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

Abstract

The application discloses a kind of silicon wafer stress dynamic detection system and method based on vortex wave sheet, including probe light source, reflector, beam expander, collimating lens, polarizer, first convex lens, silicon wafer sample clamping platform, second convex lens, vortex wave sheet, polarizer, third convex lens, CCD, PC machine;The laser output by the probe light source becomes linearly polarized light after being expanded and collimated by polarizer, is converged in the silicon wafer sample clamping platform by convex lens, is clamped at the silicon wafer sample place, is converted into parallel light by second convex lens after transmitting sample and vertically incident vortex wave sheet, then is imaged in the CCD placed behind by polarizer and third convex lens, the obtained data is transmitted to PC machine, is handled using polarization imaging algorithm to obtain phase difference image, obtains its internal stress condition.This application uses vortex wave sheet to obtain silicon wafer internal polarization information, real-time detects silicon wafer internal stress change condition, without manual operation in measurement process, measurement precision is high, simple operation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor wafer stress detection, and particularly relates to a silicon wafer stress dynamic detection system and method based on a vortex wave plate. BACKGROUND

[0002] Silicon is an important material widely used in integrated circuits, solar cells and other fields, so there are various methods for detecting its stress. According to the test principle, the methods can be divided into two categories: destructive measurement and non-destructive measurement. The destructive measurement method includes mechanical and chemical methods, which releases and measures the stress of the workpiece to obtain the residual stress state; the non-destructive measurement method measures the physical properties of the material itself without affecting the subsequent use of the workpiece, and gradually becomes the development direction.

[0003] The photoelastic method mainly uses an optical sensitive material to make a model, which is placed in a polarized light field. After a load is applied, the temporary birefringence phenomenon of the model is observed, and then the full-field topography of the stress wave propagation is obtained. This method has many advantages, such as being able to provide real-time stress distribution images, intuitively showing the stress wave propagation process and rules; without damaging the sample, the integrity of the measured object is not affected; the operation is relatively simple and the cost is low.

[0004] Photoelastic effect, i.e. stress birefringence, the refractive index characteristics of a transparent medium will change when there is stress inside, thus showing optical anisotropy. If the stress is not uniform on the crystal, the birefringence at each place will not be consistent, causing different phase differences at different points of the light wave passing through it. By using the photoelastic effect, the internal stress of optical materials can be tested, and the stress distribution of various mechanical structures can be observed.

[0005] The existing public detection of silicon stress damage mainly focuses on the residual stress field, and the commonly used methods include the Mach-Zehnder interference method and the silicon wafer reflection light polarization stress detection based on the Mueller matrix.

[0006] Among them, the silicon wafer reflection light polarization stress detection method based on the Mueller matrix makes the output continuous laser pass through the beam expander and the polarizer into the beam splitter in turn. The reflected light of the beam splitter is vertically incident into the sample after passing through the wave plate. The reflected light of the sample passes through the wave plate, the beam splitter and the polarizer in turn and finally enters the CCD. The CCD takes the polarization image of the sample and sends it to the PC. After gray processing, Mueller matrix calculation and median filtering, the phase difference image is obtained. This method needs to build three optical axes, and manual rotation of the polarizer is required during measurement, which has errors. This method can only measure the residual stress of the silicon wafer, and cannot measure the stress of the silicon wafer in real time.

[0007] Therefore, a silicon wafer stress detection system is needed to solve the above technical problems. SUMMARY

[0008] The application aims to provide a silicon wafer stress dynamic detection system and method based on a vortex wave plate, which acquires internal polarization information of a silicon wafer by using a vortex wave plate, detects stress changes in the silicon wafer in real time, realizes no manual operation in the measurement process, improves measurement accuracy, and is simple to operate.

