Wafer cleaning method and apparatus

Abstract

Embodiments of the present application provide a wafer cleaning method. The method comprises: rotating a wafer at a first rotational speed, and spraying ozone water onto the wafer until an oxide film generated by a reaction of the ozone water with the wafer completely covers the front surface of the wafer; and spraying a hydrofluoric acid solution onto the wafer to remove the oxide film, wherein the first rotational speed is greater than a critical rotational speed, and at the critical rotational speed, the number of particles generated by a reaction of the ozone water on the wafer with environmental impurities is a preset value. By means of the wafer cleaning method of the present application, a clean wafer can be obtained.

Description

Wafer Cleaning Method and Apparatus

[0001] This application claims priority to Chinese Patent Application No. 202510373498.4, filed on March 26, 2025, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0002] This application relates to the field of semiconductor technology, and more specifically, to a wafer cleaning method and apparatus. Background Technology

[0003] In the process of fabricating chips from wafers, the cleanliness of the wafer surface has a crucial impact on the chip's performance and reliability. Wafers can be subjected to various types of contamination during manufacturing, including organic matter, inorganic salts, and microparticles. Therefore, developing an effective cleaning process to ensure wafer surface cleanliness is a critical step in chip manufacturing.

[0004] In existing technologies, ozone water is commonly used to clean the surface of wafers. However, during the cleaning process with ozone water, new particles are sometimes generated on the wafer surface, leading to defects. Summary of the Invention

[0005] Embodiments of this application provide a wafer cleaning method and apparatus that enable wafers to be cleaned more thoroughly.

[0006] On one hand, this application provides a wafer cleaning method, including rotating the wafer at a first rotation speed and spraying ozone water onto the wafer until the oxide film generated by the reaction of the ozone water with the wafer completely covers the front side of the wafer; spraying hydrofluoric acid solution onto the wafer to remove the oxide film; wherein, the first rotation speed is higher than a critical rotation speed, and at the critical rotation speed, the number of particles generated by the reaction of ozone water on the wafer with impurities in the environment is a preset value.

[0007] Specifically, in the step of spraying ozone water onto the wafer, the ozone water is applied to the center of rotation of the wafer.

[0008] Specifically, during the process of spraying the hydrofluoric acid solution onto the wafer, the wafer is rotated at a speed higher than a second rotational speed, wherein the second rotational speed is lower than the first rotational speed.

[0009] Specifically, after removing the oxide film, the steps of spraying the ozone water and the hydrofluoric acid solution onto the wafer are repeated until the front side of the wafer is cleaned.

[0010] Specifically, after the wafer is cleaned, a drying fluid is passed through the wafer to dry it.

[0011] Specifically, after the front side of the wafer is cleaned and before the drying fluid is introduced into the wafer, the wafer is rotated again at a speed higher than the first rotation speed, and the ozone water is sprayed onto the wafer until the oxide film generated by the reaction of the ozone water with the wafer completely covers the front side of the wafer.

[0012] On the other hand, this application provides a wafer cleaning apparatus, comprising: a chuck configured to carry and drive the wafer to rotate; a cleaning nozzle configured to provide ozone water and hydrofluoric acid solution to the wafer; and a controller configured to control the chuck and the cleaning nozzle to perform the following steps: rotating the wafer at a first rotational speed and spraying ozone water onto the wafer until an oxide film generated by the reaction of the ozone water with the wafer completely covers the front side of the wafer; and spraying hydrofluoric acid solution onto the wafer to remove the oxide film; wherein the first rotational speed is higher than a critical rotational speed, and at the critical rotational speed, the number of particles generated by the reaction of ozone water on the wafer with impurities in the environment is a preset value.

[0013] The wafer cleaning method and apparatus of this application, during the process of rinsing the wafer with ozone water, generate an oxide film by reacting ozone water with the wafer to isolate particles attached to the wafer from the wafer. At the same time, the wafer rotation speed is controlled to prevent the ozone water from reacting with impurities in the environment to generate particles that adhere to the wafer. Hydrofluoric acid solution is also used to clean the wafer with the oxide film attached to it, thereby removing the oxide film on the front side of the wafer and removing particles from the wafer, thus cleaning the wafer thoroughly.

