KR20170001801A - Etching solution for silicon nitride layer - Google Patents

Abstract

The present invention relates to an etching solution for a silicon nitride film and, more specifically, to an etching solution having a higher etching selection ratio to a silicon nitride film than a silicon oxide film when wet-etching in a semiconductor manufacturing process. The etching solution for a silicon nitride film comprises: phosphoric acid; a silicon-based additive represented by chemical formula 1; and residual water.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a silicon nitride (SiN)

The present invention relates to a silicon nitride film etching solution, and more particularly, to an etching solution having a higher etching selectivity to a silicon nitride film than a silicon oxide film in wet etching in a semiconductor manufacturing process.

In a semiconductor process, a silicon nitride film is deposited via a CVD (Chemical Vapor Deposition) process in a structure in contact with a silicon oxide film, a polysilicon film, or a silicon wafer surface, which is removed by dry etching and wet etching.

In dry etching, fluorine-based gas and inert gas are added and the process proceeds under vacuum. Since the materials and equipment used for etching are expensive, wet etching using phosphoric acid is widely used.

The etching of the silicon nitride film by phosphoric acid proceeds through the following chemical reaction.

4H ₃ PO ₄ + 3Si ₃ N ₄ + 27H ₂ O → 4 (NH ₄ ) ₃ PO ₄ + 9H ₂ SiO ₃

When pure phosphoric acid is used as an etching solution, the etching rate of the silicon nitride film is about 20 to 50 times faster than the etching rate of the silicon oxide film, so that a selective silicon nitride film can be removed to some extent. Recently, due to the development of semiconductor technology, the size of the pattern has been reduced, and the micro-etching of the silicon oxide film has caused various defects and abnormal patterns.

In addition, the silicon nitride film reacts with phosphoric acid and changes into the H ₂ SiO ₃ form. The silicon nitride film is partially dissociated and is present in the form of Si ions in the form of a solution. Due to the principle of Le Chatelier, The etch rate of the silicon nitride film decreases.

If the silicon oxide film is also present in the solution, the etching amount is decreased for the same reason. By using this phenomenon, the method of reducing the etching rate of the silicon oxide film is mainly used by adding the silicon type additive to the etching solution from the beginning.

Specifically, an etching method has been disclosed in which phosphoric acid is heated to obtain polyphosphoric acid and then etched at a temperature of 100 ° C or higher to raise the selectivity. However, the effect of improving the selectivity by the stability of the polyphosphoric acid and the crystal structure has not been proven, And it is difficult to control the process temperature due to excessive heat generation during hydration. In addition, although an etching solution which can selectively etch by adding sulfuric acid and an oxidizing agent to phosphoric acid has been disclosed, there is a problem in that sulfuric acid addition slows down the etching rate of the silicon nitride film as well as the silicon oxide film.

In addition, in the disclosed technique, an etching method of obtaining a high selectivity by adding a small amount of nitric acid and hydrofluoric acid to phosphoric acid has a problem in that the etching rate of the silicon oxide film is increased due to the addition of hydrofluoric acid, and the silicon nitride film is selectively etched There is a problem that foreign substances adhere to the wafer surface due to excessive addition of silicon.

There are three major technologies for the production of etching solutions for silicon nitride films reported so far.

The first technique is a technique for increasing the etching rate of the silicon nitride film, and the etching rate of the silicon oxide film is also increased so that it is difficult to apply to the microfabrication process.

The second technique is a technique for slowing the etching rate of the silicon oxide film. Most of the additives are used to slow the etching rate of the silicon nitride film.

The third technique is to add a silicon fluorine compound, which increases the etching rate of the silicon nitride film and lowers the etching rate of the silicon oxide film. However, since the silicon content in the etching solution is too high, foreign matter adheres to the surface of the wafer, Is very short, and many additives can not be used.

Therefore, it is necessary to develop an etching solution of a new composition which overcomes the above disadvantages.

An object of the present invention is to provide an etching solution having a higher etching selectivity to a silicon nitride film than a silicon oxide film in a semiconductor process.

It is another object of the present invention to provide an etching solution having a silicon nitride film etched at a high etching rate.

