CN114252185B - Device and method for detecting polarization stress of silicon wafer reflected light based on Mueller matrix - Google Patents

Abstract

The present invention discloses a silicon chip reflected light polarization stress detection device and method based on Mueller matrix, which comprises a continuous laser, a beam expander, a polarizer, a beam splitter 1/4 wave plate, a CCD, a two-dimensional translation stage, and a PC. The laser is a 1550nm continuous laser, and the output continuous laser enters the beam splitter through the beam expander and the polarizer in turn. 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, the beam splitter and the polarizer in turn and finally enters the CCD. The CCD takes a sample polarization image and sends it to the PC, and performs grayscale processing, Mueller matrix calculation, and median filtering to obtain a phase difference image. According to the phase difference image after analysis filtering, the stress condition inside the sample is analyzed.

Description

Silicon wafer reflected light polarization stress detection device and method based on Mueller matrix

Technical Field

The present invention belongs to the field of semiconductor wafer stress detection, and in particular to a silicon wafer reflected light polarization stress detection device and method based on a Mueller matrix.

Background Art

In polarized light stress measurement, polarized light imaging is used to obtain the polarization characteristic image of the object by extracting the polarization information of the light beam after interacting with the material. It records more information than simple intensity imaging and can provide various characteristics of the target, such as stress size distribution, stress direction distribution, refractive index, surface roughness, etc. In the field of optics, the polarization characteristics of light waves are mainly described based on the Stokes vector and the Muller matrix. The Stokes vector is a four-dimensional vector that can describe the intensity and polarization state of a light wave. When polarized light is incident on a polarization device, its polarization state will change, and the polarization transformation characteristics of the polarization device can be described by a 4×4 matrix, called the Muller matrix. The transformation characteristics of each polarizer for polarized light can be represented by a Muller matrix.

However, the measurement of the magnitude and distribution of crystal stress in optical materials usually involves studying the relationship between glass stress and birefringence optical path difference. However, silicon crystals have the property of optical isotropy. When monochromatic light passes through them, the speed of light has nothing to do with its propagation direction and the polarization plane of the light wave, and birefringence does not occur. When stress exists in the silicon wafer, the density and crystal structure of the silicon wafer at the stress-bearing part change, and the isotropic silicon wafer becomes anisotropic optically. When polarized light enters the stressed silicon wafer, stress birefringence occurs.

Among the existing public detection methods for silicon stress damage and residual stress, the most commonly used ones mainly include Mach-Zehnder interferometry and infrared photoelasticity.

The Mach-Zehnder interferometry method uses a high-speed camera to receive the interference fringes generated during the measurement. Based on the change in the interference fringes when the laser is applied at different times and combined with the relevant knowledge of physical optics, the overall deformation of the silicon material is calculated. The strain in each direction of the silicon material can be obtained through the overall deformation of the silicon material, and finally the stress in each direction of the silicon material can be obtained from the relationship between stress and strain. However, this method cannot accurately calibrate the three lattice directions of the silicon lattice in the experiment, and when measuring the degree of the interference fringe deformation over the fringes, the decimal part is an estimated value, and its measurement result will directly affect the experimental results and cause experimental errors.

Infrared photoelastic method is to draw distribution curves of isotropic and isoclinic parameters from infrared photoelastic images of various parameters, and finally quantitatively describe the stress distribution in silicon after data processing and calculation. However, this method is complicated, inefficient and has limited accuracy.

Among the currently disclosed silicon wafer stress detection devices, there is no device that uses the polarization image of polarized light reflected by the silicon wafer to detect the polarization information of silicon wafer stress.

Summary of the invention

The purpose of the present invention is to provide a silicon wafer reflected light polarization stress detection device and method based on the Mueller matrix, which can use polarization information to detect the internal stress size and distribution of the silicon wafer, with simple operation process, high experimental accuracy and high reliability.

