JP7765206B2 - Silicon etching solution - Google Patents

Description

This disclosure relates to a silicon etching solution and an etching method using the same.

Wet etching and dry etching are used in the manufacturing process of silicon semiconductor devices for processing and removing foreign matter. For example, etching can be used to create MEMS (Micro Electro Mechanical Systems) devices with complex three-dimensional structures.

Conventional wet etching uses an alkaline aqueous solution containing potassium hydroxide, tetramethylammonium hydroxide (TMAH), or the like.
For example, Patent Document 1 proposes a method for etching a silicon wafer using an etching solution prepared by adding a cationic surfactant, an amphoteric surfactant, or an organic polymer having a polar group to an alkaline aqueous solution.
Patent Document 2 proposes an anisotropic silicon etching solution in the field of micromachining technology, which contains an alkaline compound, which is a mixture of an organic alkali and an inorganic alkali, and a silicon-containing compound.

Japanese Patent Application Laid-Open No. 2004-48026 Japanese Patent Application Laid-Open No. 2009-206335

In recent years, the semiconductor industry has seen increasing integration, which has led to demands for more complex and finer wiring, and therefore for even higher precision in etching technology.
For example, Patent Document 1 proposes an etching method for improving flatness and surface roughness. However, in recent years, requirements for the surface quality of silicon substrates have become increasingly stringent, and there is a demand for an etching method that can suppress deterioration of flatness, surface roughness, haze, etc.
In wet etching of silicon, the etching rate is thought to be slower for the (111) plane than for the (100) and (110) planes due to the crystal orientation dependence of the etching rate. For example, when a (100) single-crystal silicon substrate is etched with an alkaline solution containing hydroxy ions, the difference in etching rate between the (111) and (100) planes present minutely on the surface creates convex portions, which can cause problems such as worsening surface roughness and haze.
Furthermore, in the wet etching process of MEMS devices, an improvement in the etching rate of the (111) plane is expected to improve the processing accuracy of the surface shape and productivity.

The present disclosure therefore provides a silicon etching solution that can improve the solubility of the (111) plane of silicon during etching, and a silicon etching method using the same.

In one aspect, the present disclosure relates to a silicon etching solution comprising a cationic surfactant (component A), wherein component A is at least one of a quaternary ammonium or salt thereof having two or more alkyl groups having from 10 to 18 carbon atoms in the molecule (component A1), and a quaternary phosphonium or salt thereof having one or more alkyl groups having from 10 to 18 carbon atoms in the molecule (component A2).

In one aspect, the present disclosure relates to a silicon etching method including the step of etching silicon using the etching solution of the present disclosure or a mixture of an existing chemical and the etching solution of the present disclosure.

In one aspect, the present disclosure provides an etching solution that can improve the solubility of the (111) plane of silicon during etching.

[Etching solution]
In one aspect, the present disclosure relates to a silicon etching solution (hereinafter also referred to as the "etching solution of the present disclosure") that includes a cationic surfactant (component A), where component A is at least one of a quaternary ammonium having two or more alkyl groups having from 10 to 18 carbon atoms in the molecule or a salt thereof (component A1), and a quaternary phosphonium having one or more alkyl groups having from 10 to 18 carbon atoms in the molecule or a salt thereof (component A2).

The etching solution disclosed herein can improve the solubility of the (111) plane of silicon during etching.

In one or more embodiments, the etching solution of the present disclosure can be used for anisotropic etching, such as etching of silicon wafers, etching in micromachining (MEMS) technology, and etching in solar cell manufacturing.

Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, it is presumed as follows.
In this disclosure, at least one cationic surfactant is used, which is a quaternary ammonium or salt thereof having two or more long-chain alkyl chains (component A1) and a quaternary phosphonium or salt thereof having one or more long-chain alkyl chains (component A2). It is believed that the hydrophobic long-chain alkyl chains adsorb to the hydrophobic (111) surface, and the positively charged cationic moieties (N ⁺ , P ⁺ ) of the cationic surfactant attract negatively charged hydroxy ions, which act as a dissolving agent, thereby causing etching to proceed, or that etching is actually performed by the cationic surfactant.
Furthermore, it is believed that the etching reaction proceeds more rapidly as the hydrophobicity of the cationic surfactant increases and the amount of adsorption onto the (111) plane increases, and that a highly hydrophobic cationic surfactant having two or more long alkyl chains has better etching performance than a surfactant having one long alkyl chain.
However, the present disclosure need not be construed as being limited to these mechanisms.

[Cationic surfactant (component A)]
The etching solution of the present disclosure contains a cationic surfactant (hereinafter also referred to as "component A"). Component A is at least one of a quaternary ammonium having two or more alkyl groups having from 10 to 18 carbon atoms in the molecule or a salt thereof (hereinafter also referred to as "component A1"), and a quaternary phosphonium having one or more alkyl groups having from 10 to 18 carbon atoms in the molecule or a salt thereof (hereinafter also referred to as "component A2"). Component A1 may be one type or a combination of two or more types. Component A2 may be one type or a combination of two or more types. Component A may be one type or a combination of two or more types.
In the present disclosure, "quaternary ammonium having two or more alkyl groups each having from 10 to 18 carbon atoms in the molecule" means, in one or more embodiments, that at least two alkyl groups each having from 10 to 18 carbon atoms are bonded to a nitrogen atom. In the present disclosure, "quaternary phosphonium having one or more alkyl groups each having from 10 to 18 carbon atoms in the molecule" means, in one or more embodiments, that at least one alkyl group each having from 10 to 18 carbon atoms is bonded to a phosphorus atom. From the viewpoint of improving the solubility of the silicon (111) plane, the number of carbon atoms in the alkyl group is 10 or more, preferably 11 or more, more preferably 12 or more, and 18 or less, preferably 16 or less, and more preferably 15 or less. From the same viewpoint, the number of carbon atoms in the alkyl group is 10 or more and 18 or less, preferably 11 or more and 18 or less, preferably 12 or more and 18 or less, more preferably 12 or more and 16 or less, and even more preferably 12 or more and 15 or less. In the case of Component A1, the number of alkyl groups having from 10 to 18 carbon atoms contained in the molecule can be 2 or more, 3 or more, or 4, preferably 2 or 3, and more preferably 2. In the case of Component A2, the number can be 1 or more, 2 or more, 3 or more, or 4, preferably 1 or 2.

From the viewpoint of improving the solubility of the silicon (111) plane, component A preferably has a total number of carbon atoms in the molecule of 22 or more, more preferably 24 or more, even more preferably 26 or more, and preferably 38 or less, more preferably 34 or less, and even more preferably 32 or less. From the same viewpoint, component A preferably has a total number of carbon atoms in the molecule of 22 or more and 38 or less, more preferably 24 or more and 38 or less, even more preferably 26 or more and 38 or less, even more preferably 26 or more and 34 or less, and even more preferably 26 or more and 32 or less.

In one or more embodiments, from the viewpoint of improving the solubility of the silicon (111) plane, Component A is preferably a compound having a structure represented by the following formula (I) or the following formula (II):

In the formula (I), R ¹ may be the same or different and represent an alkyl group having from 10 to 18 carbon atoms; R ² may be the same or different and represent a hydrocarbon group having from 1 to 6 carbon atoms or -(CH ₂ CH ₂ O) _n H (where n is 1 to 3); Z is a phosphorus atom; and X ^- is a counter ion.
In the formula (II), R ¹ may be the same or different and represent an alkyl group having from 10 to 18 carbon atoms; R ² may be the same or different and represent a hydrocarbon group having from 1 to 6 carbon atoms or -(CH ₂ CH ₂ O) _n H (where n is 1 to 3); Z represents a nitrogen atom or a phosphorus atom; and X ^- represents a counter ion.
In the formulas (I) and (II), ^R2 is preferably a hydrocarbon group having 1 to 6 carbon atoms from the viewpoint of improving the solubility of the silicon (111) plane. Examples of the counter ion include chloride ion ( ^Cl- ), hydrogen carbonate ion ( _HCO3- ⁾ , and bromide ion ( ^Br- ).

