A visual measurement film stress laser detection system

Abstract

The application discloses a visual measurement film stress laser detection system, and belongs to the technical field of semiconductor manufacturing and detection. It comprises a laser measurement module, the laser measurement module at least comprising a one-dimensional linear sensor, the laser measurement module being configured to emit laser to the wafer surface and irradiate the laser reflected by the wafer to the one-dimensional linear sensor; a collection end, the collection end being configured to collect the current change of the light curtain at both ends of the one-dimensional linear sensor; a main control end in wireless communication connection with the collection end, the main control end being configured to calculate wafer film stress data according to the current change of the light curtain at both ends of the one-dimensional linear sensor, and generate visual commands according to the wafer film stress data; and sending the visual data to a visual terminal in communication connection with the main control end for real-time display. The application adopts data visualization, and manual selection of different wafer sizes and different film materials is realized through the visual platform, so that one machine is used for multiple purposes.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing and testing technology, and more specifically, relates to a visual laser testing system for measuring thin film stress. Background Technology

[0002] In the entire chip manufacturing process, semiconductor wafers need to be coated with a thin photoresist film before photolithography for light conduction. One common wafer coating process involves placing a drop of photoresist at the center of the wafer and rotating the wafer to use centrifugal force to evenly spray the photoresist onto the wafer surface; another method is to use atomized photoresist spraying to evenly coat the wafer surface with photoresist.

[0003] Regardless of the method used to coat semiconductor wafers, the uniformity of the thin film must be inspected after coating. This uniformity can be measured by assessing the stress value of the wafer's thin film to determine if it meets semiconductor process requirements. This process places high demands on the inspection methods and equipment, requiring a near-zero error rate for defective wafers. This improves chip productivity and reduces the scrap rate of finished products, thereby increasing economic benefits and lowering production costs.

[0004] Traditionally, interferometry is used to detect stress changes in thin films. However, traditional detection methods are cumbersome, have low accuracy, and are expensive, failing to meet modern requirements for improving production efficiency and quality. Summary of the Invention

[0005] 1. The problem to be solved

[0006] To address the problems of cumbersome and inaccurate traditional methods for detecting stress changes in thin films, this invention provides a visual laser detection system for measuring thin film stress. This system utilizes a laser measuring element on a measuring device to measure the radius of curvature of an average distribution point along the diameter of the wafer at any angle, thus obtaining measurement results more quickly. The visualization platform fully displays the stress value, radius of curvature, and bending degree at any point on a horizontal straight line along the diameter of the wafer surface after photolithography, enabling more intuitive and rapid detection of defective wafers.

[0007] 2. Technical Solution

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] A visual laser detection system for measuring thin film stress includes:

[0010] A laser measurement module, comprising at least a one-dimensional linear sensor, wherein the laser measurement module is configured to emit a laser beam toward the wafer surface and irradiate the one-dimensional linear sensor with the laser beam reflected from the wafer.

[0011] The acquisition end is configured to acquire the current change at both ends of the light curtain on the one-dimensional linear sensor;

[0012] The main control terminal is configured to calculate wafer thin film stress data based on the current change at both ends of the light curtain on the one-dimensional linear sensor, and generate visualization commands based on the wafer thin film stress data.

[0013] A visualization terminal is communicatively connected to the main control terminal. The visualization terminal is used to receive visualization commands from the main control terminal and to visualize the wafer thin film stress data.

[0014] The preferred technical solution is as follows:

[0015] The visual measurement thin film stress laser detection system described above also includes a mechanical structure, which includes:

[0016] A base for placing wafers of different sizes, the base being adjustable for horizontal leveling;

[0017] A one-dimensional lead screw carrying platform is fixed above the base and parallel to the base, and the laser measurement module is set on the one-dimensional lead screw carrying platform.

[0018] The visual measurement thin film stress laser detection system described above further includes the following component structure:

[0019] A permanent magnet synchronous motor is connected to a one-dimensional lead screw-driven platform, the permanent magnet synchronous motor being used to drive the one-dimensional lead screw-driven platform to move along a one-dimensional direction;

[0020] Servo drive circuit, used to drive permanent magnet synchronous motor;

[0021] An encoder, coaxially connected to the permanent magnet synchronous motor, is used to collect the current and speed values ​​of the permanent magnet synchronous motor in real time and feed them back to the main control terminal.

[0022] The laser measurement module of the visual measurement thin film stress laser detection system described above includes:

[0023] A laser is used to emit laser light of a certain wavelength and irradiate the surface of a wafer.

[0024] A reflector is used to fold and transmit laser light reflected from the wafer surface;

[0025] Driven by a one-dimensional lead screw platform, the laser moves along the one-dimensional direction of the wafer past the center point. After the laser of a certain wavelength emitted by the laser irradiates the wafer surface, it is reflected by the reflection optical path onto the light curtain of the linear sensor. After receiving the laser, the light curtain of the linear sensor will generate a transverse photoelectric effect, generating an upper current and a lower current at both ends of the light curtain of the linear sensor.

