Vortex wave plate-based silicon wafer stress dynamic detection system and method

Abstract

The invention discloses a silicon wafer stress dynamic detection system and method based on a vortex wave plate. The system comprises a probe light source, a reflector, a beam expander, a collimating mirror, a polarizer, a first convex lens, a silicon wafer sample clamping platform, a second convex lens, the vortex wave plate, an analyzer, a third convex lens, a CCD and a PC. Laser output by the probe light source is expanded and collimated and then becomes linearly polarized light through the polarizer, the linearly polarized light is converged at a silicon wafer sample clamped in the silicon wafer sample clamping platform through the convex lens, and the linearly polarized light is converted into parallel light through the second convex lens after transmitting the sample and vertically enters the vortex wave plate; and then imaging in a CCD (Charge Coupled Device) placed behind through an analyzer and a third convex lens, transmitting the obtained data to a PC (Personal Computer), processing by using a polarization imaging algorithm to obtain a phase difference image, and obtaining the internal stress condition. The internal polarization information of the silicon wafer is obtained through the vortex wave plate, the internal stress change condition of the silicon wafer is detected in real time, manual operation is not needed in the measurement process, the measurement precision is high, and operation is easy.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor wafer stress detection, and in particular relates to a silicon wafer stress dynamic detection system and method based on a vortex wave plate. Background Art

[0002] Silicon is an important material widely used in integrated circuits, solar cells and other fields, so there are many ways to detect its stress. According to the test principle, it can be divided into two categories: destructive measurement and non-destructive measurement. Destructive measurement methods include mechanical and chemical methods, which obtain the residual stress state by releasing and measuring the stress of the workpiece; non-destructive measurement methods measure the physical properties of the material itself, which does not affect the subsequent use of the workpiece and gradually becomes the development direction. The photoelastic method mainly uses optically sensitive materials to make a model, places it in a polarized light field, and after applying a load, observes the temporary birefringence phenomenon produced by the model, thereby obtaining a full-field topographic map of stress wave propagation. This method has many advantages, such as being able to provide real-time stress distribution images, intuitively showing the process and laws of stress wave propagation; no need to destroy the sample, and no impact on the integrity of the object being measured; relatively simple operation and low cost.

[0003] Photoelastic effect, also known as stress birefringence, means that when a transparent medium is stressed internally, its refractive index characteristics will change, thus showing optical anisotropy. If the stress is not uniform on the crystal, the birefringence will be inconsistent everywhere, causing different phase differences at different points on the light wave passing through it. The photoelastic effect can be used to test the internal stress of optical materials and observe the stress distribution of various mechanical structures.

[0004] Existing public detection of silicon stress damage mainly focuses on the field of residual stress, and commonly used methods include Mach-Zehnder interferometry and silicon wafer reflected light polarization stress detection based on the Mueller matrix.

[0005] Among them, the silicon wafer reflected light polarization stress detection method based on the Mueller matrix makes the output continuous laser pass through the beam expander and polarizer to enter the beam splitter, and the reflected light of the beam splitter passes through the wave plate and then vertically enters the sample. The reflected light of the sample passes through the wave plate, beam splitter and polarizer and finally enters the CCD. The CCD takes the sample polarization image and sends it to the PC for grayscale processing, Mueller matrix calculation, and median filtering to obtain the phase difference image. This method requires the construction of three optical axes, and the polarizer needs to be manually rotated during measurement, which causes errors. This method can only measure the residual stress of silicon wafers, and cannot measure the stress of silicon wafers in real time.

[0006] Therefore, there is an urgent need for a silicon wafer stress detection system and method to solve the above technical problems. Summary of the invention

[0007] The purpose of the present invention is to provide a silicon wafer stress dynamic detection system and method based on vortex wave plate, which obtains the internal polarization information of the silicon wafer by utilizing the vortex wave plate, detects the internal stress change of the silicon wafer in real time, realizes the measurement process without manual operation, improves the measurement accuracy, and is simple to operate.

