Etching solution for selectively etching silicon nitride at high temperature and preparation method thereof
By introducing a composite corrosion inhibitor consisting of tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds into the etching solution, the problem of insufficient selectivity in silicon nitride etching at high temperatures was solved. This resulted in a high etching rate for silicon nitride at high temperatures and effective suppression of titanium nitride and silicon oxide, thereby improving the stability and selectivity of the etching solution.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-19
- Publication Date
- 2026-04-03
AI Technical Summary
Existing etching solutions have poor selectivity when etching silicon nitride and silicon oxide, making it difficult to maintain a high etching rate for silicon nitride while suppressing the etching of titanium nitride and silicon oxide at high temperatures, and they also have stability issues.
A high-temperature selective etching solution for silicon nitride was prepared using a composite etching inhibitor containing tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds. By using a phosphoric acid system at high temperature to avoid oxidants and hydrofluoric acid, the stability and selectivity of the etching solution were improved.
It achieves high etching rate of silicon nitride at high temperature and effective suppression of titanium nitride and silicon oxide, with etching selectivity ratios of 23:1 and 1000:1, meeting the high temperature and high etching selectivity requirements of semiconductor processes and improving the stability and durability of the etching solution.
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of etching solution technology, specifically to an etching solution for selectively etching silicon nitride at high temperatures and its preparation method. Background Technology
[0002] Silicon nitride and titanium nitride are widely used in the semiconductor industry for high-temperature, high-power, and high-frequency electronic devices. Silicon nitride possesses excellent thermal stability, mechanical properties, and chemical stability, and its conductivity can be tuned through doping. Titanium nitride, on the other hand, exhibits good metal diffusion barrier properties and low resistivity after annealing. In recent years, with the continuous miniaturization of semiconductor devices and feature sizes, etching technology has been used extensively as the most stable, efficient, and widely applied technique for semiconductor materials.
[0003] However, during the etching process, especially in the wet etching of 3D NAND flash memory, effectively suppressing the etching of silicon oxide and titanium nitride while maintaining the etching rate of silicon nitride has become a pressing problem. Traditional etching solutions suffer from poor selectivity, poor uniformity of silicon nitride layer etching, and a tendency to generate particles, making them unsuitable for etching multilayer stacked silicon nitride and silicon oxide structures. Furthermore, existing silicon nitride etching compositions use a limited variety of silicon compounds, failing to provide high selectivity and restricting the application of many organosilicon compounds.
[0004] CN119614203A discloses an etching solution for selectively etching silicon nitride, silicon oxide, and titanium nitride. This etching solution includes an acidic substance, an oxidant, a titanium etching inhibitor, and a metal complexing agent. The key feature is that the etching inhibitor can form a thin film on the surface of titanium nitride through coordination bonds with the metal, significantly reducing the etching rate of titanium nitride and achieving an etching selectivity >20. However, the oxidant in this invention is mainly composed of one or more of hydrogen peroxide, sodium hypochlorite, and potassium permanganate. These oxidants all suffer from poor stability, resulting in a poor service life for the etching solution.
[0005] CN119286526A discloses an etching solution for selectively etching silicon nitride and titanium nitride, comprising phosphoric acid, hydrofluoric acid, a pH buffer, a solubilizer, an etching inhibitor, and water. This etching solution allows for the control of the etching selectivity ratio between silicon nitride and titanium nitride films. The pH buffer effectively stabilizes the pH of the etching solution, the solubilizer improves the solubility of the solvent in the etching solution, reduces the tension at the solid-liquid interface, and promotes the transfer rate of interphase materials, and the etching inhibitor forms a thin film on the surface of titanium nitride through coordination bonds with the metal. The etching solution achieves a silicon nitride to titanium nitride selectivity ratio between 15 and 118. However, the introduction of hydrofluoric acid in this invention has two drawbacks. First, it makes the etching solution unfriendly to the silicon oxide layer, making it unusable in common silicon nitride-silicon oxide stacks containing titanium nitride. Second, the etching solution containing hydrofluoric acid has a very poor service life at 100°C. Summary of the Invention
[0006] To address the aforementioned problems, this invention provides a high-temperature selective etching solution for silicon nitride and its preparation method. Under high-temperature conditions, this etching solution can maintain a high etching rate for silicon nitride while effectively suppressing the etching of titanium nitride and silicon oxide layers.
