Method and system for measuring BMD in monocrystalline silicon wafer

Abstract

The invention provides a method and system for measuring BMD in a monocrystalline silicon wafer, and belongs to the technical field of silicon wafer quality detection.The method for measuring the BMD in the monocrystalline silicon wafer comprises the steps that firstly, a silicon wafer to be measured needs to be subjected to heat treatment so that BMD can be evenly generated in the silicon wafer to be measured, the silicon wafer subjected to heat treatment is cleaved, and a measured sample wafer is obtained; then selecting one point on the cleavage surface of the measurement silicon wafer as a BMD measurement point; then, after the BMD measurement points are amplified to a certain measurement multiple to ensure that the features of the BMD in the visual field are clear, the BMD measurement points in the visual field are photographed and collected to obtain a measurement image, and the area of the measurement image can be determined according to the size of the visual field; the method comprises the following steps: firstly acquiring a measurement image, then performing feature matching on the acquired measurement image and a pre-stored BMD feature image so as to identify BMDs in the measurement image and count the BMDs to obtain the number of the BMDs, thereby effectively avoiding the phenomenon of large deviation of a measurement result caused by human factors; and finally, calculating the density of the BMDs in the measurement image according to the number of the BMDs and the area of the measurement image.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon wafer quality detection, and in particular to a method and a measuring system for measuring BMD in a single crystal silicon wafer. Background Art

[0002] Single crystal silicon materials account for an important proportion in the semiconductor field. BMD is a microscopic defect in silicon single crystals, which requires a long period of high-temperature heat treatment to form. BMD is particularly critical to the evaluation of silicon wafer quality, so it is necessary to strictly control the BMD in silicon wafers to prevent defective products from entering customers.

[0003] The existing conventional method for measuring BMD relies on manually confirming the number of BMDs within a specific area and calculating the density of BMDs within the silicon wafer based on the number of BMDs. However, when measuring silicon wafers with a higher BMD density, relying on manual confirmation of the number of BMDs within a specific area of ​​the silicon wafer will lead to larger deviations in the measurement results and lower accuracy. Summary of the invention

[0004] In view of this, in view of the above shortcomings, it is necessary to propose a method for measuring BMD in single crystal silicon wafers to solve the technical problem that the number of BMDs in a specific area of ​​the silicon wafer is manually confirmed, resulting in large deviations in the measurement results and low accuracy; It is also necessary to provide a measurement system for the method of measuring BMD in a single crystal silicon wafer.

[0005] In one aspect, the present invention provides a method for measuring BMD in a single crystal silicon wafer, comprising the following steps: Step 1: heat-treating the silicon wafer to be tested, and cleaving the heat-treated silicon wafer to obtain a measurement sample; Step 2: Select a point on the cleavage surface of the measured silicon wafer as a BMD measurement point; Step 3: After the BMD measurement point is magnified to a certain measurement magnification, the BMD measurement point is photographed and collected to obtain a measurement image and the area of ​​the measurement image; Step 4: feature matching the acquired measurement image with the pre-stored BMD feature image, thereby identifying and counting the BMDs in the measurement image to obtain the number of BMDs; Step 5: Calculate the density of BMD in the measurement image according to the number of BMDs and the area of ​​the measurement image.

[0006] Preferably, the pre-stored BMD characteristic images are several BMD morphological characteristic images.

[0007] Preferably, the pre-stored BMD characteristic images are several BMD morphology characteristic images with a particle size range of 1-5 μm.

[0008] Preferably, the step 4 is specifically: S 41 : grayscale processing is performed on the measurement image to highlight the characteristics of BMD and improve the recognition efficiency of BMD; S 42 : Matching the grayscaled measured image with the pre-stored feature map of the BMD to identify the position of the BMD in the measured image; S 43 : According to the position of BMD, the BMD is colored to make the BMD in the measurement image stand out and counted to obtain the number of BMD.

[0009] Preferably, in step 2, the BMD measurement point is the center point of the cleavage surface of the measured silicon wafer.

[0010] Preferably, in step 3, the magnification is 200-500 times.

[0011] Preferably, in step 3, the magnification is 500 times.