[0014] Other features and advantages of this application will become apparent from the following detailed description, or may be learned in part from practice of this application.

[0015] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application.

[0016] Overview of the attached figures

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0018] Figure 1 shows a schematic diagram of a wafer cleaning apparatus according to an embodiment of this application;

[0019] Figure 2 shows a schematic flowchart of a wafer cleaning method according to an embodiment of this application;

[0020] Figure 3 shows a schematic diagram of particle distribution before wafer cleaning according to an embodiment of this application;

[0021] Figure 4 shows a schematic diagram of particle distribution after wafer cleaning according to an embodiment of this application. Detailed Implementation

[0022] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0023] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of this application. However, those skilled in the art will recognize that the technical solutions of this application can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this application.

[0024] During the wafer cleaning process, the inventors discovered that the environment in which the wafer is located may contain volatile organic compounds (VOCs) dispersed in the air. When cleaning the wafer with ozone water, the ozone water has extremely strong oxidizing properties. The reaction between ozone water and organic compounds may generate partially oxidized hydrocarbons, carbon dioxide, and water. The hydrocarbons, carbon dioxide, and water will condense on the wafer surface and form pollution.

[0025] Please refer to Figure 1. This embodiment provides a wafer cleaning apparatus for cleaning wafers.

[0026] As shown in Figure 1, the wafer cleaning apparatus includes a cavity 1, a chuck 2 disposed within the cavity 1, and nozzles 3. The chuck 2 holds the wafer 4. The nozzles 3 include a cleaning nozzle 31 and a drying nozzle 32. The cleaning nozzle 31 sprays cleaning solutions such as ozone water (DIO3) and hydrofluoric acid solution onto the front side of the wafer 4. There are two cleaning nozzles 31: one for spraying ozone water and the other for spraying hydrofluoric acid solution. In some embodiments, the hydrofluoric acid solution is dilute hydrofluoric acid (DHF) with a mass concentration of 0.1%-1.5%. The drying nozzle 32 sprays a drying fluid such as nitrogen onto the front side of the wafer 4. The chuck 2 is rotatable, and its rotation can rotate the wafer 4. In some embodiments, the ozone water and hydrofluoric acid solution share a single cleaning nozzle 31.

[0027] The wafer cleaning apparatus also includes a controller, which sends rotation signals and speed control signals to the chuck 2 so that the chuck 2 rotates according to the rotation signals and speed control signals. The controller also sends spraying or stopping spraying signals to the cleaning nozzle 31 and the drying nozzle 32.

[0028] During the cleaning process of wafer 4 in the wafer cleaning device, the controller drives wafer 4 to rotate at a first rotational speed via chuck 2, and sprays ozone water onto wafer 4 through cleaning nozzle 31 until the oxide film generated by the reaction of ozone water and wafer 4 completely covers the front side of the wafer; hydrofluoric acid solution is then sprayed onto wafer 4 to remove the oxide film; wherein, the first rotational speed is higher than the critical rotational speed, and at the critical rotational speed, the number of particles generated by the reaction of ozone water on wafer 4 with impurities in the environment is a preset value. The preset value is set as needed.

[0029] As shown in Figure 2, this embodiment also provides a wafer cleaning method, which specifically includes the following steps:

[0030] S110: Keep the wafer rotating horizontally around its center.

[0031] S120: Spray ozone water onto the front side of the wafer until the oxide film formed by the reaction of ozone water and the wafer completely covers the front side of the wafer. The wafer rotates at a first speed, which is higher than the critical speed. At the critical speed, the number of particles generated by the reaction of ozone water on the wafer with impurities in the environment is a preset value.

[0032] A wafer consists of a front side, a back side, and a side side. The front side of the wafer is the side that needs to be cleaned during this wafer cleaning process.

[0033] Ozone water (DIO3) reacts with silicon in a wafer to form a silicon oxide film. This film adheres to the front side of the wafer, isolating particles already attached to it and protecting the wafer from new particles. As the ozone water flows across the wafer, centrifugal force washes away some of the particles, while the remaining particles are encapsulated by the oxide film for subsequent removal.