[0026] As described above, in the visual measurement laser detection system for thin film stress, the main control terminal is configured to calculate wafer thin film stress data based on the current changes at both ends of the light curtain on a one-dimensional linear sensor, including:

[0027] The upper and lower currents at both ends of the light curtain on the one-dimensional linear sensor are converted into upper and lower voltages;

[0028] The relative offset of the wafer-reflected laser at the position of the light curtain before and after coating is calculated based on the upper and lower voltage values.

[0029] The radius of curvature of the wafer before and after coating is calculated based on the relative offset of the reflected laser from the wafer at the position of the light curtain before and after coating.

[0030] The wafer thin film stress is calculated based on the radius of curvature of the wafer before and after coating.

[0031] The laser detection system for visually measuring thin film stress, as described above, calculates the relative offset of the wafer-reflected laser at the light curtain position before and after coating based on the upper and lower voltage values ​​using the following formula:

[0032]

[0033] The visualization measurement laser detection system for thin film stress described above calculates the relationship between the wafer's radius of curvature before and after coating based on the relative offset of the reflected laser light from the wafer at the light curtain position before and after coating using the following formula:

[0034]

[0035] In the above formula, the wafer diameter is D, and N is the number of measurement points, i.e., the number of measurement points per step of the one-dimensional loaded guide rail. Let Δd be the relative position value, Δx be the relative offset of the laser on the light curtain, and K be the total path length of the laser irradiation.

[0036] The laser detection system for visually measuring thin film stress, as described above, calculates the wafer thin film stress based on the wafer's radius of curvature before and after coating using the following formula:

[0037]

[0038] The laser detection system for visualizing thin film stress, as described above, further includes the following steps before generating visualization commands based on wafer thin film stress data:

[0039] Based on the wafer thin film stress data, the wafer thin film curvature distribution relationship is established by extending the distribution to the left and right directions from the wafer center point as the warp center.

[0040] The wafer thin film curvature distribution relationship of the laser detection system for visual measurement of thin film stress described above is as follows:

[0041] The relationship between the curvature distribution from the center point of the wafer to the left is as follows:

[0042] The relationship between the rightward curvature distribution from the wafer center point is as follows:

[0043] In the above formula, B represents the curvature of the current point. i-1 R represents the curvature of the previous point, and d represents the distance between two adjacent points on the wafer. i-1 Let be the radius of curvature of the previous point.

[0044] 3. Beneficial effects

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] (1) After the one-dimensional laser carrier platform of the wafer thin film stress measurement device adopts the adaptive stable motion control system, the mechanical vibration of the one-dimensional motion control platform caused by the motor rotation is greatly reduced, the measurement accuracy is improved, the requirements for wafer coating detection are greatly improved, and the chip production quality is also improved, creating conditions for generating smaller process chips.

[0047] (2) This invention is highly practical. There is no domestic design and development of thin film stress measurement devices. Domestic chip factories rely on imports for thin film stress measurement devices. These devices are expensive, have low measurement efficiency, complicated processes, high maintenance costs, and slow machine upgrades, which cannot keep up with the needs of the digital age.

[0048] (3) This invention uses a method of uniformly sampling multiple points along the wafer diameter to calculate the average stress value of the wafer. This method has high measurement efficiency and high accuracy. Furthermore, an error compensation method was designed to compensate for errors caused by the environment and mechanical errors caused by equipment machining, making the measurement results more consistent with the actual theoretical values. Compared with traditional methods, it is more comprehensive.

[0049] (4) The invention uses data visualization, which enables microscopic data to be displayed in charts, making it easier for production process personnel to understand which point on the wafer surface is a defect. Furthermore, the visualization platform allows manual selection of different wafer sizes and different coating materials for measurement, achieving multiple uses in one machine and greatly reducing equipment costs.

[0050] (5) Based on the substrate bending method and the principle of optical lever, this invention is mainly used for the detection of the radius of curvature, curvature and stress of wafers before and after coating. It is also applicable to the radius of curvature and curvature detection of non-coated surfaces of various rigid material substrates that can reflect lasers, as well as the detection of the radius of curvature, curvature and residual film of coated surfaces of various rigid material substrates that can reflect lasers, such as titanium alloy substrates, polished stainless steel substrates, etc. Attached Figure Description

[0051] Figure 1 This is a flowchart of the synchronous motor speed and load current control in this application;

[0052] Figure 2 This is a control flowchart of the visual terminal in this application;

[0053] Figure 3 This is a structural diagram of the wafer thin film stress measurement device of the laser detection system for visual measurement of thin film stress in this application;

[0054] Figure 4 This is a graph showing the wafer thin film curvature in an embodiment of this application.

[0055] Figure 5 This is a graph showing the relative position values ​​of the laser emitted by the one-dimensional linear sensor in the embodiments of this application.

[0056] Figure 6 This is a laser intensity curve diagram from an embodiment of this application;

[0057] In the diagram: 1. One-dimensional load-bearing motion control platform; 2. Base; 3, 4. Limit switches; 5. Reflector; 6. One-dimensional linear sensor; 7. Laser; 8. Permanent magnet synchronous motor; 9. Permanent magnet synchronous motor driver; 10. Main control terminal; 11. Visualization terminal. Detailed Implementation

[0058] The present invention will now be further described with reference to specific embodiments and accompanying drawings.