[0012] On the other hand, according to the measurement system of the method for measuring BMD in single crystal silicon wafers described in the above aspect, the system includes a silicon wafer magnification module, a photographing and sampling module, a storage module, a BMD identification module, and a calculation module. The silicon wafer magnification module, the photographing and sampling module, the BMD identification module, and the calculation module are electrically connected in sequence, the storage module is electrically connected to the BMD identification module, the silicon wafer magnification module is used to magnify the BMD measurement point to the measurement multiple, the photographing and sampling module is used to take photos of the BMD measurement point, the storage module stores the characteristic image of the BMD, the BMD identification module is used to identify and count the BMD in the measurement image, and the calculation module is used to calculate the density of the BMD in the measurement image.

[0013] Preferably, the measurement system for measuring BMD in a single crystal silicon wafer further includes an image processing module, the image processing module includes a preprocessing unit and a coloring unit, the preprocessing unit is electrically connected to the photo sampling module and the BMD identification module, the coloring unit is electrically connected to the BMD identification module, the preprocessing unit is used to perform grayscale processing on the measurement image, and the coloring unit colors the BMD in the measurement image.

[0014] Preferably, the measurement system for measuring BMD in a single crystal silicon wafer further comprises a silicon wafer clamping module, and the silicon wafer clamping module is used to clamp the silicon wafer so that the cleavage plane of the silicon wafer is exposed and kept horizontal.

[0015] It can be seen from the above technical scheme that the method for measuring the BMD of a single crystal silicon wafer provided by the present invention firstly performs a heat treatment on the silicon wafer to be measured so that the BMD is uniformly generated inside the silicon wafer to be measured, and the heat-treated silicon wafer is cleaved to expose the BMD inside the silicon wafer to obtain a measurement sample; then a point with a smaller degree of damage on the cleavage surface of the measured silicon wafer is selected as a BMD measurement point to prevent impurities from interfering with the identification of BMD; then the BMD measurement point is magnified to a certain measurement multiple to ensure that the characteristics of the BMD in the field of view are clear, and then the BMD measurement point in the field of view is photographed and collected to obtain a measurement image, and the area of ​​the measurement image can be determined according to the size of the field of view; and then the collected measurement image is taken. The measurement image is feature matched with the pre-stored BMD feature image, so as to identify the BMD in the measurement image and count it to obtain the number of BMDs; in order to improve the accuracy of BMD measurement, the present application selects a point with a smaller degree of damage as the BMD measurement point and magnifies it to a certain measurement multiple to ensure that the characteristics of the BMD in the field of view are clear, then takes a photo and performs feature matching with the pre-stored BMD feature image to identify the BMD in the measurement image and count it, which effectively avoids the phenomenon of large deviation and low accuracy of the measurement result due to human factors; finally, the density of BMD in the measurement image is calculated according to the number of BMDs and the area of ​​the measurement image. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flow chart of a method for measuring BMD in a single crystal silicon wafer provided in an embodiment of the present invention.

[0017] Figure 2 Schematic diagram of a measurement system for measuring BMD in a single crystal silicon wafer according to the present invention.

[0018] Figure 3 This is a diagram of measurement results of an embodiment of the method of the present invention.

[0019] Figure 4 This is a comparative measurement result of the traditional method.

[0020] Figure 5 It is a linear fitting diagram of the measurement results of the LST body micro defect testing equipment and the measurement results of the embodiment of the method of the present invention.

[0021] Figure 6 It is a linear fitting diagram of the measurement results of the LST body micro defect test equipment and the measurement results of the traditional method.

[0022] In the figure: a measurement system 10 for measuring BMD in a single crystal silicon wafer, a silicon wafer magnification module 110, a photographing and sampling module 120, a storage module 130, a BMD identification module 140, a calculation module 150, an image processing module 160, a pre-processing unit 161, a coloring unit 162, and a silicon wafer clamping module 170. DETAILED DESCRIPTION

[0023] In order to better understand the present invention, the present invention is further described below in conjunction with embodiments, but the scope of protection claimed by the present invention is not limited to the scope described in the embodiments.