Examples of Component A1 include at least one selected from didecyldimethylammonium salts, dialkyldimethylammonium salts (C12-C18 mixed products), and distearyldimethylammonium salts.
Examples of Component A2 include trihexyltetradecylphosphonium salts.

From the viewpoint of improving the solubility of the silicon (111) plane, the content of component A in the etching solution of the present disclosure is preferably 5 ppm or more, more preferably 20 ppm or more, even more preferably 50 ppm or more, and even more preferably 80 ppm or more. From the viewpoint of solution stability, the content is preferably 100,000 ppm or less, more preferably 10,000 ppm or less, and even more preferably 1,000 ppm or less. From the viewpoint of improving the solubility of the silicon (111) plane and solution stability, the content of component A in the etching solution of the present disclosure is preferably 5 ppm to 100,000 ppm, more preferably 20 ppm to 10,000 ppm, and even more preferably 80 ppm to 1,000 ppm. When component A is a combination of two or more types, the content of component A refers to the total content thereof. Note that, in this disclosure, 10,000 ppm is equivalent to 1 mass% (the same applies hereinafter).

[water]
In one or more embodiments, the etching solution of the present disclosure contains water as a medium. Examples of water include distilled water, ion-exchanged water, pure water, and ultrapure water.
The water content in the etching solution of the present disclosure is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, from the viewpoint of solution stability, and is preferably 99.9995% by mass or less, more preferably 99.9990% by mass or less, and even more preferably 99.9980% by mass or less, from the viewpoint of improving the solubility of the silicon (111) plane.

[Alkaline agent (component B)]
In one or more embodiments, the etching solution of the present disclosure may further contain an alkaline agent (hereinafter also referred to as "component B") from the viewpoint of further improving the solubility of the (111) plane of silicon. In one or more embodiments, component B does not contain component A.
In one or more embodiments, Component B includes at least one selected from inorganic alkalis and organic alkalis, and inorganic alkalis are preferred.
Examples of the inorganic alkali include ammonia; alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; and the like.
Examples of the organic alkali include hydroxyalkylamines, quaternary ammonium salts, etc. Examples of the hydroxyalkylamines include monoethanolamine, diethanolamine, methylethanolamine, methyldiethanolamine, aminoethylethanolamine, etc. Examples of the quaternary ammonium salts include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), etc.
Component B may be one type or a combination of two or more types.

In one or more embodiments, the content of component B in the etching solution of the present disclosure can be set so that the pH of the etching solution falls within a specific range.

[Other ingredients]
The etching solution of the present disclosure may further contain or be blended with other components, provided that the effects of the present disclosure are not impaired. Examples of other components include surfactants other than Component A, pH adjusters other than Component B, high-temperature stabilizers, chelating agents, solubilizers, preservatives, rust inhibitors, disinfectants, antibacterial agents, antioxidants, and antifoaming agents.

[Method of manufacturing etching solution]
In one or more embodiments, the etching solution of the present disclosure can be obtained by blending component A, water, and, as necessary, the optional components described above (component B and other components).
Therefore, in one aspect, the present disclosure relates to a method for producing an etching solution (hereinafter also referred to as the "etching solution production method of the present disclosure"), which includes a step of blending component A, water, and, as necessary, the above-described optional components (component B and other components) (hereinafter also referred to as the "blending step").
In the present disclosure, the term "blending" includes simultaneously or sequentially mixing component A, water, and, if necessary, the optional components described above (component B, other components). The order of mixing is not particularly limited. The blending can be carried out using a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, or a wet ball mill.
In the method for producing an etching solution according to the present disclosure, the preferred amount of each component to be blended can be the same as the preferred content of each component in the etching solution according to the present disclosure described above.

