Silicon nitride etching solution composition

Abstract

To provide silicon nitride etchant compositions which can suppress regrowth of silicon oxide and in which desorbed alcohol is not generated in a process to selectively etch silicon nitride with a practical etching selection ratio for silicon oxide, such as in a production of a 3D nonvolatile memory cell or the like.SOLUTION: A silicon nitride etchant composition for producing a 3D nonvolatile memory cell or the like, contains phosphoric acid, a hydrolysate of a water-soluble silicon compound, and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silicon nitride etching solution composition for manufacturing 3D non-volatile memory cells and the like, and a method for manufacturing 3D non-volatile memory cells and the like using the etching solution composition. [Background technology]

[0002] In recent years, technological advancements have been made in NAND flash memory, a type of non-volatile memory that retains data even without a power supply. NAND flash memory is used as a storage device in devices such as SmartMedia and SSDs.

[0003] Traditionally, NAND flash memory has a planar structure (Figure 1), and as miniaturization progressed, the line width narrowed, negatively impacting its lifespan and performance. Recently, development of 3D type (Figure 2) has progressed, and by stacking vertically, it is possible to manufacture with a wider line width, achieving longer lifespan, higher speed, and larger capacity compared to conventional types.

[0004] One example of a method for manufacturing 3D NAND flash memory involves the following steps: (1) on a substrate in which silicon oxide and silicon nitride are alternately stacked, (2) holes are formed by dry etching, (3) gate electrodes (p-Si electrodes) covered with an insulating film (silicon oxide) are embedded in the holes, (4) grooves (spacing) are formed in the stacked film by dry etching, (5) impurity regions are formed by ion implantation on the substrate surface, (6) silicon nitride is etched by wet etching, (7) TiN is formed as a barrier metal and W as an electrode on the exposed substrate and silicon oxide surface, and (8) TiN and W are etched together with mixed acid.

[0005] In the above step (6) (Figure 3), an etching solution composition containing phosphoric acid, ammonium ions, and a silicon compound has been disclosed as an etching solution composition for etching silicon nitride (Patent Documents 1-3). When phosphoric acid and silicon compounds are included in the etching solution composition, they react to generate Si(OH)x. In the presence of Si(OH)x, the etching rates of silicon oxide and silicon nitride decrease, but the decrease in the etching rate of silicon oxide is greater, resulting in an improved etching selectivity ratio of silicon nitride to silicon oxide. On the other hand, if there is an excess of Si(OH)x, it adheres to the silicon oxide surface beyond its saturation solubility, causing silicon oxide regrowth (hereinafter referred to as "silicon oxide regrowth") (Figure 4). Patent documents 1 to 3 describe how ammonium ions in the etching solution composition combine with Si(OH)x to form a water-soluble compound, thereby suppressing silicon oxide regrowth.

[0006] Furthermore, etching solution compositions for silicon nitride have also been disclosed, including an etching solution composition containing an inorganic acid, a siloxane compound, an ammonium compound, and a solvent (Patent Document 4), an etching solution composition containing phosphoric acid, a complex silane consisting of two or more silane compounds, and water (Patent Document 5), and an etching solution composition containing phosphoric acid, an organic compound including silicon, and an organic solvent (Patent Document 6). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent Publication No. 8940182 [Patent Document 2] U.S. Patent Publication No. 9,136,120 [Patent Document 3] U.S. Publication No. 9368647 [Patent Document 4] Japanese Patent Publication No. 2018-085513 [Patent Document 5] Japanese Patent Publication No. 2018-182312 [Patent Document 6] Japanese Patent Publication No. 2000-058500 [Patent Document 7] Japanese Patent Publication No. 2020-145343 [Overview of the project] [Problems that the invention aims to solve]

