A wafer cleaning method

Abstract

The invention discloses a wafer cleaning method, which aims to ensure the cleaning quality of the wafer while ensuring the uniformity of the oxide layer of the wafer after cleaning. The technical solution is as follows: a wafer cleaning method, comprising the following steps: S1: first using a first steam liquid to clean the wafer, and then rinsing the wafer with deionized water; wherein the first steam liquid is an acidic liquid; S2: first using a second steam liquid to clean the wafer, and then rinsing the wafer with deionized water; wherein the second steam liquid is an alkaline liquid; S3: first using a third steam liquid to clean the wafer, and then rinsing the wafer with deionized water; wherein the third steam liquid is an alkaline liquid; S4: first using a fourth steam liquid to clean the wafer, and then rinsing the wafer with deionized water; wherein the fourth steam liquid is an acidic liquid; S5: air-drying the wafer, which belongs to the technical field of wafer cleaning.

Description

Technical Field

[0001] The present invention belongs to the technical field of wafer cleaning, and more specifically, relates to a wafer cleaning method. Background Art

[0002] After the wafer has gone through the polishing process, many chemicals such as polishing liquid will remain on its surface. If these chemicals are not cleaned in time, they will contaminate the entire wafer and even make the wafer scrapped, which will lead to material waste and increased costs. Therefore, after the wafer is polished, it is necessary to enter the wafer cleaning process.

[0003] In the prior art, there are many methods for cleaning wafers. For example, Patent Publication No. CN112474550A discloses a method for cleaning a gallium oxide wafer after CMP, which comprises: S1, cleaning the gallium oxide wafer after CMP with a cleaning solution I comprising sulfuric acid, hydrogen peroxide, and deionized water, and then rinsing with deionized water; S2, cleaning the gallium oxide wafer after cleaning in S1 with a cleaning solution II comprising ammonia, hydrogen peroxide, and deionized water, and then rinsing with deionized water; S3, cleaning the gallium oxide wafer after cleaning in S2 with a cleaning solution III comprising hydrofluoric acid and deionized water, and then rinsing with deionized water; S4, cleaning the gallium oxide wafer after cleaning in S3 with a cleaning solution IV comprising hydrochloric acid, hydrogen peroxide, and deionized water, and then rinsing with deionized water; and S5, ultrasonically cleaning the gallium oxide wafer after cleaning in S4 at an ultrasonic power of 150-300W.

[0004] In the above-mentioned cleaning method, the wafer is cleaned by using cleaning liquid I, cleaning liquid II, cleaning liquid III, and cleaning liquid IV in sequence, and finally ultrasonic cleaning is adopted; wherein, cleaning liquid I contains sulfuric acid, hydrogen peroxide and deionized water, which is used to remove organic matter such as paraffin on the surface of the wafer; cleaning liquid II contains ammonia water, hydrogen peroxide and deionized water, which is used to remove crystal particles on the surface of the wafer; cleaning liquid III contains hydrofluoric acid and deionized water, which is used to remove particles such as silica sol and silicon dioxide on the surface of the wafer; cleaning liquid IV contains hydrochloric acid, hydrogen peroxide and deionized water, which is used to remove metal ions on the surface of the wafer.

[0005] In practical applications, the wafer enters the wafer epitaxial growth process after cleaning; and an oxide layer is generally formed on the surface of the cleaned wafer, but in the epitaxial growth process, the oxide layer needs to be removed.

[0006] In the prior art, wafer cleaning is generally achieved by immersion or spraying, such as the above-mentioned cleaning method for gallium oxide wafers after CMP.

[0007] The drawback of the existing technology is that cleaning the wafer by immersion or spraying is prone to uneven cleaning, which affects the uniformity of the thickness of the oxide layer finally formed on the wafer. If the thickness of the oxide layer is uneven, the effect of removing the oxide layer in the wafer epitaxial growth process will be affected, resulting in uneven oxide layer removal, thereby affecting the quality of the wafer epitaxial growth.