In this disclosure, in one or more embodiments, the "content of each component in the etching solution" refers to the content of each component in the etching solution used in the etching process, i.e., at the time of starting use in the etching process (at the time of use).

Etching solutions according to the present disclosure may be of a so-called one-component type, in which all components are premixed and supplied to the market, or of a so-called two-component type, in which components are mixed at the time of use. One embodiment of a two-component etching solution is one that is composed of an additive solution (first component) containing component A and an alkaline aqueous solution (second component) containing component B, and in which the first and second components are mixed at the time of use. The first and second components may each contain the optional components described above, as necessary.

In one or more embodiments, the etching solution of the present disclosure is preferably a neutral or alkaline etching solution. For example, from the viewpoint of improving the solubility of the silicon (111) plane, the pH of the etching solution of the present disclosure is preferably 4 or higher, more preferably 5 or higher, and even more preferably 6 or higher. In the present disclosure, the pH of the etching solution is the value of the etching solution at 25°C during use, and can be measured using a pH meter; specifically, it can be measured by the method described in the examples.

The etching solution of the present disclosure may be stored and supplied in a concentrated state, provided that its stability is not compromised. This is preferable in that it reduces production and transportation costs. This concentrated solution can then be diluted appropriately with water, etc., as needed, before use in the etching process. A dilution ratio of 5 to 100 times is preferred.

In one or more embodiments, the etching solution of the present disclosure can be applied to anisotropic etching such as etching of silicon wafers, etching in micromachining (MEMS) technology, and etching in solar cell manufacturing.
In one or more embodiments, etching using the etching solution of the present disclosure can be used in a slicing process, a lapping process, a polishing process, a CMP process, a rinsing process, a heat treatment process, a cleaning process, and a photoresist process.

[kit]
In one aspect, the present disclosure relates to a kit for producing the etching solution of the present disclosure (hereinafter also referred to as the "kit of the present disclosure").
In one or more embodiments, the kit of the present disclosure includes a kit including an additive solution containing component A. The additive solution may contain the optional components described above, as necessary.
In one or more embodiments, the kit of the present disclosure includes a kit (two-component etching solution) that contains an additive solution (first liquid) containing component A and an alkaline aqueous solution (second liquid) containing component B in a mutually unmixed state, and that is mixed at the time of use. After the first liquid and the second liquid are mixed, they may be diluted with water or an alkaline aqueous solution as needed. The first liquid or the second liquid may contain all or a part of the water used to prepare the etching solution. The first liquid and the second liquid may each contain the above-mentioned optional components as needed.
The kit of the present disclosure makes it possible to produce an etching solution that can improve the solubility of the (111) plane of silicon during etching.

[Processing object]
In one or more embodiments, the workpiece to be etched using the etching solution of the present disclosure may be silicon such as single crystal silicon, polycrystalline silicon, polysilicon, or patterned silicon. Among these, at least one selected from single crystal silicon, polycrystalline silicon, and polysilicon is preferred, at least one of single crystal silicon and polycrystalline silicon is more preferred, and single crystal silicon is even more preferred.
Examples of the workpiece include a silicon wafer, a silicon substrate, a silicon substrate having a silicon oxide film and a silicon nitride film, and a structure in which silicon is patterned.