[0059] The core requirement for wafer thin-film stress measurement is to determine whether the stress is uniform after coating on the wafer surface. Different photolithography processes use different photoresist materials, resulting in different standards for stress measurement. To address these issues, this invention designs a visual laser detection system for measuring thin-film stress that is compatible with multiple wafers of different sizes and applicable to different coating materials. The measurement results are visualized and represented through a visualization platform.

[0060] The above describes the main inventive concept of the present invention. The main inventive concept of the present invention will be specifically described below with reference to embodiments.

[0061] Example 1

[0062] A visual laser measurement system for thin film stress detection includes:

[0063] A laser measurement module, comprising at least a one-dimensional linear sensor 6, wherein the laser measurement module is configured to emit a laser beam toward the wafer surface and irradiate the one-dimensional linear sensor 6 with the laser beam reflected from the wafer.

[0064] In this embodiment, the laser measurement module is fundamental for measuring the stress of the thin film. Specifically, the laser measurement module includes:

[0065] Laser 7 is used to emit laser light of a certain wavelength and irradiate the wafer surface;

[0066] Reflector 5 is used to conduct laser light reflected from the wafer surface;

[0067] Driven by a one-dimensional lead screw platform, the laser 7 moves one-dimensionally along the diameter of the wafer, passing through the center point of the wafer. The laser of a certain wavelength emitted by the laser 7 is nearly perpendicular to the surface of the wafer and is reflected by the reflection optical path onto the light curtain of the linear sensor. After receiving the laser, the light curtain of the linear sensor will generate a photoelectric effect, generating an upper current and a lower current at both ends of the light curtain of the linear sensor.

[0068] The laser wavelength is matched with the thin film material to achieve a better reflection effect. The laser light irradiates the wafer surface and is reflected onto the reflector 5, and then shines onto the one-dimensional linear sensor 6 through the reflector 5, forming a complete measurement optical path.

[0069] The acquisition end is configured to acquire the current change at both ends of the light curtain on the one-dimensional linear sensor 6;

[0070] In order to enable the acquisition end to acquire the current change at both ends of the light curtain on the one-dimensional linear sensor 6, in this embodiment, the one-dimensional linear sensor 6 is connected to a current-to-voltage conversion module, and then the two output voltages are connected to an amplification circuit. The voltage output by the amplification circuit is connected to an analog-to-digital converter module after passing through an addition circuit and a subtraction circuit. Finally, the digital signal is communicated with the main control terminal 10 through the SPI interface (Serial Peripheral Interface).

[0071] The main control terminal 10, which is wirelessly connected to the acquisition terminal, is configured to calculate wafer thin film stress data based on the current change at both ends of the light curtain on the one-dimensional linear sensor 6, and generate visualization commands based on the wafer thin film stress data.

[0072] The main control module consists of a microcontroller, basic power supply circuits, and a clock circuit. The power supply is a switching power supply capable of simultaneously outputting 5V / 1A, ±12V / 1A, and 24V / 4A.

[0073] A visualization terminal 11 is communicatively connected to the main control terminal 10. The visualization terminal 11 is used to receive visualization commands from the main control terminal 10 and to visualize the wafer thin film stress data.

[0074] The visualization terminal 11 mainly runs visualization software on a regular computer. It includes the visualization terminal 11 as a server and establishes a complete user management mechanism, an encrypted database, visualization of the curvature radius of the thin film, visualization of laser light intensity, visualization of thin film stress, visualization of wafer curvature, 3D modeling of thin film stress, visualization of data comparison, etc.

[0075] In this embodiment, the measurement results are obtained more quickly by using the laser measurement element on the measuring device to measure the radius of curvature of the average distribution points of the wafer at any angle along the diameter direction; then, the stress value, radius of curvature, and curvature of any point on the horizontal straight line at any angle along the diameter direction of the wafer surface after photolithography are fully displayed through the visualization platform, so as to detect defective wafers more intuitively and quickly.

[0076] In building the aforementioned visualized laser measurement thin film stress detection system, to ensure compatibility with multiple wafers of different sizes and for rapid detection of thin film stress applicable to different coating materials, this system focuses on the following five aspects: 1. Adaptive stable one-dimensional loaded motion control platform; 2. Calculation of thin film curvature radius, bending degree and stress; 3. Data transmission and data visualization analysis platform; 4. Error compensation; 5. Encryption of measurement equipment and visualization platform.

[0077] For laser measurement modules, to achieve more accurate measurement results, the laser measurement element needs to move uniformly and stably along a one-dimensional direction without vibration. Therefore, this embodiment designs an adaptive stable one-dimensional load-bearing motion control platform 1 capable of adapting to various complex conditions. The adaptive stable one-dimensional load-bearing motion control platform 1 includes a mechanical structure, which includes:

[0078] Base 2, which is used to place wafers of different sizes, such as 6-inch, 8-inch, and 12-inch wafers, and the base 2 can be leveled.

[0079] A one-dimensional lead screw carrying platform is fixed above and parallel to the base 2, and the laser measurement module is set on the one-dimensional lead screw carrying platform.

