Wafer polishing laser interference closed-loop pressure control method

Abstract

The invention discloses a wafer polishing laser interference closed-loop pressure control method, and relates to the technical field of semiconductor manufacturing, and the method comprises the following steps: S1, triggering an automatic measurement program after a ceramic plate and a wafer are overturned; s2, driving a laser interference measuring head to perform non-contact scanning on T2 / T4 point positions of the wafer through a six-axis mechanical arm positioning system to obtain thickness distribution data; s3, fitting the thickness distribution data by adopting a Zernike polynomial to generate a three-dimensional distribution diagram, and calculating a pressure correction amount based on a process dynamic model and a pressure prediction model constructed by a support vector machine regression algorithm; s4, detecting a data outlier in real time through an exception handling module, and triggering an equipment protection strategy when the deviation exceeds a set threshold value; and S5, a pressure control instruction is transmitted to the polishing head through the PROFINET bus by means of the PLC. Through non-contact laser interference measurement, the laser interference technology is applied to thickness detection of the polished wafer for the first time, the single measurement time is shorter than 20 seconds, and the detection efficiency is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a wafer polishing laser interference closed-loop pressure control method. Background Art

[0002] Wafer polishing refers to the process of removing unevenness, flaws, and impurities from the surface of silicon wafers through mechanical grinding and chemical action, making the wafer surface flat, smooth, and defect-free. Wafer polishing is a very important surface treatment process in semiconductor manufacturing and is commonly used in the manufacture of chips, LEDs, and solar cells. The main purpose of wafer polishing is to ensure the flatness of the wafer surface to meet the needs of manufacturing high-precision chips. In the chip manufacturing process, especially in the photolithography process, the wafer surface must be extremely flat. As the chip process continues to shrink, the imaging resolution requirements of the photolithography machine are getting higher and higher, and the depth of focus is reduced. The undulations on the wafer surface must be within the depth of focus to ensure the clarity of the photolithography image. The existing technology has the following problems:

[0003] In traditional wafer polishing processes, thickness detection relies on manual measurement of T2 / T4 point data using a micrometer and manual calculation to adjust equipment pressure parameters. This method has the following problems:

[0004] 1. Response delay: Each adjustment takes 5 to 10 minutes, resulting in low process efficiency;

[0005] 2. Risk of human error: The deviation rate of ±0.5μm exceeds 15%, affecting product consistency;

[0006] 3. Low equipment utilization rate: Downtime adjustment time accounts for 8% to 12%, resulting in serious waste of resources.

[0007] The above problems result in high cost and low precision of wafer polishing process, which makes it difficult to meet the needs of high-precision semiconductor manufacturing. Summary of the Invention

[0008] The present invention provides a wafer polishing laser interference closed-loop pressure control method to solve the problems raised in the above background technology.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A wafer polishing laser interference closed-loop pressure control method comprises the following steps:

[0011] S1: Automatic measurement procedure is triggered after the ceramic plate and wafer are flipped;

[0012] S2: The six-axis robotic arm positioning system drives the laser interferometer measurement head to perform non-contact scanning of the wafer T2 / T4 points to obtain thickness distribution data;

[0013] S3: using a Zernike polynomial to fit the thickness distribution data to generate a three-dimensional distribution graph, and calculating a pressure correction amount based on a pressure prediction model constructed based on a process dynamics model and a support vector machine regression algorithm;

[0014] S4: Detect data outliers in real time through the exception handling module, and trigger device protection strategies when the deviation exceeds the set threshold;

[0015] S5: Transmit pressure control instructions to the polishing head via the PLC controller via the PROFINET bus;

[0016] S6: The polishing head performs pressure adjustment and feeds back a confirmation signal. The process parameters and adjustment status are displayed in real time through the industrial-grade HMI interactive terminal, completing closed-loop control.

[0017] A further improvement of the technical solution of the present invention is that the laser interferometer measuring head adopts the Michelson interference principle, has a measurement accuracy of ±0.1μm, a single non-contact scanning time of less than 20 seconds, and a scanning range covering 20% to 80% of the wafer diameter.