[Etching method]
In one aspect, the present disclosure relates to an etching method (hereinafter also referred to as the "etching method of the present disclosure") that includes a step of etching silicon using the etching solution of the present disclosure or a mixed solution of an existing chemical and the etching solution of the present disclosure (hereinafter also referred to as the "etching step"). Use of the etching method of the present disclosure can improve the solubility of the (111) plane of silicon during etching, thereby improving the productivity of semiconductor substrates with improved quality.
Examples of existing chemicals include ammonia, TMAH, potassium hydroxide, and SC-1 (aqueous solution containing ammonia and hydrogen peroxide).
In one or more embodiments, the mixed solution can be prepared by blending an existing chemical agent with the etching solution of the present disclosure. For example, in one or more embodiments, the mixed solution can be obtained by adding ammonia, hydrogen peroxide, and the etching solution of the present disclosure to ultrapure water. In one or more embodiments, the mixed solution can be obtained by mixing SC-1, which is prepared by mixing ultrapure water, ammonia, and hydrogen peroxide, with the etching solution of the present disclosure.
The existing drug used in preparing the mixed solution is preferably blended so that the proportion of the existing drug in the mixed solution is 90 mass % or more, for example.
The etching solution of the present disclosure used to prepare the mixed solution is preferably formulated so that the concentration of Component A in the mixed solution is 5 ppm to 10 mass %.

In the etching step, examples of the etching method include immersion etching and single wafer etching.
In the etching step, the etching temperature of the etching solution is not particularly limited, and may be, for example, 25° C. or higher and 80° C. or lower.
In the etching step, the etching time can be appropriately set depending on the structure and material of the silicon substrate and the etching treatment conditions, and may be, for example, from 1 minute to 120 minutes.

In one or more embodiments, the etching method of the present disclosure may include, in addition to the etching step, a cleaning step, a rinsing step, a drying step, etc. The cleaning step and/or rinsing step may be performed before, after, or both (before and after) the etching step. The drying step may be performed after the cleaning step and/or rinsing step. For example, the etching method of the present disclosure may include, after the etching step, a rinsing step in which the silicon after the etching process is rinsed with water or the like, and a drying step in which the silicon after the rinsing is dried.

The present disclosure will be explained in detail below using examples, but the present disclosure is not limited to these examples in any way.

1. Preparation of Etching Solutions (Examples 1 to 12 and Comparative Examples 1 to 3)
(Examples 1 to 10, Comparative Example 3)
The cationic surfactant (component A or non-component A) shown in Table 1 and ultrapure water were mixed to obtain etching solutions of Examples 1 to 10 and Comparative Example 3.
(Examples 11 and 12)
The cationic surfactant (component A), ammonia (component B), and ultrapure water shown in Table 1 were mixed to obtain etching solutions of Examples 11 and 12.
(Comparative Example 1)
The etching solution used in Comparative Example 1 was ultrapure water.
(Comparative Example 2)
An etching solution of Comparative Example 2 was obtained by mixing ammonia (component B) and ultrapure water.
The content of each component in Table 1 is the content (ppm, active ingredient) of each component when the polishing composition is used. The content of water is the remainder excluding component A or non-component A and component B.

The following components were used to prepare the etching solution.
(Component A)
Didecyldimethylammonium chloride [Kao Corporation, Kotamine D10E] (in formula (II), R ¹ : C ₁₀ H ₂₁ , R ² : CH ₃ , Z: N, X: Cl ⁻ )
Dialkyl (C12-18) dimethylammonium chloride [Kao Corporation, Kohtamin D2345P] (in formula (II), R ¹ is a C12-18 alkyl group, R ² is CH ₃ , Z is N, and X is Cl ⁻ )
Distearyldimethylammonium chloride [manufactured by Tokyo Chemical Industry Co., Ltd.] (in formula (II), R ¹ : C ₁₈ H ₃₇ , R ² : CH ₃ , Z: N, X: Cl ⁻ )
Didecyldimethylammonium bicarbonate [Carboquat HE, manufactured by Lonza Japan] (in formula (II), R ¹ : C ₁₀ H ₂₁ , R ² : CH ₃ , Z: N, X: HCO ₃ ⁻ )
Trihexyltetradecylphosphonium bromide [manufactured by Tokyo Chemical Industry Co., Ltd.] (in formula (I), R ¹ : C ₁₄ H ₂₉ , R ² : C ₆ H ₁₃ , Z: P, X: Br ⁻ )
(Non-ingredient A)
Lauryltrimethylammonium chloride [Kao Corporation, Kotamin 24P]
(Component B)
_NH3 : Ammonia [28% by mass ammonia water, manufactured by Kishida Chemical Co., Ltd., special grade reagent]

2. Measurement method for each parameter [pH of etching solution]
The pH value of the etching solution at 25° C. was measured using a pH meter (manufactured by DKK-Toa Corporation), and was the value measured one minute after the electrode of the pH meter was immersed in the etching solution.