[0008] As the number of stacked 3D NAND memory cells increases, the inventors diligently studied how to improve the etching selectivity ratio of silicon nitride to silicon oxide, and as a result, found an etching solution composition containing phosphoric acid, one or more silane coupling agents, and water, but without ammonium ions (Patent Document 7). However, general silane coupling agents have alkoxy groups, and hydrolysis generates alcohol, which is a VOC (Volatile Organic Compound). In this case, acids such as phosphoric acid act as catalysts, and a violent hydrolysis reaction can occur, which is dangerous. In addition, silane coupling agents with alkoxy groups take time to dissolve in an aqueous phosphoric acid solution, which leads to increased manufacturing costs. Furthermore, with the increase in the number of stacked 3D NAND cells, the amount of Si(OH)x generated when silicon nitride is dissolved is increasing, and the amount of silane coupling agent needed to suppress silicon oxide regrowth is also increasing. As a result, the amount of alcohol generated when phosphoric acid is added is also large, and depending on the composition, the solution may fall under the category of hazardous materials under the Fire Service Act, making it difficult to use with conventional etching equipment. Therefore, the present inventors have been investigating the objective of providing a silicon nitride etching solution composition that can selectively etch silicon nitride with a practical etching selectivity ratio to silicon oxide in the manufacturing of 3D non-volatile memory cells, suppress silicon oxide regrowth, and prevent the generation of desorbed alcohols during mixing. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors have diligently conducted research and have found that a silicon nitride etching composition containing phosphoric acid and a hydrolysate of a water-soluble silicon compound can selectively etch silicon nitride with a practical etching selectivity ratio to silicon oxide in the manufacturing of 3D non-volatile memory cells, suppress the regrowth of silicon oxide, improve the solubility of the hydrolysate of the silicon compound in phosphoric acid, and suppress the generation of desorbed alcohol when the silicon compound is added by using the hydrolysate. Further research has led to the completion of the present invention.

[0010] The inventors of the present invention hypothesize the following reasons why a silicon nitride etching composition containing phosphoric acid, a hydrolysate of a water-soluble silicon compound, and water can selectively etch silicon nitride with a practical etching selectivity ratio to silicon oxide in the manufacturing of 3D non-volatile memory cells, etc., suppress silicon oxide regrowth, improve the solubility of the hydrolysate of the silicon compound in phosphoric acid, and suppress the generation of desorbed alcohol during the hydrolysis reaction. In other words, the etching solution composition contains phosphoric acid and hydrolysates of water-soluble silicon compounds, which react and adsorb onto the silicon oxide surface, resulting in an improved etching selectivity ratio of silicon nitride to silicon oxide. Furthermore, it is presumed that the inclusion of hydrolysates of water-soluble silicon compounds in the etching solution composition prevents the adhesion of Si(OH)x to the silicon oxide surface, thereby suppressing silicon oxide regrowth (Figure 5). In addition, it is presumed that using hydrolysates of water-soluble silicon compounds significantly improves solubility in phosphoric acid and suppresses the generation of desorbed alcohols.

[0011] In other words, the present invention relates to the following: [1] The present invention relates to a silicon nitride etching solution composition containing phosphoric acid, a hydrolysate of one or more water-soluble silicon compounds, and water. [2] The present invention relates to the etching solution composition described in [1], wherein the hydrolysate of the water-soluble silicon compound is a hydrolysate of the silane coupling agent.

[0012] [3] The present invention relates to an etching solution composition according to [1]-[2], wherein the hydrolysis product of a water-soluble silicon compound is a hydrolysis condensate of a silane coupling agent containing a three-dimensional structure. [4] The present invention relates to etching solution compositions according to [1] to [3], wherein the hydrolysate of a water-soluble silicon compound is an aminoalkoxysilane hydrolysis condensate and / or a mercaptoalkoxysilane hydrolysis condensate. [5] The present invention relates to an etching solution composition according to [1] to [4], wherein the hydrolysate of a water-soluble silicon compound is a 3-aminopropyltrialkoxysilane hydrolysis condensate. [6] The present invention relates to the etching solution composition according to [1] to [5], further comprising at least one selected from sulfuric acid or a salt thereof, or an aliphatic sulfonic acid or a salt thereof. [7] The present invention relates to an etching solution composition according to [1] to [6], further comprising at least one selected from inorganic silicates, tetramethoxysilane, tetraethoxysilane, hydrolysates of tetramethoxysilane, and hydrolysates of tetraethoxysilane. [8] The present invention relates to the etching solution composition described in [7], comprising at least one selected from sodium silicate, potassium silicate, and tetramethylammonium silicate as an inorganic silicate. [9] The present invention relates to an etching method for silicon nitride that has high etching selectivity for silicon oxide, characterized by using a composition comprising phosphoric acid, a hydrolysate of one or more water-soluble silicon compounds, and water. [Effects of the Invention]