In addition, the present invention can further suppress the etching of the silicon oxide film when the silicon wafer is etched, thereby preventing deterioration of electrical characteristics of the semiconductor device and damage of the oxide film.

It is another object of the present invention to provide a stable etching solution at a high temperature without leaving any foreign matter on the silicon surface.

In order to solve the above problems,

The present invention relates to a process for the preparation of A silicon-based additive represented by the following formula (1); And a residual amount of water, the silicon nitride film etching solution comprising:

[Chemical Formula 1]

Wherein, R ₁ is hydrogen, hydroxy, C ₁ -C ₁₀ Alkyl or C ₁ -C ₁₀ alkoxy, R ₂ and R ₃ independently of one another are hydrogen, hydroxy, C ₁ -C ₁₀ Alkyl, or C ₁ -C ₁₀ alkoxy, to C ₁ -C ₁₀ alkyl sulfonate, and represented by the formula (2) is selected from C ₁ -C ₁₀ alkyl sulfonic acids represented by the formula 3, R ₄ is represented by the formula (2) to C ₁ -C ₁₀ alkyl sulfonate, or to which a C ₁ -C ₁₀ alkyl sulfonic acid of the formula (3),

(2)

(3)

Wherein R ₅ and R ₆ are independently selected from hydrogen, hydroxy, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy and C ₁ -C ₁₀ haloalkyl, and n is an integer from 0 to 10 to be.

By providing the silicon nitride film etching solution, the silicon nitride film can be selectively removed from the silicon wafer in which the silicon nitride film and the silicon oxide film exist simultaneously in the semiconductor process.

The present invention provides an etching solution having a high silicon nitride film / oxide film selection ratio and excellent etching efficiency of a silicon nitride film and etching inhibition of a silicon oxide film by including a silicon type additive having an alkyl sulfonate or an alkyl sulfonic acid as a substituent in a phosphoric acid etching solution do.

In addition, the etching solution of the present invention is excellent in high-temperature stability and is free from foreign matters such as wafers and by-products such as sulfuric acid, and is effective in etching a silicon nitride film in a fine process.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art to which the invention pertains. Only. Like reference numerals refer to like elements throughout the specification.

Hereinafter, the present invention will be described in detail.

The present invention relates to a process for the preparation of A silicon-based additive represented by the following formula (1); And water in a remaining amount.

[Chemical Formula 1]

Wherein, R ₁ is hydrogen, hydroxy, C ₁ -C ₁₀ Alkyl or C ₁ -C ₁₀ alkoxy

The hydroxy means -OH.

The C ₁ -C ₁₀ Alkyl means a radical of a saturated aliphatic group having from 1 to 10 carbon atoms, including straight chain alkyl groups, branched alkyl groups, cycloalkyl (alicyclic) groups, alkyl substituted cycloalkyl groups and cycloalkyl substituted alkyl groups.

The straight chain or branched chain alkyl group has 10 or fewer carbon atoms in its main chain (for example, a straight chain of C ₁ -C ₁₀ , a C ₃ -C ₁₀ chain), preferably 8 or less, more preferably 5 or less carbons Have an atom.

Specific examples of the alkyl group include methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, Methylbut-2-yl, 2,2,2-trimethylet-1-yl, n-hexyl, n-heptyl and n-octyl.

Likewise, preferred cycloalkyls have 3-10 carbon atoms in their ring structure, preferably 3, 4, 5, 6 or 7 carbon atoms.

Specifically, the cycloalkyl group may be cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexylmethyl, cycloheptyl, bicyclo [2.1.1] hexyl, bicyclo [2.2.1] heptyl, decalinyl or adamantyl .

The alkoxy means both an -O- (alkyl) group and an -O- (unsubstituted cycloalkyl) group, and is a straight chain or branched hydrocarbon having one or more ether groups and 1 to 10 carbon atoms, Alkyl, cycloalkyl are as defined above.

Specific examples include methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, tert-butoxy, sec-butoxy, n-pentoxy, n- But are not limited to, cyclopropyloxy, cyclobutyloxy, cyclopentyloxy, cyclohexyloxy, and the like.