[0034] During the formation of the silicon oxide thin film, to prevent impurities in the cavity environment from being oxidized by ozone water and forming particles that adhere to the wafer, the wafer rotation speed is controlled. This controls the residence time of the ozone water on the front side of the wafer, ensuring that the ozone water on the wafer front does not have enough time to react with impurities in the cavity environment to form particles. Specifically, the wafer is rotated at a first rotation speed, which is higher than a critical rotation speed. At the critical rotation speed, the number of particles formed by the reaction between the ozone water on the wafer and impurities in the environment is a preset value. This preset value precisely matches the number of newly added particles on the wafer allowed by the process during ozone water cleaning, and is greater than or equal to zero. The number of newly added particles on the wafer can be detected by a testing instrument. When a wafer is placed in an environment, a layer of dispersed impurities mixed in with the air, such as volatile organic compounds (VOCs), adheres to its front side. Ozone water seeps into the air and reacts chemically with these impurities. Simultaneously, the ozone water directly contacts the wafer to form an oxide film. However, the time required for the ozone water to seep into the air and react with the impurities to form particles is much longer than the time required for the oxide film to form on the wafer's front side. Therefore, controlling the time ozone water remains on the wafer's front side to avoid particle formation will not affect the formation of the oxide film through ozone water oxidation. Furthermore, reducing the time ozone water remains on the wafer's front side can reduce residual moisture on the wafer's front side.

[0035] The first rotational speed in step S120 is determined experimentally. Specifically, before step S120, experiments are conducted using the conditions in step S120, rotating the wafer at different speeds. The first rotational speed is determined based on the distribution of particles on the front side of the wafer corresponding to different rotational speeds. For example, when the preset value is zero, the wafer is rotated at the experimental speed. When the oxide film formed by the reaction of ozone water with the wafer completely covers the front side of the wafer, if new particles appear on the front side of the wafer compared to before cleaning with ozone water, it is confirmed that the experimental speed is less than or equal to the critical speed, and the experimental speed cannot be used as the first rotational speed. If no new particles appear on the front side of the wafer compared to before cleaning with ozone water, it is confirmed that the experimental speed is higher than the critical speed, and the experimental speed can be used as the first rotational speed.

[0036] The preferred landing point for the ozone water is the center of the wafer. Although the centrifugal force on the ozone water at the wafer center is zero, when the ozone water falls onto the wafer from a position higher than the wafer, its gravitational potential energy is converted into kinetic energy. The ozone water impacts impurities at the ozone water location, causing these impurities at the wafer center to be splashed out of the wafer center. Therefore, the ozone water will not react with impurities at the wafer center to form particles that adhere to the wafer center. Furthermore, when the landing point of the ozone water is at the wafer center, the forces exerted on the ozone water on the wafer are symmetrical about the wafer center during the wafer's rotation. This allows for better control of the ozone water's residence time on the wafer.

[0037] S130: Rotate the wafer at the second rotation speed and spray hydrofluoric acid solution onto the front side of the wafer until the oxide film on the front side of the wafer is completely removed.

[0038] After step S120, a silicon oxide film is coated on the front side of the wafer. The hydrofluoric acid solution reacts with the silicon oxide film to generate a salt solution. Wafer rotation allows the salt solution to leave the wafer, thus removing the silicon oxide film and the particles encapsulated by the film. Furthermore, the front side of the wafer after removing the silicon oxide film is smoother, reducing the likelihood of particle adhesion.

[0039] The second rotational speed in step S130 is determined experimentally. Specifically, before step S120, experiments are conducted using the conditions in step S130. The second rotational speed is lower than the first rotational speed to ensure sufficient reaction between the hydrofluoric acid solution and the oxide film, thus conserving the amount of hydrofluoric acid solution used. Simultaneously, the second rotational speed prevents the hydrofluoric acid solution from over-etching the wafer; that is, the second rotational speed is lower than the wafer rotational speed at which the hydrofluoric acid solution just completely removes the oxide film when flowing through the wafer. Furthermore, the second rotational speed is less than or equal to the wafer rotational speed at which the hydrofluoric acid solution just reacts with the oxide film, ensuring that the hydrofluoric acid solution does not fail to react with the oxide film in time.

