An alkaline silicon etching solution and its application

Abstract

This invention discloses an alkaline silicon etching solution and its application. It comprises an inorganic metal hydroxide, hydroxylamine, and further comprises catechol and / or resorcinol; by weight percentage, the alkaline silicon etching solution contains 0.1%-2.5% of the catechol and / or resorcinol. By adding 0.1%-2.5% catechol and / or resorcinol, the etching rate stability of the etching solution can be significantly improved. This is because catechol and / or resorcinol have reducing properties and can preferentially react with oxidants such as oxygen in the solution, reducing the possibility of hydroxylamine oxidation and inhibiting its decomposition. Simultaneously, by controlling the added catechol and / or resorcinol to a specific amount, excessive adsorption of catechol and / or resorcinol onto the silicon surface is avoided, which would affect the effectiveness. The etching solution of this invention has a high initial etching rate and high etching rate stability.

Description

Technical Field

[0001] This invention specifically relates to an alkaline silicon etching solution and its application. Background Technology

[0002] Anisotropic etching of single-crystal silicon is widely used in the fabrication of various microstructures in the field of microelectromechanical systems (MEMS). It is also widely used for surface texturing of single-crystal silicon to reduce light reflection and improve the efficiency of crystalline silicon solar cells. In wet processing of single-crystal silicon, the etching rate is a major factor affecting productivity. A slower silicon etching rate significantly increases device fabrication time, thereby reducing production efficiency. Therefore, in the MEMS industry employing wet anisotropic etching for silicon bulk micromachining, especially when using undercutting processes to remove underlying material to fabricate deep cavities and freestanding microstructures, the silicon etching rate is of great concern.

[0003] Commonly used wet anisotropic silicon etching solutions are alkaline, such as potassium hydroxide (KOH) solution and tetramethylammonium hydroxide (TMAH) solution. Among these, the etching rate of tetramethylammonium hydroxide solution is significantly affected by temperature and concentration, and its safety is insufficient. Potassium hydroxide (KOH) solution exhibits anisotropic etching properties towards silicon. <100> The etching rate of the crystal orientation is much faster than <111> Crystal orientation.

[0004] Although potassium hydroxide exhibits a higher silicon etching rate compared to tetramethylammonium hydroxide solution at the same concentration, it is still relatively low, for example, only 1 µm / min at 80°C, which is insufficient to meet the high silicon etching rate requirements of the MEMS field. Furthermore, in silicon-based micro / nano fabrication (such as MEMS and semiconductor manufacturing), the performance of the etching solution directly affects the device's precision, yield, and reliability. Currently, controlling the etching rate, surface smoothness, and stability of silicon etching solutions still presents challenges and difficulties.

[0005] For potassium hydroxide etching solutions, the following problems typically exist: 1. Bubble problem: In alkaline etching solutions, the reaction between silicon and hydroxide ions generates hydrogen bubbles. These bubbles adhere to the silicon wafer surface, acting as a false mask, increasing the roughness of the etched surface, and may also damage the microstructure. Furthermore, the bubbles adhering to the silicon surface hinder the contact between the etching solution and the silicon wafer, reducing the etching rate; 2. Crystal orientation influence: KOH etching is anisotropic, and the etching rate is severely affected by the silicon crystal orientation. The etching rates differ greatly between different crystal planes. On the wafer plane of (100) silicon, the etching rate varies significantly with the crystal orientation. <110> Oriented rectangular openings result in rapid etching of the exposed {100} plane, while the {111} plane is etched slowly, which may cause problems such as mask alignment. Even small rotational errors can lead to feature weakening and enlargement.

[0006] Adding hydroxylamine to KOH solution can significantly improve the initial etching rate of silicon. For example, adding 15% hydroxylamine to a 20 wt% KOH solution can achieve an etching rate four times that of pure 20 wt% KOH solution for Si{110}. This is because hydroxylamine participates in the redox reaction of silicon, promoting the chemical reaction on the silicon surface to generate silicon dioxide, and also helps to quickly remove hydrogen bubbles generated during etching from the silicon surface. However, hydroxylamine is very unstable in strongly alkaline KOH solution and decomposes rapidly, leading to a decrease in the effective hydroxylamine content in the etching solution and affecting its effectiveness.

