Method for testing thickness of epitaxial wafer
By performing concentration tests at sampling points along a spiral line on the epitaxial wafer, the problems of long testing time and insufficient accuracy in the existing technology are solved, efficient and accurate epitaxial wafer concentration evaluation is achieved, and the risk of epitaxial wafer damage is reduced.
Patent Information
- Application Number
- CN202510892272.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-30
- Publication Date
- 2025-09-12
AI Technical Summary
Existing epitaxial wafer concentration testing methods have problems such as long testing time, insufficient accuracy and easy damage to the epitaxial wafer. Especially in silicon carbide epitaxial wafers, the high concentration at the edge and low concentration in the center lead to high test results, posing a risk of device failure.
A spiral sampling method is used to test the concentration value at sampling points spaced along the spiral on the epitaxial layer of the epitaxial wafer. The center of the spiral coincides with the center of the epitaxial wafer, and the area is divided by evenly distributed bisectors to form sampling points. The number of sampling points is reduced to improve test efficiency and accuracy.
While ensuring test accuracy, the test time is significantly shortened, the efficiency and accuracy of epitaxial wafer thickness testing are improved, the risk of epitaxial wafer damage is reduced, and the representativeness of the test results is improved.
Smart Images
Figure CN120629495A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of epitaxial wafer thickness testing, and in particular to an epitaxial wafer thickness testing method. Background Art
[0002] Due to the different growth rates of silicon carbide epitaxial growth and the air-suspended rotating single-wafer horizontal growth epitaxial furnace, there will be uneven epitaxial layer thickness. Therefore, there is a need for a distribution test method for epitaxial wafer thickness that can be used to judge whether the epitaxial layer thickness growth of the epitaxial wafer is uniform. In the prior art, the distribution test method for epitaxial wafer thickness is as follows: Method A: Please refer to Figure 10 , take the center of the epitaxial wafer A1 as a sampling point A21, and select 6 different directions at intervals in the center of the epitaxial wafer, and select 7 sampling points A22 at intervals in each direction, and take a sampling point A23 at the edge position in the middle of two directions, and take another sampling point A23 on the opposite side of the sampling point, a total of 45 sampling points are taken for testing. This method is more accurate, but the test time is longer (usually close to an hour), and currently mainly uses a probe to contact the sampling point of the epitaxial wafer to test the concentration value of the sampling point, because the probe of the contact mercury probe CV (Capacitance-Voltage, capacitance-voltage test) is easy to adhere to particles, and the particles are easy to pierce the epitaxial wafer when contacting the sampling point of the epitaxial wafer. During the test, due to the large number of test points, it is inevitable to pierce the surface of the epitaxial wafer, resulting in pressure damage problems, resulting in a significant decrease in the surface availability of the silicon carbide epitaxial wafer.
[0003] Method B: Please refer to Figure 11 , a main direction is selected with the center of the epitaxial wafer B1 as the starting point. Including the center point of the epitaxial wafer B1, 7 sampling points B21 are selected in the main direction, and a point B22 is selected from the edge of the epitaxial wafer in the secondary directions with angles of 90°, 180° and 270° respectively different from the main direction. A total of 10 points need to be taken for concentration value testing, and 4 of them are located at the edge of the epitaxial wafer. Method B has a shorter testing time than method A, but because the epitaxial wafer is grown by self-rotation and is affected by the edge effect of the epitaxial furnace concentration, the epitaxial wafer will show a distribution state with high concentration at the edge and low concentration in the center. In addition, method B only tests the concentration in one direction, and 40% of the sampling points are located at the edge of the epitaxial wafer, which will make the calculated concentration average value higher than the actual situation. If the test results of this method are used in the later processing of chips, the BV (Breakdown Voltage) of the product may be too low, and there will be a risk of device failure. Summary of the Invention
[0004] The purpose of this application is to provide a method for testing the thickness of an epitaxial wafer, which can not only reduce the testing time but also ensure the accuracy of the test.
[0005] To achieve the above objectives, the present application provides a method for testing the thickness of an epitaxial wafer, comprising: Provide epitaxial wafers; A plurality of sampling points are taken at intervals along a spiral line on the epitaxial layer of the epitaxial wafer to perform a concentration value test, and the center of the spiral line coincides with the center of the epitaxial wafer.
[0006] Optionally, the epitaxial wafer is evenly divided into a plurality of regions by a plurality of equally dividing lines passing through the center of the epitaxial wafer, and the spiral line intersects with each of the equally dividing lines to form the sampling points.
[0007] Optionally, the epitaxial wafer is circular, and the bisector is the radius of the epitaxial wafer.
[0008] Optionally, the spiral line intersects each of the bisectors to form at least two sampling points, and one of the two sampling points is located at the center of the epitaxial wafer.