[0040] S140: Repeat steps S120 and S130 until the front side of the wafer is cleaned.

[0041] Repeatedly cleaning the front side of the wafer with ozone water and hydrofluoric acid solution can further remove tiny particles remaining on the front side of the wafer, making the front side of the wafer cleaner.

[0042] S150: Spray ozone water onto the front side of the wafer again until the oxide film formed by the reaction of ozone water and the wafer completely covers the front side of the wafer, wherein the wafer rotation speed is not lower than the first rotation speed.

[0043] A wafer rotating at a speed not lower than the first rotational speed ensures that the time ozone water remains at any position on the wafer is less than the time it takes for the ozone water to react with impurities in the cavity environment to form particles, thus obtaining a clean oxide film. Step S150 forms a clean oxide film on the front side of the wafer to protect it.

[0044] S160: Pour nitrogen gas into the wafer to dry the wafer.

[0045] Nitrogen purging helps remove residual moisture and tiny particles from the front side of the wafer, ensuring that the front side is dry and clean, which can further prevent particles from falling onto the front side of the wafer in subsequent processes.

[0046] In the wafer cleaning method of this application, the wafer rotation speed is controlled during the process of rinsing the wafer with ozone water to prevent the ozone water from reacting with impurities in the environment to generate particles that adhere to the wafer. Hydrofluoric acid solution is also used to clean the wafer after the oxide film is formed by rinsing with ozone water to remove the oxide film on the front side of the wafer, thereby removing particles on the wafer and cleaning the wafer thoroughly.

[0047] The wafer was cleaned using the above method. The distribution of particles with a diameter of 26 nm or more on the front side of the wafer before cleaning is shown in Figure 3. The distribution of particles with a diameter of 26 nm or more on the front side of the wafer after cleaning is shown in Figure 4. It can be seen that the cleaning method of this application can effectively remove particles on the front side of the wafer without adding any new particles.

[0048] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0049] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A wafer cleaning method, characterized in that, include: The wafer is rotated at a first rotation speed, and ozone water is sprayed onto the wafer until the oxide film generated by the reaction of the ozone water with the wafer completely covers the front side of the wafer. Hydrofluoric acid solution is sprayed onto the wafer to remove the oxide film; Wherein, the first rotational speed is higher than the critical rotational speed, and at the critical rotational speed, the number of particles generated by the reaction of ozone water on the wafer with impurities in the environment is a preset value.

2. The wafer cleaning method according to claim 1, characterized in that, In the step of spraying ozone water onto the wafer, the ozone water is applied to the center of rotation of the wafer.

3. The wafer cleaning method according to claim 2, characterized in that, During the process of spraying the hydrofluoric acid solution onto the wafer, the wafer is rotated at a second rotational speed, wherein the second rotational speed is lower than the first rotational speed.

4. The wafer cleaning method according to claim 2, characterized in that, After removing the oxide film, the steps of spraying the ozone water and the hydrofluoric acid solution onto the wafer are repeated until the front side of the wafer is cleaned.

5. The wafer cleaning method according to claim 4, characterized in that, After the front side of the wafer is cleaned, a drying fluid is passed through the wafer to dry it.

6. The wafer cleaning method according to claim 5, characterized in that, After the front side of the wafer is cleaned, and before the drying fluid is introduced into the wafer, the wafer is rotated again at a speed higher than the first rotation speed, and the ozone water is sprayed onto the wafer until the oxide film generated by the reaction of the ozone water with the wafer completely covers the front side of the wafer.

7. A wafer cleaning apparatus, characterized in that, include: A chuck, configured to carry and drive the wafer to rotate; The cleaning nozzle is configured to supply the wafer with an ozone water and hydrofluoric acid solution. The controller is configured to control the chuck and the cleaning nozzle to perform the following steps: The wafer is rotated at a first rotation speed, and ozone water is sprayed onto the wafer until the oxide film generated by the reaction of the ozone water with the wafer completely covers the front side of the wafer. Hydrofluoric acid solution is sprayed onto the wafer to remove the oxide film; Wherein, the first rotational speed is higher than the critical rotational speed, and at the critical rotational speed, the number of particles generated by the reaction of ozone water on the wafer with impurities in the environment is a preset value.

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