R ₂ and R ₃ are independently of each other hydrogen, hydroxy, C ₁ -C ₁₀ Alkyl or C ₁ -C ₁₀ alkoxy, a C ₁ -C ₁₀ alkylsulfonate represented by the following formula (2), and a C ₁ -C ₁₀ alkylsulfonic acid represented by the following formula (3).

The matters concerning the alkyl and alkoxy are the same as those of R ₁ .

The alkylsulfonic acid refers to a compound in which sulfo-SO ₃ H is substituted in a hydrocarbon, and the alkylsulfonate represented by the following formula (2) has a salt form of the following formula (3).

By having the above alkyl sulfonate and alkyl sulfonic acid as a substituent, an etching solution having a high silicon nitride / oxide etching selectivity and a high silicon nitride etching rate can be obtained without generating foreign substances or sulfuric acid, Can be implemented.

The alkyl moiety of the sulfonic acid and the sulfonate is the same as the alkyl of R ₁ .

R ₄ is a C ₁ -C ₁₀ alkylsulfonate represented by the following formula (2) or a C ₁ -C ₁₀ alkylsulfonic acid represented by the following formula (3).

The matters concerning the alkyl sulfonate and the alkyl sulfonic acid are the R < _{2 >} And R < ₃ >.

(2)

(3)

물결 형상은 상기 화학식 1의 R₄가 단일 결합으로 치환되는 치환기를 의미한다.remind

The wavy configuration means a substituent in which R ₄ in the formula (1) is substituted with a single bond.

Wherein R ₅ and R ₆ are independently selected from hydrogen, hydroxy, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy and C ₁ -C ₁₀ haloalkyl, and n is an integer from 0 to 10 to be.

Wherein the alkyl and alkoxy are the same as R ₁ and R ₅ or R ₆ may be alkyl, alkoxy or haloalkyl in which at least one carbon atom is substituted with nitrogen.

Particularly, when nitrogen is contained in the carbon chains of R ₅ and R ₆ , the etching rate of the silicon oxide film decreases.

The zeta potential is similar to that of the silicon oxide film due to the high electronegativity of the nitrogen atom itself and the non-covalent electron pair, which easily surrounds the silicon oxide film and interferes with the etching by phosphoric acid, thereby reducing the etching rate of the silicon oxide film.

Specifically, the haloalkyl means alkyl substituted with fluoro (-F), chloro (-Cl), bromo (-Br) or iodo (-I).

The alkyl may include one or more non-hydrogen substituents if the attachment does not violate the valence electron requirements.

For example, haloalkyl refers to -CH2 (halo), -CH (halo) 2 or -C (halo) 3, and the methyl group in which at least one of the hydrogens of the methyl group is replaced by halogen.

Specific examples include, but are not limited to, trifluoromethyl, trichloromethyl, tribromomethyl, and triiodomethyl.

The water contained in the silicon nitride film etching solution is not particularly limited, and it is preferable to use deionized water.

In addition, the etching composition of the present invention may further include any additive conventionally used in the art to improve the etching performance. As the additive, a surfactant, a metal ion blocking agent, a corrosion inhibitor and the like can be used.

In general silicone additives, the solubility of phosphoric acid is poor, so the functional groups that can be dissolved in phosphoric acid are added to control solubility.

However, since the silicon nitride film etching process uses phosphoric acid at a high temperature, these functional groups may have high reactivity, and the silicone additive may be deformed due to the side reaction, resulting in precipitation of silicon dioxide (SiO ₂ ) can do.

Specifically, an additive having a silyl alcohol or the like as a substituent has an excellent effect in reducing the etching rate of a silicon oxide film, but is not suitable for use in an etching process which is a high temperature acidic condition due to a low boiling point.

In addition, the silyl alcohol easily undergoes dehydration condensation reaction under a high temperature acidic condition, so that it may change into a siloxane form or precipitate silicon dioxide particles, which may cause particle problems on a semiconductor wafer.

In addition, the etching solution containing a silicon additive having a sulfate as a substituent progresses decomposition of a silicon portion and a sulfate portion under an acidic condition at a high temperature, and finally generates a silicon salt and sulfuric acid.