[0080] It is worth further explaining that, for the adaptive stabilizing one-dimensional load-carrying motion control platform 1, its main function is to ensure the accuracy of the measurement results of the laser measurement module. Based on the above reasons, in this embodiment, the machine structure further includes:

[0081] A permanent magnet synchronous motor 8 is connected to a one-dimensional lead screw carrying platform. The permanent magnet synchronous motor 8 is used to drive the one-dimensional lead screw carrying platform to move along a one-dimensional direction. Two infrared limit switches are installed at the left and right ends of the one-dimensional lead screw carrying platform, namely limit switch 3 and limit switch 4.

[0082] A servo drive circuit is used to drive a permanent magnet synchronous motor 8 to work. The servo drive circuit includes at least one permanent magnet synchronous motor driver 9.

[0083] An encoder coaxially connected to the permanent magnet synchronous motor 8 is used to collect the current and speed values ​​of the permanent magnet synchronous motor 8 in real time and feed them back to the main control terminal 10.

[0084] like Figure 2 As shown, in actual operation, the method for controlling the speed and load current of the permanent magnet synchronous motor 8 is as follows:

[0085] Load current control forms an inner loop feedback, while motor speed forms an outer loop feedback. First, the three-phase currents (A, B, and C) of the permanent magnet synchronous motor 8 are sampled, and the electrical angle is obtained via an encoder. Based on the electrical angle, the three-phase currents are sequentially subjected to Clark and Park transformations, and the error is calculated by comparing this result with the set current value. This error value is then substituted into the current regulator for PI (Proportional-Integral) control, followed by an inverse Park transformation before being input to the motor's three phases via the motor drive. This completes one cycle of load current control. Second, the encoder obtains the motor speed, and after error compensation, the speed is compared with the set speed for error calculation. The error result is then substituted into the speed regulator for PI control, and the calculated result serves as the input for load current control. Combining the inner loop feedback of the load current, a complete speed and load current control is achieved.

[0086] In this embodiment, by real-time multi-level closed-loop control of the speed and load current of the permanent magnet synchronous motor 8, the motor can run stably and smoothly during the start-up and shutdown process and during the process of sudden increase in load, which greatly reduces motor vibration and improves the stability of measurement results.

[0087] Example 2

[0088] The implementation is essentially the same as in Example 1. As can be seen from Example 1, for the main control terminal, it is configured to calculate wafer thin-film stress data based on the current changes at both ends of the light curtain on the one-dimensional linear sensor, and generate visualization commands based on the wafer thin-film stress data. Therefore, for the main control terminal, how to calculate wafer thin-film stress data based on the current changes at both ends of the light curtain on the one-dimensional linear sensor is a technical problem that urgently needs to be solved in this embodiment. Based on this, further, the main control terminal is configured to calculate wafer thin-film stress data based on the current changes at both ends of the light curtain on the one-dimensional linear sensor, including:

[0089] S1. Convert the upper and lower currents at both ends of the light curtain on the one-dimensional linear sensor into upper and lower voltages;

[0090] S2. Calculate the relative offset of the wafer reflected laser at the position of the light curtain before and after coating based on the upper and lower voltage values;

[0091] S3. Calculate the radius of curvature of the wafer before and after coating based on the relative offset of the reflected laser from the wafer at the position of the light curtain before and after coating.

[0092] S4. Calculate the wafer thin film stress based on the radius of curvature of the wafer before and after coating.

[0093] For step S1, in this embodiment, a reference voltage circuit and a bias resistor are first added to both ends of the light curtain to convert the current change at both ends of the light curtain on the one-dimensional linear sensor into upper voltage and lower voltage changes.

[0094] For step S2, the formula for calculating the relative offset of the reflected laser at the light curtain position is derived from the upper and lower voltage values. Specifically, the formula for calculating the relative offset of the reflected laser at the light curtain position before and after coating, based on the upper and lower voltage values, is as follows:

[0095]

[0096] For step S3, based on the relative offset of the wafer's reflected laser at the light curtain position before and after coating, the relationship between the wafer's radius of curvature before and after coating is calculated as follows:

[0097]

[0098] In the above formula, the wafer diameter is D, and N is the number of measurement points, i.e., the number of measurement points per step of the one-dimensional loaded guide rail. Let Δd be the relative position value, Δx be the relative offset of the laser on the light curtain, and K be the total path length of the laser irradiation.

[0099] It is worth noting that, in this embodiment, the principle for calculating the radius of curvature of the wafer before and after coating based on the relative offset of the reflected laser light from the wafer at the position of the light curtain is as follows:

[0100] Using a 6-inch coated wafer as the test sample, with a diameter of D, the entire measurement involves N measurement points, i.e., the one-dimensional loaded guide rail travels for each step. Let Δd be the relative position value, and Δx be the relative offset of the laser on the light curtain. The entire optical path for laser measurement is from the laser emitter illuminating the wafer surface. Because the coated wafer has a reflective radius of curvature, the laser beam, after hitting the wafer, reflects off the mirror used for laser measurement, and then is reflected again by the mirror to the one-dimensional linear sensor. The total path length of the laser irradiation is K, from which the above formula for calculating the average radius of curvature of the fitted wafer can be obtained.

