Method for improving imaging definition of stacking fault of silicon carbide substrate

Abstract

The invention discloses a method for improving the stacking fault imaging definition of silicon carbide substrates, which comprises the following steps of: firstly, screening out the silicon carbide substrates with unclear stacking fault imaging through stacking fault imaging detection, cleaning the screened silicon carbide substrates, and adsorbing the silicon carbide substrates on an adsorption pad of a polishing head in a polishing chamber; maintaining the polishing chamber at the temperature and pressure required by polishing, continuously introducing a silicon oxide polishing solution into the polishing pad, then controlling the polishing head and the polishing disc to rotate for 2 hours so as to enable the polishing pad to polish the silicon carbide substrate, taking out the polished silicon carbide substrate, and cleaning the silicon carbide substrate by using a hydrofluoric acid solution, therefore, the silicon carbide substrate stacking fault imaging definition is improved, stacking faults can be clearly distinguished in stacking fault imaging detection, the number and area of the stacking faults on the silicon carbide substrate can be accurately judged, and then the qualified silicon carbide substrate which can be used for epitaxial growth can be accurately screened out.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal synthesis, and in particular to a method for improving the imaging clarity of stacking faults on a silicon carbide substrate. Background Art

[0002] Silicon carbide (SiC) semiconductor materials offer advantages such as high thermal conductivity, high breakdown field strength, high saturated electron drift velocity, and high bonding energy. They are well suited to the harsh application requirements of modern electronics, such as high temperature, high power, high voltage, high frequency, and high radiation. SiC epitaxial wafers are a key raw material for SiC power electronic devices. In addition to the epitaxial growth process on SiC substrate wafers, a complete SiC epitaxial wafer production line requires additional cleaning, polishing, and inspection processes and steps before and after epitaxial growth.

[0003] Before using silicon carbide substrates for production and manufacturing, they need to be selected based on their defects. If there are too many defects in the silicon carbide substrate, it will affect the available area of ​​the wafer after epitaxial growth, resulting in increased production costs and waste of production materials.

[0004] Stacking faults (SF) are a type of defect in silicon carbide substrates. During incoming material inspection of silicon carbide substrates, if there are too many sub-damage layers on the surface of the silicon carbide substrate, the stacking faults cannot be clearly imaged in the defect imaging equipment, which in turn affects the results of screening silicon carbide substrates based on the number and area of ​​stacking faults. It may happen that a silicon carbide substrate that should be judged as unqualified is mistakenly judged as qualified. When unqualified silicon carbide substrates are used for epitaxial growth, it will lead to defective wafers after epitaxial growth, resulting in low silicon carbide substrate yield. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the clarity of stacking fault imaging on silicon carbide substrates, which is conducive to clearly distinguishing stacking faults in stacking fault imaging detection, accurately judging the number and area of ​​stacking faults on silicon carbide substrates, and then accurately screening out qualified silicon carbide substrates that can be used for epitaxial growth, thereby improving the yield of silicon carbide wafers after epitaxial growth.

[0006] In order to achieve the above object, the present invention discloses a method for improving the imaging clarity of stacking faults on a silicon carbide substrate, which comprises the following steps: S1. Perform stacking fault imaging detection on silicon carbide substrates and screen out silicon carbide substrates with unclear stacking fault imaging; S2. Cleaning the screened silicon carbide substrate; S3, adsorbing the cleaned silicon carbide substrate onto an adsorption pad of a polishing head in a polishing chamber; S4, maintaining the temperature and pressure of the polishing chamber at the temperature and pressure required for polishing, continuously passing a silicon oxide polishing liquid to a polishing pad on a polishing plate in the polishing chamber, and controlling the rotation of the polishing head and the polishing plate for 2 hours so that the polishing pad polishes the silicon carbide substrate adsorbed on the polishing head; S5, taking the polished silicon carbide substrate out of the polishing chamber; S6. Cleaning the polished silicon carbide substrate using a hydrofluoric acid solution.

[0007] Furthermore, the step S1 includes: S11, placing the silicon carbide substrate into a defect imaging device to obtain a defect imaging image; S12. Determine whether the vertical lines in the defect imaging image are continuous and complete. If so, determine that the stacking fault imaging of the silicon carbide substrate is clear. Otherwise, determine that the stacking fault imaging of the silicon carbide substrate is unclear.