[0007] Although some existing technologies add other auxiliary components to alkaline silicon etching solutions containing hydroxylamine to inhibit the decomposition of hydroxylamine, these auxiliary components may inhibit the silicon etching rate and reduce the silicon etching rate, such as the initial etching rate. This makes it difficult for alkaline etching solutions to achieve a high initial etching rate. The challenge lies in how to achieve a high initial etching rate while ensuring that the etching solution is stable and that the hydroxylamine does not decompose significantly (thus ensuring that the etching solution can maintain a high etching rate level even after long-term storage). Summary of the Invention

[0008] The technical problem to be solved by this invention is to address the shortcomings and deficiencies of existing technologies by providing an improved alkaline silicon etching solution. This etching solution exhibits a high initial etching rate and high stability, maintaining a high etching rate even after prolonged exposure, such as several days; that is, it demonstrates high etching rate stability and high safety. To solve the above technical problems, this invention adopts the following technical solution:

[0009] An alkaline silicon etching solution is disclosed, comprising an inorganic metal hydroxide, hydroxylamine, and further comprising catechol and / or resorcinol; by weight percentage, the alkaline silicon etching solution contains 0.1%-2.5% of the catechol and / or resorcinol. While adding hydroxylamine to a potassium hydroxide solution etching solution can increase the initial etching rate, the inventors of this application have discovered that the hydroxylamine component in the etching solution is unstable and prone to rapid decomposition after preparation, resulting in a reduction in the effective hydroxylamine content. This leads to a significant decrease in the etching rate after prolonged storage, indicating low etching rate stability. Typically, etching solutions containing potassium hydroxide and hydroxylamine are difficult to use after one day of storage following preparation, as the etching rate has already significantly decreased by then.

[0010] The inventors of this application discovered through research that adding 0.1%-2.5% catechol and / or resorcinol to an etching solution containing potassium hydroxide and hydroxylamine can significantly improve the etching rate stability of the etching solution. As mentioned earlier, hydroxylamine is very unstable in potassium hydroxide solution. Without a stabilizer, hydroxylamine decomposes rapidly after the etching solution is prepared, leading to a decrease in the etching rate of the potassium hydroxide solution, i.e., poor etching rate stability. The catechol and / or resorcinol added in this application have reducing properties and can preferentially react with oxidants (such as oxygen, hydrogen peroxide, etc.) in the etching solution, becoming oxidized themselves and consuming the oxidants in the system. This reduces the possibility of hydroxylamine being oxidized, indirectly protecting hydroxylamine and preventing its decomposition, thus maintaining its stability for a longer period. This, in turn, keeps the effective hydroxylamine content stable, resulting in an etching solution that not only has a high initial etching rate but also maintains a stable etching rate over a long period, i.e., the etching rate remains high even after the etching solution has been left for a long time, thus improving the stability of the etching rate. Meanwhile, by controlling the amount of added catechol and / or resorcinol to a specific level, namely 0.1%-2.5% by weight of the etching solution, this application can further improve the etching rate stability of the etching solution. This is because although the added catechol and / or resorcinol can prevent the decomposition of hydroxylamine, if the amount is too large, the excess catechol and / or resorcinol will be adsorbed onto the silicon surface to be etched or the surface of the silicon etched product that has already been etched, which will affect its reaction with the oxidant and the effect of preventing the decomposition of hydroxylamine.

[0011] The hydroxylamine component in the etching solution of this application exhibits high stability and will not decompose even after prolonged storage, such as several days. This ensures that the etching solution maintains a high etching rate even after extended storage, significantly improving its lifespan while guaranteeing a high etching rate. Other additives, such as alcohols and alkanolamines, struggle to achieve both an initial high etching rate and a consistently high etching rate after prolonged storage.