[0101] For step S4, the final result of the wafer thin film stress is to compare the radius of curvature of the wafer before and after coating. According to the Stoney calculation formula, the thin film stress value is:

[0102]

[0103] In this embodiment, the average stress value of the wafer is calculated by uniformly sampling multiple points along the wafer diameter direction. This method offers high measurement efficiency and accuracy. In practical applications, the radius of curvature of the average distribution points along the wafer diameter direction can be measured using a laser measurement element on the measuring equipment, allowing for faster acquisition of measurement results and enhancing practicality.

[0104] Example 3

[0105] The method is essentially the same as in Example 2. To more intuitively understand the unevenness of the wafer surface and visualize it, we need to know the curvature of the wafer film on each acquisition. Therefore, in this embodiment, it further includes:

[0106] Based on the wafer thin film stress data, the wafer thin film curvature distribution relationship is established by extending the distribution to the left and right directions from the wafer center point as the warp center.

[0107] Specifically, it includes:

[0108] The relationship between the curvature distribution from the center point of the wafer to the left is as follows:

[0109] The relationship between the rightward curvature distribution from the wafer center point is as follows:

[0110] In the above formula, B represents the curvature of the current point. i-1 R represents the curvature of the previous point, and d represents the distance between two adjacent points on the wafer. i-1 Let be the radius of curvature of the previous point.

[0111] In this embodiment, by establishing a wafer thin film curvature distribution model, the curvature of the wafer thin film on each wafer can be determined. Furthermore, during data visualization, the visualization platform can not only fully display the stress value and radius of curvature at any point on a horizontal straight line along any angle in the diameter direction of the wafer surface after photolithography, but also visualize the unevenness of the wafer surface through curvature, thereby enabling more intuitive and faster detection of defective wafers.

[0112] Example 4

[0113] This embodiment is essentially the same as Example 3. The difference is that the visualization terminal is divided into two parts: one part is used to handle distributed data transmission and access, and the other part is used for visualization and analysis of measurement data from ordinary computer terminal devices.

[0114] In this embodiment, the distributed data transmission requires multiple computers running visualization platforms to access the measuring equipment simultaneously. After the measuring equipment completes the test, the data can be synchronized to multiple visualization platforms in parallel. At the same time, multiple visualization platforms can also issue measurement commands to the testing equipment simultaneously. The test commands sent between different visualization platforms are independent of each other and will not interfere with each other. The command issued by the previous visualization platform will be executed only after the command issued by the next visualization platform is completed. This realizes one machine for multiple controls. In the production process, it can ensure that multiple operators can control one device at the same time, shorten the machine's idle time during the measurement process, and greatly improve production efficiency.

[0115] More specifically, the flowchart for the visualization and analysis of measurement data from computer terminal devices is as follows: Figure 2 As shown, the system can be divided into several functional parts: system initialization, pre-coating standard wafer measurement, post-coating wafer thin film stress measurement, laser debugging, horizontal debugging, center point position adjustment, visual representation of thin film curvature radius, visual representation of wafer bending degree, visual representation of laser intensity, graphical representation of the relative position of the laser reflected to the one-dimensional position sensor, and graphical representation of measurement results. Before measurement, system initialization is performed, including clearing the device's memory, removing redundant data, and the permanent magnet synchronous motor on the one-dimensional load-bearing motion control platform re-finding the left and right limit positions of the one-dimensional load-bearing motion platform and the wafer center point position, returning to the initial position to await the measurement signal. Before the visualization platform sends the pre-coating standard wafer measurement signal to the measurement device, the "Pre-coating Standard Wafer Measurement Settings" window on the visualization platform sets the wafer substrate thickness, the laser measurement angle along the diameter direction, the wafer size, the number of laser acquisition points, the edge width (excluding the outermost edge of the wafer in the measurement width), and the laser wavelength. Before sending the wafer measurement signal after coating to the measurement equipment via the visualization platform, the coefficients of different coating materials can be selected, etc.

[0116] Example 5

[0117] The results are essentially the same as in Example 4. Error analysis of the visual thin-film stress laser detection system in this application reveals that the errors in thin-film stress measurement mainly originate from two aspects: firstly, the component processing errors of the laser optical measurement element itself; and secondly, the errors in the obtained fitted radius of curvature after wafer thin-film measurement caused by environmental and other uncontrollable factors, which deviate from the theoretically calculated value.

[0118] Regarding the error in the first aspect, this embodiment eliminates it by manually setting error compensation parameters on the visualization terminal. During laser debugging, the relative offset position of the reflection point on the one-dimensional linear sensor and the laser intensity are observed on the visualization terminal. The fixing screws of the laser are then manually adjusted to ensure that the laser is horizontal. The error compensation parameters are then adjusted on the visualization terminal so that when the laser illuminates the exact center of the wafer, the reflection point on the one-dimensional linear sensor is located in the exact center of the light curtain, and the output position deviation value is zero, thus eliminating the component processing error of the laser optical measurement element itself.