The technical solution to realize the present invention is: a silicon wafer reflected light polarization stress detection device based on Mueller matrix, including a continuous laser, a beam expander lens, a first polarizer, a beam splitter, a quarter wave plate, a two-dimensional translation stage, a second polarizer, a CCD, and a PC; the continuous laser, the beam expander lens, the first polarizer, and the beam splitter are arranged in sequence along the first optical axis, the reflected light path of the beam splitter is the second optical axis, the quarter wave plate and the two-dimensional translation stage are arranged in sequence along the second optical axis, a silicon wafer sample is placed on the two-dimensional translation stage, the transmitted light path of the beam splitter is the third optical axis, and the second polarizer is arranged in sequence along the third optical axis. The PC is electrically connected to the CCD; the continuous laser output laser is converted into linear polarized light after passing through the beam expander lens and the first polarizer in sequence, and enters the beam splitter. After being reflected by the beam splitter and entering the 1/4 wave plate to become right-handed circularly polarized light, it is emitted to the silicon wafer sample located on the two-dimensional translation stage. The two-dimensional translation stage moves row by row and column by column in the two-dimensional direction. After being reflected by the silicon wafer sample, the light beam carrying the surface information of the silicon wafer sample passes through the 1/4 wave plate, the beam splitter, and the second polarizer in sequence, and is received by the target surface of the CCD to obtain a polarized image. The CCD transmits the collected image to the PC for processing.

A detection method of a silicon wafer reflected light polarization stress detection device based on a Mueller matrix comprises the following steps:

Step 1: Do not place the quarter wave plate yet, adjust the angles of the first polarizer and the second polarizer so that the transmission axes of the first polarizer and the second polarizer are parallel and the field of view is the brightest.

Step 2: Place a quarter wave plate and rotate it so that the optical axis of the quarter wave plate forms an angle of 45° with the transmission axis of the first polarizer. At this time, the outgoing light passing through the quarter wave plate is circularly polarized light.

Step 3: Adjust the beam splitter so that the light beam is incident vertically on the silicon wafer sample.

Step 4: Use the two-dimensional translation stage to perform matrix movement until the CCD completes scanning and detection of the silicon wafer sample.

Step 5: The CCD acquires the polarization image of the silicon wafer sample and obtains a 0° image.

Step 6: Rotate the second polarizer 45° clockwise and return the two-dimensional translation stage to its initial position.

Step 7: Repeat steps 4, 5, and 6 three times to obtain a 45° image, a 90° image, and a 135° image, respectively.

Step 8: The PC processes the polarization image of the silicon wafer sample to obtain a filtered phase difference image.

Compared with the prior art, the present invention has the following significant advantages: simple operation process, high reliability, no need for manual estimation of measurement values when acquiring data, thereby affecting the experimental accuracy, and no need to calibrate the lattice direction of the silicon wafer during detection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a silicon wafer reflected light polarization stress detection device based on a Mueller matrix according to the present invention.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; "connection" can be a mechanical connection or an electrical connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

The following will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention in combination with this design example.

In conjunction with FIG1 , the silicon wafer reflected light polarization stress detection device based on the Mueller matrix of the present invention comprises a continuous laser 1, a beam expander lens 2, a first polarizer 3, a beam splitter 4, a quarter wave plate 5, a two-dimensional translation stage 6, a second polarizer 8, a CCD 9, and a PC 10. The continuous laser 1, the beam expander lens 2, the first polarizer 3, and the beam splitter 4 are sequentially arranged along the first optical axis, the reflection light path of the beam splitter 4 is the second optical axis, the quarter wave plate 5 and the two-dimensional translation stage 6 are sequentially arranged along the second optical axis, a silicon wafer sample 7 is placed on the two-dimensional translation stage 6, the transmission light path of the beam splitter 4 is the third optical axis, the second polarizer 8 and the CCD 9 are sequentially arranged along the third optical axis, and the PC 10 is electrically connected to the CCD 9. The laser outputted by the continuous laser 1 passes through the beam expander lens 2 and the first polarizer 3 in sequence, enters the beam splitter 4, is reflected by the beam splitter 4 into the quarter wave plate 5, and is projected onto the silicon wafer sample 7. After being reflected by the silicon wafer sample 7, the light beam carrying the surface information of the silicon wafer sample 7 passes through the 1/4 wave plate 5, the beam splitter 4, and the second polarizer 8 in sequence, and is received by the target surface of CCD9. CCD9 transmits the collected image to the PC 10.

