High etching rate and high smoothness silicon etching solution for wafer backside thinning

Abstract

The application discloses a high-etching-rate and high-smoothness silicon etching solution for wafer back thinning, which comprises HNO3, HF, H2SO4, H3PO4 and the rest water. The etching solution is compounded by HNO3, HF, H2SO4 and H3PO4 in a specific ratio, and can realize high etching rate and low roughness. The high etching rate can significantly improve the process efficiency of the thinning step, meet the process time of the etching machine, and meet the requirements of large-scale commercial production on efficiency and cost. The silicon etching solution can be used for wafer back thinning, and can realize the process requirements of fast etching (shortening process time) and smooth surface (low roughness).

Description

Technical Field

[0001] This invention belongs to the field of semiconductor chip processing and manufacturing technology. Specifically, it relates to a silicon etching solution that can achieve a combination of high etching rate and ultra-smooth surface on silicon wafers. Background Technology

[0002] In semiconductor manufacturing, microelectromechanical systems (MEMS), and back-illuminated (BSI) image sensors, precision machining of silicon materials is one of the core processes. Silicon etching technology, as a key means to achieve specific morphologies, dimensions, and surface qualities of silicon materials, directly affects the performance, reliability, and production cost of devices. Silicon etching solutions are often used in silicon wafer thinning processes. To ensure production efficiency, a high silicon etching rate is usually required. However, during rapid etching, it is often difficult to control the surface quality of the wafer after etching, making it impossible to meet the surface roughness requirements of subsequent processes. For example, the silicon thinning process in back-illuminated (BSI) image sensors has extremely stringent and interrelated requirements regarding etching rate and surface roughness. Specifically: (1) Low surface roughness requirement: After mechanical grinding, BSI devices need to be thinned and polished with silicon etchant to eliminate the scratches caused by the previous grinding step. The smoothness of the thinned silicon surface has a decisive impact on the quantum efficiency (QE) and crosstalk of the device. A rough surface will form strong light scattering, causing some photons to be unable to effectively penetrate the silicon surface and be absorbed by the photodiode below, resulting in photon loss. In addition, scattered photons may deviate from the original target pixel and enter the adjacent pixel, resulting in color distortion, image blurring and overall signal-to-noise ratio reduction. (2) High etching rate requirement: After mechanical grinding, a 10-20 µm damage layer usually remains that needs to be removed by wet etching. If the etching rate is too slow (e.g., <0.5 µm / min), this step will consume a lot of time and limit production capacity. In addition, a long etching process will amplify the small non-uniformities of the process (such as temperature, liquid flow, etc.) and increase the risk of wafer defects. Rapid etching helps to shorten the window time of this sensitive process, thereby better controlling uniformity.

[0003] However, there is an inherent contradiction between high etching rate and low surface roughness. Traditional silicon etching solutions usually either pursue high speed but rough surface, which cannot meet the wafer surface quality requirements; or pursue smooth surface but slow etching rate, which is not conducive to improving production capacity.

[0004] Therefore, developing a silicon etching solution that can achieve both high etching rate and low surface roughness has become an urgent technical problem to be solved in the current silicon material processing field. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects in the prior art and provide a high-etching-rate, high-smoothness silicon etchant for wafer backside thinning, which can achieve both high etching rate and low surface roughness.

[0006] To achieve the above objectives, the technical solution of this invention is to design a high-etching-rate, high-smoothness silicon etchant for wafer backside thinning, comprising, by weight percentage, 30-43% HNO3, 2-4% HF, 6-9% H2SO4, 15-17% H3PO4, and the balance being water. This silicon etchant achieves an etching rate ER > 2.9 μm / min and a surface roughness Ra < 5.5 nm.

[0007] Furthermore, the total weight percentage of HNO3, HF, H2SO4, and H3PO4 is 53-73%; Furthermore, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 60.6-73%.

[0008] Furthermore, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 64-73%.

[0009] Furthermore, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 64-71.8%.

[0010] Furthermore, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 64-70.15%.