[0013] The etching liquid composition of the present invention can selectively etch silicon nitride with a practical etching selectivity for silicon oxide in the production of 3D non-volatile memory cells and the like, suppress the regrowth of silicon oxide, and further has no generation of desorbed alcohol during the hydrolysis reaction. In other words, it is possible to selectively etch silicon nitride safely, in a short time, and more economically without separately dissolving silicon nitride in the etching liquid composition. Further, since the regrowth of silicon oxide can be suppressed even when the etching liquid composition does not contain ammonium ions, the production cost of the etching liquid composition can be reduced. In addition, when the etching liquid composition of the present invention further contains sulfuric acid or its salt, aliphatic sulfonic acid or its salt, inorganic silicate, tetramethoxysilane, tetraethoxysilane, a hydrolyzate of tetramethoxysilane, or a hydrolyzate of tetraethoxysilane, the etching selectivity of silicon nitride with respect to silicon oxide can be further improved.

Brief Description of the Drawings

[0014] [Figure 1] It is a diagram showing the structure of a planar NAND flash memory. [Figure 2] It is a diagram showing the structure of a 3D NAND flash memory. [Figure 3] It is a diagram showing before and after the etching of silicon nitride. [Figure 4] It is a diagram showing the principle of the regrowth of silicon oxide. [Figure 5] It is a diagram showing the principle of suppressing the regrowth of silicon oxide.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail based on preferred embodiments of the present invention. The present invention relates to a silicon nitride etching liquid composition containing phosphoric acid, a hydrolyzate of one or more water-soluble silicon compounds, and water, having a high etching selectivity for silicon oxide, and suppressing the regrowth of silicon oxide.

[0016] The etching solution composition of the present invention is a silicon nitride etching solution composition for manufacturing 3D non-volatile memory cells and the like. 3D non-volatile memory refers to any 3D type of non-volatile memory, and is not particularly limited in terms of memory type or arithmetic format, such as 3D NAND flash memory. The etching solution composition of the present invention is particularly suitable for manufacturing 3D non-volatile memory with high stacking or a high aspect ratio of unit cells, such as those with a silicon oxide film thickness of 10 nm to 50 nm.

[0017] The hydrolysate of the water-soluble silicon compound used in the present invention is not particularly limited, but formula 1 [ka] R 1 R is either an H atom or an alkyl group that is identical to or different from each other. 2 However, R is a C1-10 alkyl group containing at least one selected from the group of H, N, S, Cl and F atoms, which are either identical or different from each other, 3 Equation 2 [ka] R 3 , R 1 O or OR 1 The compound is represented by formula 1, in which the atoms and Si may condense to form a ring, and m and n are integers from 1 to 1000. The compound represented by formula 1 is preferably an aminoalkoxysilane hydrolysate or a mercaptoalkoxysilane hydrolysate, more preferably a 3-aminopropyltrialkoxysilane hydrolysate, where R1 is one of a H atom, a methyl group, or an ethyl group, and R 2 Compounds represented by a 3-aminopropyl group are even more preferred. Also, m and n are integers from 1 to 1000, preferably from 1 to 500, and more preferably from 1 to 100.

[0018] Hydrolyzed water-soluble silicon compounds may be used alone or in combination. The concentration of the hydrolyzed water-soluble silicon compounds in the etching solution composition is not particularly limited, but is preferably 0.01 to 30% by weight, more preferably 0.5 to 30% by weight, and even more preferably 0.5 to 25% by weight.