When sulfuric acid is added in the silicon nitride film etching process, there is a disadvantage that the etching rate of the silicon nitride film is reduced, and the sulfur component of sulfuric acid remains on the silicon surface, which may deteriorate the device characteristics.

In order to solve such problems, the silicon-based additive contained in the silicon nitride film etching solution of the present invention includes an alkyl sulfonate or an alkyl sulfonic acid represented by the above formula (2) or (3) as a substituent.

As a result, the etching solution of the present invention has a very high silicon nitride / oxide selectivity and can improve the etching rate of the silicon nitride film.

In addition, since etching of the silicon oxide film can be efficiently suppressed, damage to the oxide film is prevented, and the electrical characteristics of the semiconductor device as an etching result are excellent.

In addition, since it is stable at a high temperature, foreign substances such as silicon dioxide are not generated, and the etching rate of the silicon nitride film is reduced or substrate defects are not caused.

In addition, since the silicon nitride film etching solution of the present invention exists in the form of silicon-carbon-sulfonic acid or sulfonate, it can be stable even at a high temperature, so that the etching rate of the silicon nitride film is improved because sulfuric acid is not generated, And does not deteriorate the semiconductor device characteristics.

The phosphoric acid may be contained in an amount of 70 to 90 parts by weight, preferably 70 to 85 parts by weight, more preferably 75 to 85 parts by weight, based on 100 parts by weight of the etching solution.

If phosphoric acid is contained in an amount of less than 70 parts by weight with respect to 100 parts by weight of the etching solution, foreign matter may be generated or the etching rate of the silicon nitride film may be lowered, so that the nitride film may not be easily removed.

When the phosphoric acid is contained in an amount exceeding 90 parts by weight, the silicon oxide film etch rate is also increased, which may reduce the selectivity of the silicon nitride film / oxide film.

0.01 to 1.0 part by weight, preferably 0.1 to 0.7 part by weight, and more preferably 0.2 to 0.4 part by weight of the silicone additive may be included in 100 parts by weight of the etching solution.

When the silicon-based additive is added to less than 0.01 per 100 parts by weight of the etching solution, the etching rate of the silicon oxide film is not reduced, or the stability of the etching process is not maintained at a high temperature.

Further, when the silicon-based additive is added in an amount exceeding 1.0 part by weight, there arises a problem that it is difficult to produce an etching solution such as a silicon particle is aggregated on a wafer due to an increase in manufacturing cost and an increase in viscosity due to a polymer material.

Accordingly, when the phosphoric acid and silicon additive are included in the above range, the etching solution can realize a high silicon oxide / nitride film selectivity and an improved silicon nitride film etching rate while maintaining an appropriate level of high temperature stability in a semiconductor process.

Also, the etching solution may be an alkylammonium fluoride, such as tetrabutylammonium fluoride, methylammonium fluoride, tridodecylammonium fluoride, or MgF2, H2SiF6, NaF , At least one selected from NaHF2, NH4F, NH4HF2, NH4BF4, KF, KHF2, AlF3 and H2TiF6.

Specifically, the fluorine compound may be contained in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the etching solution.

The fluorine compound greatly improves the etching rate of the silicon nitride film. If the fluorine compound is added in an amount exceeding the above range, the etching rate of the silicon oxide film is also increased.

When etching is performed on a semiconductor wafer with a silicon nitride film etching solution according to the present invention, the etching rate of the silicon nitride film of the etching solution is 30 to 80 Å / min, and the etching rate of the silicon oxide film is 0 to 0.8 Å / min And the selectivity of the nitride film / oxide film may be 80 or more, preferably ∞.

In particular, the silicon nitride / oxide selectivity may be ∞ when the silicon nitride film is selectively etched while the etch rate for the silicon oxide film is close to zero.

Therefore, when the silicon nitride film and the silicon oxide film are mixed, the silicon nitride film etching solution of the present invention has a high selectivity by etching and removing the silicon nitride film without causing an etching effect on the silicon oxide film.

The present invention can provide a silicon nitride film having a high silicon nitride film etching rate and a very low silicon nitride film etching rate as described above by including the silicon-based additive having the alkyl sulfonate or alkyl sulfonic acid as a substituent in the etching solution, Selection ratio can be implemented.

