Silicon etching solution, and method for manufacturing silicon devices and method for treating silicon substrates using said etching solution

Abstract

A silicon etching liquid which is characterized by containing a quaternary ammonium hydroxide represented by formula (1), a quaternary ammonium salt represented by formula (2) and water, and which is also characterized in that the concentration of the quaternary ammonium salt represented by formula (2) is more than 1% by mass but not more than 50% by mass.　(1): R1R2R3R4N+·OH- (In formula (1), R1, R2, R3 and R4 may be the same groups or different groups, and each represents an optionally substituted alkyl group, aryl group or a benzyl group.)　(2): R5R6R7R8N+·X- (In formula (2), R5, R6, R7 and R8 may be the same groups or different groups, and each represents an optionally substituted alkyl group having from 1 to 16 carbon atoms; and X represents BF4, a fluorine atom, a chlorine atom or a bromine atom.)

Description

[Technical Field]

[0001] The present invention relates to a silicon etching solution used in the surface processing or etching process when manufacturing various silicon devices. The present invention also relates to a method for manufacturing silicon devices using the etching solution. The present invention also relates to a method for treating a silicon substrate containing a silicon material using the etching solution. [Background technology]

[0002] Silicon etching is used in various processes in the manufacturing of semiconductor devices. In recent years, silicon processing processes have become increasingly common due to the stacking of memory cells and the shift to three-dimensional logic device manufacturing. Due to the increasing density of devices, the silicon etching process used in these processes faces increasingly stringent requirements for post-etching smoothness, etching precision, and etching selectivity with respect to other materials. It is also used in processes such as wafer thinning. These various silicon devices require high integration, miniaturization, high sensitivity, and high functionality depending on their application. To meet these requirements, silicon etching is considered an important microfabrication technology in the manufacture of these silicon devices. Silicon etching can be performed using a hydrofluoric acid-nitric acid aqueous solution or alkaline etching. Etching with the former hydrofluoric acid-nitric acid aqueous solution can etch silicon isotropically regardless of its crystal orientation, and can uniformly etch single crystal silicon, polysilicon, and amorphous silicon. However, because the hydrofluoric acid-nitric acid aqueous solution oxidizes silicon and etches it as a silicon oxide film, it does not have etching selectivity for silicon relative to silicon oxide film, and therefore cannot be used in semiconductor manufacturing processes that leave a silicon oxide film behind.

[0003] Next, alkaline etching of silicon exhibits crystalline anisotropy, unlike etching with a hydrofluoric acid-nitric acid solution. Crystalline anisotropy refers to the property of silicon's crystalline orientation causing differences in etching rate (etching anisotropy). Taking advantage of this property, alkaline etching is used to process silicon devices with complex three-dimensional structures on single-crystal silicon and to smooth silicon surfaces. Furthermore, alkaline etching has the advantage of high etching selectivity for silicon over silicon nitride as well as silicon over silicon oxide, making it suitable for use in semiconductor manufacturing processes that leave silicon oxide behind. High selectivity here refers to the property of exhibiting particularly high silicon etching selectivity for a specific material. For example, when etching a substrate containing a silicon film (single-crystal silicon, polysilicon, or amorphous silicon) and another film (e.g., silicon oxide), if only the silicon film is etched and the silicon oxide film is not etched, this is considered to have high etching selectivity for silicon over silicon oxide. Alkaline etching solutions have selectivity for silicon oxide and silicon nitride, allowing them to selectively etch silicon films.

[0004] As the etching solution, an aqueous solution of a common alkaline chemical such as KOH, hydrazine, or tetramethylammonium hydroxide (hereinafter also referred to as TMAH) can be used (see Patent Documents 1 and 2). Among them, KOH or TMAH, which are low in toxicity and easy to handle, are preferably used alone. Among these, TMAH is more preferably used when considering the contamination of metal impurities and etching selectivity with silicon oxide films.