[0119] Regarding the second aspect of error, based on Example 4, this example further establishes an error compensation formula after analyzing and comparing the error patterns of the average fitted radius of curvature of the wafer before and after wafer coating relative to the theoretical value:

[0120]

[0121] In the above formula, R&& is the standard theoretical radius of curvature, C2 and C1 are compensation coefficients, R is the radius of curvature at each measurement point, N is the number of measurement points, and K C2 K is the proportionality coefficient. C1 is the integral coefficient.

[0122] This error compensation is applicable to different coating materials and wafers of different sizes, once set up under the same environment. It can control the deviation from the theoretical value within ±1%.

[0123] Example 6

[0124] The results are essentially the same as in Example 5. For the visual measurement thin film stress laser detection system of this application, security must be ensured for both the laser measurement module (as the measuring device) and the visualization terminal, both in controlling the measuring device and in data transmission and interaction between the laser measurement module and the visualization terminal.

[0125] Based on this, this embodiment, building upon embodiment 5, further sets a one-to-one corresponding key in the control process of the measuring device and the data transmission and interaction process between the laser measuring module and the visualization terminal. This key consists of 32 strings encrypted with an encryption algorithm. The encrypted key file is upgraded to the control unit of the measuring device and the system file of the visualization terminal through USB flash drive upgrade and file correction methods. After the measuring device and the visualization terminal are connected, they exchange and parse the key. After both parties confirm that the key is correct, the visualization terminal can control the measuring device and transmit and interact with the measurement data.

[0126] Example 7

[0127] To further illustrate the mechanism of the visual measurement thin film stress laser detection system in this application, this embodiment, based on embodiment 6, provides the workflow of the visual measurement thin film stress laser detection system in embodiment 6.

[0128] The implementation process of the visual measurement thin film stress laser detection system in this embodiment includes the following steps:

[0129] Step 1: Implement encrypted binding between the measurement equipment and the visualization platform. This ensures a one-to-one correspondence between the visualization terminal connected to the industrial LAN and the visualization platform terminal during production, preventing measurement data corruption. It also guarantees network security, preventing unauthorized access to the equipment. Develop software to generate a key and randomly generate administrator usernames and passwords. This software automatically generates a 32-character random key string, encrypts it using an encryption algorithm, and imports the encrypted key and administrator username / password into a USB drive. A corresponding calibration file is also generated.

[0130] Step Two: The visualization platform uses the encrypted upgrade key, administrator username, and password from the USB drive. Its internal decryption algorithm parses the encrypted upgrade file, and a verification file is used to confirm the file's correctness. Finally, the decrypted key is saved to the visualization platform system. The measurement device also reads the encrypted file from the USB drive, decrypts it using its internal algorithm, and saves it to the processor's power-off storage unit. The visualization platform software is then opened. As a client, the software inputs the measurement device's IP address and port to connect to the measurement device, which acts as a server. Upon successful connection, the visualization platform software automatically sends the decrypted key file to the device and compares it with the decrypted key stored in the power-off storage unit of the device's main control chip. If the comparison is successful, the measurement device sends a confirmation signal to the visualization platform. Upon receiving the signal, the visualization platform enters the administrator login interface, where the administrator's username and password are entered to access the main control interface.

[0131] Step 3: Before leaving the factory, the machine undergoes zeroing. Zeroing aims to reposition the permanent magnet synchronous motor on the one-dimensional carrier platform, ensuring the optical measuring element is centered on the wafer during laser debugging, by moving the lead screw on the platform to its left and right limit positions, and during the horizontal leveling of the bottom wafer tray. The permanent magnet synchronous motor drives the optical measuring element along the one-dimensional direction of the carrier platform, starting from the left limit switch and ending at the right limit switch. The number of pulses during the entire motor movement is recorded. The number of motor pulses at the wafer center point is half the total number of pulses. For more accurate centering, the left limit switch on the carrier platform must be vertically aligned with the wafer left position correction port on the base tray, and the right limit switch on the carrier platform must be vertically aligned with the wafer right position correction port on the base tray. Finally, the visualization platform sends clear and initialization commands to remove redundant data from the measurement equipment's storage unit and initialize the equipment settings, putting the machine into a measurement-ready state. Zeroing can also be performed when necessary after handling vibrations or long-term operation.

[0132] Step 4: Before measurement, the laser optical measurement element and the bottom wafer tray platform need to be calibrated to ensure that the laser reflected from the wafer reaches the one-dimensional linear sensor. Calibration involves automatically moving the optical measurement element to the center of the one-dimensional load motion, ensuring the laser accurately hits the center of the wafer. Observe the laser intensity and its relative position on the one-dimensional linear position sensor displayed on the visualization platform. Generally, a laser intensity between 600mV and 3000mV is sufficient, and the relative position value on the one-dimensional linear position sensor should be maintained at 0±0.03mm. After adjustment, move the optical measurement element to both ends of the wafer via the visualization platform, ensuring the laser hits the left and right edges of the wafer. Observe the relative position values ​​of the laser at each end on the one-dimensional linear position sensor. Adjust the horizontal and vertical adjustment screws of the laser fixing element, the reflector fixing element, and the one-dimensional linear sensor fixing element, as well as the horizontal adjustment screw of the bottom wafer tray, until the sum of the relative position values ​​of the laser at each end of the wafer on the one-dimensional linear position sensor is approximately zero. Then repeat the above steps. After repeated adjustments, ensuring the laser illuminates the exact center of the wafer requires that the relative position value of the laser on the one-dimensional linear position sensor remains at 0 ± 0.03 mm, and the sum of the relative position values ​​of the laser on both sides of the wafer on the one-dimensional linear position sensor is approximately 0. Both conditions must be met simultaneously. This equipment is a high-precision measuring device. Considering that the one-dimensional carrier platform cannot guarantee perfect precision in the manufacturing process, error compensation is manually set to offset manufacturing process errors. These errors include mechanical errors from the laser, reflector, and the fixed structure of the one-dimensional linear sensor. Therefore, an error compensation parameter adjustment function is set in the visualization platform. Generally, the structural error compensation is within ±0.015% of the actual value and can be adjusted according to the actual situation.