[0007] The technical solution of the present invention is an etching solution for selectively etching silicon nitride at high temperature, comprising the following raw materials by mass fraction: 84-88% acidic substances, 4-6% composite corrosion inhibitor, and the balance being water; the composite corrosion inhibitor contains tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds.
[0008] Optionally, the acidic substance is phosphoric acid.
[0009] Optionally, the tungstate compound is one or more of the following: ammonium paratungstate, sodium tungstate, sodium metatungstate monohydrate, tungstic acid, tetra-N-butylammonium decatungstate, tetrabutyl phosphotungstate, sodium phosphotungstate, and ammonium tetrathiotungstate.
[0010] Optionally, the hydroxyphosphonic acid compound is one or more of the following: hydroxyethylidene diphosphonic acid, hydroxymethylphosphonic acid monoethyl ester, hydroxymethylphosphonic acid diethyl ester, 2-hydroxyphosphonoacetic acid, 4-hydroxyphosphonic acid phenyl ester, (4-hydroxybenzyl)phosphonic acid, 3-hydroxyphenylphosphonic acid, hydroxy(phenyl)methylphosphonic acid, 2-hydroxy-4-phosphonobutyric acid, (2-amino-1-hydroxyethyl)phosphonic acid, and zoledronic acid.
[0011] Optionally, the epoxy silane compound is one or more of the following: 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, [8-(epoxypropyloxy)-n-octyl]trimethoxysilane, tris(epoxypropoxypropyldimethylsiloxy)phenylsilane, and methacrylate trioxosiloxane.
[0012] Optionally, the molar ratio of tungstate compound, hydroxyphosphonic acid compound, and epoxysilane compound is 1:1 to 2:2 to 3. In a more preferred embodiment, the molar ratio of tungstate compound, hydroxyphosphonic acid compound, and epoxysilane compound is 1:1:2.
[0013] This invention also relates to a method for preparing the etching solution, the specific steps of which are as follows: A composite etching inhibitor is prepared by adding tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds to deionized water at room temperature and mixing them. The composite etching inhibitor is then added to an acidic substance at 50-60°C and mixed to obtain a high-temperature selective etching solution for silicon nitride.
[0014] The present invention also relates to the application of the etching solution in high-temperature selective etching of silicon nitride, wherein the etching temperature is above 100°C.
[0015] The present invention has the following beneficial effects: The etching solution provided by this invention is a phosphoric acid system, free of oxidants and hydrofluoric acid, resulting in a longer service life and avoiding corrosion problems caused by oxidants and hydrofluoric acid, thus improving the stability and durability of the etching solution. A composite corrosion inhibitor is prepared using tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds, effectively inhibiting the etching of titanium nitride and silicon oxide while maintaining a high etching rate for silicon nitride. The tungstate compounds assist the hydroxyphosphonic acid compounds in adsorbing and inhibiting etching on the surfaces of titanium nitride and silicon oxide, while the addition of epoxy silane compounds further enhances the etching effect, primarily acting on silicon oxide. The three components of the composite corrosion inhibitor work together to achieve a high selectivity etching ratio for silicon nitride.
[0016] The etching solution provided by this invention solves the problem of insufficient selectivity in traditional etching compositions. It achieves an etching selectivity greater than 23 for silicon nitride and titanium nitride on a single-layer wafer, and an etching selectivity greater than 1000 for silicon nitride and silicon oxide. This etching solution is suitable for etching in high-temperature environments, exhibiting good stability and selectivity. It effectively solves the problem of instability of acidic formulations in high-temperature environments in existing technologies, and meets the high-temperature, high etching selectivity requirements of silicon nitride and titanium nitride in semiconductor manufacturing processes. Detailed Implementation
[0017] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all raw materials and reagents used are commercially available.