[0024] Please see Figure 1 In one aspect, the present invention provides a method for measuring BMD in a single crystal silicon wafer, comprising the following steps: Step 1: heat-treating the silicon wafer to be tested, and cleaving the heat-treated silicon wafer to obtain a measurement sample; Step 2: Select a point on the cleavage surface of the measured silicon wafer as a BMD measurement point; Step 3: After the BMD measurement point is magnified to a certain measurement magnification, the BMD measurement point is photographed and collected to obtain a measurement image and the area of ​​the measurement image; Step 4: feature matching the acquired measurement image with the pre-stored BMD feature image, thereby identifying and counting the BMDs in the measurement image to obtain the number of BMDs; Step 5: Calculate the density of BMD in the measurement image according to the number of BMDs and the area of ​​the measurement image.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: by selecting a point with a smaller degree of damage as the BMD measurement point and magnifying it to a certain measurement multiple to ensure that the features of the BMD in the field of view are clear, taking photos and sampling, and matching the features with the pre-stored BMD feature image, the BMD in the measurement image is identified and counted, effectively avoiding the phenomenon of large deviation and low accuracy of the measurement result due to human factors; finally, the density of the BMD in the measurement image is calculated according to the number of BMDs and the area of ​​the measurement image.

[0026] In one embodiment, in order to identify the BMD in the measurement image, the pre-stored BMD characteristic images are several morphological characteristic images of the BMD.

[0027] In one embodiment, in order to improve the accuracy of BMD identification and prevent interference from impurities, the pre-stored BMD characteristic images are several BMD morphological characteristic images with a particle size range of 1-5 μm.

[0028] In one embodiment, the step 4 is specifically: S 41 : grayscale processing is performed on the measurement image to highlight the characteristics of BMD and improve the recognition efficiency of BMD; S 42: Matching the grayscaled measured image with the pre-stored feature map of the BMD to identify the position of the BMD in the measured image; S 43 : According to the position of BMD, the BMD is colored to make the BMD in the measurement image stand out and counted to obtain the number of BMD.

[0029] In one embodiment, in step 2, in order to prevent damage to the silicon wafer during the cleavage process from interfering with the identification of BMD, the BMD measurement point is the center point of the cleavage surface of the measured silicon wafer.

[0030] In one embodiment, in step 3, the magnification is 200-500 times so that the features of BMD in the field of view are clear.

[0031] In one embodiment, in step 3, the magnification is 500 times, which not only ensures that the characteristics of the BMD in the field of view are clear, but also ensures that the number of BMDs in the field of view is sufficient, avoiding errors caused by the BMD measurement point being a single point and representing the state of the entire silicon wafer.

[0032] Please see Figure 2 On the other hand, the measurement system 10 of the method for measuring BMD in a single crystal silicon wafer provided by the present invention includes a silicon wafer magnification module 110, a photographing and sampling module 120, a storage module 130, a BMD identification module 140, and a calculation module 150. The silicon wafer magnification module 110, the photographing and sampling module 120, the BMD identification module 140, and the calculation module 150 are electrically connected in sequence, the storage module 130 is electrically connected to the BMD identification module 140, the silicon wafer magnification module 110 is used to magnify the BMD measurement point to the measurement multiple, the photographing and sampling module 120 is used to take photos and collect the BMD measurement point, the storage module 130 stores the characteristic image of BMD, the BMD identification module 140 is used to identify and count the BMD in the measurement image, and the calculation module 150 is used to calculate the density of the BMD in the measurement image.

[0033] In one embodiment, the measurement system 10 for measuring BMD in a single crystal silicon wafer further includes an image processing module 160, the image processing module 160 includes a preprocessing unit 161 and a coloring unit 162, the preprocessing unit 161 is electrically connected to the photo sampling module 120 and the BMD identification module 140, the coloring unit 162 is electrically connected to the BMD identification module 140, the preprocessing unit 161 is used to grayscale the measurement image, and the coloring unit 162 colors the BMD in the measurement image.

[0034] In one embodiment, the measurement system 10 for measuring BMD in a single crystal silicon wafer further includes a silicon wafer clamping module 170, and the silicon wafer clamping module 170 is used to clamp the silicon wafer so that the cleavage plane of the silicon wafer is exposed and kept horizontal.

[0035] In the present invention, the silicon wafer clamping module 170 may be a silicon wafer BMD auxiliary positioning device disclosed in a Chinese invention patent with publication number “CN114280631A” and titled “Silicon wafer BMD auxiliary positioning device and silicon wafer BMD measurement method”.

[0036] The following embodiments of the method of the present invention and comparative examples of the conventional method are used to illustrate the measurement process and results of the BMD of a single crystal silicon wafer.