3. Evaluation of etching solution [amount dissolved on 111 plane]
An 8-inch (111) plane single crystal silicon was cut into 4 x 4 cm pieces using a diamond cutter to prepare a test specimen. The mass (g) of the test specimen was measured to four decimal places using an electronic balance (manufactured by Sartorius). The test specimen was then immersed in acetone for 1 minute so that the entire surface was immersed, then rinsed with ultrapure water, then immersed in ammonium hydrofluoride diluted to 1% with ultrapure water for 1 minute so that the entire surface was immersed, then rinsed with ultrapure water, and then dried with an air blower.
100 g of the prepared etching solution was weighed into a disposable cup, and the entire surface of the test piece was immersed in the solution. The test piece was then placed in a thermostatic chamber (manufactured by ESPEC, model: PU-4J) set at 60°C for 24 hours to perform etching. The test piece was then removed from the thermostatic chamber, rinsed with ultrapure water, and dried with an air blower. The mass (g) of the test piece was then measured to four decimal places using an electronic balance (manufactured by Sartorius). The weight of the test piece after immersion was subtracted from the weight of the test piece before immersion, and the difference was defined as the amount of 111-surface dissolution (mg).
The silicon wafers used were as follows:
Type: (111) 4° off single-sided mirror wafer Resistivity: ≦1 Ω cm
Thickness: 1000±25 μm
Orientation flat: Notch specification Particle: Any

As shown in Table 1, the etching solutions of Examples 1 to 12 containing a specific cationic surfactant (component A) had improved solubility of the silicon (111) plane compared to Comparative Examples 1 to 3 which did not contain component A. The etching solutions of Examples 11 and 12 containing a specific cationic surfactant (component A) and an alkaline agent (component B) had improved solubility of the silicon (111) plane compared to Examples 1 to 10 which did not contain component B.
The solubility of the (111) surface of silicon was further improved.

The etching solution disclosed herein is useful as an etching solution that can improve the solubility of the (111) surface of silicon.

Claims (6)

containing a cationic surfactant (component A),
An etching solution for single crystal silicon, wherein component A is a quaternary ammonium or a salt thereof (component A1) having two or more alkyl groups having 10 to 18 carbon atoms in the molecule, and ^when component A1 is a salt, the counter ion is a chloride ion ( ^Cl- ) or a bicarbonate ion ( _HCO3- ). The etching solution according to claim 1, wherein component A has a total number of carbon atoms in the molecule of 22 or more and 38 or less. 3. The etching solution according to claim 1, wherein component A is a compound having a structure represented by the following formula (II):
In the formula (II), R ¹ may be the same or different and represent an alkyl group having from 10 to 18 carbon atoms; R ² may be the same or different and represent a hydrocarbon group having from 1 to 6 carbon atoms or -(CH ₂ CH ₂ O) _n H (wherein n is 1 to 3); Z is a nitrogen atom; and X ^- is a counter ion, which is a chloride ion (Cl ^- ) or a bicarbonate ion (HCO ₃ ^- ). The etching solution according to any one of claims 1 to 3, further comprising an alkaline agent (component B). The etching solution according to any one of claims 1 to 4, which is a neutral or alkaline etching solution. 6. A silicon etching method comprising the step of etching single crystal silicon using the etching solution according to claim 1 or a mixed solution of ultrapure water, ammonia, hydrogen peroxide and the etching solution according to claim 1.