[0009] To achieve the object of the application, in one aspect, the application provides a silicon wafer stress dynamic detection system based on a vortex wave plate, which comprises a silicon wafer sample placed in the detection system, laser emitted by a probe light source is reflected by a mirror into a common first optical axis, the size of the light beam is adjusted by a beam expander and a collimator, and then the light beam becomes linearly polarized light after passing through a polarizer, is focused on the silicon wafer sample clamped in a silicon wafer sample clamping platform by a first convex lens, is converted into parallel light by a second convex lens after being transmitted through the silicon wafer sample, and is perpendicularly incident on a vortex wave plate, and then is imaged on a CCD placed behind by a polarizer and a third convex lens 11, and the obtained data is transmitted to a PC, which uses a polarization imaging algorithm to process the data to obtain a phase difference image and acquire internal stress conditions of the silicon wafer sample.

[0010] The common first optical axis is sequentially composed of the beam expander, the collimator, the polarizer, the first convex lens, the silicon wafer sample clamping platform, the second convex lens, the vortex wave plate, the polarizer, the third convex lens, and the CCD.

[0011] The polarization imaging algorithm specifically comprises the following steps: first, processing the image taken by the CCD when no silicon wafer sample, the polarizer and the vortex wave plate are placed, taking the light transmission axis angle 0° of the polarizer as a reference, calibrating 360° in a clockwise direction, selecting a circle with the maximum light intensity in the image, and recording the light circle radius at this time; and then processing the image taken by the CCD when all components are placed, selecting 0°, 45°, 90° and 135° according to the light circle radius, processing the image in terms of gray scale, extracting the gray scale value, substituting the gray scale value into a Mueller matrix for calculation, obtaining the phase delay and azimuth angle data and image of the measurement position of the silicon wafer sample, analyzing the data and image, and obtaining the stress conditions of the silicon wafer sample by analyzing the fact that the principal stress difference of the silicon wafer sample is proportional to the phase delay.

[0012] The probe light source is a fiber laser with a maximum output power of 2W and an output wavelength of 1550nm.

[0013] The silicon wafer sample clamping platform is connected with a two-dimensional moving platform, and the clamped silicon wafer sample is uniformly detected by the probe light by operating the two-dimensional moving platform.

[0014] The laser damage and mechanical pressure stress measures taken on the silicon wafer sample in the detection process of the system do not affect the operation of the probe light path, so that dynamic measurement is realized.

[0015] The area where the silicon wafer sample is located in the silicon wafer sample clamping platform coincides with the focal point of converging light rays of the first convex lens.

[0016] In another aspect, the application also provides a silicon wafer stress dynamic detection method based on a vortex wave plate, comprising the following steps:

[0017] Step 1: temporarily do not put in the silicon wafer sample, the polarizer and the vortex wave plate, turn on the power supply after adjusting the power of the probe light source to the lowest, rotate the polarizer to observe the image in the CCD, and stop when the image light intensity reaches the maximum;

[0018] Step 2: place the vortex wave plate, turn on the probe light source and adjust it to the clear and complete image obtained by the CCD, and record the image light intensity distribution obtained by the CCD at this time;

[0019] Step 3: place the polarizer, remove the vortex wave plate, turn on the probe light source, and adjust the angle of the polarizer so that the image light intensity in the CCD reaches the maximum;

[0020] Step 4: put in all components including the silicon wafer sample, turn on the probe light source, and record the image obtained by the CCD;

[0021] Step 5: adjust the two-dimensional moving platform connected to the silicon wafer sample clamping platform, scan the silicon wafer sample, and record the image taken by the CCD;

[0022] Step 6: process the obtained image on the PC by using the polarization imaging algorithm to obtain the filtered phase difference image;

[0023] Step 6-1: take the polarizer light transmission axis angle of 0° as the reference, and calibrate the image obtained in step 2 by 360° in the clockwise direction;

[0024] Step 6-2: select a circle with the maximum light intensity in the image obtained in step 2, and record the light circle radius at this time;

[0025] Step 6-3: process the images obtained in steps 4 and 5, and then select the images at 0°, 45°, 90° and 135° according to the light circle radius obtained in step 6-2 for gray scale processing and extracting the gray scale values;

[0026] Step 6-4: substitute the gray scale values into the Mueller matrix to calculate the phase delay and azimuth angle data and image at the measurement position of the silicon wafer sample;

[0027] Step 6-5: analyzing the data and images, by analyzing the principal stress difference of the silicon wafer sample being proportional to the phase delay, the stress condition of the silicon wafer sample is obtained, and the greater the principal stress difference is, the greater the stress value is.