[0005] Regarding etching using alkali, Patent Document 1 discloses an etching solution for silicon substrates for solar cells, which contains an alkali hydroxide, water, and a polyalkylene oxide alkyl ether. Patent Document 2 discloses an etching solution for silicon substrates for solar cells, which contains an alkaline compound, an organic solvent, a surfactant, and water. Patent Document 2 lists TMAH as an example of an alkaline compound and a polyalkylene oxide alkyl ether as an example of an organic solvent, but the alkaline compounds actually used are sodium hydroxide and potassium hydroxide. Patent Document 3 also discloses an alkaline etching solution that can selectively remove silicon relative to silicon-germanium. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-141139 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-227304 [Patent Document 3] Japanese Patent Application Publication No. 2019-050364 Summary of the Invention [Problem to be solved by the invention]

[0007] While alkaline etching solutions have the advantages described above, they have the drawback of having a low etching rate for the (111) plane of silicon, which can sometimes result in the formation of pyramidal hillocks surrounded by (111) planes, reducing the surface smoothness during silicon etching or leaving etching residue. While increasing the alkaline concentration can solve this problem, considering cost, safety, and ease of waste liquid disposal, it is preferable to reduce the alkaline concentration in the silicon etching solution. However, lowering the alkaline concentration makes it more likely that pyramidal hillocks surrounded by (111) planes will form, reducing the etching smoothness and causing surface roughness. Therefore, a silicon etching solution that can suppress the formation of hillocks on the silicon surface by lowering the alkaline concentration and that has a high etching selectivity with respect to silicon oxide films is desired. Here, the etching selectivity with respect to silicon oxide films represents the value obtained by dividing the silicon etching rate by the silicon oxide etching rate.

[0008] The etching solutions described in Patent Documents 1 and 2 use NaOH or KOH as alkaline compounds. As mentioned above, alkaline etching has higher selectivity for silicon oxide films compared to hydrofluoric acid-nitric acid aqueous solutions, but alkali metal hydroxides have a higher etching rate for silicon oxide films compared to quaternary ammonium hydroxide. Therefore, when silicon oxide films are used as mask materials or part of pattern structures during silicon film etching, the silicon oxide films that should remain during silicon etching are also etched during prolonged processing. Furthermore, with the trend toward miniaturization, the etching tolerance for oxide films has decreased, making it impossible to selectively etch only the silicon film without etching the silicon oxide film. Furthermore, these etching solutions aim to increase crystalline anisotropy and roughen the surface, and therefore cannot smoothly etch silicon films. The etching solution described in Patent Document 3 is a chemical solution that can selectively remove silicon relative to silicon and germanium, but there is no mention of smooth silicon etching.

[0009] Therefore, an object of the present invention is to provide a silicon etching solution that can suppress the generation of hillocks on a silicon surface while maintaining a low alkali concentration and that has a high selectivity with respect to a silicon oxide film. [Means for solving the problem]

[0010] After extensive efforts, the inventors have found that the above-mentioned problems can be solved by using a silicon etching solution containing a quaternary ammonium hydroxide represented by formula (1), a quaternary ammonium salt represented by formula (2), and water.

[0011] That is, the first aspect of the present invention is The present invention relates to a silicon etching solution comprising a quaternary ammonium hydroxide represented by the following formula (1), a quaternary ammonium salt represented by the following formula (2), and water, wherein the concentration of the quaternary ammonium salt represented by formula (2) is greater than 1 mass % and not more than 50 mass %: R 1 R 2 R 3 R 4 N + OH - (1) (In formula (1), R 1 , R 2 , R 3 and R 4 are alkyl, aryl or benzyl groups which may have a substituent, and may be the same or different groups. R 5 R 6 R 7 R 8 N + X - (2) (In formula (2), R 5 , R 6 , R 7 and R 8 are alkyl groups having 1 to 16 carbon atoms which may have a substituent, and may be the same or different groups. X is BF4, a fluorine atom, a chlorine atom, or a bromine atom.

[0012] In the first aspect of the present invention, the concentration of the quaternary ammonium hydroxide represented by the formula (1) is preferably 0.05 mol / L or more and 1.1 mol / L or less.

[0013] In the first aspect of the present invention, the total number of carbon atoms in the molecule of the quaternary ammonium salt represented by the formula (2) is preferably 4 or more and 12 or less.

[0014] The second invention of the present invention is a method for treating a silicon substrate containing at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, the method comprising a step of etching the silicon material using the silicon etching solution of the first invention of the present invention.

[0015] A third aspect of the present invention is a method for manufacturing a silicon device having at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, the method comprising: The first aspect of the present invention is a method for manufacturing a silicon device, comprising the step of etching the silicon material using the silicon etching solution of the present invention. [Effects of the Invention]

[0016] The silicon etching solution of the present invention can smoothly etch the surface of a silicon substrate containing at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, while maintaining a low concentration of quaternary ammonium hydroxide, and can perform silicon etching with a high selectivity to a silicon oxide film.

