be precisely processed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an etching apparatus of the present invention.

FIG. 2 is a schematic view showing the appearance of a silicon substrate by the etching method of the present invention.

FIG. 3 is a schematic view showing the appearance of a silicon substrate by a conventional etching method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stirrer with temperature control 2 Temperature sensor 3 Etching tank 4 Etching solution 5 Substrate holder 6 Stirrer 7 Silicon substrate 8 Cooling pipe 21 Mask pattern 22 Undercut width 23 Silicon substrate etching wall 24 Silicon substrate etching surface 31 Mask pattern 32 Micro Pyramid 33 Silicon substrate etching wall 34 Silicon substrate etching surface

Claims (8)

[Claims] 1. An etching method for anisotropically etching a silicon substrate with an alkaline aqueous solution, wherein said aqueous solution contains at least one of polyethylene glycol and polypropylene glycol, and 3-oxy-2-methylanthraquinone, hydroquinone and catechol disulfonic acid. A method of etching a silicon substrate, wherein at least one of them is added. 2. The method of claim 1, wherein the polyethylene glycol has an average molecular weight of 200 to 600. 3. The method according to claim 1, wherein the amount of the polyethylene glycol added is 0.1% to 10%. 4. The method according to claim 1, wherein the average molecular weight of the polypropylene glycol is 400 to 1,000. 5. The method for etching a silicon substrate according to claim 1, wherein the addition amount of the polypropylene glycol is 0.1% to 10%. 6. The method according to claim 1, wherein the amount of the 3-oxy-2-methylanthraquinone is 1% to 10%. 7. The amount of the hydroquinone added is 1% to 10%.
2. The method of claim 1, wherein 8. The method according to claim 1, wherein the amount of the catechol disulfonic acid is 0.1% to 5%.