[0012] In some embodiments, the alkaline silicon etching solution contains 0.3%-2.5% of the catechol and / or resorcinol by weight percentage. The alkaline silicon etching solution may contain, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.2%, 2.3%, 2.4%, or 2.5% of catechol and / or resorcinol.

[0013] In some embodiments, the alkaline silicon etching solution contains 0.7%-2.5% of the catechol and / or resorcinol by weight percentage.

[0014] In some embodiments, the alkaline silicon etching solution contains 0.8%-1.2% of the catechol and / or resorcinol by weight. Within this dosage range, optimal etching rate stability and high etching rates can be achieved.

[0015] In some embodiments, the inorganic metal hydroxide is selected from one or more combinations of potassium hydroxide, cesium hydroxide, and sodium hydroxide. The inorganic metal hydroxide is the main component of the etching process.

[0016] In some embodiments, the alkaline silicon etching solution contains 10%-30% inorganic metal hydroxide by weight percentage. The alkaline silicon etching solution may contain, for example, 10%, 15%, 20%, 25%, or 30% inorganic metal hydroxide.

[0017] In some embodiments, the alkaline silicon etching solution contains 20%-30% inorganic metal hydroxide by weight percentage.

[0018] In some embodiments, the alkaline silicon etchant contains 1%-15% hydroxylamine by weight. The alkaline silicon etchant may contain, for example, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10%, or 15% hydroxylamine. Hydroxylamine can increase the initial etching rate.

[0019] In some embodiments, the alkaline silicon etching solution contains 5%-10% hydroxylamine by weight percentage.

[0020] In some embodiments, the alkaline silicon etching solution also contains a chelating agent.

[0021] In some embodiments, the chelating agent is selected from ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), ethylenediaminedisuccinic acid (EDDS), diethyltriaminepentaacetic acid (DTPA), ethylene glycol tetraacetic acid (EGTA), hypozinotriacetic acid (NTA), glucoheponic acid, hydroxyethylethylenediaminetriacetic acid (HEDTA), glutamic acid-N,N-diacetic acid (GLDA), iminodisuccinic acid (IDS), methylglycine diacetic acid (MGDA), and their salts. Adding a chelating agent alone cannot effectively inhibit the decomposition of hydroxylamine.

[0022] In some embodiments, the alkaline silicon etching solution contains 0.001%-3% chelating agent by weight percentage. The alkaline silicon etching solution may contain, for example, 0.001%, 0.01%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, or 3.0% chelating agent.

[0023] In some embodiments, the alkaline silicon etching solution also contains water. The water may be, for example, ultrapure water.

[0024] In some embodiments, the alkaline silicon etching solution comprises, by weight percentage, 10%-30% inorganic metal hydroxide, 1%-15% hydroxylamine, 0.1%-2.5% catechol and / or resorcinol, 0.001%-3% chelating agent, and the balance being water.

[0025] This invention also provides the use of the aforementioned alkaline silicon etching solution for silicon etching in the fields of microelectromechanical systems (MEMS) or photovoltaics (solar cells). Both of these fields have very high requirements for silicon etching.

[0026] Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0027] 1) This invention, by adding 0.1%-2.5% catechol and / or resorcinol to an etching solution containing inorganic hydroxides and hydroxylamine, achieves the goal of inhibiting hydroxylamine decomposition, maintaining the etching rate level even after long-term storage, while simultaneously significantly increasing the initial etching rate of the etching solution. In other words, the etching solution of this invention exhibits a high initial etching rate and good stability; even after prolonged storage, hydroxylamine remains largely undecomposed, and the etching rate remains high even after storage.

[0028] 2) The alkaline etching solution of the present invention can achieve a etching rate of up to 5.14 µm / min on the silicon {100} plane, which is higher than the level of the prior art, and the storage time is longer.

[0029] 3) The alkaline etching solution of the present invention has a high etching rate on different planes of silicon.

[0030] 4) The alkaline etching solution of the present invention can maintain a high etching rate even after being placed for 8 or even 40 days after preparation, and the service life of the etching solution is far higher than that of the prior art.