[0017] In particular, in the etching process of silicon substrates, the generation of pyramidal hillocks surrounded by 111 faces can be suppressed, and roughness of the silicon surface (100 face) can be suppressed. Furthermore, since the quaternary ammonium hydroxide concentration can be kept low, toxicity and waste liquid treatment costs can be reduced. Therefore, the silicon etching solution of the present invention is particularly useful as a silicon etching solution for etching a silicon surface (100 face) smoothly. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes in detail the embodiments of the present invention, but these descriptions are examples (typical examples) of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not deviate from the gist of the invention. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less.

[0019] The present invention includes the following items. Item 1: A silicon etching solution comprising a quaternary ammonium hydroxide represented by the following formula (1), a quaternary ammonium salt represented by the following formula (2), and water, wherein the concentration of the quaternary ammonium salt represented by formula (2) is greater than 1 mass % and not more than 50 mass %. R 1 R 2 R 3 R 4 N + OH - (1) (In formula (1), R 1 , R 2 , R 3 and R 4 are alkyl, aryl or benzyl groups which may have a substituent, and may be the same or different groups. R 5 R 6 R 7 R 8 N + X - (2) (In formula (2), R 5 , R 6 , R 7 and R 8 are alkyl groups having 1 to 16 carbon atoms which may have a substituent, and may be the same or different groups. X is BF4, a fluorine atom, a chlorine atom, or a bromine atom. Item 2. The silicon etching solution according to Item 1, wherein the concentration of the quaternary ammonium hydroxide represented by the formula (1) is 0.05 mol / L or more and 1.1 mol / L or less. Item 3. The silicon etching solution according to Item 1 or 2, wherein the total number of carbon atoms in the molecule of the quaternary ammonium salt represented by formula (2) is 4 or more and 12 or less. Item 4: A method for treating a silicon substrate containing at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, Item 4. A method for treating a silicon substrate, comprising the step of etching the silicon material using the silicon etching solution according to any one of Items 1 to 3. Item 5: A method for manufacturing a silicon device having at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, Item 4. A method for manufacturing a silicon device, comprising the step of etching the silicon material using the silicon etching solution according to any one of Items 1 to 3.

[0020] The isotropic silicon etching solution of the present invention is a silicon etching solution containing a quaternary ammonium hydroxide represented by the following formula (1), a quaternary ammonium salt represented by the following formula (2), and water, wherein the concentration of the quaternary ammonium salt represented by formula (2) is more than 1 mass % and not more than 50 mass %. R 1 R 2 R 3 R 4 N + OH - (1) In formula (1), R1 , R 2 , R 3 and R 4 represents an alkyl group, an aryl group, or a benzyl group, each of which may have a substituent, and may be the same or different groups. R 5 R 6 R 7 R 8 N + X - (2) In formula (2), R 5 , R 6 , R 7 and R 8 are alkyl groups having 1 to 16 carbon atoms which may have a substituent, and may be the same or different groups. X is BF4, a fluorine atom, a chlorine atom, or a bromine atom.

[0021] In the quaternary ammonium hydroxide represented by the above formula (1), R 1 , R 2 , R 3 and R 4 represents an alkyl group, an aryl group, or a benzyl group, each of which may have a substituent, and may be the same or different groups.

[0022] The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, and the aryl group is preferably an aryl group having 6 to 10 carbon atoms.

[0023] In addition, the substituents that the alkyl group, aryl group, and benzyl group may have are not particularly limited, and examples thereof include a halogenyl group, a hydroxy group, an alkoxy group having 1 to 20 carbon atoms, -C≡N, -NH3, -C(=O)OH, -C(=O)OR', -C(=O)R', -SH, and -SiR a R b R c , -BH, -SeH, a monovalent aromatic hydrocarbon ring group, or a monovalent aromatic heterocyclic group; R', R a , R b , and R ccan represent hydrogen or an alkyl group having 1 to 20 carbon atoms, and may be the same or different groups. A hydroxy group is particularly preferred as a substituent because it has good solubility in water.