[0009] Optionally, the number of the bisectors is 8.
[0010] Optionally, an end of the spiral line intersects one of the bisectors at a first distance from an edge of the epitaxial wafer.
[0011] Optionally, the number of the sampling points is 10.
[0012] The present application takes multiple sampling points at intervals along the spiral line to test the concentration value. Since the center of the spiral line coincides with the center of the epitaxial wafer, when selecting sampling points at intervals on the spiral line, sampling points in different directions and at different distances from the center of the epitaxial wafer can be taken into account. There is no need to sample too many sampling points for testing, and the data of the sampling points are more representative, which can improve the efficiency of the epitaxial wafer concentration value test and ensure the accuracy of the test. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 Schematic diagram of the process of the epitaxial wafer density testing method according to an embodiment of the present application.
[0014] Figure 2 Schematic diagram of sampling points for the epitaxial wafer density testing method according to an embodiment of the present application.
[0015] Figure 3 Schematic diagram of coordinates obtained according to various epitaxial wafer density test methods.
[0016] Figure 4 Based on Figure 3Schematic diagram of the sampling points of the epitaxial wafer generated by the coordinates of each epitaxial wafer concentration test method.
[0017] Figure 5 for Figure 3 Comparison of experimental results of various epitaxial wafer density test methods.
[0018] Figures 6 to 9 This is a comparison chart of the experimental results of the epitaxial wafer density testing method of the present application and method A in the background art.
[0019] Figure 10 Schematic diagram of sampling points of method A in the background technology.
[0020] Figure 11 Schematic diagram of sampling points of method B in background technology. DETAILED DESCRIPTION
[0021] In order to explain the technical content, structural features, achieved objectives and effects of this application in detail, the following is a detailed description in conjunction with the implementation methods and the accompanying drawings.
[0022] See also Figure 1 and Figure 2 , the present application discloses a method for testing the thickness of an epitaxial wafer, comprising: S1, providing an epitaxial wafer 1.
[0023] S2 , taking a number of sampling points 3 at intervals along a spiral line 2 on the epitaxial layer 11 of the epitaxial wafer 1 to perform a concentration value test, with the center of the spiral line 2 coinciding with the center of the epitaxial wafer 1 .
[0024] The present application selects multiple sampling points 3 at intervals along the spiral line 2 to perform concentration value testing. Since the center of the spiral line 2 coincides with the center of the epitaxial wafer 1, and the epitaxial wafer 1 is grown by self-rotation, when selecting sampling points 3 at intervals on the spiral line 2, sampling points 3 in different directions and at different distances from the center of the epitaxial wafer 1 can be taken into account. This sampling method also conforms to the growth law of the self-rotation growth of the epitaxial wafer 1. Therefore, the epitaxial wafer concentration test method of the present application does not require sampling too many sampling points 3 for testing, and the data of the sampling points 3 are more representative, which can improve the efficiency of the epitaxial wafer 1 concentration value test and ensure the accuracy of the test.
[0025] See also Figure 2 In some embodiments, the epitaxial wafer 1 is evenly divided into several areas by several bisectors 4 passing through the center of the epitaxial wafer 1. The spiral line 2 intersects with each bisector 4 to form sampling points 3, which can make the distribution of the sampling points 3 more uniform.
[0026] It can be understood that the aforementioned spiral line 2 and bisector line 4 are merely auxiliary lines used to conveniently illustrate the position of the sampling point 3 and are not actual lines.
[0027] Specifically, the epitaxial wafer 1 is circular, and the bisector 4 is the radius of the epitaxial wafer 1 .
[0028] More specifically, the spiral line 2 intersects each bisector 4 to form at least two sampling points 3, one of which is located at the center of the epitaxial wafer 1. It will be understood that in this specific example, if a sampling point has been sampled once, it does not need to be sampled again.
[0029] More specifically, the number of the bisecting lines 4 is 8. That is, the 8 bisecting lines 4 evenly divide the epitaxial wafer 1 into 8 regions.
[0030] See also Figure 2 In some embodiments, the end of the spiral line 2 intersects one of the bisectors 4 at a first distance from the edge of the epitaxial wafer 1 .
[0031] Optionally, the first distance is 5 mm.
[0032] See also Figure 2 In some embodiments, the number of sampling points 3 is ten.
[0033] In some embodiments, the material of the epitaxial wafer 1 includes silicon carbide.
[0034] See also Figure 5 , the existing epitaxial wafer density test method also includes method C. Method C ( Figure 5 Newpattern4) takes 2 sampling points in each of the four directions, where two adjacent directions are perpendicular to each other, takes the center of the epitaxial wafer as a sampling point, and takes a sampling point on the edge of the epitaxial wafer between two adjacent directions, for a total of 10 sampling points.