[0011] Furthermore, the total weight percentage of HNO3, HF, H2SO4, and H3PO4 is 66-70.5%; Preferably, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 68-70%; Preferably, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 68.4-69.9%; specifically, it can be any one of the values ​​68.4, 68.9, 69, 69.1, 69.15, 69.4, 69.65, 69.9 or any one of any two values ​​within the range. More preferably, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 68.9-69.65%; Most preferably, the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 68.9-69.15%.

[0012] Furthermore, by weight percentage (100%), it comprises 35-43% HNO3, 2.6-4% HF, 7-9% H2SO4, 16-17% H3PO4, and the balance being water; the total weight percentage of HNO3, HF, H2SO4, and H3PO4 is 60.6-73%. This silicon etching solution can achieve an etching rate ER > 4.5 μm / min and a surface roughness Ra < 5.0 nm.

[0013] Furthermore, by weight percentage (100%), it comprises 38-43% HNO3, 3-4% HF, 7-9% H2SO4, 16-17% H3PO4, and the balance being water. The total weight percentage of HNO3, HF, H2SO4, and H3PO4 is 64-73%. This silicon etching solution can achieve an etching rate ER > 6.0 μm / min and a surface roughness Ra < 5.0 nm.

[0014] Furthermore, by weight percentage (100%), it comprises 38-42% HNO3, 3-3.8% HF, 7-9% H2SO4, 16-17% H3PO4, and the balance being water. The total weight percentage of HNO3, HF, H2SO4, and H3PO4 is 64-71.8%. This silicon etching solution can achieve an etching rate ER > 6.0 μm / min and a surface roughness Ra < 4.3 nm.

[0015] Furthermore, by weight percentage (100%), it comprises 38-41.5% HNO3, 3-3.65% HF, 7-9% H2SO4, 16-17% H3PO4, and the balance being water; the total weight percentage of HNO3, HF, H2SO4, and H3PO4 is 64-70.15%. This silicon etching solution can achieve an etching rate ER > 6.0 μm / min and a surface roughness Ra < 3.0 nm.

[0016] Furthermore, by weight percentage, the silicon etching solution is any one of the following: and the etching rate ER > 6.6 μm / min and the surface roughness Ra < 2.0 nm can be achieved by any one of the following silicon etching solutions; (1) By weight percentage, it comprises 40.5-41.5% HNO3, 3.4-3.65% HF, 8-8.5% H2SO4, 16.5-17% H3PO4 and the balance water; the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 68.4-69.9%; (2) By weight percentage, it includes 41.5% HNO3, 3.4% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (3) By weight percentage, it includes 40.5% HNO3, 3.4% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (4) It comprises 41% HNO3, 3.65% HF, 8.25% H2SO4, 17% H3PO4 and the balance water, by weight percentage.

[0017] Furthermore, by weight percentage, the silicon etching solution is any one of the following, and an etching rate ER > 6.7 μm / min and a surface roughness Ra < 1.4 nm can be achieved by any one of the following silicon etching solutions; (1) By weight percentage, it comprises 41% HNO3, 3.4-3.65% HF, 8-8.5% H2SO4, 16.5% H3PO4 and the balance water; the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 68.9-69.65%; (2) By weight percentage, it includes 41% HNO3, 3.65% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (3) By weight percentage, it includes 41% HNO3, 3.6% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (4) By weight percentage, it includes 41% HNO3, 3.65% HF, 8.5% H2SO4, 16.5% H3PO4 and the balance water; (5) By weight percentage, it includes 41% HNO3, 3.65% HF, 8.25% H2SO4, 16.5% H3PO4 and the balance water; (6) It comprises 41% HNO3, 3.4% HF, 8% H2SO4, 16.5% H3PO4 and the balance water, by weight percentage (100%). (7) It comprises 41% HNO3, 3.5% HF, 8% H2SO4, 16.5% H3PO4 and the balance water, by weight percentage.

[0018] Furthermore, by weight percentage, the silicon etching solution is any one of the following, and any one of the following silicon etching solutions can achieve an etching rate ER ≥ 6.99 μm / min and a surface roughness Ra ≤ 1 nm. (1) By weight percentage, it comprises 41% HNO3, 3.65% HF, 8.25% H2SO4, 16-16.25% H3PO4 and the balance water; the total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 68.9-69.15%; (2) By weight percentage, it includes 41% HNO3, 3.65% HF, 8.25% H2SO4, 16.25% H3PO4 and the balance water; (3) It comprises 41% HNO3, 3.65% HF, 8.25% H2SO4, 16% H3PO4 and the balance water, by weight percentage.