[0008] In order to achieve the purpose of the present invention, on the one hand, the present invention provides a silicon wafer stress dynamic detection system based on a vortex wave plate, which includes placing a silicon wafer sample in the detection system, and the laser emitted by the detection light source is reflected by a reflector into a common first optical axis, and the light beam size is adjusted by a beam expander and a collimator, and then it is converted into linearly polarized light after passing through a polarizer, and is converged on the silicon wafer sample clamping position in the silicon wafer sample clamping platform through a first convex lens, and after transmitting the silicon wafer sample, it is converted into parallel light through a second convex lens and vertically incident on a vortex wave plate, and then imaged by an analyzer and a third convex lens 11 in a CCD placed at the rear, and the obtained data is transmitted to a PC, and the PC uses a polarization imaging algorithm to process to obtain a phase difference image to obtain its internal stress condition; The common first optical axis is composed of the beam expander, the collimator, the polarizer, the first convex lens, the silicon wafer sample holding platform, the second convex lens, the vortex wave plate, the analyzer, the third convex lens, and the CCD in sequence.

[0009] The polarization imaging algorithm is specifically as follows: first, the image taken by the CCD when the silicon wafer sample and the analyzer are not placed is processed, and the transmission axis angle of the polarizer is 0° as a reference, and 360° calibration is performed in a clockwise direction, and then a circle with the largest light intensity in the image is selected, and the aperture radius at this time is recorded; then the image taken by the CCD when all components are placed is processed, and according to the aperture radius, 0°, 45°, 90°, and 135° are selected to perform grayscale processing on the image, and the grayscale value is extracted, and the grayscale value is substituted into the Mueller matrix for calculation to obtain the phase delay amount and azimuth angle data and image at the measurement point of the silicon wafer sample, and the data and image are analyzed, and the stress condition of the silicon wafer sample is obtained by analyzing that the principal stress difference of the silicon wafer sample is proportional to the phase delay amount.

[0010] The detection light source is a fiber laser with a maximum output power of 2W and an output wavelength of 1550nm.

[0011] The silicon wafer sample holding platform is connected to the two-dimensional moving platform, and the two-dimensional moving platform is manipulated to make the held silicon wafer sample uniformly detected by the detection light.

[0012] During the detection process of the system, laser damage and mechanical pressure are used to generate stress on the silicon wafer sample without affecting the operation of the detection optical path to achieve dynamic measurement.

[0013] The area where the silicon wafer sample is located in the silicon wafer sample clamping platform coincides with the focus of the converging light of the first convex lens.

[0014] On the other hand, the present invention also provides a method for dynamic detection of silicon wafer stress based on a vortex wave plate, comprising the following steps: Step 1: temporarily do not put in the silicon wafer sample, the polarizer, and the vortex wave plate, adjust the power of the detection light source to the lowest, turn on the power, rotate the polarizer to observe the image in the CCD, and stop when the image light intensity reaches the maximum; Step 2: Place the vortex wave plate, turn on the detection light source and adjust until the image obtained by the CCD is clear and complete, and record the light intensity distribution of the image obtained by the CCD at this time; Step 3: Place the analyzer, remove the vortex wave plate, turn on the detection light source, and adjust the analyzer angle so that the image light intensity in the CCD reaches the maximum; Step 4: Place all components including the silicon wafer sample, turn on the detection light source, and record the image obtained by the CCD; Step 5: adjusting the two-dimensional moving platform connected to the silicon wafer sample holding platform, scanning the silicon wafer sample, and recording the image taken by the CCD; Step 6: Processing the obtained image using a polarization imaging algorithm on the PC to obtain a filtered phase difference image; Step 6-1: Taking the polarizer transmission axis angle of 0° as a reference, calibrate the image obtained in step 2 in a 360° clockwise direction; Step 6-2: Select the circle with the largest light intensity in the image obtained in step 2, and record the aperture radius at this time; Step 6-3: Process the images obtained in step 4 and step 5, and then select the images at 0°, 45°, 90°, and 135° for grayscale processing according to the aperture radius obtained in step 6-2, and extract the grayscale value; Step 6-4: Substituting the grayscale value into the Mueller matrix for calculation, obtaining the phase delay and azimuth angle data and image at the measurement point of the silicon wafer sample; Step 6-5: Analyze the data and images, and obtain the stress condition of the silicon wafer sample by analyzing that the principal stress difference of the silicon wafer sample is proportional to the phase delay. The greater the principal stress difference, the greater the stress value.