In addition, since high temperature stability is realized, foreign substances are not generated, and substrate defects can be prevented, sulfuric acid is not generated, and the etching rate of the silicon nitride film can be maintained, and excellent semiconductor device characteristics can be realized.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto.

Example  And Comparative Example

The compositions of the examples and comparative examples are shown in Table 1 below.

division additive Example 1 Phosphoric acid (85% by mass aqueous solution) + 3- (trihydrosilyl) propane-1-sulfonic acid (0.1% Example 2 Phosphoric acid (85% by mass aqueous solution) + 3- (trihydrosilyl) propane-1-sulfonic acid (0.1% Example 3 Phosphoric acid (85% by mass aqueous solution) + 3- (trihydrosilyl) propane-1-sulfonic acid (0.1% Example 4 Phosphoric acid (90 mass% aqueous solution) + 3- (trihydrosilyl) propane-1-sulfonic acid (0.3 mass% Example 5 Phosphoric acid (90 mass% aqueous solution) + 3- (trihydrosilyl) propane-1-sulfonic acid (0.3 mass% Example 6 Phosphoric acid (90 mass% aqueous solution) + 3- (trimethylsilyl) propane-sulfonic acid (0.3 mass%) Example 7 Phosphoric acid (90 mass% aqueous solution) + 3- (trimethylsilyl) propane-sulfonic acid (0.3 mass%) Example 8 Phosphoric acid (90 mass% aqueous solution) + 3- (trimethylsilyl) ethane-sulfonic acid (0.3 mass%) Example 9 Phosphoric acid (90 mass% aqueous solution) + 3- (trimethylsilyl) ethane-sulfonic acid (0.3 mass%) Comparative Example 1 Phosphoric acid (85 mass% aqueous solution) Comparative Example 2 Phosphoric acid (90 mass% aqueous solution) Comparative Example 3 Phosphoric acid (85 mass% aqueous solution) Comparative Example 4 Phosphoric acid (85 mass% aqueous solution) + sulfuric acid (5 mass%) Comparative Example 5 Phosphoric acid (85% by mass aqueous solution) + trimethoxysilyl sulfate (0.2% by mass) Comparative Example 6 Phosphoric acid (85% by mass aqueous solution) + trimethoxysilyl sulfate (0.2% by mass)

Experimental Example

The etching compositions prepared according to the above Examples and Comparative Examples were etched by inserting a silicon nitride film and a silicon oxide film on the substrate while changing the etching temperature.

The silicon nitride film and the silicon oxide film were both planarized before being put into the etching composition. The planarization process was performed by immersing the film in a diluted hydrofluoric acid for 30 seconds after diluting 50% by mass of hydrofluoric acid with 200: 1.

The etch rate was determined by etching the silicon nitride film and the silicon oxide film for 300 seconds using a Nano-View (SE MG-1000; Ellipsometry), and then measuring the difference between the thickness before etch and the thickness after etch, ).

The formula for determining the selection ratio is as follows.

A: silicon nitride film etch rate, B: silicon oxide etch rate. C: Selection ratio

The formula for determining the etching rate difference of the silicon nitride film is as follows.

A: The silicon nitride film etch rate of the etch solution heated at a temperature of 150-170 < 0 > C for 2 hours.

B: Silicon nitride etch rate of the etch solution heated at a temperature of 150 to 170 占 폚 for 24 hours.

The results are shown in Table 2 below.

division Heating time (H) Process temperature Silicon nitride film etch rate Silicon oxide etch rate Selection ratio
(Nitride film / oxide film) Etching rate difference of silicon nitride film Example 1 2 150 32.4 0 - - Example 2 2 160 53.5 0.2 268 2.0% Example 3 24 160 52.4 0.2 262 Example 4 2 170 70.3 0.3 234 2.1% Example 5 24 170 68.8 0.3 229 Example 6 2 170 71.1 0.7 101.6 2.5% Example 7 24 170 69.3 0.8 84.9 Example 8 2 170 69.5 0.6 115.8 2.3% Example 9 24 170 67.9 0.7 97.4 Comparative Example 1 2 150 32.8 1.2 27.3 - Comparative Example 2 2 170 63.3 3.1 20.4 - Comparative Example 3 2 160 54.0 1.6 33.7 14.3% Comparative Example 4 2 160 46.3 1.3 35.6 Comparative Example 5 2 160 53.3 0.8 66.6 8.4% Comparative Example 6 24 160 48.8 1.1 44.4

As shown in Table 2, the silicon nitride film etching solutions according to Examples 1 to 9 have a higher selectivity than the etching solutions according to Comparative Examples 1 to 6.