[0019] In the above technical solution, the corrosion rate of about 7 µm / min (7.00±0.01 µm / min) and the surface roughness Ra≤1nm can be achieved by the above component ratio. This higher corrosion rate can significantly improve the process efficiency of the thinning step, which is in line with the process time of the etching machine and meets the requirements of efficiency and cost for large-scale commercial production.

[0020] Furthermore, it also includes additives, which are one or more of surfactants and defoamers.

[0021] Adding surfactants reduces the surface tension of the etching solution, facilitating rapid spreading and wetting of the silicon wafer and improving mass transfer. This allows fresh etching solution to reach the reaction interface more effectively, and byproducts to leave quickly, resulting in more uniform and repeatable etching results. Considering the need for good chemical stability in the etching solution system, nonionic surfactants are used, such as fatty alcohol polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, fatty acid polyoxyethylene esters, polysorbates, alkanolamides, lauryl glucoside, and fatty acid glycerides; the addition amount is 0.01%-0.1% of the total weight of the etching solution.

[0022] Defoamers are added to reduce the uneven roughness caused by chemical foaming. During the reaction between the silicon etching solution and the silicon wafer, a large number of bubbles are generated. The bubble masking effect leads to increased roughness. Adding defoamers accelerates bubble breakage, reduces the bubble masking effect, and thus further reduces roughness. Defoamers used include organosilicon compounds, such as polydimethylsiloxane; polyether compounds, such as ethylene oxide block copolymers; and higher alcohols, such as octanol, decanol, and lauryl alcohol. The addition amount is 0.005%-0.01% of the total weight of the etching solution.

[0023] The silicon etching solution described in this invention can be used for back-side thinning of wafers to achieve the process requirements of rapid etching (shortening process time) and smooth surface (low roughness).

[0024] The advantages and beneficial effects of this invention are as follows: (1) The etching solution described in this invention can achieve high etching rate and low roughness by compounding HNO3, HF, H2SO4 and H3PO4 in a specific ratio. The higher etching rate can significantly improve the process efficiency of the thinning step, match the process time of the etching machine, and meet the requirements of efficiency and cost for large-scale commercial production.

[0025] (2) The silicon etching solution described in this invention can be used for back-side thinning of wafers to achieve the process requirements of rapid etching (shortening process time) and smooth surface (low roughness). Attached Figure Description

[0026] Figure 1 SEM image of the wafer surface after etching with the etching solution described in Example 1; Figure 2 SEM image of the wafer surface after etching with the etching solution described in Example 3; Figure 3 SEM image of the wafer surface after etching with the etching solution described in Example 22; Figure 4 The image shows a SEM image of the wafer surface after etching with the etching solution described in Example 23. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0028] (I) Implementation Examples A high-etching-rate, high-smoothness silicon etching solution for wafer backside thinning comprises HNO3, HF, H2SO4, H3PO4, and the balance water. The weight percentages of each component in Examples 1-22 are shown in the table below (100% by weight). Example 23: A high-etching-rate, high-smoothness silicon etchant for back-side thinning of wafers, comprising, by weight 100%, 41% HNO3, 3.65% HF, 8.25% H2SO4, 16.25% H3PO4, 0.05% polysorbate, and the balance being water.

[0029] (ii) Performance Testing Testing instrument: 3D laser microscope; Test method: Preheat the silicon etching solution to 25°C, immerse half of the silicon wafer in the silicon etching solution for 2 minutes, then remove it, rinse it with water and dry it with N2. Measure the height difference between the immersed and unimmersed parts (i.e., the thickness of the etched silicon). Divide this height difference by the etching time to get the etching rate. Roughness can be measured directly with a microscope. As can be seen from Examples 1-22, the etching solution of the present invention, by compounding HNO3, HF, H2SO4 and H3PO4 in a specific ratio, can synergistically achieve high etching rate and low roughness; the higher etching rate can significantly improve the process time of the thinning step, which is compatible with the process time of the etching machine and meets the efficiency and cost requirements of large-scale commercial production.