[0018] A high-temperature selective etching solution for silicon nitride comprises the following raw materials by mass fraction: 84-88% acidic substances, 4-6% composite etching inhibitor, and the balance being water; the composite etching inhibitor contains tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds.
[0019] In some embodiments, the acidic substance is phosphoric acid. Hydrofluoric acid should be avoided to ensure the stability and durability of the etching solution.
[0020] In some embodiments, the tungstate compound is one or more selected from ammonium paratungstate, sodium tungstate, sodium metatungstate monohydrate, tungstic acid, tetra-N-butylammonium decatungstate, tetrabutylphosphotungstate, sodium phosphotungstate, and ammonium tetrathiotungstate. Sodium metatungstate monohydrate is preferred.
[0021] In some embodiments, the hydroxyphosphonic acid compound is one or more selected from hydroxyethylidene diphosphonic acid, hydroxymethylphosphonic acid monoethyl ester, hydroxymethylphosphonic acid diethyl ester, 2-hydroxyphosphonoacetic acid, 4-hydroxyphosphonic acid phenyl ester, (4-hydroxybenzyl)phosphonic acid, 3-hydroxyphenylphosphonic acid, hydroxy(phenyl)methylphosphonic acid, 2-hydroxy-4-phosphonobutyric acid, (2-amino-1-hydroxyethyl)phosphonic acid, and zoledronic acid. 2-hydroxyphosphonoacetic acid is preferred.
[0022] In some embodiments, the epoxy silane compound is one or more selected from 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, [8-(epoxypropoxy)-n-octyl]trimethoxysilane, tris(epoxypropoxypropyldimethylsiloxy)phenylsilane, and methacrylate trioxane. Preferably, it is 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane.
[0023] In some embodiments, the molar ratio of the tungstate compound, the hydroxyphosphonic acid compound, and the epoxysilane compound is 1:1 to 2:2 to 3. In a more preferred embodiment, the molar ratio of the tungstate compound, the hydroxyphosphonic acid compound, and the epoxysilane compound is 1:1:2.
[0024] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.
[0025] Example 1 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The solution comprises 86% phosphoric acid, 4% composite etching inhibitor, and the balance being deionized water by mass percentage. The composite etching inhibitor contains ammonium paratungstate, hydroxyethylidene diphosphonic acid, and 3-glycidyl etheroxypropyltriethoxysilane in a molar ratio of 1:1:2.
[0026] Preparation method: Ammonium paratungstate, hydroxyethylidene diphosphonic acid and 3-glycidyl etheroxypropyltriethoxysilane are added sequentially to deionized water at room temperature to prepare a composite corrosion inhibitor. The composite corrosion inhibitor is then added to an acidic substance at 50~60℃ and mixed to obtain a highly selective etching silicon nitride etching solution. Example 2 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the tungstate compound in the composite etching inhibitor is replaced by sodium tungstate instead of ammonium paratungstate.
[0027] Example 3 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the tungstate compound in the composite etching inhibitor is replaced by sodium metatungstate monohydrate instead of ammonium paratungstate.
[0028] Example 4 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the hydroxyphosphonic acid compound in the composite etching inhibitor is replaced by diethyl hydroxymethylphosphonate instead of hydroxyethylidene diphosphonic acid.
[0029] Example 5 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the hydroxyphosphonic acid compound in the composite etching inhibitor is replaced by 2-hydroxyphosphonoacetic acid instead of hydroxyethylidene diphosphonic acid.
[0030] Example 6 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the hydroxyphosphonic acid compound in the composite etching inhibitor is replaced by 4-hydroxyphosphonic acid phenyl ester instead of hydroxyethylidene diphosphonic acid.
[0031] Example 7 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the epoxy silane compound in the composite etching inhibitor is replaced by 3-glycidyl etheroxypropyltriethoxysilane instead of 3-glycidyl etheroxypropylmethyldiethoxysilane.