[0028] Compared with the prior art, the significant progress of the present application is that the operation of the present application is simple, manual rotation of the polarizer is not required in the operation process, manual error is reduced, the residual stress of the silicon wafer can be measured, the dynamic stress of the silicon wafer can be detected in real time, the experimental precision is improved, and the number of selected data in data processing is increased to improve the experimental precision.

[0029] To more clearly illustrate the functional characteristics and structural parameters of the present application, the following further describes the present application in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings described herein are used to provide further understanding of the present application, constitute a part of the present application, and the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0031] Figure 1 is a schematic diagram of the detection system of the present application.

[0032] In the drawings, the reference signs are: a probe light source 1, a mirror 2, a beam expander 3, a collimator 4, a polarizer 5, a first convex lens 6, a silicon wafer sample clamping platform 7, a second convex lens 8, a vortex wave plate 9, an analyzer 10, a third convex lens 11, a CCD 12, and a PC 13. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] The silicon wafer stress dynamic detection system based on the vortex wave plate of the present application combines the advantages of the vortex wave plate and the silicon wafer stress dynamic detection system, and has the following advantages: Figure 1The system comprises a silicon wafer sample placed in the detection system, a detection light source 1 emits laser light which is reflected by a mirror 2 into a first common optical axis, the size of the light beam is adjusted by a beam expander 3 and a collimator 4, then the light passes through a polarizer 5 and becomes linearly polarized light, and is focused by a first convex lens 6 on the silicon wafer sample clamped in a clamping platform 7, and then the light is converted into parallel light by a second convex lens 8 and vertically incident on a vortex wave plate 9, and then the light is imaged on a CCD 12 placed behind by a polarizer 10 and a third convex lens 11, and the obtained data is transmitted to a PC 13, and the PC 13 processes the data using a polarization imaging algorithm to obtain a phase difference image and obtain the internal stress of the silicon wafer sample.

[0035] The first common optical axis is sequentially formed by the beam expander 3, the collimator 4, the polarizer 5, the first convex lens 6, the silicon wafer sample clamping platform 7, the second convex lens 8, the vortex wave plate 9, the polarizer 10, the third convex lens 11, and the CCD 12.

[0036] The polarization imaging algorithm specifically comprises: first, processing the image taken by the CCD 12 when the silicon wafer sample, the polarizer 10 and the vortex wave plate 9 are not placed, taking the light transmission axis angle of the polarizer 5 as the reference, and calibrating 360° in the clockwise direction, then selecting a circle with the maximum light intensity in the image and recording the light circle radius at this time; then processing the image taken by the CCD 12 when all components are placed, selecting 0°, 45°, 90° and 135° according to the light circle radius, and processing the image in grayscale, and based on this, increasing the selected data according to the required accuracy, extracting the grayscale value, substituting the grayscale value into the Mueller matrix for calculation, obtaining the phase delay and azimuth angle data and image of the measurement position of the silicon wafer sample, analyzing the data and image, and obtaining the stress of the silicon wafer sample by analyzing the fact that the principal stress difference of the silicon wafer sample is proportional to the phase delay.

[0037] The detection light source 1 is an optical fiber laser with a maximum output power of 2W and an output wavelength of 1550nm.

[0038] 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 operating the two-dimensional moving platform.

[0039] The silicon wafer sample is subjected to laser damage and mechanical stress to generate stress during the detection process of the system, which does not affect the operation of the detection light path, and dynamic measurement is realized.