[0024] R 1 , R 2 , R 3 and R 4 Examples of the alkyl group include an unsubstituted alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a sec-butyl group, or a tert-butyl group; an alkyl group having 1 to 4 carbon atoms and substituted with a hydroxy group, such as a hydroxymethyl group, a hydroxyethyl group, a hydroxy-n-propyl group, a hydroxy-i-propyl group, a hydroxy-n-butyl group, a hydroxy-i-butyl group, a hydroxy-sec-butyl group, or a hydroxy-tert-butyl group; a phenyl group; a tolyl group; an o-xylyl group; and a benzyl group.

[0025] R 1 , R 2 , R 3 and R 4 The total number of carbon atoms in R is preferably 20 or less from the viewpoint of solubility. 1 , R 2 , R 3 and R 4 is preferably an alkyl group having 1 to 4 carbon atoms, or an alkyl group having 1 to 4 carbon atoms substituted with a hydroxy group, and it is particularly preferred that at least three of them are the same alkyl group.

[0026] Examples of quaternary ammonium hydroxides represented by formula (1) include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), ethyltrimethylammonium hydroxide (ETMAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), trimethyl-2-hydroxyethylammonium hydroxide (choline hydroxide), dimethylbis(2-hydroxyethyl)ammonium hydroxide, methyltris(2-hydroxyethyl)ammonium hydroxide, trimethylphenylammonium hydroxide, and benzyltrimethylammonium hydroxide. Among these, TMAH, choline hydroxide, TEAH, ETMAH, TPAH, and TBAH are preferred. In particular, TMAH, choline hydroxide, ETMAH, TEAH, and TPAH are most suitable due to their high silicon etching rate.

[0027] The concentration of the quaternary ammonium hydroxide represented by formula (1) in the silicon etching solution can be the same as that of conventional silicon etching solutions, and is preferably in the range of 0.05 mol / L or more and 1.1 mol / L or less, since this provides an excellent etching effect without causing crystal precipitation.Moreover, the concentration of the quaternary ammonium hydroxide is more preferably in the range of 0.05 mol / L or more and 0.6 mol / L or less.

[0028] The quaternary ammonium represented by formula (1) may be used singly or in combination of two or more different types.

[0029] The silicon etching solution of the present invention is characterized by containing a quaternary ammonium salt represented by the above formula (2). By containing the quaternary ammonium salt represented by formula (2), the silicon surface is not roughened and can be smoothly etched.

[0030] In the quaternary ammonium salt represented by formula (2), R5 , R 6 , R 7 and R 8 are alkyl groups having 1 to 16 carbon atoms which may have a substituent, and may be the same or different groups. The substituent that the alkyl group can have is not particularly limited, and examples thereof include a halogenyl group, a hydroxy group, an alkoxy group having 1 to 20 carbon atoms, -C≡N, -NH3, -C(=O)OH, -C(=O)OR', -C(=O)R', -SH, and -SiR a R b R c , -BH, -SeH, a monovalent aromatic hydrocarbon ring group, or a monovalent aromatic heterocyclic group; R', R a , R b , and R c can represent hydrogen or an alkyl group having 1 to 20 carbon atoms, and may be the same or different groups. A hydroxy group is particularly preferred as a substituent because it has good solubility in water.

[0031] R 5 , R 6 , R 7 and R 8 Examples of the alkyl group include unsubstituted alkyl groups having 1 to 16 carbon atoms, such as a methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, tert-butyl group, hexyl group, octyl group, decyl group, dodecyl group, tetradecyl group, and hexadecyl group; and alkyl groups having 1 to 4 carbon atoms substituted with a hydroxy group, such as a hydroxymethyl group, hydroxyethyl group, hydroxy-n-propyl group, hydroxy-i-propyl group, hydroxy-n-butyl group, hydroxy-i-butyl group, hydroxy-sec-butyl group, and hydroxy-tert-butyl group.

[0032] From the viewpoints of solubility in water and the ability to smoothly etch a silicon surface, the total number of carbon atoms in the molecule of the quaternary ammonium salt represented by formula (2) is preferably 4 or more, more preferably 8 or more, and even more preferably 11 or more, and is preferably 20 or less, more preferably 15 or less, even more preferably 14 or less, and particularly preferably 12 or less.

[0033] Also, R 5 , R 6 , R 7 and R 8 Although all of R may be the same group, it is preferable that at least one of them is a different group. 5 , R 6 , R 7 and R 8 At least one group is an alkyl group having 2 to 16 carbon atoms, and the remaining groups are alkyl groups having 1 to 4 carbon atoms, more preferably alkyl groups having 1 to 2 carbon atoms, and particularly preferably methyl groups having 1 carbon atom.