[0008] In the above-mentioned gallium oxide wafer post-CMP cleaning method, the cleaning liquids are used in the following order: acidic cleaning liquid, alkaline cleaning liquid, acidic cleaning liquid, and acidic cleaning liquid. Excessive acidic cleaning liquid is used, and cleaning is performed by immersion. This cleaning method easily causes excessive corrosion of the oxide layer. After the wafer is cleaned, a natural oxide layer is generated when the wafer surface is exposed to air. The thickness of the natural oxide layer is uncontrollable and uneven, making it difficult to remove during the wafer epitaxial growth process, thereby affecting the quality of the wafer epitaxial growth. Summary of the Invention

[0009] The main purpose of the present invention is to provide a wafer cleaning method, which aims to ensure the cleaning quality of the wafer while ensuring the uniformity of the oxide layer of the wafer after cleaning.

[0010] According to a first aspect of the present invention, there is provided a wafer cleaning method comprising the following steps:

[0011] S1: first cleaning the wafer with a first steam solution, and then rinsing the wafer with deionized water; wherein the first steam solution is an acidic solution;

[0012] S2: first cleaning the wafer with a second steam solution, and then rinsing the wafer with deionized water; wherein the second steam solution is an alkaline solution;

[0013] S3: first cleaning the wafer with a third steam solution, and then rinsing the wafer with deionized water; wherein the third steam solution is an alkaline solution;

[0014] S4: first cleaning the wafer with a fourth steam solution, and then rinsing the wafer with deionized water; wherein the fourth steam solution is an acidic solution;

[0015] S5: air-dry the wafer;

[0016] Wherein, the second steam liquid and the third steam liquid are both aqueous solutions containing ammonium hydroxide and hydrogen peroxide;

[0017] The concentration of ammonium hydroxide in the second steam liquid is 14 wt%-20 wt%; the concentration of hydrogen peroxide in the second steam liquid is 6 wt%-12 wt%;

[0018] The concentration of ammonium hydroxide in the third steam liquid is 8.4 wt % to 11.2 wt %; the concentration of hydrogen peroxide in the third steam liquid is 18 wt % to 21 wt %.

[0019] In a specific embodiment of the present invention, the first steam liquid is an aqueous solution formed by mixing nitric acid with a concentration of 17wt%-18wt% and hydrochloric acid with a concentration of 25.5wt%-28.5wt%.

[0020] In a specific embodiment of the present invention, the fourth steam liquid is a dilute sulfuric acid solution with a concentration of 0.97 wt %.

[0021] In a specific embodiment of the present invention, the cleaning time of the first steam liquid, the second steam liquid, the third steam liquid and the fourth steam liquid on the wafer is 28s-35s;

[0022] The time for rinsing the wafer with deionized water in S1, S2, and S3 is 25s-35s; the time for rinsing the wafer with deionized water in S4 is 60s-70s.

[0023] In a specific embodiment of the present invention, the wafer is dried by hot nitrogen in S5.

[0024] In a specific embodiment of the present invention, the wafer is arranged vertically during cleaning.

[0025] In a specific embodiment of the present invention, before performing S1, the sample is rinsed with deionized water for 20s-30s.

[0026] One of the above technical solutions of the present invention has at least one of the following advantages or beneficial effects:

[0027] In the present invention, the wafer is cleaned in sequence by an acidic first steam liquid, an alkaline second steam liquid, an alkaline third steam liquid, and an acidic fourth steam liquid.

[0028] The hydrogen peroxide in the second and third steam chemical liquids will cause an oxide layer to form on the wafer during the cleaning process. The chemical liquids used in the cleaning process are all steam chemical liquids. During cleaning, the steam chemical liquids can be evenly attached to the wafer, ensuring that they can evenly clean the wafer and at the same time, making the thickness of the oxide layer formed on the wafer more uniform. The fourth steam chemical liquid is used to lightly etch the formed oxide layer to form an oxide layer of a preset thickness.

[0029] The present invention replaces the natural oxidation method with a chemical solution to generate an oxide layer on the wafer surface, the thickness of which is uniform and controllable, so that the oxide layer on the wafer surface can be evenly removed during the epitaxial growth process, thereby ensuring the quality of the wafer epitaxial growth. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0031] Figure 1 is a flow chart of embodiment 1 of the present invention;

[0032] Figure 2 Schematic diagram of wafer thickness measurement points in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0034] The following disclosure provides many different embodiments or examples for implementing different solutions of the present invention.