[0018] A further improvement of the technical solution of the present invention is that the six-axis robotic arm positioning system is driven by a servo motor and equipped with a grating scale feedback device, with a positioning accuracy of ±0.05mm, which can realize the posture adjustment of the measuring head within the tilt range of ±1° on the wafer surface.

[0019] A further improvement of the technical solution of the present invention is that the pressure prediction model is trained on 1,000 sets of historical process parameters and corresponding thickness data through a support vector machine regression algorithm. The process parameters include polishing pressure, rotation speed, and slurry concentration. The radial basis function is used as the kernel function, and the parameters are optimized to make the prediction error less than ±0.15μm.

[0020] A further improvement of the technical solution of the present invention is that the abnormality handling module adopts the 3σ principle to detect data outliers. When the deviation between the measured thickness and the predicted thickness exceeds ±0.1μm, the polishing head pressure locking mechanism is automatically triggered, and an audible and visual alarm is issued through the HMI terminal.

[0021] A further improvement of the technical solution of the present invention is that the PLC controller and the polishing head communicate in real time via PROFINETIO, adopting IRT mode, with instruction transmission delay less than 50ms, communication cycle of 1ms, and supporting data verification and retransmission mechanism.

[0022] A further improvement of the technical solution of the present invention is that the industrial-grade HMI interactive terminal is equipped with a 10.1-inch touch screen, which displays the laser measurement three-dimensional cloud map, pressure correction curve and equipment OEE in real time, and supports historical data query and process parameter recipe storage functions.

[0023] A further improvement of the technical solution of the present invention is that the Zernike polynomial fitting algorithm uses a 36th-order polynomial, the fitting error of the wafer thickness data is less than 0.08 μm, and local thickness abnormal areas with a diameter greater than 50 μm can be identified.

[0024] Due to the adoption of the above technical solution, the present invention has the following technical advancements compared to the prior art:

[0025] 1. The present invention provides a closed-loop pressure control method for wafer polishing laser interference. Through non-contact laser interferometry measurement, laser interferometry technology is applied to the thickness detection of polished wafers for the first time. The single measurement time is less than 20 seconds, which significantly improves the detection efficiency.

[0026] 2. The present invention provides a closed-loop pressure control method for wafer polishing laser interference. Through an adaptive pressure control algorithm and based on a process dynamics model, the pressure correction amount is calculated in real time, the thickness uniformity is improved by 35%, the laser interference measurement accuracy reaches ±0.1μm, and the deviation rate is reduced to <5%, achieving high-precision detection.

[0027] 3. The present invention provides a wafer polishing laser interference closed-loop pressure control method, which uses digital twin pre-optimization: using the support vector machine regression algorithm to build a pressure prediction model, optimize process parameters, reduce manual intervention by more than 90%, and realize full-process closed-loop control from detection to pressure adjustment, thereby improving equipment utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0029] The present invention is described in further detail below in conjunction with the embodiments:

[0030] Example 1

[0031] like Figure 1 As shown, the present invention provides a wafer polishing laser interference closed-loop pressure control method, comprising the following steps:

[0032] S1: Automatic measurement procedure is triggered after the ceramic plate and wafer are flipped;

[0033] S2: The six-axis robotic arm positioning system drives the laser interferometer measurement head to perform non-contact scanning of the wafer T2 / T4 points to obtain thickness distribution data;

[0034] S3: using a Zernike polynomial to fit the thickness distribution data to generate a three-dimensional distribution graph, and calculating a pressure correction amount based on a pressure prediction model constructed based on a process dynamics model and a support vector machine regression algorithm;

[0035] S4: Detect data outliers in real time through the exception handling module, and trigger device protection strategies when the deviation exceeds the set threshold;

[0036] S5: Transmit pressure control instructions to the polishing head via the PLC controller via the PROFINET bus;

[0037] S6: The polishing head performs pressure adjustment and feeds back a confirmation signal. The process parameters and adjustment status are displayed in real time through the industrial-grade HMI interactive terminal, completing closed-loop control.