The continuous laser 1 is a single-mode laser with a maximum output power of 2W and an output wavelength of 1550nm. The light beam is output after passing through the beam expander lens 2, and its spot diameter is greater than 8mm. The beam after expansion is converted into linear polarized light through the first polarizer 3, and the modulated linear polarized light is incident on the beam splitter 4 and the 1/4 wave plate 5. The output beam through the 1/4 wave plate 5 is converted into right-handed circularly polarized light, and the polarized light is vertically incident on the silicon wafer sample 7. The silicon wafer sample 7 is placed on the two-dimensional translation stage 6, and the two-dimensional translation stage 6 moves row by row and column by column in the two-dimensional direction. After being reflected by the silicon wafer sample 7, the reflected light passes through the 1/4 wave plate 5, the beam splitter 4, the second polarizer 8, and the CCD9 in turn, and the polarization image is captured by the CCD9 to obtain the polarization information. The PC 10 is responsible for collecting and processing image data.

The present invention provides a detection method for a silicon wafer reflected light polarization stress detection device based on a Mueller matrix, comprising the following steps:

Step 1: Do not place the quarter wave plate 5 for the time being, adjust the angles of the first polarizer 3 and the second polarizer 8 so that the transmission axes of the first polarizer 3 and the second polarizer 8 are parallel and the field of view is the brightest.

Step 2: Place the 1/4 wave plate 5 and rotate the 1/4 wave plate 5 so that the optical axis direction of the 1/4 wave plate 5 forms an angle of 45° with the light transmission axis of the first polarizer 3. At this time, the outgoing light passing through the 1/4 wave plate 5 is circularly polarized light.

Step 3: Adjust the beam splitter 4 so that the light beam is incident vertically on the silicon wafer sample 7.

Step 4: Use the two-dimensional translation stage 6 to perform matrix movement until the CCD 9 completes scanning and detection of the silicon wafer sample 7.

Step 5: CCD9 acquires the polarization image of the silicon wafer sample 7 and obtains a 0° image.

Step 6: Rotate the second polarizer 8 clockwise by 45° and return the two-dimensional translation stage 6 to its initial position.

Step 7: Repeat steps 4, 5, and 6 three times to obtain a 45° image, a 90° image, and a 135° image, respectively.

Step 8: The PC 10 processes the polarization image of the silicon wafer sample 7 to obtain a filtered phase difference image, as follows:

Step 8-1: grayscale the 0° image, 45° image, 90° image, and 135° image to obtain grayscale data of each image.

Step 8-2: The grayscale data of the image represent the polarization image information at 0°, 45°, 90°, and 135° respectively. Substitute them into the Mueller matrix for calculation to obtain the phase difference image of silicon wafer sample 7.

Step 8-3: Perform median filtering on the phase difference image of the silicon wafer sample 7 to obtain a filtered phase difference image.

Step 8-4: Analyze the filtered phase difference image. The larger the phase difference value is, the greater the stress value of the silicon wafer sample 7 is. Otherwise, the stress value is smaller.