[0034] X is BF4, a fluorine atom, a chlorine atom, or a bromine atom, and is preferably a chlorine atom or a bromine atom.

[0035] Specific examples of quaternary ammonium salts represented by formula (2) that can be suitably used in the present invention include tetramethylammonium salt, tetraethylammonium salt, tetrapropylammonium salt, tetrabutylammonium salt, ethyltrimethylammonium salt, butyltrimethylammonium salt, hexyltrimethylammonium salt, octyltrimethylammonium salt, decyltrimethylammonium salt, dodecyltrimethylammonium salt, tetradecyltrimethylammonium salt, and hexadecyltrimethylammonium salt. Among these, octyltrimethylammonium salt, decyltrimethylammonium salt, dodecyltrimethylammonium salt, tetradecyltrimethylammonium salt, and hexadecyltrimethylammonium salt are more preferred, and octyltrimethylammonium salt, decyltrimethylammonium salt, and dodecyltrimethylammonium salt are particularly preferred.

[0036] The quaternary ammonium salt represented by formula (2) may be used singly or in combination of two or more different types.

[0037] The quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2) may have the same quaternary ammonium cation. When the cation of the quaternary ammonium hydroxide represented by formula (1) and the cation of the quaternary ammonium salt represented by formula (2) are the same, the concentration of the quaternary ammonium cation of the quaternary ammonium salt represented by formula (2) can be calculated from the concentration of the anion of the quaternary ammonium salt represented by formula (2). Specifically, the concentrations of the anion and cation are equivalent in molar ratio, and the concentration of the quaternary ammonium cation of the quaternary ammonium salt represented by formula (2) can be calculated from the concentration of the cation. Specifically, the concentration is the quaternary ammonium cation concentration of the entire etching solution minus the concentration of the cation of the quaternary ammonium hydroxide represented by formula (1). In this embodiment, when the silicon etching solution contains cations and anions constituting the quaternary ammonium hydroxide represented by formula (1) and cations and anions constituting the quaternary ammonium salt represented by formula (2), it can be treated as containing the quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2).

[0038] The concentration of the quaternary ammonium salt represented by formula (2) in the silicon etching solution is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 35% by mass or less, even more preferably 1% by mass or more and 20% by mass or less, particularly preferably 1% by mass or more and 15% by mass or less, and most preferably 1.5% by mass or more and 15% by mass or less, because this allows for smooth etching without roughening the silicon surface even when the concentration of the quaternary ammonium hydroxide represented by formula (1) is low. Specifically, this reduces the roughness of the silicon 100-facet surface and suppresses the formation of pyramidal hillocks surrounded by 111-facets, thereby enabling smooth etching. Furthermore, in the silicon etching solution, the ratio of the concentration of the quaternary ammonium salt represented by formula (2) to the concentration of the quaternary ammonium hydroxide represented by formula (1) (formula (2) / formula (1)) is not particularly limited, but from the viewpoint that adding too little of the quaternary ammonium salt represented by formula (2) will prevent smooth etching and adding too much of the quaternary ammonium salt represented by formula (2) will contribute to a decrease in the etching rate, the molar ratio is usually 0.02 or more and 10.00 or less, preferably 0.03 or more and 5.00 or less, and more preferably 0.04 or more and 2.50 or less.

[0039] The form of water in the silicon etching solution is not particularly limited, and any known water can be used, and ultrapure water with reduced metal impurities is particularly preferred. The content of water in the silicon etching solution is also not particularly limited, and is usually 30% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and 99% by mass or less, preferably 98% by mass or less, and more preferably 97% by mass or less.

[0040] In addition to the quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2), surfactants and the like may be added to the silicon etching solution as long as the objective of the present invention is not impaired. However, because these may affect the etching properties, the content of these surfactants is preferably 1% by mass or less, and more preferably, they are not included (below the detection limit). Therefore, the silicon etching solution preferably consists essentially of the quaternary ammonium hydroxide represented by formula (1), the quaternary ammonium salt represented by formula (2), and water, and the content of other components is preferably 1% by mass or less, and more preferably, they are not included. In other words, it is preferable that the entire amount of the silicon etching solution, other than the quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2), is water.