[0031] 5) The alkaline etching solution of the present invention is safer and has a higher etching rate than the TMAH system. Attached Figure Description

[0032] Figure 1 This is a metallographic microscope image of a polished silicon 100-sided surface after etching, taken 0 days after being placed in the etching solution in Example 1.

[0033] Figure 2 This is a metallographic microscope image of a polished silicon 100-sided surface after etching, taken 8 days after being placed in the etching solution in Example 1.

[0034] Figure 3 This is a metallographic microscope image of the 100-sided polished silicon after etching, taken 0 days after being placed in the etching solution in Example 5.

[0035] Figure 4 The image shown is a metallographic microscope image of a polished silicon 100-sided surface after etching, taken 0 days after being placed in the etching solution, as a comparative example 4.

[0036] Figure 5 This is a metallographic microscope image of a polished silicon 100-sided surface after etching, taken 0 days after being placed in the etching solution, as a comparative example 5. Detailed Implementation

[0037] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described.

[0038] Preparation and visual observation of the stability of silicon etching solution (this observation is performed before etching, and stability observation is one of the methods to characterize the stability of the etching solution): After the components of the silicon etching solution are thoroughly mixed, the generation of bubbles inside the solution is observed under static conditions. The results and their definitions are as follows:

[0039] Virtually no bubbles: No obvious bubbles are visible to the naked eye, and there are very few bubbles in the solution that disappear quickly;

[0040] Significantly more bubbles: Bubbles are visible to the naked eye, and the number of bubbles continues to increase.

[0041] The silicon single crystal etching process is as follows: Silicon {100} and {110} single crystal samples of 2cm × 2cm are weighed m before the experiment. 前 After immersing in a 0.2% ammonium fluoride solution at a pH of approximately 3 for 5 minutes to remove the surface silicon oxide layer, the sample was rinsed thoroughly with water. Then, the silicon single crystal sample was etched in the example solution at 80°C for 20 minutes. After removing the sample, it was rinsed thoroughly with water, dried with nitrogen, and weighed (m). 后 According to the weight loss Δm (=m 前 - m 后 Calculate the corrosion rate of silicon single crystals using the following formula:

[0042] Silicon single crystal corrosion rate = Δm / (ρ*a*t)

[0043] Where ρ is the density of silicon, 2.33 g / cm³. 3 , where a is the etching area of ​​the silicon single crystal and t is the etching time.

[0044] Example 1: This example provides an alkaline etching solution and uses it for etching silicon:

[0045] The composition of the alkaline etching solution is as follows: by weight percentage, KOH accounts for 24%, hydroxylamine accounts for 10%, EDTA accounts for 0.1%, ultrapure water accounts for 64.9%, and catechol accounts for 1%. The stability of the etching solution observed by the naked eye and the initial etching rate of silicon (etching was carried out immediately after the etching solution was prepared) are shown in Table 1.

[0046] Examples 2-5 and Comparative Examples 1-3: Examples 2-5 and Comparative Examples 1-3 are basically the same as Example 1, except that the composition of the alkaline etching solution is not exactly the same, as shown in Table 1 below. Comparative Examples 1-3 used excessive amounts of catechol or resorcinol. The results are shown in Table 1 below ( / indicates no addition).

[0047]

