Non-contact wafer center calibration mechanism based on least square method and control method

Abstract

The invention discloses a non-contact wafer center calibration mechanism based on a least square method and a control method, and the mechanism comprises a pedestal supporting mechanism which is used for installing all assemblies; the moving module is driven by a moving servo motor and is configured to perform displacement adjustment in the linear direction; the sucking disc is arranged on the base supporting mechanism and is used for adsorbing and fixing the wafer through vacuum; the rotary DD motor is connected with the suction cup and is configured to drive the wafer to rotate by 360 degrees; the lifting cylinder is configured to lift up or put down the wafer; the CCD laser sensor is arranged at a detection position of the circumference of the wafer and is configured to acquire distance data of the circumference of the wafer at an interval of 0.1 degree; and a PLC controller. The method has the beneficial effects of high precision and high efficiency: the non-contact CCD laser sensor is combined with 0.1-degree high-resolution data acquisition, so that wafer damage or pollution caused by mechanical contact is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor equipment, in particular to a non-contact wafer center calibration mechanism based on least squares method and a control method. BACKGROUND

[0002] In the field of semiconductor manufacturing, wafer center calibration is a key pre-process for wafer chamfering, cutting, and photolithography. Accurate center positioning directly affects the quality and yield of subsequent processing. Traditional wafer calibration techniques mainly rely on mechanical contact methods, such as using mechanical probes or positioning pins to contact the wafer edge to indirectly calculate the center position. However, such methods have significant drawbacks:

[0003] Limited accuracy: Mechanical contact is easily disturbed by factors such as probe wear and wafer edge burrs, resulting in measurement errors (usually > 5 μm), making it difficult to meet the sub-micron accuracy requirements of advanced processes (such as below 7 nm).

[0004] Low efficiency: Multiple adjustments of probe positions and repeated verifications are required, resulting in long calibration times and affecting production line throughput.

[0005] Risk of wafer damage: Mechanical contact may scratch the wafer surface or edge, especially in ultra-thin wafer (thickness < 100 μm) processing, where this problem is more pronounced.

[0006] In recent years, non-contact calibration techniques (such as optical sensors or laser ranging) have been gradually introduced to indirectly calculate the center by measuring the wafer edge distance. However, existing non-contact solutions still have the following problems:

[0007] Insufficient data fitting algorithm: Most solutions use simple geometric averaging or symmetry assumptions, without fully considering random deformation of the wafer edge or measurement noise, resulting in large deviations between the fitted center and the actual center.

[0008] Poor hardware compatibility: Sensor data acquisition and control of execution mechanisms (such as motors and air cylinders) lack real-time linkage, and the calibration process relies on manual intervention, with low automation level.

[0009] Limited adaptability: Existing equipment is difficult to accommodate calibration requirements for different diameters (such as 200 mm and 300 mm wafers) or special shapes (such as notched wafers).

[0010] To address the above problems, the present application proposes a non-contact wafer center calibration mechanism based on least squares method and a control method, which realizes efficient, high-precision, and non-destructive center calibration through the coordinated design of high-precision data acquisition, mathematical optimization algorithm, and automated execution mechanism, providing reliable technical support for semiconductor manufacturing processes. SUMMARY

[0011] The technical problem solved by the present application is to provide a non-contact wafer center calibration mechanism and control method based on the least square method, which solves one or more of the above technical problems.

[0012] To solve the above technical problems, the present application adopts one technical solution: a non-contact wafer center calibration mechanism based on the least square method, which is characterized by comprising

[0013] A base support mechanism for mounting various components;

[0014] A moving module driven by a moving servo motor and configured to adjust displacement in a straight line direction;

[0015] A suction cup arranged on the base support mechanism and configured to fix the wafer by vacuum adsorption;

[0016] A rotating DD motor connected to the suction cup and configured to drive the wafer to rotate by 360°;

[0017] A lifting cylinder configured to lift or lower the wafer;

[0018] A CCD laser sensor arranged at a detection position of the wafer circumference and configured to collect distance data of the wafer circumference at an interval of 0.1°;

[0019] A PLC controller connected to the CCD laser sensor, the rotating DD motor, the moving servo motor, and the lifting cylinder, comprising a high-speed counter module and a high-precision analog module, and configured to store 3600 collected data points of the circumference and calculate the wafer center coordinates and eccentricity by the least square method;

[0020] The PLC controller is further configured to: construct a circular equation linearization model based on the data points of the circumference, obtain the wafer center coordinates (a, b) by solving the linear equation set, control the rotating DD motor to adjust the wafer angle, and drive the moving module and the lifting cylinder to move cooperatively to make the wafer center coincide with the origin of the coordinate system.