[0041] The mechanism by which the addition of a quaternary ammonium salt represented by formula (2) can suppress the formation of pyramidal hillocks surrounded by 111 faces on the silicon surface after silicon etching is not entirely clear, even when the concentration of quaternary ammonium hydroxide represented by formula (1) above is low, which tends to roughen the silicon surface. However, the inventors speculate as follows: In alkaline silicon etching, water in the etching solution contributes to the reaction, and the water concentration significantly affects the behavior of silicon etching. It has generally been shown that increasing the alkali concentration and reducing the water concentration can suppress the formation of pyramidal hillocks surrounded by 111 faces. The inventors believe that the addition of a quaternary ammonium salt represented by formula (2) above promotes ion hydration and reduces the number of free water molecules, thereby reducing the concentration of water that contributes to silicon etching, even when the concentration of quaternary ammonium hydroxide represented by formula (1) above is low, thereby suppressing the formation of pyramidal hillocks surrounded by 111 faces.

[0042] In this case, to improve the smoothness of the silicon surface, it is preferable to make the etching rate ratio (100 / 111) of the silicon 100 plane to the 111 plane close to 1, more preferably 3.2 or less, and even more preferably 2.8 or less. The etching rate ratio (100 / 111) decreases and approaches 1 by adding the quaternary ammonium salt shown in formula (2) above, and the present inventors believe that this also contributes to the suppression of the generation of pyramidal hillocks surrounded by 111 planes.

[0043] In the silicon etching solution, the quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2) are ionized and dissociated to form the quaternary ammonium hydroxide cation represented by formula (1'), the quaternary ammonium cation represented by the following formula (2'), and X - It is as follows. R 1 R 2 R 3 R 4 N + (1') In formula (1'), R 1 , R 2 , R 3 and R 4 has the same meaning as in the above formula (1). R 5 R 6 R 7 R 8 N + (2') In the formula, R 5 , R 6 , R 7 and R 8 has the same meaning as in the above formula (2). Therefore, a silicon etching solution containing these ion species is the silicon etching solution of the present invention.

[0044] At this time, it goes without saying that the equation (1') Hydroxide The quaternary ammonium cation is the same concentration as the quaternary ammonium hydroxide shown in formula (1), and the quaternary ammonium cation shown in formula (2') and X - is the same concentration as the quaternary ammonium salt represented by formula (2). The composition of the silicon etching solution of the present invention can be confirmed by analyzing and quantifying the ionic components and their concentrations in the solution, and converting them into the quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2). The quaternary ammonium cation can be identified by liquid chromatography, ion chromatography, or OH - Ions are neutralized by titration, X - The ions can be measured by ion chromatography.

[0045] (Method of manufacturing silicon etching solution) The method for producing the silicon etching solution of the present invention is not particularly limited. Quaternary ammonium hydroxide represented by formula (1) and a quaternary ammonium salt represented by formula (2) are mixed with water to a predetermined concentration, and the quaternary ammonium hydroxide and the quaternary ammonium salt are dissolved in water. The quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2) may be used as they are, or each may be used as an aqueous solution. Alternatively, either the quaternary ammonium hydroxide represented by formula (1) or the quaternary ammonium salt represented by formula (2) may be made into an aqueous solution, and the other may be directly mixed with the aqueous solution.

[0046] The silicon etching solution of the present invention can also be produced by using a quaternary ammonium hydroxide represented by the following formula (2-1) instead of the quaternary ammonium salt represented by formula (2), preparing an aqueous solution containing the quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium hydroxide represented by formula (2-1), and then adding an appropriate amount of an acid represented by HX (X has the same meaning as in formula (2)) to the aqueous solution. R 5 R 6 R 7 R 8 N + OH - (2-1) In formula (2-1), R 5 , R 6 , R 7 and R 8 has the same meaning as in formula (2).