[0030] The silicon etching solution described in this invention can be used for back-side thinning of wafers, achieving the process requirements of rapid etching (shortening process time) and smooth surface (low roughness).

[0031] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-etching-rate, high-smoothness silicon etchant for back-side thinning of wafers, characterized in that, It comprises 30-43% HNO3, 2-4% HF, 6-9% H2SO4, 15-17% H3PO4, and the balance being water, by weight percentage (100%).

2. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, The total weight percentage of HNO3, HF, H2SO4 and H3PO4 is 53-73%.

3. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, It comprises 35-43% HNO3, 2.6-4% HF, 7-9% H2SO4, 16-17% H3PO4 and the balance water, by weight percentage (100%).

4. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, It comprises 38-43% HNO3, 3-4% HF, 7-9% H2SO4, 16-17% H3PO4 and the balance water, by weight percentage (100%).

5. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, It comprises 38-42% HNO3, 3-3.8% HF, 7-9% H2SO4, 16-17% H3PO4 and the balance water, by weight percentage (100%).

6. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, It comprises 38-41.5% HNO3, 3-3.65% HF, 7-9% H2SO4, 16-17% H3PO4 and the balance water by weight; the silicon etching solution can achieve an etching rate ER > 6.0 μm / min and a surface roughness Ra < 3.0 nm.

7. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, By weight percentage, the silicon etching solution is any one of the following: and the etching rate ER > 6.6 μm / min and the surface roughness Ra < 2.0 nm can be achieved by any one of the following silicon etching solutions; (1) By weight percentage, it includes 40.5-41.5% HNO3, 3.4-3.65% HF, 8-8.5% H2SO4, 16.5-17% H3PO4 and the balance water; (2) By weight percentage, it includes 41.5% HNO3, 3.4% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (3) By weight percentage, it includes 40.5% HNO3, 3.4% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (4) It comprises 41% HNO3, 3.65% HF, 8.25% H2SO4, 17% H3PO4 and the balance water, by weight percentage.

8. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, By weight percentage, the silicon etching solution is any one of the following, and an etching rate ER > 6.7 μm / min and a surface roughness Ra < 1.4 nm can be achieved by any one of the following silicon etching solutions; (1) By weight percentage, it includes 41% HNO3, 3.4-3.65% HF, 8-8.5% H2SO4, 16.5% H3PO4 and the balance water; (2) By weight percentage, it includes 41% HNO3, 3.65% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (3) By weight percentage, it includes 41% HNO3, 3.6% HF, 8% H2SO4, 16.5% H3PO4 and the balance water; (4) By weight percentage, it includes 41% HNO3, 3.65% HF, 8.5% H2SO4, 16.5% H3PO4 and the balance water; (5) By weight percentage, it includes 41% HNO3, 3.65% HF, 8.25% H2SO4, 16.5% H3PO4 and the balance water; (6) It comprises 41% HNO3, 3.4% HF, 8% H2SO4, 16.5% H3PO4 and the balance water, by weight percentage (100%). (7) It comprises 41% HNO3, 3.5% HF, 8% H2SO4, 16.5% H3PO4 and the balance water, by weight percentage.

9. The high-etching-rate, high-smoothness silicon etchant for wafer backside thinning according to claim 1, characterized in that, By weight percentage, the silicon etchant is any one of the following, and an etching rate ER ≥ 6.99 μm / min and a surface roughness Ra ≤ 1 nm can be achieved with any one of the following silicon etchants: (1) By weight percentage, it includes 41% HNO3, 3.65% HF, 8.25% H2SO4, 16-16.25% H3PO4 and the balance water; (2) By weight percentage, it includes 41% HNO3, 3.65% HF, 8.25% H2SO4, 16.25% H3PO4 and the balance water; (3) It comprises 41% HNO3, 3.65% HF, 8.25% H2SO4, 16% H3PO4 and the balance water, by weight percentage.

10. A high-etching-rate, high-smoothness silicon etchant for wafer backside thinning as described in any one of claims 1-9, characterized in that, It also includes additives, which are one or more of surfactants and defoamers.

11. A high-etching-rate, high-smoothness silicon etchant for back-side thinning of a wafer, as described in any one of claims 1-10, for back-side thinning of a wafer.

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