[0035] Example 1

[0036] Reference Figure 1 As shown, a wafer cleaning method for cleaning a four-inch silicon carbide wafer includes the following steps:

[0037] S1: first cleaning the wafer with a first steam solution, and then rinsing the wafer with deionized water; wherein the first steam solution is an acidic solution;

[0038] Specifically, the first steam liquid is an aqueous solution composed of a mixture of nitric acid with a concentration of 17.75wt% and hydrochloric acid with a concentration of 27.75wt%. That is, the first steam liquid is aqua regia, which has a stronger oxidizing ability than sulfuric acid and the like, can oxidize stable metals, and can effectively remove metal impurities with a good removal effect.

[0039] After the wafer is cleaned by the first steam solution for a rated time, low-temperature nitrogen is introduced to condense the first steam solution, and then the wafer is rinsed with deionized water to evenly distribute the contact time between each part of the wafer and the steam solution.

[0040] S2: first cleaning the wafer with a second steam solution, and then rinsing the wafer with deionized water; wherein the second steam solution is an alkaline solution;

[0041] After the wafer is cleaned by the second steam solution for a rated time, the second steam solution is condensed by introducing low-temperature nitrogen, and then the wafer is rinsed with deionized water to evenly distribute the contact time between each part of the wafer and the steam solution.

[0042] S3: first cleaning the wafer with a third steam solution, and then rinsing the wafer with deionized water; wherein the third steam solution is an alkaline solution;

[0043] After the wafer is cleaned by the third steam solution for a rated time, the third steam solution is condensed by introducing low-temperature nitrogen, and then the wafer is rinsed with deionized water to evenly distribute the contact time between each part of the wafer and the steam solution.

[0044] Wherein, the second steam liquid and the third steam liquid are both aqueous solutions containing ammonium hydroxide and hydrogen peroxide;

[0045] The concentration of ammonium hydroxide in the second steam liquid is 14 wt %; the concentration of hydrogen peroxide in the second steam liquid is 6 wt %;

[0046] The concentration of ammonium hydroxide in the third steam chemical liquid is 11.2 wt %; the concentration of hydrogen peroxide in the third steam chemical liquid is 18 wt %.

[0047] Specifically, the second steam liquid and the third steam liquid are both aqueous solutions mixed with ammonium hydroxide and hydrogen peroxide. The difference between the two is that the amount of ammonium hydroxide in the second steam liquid is greater than that of hydrogen peroxide, making the second steam liquid more corrosive and less oxidizing, which is conducive to the removal of large particles; while the amount of ammonium hydroxide in the third steam liquid is less than that of hydrogen peroxide, making the third steam liquid more oxidizing than corrosive, which is conducive to the removal of small particles.

[0048] During the cleaning process, hydrogen peroxide first oxidizes the wafer, and then ammonium hydroxide corrodes the oxide layer, thereby removing particles. Specifically, since large particles are easier to remove, the amount of hydrogen peroxide used in the second steam solution is relatively small, so the thickness of the oxide layer formed by it is also thinner, which acts as a pre-formation of the oxide layer. Since small particles are more difficult to remove, a third steam solution with stronger oxidizing ability is required.

[0049] The third steam liquid will generate an oxide layer on the surface of the wafer while removing small particles of impurities. By replacing natural oxidation with the liquid to generate an oxide layer on the wafer, the uniformity of its thickness can be ensured, thereby facilitating the uniform removal of the oxide layer during the wafer epitaxial growth process, thereby ensuring the quality of the wafer epitaxial growth.

[0050] That is, in this embodiment, the second steam chemical liquid and the third steam chemical liquid are used to form an oxide layer on the surface of the wafer, so that the thickness of the generated oxide layer is controllable.

[0051] S4: first cleaning the wafer with a fourth steam solution, and then rinsing the wafer with deionized water; wherein the fourth steam solution is an acidic solution;

[0052] After the wafer is cleaned by the fourth steam solution for a rated time, the fourth steam solution is condensed by introducing low-temperature nitrogen, and then the wafer is rinsed with deionized water to evenly distribute the contact time between various parts of the wafer and the steam solution.