[0047] The silicon etching solution of the present invention can be used in a method for treating a silicon substrate. Another embodiment of the present invention is a method for treating a silicon substrate containing at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, and the method includes a step of etching the silicon material using the silicon etching solution. The silicon single crystal film, the polysilicon film, and the amorphous silicon film can also be collectively referred to as a silicon film. Therefore, the silicon etching solution described above can also be suitably used in a method for manufacturing a silicon device. Another embodiment of the present invention is a method for manufacturing a silicon device having at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, the method comprising the step of etching the silicon material using the silicon etching solution described above. The method for treating the silicon substrate and the etching method in the etching step in the method for manufacturing a silicon device are not particularly limited except for using the silicon etching solution described above, and can be carried out by a known method, such as the method described below in relation to wet etching. The above-described silicon substrate processing method and silicon device manufacturing method may include a step other than the etching step, such as a step of preparing an object to be etched. In this specification, silicon wafers, silicon single crystal films, polysilicon films, and amorphous silicon films are collectively referred to as silicon materials. The term "substrate" is used in the silicon device manufacturing process, and is also referred to as a silicon substrate in this specification.

[0048] The substrate processing method according to the first embodiment using the silicon etching solution of the present invention includes the following steps: a substrate holding step of holding the substrate in a horizontal position; and a processing liquid supplying step of supplying the isotropic silicon etching liquid of the present invention onto the main surface of the substrate while rotating the substrate about a vertical axis of rotation passing through the center of the substrate.

[0049] The substrate processing method according to the second embodiment using the silicon etching solution of the present invention comprises: a substrate holding step of holding a plurality of substrates in an upright position; and immersing the substrate in an upright position in the isotropic silicon etching solution of the present invention stored in a treatment tank.

[0050] In a preferred embodiment of the present invention, the silicon etching solution can be used in the manufacture of a device, which includes a step of supplying the silicon etching solution to smoothly etch at least one silicon material selected from the group consisting of a silicon single crystal film, a polysilicon film, and an amorphous silicon film included in a silicon substrate.

[0051] The temperature of the silicon etching solution during etching in each of the above-described embodiments may be appropriately determined within a range of 20°C or higher and 95°C or lower, taking into consideration the desired etching rate, the shape of silicon after etching, the surface state, productivity, etc., and is preferably set within a range of 50°C or higher and 90°C or lower.

[0052] Wet etching of silicon materials may be performed by simply immersing the object to be etched in a silicon etching solution, but it is also possible to employ an electrochemical etching method in which a constant potential is applied to the object to be etched, such as an anodic oxidation method in which a positive voltage is applied after the silicon material is immersed in a silicon etching solution.

[0053] Examples of silicon materials that are the subject of etching in the present invention include single crystal silicon, polysilicon, and amorphous silicon. These materials may contain non-target films, such as silicon oxide films, silicon nitride films, or metal films (e.g., aluminum films), that are not the subject of etching. Examples include a silicon single crystal on which a silicon oxide film, silicon nitride film, or metal film is laminated to form a pattern, a polysilicon film or resist film formed or applied thereon, and a structure in which a metal portion, such as aluminum, is covered with a protective film and a silicon pattern is formed. [Example]

[0054] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0055] Example 1 Tetramethylammonium hydroxide (TMAH) was used as the quaternary ammonium hydroxide represented by formula (1), and tetramethylammonium hydroxide (TMAH) was used as the quaternary ammonium salt represented by formula (2). Octyl Trimethylammonium Chloride A silicon etching solution having the composition shown in Table 1 was prepared using the above and the remainder being water.

[0056] <Evaluation of surface roughness of silicon single crystal substrates> A 2cm x 2cm silicon single crystal substrate (100 face) was immersed for 10 minutes in the silicon etching solution heated to the solution temperature (treatment temperature) listed in Table 1, and the silicon etching rate (R 100 ) was measured. The target silicon single crystal substrates had their native oxide film removed using a chemical solution. The etching rate was determined by measuring the weight of the silicon single crystal substrate (100 face) before and after etching, converting the amount of silicon single crystal substrate etched from the weight difference before and after treatment, and dividing this by the etching time. Similarly, a 2cm x 2cm silicon single crystal substrate (111 face) was immersed for 120 minutes, and the silicon etching rate (R 111) and the etching rate ratio (R 100 / R 111 ) was sought.

[0057] The surface condition of the silicon single crystal substrate (100 plane) after etching by about 1 μm was visually observed and observed with a field emission scanning electron microscope (FE-SEM) and evaluated according to the following criteria. The results are shown in Table 1.

[0058] <Evaluation criteria for surface roughness of silicon single crystal substrate (100 surface)> (Visual observation results) 5. The surface of the substrate is completely free of any white turbidity and is mirror-finished. 3. There is a slight white cloudiness on the surface of the substrate, but it is a mirror finish. 1 The substrate surface is completely cloudy and white, but the mirror finish remains. 0 The substrate surface is completely cloudy and has lost its mirror finish due to severe surface roughness.