[0008] Furthermore, in step S4, the temperature required for polishing is 20°C-40°C, and the pressure required for polishing is 100g / cm 2 -500g / cm 2 .

[0009] Furthermore, in step S4, the particle size of silicon oxide in the silicon oxide polishing liquid is 50 nm-150 nm.

[0010] Furthermore, the flow rate of the silicon oxide polishing liquid is 500 ml / min-2000 ml / min, and the rotation speed of the polishing head and the polishing disk is 20 RPM / min-80 RPM / min. Furthermore, in step S6, the concentration of the hydrofluoric acid solution is 0.1% to 10%.

[0011] The present invention improves the problem of unclear stacking fault imaging of a silicon carbide substrate by polishing. First, silicon carbide substrates with unclear stacking fault imaging are screened out through stacking fault imaging detection. The screened silicon carbide substrates are cleaned and adsorbed on an adsorption pad of a polishing head in a polishing chamber. The polishing chamber is maintained at a temperature and pressure required for polishing, and silicon oxide polishing liquid is continuously introduced into the polishing pad. Then, the polishing head and the polishing disk are controlled to rotate for 2 hours so that the polishing pad polishes the silicon carbide substrate. After the polished silicon carbide substrate is taken out of the polishing chamber, the polished silicon carbide substrate is cleaned with a hydrofluoric acid solution, thereby achieving improvement in the clarity of the stacking fault imaging of the silicon carbide substrate. This is beneficial for clearly distinguishing stacking faults in stacking fault imaging detection, accurately judging the number and area of ​​stacking faults on the silicon carbide substrate, and then accurately screening out qualified silicon carbide substrates that can be used for epitaxial growth, thereby improving the yield rate of silicon carbide wafers after epitaxial growth. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a flow chart of a method for improving the imaging clarity of stacking faults in a silicon carbide substrate according to an embodiment of the present invention.

[0013] Figure 2 This is a defect imaging diagram with clear stacking fault imaging in the method for improving the stacking fault imaging clarity of a silicon carbide substrate according to an embodiment of the present invention.

[0014] Figure 3 This is a defect imaging diagram of unclear stacking fault imaging in the method for improving the imaging clarity of stacking faults in a silicon carbide substrate according to an embodiment of the present invention.

[0015] Figure 4 This is a defect imaging diagram of a silicon carbide substrate before CMP treatment in a method for improving the imaging clarity of stacking faults in a silicon carbide substrate according to an embodiment of the present invention.

[0016] Figure 5 This is a defect imaging diagram of a silicon carbide substrate after CMP treatment in a method for improving the imaging clarity of stacking faults in a silicon carbide substrate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to explain the technical content, structural features, achieved objectives and effects of the present invention in detail, the following is a detailed description in conjunction with the embodiments and the accompanying drawings.

[0018] The method for improving the image clarity of stacking faults on a silicon carbide substrate provided by the present invention utilizes a polishing machine to polish the silicon carbide substrate. The polishing machine primarily comprises a polishing head, a polishing plate, and a polishing chamber. The structures and operating principles of these components are conventional in the art and are therefore not described in detail.

[0019] See also Figures 1 to 5 The present invention discloses a method for improving the imaging clarity of stacking faults on a silicon carbide substrate, which comprises the following steps: S1. Perform stacking fault imaging detection on silicon carbide substrates and screen out silicon carbide substrates with unclear stacking fault imaging; Furthermore, step S1 includes: S11, placing the silicon carbide substrate into a defect imaging device to obtain a defect imaging image; S12. Determine whether the vertical lines in the defect imaging image are continuous and complete. If so, determine that the stacking fault imaging of the silicon carbide substrate is clear. Otherwise, determine that the stacking fault imaging of the silicon carbide substrate is unclear.