[0133] Step 5: Perform pre-coating measurement of the wafer. Input the basic thickness and measurement angle of the wafer to begin measurement. When the laser on the optical measurement element, driven by the carrier platform, illuminates the surface of the wafer, it is reflected by a series of optical reflection elements and then illuminates the one-dimensional linear position sensor. Corresponding small currents I1 and I2 are generated at the two ends of the sensor. These are converted into V1 and V2 by an external current-to-voltage circuit. Therefore, the laser intensity is P = V1 + V2. The average fitted radius of curvature of the wafer is:

[0134]

[0135] The curvature distribution of the wafer center at each sampling point, pointing to the left, is as follows:

[0136]

[0137] The formula for the rightward distribution of curvature from the wafer center is:

[0138]

[0139] Based on the above steps, the generated data is automatically saved to the database, and the relevant charts are saved locally. The implementation method for acquiring data points at a certain angle along the diameter direction is as follows: During the laser scanning along the wafer diameter, the analog signal returned from the one-dimensional linear sensor contains noise. Therefore, a Kalman filter is used to filter the data during the analog-to-digital conversion process, filtering out data with significant errors caused by ambient light, dust, and other factors. Generally, for thin film stress measurement, 50 to 2000 data points along the diameter direction are sufficient to reflect the stress distribution along a certain diameter of the wafer. Due to the low yield rate of chip fabrication at the wafer edge, a portion is usually removed, a process called edge trimming. For example, for a 6-inch (150mm) wafer, assuming the edge trimming width is M (mm), when the laser begins to irradiate the wafer surface (when the one-dimensional linear position sensor receives the reflected laser and the laser intensity reaches a certain required value), the motor moves an edge trimming width of M (mm), and then the motor moves... The relative position values ​​of the current sensor laser offset are recorded in a one-dimensional array. This array of length N is a set of relative position values ​​of the sensor laser offset at N points in the diameter direction. Then, it is sent to the visualization platform, substituted into the above formula for calculation, and the final result is obtained.

[0140] Step 6: After the wafer is coated with a specific photolithography film, a second measurement is required. In the visualization platform settings window, set the wafer substrate thickness, number of acquisition points, acquisition angle along the diameter direction, coating thickness, wafer size, wafer edge size, and laser wavelength. Select the corresponding Young's modulus coefficient in the thin film material table. After the measurement, the data obtained is in the same form as in Step 5. Finally, calculate the thin film stress value as shown in Formula (3). Finally, save the results of the two measurements to the database. The database header includes the measurement timestamp, wafer size, wafer substrate thickness, coating thickness, edge width, fitted average radius of curvature, thin film stress value, Young's modulus, laser wavelength, laser intensity, measurement angle along the diameter direction, and the relative position value of the laser reflection at the midpoint of the laser irradiation to the one-dimensional linear sensor. All data is saved in the database. All test result data can be added, deleted, searched, and sorted at will in the database. Data tables can be exported to be compatible with various office viewing tools. Each measurement data should be saved and can be reopened to view the corresponding data chart curves for comparison and contrast testing.

[0141] Step Seven: Theoretical calculations in materials science and optics can obtain the standard radii of curvature of the pre-coated and post-coated wafers. Measurement equipment is required to measure both the pre-coated and post-coated wafers separately. The test results must have an error margin of ±1% compared to the theoretical calculations. However, due to uncontrollable environmental factors in practical engineering applications, such as temperature, humidity, and dust levels in the production environment, compensation is needed for the average fitted radius of curvature of the measured results. The compensation parameters only need to be set once on-site after the machine leaves the factory and do not require further setting. The compensation coefficient of this invention is automatically generated. After inputting the standard theoretical values ​​before and after wafer coating into the visualization platform, steps five and six are repeated. The system automatically calculates the compensation coefficient using a calculation formula. The next round of measurement results will then incorporate the compensation coefficient until the error margin between the measured results and the theoretical calculations is controlled within ±1%. At this point, the compensation coefficient calculation stops, and the final compensation coefficient is stored internally. Subsequent measurement compensation coefficients are used as constants in the measurement results. Because the compensation coefficient used for the average fitted radius of curvature of the wafer before coating is the same as the compensation coefficient after coating, and the difference between the radius of curvature before coating and after coating is large, there is no direct relationship between the two. Therefore, as long as the compensation coefficient is substituted into the results of these two to calculate the average fitted radius, it meets the requirements of the theoretical standard value. The deviation it compensates for is the deviation caused by other uncontrollable environmental factors under the same environment.