[0040] The area where the silicon wafer sample is located in the silicon wafer sample clamping platform 7 coincides with the focal point of the converging light rays of the first convex lens 6.

[0041] In another aspect, the present application also provides a vortex wave plate based silicon wafer stress dynamic detection method, comprising the following steps:

[0042] Step 1: temporarily do not put in the silicon wafer sample, the polarizer 11, the vortex wave plate 9, turn on the power after adjusting the power of the probe light source 1 to the lowest, rotate the polarizer 5 and observe the image in the CCD 12, stop when the image light intensity reaches the maximum; the operator can judge the maximum light intensity by himself, without being too accurate.

[0043] Step 2: place the vortex wave plate 9, turn on the probe light source 1 and adjust it to the clear and complete image obtained by the CCD, record the image light intensity distribution obtained by the CCD 12 at this time;

[0044] Step 3: place the polarizer 11, remove the vortex wave plate 9, turn on the probe light source 1, 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 accurate.

[0045] Step 4: put in all components including the silicon wafer sample, turn on the probe light source 1 and record the image obtained by the CCD 12;

[0046] Step 5: adjust the two-dimensional moving platform connected with the silicon wafer sample clamping platform 7, scan the silicon wafer sample and record the image taken by the CCD 12;

[0047] Step 6: process the obtained image on the PC 13 by using the polarization imaging algorithm to obtain the filtered phase difference image;

[0048] Step 6-1: take the polarizer light transmission axis angle 0° as the reference, and calibrate the image obtained in step 2 by 360° in the clockwise direction;

[0049] Step 6-2: select a circle with the maximum light intensity in the image obtained in step 2 and record the light circle radius at this time;

[0050] Step 6-3: process the images obtained in steps 4 and 5, then select the 0°, 45°, 90° and 135° images for gray scale processing according to the light circle radius obtained in step 6-2, and increase the selected data according to the required accuracy on this basis to extract the gray scale value;

[0051] Step 6-4: substitute the gray scale value into the Mueller matrix to calculate the phase delay and azimuth angle data and image of the measurement position of the silicon wafer sample;

[0052] Step 6-5: analyzing the data and images, by analyzing the principal stress difference of the silicon wafer sample is proportional to the phase retardation, the stress of the silicon wafer sample is obtained, the greater the principal stress difference, the greater the stress value.

[0053] It should be noted that the relational terms herein, such as first and second, and the like, are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0054] While embodiments of the application have been shown and described, it is to be understood that the application is not limited to the details of the embodiments described, since numerous modifications, changes, substitutions, and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present application, which is defined by the following claims and their equivalents.

Claims

1. A vortex wave plate based silicon wafer stress dynamic detection system, characterized in that, a silicon wafer sample is placed in the detection system, laser emitted by a probe light source (1) is reflected by a mirror (2) into a common first optical axis, the size of the light beam is adjusted by a beam expander (3) and a collimator (4), then the light beam becomes linearly polarized light after passing through a polarizer (5), and the linearly polarized light is focused on the silicon wafer sample clamped in a silicon wafer sample clamping platform (7) by a first convex lens (6), then the light beam is converted into parallel light by a second convex lens (8) and the parallel light is perpendicularly incident on a vortex wave plate (9), then the light beam is imaged on a CCD (12) placed behind by a polarizer (10) and a third convex lens (11), and the data obtained are transmitted to a PC (13), the PC (13) processes the data using a polarization imaging algorithm to obtain a phase difference image and the internal stress of the silicon wafer sample is obtained. 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 clamping platform (7), the second convex lens (8), the vortex wave plate (9), the polarizer (10), the third convex lens (11) and the CCD (12) in sequence.