[0020] It should be noted that, in this embodiment, the defect imaging device is a wafer defect optical inspection device of model KLA Candela8520, which realizes defect imaging of the silicon carbide substrate based on the principle of photoluminescence imaging. Since the stacking fault (SF) itself has a classic morphology, the imaging effect of the stacking fault on the silicon carbide substrate can be judged by the judgment method of step S12. For example, Figure 2 As shown in FIG, if there is a detailed and complete vertical bar image in the defect imaging diagram, then it can be accurately judged as a stacking fault defect based on this image. Therefore, it can be judged that the stacking fault image of the silicon carbide substrate is clear and qualified, and no subsequent polishing step is required; and as shown in FIG. Figure 3 As shown, if the middle of the vertical bar in the defect imaging diagram is disconnected, it is impossible to determine whether the image is a stacking fault defect. Therefore, the stacking fault image of the silicon carbide substrate is judged to be unclear and unqualified, and a subsequent polishing step is required. However, this is not limiting, and other judgment methods or standards can also be used to determine whether the stacking fault image of the silicon carbide substrate is clear.

[0021] S2. Cleaning the screened silicon carbide substrate; It should be noted that in this embodiment, the surface (Si surface) of the screened silicon carbide substrate is cleaned by pickling and brushing according to the RAC standard cleaning method to remove particles on the surface of the silicon carbide substrate, ensure the cleanliness of the silicon carbide substrate, prevent the particles from causing additional scratches on the surface of the silicon carbide substrate during the subsequent CMP treatment, avoid excessive scratches on the surface of the silicon carbide substrate, and further avoid more fatal defects in the silicon carbide wafer during the subsequent epitaxial growth process.

[0022] S3, adsorbing the cleaned silicon carbide substrate onto an adsorption pad of a polishing head in a polishing chamber; Specifically, in this embodiment, the polishing head is a conventional ceramic disk in a polishing machine device that is attached with an adsorption pad for adsorbing wafers and can achieve self-rotation, so it will not be described in detail.

[0023] S4. Maintaining the temperature and pressure of the polishing chamber at the temperature and pressure required for polishing, continuously passing silicon oxide polishing liquid to the polishing pad on the polishing plate in the polishing chamber, and controlling the rotation of the polishing head and the polishing plate for 2 hours so that the polishing pad polishes the silicon carbide substrate adsorbed on the polishing head; Furthermore, in step S4, the particle size of silicon oxide in the silicon oxide polishing liquid is 50 nm-150 nm.

[0024] Furthermore, in step S4, the flow rate of the silicon oxide polishing liquid is 500 ml / min-2000 ml / min, and the rotation speed of the polishing head and the polishing disk is 20 RPM / min-80 RPM / min.

[0025] Furthermore, in step S4, the temperature required for polishing is 20°C-40°C, and the pressure required for polishing is 100 g / cm 2 -500g / cm 2 .

[0026] It is understandable that before using the silicon carbide substrate for epitaxial growth, a silicon oxide polishing liquid is used in conjunction with a polishing machine to perform chemical mechanical polishing (CMP) on the silicon carbide substrate with abnormal stacking fault imaging, so as to remove 0.1um-1um thickness on the surface of the silicon carbide substrate and make the surface roughness Ra of the silicon carbide substrate less than 0.1nm, thereby removing the sub-damage layer on the surface of the silicon carbide substrate and changing the surface state of the silicon carbide substrate so that the stacking faults that cannot be clearly imaged can be imaged normally and clearly after CMP treatment.

[0027] See Figure 4 and Figure 5 , the defect imaging diagram of the silicon carbide substrate after CMP treatment ( Figure 4 ) and defect imaging of silicon carbide substrate before CMP treatment ( Figure 5 ) by comparing, Figure 5 Medium stacking fault ratio Figure 4 The stacking faults in the silicon carbide substrate are displayed more clearly, so the available area of ​​the silicon carbide wafer obtained by subsequent epitaxial growth can be accurately determined by judging the number and area of ​​the stacking faults in the silicon carbide substrate, effectively improving the accuracy of incoming material inspection to determine whether the silicon carbide substrate itself is qualified, which is beneficial to improving the efficiency of the production line and reducing the manufacturing cost of silicon carbide epitaxial wafers.

[0028] S5. Taking the polished silicon carbide substrate out of the polishing chamber; S6. Cleaning the polished silicon carbide substrate using a hydrofluoric acid solution.