[0015] Compared with the prior art, the significant improvements of the present invention are: the operation of the present invention is simple, and there is no need to manually rotate the polarizer during the operation, thereby reducing human errors; the residual stress of the silicon wafer can be measured, and the real-time dynamic stress detection of the silicon wafer can also be performed; the experimental accuracy is improved, and the number of selected data in data processing can be increased to improve the experimental accuracy.

[0016] In order to more clearly illustrate the functional characteristics and structural parameters of the present invention, further description is given below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 It is a schematic diagram of the detection system of the present invention.

[0018] The reference numerals in the figure are: detection light source 1, reflector 2, beam expander 3, collimator 4, polarizer 5, first convex lens 6, silicon wafer sample holding platform 7, second convex lens 8, vortex wave plate 9, analyzer 10, third convex lens 11, CCD 12, PC 13. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] The present invention is a silicon wafer stress dynamic detection system based on vortex wave plate, combined with Figure 1 The system includes placing a silicon wafer sample in the detection system, and the laser emitted by the detection light source 1 is reflected by the reflector 2 into the common first optical axis, and the beam size is adjusted by the beam expander 3 and the collimator 4, and then it is converted into linear polarized light after passing through the polarizer 5, and is converged on the silicon wafer sample clamping platform 7 by the first convex lens 6, and after transmitting the silicon wafer sample, it is converted into parallel light by the second convex lens 8 and vertically incident on the vortex wave plate 9, and then imaged by the analyzer 10 and the third convex lens 11 in the CCD 12 placed at the rear, and the obtained data is transmitted to the PC 13, and the PC 13 uses the polarization imaging algorithm to process to obtain the phase difference image, and obtain its internal stress condition; The common first optical axis is composed of the beam expander 3, the collimator 4, the polarizer 5, the first convex lens 6, the silicon wafer sample holding platform 7, the second convex lens 8, the vortex wave plate 9, the analyzer 10, the third convex lens 11, and the CCD 12 in sequence.

[0021] The polarization imaging algorithm is specifically as follows: first, the image taken by the CCD12 when the silicon wafer sample and the analyzer 10 are not placed is processed, and the transmission axis angle of the polarizer 5 is 0° as a reference, and 360° calibration is performed in a clockwise direction, and then a circle with the largest light intensity in the image is selected, and the aperture radius at this time is recorded; then the image taken by the CCD12 when all components are placed is processed, and according to the aperture radius, 0°, 45°, 90°, and 135° are selected to perform grayscale processing on the image. On this basis, additional selected data can be added according to accuracy requirements, and grayscale values ​​are extracted. The grayscale values ​​are substituted into the Mueller matrix for calculation to obtain the phase delay amount and azimuth angle data and images at the measurement location of the silicon wafer sample, and the data and images are analyzed. By analyzing that the principal stress difference of the silicon wafer sample is proportional to the phase delay amount, the stress condition of the silicon wafer sample is obtained.

[0022] The detection light source 1 is a fiber laser with a maximum output power of 2W and an output wavelength of 1550nm.

[0023] The silicon wafer sample holding platform 7 is connected to the two-dimensional moving platform, and the two-dimensional moving platform is manipulated to make the held silicon wafer sample uniformly detected by the detection light.

[0024] During the detection process of the system, laser damage and mechanical pressure are used to generate stress on the silicon wafer sample without affecting the operation of the detection optical path to achieve dynamic measurement.

