Method for cleaning metal on surface of silicon wafer with weak acid

Abstract

The invention discloses a method for cleaning metal on the surface of a silicon wafer with weak acid, which is characterized in that a dilute hydrofluoric acid solution of RCA is replaced with a boric acid solution, the silicon wafer is immersed in the boric acid solution for cleaning according to the process, the boric acid solution reacts with the silicon wafer, and the metal on the surface of the silicon wafer reacts with boric acid, so that the adhesion of the metal on the surface of the silicon wafer can be reduced, and the silicon wafer is not damaged. According to the method, in the cleaning process, nitric acid and boric acid need to be supplemented midway, so that metal on the surface of a silicon wafer can continuously react with boric acid. According to the method, a heating device and ultrasonic cleaning are used, more metal on the surface of the silicon wafer can be dissolved in a boric acid solution, and metal residues on the surface of the silicon wafer are reduced.

Description

Technical Field

[0001] This invention provides a method for cleaning the surface metal of a silicon wafer with a weak acid. This invention is mainly used in the surface treatment process of silicon wafers. Background Technology

[0002] In semiconductor device manufacturing, silicon wafers undergo surface treatment, specifically the formation of a silicon oxide layer on the wafer surface. This is a crucial process for ensuring chemical and electrical properties. Cleaning the silicon wafers is essential during surface treatment; low surface cleanliness negatively impacts the yield of the surface treatment process. Current silicon wafer cleaning methods include physical and chemical cleaning. Physical cleaning methods include mechanical tools such as brush cleaning, ultrasonic cleaning, and aerosol purging. Chemical cleaning, such as the common RCA cleaning, removes fine particles, organic matter, oil, and metal contaminants adhering to the silicon wafer surface through chemical reactions.

[0003] Before surface treatment, silicon wafers need to undergo RCA (Removal by Acid-Coating) to remove surface metals. However, when multiple wafers are cleaned together, a very small amount of metal will always remain on the wafer surface. Furthermore, in RCA cleaning agents, most metals dissolve in the agent, with very little metal reacting with the agent to form particulate precipitates. During the cleaning process, the metal-dissolving agent may carry metal to other agents, causing metal contamination. For some processes, the silicon oxide layer needs to be cleaned with dilute hydrofluoric acid. However, dilute hydrofluoric acid removes the thin oxide layer, thus failing to meet process requirements.

[0004] This method was developed to efficiently remove metals from the surface of silicon wafers. It removes more metals from the silicon wafer surface, generates other water-insoluble compounds, reduces the amount of metal dissolved in the cleaning agent, and further minimizes the possibility of contaminating other cleaning agents. Furthermore, it can remove metals adhering to the silicon wafer surface without damaging the silicon oxide layer. The addition of nitric acid, boric acid, and ultrapure water during the cleaning process ensures the stable cleaning effect of the boric acid cleaning agent. Summary of the Invention

[0005] This invention discloses a method for cleaning the surface metal of a silicon wafer with a weak acid solution. The weak acid solution is used to immerse the monocrystalline silicon wafer, and the metal on the surface of the silicon wafer is removed through a chemical reaction. With the assistance of an ultrasonic cleaning and liquid heating device, nitric acid, boric acid, and ultrapure water are added successively during the process to improve the removal rate of metal on the surface of the silicon wafer.

[0006] In one embodiment of the present invention, the weak acid is boric acid, which does not react with monocrystalline silicon, and the boric acid reacts with the surface metal of the monocrystalline silicon wafer to generate water-soluble alkali metal borates or other borates that are difficult to dissolve in water, which can effectively reduce the adhesion of metal to the surface of the monocrystalline silicon wafer.

[0007] In one embodiment of the present invention, the method can be used for both monocrystalline silicon and polycrystalline silicon, and boric acid can only react with silicon at high temperature. The temperature of the present invention does not exceed 60°C.

[0008] In one embodiment of the present invention, the ultrasonic cleaning can pulverize and peel off the newly formed insoluble borates, achieving a high-efficiency cleaning purpose.

[0009] In one embodiment of the present invention, the heating device can promote further reaction between boric acid and metal oxides or ions on the monocrystalline silicon wafer, thereby improving the removal rate of metal on the surface of the monocrystalline silicon wafer.

[0010] In one embodiment of the present invention, the addition of nitric acid, boric acid, and ultrapure water during the process is to continuously remove metal from the surface of the silicon wafer.

[0011] In summary, this invention can effectively remove metal from the surface of silicon wafers. When a polycrystalline silicon layer is grown on the surface of the silicon oxide layer, the metal on the silicon wafer surface can be removed without damaging the silicon oxide layer. Furthermore, it reduces the amount of metal dissolved in boric acid, avoiding contamination of other reagents. Attached Figure Description

[0012] Figure 1 A schematic diagram of the planar structure of the present invention.