2. The vortex wave plate based silicon wafer stress dynamic detection system of claim 1, wherein, The polarization imaging algorithm is specifically as follows: first, the image taken by the CCD (12) when no silicon wafer sample, the polarizer (10) and the vortex wave plate (9) are placed is processed, the angle of the transparent axis of the polarizer (5) is taken as the reference, the image is calibrated in the clockwise direction for 360°, then a circle with the maximum light intensity in the image is selected, and the radius of the circle is recorded; then the image taken by the CCD (12) when all the components are placed is processed, the image is processed in terms of the gray scale at 0°, 45°, 90° and 135° according to the radius, the gray scale values are extracted, the gray scale values are substituted into a Mueller matrix for calculation, the phase retardation and azimuth angle data and image of the measurement position of the silicon wafer sample are obtained, the data and image are analyzed, the stress of the silicon wafer sample is obtained by analyzing the fact that the principal stress difference of the silicon wafer sample is proportional to the phase retardation.

3. The vortex wave plate based silicon wafer stress dynamic detection system of claim 1, wherein, The probe light source (1) is a fiber laser, the maximum output power is 2W, and the output wavelength is 1550nm.

4. The vortex wave plate based silicon wafer stress dynamic detection system of claim 1, wherein, The silicon wafer sample clamping platform (7) is connected with a two-dimensional moving platform, and the silicon wafer sample clamped is uniformly detected by operating the two-dimensional moving platform.

5. The vortex-wave-plate based silicon wafer stress dynamic detection system of claim 1, wherein, The silicon wafer sample is subjected to laser damage and mechanical pressure to generate stress during the detection process of the system, and the operation of the probe light path is not affected, so that dynamic measurement is realized.

6. The vortex-wave-plate based silicon wafer stress dynamic detection system of claim 1, wherein, The area where the silicon wafer sample is located in the silicon wafer sample clamping platform (7) coincides with the focal point of the converging light rays of the first convex lens (6).

7. A detection method for implementing the vortex wave-plate based silicon wafer stress dynamic detection system of any one of claims 1-6, characterized in that, The following steps are included: Step 1: do not place a silicon wafer sample, the polarizer (10) and the vortex wave plate (9), turn on the power supply after the power of the probe light source (1) is adjusted to the minimum, rotate the polarizer (5) and observe the image in the CCD (12), and stop when the light intensity of the image reaches the maximum. Step 2: Place the vortex wave plate (9), turn on the probe light source (1) and adjust the image on the CCD to be clear and complete, and record the light intensity distribution of the image on the CCD (12) at this time; Step 3: Place the polarizer (10), remove the vortex wave plate (9), turn on the probe light source (1), and adjust the angle of the polarizer (10) so that the light intensity in the image on the CCD (12) reaches a maximum; Step 4: Place all components including the silicon wafer sample, turn on the probe light source (1), and record the image on the CCD (12); Step 5: Adjust the two-dimensional moving platform connected to the silicon wafer sample clamping platform (7), scan the silicon wafer sample, and record the images taken by the CCD (12); Step 6: Process the obtained images on the PC (13) using the polarization imaging algorithm to obtain the filtered phase difference image.

8. The detection method for implementing the silicon wafer stress dynamic detection system based on vortex wave plate according to claim 7, characterized in that, The specific steps of processing the obtained images on the PC (13) using the polarization imaging algorithm in Step 6 are as follows: Step 6-1: Take the 0° angle of the polarizer transmission axis as the reference, and calibrate the image obtained in Step 2 by 360° in the clockwise direction; Step 6-2: Select a circle with the maximum light intensity from the image obtained in Step 2, and record the radius of the circle at this time; Step 6-3: Process the images obtained in Steps 4 and 5, and then select the images at 0°, 45°, 90°, and 135° according to the circle radius obtained in Step 6-2, and perform grayscale processing to extract the grayscale values; Step 6-4: Substitute the grayscale values into the Mueller matrix to calculate the phase retardation and azimuth angle data and images at the measurement position of the silicon wafer sample; Step 6-5: Analyze the data and images, and through the analysis that the principal stress difference of the silicon wafer sample is proportional to the phase retardation, obtain the stress condition of the silicon wafer sample, and when the principal stress difference is larger, the stress value is larger.

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