[0053] Specifically, the fourth steam liquid is a dilute sulfuric acid solution with a concentration of 0.97wt%, which is used to corrode the oxide layer produced after steps S3 and S4, so that the wafer generates an oxide layer of a preset thickness, which facilitates the uniform removal of the oxide layer on the wafer surface during the epitaxial process and ensures the quality of the wafer epitaxial growth.

[0054] S5: air-dry the wafer;

[0055] Specifically, it dries the wafer with hot nitrogen air;

[0056] In practical applications, the wafers may be dried by combining air drying and spin drying, which is not limited in this embodiment.

[0057] In this embodiment, the liquid medicine used in the cleaning process is steam liquid medicine. During cleaning, the steam liquid medicine can be evenly attached to the wafer, ensuring that it can evenly clean the wafer, and at the same time, making the oxide layer generated on the wafer more uniform.

[0058] Specifically, the cleaning time of the first steam liquid, the second steam liquid, the third steam liquid, and the fourth steam liquid on the wafer is 30 seconds;

[0059] The time for rinsing the wafer with deionized water in S1, S2, and S3 is 30 s;

[0060] The time for rinsing the wafer with deionized water in S4 is 60 s;

[0061] The cleaning time and deionized water rinsing time are set according to actual applications, and this embodiment does not limit this. The above time allows the wafer cleaned in this embodiment to generate an oxide layer of about 0.92-1.00 nm; the cleaning time and deionized water rinsing time of the wafer are set according to actual production conditions.

[0062] Preferably, during cleaning, the wafer is arranged vertically; specifically, when the wafer is rinsed with deionized water, the wafer will not form a supporting structure, avoiding deionized water and steam liquid to remain on the wafer, thereby avoiding mixing of steam liquid, thereby ensuring the uniform thickness of the oxide layer generated on the wafer.

[0063] In this embodiment, before S1 is performed, the wafer is rinsed with deionized water for 20 seconds to perform a pre-cleaning process before cleaning to ensure a cleaning effect.

[0064] Example 2

[0065] It is substantially the same as Example 1, except that:

[0066] The concentration of ammonium hydroxide in the second steam liquid is 20 wt %; the concentration of hydrogen peroxide in the second steam liquid is 12 wt %;

[0067] The concentration of ammonium hydroxide in the third steam chemical liquid is 8.4 wt %; the concentration of hydrogen peroxide in the third steam chemical liquid is 21 wt %.

[0068] Cleaning effect analysis

[0069] Table 1 Cleaning effect table

[0070] Copper content Number of particles Yield Example 1 0.1 ＜2 >92％ Example 2 0.12 ＜2 >91.5％

[0071] The above cleaning effect is tested using Tencor machine testing and Txrf testing.

[0072] Comparative Example 1

[0073] The method is substantially the same as Example 1, except that the third steam liquid used in S3 is an acidic liquid, which is a hydrofluoric acid solution with a concentration of 4.45 wt%.

[0074] Oxide layer thickness analysis

[0075] Among them, THK refers to the thickness of the oxide layer;

[0076] Table 2 Measurement results of oxide layer thickness

[0077]

[0078] The measurement positions in the above table refer to Figure 2 As shown, the instrument used for measurement is an ellipsometer;

[0079] Since S3 in Comparative Example 1 uses hydrofluoric acid, which uses an acidic solution to clean the wafer to remove small particles of impurities on the wafer, it will corrode the oxide layer produced by S2 during the cleaning process, so that the wafer does not have an oxide layer after cleaning. Therefore, the wafer will produce a natural oxide layer after contact with air. The thickness of the natural oxide layer is uncontrollable, so the thickness of the generated natural oxide layer is uneven. That is, it cannot be evenly removed during the wafer epitaxial growth process, which easily affects the quality of the wafer epitaxial growth.

[0080] In Example 1, the alkaline third steam solution is used to remove small particle impurities on the wafer. While removing the small particle impurities on the wafer, an oxide layer of preset thickness can be generated according to production requirements. The oxide layer is generated by replacing natural oxidation with the solution, and the thickness of the oxide layer is controllable and uniform. That is, the oxide layer can be evenly removed in the wafer epitaxial growth process, thereby ensuring the quality of the wafer epitaxial growth.