[0048] As shown in Table 1, this application solves the problem of instability (e.g., unstable etching rate) in traditional potassium hydroxide and hydroxylamine solutions by adding a specific amount of catechol and / or resorcinol to an alkaline etching solution containing potassium hydroxide and hydroxylamine. (After preparation, before etching, bubbles are generated due to the decomposition of hydroxylamine, which is a characteristic of etching solution instability.) By adding catechol and / or resorcinol, they can react with oxidants such as oxygen in the solution first, thereby avoiding the decomposition of hydroxylamine caused by the reaction between the oxidant and hydroxylamine. This ensures that the effective amount of hydroxylamine in the etching solution remains high. Simultaneously, the amount must be controlled carefully; otherwise, it will adsorb onto the silicon surface, affecting the aforementioned effects. Therefore, the alkaline etching solution of this invention has a high initial etching rate and high etching rate stability. A comparison of Examples 1 and 4 (both with the same amount of catechol) shows that within a certain range, increasing the amount of hydroxylamine can improve the etching rate. As can be seen from the comparison of Examples 1-4 and Comparative Example 1, when the hydroxylamine dosage remains constant at 10%, the etching rate is highest when the catechol dosage is 1%, which is greater than that of Example 2 when the etching rate is 0.7%. When the catechol dosage increases from 1% to 2.5%, although the initial etching rate decreases by 0.24, this decrease is not as significant as the decrease of more than 0.70 when the catechol dosage increases from 2.5% to 5%. In other words, when the catechol dosage exceeds 2.5%, the initial etching rate decreases more rapidly. This invention controls the dosage of catechol and / or resorcinol below 2.5% to achieve better results.

[0049] Comparative Example 4: Basically the same as Example 1, except that the composition of the alkaline etching solution was: 24% KOH and 76% ultrapure water by weight percentage. The initial etching rate of the {100} plane was 1.36 µm / min, which was much lower than the etching rate of Example 1.

[0050] In addition, the etching solutions of Example 1 and Comparative Example 4 were tested on different silicon materials to obtain the etching rates of different silicon planes. The results are shown in Table 2 below. It can be seen that the etching solution of Example 1 has a high initial etching rate for various types of silicon.

[0051]

[0052] Comparative Example 5: Basically the same as Example 1, except that catechol was not added to the alkaline etching solution, and the amount of ultrapure water was adjusted to 65.9%. The etching solution showed significantly more bubbles upon visual observation, and the etching rate for the {100} plane was 3.98 µm / min, significantly lower than the etching rate of Example 1. Therefore, this invention, by adding catechol, can improve the stability of the etching solution and increase the initial etching rate.

[0053] After the etching solutions of Examples 1, 5, and Comparative Example 5 were prepared, they were left to stand for a period of time before etching, and the corresponding etching rates on the {100} plane were tested. The results are shown in Table 3 below, where "-" indicates that the etching was not tested.

[0054]

[0055] In Comparative Example 5, the etching rate decreased significantly after one day of storage, making it unnecessary to test the etching rate after three days. As shown in Table 3, this invention, by adding specific amounts of catechol or resorcinol, improves the hydroxylamine decomposition stability of the alkaline etching solution containing potassium hydroxide and hydroxylamine. This allows the etching solution to remain stable for an extended period, maintaining a high etching rate even after prolonged storage. In contrast, existing etching solutions experience a significant decrease in etching rate after prolonged storage due to the instability and decomposition of hydroxylamine.

[0056] Among them, the metallographic microscope image of the polished silicon 100 face after etching after 0 days of etch solution placement in Example 1 is shown below. Figure 1 As shown, the image after 8 days is as follows. Figure 2 As shown; Metallurgical microscope image of Example 5 after 0 days in the etching solution. Figure 3 As shown; metallographic microscope images of Comparative Examples 4 and 5 after 0 days in the etching solution are shown below. Figure 4-5As shown, after 8 days, the surface condition of the silicon 100 surface etched by the etching solution of Example 1 showed no significant change. The surface condition of the silicon 100 surface etched by the etching solution containing resorcinol in Example 5 was rougher than that of Example 1, but better than that of Comparative Example 5. Although the potassium hydroxide solution in Comparative Example 4 had a relatively low corrosion rate, its surface condition was worse than that of Example 1. The surface condition of the silicon 100 surface etched by the silicon etching solution containing hydroxylamine in Comparative Example 5 without added catechol was significantly rougher than that of Example 1.

[0057] Comparative Examples 6-8: Basically the same as Example 1, except that catechol was replaced with glycerol, xylitol, and sorbitol, respectively. The stability of the etching solution observed by the naked eye and the initial etching rate on the {100} plane are shown in Table 4 below:

[0058]

[0059] As can be seen from Table 4, when glycerol, xylitol or sorbitol are used instead of the catechol or resorcinol of the present invention, more bubbles are generated when the etching solution is placed, the etching solution is unstable, and the etching rate is reduced.