[0029] Furthermore, in step S6, the concentration of the hydrofluoric acid solution is 0.1% to 10%.

[0030] It is understandable that CMP treatment will cause a large amount of residual particles to appear on the surface of the silicon carbide substrate. Therefore, the silicon carbide substrate is cleaned again with a hydrofluoric acid solution to ensure the complete removal of the sub-damage layer and avoid the introduction of excessive particles or dirt on the surface of the silicon carbide substrate after CMP treatment, which will lead to fatal defects in the silicon carbide wafers obtained by subsequent epitaxial growth.

[0031] The present invention improves the problem of unclear stacking fault imaging of a silicon carbide substrate by polishing. First, silicon carbide substrates with unclear stacking fault imaging are screened out through stacking fault imaging detection. The screened silicon carbide substrates are cleaned and adsorbed on an adsorption pad of a polishing head in a polishing chamber. The polishing chamber is maintained at a temperature and pressure required for polishing, and silicon oxide polishing liquid is continuously introduced into the polishing pad. Then, the polishing head and the polishing disk are controlled to rotate for 2 hours so that the polishing pad polishes the silicon carbide substrate. After the polished silicon carbide substrate is taken out of the polishing chamber, the polished silicon carbide substrate is cleaned with a hydrofluoric acid solution, thereby achieving improvement in the clarity of the stacking fault imaging of the silicon carbide substrate. This is beneficial for clearly distinguishing stacking faults in stacking fault imaging detection, accurately judging the number and area of ​​stacking faults on the silicon carbide substrate, and then accurately screening out qualified silicon carbide substrates that can be used for epitaxial growth, thereby improving the yield rate of silicon carbide wafers after epitaxial growth.

[0032] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention are still within the scope of the present invention.

Claims

1. A method for improving the imaging clarity of stacking faults on silicon carbide substrates, characterized in that: The steps include: S1. Perform stacking fault imaging detection on silicon carbide substrates and screen out silicon carbide substrates with unclear stacking fault imaging; S2. Cleaning the screened silicon carbide substrate; S3, adsorbing the cleaned silicon carbide substrate onto an adsorption pad of a polishing head in a polishing chamber; S4, maintaining the temperature and pressure of the polishing chamber at the temperature and pressure required for polishing, continuously passing a silicon oxide polishing liquid to a polishing pad on a polishing plate in the polishing chamber, and controlling the rotation of the polishing head and the polishing plate for 2 hours so that the polishing pad polishes the silicon carbide substrate adsorbed on the polishing head; S5, taking the polished silicon carbide substrate out of the polishing chamber; S6. Cleaning the polished silicon carbide substrate using a hydrofluoric acid solution.

2. The method for improving the imaging clarity of stacking faults in silicon carbide substrates according to claim 1, characterized in that: The step S1 comprises: S11, placing the silicon carbide substrate into a defect imaging device to obtain a defect imaging image; S12. Determine whether the vertical lines in the defect imaging image are continuous and complete. If so, determine that the stacking fault imaging of the silicon carbide substrate is clear. Otherwise, determine that the stacking fault imaging of the silicon carbide substrate is unclear.

3. The method for improving the imaging clarity of stacking faults in silicon carbide substrates according to claim 1, wherein: In step S4, the temperature required for polishing is 20°C-40°C, and the pressure required for polishing is 100 g / cm 2 -500g / cm 2 .

4. The method for improving the imaging clarity of stacking faults in silicon carbide substrates according to claim 1, characterized in that: In step S4, the particle size of silicon oxide in the silicon oxide polishing liquid is 50 nm to 150 nm.

5. The method for improving the imaging clarity of stacking faults in silicon carbide substrates according to claim 1, wherein: The flow rate of the silicon oxide polishing liquid is 500 ml / min-2000 ml / min, and the rotation speed of the polishing head and the polishing disk is 20 RPM / min-80 RPM / min.

6. The method for improving the imaging clarity of stacking faults in silicon carbide substrates according to claim 1, characterized in that: In step S6, the concentration of the hydrofluoric acid solution is 0.1% to 10%.

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