[0032] Example 8 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the epoxy silane compound in the composite etching inhibitor is replaced by 3-glycidyl etheroxypropyltriethoxysilane instead of 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane.
[0033] Example 9 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the epoxy silane compound in the composite etching inhibitor is replaced by 5,6-epoxyhexyltriethoxysilane instead of 3-glycidyl etheroxypropyltriethoxysilane.
[0034] Example 10 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the molar ratio of the composite etching inhibitor is adjusted to 1:1:3.
[0035] Example 11 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the molar ratio of the composite etching inhibitor is adjusted to 1:2:2.
[0036] Comparative Example 1 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The solution is formulated with 86% phosphoric acid (an acidic substance) and the balance being deionized water.
[0037] Comparative Example 2 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formula and preparation method are the same as in Example 1, except that the phosphoric acid (acidic substance) content is changed to 83%.
[0038] Comparative Example 3 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the tungstate compound ammonium paratungstate in the composite etching inhibitor is not added.
[0039] Comparative Example 4 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the hydroxyphosphonic acid compound hydroxyethylidene diphosphonic acid in the composite etching inhibitor is not added.
[0040] Comparative Example 5 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the epoxy silane compound 3-glycidyl etheroxypropyltriethoxysilane in the composite etching inhibitor is not added.
[0041] Comparative Example 6 An etching solution for selective etching of silicon nitride at high temperature and its preparation method are disclosed. The formulation and preparation method are the same as in Example 1, except that the epoxy silane compound 3-glycidyl etheroxypropyltriethoxysilane in the composite etching inhibitor is replaced with methyltriethoxysilane.
[0042] Etching method (1) Take a regular square with a size of 1.5*1 cm on a silicon substrate containing a single film layer of silicon nitride, titanium nitride and silicon oxide as a test piece; (2) The initial thickness of silicon nitride and silicon oxide wafers was measured using an ellipsometry, and the initial thickness of titanium nitride was measured using a four-probe thickness gauge. (3) Immerse the test piece in anhydrous isopropanol and ultrapure water in sequence. After 1 min, remove it and blow it dry with nitrogen to obtain a clean test piece. (4) Place the clean test pieces into the acidic etching solution prepared in the above examples and comparative examples respectively. Fix the test pieces with an etching support and place them in the etching solution at 160°C. After 10 minutes, take out the test pieces, rinse them with deionized water, and complete the etching. (5) After taking it out, wash it with 70°C ultrapure water for 10 seconds, then dry the sample with nitrogen gas, test the thickness of silicon nitride and titanium nitride after etching, and calculate the corresponding etching rate by comparing the change in sample thickness before and after etching.
[0043] See Table 1 below for details.
[0044] Table 1. Etching performance of different film layers by etching solution formulation.
[0045] The results show that, by comparing Comparative Example 1 and Example 1 in Table 1 (different examples and comparative examples), the etching rates of silicon nitride are similar, but the etching rates of titanium nitride and silicon oxide differ significantly. Comparative Example 1 shows a significantly faster etching rate for both titanium nitride and silicon oxide compared to Example 1, indicating that the composite etching inhibitor has a significant effect on inhibiting the etching of titanium nitride and silicon oxide. Comparative Example 2 only reduced the phosphoric acid concentration of the etching solution. The reduction in the phosphoric acid content of the main etching component caused a slight decrease in the etching rate of each individual wafer, with a larger decrease in silicon nitride, which in turn led to a decrease in the selectivity ratio between silicon nitride and titanium nitride / silicon oxide. Compared to Example 1, Comparative Examples 3, 4, and 5 lack one compound from the composite etching inhibitor. It can be seen that the absence of any one compound fails to simultaneously satisfy the requirement that the etching selectivity ratio of silicon nitride / titanium nitride is greater than 23 and the etching selectivity ratio of silicon nitride / silicon oxide is greater than 1000. In