Specifically, the etching solutions of Comparative Examples 1 to 3 contain only phosphoric acid, and the etching rate of the silicon oxide film is also high, which may cause substrate defects during etching.

In addition, the difference in etching rate of the silicon nitride film is significant when the etch rate is reduced due to denaturation of the silicon additive after the etching solution is prepared, Comparative Example 4 includes sulfuric acid, and Comparative Examples 5 and 6 include silyl sulfate The silicon based additive generates silicon salt and sulfuric acid at a high temperature. As a result, it can be seen that the etch rate of the silicon nitride film is greatly increased, and the etching rate difference (%) of the nitride film is large.

In contrast, the etching solutions according to the present invention of Examples 1 to 9 are excellent in high-temperature stability, so that even when the process temperature is 150 to 170 ° C, the amounts of foreign substances and side reactions are almost zero, The difference in the etching rate of the nitride film is very small, and the high silicon nitride film etching rate and the very low silicon oxide film etching rate can be realized, so that a high aspect ratio can be obtained in the semiconductor process.

Claims (7)

Phosphoric acid;
A silicon-based additive represented by the following formula (1); And
Residual water;
/ RTI >
Silicon nitride film etching solution:

[Chemical Formula 1]

Wherein R ₁ is hydrogen, hydroxy, C ₁ -C ₁₀ alkyl or C ₁ -C ₁₀ alkoxy,
R ₂ and R ₃ independently of one another are hydrogen, hydroxy, C ₁ -C ₁₀ Alkyl or C ₁ -C ₁₀ alkoxy, a C ₁ -C ₁₀ alkylsulfonate represented by the following formula (2) and a C ₁ -C ₁₀ alkylsulfonic acid represented by the following formula (3)
R ₄ is a C ₁ -C ₁₀ alkylsulfonate represented by the following formula (2) or a C ₁ -C ₁₀ alkylsulfonic acid represented by the following formula (3)

(2)

(3)

Wherein R ₅ and R ₆ are independently from each other selected from hydrogen, hydroxy, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy and C ₁ -C ₁₀ haloalkyl,
And n is an integer of 0 to 10.
The method according to claim 1,
Wherein R ₅ or R ₆ comprises at least one carbon is alkyl substituted with nitrogen, alkoxy or haloalkyl,
Silicon nitride etch solution.
The etching solution according to claim 1, wherein, with respect to 100 parts by weight of the etching solution,
70 to 90 parts by weight of the phosphoric acid,
0.01 to 1.0 part by weight of the silicone additive,
As a result,
Silicon nitride etch solution.
The method according to claim 1,
The etch solution may comprise at least one of Alkylammonium fluoride, MgF ₂ , H ₂ SiF ₆ , NaF, NaHF ₂ , NH ₄ F, NH ₄ HF ₂ , NH ₄ BF ₄ , KF, KF ₂ , AlF ₃ and H ₂ further comprising at least one fluorine compound selected from the TiF _6,
Silicon nitride etch solution.
5. The method of claim 4,
Wherein the fluorine compound is contained in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the etching solution,
Silicon nitride etch solution.
The method according to claim 1,
Wherein the silicon nitride film / oxide film selection ratio of the etching solution is 80 or more,
Silicon nitride etch solution.
The method according to claim 1,
The etching rate of the silicon nitride film of the etching solution heated at a temperature of 150 to 170 DEG C for 2 hours is defined as A,
And the etching rate of the silicon nitride film of the etching solution heated at a temperature of 150 to 170 DEG C for 24 hours is represented by B,
Silicon nitride etch rate difference (

) Is 2.0 to 2.3%
Silicon nitride etch solution.