[0021] In some embodiments, the detection resolution of the CCD laser sensor is ≤1 μm, and the distance between the installation position of the CCD laser sensor and the edge of the wafer is adjustable to adapt to wafers of different diameters.

[0022] In some embodiments, the PLC controller further comprises:

[0023] A data preprocessing module for noise filtering and outlier rejection of the 3600 collected data points;

[0024] A real-time feedback module for dynamically adjusting the motion parameters of the moving servo motor and the rotating DD motor according to the eccentricity.

[0025] In some embodiments, the chuck surface is provided with an annular groove for enhancing the uniformity of vacuum adsorption and preventing the wafer from slipping during calibration.

[0026] The control method of the non-contact wafer center calibration mechanism based on the least square method comprises the following steps:

[0027] Data acquisition: rotate the wafer by rotating the DD motor, and collect the distance data p of the wafer circumference every 0.1° by the CCD laser sensor, converting 3600 data points (x_i, y_i);

[0028] Center calculation: linearize the circle equation (x-a) 2 +(y-b) 2 =r 2 to ax_i+by_i+c=x_i 2 +y_i 2 , and construct the objective function; take the partial derivative of a, b, and c and set it to zero to form a linear equation group, and solve the center coordinates (a, b) by matrix operation;

[0029] Center calibration: calculate the distance L from the wafer center to the origin of the coordinate system and the angle θ relative to the Y axis according to the center coordinates (a, b); control the rotating DD motor to rotate the wafer by θ angle, and drive the moving module to move by distance L along the straight line direction, so that the wafer center is aligned with the origin of the coordinate system;

[0030] Recheck verification: repeat steps 1 to 3 until the center calibration accuracy reaches the set threshold.

[0031] In some embodiments, the matrix form of the linear equation group in step 2 is:

[0032]

[0033] Where n is the total number of data points.

[0034] In some embodiments, the set threshold of the recheck verification in step 4 is that the center offset is ≤0.5μm, and if the threshold is not reached, the displacement of the moving module and the rotation angle are corrected by an iterative optimization algorithm.

[0035] In some embodiments, the calculation formula of the distance L in step 3 is:

[0036]

[0037] The calculation formula of the angle θ is:

[0038]

[0039] When b=0, θ is directly taken as 90° or 270°.

[0040] The beneficial effects of the present application are: high precision and high efficiency: the non-contact CCD laser sensor combines 0.1° high-resolution data acquisition, avoiding wafer damage or contamination caused by mechanical contact; the least square method algorithm effectively eliminates random errors, and the center calculation accuracy can reach sub-micron level (≤0.5 μm), which is significantly better than the traditional mechanical calibration method; strong adaptability: the installation position of the CCD sensor can be adjusted to support the measurement requirements of wafers of different diameters (such as 200mm / 300mm); the PLC real-time feedback module dynamically adjusts the actuator parameters to adapt to the change of wafer eccentricity; high reliability: the design of the annular groove on the surface of the chuck enhances the uniformity of vacuum adsorption and prevents the wafer from sliding during calibration; the re-measurement mechanism combined with the iterative optimization algorithm ensures that the calibration result is stable and reliable; high degree of automation: from data acquisition, processing to calibration, the whole process is controlled by PLC without manual intervention, which greatly improves the automation level of the semiconductor manufacturing process. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0042] Figure 1 is a structural schematic diagram of a non-contact wafer center calibration mechanism based on the least square method.

[0043] Figure 2 is a front view of a non-contact wafer center calibration mechanism based on the least square method. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0045] As shown in Figure 1 and Figure 2 , the non-contact wafer center calibration mechanism of the present application is composed of the following core components:

[0046] Base support mechanism 1: as the base of the overall structure, it fixes the moving module 2, the chuck 8, the rotary DD motor 3 and the lifting cylinder 5.