[0013] Description of Figure Numbers:

[0014] 100 weak acid solution

[0015] 200 silicon wafers Detailed Implementation

[0016] The following detailed description, in conjunction with the accompanying drawings, illustrates the specific implementation method of a weak acid cleaning method for the surface metal of a silicon wafer provided by the present invention.

[0017] This invention discloses a method for cleaning the surface metal of a silicon wafer 200 using a weak acid solution 100, wherein the weak acid solution 100 is a boric acid solution, and the surface of the silicon wafer 200 may have a layer of polycrystalline silicon, a silicon oxide layer, or monocrystalline silicon. When the surface metal of the silicon wafer 200 comes into contact with the weak acid solution 100, a chemical reaction occurs, removing most of the metal from the surface of the silicon wafer 200 without damaging it, thereby achieving the purpose of metal removal.

[0018] The weak acid solution 100 is boric acid. During cleaning, the weak acid solution 100 comes into contact with alkali metals such as sodium, potassium, calcium, and magnesium on the surface of the silicon wafer 200, forming alkali metal borates that are readily soluble in water. The weak acid solution 100 also reacts with metals such as iron, nickel, and copper on the surface of the silicon wafer 200 to form water-insoluble borates. At the end of the cleaning process, the metal content on the surface of the silicon wafer 200 is reduced, and water-insoluble borates and water-soluble alkali metal borates are formed, thereby reducing the metal adhering to the silicon wafer surface and avoiding metal contamination.

[0019] The weak acid solution 100 incorporates an ultrasonic device to remove fine particles from the surface of the silicon wafer 200, as well as water-insoluble borates that have formed on the surface. This prevents the formation of a passivation layer from the water-insoluble borates on the silicon wafer 200 surface, thus inhibiting further reaction between the weak acid solution 100 and the silicon wafer 200. A heating device is added to the weak acid solution 100 (the heating temperature should not exceed 60°C) to promote the dissolution of boric acid in water and to dissolve more alkali metals from the surface of the silicon wafer 200 in the weak acid solution 100, reducing the adhesion of alkali metals to the surface of the silicon wafer 200. Nitric acid, boric acid, and ultrapure water are added during the cleaning process to maintain a certain pH and boric acid level, ensuring that the weak acid solution 100 continues to react with the surface metals of the silicon wafer 200, achieving the desired metal removal effect.

[0020] This invention discloses a method for cleaning the surface metal of a silicon wafer using a weak acid. The method involves reacting boric acid with the surface metal of the silicon wafer, allowing the boric acid solution to dissolve more alkali metals and form water-insoluble borates. This significantly reduces the amount of metal ions in the water, preventing premature saturation and precipitation of metal salts. Furthermore, the boric acid can clean the surface metal of the silicon oxide layer without damaging it, even at low temperatures.

[0021] It should be understood that the specific embodiments described herein are for understanding the present invention only and are not intended to limit the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

Claims

1. A method for cleaning the surface metal of a silicon wafer with a weak acid, characterized in that, The method involves immersing a single-crystal silicon wafer in a weak acid solution to remove metal from the surface of the wafer through a chemical reaction. With the assistance of an ultrasonic cleaning and liquid heating device, nitric acid, boric acid, and ultrapure water are added successively to improve the removal rate of metal from the surface of the silicon wafer.

2. The method for cleaning the surface metal of a silicon wafer with a weak acid according to claim 1, characterized in that, The weak acid is boric acid, which does not react with monocrystalline silicon. Instead, boric acid reacts with the surface metal of the monocrystalline silicon wafer to form water-soluble alkali metal borates or other water-insoluble borates, which can effectively reduce the adhesion of metal to the surface of the monocrystalline silicon wafer.

3. The method for cleaning the surface metal of a silicon wafer with a weak acid according to claim 1, characterized in that, The method described can be used for both monocrystalline and polycrystalline silicon, and boric acid can only react with silicon at high temperatures.

4. The method for cleaning the surface metal of a silicon wafer with a weak acid according to claim 1, characterized in that, The ultrasonic cleaning described above can crush and peel off newly formed insoluble borates, achieving a high-efficiency cleaning purpose.

5. The method for cleaning the surface metal of a silicon wafer with a weak acid according to claim 1, characterized in that, The heating device can promote the further reaction between boric acid and the metal oxides or ions of the monocrystalline silicon wafer, thereby improving the removal rate of metal on the surface of the monocrystalline silicon wafer.

6. The method for cleaning the surface metal of a silicon wafer with a weak acid according to claim 1, characterized in that, The addition of nitric acid, boric acid, and ultrapure water during the process is to continuously remove metal from the surface of the silicon wafer.

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