[0059] (FE-SEM observation results) Three randomly selected locations were observed at a magnification of 20,000 times, and a 50 μm square was observed to check for the presence or absence of hillocks. 5. No hillocks were observed on the entire surface of the evaluation substrate. 3. Small hillocks were observed on the evaluation substrate. 0: Many hillocks were observed on the evaluation substrate.

[0060] <Evaluation of the selectivity between silicon single crystal and silicon oxide film, and silicon nitride film> Wafers with 2 cm x 2 cm silicon oxide and silicon nitride films formed thereon were immersed for 10 minutes in a silicon etching solution heated to the solution temperature (processing temperature) listed in Table 1, and the etching rates of the silicon oxide and silicon nitride films at that temperature were measured. The etching rates were determined by measuring the film thickness of the silicon oxide and silicon nitride films before and after etching with a spectroscopic ellipsometer, converting the amount of silicon oxide and silicon nitride film etched from the difference in film thickness before and after processing, and dividing this by the etching time. Next, the etching rate (R 100 ) to determine the etching rate ratio (R 100 / silicon oxide film), (R 100 The results are shown in Table 1.

[0061] <Evaluation criteria for the selectivity between silicon single crystal and silicon oxide film, and silicon nitride film> Evaluation criteria for the selectivity between silicon single crystal and silicon oxide film (Si (100) / SiO2) A: 1000 or more B: 700 or more but less than 1000 C: 500 or more but less than 700 D: Less than 500 Evaluation criteria for the selectivity between silicon single crystal and silicon nitride film (Si(100) / SiN) A: 1000 or more B: 700 or more but less than 1000 C: 500 or more but less than 700 D: Less than 500 In the above evaluation, a grade of B or higher indicates good selectivity. Here, the selectivity ratio (Si (100) / SiO2) of the inorganic alkali potassium hydroxide (KOH) is approximately 250, which is classified as D according to the above evaluation criteria.

[0062] Examples 2 to 20 The properties were evaluated in the same manner as in Example 1, except that the silicon etching solutions having the compositions shown in Table 1, in which the types and amounts of the quaternary ammonium hydroxide represented by formula (1) and the quaternary ammonium salt represented by formula (2) were varied, were used and etching was performed at the temperatures shown in Table 1. The evaluation results are shown in Table 1.

[0063] Comparative Examples 1 to 5 The properties were evaluated in the same manner as in Example 1, except that the silicon etching solution used did not contain the quaternary ammonium salt represented by formula (2) and had the composition shown in Table 1. The results are shown in Table 1.

[0064] [Table 1]

Claims

1. 1. A silicon etching solution comprising a quaternary ammonium hydroxide represented by the following formula (1), a quaternary ammonium salt represented by the following formula (2), and water, wherein the concentration of the quaternary ammonium salt represented by the formula (2) is greater than 1 mass % and not more than 50 mass %: R １ R ２ R ３ R ４ N ＋ ・OH － (1) (In formula (1), R １ , R ２ , R ３ and R ４ are alkyl, aryl or benzyl groups which may have a substituent, and may be the same or different groups. R ５ R ６ R ７ R ８ N ＋ ・X － (2) (In formula (2), R ５ , R ６ , R ７ and R ８ are alkyl groups having 1 to 16 carbon atoms which may have a substituent, at least one of which is a different group; and X is a chlorine atom or a bromine atom.

2. 2. The silicon etching solution according to claim 1, wherein the concentration of the quaternary ammonium hydroxide represented by the formula (1) is 0.05 mol / L or more and 1.1 mol / L or less.

3. 3. The silicon etching solution according to claim 1, wherein the total number of carbon atoms in the molecule of the quaternary ammonium salt represented by formula (2) is 4 or more and 12 or less.

4. A method for treating a silicon substrate containing at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film, comprising: A method for treating a silicon substrate, comprising the step of etching the silicon material with the silicon etching solution according to any one of claims 1 to 3.

5. A method for manufacturing a silicon device having at least one silicon material selected from the group consisting of a silicon wafer, a silicon single crystal film, a polysilicon film, and an amorphous silicon film. A manufacturing method comprising: A method for manufacturing a silicon device, comprising the step of etching the silicon material using the silicon etching solution according to any one of claims 1 to 3.

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