[0019] The etching solution composition of the present invention contains phosphoric acid. The concentration of phosphoric acid in the etching solution composition is not particularly limited, but is preferably 40 to 95% by weight, and more preferably 50 to 95% by weight.

[0020] The etching solution composition of the present invention contains the hydrolysate of the above-mentioned water-soluble silicon compound and phosphoric acid, which react and adsorb onto the silicon oxide surface, thereby selectively etching silicon nitride from silicon oxide. Furthermore, the adhesion of Si(OH)x to the silicon oxide surface is prevented, regrowth of silicon oxide can be suppressed, and no desorbed alcohol is generated during the hydrolysis reaction.

[0021] The etching solution composition of the present invention comprises water, phosphoric acid, hydrolysates of water-soluble silicon compounds, and the remainder of the following additional components that may be included.

[0022] The etching solution composition of the present invention may further contain sulfuric acid or a salt thereof, or an aliphatic sulfonic acid or a salt thereof, thereby improving the etching selectivity of silicon nitride over silicon oxide.

[0023] The etching solution composition of the present invention may further contain inorganic silicates, tetramethoxysilane, tetraethoxysilane, hydrolysates of tetramethoxysilane, and hydrolysates of tetraethoxysilane, which is preferable because it improves the selectivity ratio of silicon oxide films to silicon nitride films. The inorganic silicates, tetramethoxysilane, tetraethoxysilane, hydrolysates of tetramethoxysilane, and hydrolysates of tetraethoxysilane form Si(OH)x in the etching solution composition. The inorganic silicate is not particularly limited, but sodium silicate, potassium silicate, and tetramethylammonium silicate are preferred.

[0024] The etching solution composition of the present invention may contain additional components other than sulfuric acid or its salts, aliphatic sulfonic acid or its salts, inorganic silicates, tetramethoxysilane, tetraethoxysilane, hydrolysates of tetramethoxysilane, and hydrolysates of tetraethoxysilane, as long as they do not interfere with the etching of silicon nitride. Examples include fluorine compounds. The etching solution composition of the present invention is preferable if it further contains a fluorine compound, as this increases the etching rate of silicon nitride. Preferred fluorine compounds include hydrofluoric acid, ammonium fluoride, and hexafluorosilicic acid, with hexafluorosilicic acid being more preferred.

[0025] The etching solution composition of the present invention does not necessarily have to contain ammonium ions. Even without containing ammonium ions, the etching solution composition of the present invention can suppress silicon dioxide regrowth.

[0026] Furthermore, the present invention relates to a method for manufacturing a 3D non-volatile memory cell, the like, which includes etching silicon nitride using an etching solution composition according to the present invention. Moreover, the present invention also relates to a 3D non-volatile memory cell, the like, obtained by the said method. [Examples]

[0027] Next, the etching solution composition of the present invention will be described in more detail by the following examples and comparative examples, but the present invention is not limited to these.

[0028] <Evaluation 1: Etching selectivity ratio of silicon nitride film / silicon oxide film> (Wafer preparation (before immersion)) A silicon nitride wafer (before immersion) was obtained by cutting a silicon nitride film onto a Si substrate into a 20 mm x 15 mm size. Similarly, a silicon oxide wafer (before immersion) was obtained using a silicon oxide film on a substrate.

[0029] (Pretreatment of Silicon Nitride Wafer) The above silicon nitride wafer (before immersion) was immersed in a 0.6 wt% hydrofluoric acid aqueous solution and allowed to stand at 25°C for 90 seconds. Then, the wafer was taken out and rinsed with ultrapure water (DIW) for 1 minute to obtain a silicon nitride wafer (after pretreatment).