Claims (5)

1. A silicon wafer reflected light polarization stress detection device based on Mueller matrix, characterized in that it comprises a continuous laser (1), a beam expander lens (2), a first polarizer (3), a beam splitter (4), a quarter wave plate (5), a two-dimensional translation stage (6), a second polarizer (8), a CCD (9), and a PC (10); the continuous laser (1), the beam expander lens (2), the first polarizer (3), and the beam splitter (4) are arranged in sequence along a first optical axis, the reflected light path of the beam splitter (4) is a second optical axis, the quarter wave plate (5) and the two-dimensional translation stage (6) are arranged in sequence along the second optical axis, a silicon wafer sample (7) is placed on the two-dimensional translation stage (6), the transmitted light path of the beam splitter (4) is a third optical axis, the second polarizer (8), the CCD (9) and the PC (10) are arranged in sequence along the third optical axis The CD (9) and the PC (10) are electrically connected to the CCD (9); the laser outputted by the continuous laser (1) is successively converted into linear polarized light after passing through a beam expander lens (2) and a first polarizer (3), and enters a beam splitter (4). After being reflected by the beam splitter (4) and entering a quarter wave plate (5) to be converted into right-handed circularly polarized light, the light is irradiated onto a silicon wafer sample (7) located on a two-dimensional translation stage (6). The two-dimensional translation stage (6) moves row by row and column by column in a two-dimensional direction, and after being reflected by the silicon wafer sample (7), a light beam carrying the surface information of the silicon wafer sample (7) passes through the quarter wave plate (5), the beam splitter (4) and the second polarizer (8) in sequence, and is then received by the target surface of the CCD (9) to obtain a polarized image. The CCD (9) transmits the collected image to the PC (10) for processing. 2. The silicon wafer reflected light polarization stress detection device based on the Mueller matrix according to claim 1 is characterized in that the continuous laser (1) is a single-mode laser with a maximum output power of 2W and an output wavelength of 1550nm. 3. The silicon wafer reflected light polarization stress detection device based on the Mueller matrix according to claim 1 is characterized in that: the light beam is output after passing through the beam expander lens (2), and its spot diameter is greater than 8 mm. 4. A detection method for a silicon wafer reflected light polarization stress detection device based on a Mueller matrix according to any one of claims 1 to 3, characterized in that it comprises the following steps: Step 1: temporarily do not place the quarter wave plate (5), adjust the angles of the first polarizer (3) and the second polarizer (8) so that the transmission axes of the first polarizer (3) and the second polarizer (8) are parallel and the field of view is the brightest; Step 2: placing a quarter wave plate (5), and rotating the quarter wave plate (5) so that the optical axis direction of the quarter wave plate (5) forms an angle of 45° with the light transmission axis of the first polarizer (3), and at this time, the outgoing light passing through the quarter wave plate (5) is circularly polarized light; Step 3: Adjust the beam splitter (4) so that the light beam is incident vertically onto the silicon wafer sample (7); Step 4: Using the two-dimensional translation stage (6) to perform matrix movement until the CCD (9) completes scanning and detection of the silicon wafer sample (7); Step 5: The CCD (9) acquires a polarization image of the silicon wafer sample (7) to obtain a 0° image; Step 6: Rotate the second polarizer (8) clockwise by 45° and return the two-dimensional translation stage (6) to its initial position; Step 7: Repeat steps 4, 5, and 6 three times to obtain a 45° image, a 90° image, and a 135° image respectively; Step 8: The PC (10) processes the polarization image of the silicon wafer sample (7) to obtain a filtered phase difference image. 5. The detection method of the silicon wafer reflected light polarization stress detection device based on the Mueller matrix according to claim 4 is characterized in that in step 8, the PC (10) processes the polarization image of the silicon wafer sample (7) to obtain a filtered phase difference image, which is specifically as follows: Step 8-1: grayscale processing is performed on the 0° image, the 45° image, the 90° image, and the 135° image to obtain grayscale data of each image; Step 8-2: The grayscale data of the image represent the polarization image information at 0°, 45°, 90°, and 135° respectively, and they are substituted into the Mueller matrix for calculation to obtain the phase difference image of the silicon wafer sample (7); Step 8-3: performing median filtering on the phase difference image of the silicon wafer sample (7) to obtain a filtered phase difference image; Step 8-4: Analyze the filtered phase difference image. The larger the phase difference value is, the greater the stress value of the silicon wafer sample (7); otherwise, the smaller it is.