[0025] The area where the silicon wafer sample is located in the silicon wafer sample clamping platform 7 coincides with the focus of the converging light of the first convex lens 6 .

[0026] On the other hand, the present invention also provides a method for dynamic detection of silicon wafer stress based on a vortex wave plate, comprising the following steps: Step 1: Do not put in the silicon wafer sample, the polarizer 11, and the vortex wave plate 9 for the time being, adjust the power of the detection light source 1 to the lowest and then turn on the power, rotate the polarizer 5 to observe the image in the CCD12, and stop when the image light intensity reaches the maximum; the operator can judge the maximum light intensity by himself without being too precise.

[0027] Step 2: Place the vortex wave plate 9, turn on the detection light source 1 and adjust until the image obtained by the CCD is clear and complete, and record the light intensity distribution of the image obtained by the CCD 12 at this time; Step 3: Place the polarizer 11, remove the vortex wave plate 9, turn on the detection light source 1, and adjust the angle of the polarizer 11 so that the image light intensity in the CCD 12 reaches the maximum; the operator can judge the maximum light intensity by himself without being too precise.

[0028] Step 4: Place all components including the silicon wafer sample, turn on the detection light source 1, and record the image obtained by the CCD 12; Step 5: Adjust the two-dimensional moving platform connected to the silicon wafer sample holding platform 7 to scan the silicon wafer sample and record the image taken by the CCD 12; Step 6: Processing the obtained image using a polarization imaging algorithm on the PC 13 to obtain a filtered phase difference image; Step 6-1: Taking the polarizer transmission axis angle of 0° as a reference, calibrate the image obtained in step 2 in a 360° clockwise direction; Step 6-2: Select the circle with the largest light intensity in the image obtained in step 2, and record the aperture radius at this time; Step 6-3: Process the images obtained in step 4 and step 5, and then select the images at 0°, 45°, 90°, and 135° for grayscale processing according to the aperture radius obtained in step 6-2. On this basis, additional selected data can be added according to accuracy requirements to extract grayscale values; Step 6-4: Substituting the grayscale value into the Mueller matrix for calculation, obtaining the phase delay and azimuth angle data and image at the measurement point of the silicon wafer sample; Step 6-5: Analyze the data and images, and obtain the stress condition of the silicon wafer sample by analyzing that the principal stress difference of the silicon wafer sample is proportional to the phase delay. The greater the principal stress difference, the greater the stress value.

[0029] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0030] Although 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 present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A silicon wafer stress dynamic detection system based on vortex wave plate, characterized in that: A silicon wafer sample is placed in the detection system, and the laser light emitted by the detection light source (1) is reflected by the reflector (2) and enters the common first optical axis. The light beam size is adjusted by the beam expander (3) and the collimator (4), and then the light beam is converted into linear polarized light after passing through the polarizer (5). The light beam is converged at the location where the silicon wafer sample is clamped in the silicon wafer sample clamping platform (7) through the first convex lens (6), and then the light beam is converted into parallel light through the second convex lens (8) after passing through the silicon wafer sample and vertically incident on the vortex wave plate (9). The light beam is then imaged in the CCD (12) placed at the rear through the analyzer (10) and the third convex lens (11), and the obtained data is transmitted to the PC (13). The PC (13) uses a polarization imaging algorithm to process the light to obtain a phase difference image, and obtain the internal stress condition. The common first optical axis is sequentially composed of the beam expander (3), the collimator (4), the polarizer (5), the first convex lens (6), the silicon wafer sample holding platform (7), the second convex lens (8), the vortex wave plate (9), the analyzer (10), the third convex lens (11), and the CCD (12).