[0038] Example 2

[0039] like Figure 1 As shown, based on Example 1, the present invention provides a technical solution: Preferably, the laser interferometer measuring head adopts the Michelson interference principle, the measurement accuracy is ±0.1μm, the single non-contact scanning time is less than 20 seconds, and the scanning range covers 20% to 80% of the wafer diameter. The six-axis robotic arm positioning system is driven by a servo motor and equipped with a grating scale feedback device, with a positioning accuracy of ±0.05mm, which can realize the posture adjustment of the measuring head within the tilt range of ±1° on the wafer surface.

[0040] In this embodiment, the laser interferometer measurement head has a built-in semiconductor laser with a wavelength of 635nm±5nm, a beam splitter prism, and a charge-coupled device detector. The measuring light path passes through a collimating lens to form a light spot with a diameter of 0.1mm, ensuring that the wafer surface is not damaged during non-contact measurement. Through a temperature compensation algorithm with a compensation range of 20℃±5℃ and an optical path calibration mechanism, a thickness measurement accuracy of ±0.1μm is achieved. The single scanning time is ≤18 seconds, and the scanning area covers a circular area of 25% to 75% of the wafer diameter.

[0041] Example 3

[0042] like Figure 1 As shown, on the basis of Example 1, the present invention provides a technical solution: preferably, the pressure prediction model is trained on 1000 sets of historical process parameters and corresponding thickness data through a support vector machine regression algorithm. The process parameters include polishing pressure, rotation speed, and slurry concentration. The radial basis function is used as the kernel function, and the parameters are optimized to make the prediction error less than ±0.15μm. The abnormality processing module adopts the 3σ principle to detect data outliers. When the deviation between the measured thickness and the predicted thickness exceeds ±0.1μm, the polishing head pressure locking mechanism is automatically triggered, and an audible and visual alarm is issued through the HMI terminal. The PLC controller and the polishing head communicate in real time through PROFINETIO, adopting the IRT mode, the command transmission delay is less than 50ms, the communication cycle is 1ms, and the data verification and retransmission mechanism is supported.

[0043] In this embodiment, historical process data includes parameters such as polishing pressure of 1 to 5 bar, rotation speed of 50 to 200 rpm, and slurry concentration of 5% to 15%. The kernel function is a radial basis function with parameter γ = 0.5 and penalty factor C = 10. Based on the process dynamics model, the pressure correction is calculated in real time with a correction step of 0.05 bar to ensure that the thickness uniformity is improved by ≥ 35%. At the same time, after the exception handling module is triggered, the system automatically performs the following operations: the polishing head pressure is locked to the current value ± 5%; the HMI terminal issues an audible and visual alarm, which includes an 85dB buzzer and a red warning light; and an exception log is generated, including timestamps, deviation data, and device status. PLC controller: A Siemens S7-1500 series PLC is selected, equipped with a PROFINETIO controller module, supporting IRT communication mode, command transmission delay ≤ 40ms, PROFINET communication uses a 1ms cycle synchronization mechanism, and a data transmission rate of 100Mbps. Redundant power supplies and shielded cables are used to ensure communication anti-interference.

[0044] Example 4

[0045] like Figure 1 As shown, based on Example 1, the present invention provides a technical solution: preferably, the industrial-grade HMI interactive terminal is equipped with a 10.1-inch touch screen, which displays the laser measurement three-dimensional cloud map, pressure correction curve and equipment OEE in real time, supports historical data query and process parameter recipe storage functions, and the Zernike polynomial fitting algorithm uses a 36th-order polynomial. The fitting error of the wafer thickness data is less than 0.08μm, and the local thickness abnormal area with a diameter greater than 50μm can be identified.

[0046] In this embodiment, the Zernike polynomial fitting algorithm fits the data of 200×200 sampling points on the wafer surface, with a fitting error of ≤0.07μm. It can identify local thickness abnormal areas with a diameter of ≥50μm, and generate an STL format three-dimensional model based on the fitting data. The thickness deviation is intuitively displayed through color scale mapping, and the color scale accuracy is 0.1μm.

[0047] The following is a detailed description of the working principle of the wafer polishing laser interference closed-loop pressure control method.