[0037] Embodiment: Cut single crystal silicon into silicon wafers with a thickness of 1 mm, quickly heat the silicon wafer to 1200°C at 85°C / s, introduce 60 bar nitrogen to react for 25 minutes, introduce 70 bar argon and maintain for 7 minutes, then cool to 900°C at a rate of 30°C / min to react for 3 hours, then heat to 1100°C at a rate of 5°C / min to obtain a sample, then mechanically polish the sample to remove 35 μm of thickness on the front and back sides of the sample, then cleave the middle of the sample to obtain a measuring silicon wafer, wipe the end face of the measuring silicon wafer with anhydrous ethanol, and use a 100-grade non-woven fabric to dip a small amount of alcohol to wipe the surface of the measuring silicon wafer, and use a tiger skin blower to quickly dry and clean the wiped surface to ensure that there is no interference on the surface of the measuring silicon wafer, clamp the measuring silicon wafer into the silicon wafer clamping module 170, so that the cleavage surface of the measuring silicon wafer The wafer is exposed and kept horizontal at all times. The center point of the cleavage surface of the measuring silicon wafer is selected as the BMD measuring point. The BMD measuring point is placed under the silicon wafer magnification module 110 and magnified 500 times. When the display image of the silicon wafer magnification module 110 is completely clear, the photographing sampling module 120 is used to take a photo to obtain a measurement image and the area of ​​the measurement image. Then the pre-processing unit 161 grayscales the measurement image. Subsequently, the BMD recognition module 140 performs feature matching according to the feature map of the BMD pre-stored in the storage module 130, thereby identifying the position of the BMD in the measurement image. Then the coloring unit 162 colors the BMD. The BMD recognition module 140 counts the colored BMD to obtain the number of BMDs. Finally, the calculation module 150 divides the number of BMDs by the area of ​​the measurement image to obtain the density of BMDs in the measuring silicon wafer. The measurement result is as follows: Figure 3 shown.

[0038] Comparative example: Cut single crystal silicon into 1mm thick silicon wafers, quickly heat the silicon wafer to 1200℃ at 85℃ / s, introduce 60bar nitrogen to react for 25min, introduce 70bar argon to maintain for 7min, then cool to 900℃ at 30℃ / min to react for 3h, then heat to 1100℃ at 5℃ / min to obtain a sample, then mechanically polish the sample to remove 35μm thickness on the front and back sides of the sample, then cleave the middle of the sample to obtain a measuring silicon wafer, wipe the end face of the measuring silicon wafer with anhydrous ethanol, and use a 100-grade non-woven fabric to dip in a small amount of alcohol to wipe the surface of the measuring silicon wafer, and use a tiger skin blower to quickly dry and clean the wiped surface to ensure that there is no surface of the measuring silicon wafer. Interference, clamp the measured silicon wafer into the silicon wafer clamping module 170, so that the cleavage surface of the measured silicon wafer is exposed and always kept horizontal, place the fixed measured silicon wafer together with the silicon wafer clamping module 170 under the microscope, select the center point of the cleavage surface of the measured silicon wafer as the BMD measurement point, use 500 times magnification, focus clearly, adjust the measured silicon wafer and the silicon wafer clamping module 170, ensure that the observation surface of the measured silicon wafer is parallel to the edge of the field of view, probe from the edge of the observation surface (polished surface) down to 100μm, manually select an area with more than 40 BMDs (the area is ≤100*200μm), manually identify and count the BMDs in the selected area, and then divide the number of BMDs by the area of ​​the area to obtain the density of BMDs in the measured silicon wafer. The measurement results are as follows: Figure 4 shown.

[0039] Further, in order to verify the accuracy of the measurement results of the embodiment of the method of the present invention and the comparative example of the conventional method, the BMD of a large number of measured silicon wafers in the above embodiment and the comparative example was measured by using an LST body micro defect test device, and the measurement results of the LST body micro defect test device were linearly fitted with the measurement results of the embodiment of the method of the present invention. Figure 5 As shown, the first trend formula is y = 1.4275x +2E+0.9, R 2 =0.8811, where y is the measurement result of the LST body micro-defect test equipment, x is the measurement result of the embodiment of the method of the present invention, R 2 The coefficient of determination indicates the closeness between the estimated value of the trend line and the actual data. It is a measure of the reliability of the trend line. 2 When it is close to 1, the trend formula is most reliable, and the R of the trend line 2 When it is close to 0, the reliability of the trend formula is the smallest. The measurement results of the LST body micro defect test equipment and the measurement results of the traditional method are linearly fitted again. Figure 6 As shown, the second trend formula is y = 0.988x —8E+0.8, R 2=0.6989, wherein y is the measurement result of the LST body micro-defect test device, and x is the measurement result of the embodiment of the method of the present invention. It can be seen that the measurement result of the embodiment of the method of the present invention and the measurement result of the LST body micro-defect test device have a high degree of consistency, while the measurement result of the conventional method comparison example and the measurement result of the LST body micro-defect test device have a low degree of consistency.