[0035] In combination with the above embodiments, a comparative experiment on the concentration of epitaxial wafers is conducted using the epitaxial wafer concentration test method of the present application, method C, and method B in the background art.
[0036] See also Figures 3 to 5 In newpattern2 and newpattern3, according to method B, several epitaxial wafers are taken, and different directions are determined as main directions for each epitaxial wafer. Each sampling point is determined according to the corresponding main direction, and the sampling point coordinates and the sampling point diagram composed of the sampling point coordinates are obtained. Figure 3 and Figure 4 In the newpattern1, according to the epitaxial wafer density test method of the present application, 10 sampling points located on the bisector 4 are selected along the spiral line 2 on the epitaxial wafer to obtain the sampling point coordinates and the sampling point schematic diagram composed of the sampling point coordinates. Figures 3 to 5In newpattern4, according to method C, sampling points are selected on the epitaxial layer of the epitaxial wafer to obtain the sampling point coordinates and a sampling point schematic diagram composed of the sampling point coordinates.
[0037] Conduct a concentration test on newpattern1 to newpattern4, and use the test results of method A as a base point to compare the experimental results of newpattern1 to newpattern4 with the concentration and thickness values measured by method A. Repeat the experiment multiple times to obtain multiple difference values. Calculate the corresponding average values based on these difference values to obtain the difference average values of each indicator. Summarize the difference average values of each indicator to obtain the following: Figure 5 In the experimental result table shown, the smaller the average difference of each index is, the closer the result of the new pattern is to that of method A, and the more accurate the test result will be when the actual concentration value is tested. Figure 5 As can be seen from the data results, newpattern1 has the smallest average difference in multiple indicators. In other words, newpattern1 is closer to the test results of method A than the other newpatterns, and its test results are more accurate than those of methods B and C.
[0038] See also Figures 6 to 9 In combination with the above embodiments, the present application also uses the epitaxial wafer concentration test method of the present application and method A to conduct a more detailed comparative experiment on the sample mean and sample uniformity in terms of concentration. Figures 6 to 9 The various indicators in the test are all test indicators well known to those skilled in the art and will not be described in detail.
[0039] The sample averages were compared using the above method A and the concentration test method of this application, and the results were: Figure 6 and Figure 7 The experimental results, in Figure 6 and Figure 7 In the figure, 45PT_AVERAGE is the test result corresponding to method A, and 10PT_AVERAGE is the test result of the concentration test method of this application. Figure 6 and Figure 7 From the above, there is no significant difference in the sample mean between Method A and the consistency test method of this application.
[0040] The sample uniformity was compared using the above method A and the concentration test method of this application, and the results were: Figure 8 and Figure 9 The experimental results, in Figure 8 and Figure 9In the figure, 45PT_Uni is the test result corresponding to method A, and 10PT_Uni is the test result of the consistency test method of this application. Figure 8 and Figure 9 From the above, there is no significant difference in sample uniformity between Method A and the concentration test method of this application.
[0041] In summary, the epitaxial wafer concentration test method of the present application has no significant difference in test accuracy compared to method A, and the number of sampling points is also less than that of method A. In other words, the epitaxial wafer concentration test method of the present application can improve the efficiency of epitaxial wafer concentration testing while ensuring test accuracy.
[0042] The above disclosure is only the preferred embodiment of the present application, which certainly cannot be used to limit the scope of rights of the present application. Therefore, equivalent changes made according to the scope of the patent application of the present application are still within the scope covered by the present application.
Claims
1. A method for testing the thickness of an epitaxial wafer, characterized in that: include: Provide epitaxial wafers; A plurality of sampling points are taken at intervals along a spiral line on the epitaxial layer of the epitaxial wafer to perform a concentration value test, and the center of the spiral line coincides with the center of the epitaxial wafer.
2. The epitaxial wafer thickness testing method according to claim 1, wherein: The epitaxial wafer is evenly divided into a plurality of regions by a plurality of equally dividing lines passing through the center of the epitaxial wafer, and the spiral line intersects with each of the equally dividing lines to form the sampling points.
3. The epitaxial wafer thickness testing method according to claim 2, wherein: The epitaxial wafer is circular, and the bisector is the radius of the epitaxial wafer.
4. The epitaxial wafer thickness testing method according to claim 3, wherein: The spiral line intersects each of the bisectors to form at least two sampling points, and one of the two sampling points is located at the center of the epitaxial wafer.
5. The epitaxial wafer thickness testing method according to claim 3, wherein: The number of the bisectors is 8.
6. The epitaxial wafer thickness testing method according to claim 3, wherein: An end of the spiral line intersects one of the bisectors at a first distance from an edge of the epitaxial wafer.
7. The epitaxial wafer thickness testing method according to any one of claims 1 to 6, wherein: The number of the sampling points is 10.