[0047] Mobile module 2: Driven by mobile servo motor 4, it moves along the X / Y axis linear guide rail to adjust the position of wafer 6.

[0048] Suction cup 8: The surface is provided with an annular groove, which can fix wafer 6 by vacuum adsorption and prevent it from sliding during calibration.

[0049] Rotary DD motor 3: Directly drives the rotation of suction cup 8, which drives wafer 6 to complete 360° rotation with 0.1° resolution, ensuring the continuity of data acquisition.

[0050] Lifting cylinder 5: Located below suction cup 8, it is used to lift or lower wafer 6, and cooperates with mobile module 2 to complete position calibration.

[0051] CCD laser sensor 7: Installed on the edge of wafer to detect the position, its detection resolution is ≤1μm, and it collects the distance data of wafer circumference through non-contact measurement.

[0052] PLC controller: Integrates high-speed counter module (for accurate timing) and high-precision analog module (for signal conversion), which processes sensor data in real time and controls the action of actuator.

[0053] The working principle of the technical solution is:

[0054] Data acquisition stage:

[0055] Rotary DD motor 3 drives wafer to rotate at a constant speed, and CCD laser sensor 7 collects the distance value of wafer edge every 0.1°, a total of 3600 data points; through the coordinate conversion formula:

[0056] x i =ρ i ·sin(θ i ),y i =ρ i ·cos(θ i )

[0057] Convert polar coordinate data to data points (x _i ,y _i ) in rectangular coordinate system.

[0058] Data processing stage:

[0059] After preprocessing the data by PLC controller, removing noise and outliers, the least square method is used to fit the circle equation. By constructing a linear equation group:

[0060]

[0061] Solve the coordinates of the center (a, b) and the radius r.

[0062] Calibration stage:

[0063] PLC calculates the distance from the wafer center to the origin of the coordinate system according to the center coordinates and the angle θ = arctan(a / b), the rotating DD motor 3 drives the wafer to rotate by θ angle, and the moving module 2 moves by the distance L in the straight line direction, so that the wafer center is aligned with the origin of the coordinate system.

[0064] Re-measurement stage:

[0065] Repeat the above steps, if the center offset is greater than 0.5 μm, correct the moving distance and rotation angle by iterative optimization algorithm until the accuracy requirement is met.

[0066] The technical solution has the advantages that:

[0067] High precision and high efficiency: non-contact CCD laser sensor 7 combined with 0.1° high resolution data acquisition, avoids wafer damage or pollution caused by mechanical contact; least square method algorithm effectively eliminates random error, and the center calculation accuracy can reach sub-micron level (≤0.5 μm), which is significantly better than the traditional mechanical calibration method.

[0068] Strong adaptability: the installation position of the CCD sensor can be adjusted to support the measurement requirements of wafers of different diameters (such as 200mm / 300mm); the PLC real-time feedback module dynamically adjusts the parameters of the actuator to adapt to the change of the wafer eccentricity.

[0069] High reliability: the surface annular groove design of the suction cup 8 enhances the uniformity of vacuum adsorption and prevents the wafer from sliding during calibration; the re-measurement mechanism combined with the iterative optimization algorithm ensures the stability and reliability of the calibration results.

[0070] High degree of automation: from data acquisition, processing to calibration, the whole process is controlled by PLC without manual intervention, which greatly improves the automation level of the semiconductor manufacturing process.

[0071] Implementation example

[0072] Calibration process: place a 300mm wafer on the suction cup 8, start vacuum adsorption and fixation; rotate the wafer at a speed of 10r / min by rotating the DD motor 3, and collect 3600 data points by the CCD laser sensor 7; calculate the center coordinates (a=0.12mm, b=-0.08mm) by the PLC, and obtain L=0.144mm and θ=56.3°; adjust the wafer to θ angle by the rotating DD motor 3, and move the moving module 2 along the X axis by 0.144mm to complete the calibration; after re-measurement, the center offset is reduced to 0.3 μm, which meets the threshold requirement.

[0073] Abnormal processing: if the re-measurement offset exceeds the limit, the PLC automatically triggers secondary calibration, adjusts the step distance of the moving module 2 step motor (such as 1 μm / step), and adjusts the step distance until the accuracy meets the standard.