[0142] It's worth noting that, since wafers are circular, a notch is cut into each wafer to determine relative positions. The radius from the notch to the center of the wafer is defined as 0 degrees. The aforementioned "an angle along the diameter direction" is relative to this 0 degrees. After measuring the relevant parameters along the diameter direction at various angles, the relevant parameters at any point on the entire wafer surface can be fitted.

[0143] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A visualizing measuring thin film stress laser detection system, characterized in that, The application relates to a wafer thin film stress data acquisition and visualization system. The system comprises: a laser measurement module, which at least comprises a one-dimensional linear sensor, the laser measurement module being configured to emit laser to the wafer surface and irradiate the laser reflected by the wafer onto the one-dimensional linear sensor, and the reflected point on the one-dimensional linear sensor is located at the middle position of the light curtain when the laser is irradiated on the wafer central position point, and the output position deviation value is zero; a collection end, which is configured to collect the current change of the light curtain at both ends of the one-dimensional linear sensor; a main control end, which is configured to calculate wafer thin film stress data according to the current change of the light curtain at both ends of the one-dimensional linear sensor, and generate a visualization command according to the wafer thin film stress data; a visualization terminal in communication connection with the main control end, which is used for receiving the visualization command of the main control end and visualizing the wafer thin film stress data; Before the visualization command is generated according to the wafer thin film stress data, the system further comprises: establishing a wafer thin film bending degree distribution relationship according to the wafer thin film stress data, taking the wafer center point as the warping center and extending to the left and right directions of the center point; The distribution relationship of the left bending degree of the wafer center point is as follows: ; The distribution relationship of the right bending degree of the wafer center point is as follows: ; In the above formula, B is the bending degree of the current point, is the bending degree of the previous point, d is the distance between two adjacent points on the wafer, is the radius of curvature of the previous point; the wafer thin film bending degree distribution relationship is: calculating the wafer thin film stress data further comprises: calculating the wafer thin film stress according to the curvature radii of the wafers before and after coating, wherein, is the standard theoretical radius of curvature, , is a compensation factor, R is the radius of curvature of each measurement point, N is the number of measurement points, is a proportionality factor, is an integration factor; the compensation relationship formula is: the main control end is configured to calculate the wafer thin film stress data according to the current change of the light curtain at both ends of the one-dimensional linear sensor, which comprises: converting the upper current and the lower current of the light curtain at both ends of the one-dimensional linear sensor into upper voltage and lower voltage; calculating the relative offset of the reflected laser of the wafers before and after coating in the light curtain position according to the upper voltage and the lower voltage; calculating the curvature radii of the wafers before and after coating according to the relative offset of the reflected laser of the wafers before and after coating in the light curtain position; calculating the wafer thin film stress according to the curvature radii of the wafers before and after coating; ； the calculation formula for calculating the relative offset of the reflected laser of the wafers before and after coating in the light curtain position according to the upper voltage and the lower voltage is: ； In the above formula, the wafer diameter is D, N is the number of measurement points, i.e. each time the one-dimensional belt track is moved is the relative position value Δd, the relative offset of the laser on the light curtain is Δx, and the path length of the entire laser irradiation is the optical path K.

2. The visualizing measuring thin film stress laser detection system according to claim 1, wherein, the relationship formula for calculating the curvature radii of the wafers before and after coating according to the relative offset of the reflected laser of the wafers before and after coating in the light curtain position is: the system further comprises a mechanical structure, which comprises: a base, which is used for placing wafers of different sizes, and the base can be horizontally leveled; 3. The visualizing measuring thin film stress laser detection system of claim 2, wherein, a one-dimensional lead screw belt platform fixed above the base and parallel to the base, and the laser measurement module is arranged on the one-dimensional lead screw belt platform. The mechanical structure further comprises: a permanent magnet synchronous motor connected with the one-dimensional lead screw belt platform, which is used for driving the one-dimensional lead screw belt platform to move in a one-dimensional direction; a servo drive circuit, which is used for driving the permanent magnet synchronous motor to work; 4. The visualizing measuring thin film stress laser detection system of claim 1, wherein, an encoder coaxially connected with the permanent magnet synchronous motor, which is used for collecting the current value and the speed value of the permanent magnet synchronous motor in real time and feeding back to the main control end. The laser measurement module comprises: a laser, which is used for emitting laser of a certain wavelength and irradiating to the wafer surface; a reflector, which is used for folding and guiding the laser reflected by the wafer surface to form a light path; The laser is driven by a one-dimensional rod belt platform to move along the center point of the wafer in the wafer diameter direction, and after the laser of a certain wavelength emitted by the laser irradiates the wafer surface, it is reflected to the light curtain of the linear sensor through the reflection light path, and the light curtain of the linear sensor will produce transverse photoelectric effect after receiving the laser, and upper current and lower current are generated at both ends of the light curtain of the linear sensor.

5. The visualizing measuring thin film stress laser detection system of claim 1, wherein, According to the curvature radius of the wafer before and after coating, the relationship formula for calculating the wafer film stress is: 。

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