[0060] Comparative Example 9: Basically the same as Example 1, except that 1% catechol was replaced with 10% isopropanol, and the amount of ultrapure water was adjusted accordingly to 55.9%. The result showed that the etching solution separated, and etching could not be performed. The reason is that isopropanol is insoluble in the etching solution system of this example. When the weight percentage composition of the etching solution is as follows: KOH 24%, hydroxylamine 10%, EDTA 0.1%, ultrapure water 60.9%, and isopropanol 5%, isopropanol can dissolve in this etching solution system, but the initial etching rate of the silicon 100 surface drops to 1.10 µm / min.

[0061] Comparative Example 10: Basically the same as Example 1, except that hydroxylamine was replaced with hydroxylamine sulfate. The results showed that the etching solution still contained crystals, making etching impossible. This is because hydroxylamine sulfate has low solubility in the potassium hydroxide aqueous solution of the example, and most of it remains undissolved, forming crystals.

[0062] Comparative Example 11: Basically the same as Example 1, except that catechol was replaced with monoethanolamine. The etching rate for the {100} plane decreased to 2.16 µm / min, significantly lower than the etching rate in Example 1.

[0063] Comparative Examples 12-14: Basically the same as Example 1, except that the potassium hydroxide system was replaced with a TMAH system, and the amounts of some components were changed (TMAH is a toxic substance, and the mass concentration of TMAH aqueous solution in industrial applications is usually not very high). The results of visual observation of stability and initial corrosion rate are shown in Table 5 below:

[0064]

[0065] As shown in Table 5, when using the TMAH system, even with the addition of catechol, the initial corrosion rate is significantly lower than that of KOH, and far lower than the initial corrosion rate of the present invention.

[0066] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An alkaline silicon etching solution, characterized in that: The alkaline silicon etching solution contains inorganic metal hydroxide, hydroxylamine, and also contains catechol and / or resorcinol; by weight percentage, the alkaline silicon etching solution contains 0.7%-2.5% of the catechol and / or resorcinol, 10%-30% of the inorganic metal hydroxide, and 1%-15% of the hydroxylamine.

2. The alkaline silicon etching solution according to claim 1, characterized in that: The alkaline silicon etching solution contains 0.8%-1.2% of the catechol and / or resorcinol by weight percentage.

3. The alkaline silicon etching solution according to claim 1, characterized in that: The inorganic metal hydroxide is selected from one or more combinations of potassium hydroxide, cesium hydroxide, and sodium hydroxide.

4. The alkaline silicon etching solution according to claim 1, characterized in that: The alkaline silicon etching solution also contains a chelating agent.

5. The alkaline silicon etching solution according to claim 4, characterized in that: The chelating agent is selected from one or more combinations of ethylenediaminetetraacetic acid, aminotriacetic acid, ethylenediaminedisuccinic acid, diethyltriaminepentaacetic acid, ethylene glycol tetraacetic acid, hypozinotriacetic acid, glucoheponic acid, hydroxyethylethylenediaminetriacetic acid, glutamic acid-N,N-diacetic acid, iminodisuccinic acid, methylglycine diacetic acid, and their salts.

6. The alkaline silicon etching solution according to claim 4, characterized in that: The alkaline silicon etching solution contains 0.001%-3% chelating agent by weight percentage.

7. The alkaline silicon etching solution according to claim 1, characterized in that: The alkaline silicon etching solution also contains water.

8. The alkaline silicon etching solution according to claim 1, characterized in that: By weight percentage, the alkaline silicon etching solution consists of 10%-30% inorganic metal hydroxide, 1%-15% hydroxylamine, 0.7%-2.5% catechol and / or resorcinol, 0.001%-3% chelating agent, and the balance being water.

9. The use of the alkaline silicon etching solution according to any one of claims 1-8 for silicon etching in the field of microelectromechanical systems or photovoltaics.

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