[0074] The above merely illustrates the embodiments of the present application, and is not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process conversion, or direct or indirect application in other related technical fields, made by using the content of the present application, are also included in the patent protection scope of the present application.

Claims

1. A non-contact wafer center calibration mechanism based on the least squares method, characterized by: include A base support mechanism (1) for mounting various components; A moving module (2) is driven by a moving servo motor (4) and is configured to perform displacement adjustment in a linear direction; A suction cup (8) is provided on the base support mechanism (1) and fixes the wafer by vacuum adsorption; a rotating DD motor (3), connected to the suction cup (8), configured to drive the wafer to rotate 360°; A lifting cylinder (5) configured to lift or lower the wafer; A CCD laser sensor (7) is provided at a detection position on the circumference of the wafer and is configured to collect distance data on the circumference of the wafer at 0.1° intervals; A PLC controller is connected to the CCD laser sensor (7), the rotating DD motor (3), the moving servo motor (4) and the lifting cylinder (5), and includes a high-speed counter module and a high-precision analog module for storing the collected 3600 circumferential data points and calculating the wafer center coordinates and eccentricity through a least squares algorithm; The PLC controller is further configured to: construct a circle equation linearization model based on the circumference data points, obtain the circle center coordinates (a, b) by solving the linear equation group, and control the rotating DD motor (3) to adjust the wafer angle, drive the moving module (2) and the lifting cylinder (5) to work together, so that the wafer center coincides with the origin of the coordinate system.

2. The non-contact wafer center calibration mechanism based on the least squares method according to claim 1, characterized in that: The detection resolution of the CCD laser sensor (7) is ≤1 μm, and the distance between its installation position and the edge of the wafer is adjustable to accommodate wafers of different diameters.

3. The non-contact wafer center calibration mechanism based on the least squares method according to claim 1, characterized in that: The PLC controller also includes: Data preprocessing module, used to filter noise and remove outliers on the 3600 collected data points; The real-time feedback module dynamically adjusts the motion parameters of the mobile servo motor (4) and the rotary DD motor (3) according to the eccentricity.

4. The non-contact wafer center calibration mechanism based on least squares method according to claim 1, characterized in that: The surface of the suction cup (8) is provided with an annular groove for enhancing the uniformity of vacuum adsorption and preventing the wafer from sliding during the calibration process.

5. A control method for a non-contact wafer center calibration mechanism based on the least squares method, characterized in that: The steps include:

1. Data acquisition: The DD motor (3) drives the wafer to rotate once, and the CCD laser sensor (7) collects the distance data ρ of the wafer circumference every 0.1° and converts it into 3600 data points (x _i ,y _i ); 2. Calculate the center of the circle: Subtract the circle equation (xa) 2 +(yb) 2 =r 2 Linearization to ax _i +by _i +c=x _i 2 +y _i 2 , construct the objective function; calculate the partial derivatives of a, b, and c and set them to zero to form a linear equation system, and solve the coordinates of the circle center (a, b) through matrix operations; 3. Center calibration: Calculate the distance L from the center of the wafer to the origin of the coordinate system and the angle θ relative to the Y axis based on the center coordinates (a, b); control the rotary DD motor (3) to rotate the wafer by an angle θ, and at the same time drive the moving module (2) to move a distance L in a straight line direction, so that the center of the wafer is aligned with the origin of the coordinate system; 4. Retest and verify: Repeat steps 1 to 3 until the center calibration accuracy reaches the set threshold.

6. The control method of the non-contact wafer center calibration mechanism based on the least squares method according to claim 5, characterized in that: The matrix form of the linear equations described in step 2 is: Where n is the total number of data points.

7. The control method of the non-contact wafer center calibration mechanism based on the least squares method according to claim 5, characterized in that: The set threshold value for the retest verification in step 4 is the center offset ≤ 0.5 μm. If the threshold value is not reached, the displacement and rotation angle of the mobile module (2) are corrected through an iterative optimization algorithm.

8. The control method of the non-contact wafer center calibration mechanism based on the least squares method according to claim 5, characterized in that: The calculation formula for the distance L in step 3 is: The angle θ is calculated as: When b=0, θ is directly set to 90° or 270°.

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