2. A silicon wafer stress dynamic detection system based on vortex wave plate according to claim 1, characterized in that: The polarization imaging algorithm is specifically as follows: first, the image captured by the CCD (12) when the silicon wafer sample and the analyzer (10) are not placed is processed, and the transmission axis angle of the polarizer (5) is used as a reference to 0°, and 360° calibration is performed in a clockwise direction, and then a circle with the largest light intensity in the image is selected, and the aperture radius at this time is recorded; then, the image captured by the CCD (12) when all components are placed is processed, and according to the aperture radius, 0°, 45°, 90°, and 135° are selected to perform grayscale processing on the image, and the grayscale value is extracted, and the grayscale value is substituted into the Mueller matrix for calculation to obtain the phase delay amount and azimuth angle data and image at the measurement point of the silicon wafer sample, and the data and image are analyzed, and the stress condition of the silicon wafer sample is obtained by analyzing that the principal stress difference of the silicon wafer sample is proportional to the phase delay amount.

3. The silicon wafer stress dynamic detection system based on vortex wave plate according to claim 1 is characterized in that: The detection light source (1) is a fiber laser with a maximum output power of 2W and an output wavelength of 1550nm.

4. The silicon wafer stress dynamic detection system based on vortex wave plate according to claim 1 is characterized in that: The silicon wafer sample clamping platform (7) is connected to a two-dimensional moving platform, and the clamped silicon wafer sample is uniformly detected by the detection light by manipulating the two-dimensional moving platform.

5. The silicon wafer stress dynamic detection system based on vortex wave plate according to claim 1 is characterized in that: During the detection process of the system, laser damage and mechanical pressure are used to generate stress on the silicon wafer sample without affecting the operation of the detection optical path to achieve dynamic measurement.

6. The silicon wafer stress dynamic detection system based on vortex wave plate according to claim 1 is characterized in that: The area where the silicon wafer sample is located in the silicon wafer sample clamping platform (7) coincides with the focus of the convergent light of the first convex lens (6).

7. A detection method for a silicon wafer stress dynamic detection system based on a vortex wave plate according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: temporarily placing the silicon wafer sample, the polarizer (10), and the vortex wave plate (9), adjusting the power of the detection light source (1) to the lowest and then turning on the power supply, rotating the polarizer (5) to observe the image in the CCD (12), and stopping when the image light intensity reaches the maximum; Step 2: placing the vortex wave plate (9), turning on the detection light source (1) and adjusting the image obtained by the CCD until it is clear and complete, and recording the light intensity distribution of the image obtained by the CCD (12) at this time; Step 3: placing the polarizer (10), removing the vortex wave plate (9), turning on the detection light source (1), and adjusting the angle of the polarizer (10) so that the image light intensity in the CCD (12) reaches a maximum; Step 4: Place all components including the silicon wafer sample, turn on the detection light source (1), and record the image obtained by the CCD (12); Step 5: adjusting the two-dimensional moving platform connected to the silicon wafer sample clamping platform (7), scanning the silicon wafer sample, and recording the image captured by the CCD (12); Step 6: Processing the obtained image using a polarization imaging algorithm on the PC (13) to obtain a filtered phase difference image.

8. The method for dynamic detection of silicon wafer stress based on vortex wave plate according to claim 7, characterized in that: The step 6 is to process the obtained image using a polarization imaging algorithm on the PC (13), and the specific steps are as follows: Step 6-1: Taking the polarizer transmission axis angle of 0° as a reference, calibrate the image obtained in step 2 in a 360° clockwise direction; Step 6-2: Select the circle with the largest light intensity in the image obtained in step 2, and record the aperture radius at this time; Step 6-3: Process the images obtained in step 4 and step 5, and then select the images at 0°, 45°, 90°, and 135° for grayscale processing according to the aperture radius obtained in step 6-2, and extract the grayscale value; Step 6-4: Substituting the grayscale value into the Mueller matrix for calculation, obtaining the phase delay and azimuth angle data and image at the measurement point of the silicon wafer sample; Step 6-5: Analyze the data and images, and obtain the stress condition of the silicon wafer sample by analyzing that the principal stress difference of the silicon wafer sample is proportional to the phase delay. The greater the principal stress difference, the greater the stress value.

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