[0081] Comparative Example 2

[0082] It is basically the same as Example 1, except that: in S1, S2, S3, and S4, the wafers are cleaned by spraying and rinsing, that is, the chemical solution used is the same, but it is not cleaned by steam chemical solution.

[0083] Oxide layer thickness analysis

[0084] Table 3 Measurement results of oxide layer thickness

[0085]

[0086] The measurement positions in the above table refer to Figure 2 As shown, the instrument used for measurement is an ellipsometer;

[0087] The wafers cleaned in Example 1 and Comparative Example 2 were both placed vertically.

[0088] Since Comparative Example 2 cleans the wafer by flushing, it is easy to cause uneven cleaning of the wafer, resulting in uneven thickness of the generated oxide layer; for example, during the flushing process, the flushing liquid on the upper part of the wafer will flow to the lower part of the wafer, causing the lower part of the wafer to be cleaned twice, resulting in uneven cleaning.

[0089] When cleaning the wafer by immersion, the immersion time of the upper and lower parts of the wafer will be different during the process of the wafer entering the chemical solution during cleaning and during the process of the wafer being separated from the wafer after cleaning, resulting in uneven cleaning of the wafer, and thus uneven thickness of the oxide layer generated on the wafer after cleaning.

[0090] In Example 1, the wafer is cleaned by means of steam liquid. The steam can evenly wrap the wafer and evenly adhere to the wafer, so that the wafer is cleaned evenly. After a single cleaning is completed, the steam liquid is condensed by introducing low-temperature nitrogen, so that the steam liquid is separated from the wafer, and then the wafer is rinsed with deionized water before entering the next cleaning step. The contact time between each part of the wafer and the steam liquid is evenly distributed, so that the oxide layer generated on the wafer after cleaning is uniform, thereby ensuring that the oxide layer can be evenly removed in the wafer epitaxial process and ensuring the quality of the wafer epitaxial growth.

[0091] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A wafer cleaning method, characterized in that: The steps include: S1: first cleaning the wafer with a first steam solution, and then rinsing the wafer with deionized water; wherein the first steam solution is an acidic solution; S2: first cleaning the wafer with a second steam solution, and then rinsing the wafer with deionized water; wherein the second steam solution is an alkaline solution; S3: first cleaning the wafer with a third steam solution, and then rinsing the wafer with deionized water; wherein the third steam solution is an alkaline solution; S4: first cleaning the wafer with a fourth steam solution, and then rinsing the wafer with deionized water; wherein the fourth steam solution is an acidic solution; S5: air-dry the wafer; Wherein, the second steam liquid and the third steam liquid are both aqueous solutions containing ammonium hydroxide and hydrogen peroxide; The concentration of ammonium hydroxide in the second steam liquid is 14 wt%-20 wt%; the concentration of hydrogen peroxide in the second steam liquid is 6 wt%-12 wt%; The concentration of ammonium hydroxide in the third steam liquid is 8.4 wt % to 11.2 wt %; the concentration of hydrogen peroxide in the third steam liquid is 18 wt % to 21 wt %.

2. The wafer cleaning method according to claim 1, wherein: The first steam liquid is an aqueous solution formed by mixing nitric acid with a concentration of 17wt%-18wt% and hydrochloric acid with a concentration of 25.5wt%-28.5wt%.

3. The wafer cleaning method according to claim 1, wherein: The fourth steam liquid is a dilute sulfuric acid solution with a concentration of 0.97 wt %.

4. The wafer cleaning method according to claim 1, wherein: The cleaning time of the first steam solution, the second steam solution, the third steam solution and the fourth steam solution on the wafer is 28s-35s; The time for rinsing the wafer with deionized water in S1, S2, and S3 is 25s-35s; the time for rinsing the wafer with deionized water in S4 is 60s-70s.

5. The wafer cleaning method according to claim 1, wherein: The wafer is air-dried by hot nitrogen gas in S5.

6. The wafer cleaning method according to claim 1, wherein: During cleaning, the wafers are arranged vertically.

7. The wafer cleaning method according to claim 1, wherein: Before proceeding to S1, rinse with deionized water for 20s-30s.

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