[0040] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for measuring BMD in a single crystal silicon wafer, characterized in that: The following steps are involved: Step 1: heat-treating the silicon wafer to be tested, and cleaving the heat-treated silicon wafer to obtain a measurement sample; Step 2: Select a point on the cleavage surface of the measured silicon wafer as a BMD measurement point; Step 3: After the BMD measurement point is magnified to a certain measurement magnification, the BMD measurement point is photographed and collected to obtain a measurement image and the area of ​​the measurement image; Step 4: feature matching the acquired measurement image with the pre-stored BMD feature image, thereby identifying and counting the BMDs in the measurement image to obtain the number of BMDs; Step 5: Calculate the density of BMD in the measurement image according to the number of BMDs and the area of ​​the measurement image.

2. The method for measuring BMD in a single crystal silicon wafer according to claim 1, characterized in that: The pre-stored BMD characteristic images are several BMD morphological characteristic images.

3. The method for measuring BMD in a single crystal silicon wafer according to claim 2, characterized in that: The pre-stored BMD characteristic images are several BMD morphological characteristic images with a particle size range of 1-5 μm.

4. The method for measuring BMD in a single crystal silicon wafer according to claim 2 or 3, characterized in that: The step 4 is specifically as follows: S 41 : grayscale processing is performed on the measurement image to highlight the characteristics of BMD and improve the recognition efficiency of BMD; S 42 : Matching the grayscaled measured image with the pre-stored feature map of the BMD to identify the position of the BMD in the measured image; S 43 : According to the position of BMD, the BMD is colored to make the BMD in the measurement image stand out and counted to obtain the number of BMD.

5. The method for measuring BMD in a single crystal silicon wafer according to claim 1, characterized in that: In step 2, the BMD measurement point is the center point of the cleavage surface of the measured silicon wafer.

6. The method for measuring BMD in a single crystal silicon wafer according to claim 1, characterized in that: In step 3, the magnification is 200-500 times.

7. The method for measuring BMD in a single crystal silicon wafer according to claim 1, characterized in that: In step 3, the magnification is 500 times.

8. A measuring system for the method for measuring BMD in a single crystal silicon wafer according to any one of claims 1 to 7, characterized in that: The method comprises a silicon wafer magnification module, a photographing and sampling module, a storage module, a BMD identification module and a calculation module. The silicon wafer magnification module, the photographing and sampling module, the BMD identification module and the calculation module are electrically connected in sequence. The storage module is electrically connected to the BMD identification module. The silicon wafer magnification module is used to magnify the BMD measurement point to the measurement multiple. The photographing and sampling module is used to take photos of the BMD measurement point. The storage module stores the characteristic image of the BMD. The BMD identification module is used to identify and count the BMD in the measurement image. The calculation module is used to calculate the density of the BMD in the measurement image.

9. The method for measuring BMD in a single crystal silicon wafer according to claim 8, characterized in that: The measurement system for measuring BMD in a single crystal silicon wafer also includes an image processing module, which includes a preprocessing unit and a coloring unit. The preprocessing unit is electrically connected to the photo sampling module and the BMD identification module, and the coloring unit is electrically connected to the BMD identification module. The preprocessing unit is used to grayscale the measurement image, and the coloring unit colors the BMD in the measurement image.

10. The system for measuring BMD in a single crystal silicon wafer according to claim 8 or 9, characterized in that: The measuring system for measuring BMD in a single crystal silicon wafer further comprises a silicon wafer clamping module, wherein the silicon wafer clamping module is used to clamp the silicon wafer so that the cleavage plane of the silicon wafer is exposed and kept horizontal.

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