[0030] (Immersion of Wafer in Etching Solution Composition) The above silicon nitride wafer (after pretreatment) was immersed in 100 mL of an etching solution composition having the composition shown in Table 1 and stirred and immersed at 160°C for 5 to 10 minutes. Then, the wafer was taken out and rinsed with ultrapure water (DIW) for 1 minute to obtain a silicon nitride wafer (after immersion). Note that, as the hydrolyzate of the water-soluble silicon compound in Table 1, a hydrolytic condensate of 3-aminopropyltriethoxysilane having a three-dimensional structure and more specifically assumed to be represented by Formula 3, [Chemical Formula] R 3 is represented by Formula 4 [Chemical Formula] R 3 , HO or OH and Si may undergo dehydration condensation to form a ring, and m and n represent integers from 1 to 100, and a hydrolyzate of 3-aminopropyltriethoxysilane represented by this was used. Also, the silicon oxide wafer (before immersion) was immersed in 100 mL of an etching solution composition having the composition shown in Table 1 and stirred and immersed at 160°C for 10 to 20 minutes. Then, the wafer was taken out and rinsed with ultrapure water (DIW) for 1 minute to obtain a silicon oxide wafer (after immersion).

[0031] [Table 1]

[0032] (Measurement of Etching Rate of Etching Solution Composition) The film thickness of the silicon nitride (after pretreatment) or silicon oxide wafer (before immersion) was measured using a spectroscopic ellipsometer (JAWoollam, model number: RC2®), and the film thickness of the silicon nitride or silicon oxide wafer (after immersion) was measured using a spectroscopic ellipsometer (JAWoollam, model number: RC2®). From the difference in film thickness before and after immersion, the etching rate of the etching solution composition for silicon nitride or silicon oxide was calculated, and the etching selectivity ratio of the silicon nitride film / silicon oxide film was calculated by dividing the etching rate of silicon nitride by the etching rate of silicon oxide. The results are shown in Table 2.

[0033] <Evaluation 2: Presence or absence of silicon dioxide regrowth> (Wafer preparation (before immersion)) A substrate in which silicon nitride and silicon oxide films were alternately stacked, and grooves (spacing) were formed in the stacked films by dry etching, was used, and a wafer for evaluation was obtained by cutting it to a size of 20 mm x 15 mm.

[0034] (Pre-processing of evaluation wafers) The evaluation wafer (before immersion) described above was immersed in a 0.6 wt% hydrofluoric acid aqueous solution and left standing at 25°C for 90 seconds. After that, the wafer was removed and rinsed with ultrapure water (DIW) for 1 minute to obtain the evaluation wafer (after pretreatment).

[0035] (Immersion of wafer in etching solution composition) The evaluation wafer (after pretreatment) described above was immersed in 100 mL of an etching solution composition having the composition shown in Table 1, and stirred and immersed at 160°C for 240 minutes. After that, the wafer was removed and rinsed with ultrapure water (DIW) for 1 minute to obtain the evaluation wafer (after immersion).

[0036] (Confirmation of silicon dioxide regrowth in etching solution composition) The evaluation wafers (after immersion) were observed using a FE-SEM (Hitachi High-Technologies, model number: SU8220) to check for the presence or absence of silicon dioxide regrowth. The results are shown in Table 2.

[0037] Table 2

Claims

1. Phosphate and Equation 1 【Chemistry 1】 R1 is either a H atom or an alkyl group that is the same as or different from each other, R2 is a C1-10 alkyl group that is the same as or different from each other and contains at least one selected from the group consisting of H, N, S, Cl and F atoms, and R3 is formula 2 【Chemistry 2】 A silicon nitride etching solution composition containing one or more hydrolyzed water-soluble silicon compounds represented by R3, R1O or OR1 and Si, where R3, R1O, or OR1 and Si may condense to form a ring, and m and n are integers from 1 to 1000, and water.

2. The etching solution composition according to claim 1, further comprising at least one selected from sulfuric acid or a salt thereof, or an aliphatic sulfonic acid or a salt thereof.

3. The etching solution composition according to claim 1, further comprising at least one selected from inorganic silicates, tetramethoxysilane, tetraethoxysilane, hydrolysates of tetramethoxysilane, and hydrolysates of tetraethoxysilane.

4. The etching solution composition according to claim 3, comprising at least one selected from sodium silicate, potassium silicate, and tetramethylammonium silicate as an inorganic silicate.

5. A method for etching silicon nitride, characterized by using the composition described in any one of claims 1 to 4, which has high etching selectivity for silicon oxide.

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