[0048] like Figure 1As shown, the laser beam is divided into measurement light and reference light by a spectroscopic prism. The measurement light is reflected after irradiating the wafer surface and forms interference fringes with the reference light on the CCD surface. The relationship between the fringe displacement Δx and the laser wavelength λ is: Δd = Δx·λ / 2, and the wafer thickness change Δd is calculated to achieve sub-micron precision detection. The support vector machine maps the process parameters to a high-dimensional space through the RBF kernel function to construct a pressure-thickness nonlinear relationship model. When the current measured thickness data is input, the model outputs the optimal polishing pressure value, reducing the manual intervention rate by ≥90%. The system establishes a polishing pressure-material removal rate model based on Newton's second law: dH / dt = K·P·v, where K is the process constant, P is the pressure, and v is the polishing head speed. Dynamic control of the thickness H is achieved by real-time correction of the pressure P, ensuring that the equipment utilization rate is ≥95%.

[0049] While the present invention has been generally described above, modifications and improvements are readily apparent to those skilled in the art. Therefore, modifications and improvements that do not depart from the spirit of the present invention are intended to be within the scope of the present invention.

Claims

1. A wafer polishing laser interferometer closed-loop pressure control method, characterized by: The following steps are involved: S1: Automatic measurement procedure is triggered after the ceramic plate and wafer are flipped; S2: The six-axis robotic positioning system drives the laser interferometer measurement head to perform non-contact scanning of the wafer T2 / T4 points to obtain thickness distribution data; S3: using a Zernike polynomial to fit the thickness distribution data to generate a three-dimensional distribution graph, and calculating a pressure correction amount based on a pressure prediction model constructed based on a process dynamics model and a support vector machine regression algorithm; S4: Detect data outliers in real time through the exception handling module, and trigger device protection strategies when the deviation exceeds the set threshold; S5: Transmit pressure control instructions to the polishing head via the PLC controller via the PROFINET bus; S6: The polishing head performs pressure adjustment and feeds back a confirmation signal. The process parameters and adjustment status are displayed in real time through the industrial-grade HMI interactive terminal to complete closed-loop control.

2. The wafer polishing laser interference closed-loop pressure control method according to claim 1, characterized in that: The laser interferometer measuring head adopts the Michelson interference principle, has a measurement accuracy of ±0.1μm, a single non-contact scanning time of less than 20 seconds, and a scanning range covering 20% to 80% of the wafer diameter.

3. The wafer polishing laser interference closed-loop pressure control method according to claim 1, characterized in that: The six-axis robotic arm positioning system is driven by a servo motor and equipped with a grating scale feedback device. The positioning accuracy reaches ±0.05mm, and the posture adjustment of the measuring head can be achieved within a tilt range of ±1° on the wafer surface.

4. The wafer polishing laser interference closed-loop pressure control method according to claim 1, characterized in that: The pressure prediction model is trained on 1,000 sets of historical process parameters and corresponding thickness data using a support vector machine regression algorithm. The process parameters include polishing pressure, rotation speed, and slurry concentration. A radial basis function is used as the kernel function, and the parameters are optimized to make the prediction error less than ±0.15 μm.

5. The wafer polishing laser interference closed-loop pressure control method according to claim 1, characterized in that: The abnormality handling module uses the 3σ principle to detect data outliers. When the deviation between the measured thickness and the predicted thickness exceeds ±0.1μm, the polishing head pressure locking mechanism is automatically triggered and an audible and visual alarm is issued through the HMI terminal.

6. The wafer polishing laser interference closed-loop pressure control method according to claim 1, characterized in that: The PLC controller and the polishing head communicate in real time via PROFINETIO, using IRT mode, with instruction transmission delay less than 50ms, communication cycle of 1ms, and support for data verification and retransmission mechanism.

7. The wafer polishing laser interference closed-loop pressure control method according to claim 1, characterized in that: The industrial-grade HMI interactive terminal is equipped with a 10.1-inch touch screen, which displays the laser measurement three-dimensional cloud map, pressure correction curve and equipment OEE in real time, and supports historical data query and process parameter recipe storage functions.

8. The wafer polishing laser interference closed-loop pressure control method according to claim 1, characterized in that: The Zernike polynomial fitting algorithm uses a 36th-order polynomial, and the fitting error of wafer thickness data is less than 0.08 μm, and local thickness abnormality areas with a diameter greater than 50 μm can be identified.

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