Comparative Examples 3 and 4, the etching rate of titanium nitride was significantly faster (compared to Example 1). This indicates that the tungstate compound and hydroxyphosphonic acid compound in the composite corrosion inhibitor have a significant impact on the corrosion inhibition effect of titanium nitride, and there should be a certain synergistic effect between the two, jointly affecting the corrosion inhibition effect of titanium nitride during the etching process of silicon nitride. In Comparative Examples 3 and 4, the etching rate of silicon oxide was also slightly faster, which also indicates that there is a certain synergistic effect between the tungstate compound, hydroxyphosphonic acid compound, and epoxy silane compound in the composite corrosion inhibitor. The absence of the tungstate compound and hydroxyphosphonic acid compound affects the etching rate of silicon oxide. In Comparative Example 5, the etching rate of silicon oxide was found to be significantly faster, indicating that the epoxy silane compound is the main corrosion inhibitor of silicon oxide in the composite catalyst, and the tungstate compound and hydroxyphosphonic acid compound only have a weak synergistic effect. Compared to Example 1, in Comparative Example 6, the selectivity ratios of silicon nitride / titanium nitride and silicon nitride / silicon oxide decreased after replacing the silicon nitride / titanium nitride and silicon nitride / silicon oxide compounds with epoxy groups. This indicates that epoxy group-containing silane compounds are indispensable in composite corrosion inhibitors. Examples 10-11 adjusted the proportions of each component in the composite corrosion inhibitor, and the etching results of the etching solution on each individual wafer showed that there is an optimal proportion of each component in the composite corrosion inhibitor.
[0046] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.
Claims
1. A high-temperature selective etching solution for silicon nitride, characterized in that, It contains the following raw materials by mass fraction: 84-88% acidic substances, 4-6% composite corrosion inhibitor, and the balance being water; the composite corrosion inhibitor contains tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds.
2. The etching solution according to claim 1, characterized in that: The acidic substance is phosphoric acid.
3. The etching solution according to claim 1, characterized in that: The tungstate compounds are one or more of the following: ammonium paratungstate, sodium tungstate, sodium metatungstate monohydrate, tungstic acid, tetra-N-butylammonium decatungstate, tetrabutyl phosphotungstate, sodium phosphotungstate, and ammonium tetrathiotungstate.
4. The etching solution according to claim 1, characterized in that: The hydroxyphosphonic acid compound is one or more of the following: hydroxyethylidene diphosphonic acid, hydroxymethylphosphonic acid monoethyl ester, hydroxymethylphosphonic acid diethyl ester, 2-hydroxyphosphonoacetic acid, 4-hydroxyphosphonic acid phenyl ester, (4-hydroxybenzyl)phosphonic acid, 3-hydroxyphenylphosphonic acid, hydroxy(phenyl)methylphosphonic acid, 2-hydroxy-4-phosphonobutyric acid, (2-amino-1-hydroxyethyl)phosphonic acid, and zoledronic acid.
5. The etching solution according to claim 1, characterized in that: The epoxy silane compounds are one or more of the following: 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, [8-(epoxypropyloxy)-n-octyl]trimethoxysilane, tris(epoxypropoxypropyldimethylsiloxy)phenylsilane, and methacrylate trioxosiloxane.
6. The etching solution according to any one of claims 1 to 5, characterized in that: The molar ratio of tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds is 1:1~2:2~3.
7. The etching solution according to claim 6, characterized in that: The molar ratio of tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds is 1:1:
2.
8. The method for preparing the etching solution according to claims 1-7, characterized in that, The specific steps are as follows: A composite etching inhibitor is prepared by adding tungstate compounds, hydroxyphosphonic acid compounds, and epoxy silane compounds to deionized water at room temperature and mixing them. The composite etching inhibitor is then added to an acidic substance at 50-60°C and mixed to obtain a high-temperature selective etching solution for silicon nitride.
9. The application of the etching solution according to any one of claims 1 to 7 in high-temperature selective etching of silicon nitride.
10. The application according to claim 9, characterized in that: The etching temperature is above 100℃.
Citation Information
Patent Citations
Etching solution for selectively etching silicon nitride and titanium nitride and preparation method thereof
CN119286526A