A Z-axis verticality calibration device and calibration method for an alignment motion stage

Abstract

The invention relates to the field of photolithography equipment, and discloses a Z-axis verticality calibration device and a calibration method for an alignment motion stage, comprising an industrial computer main control module, an alignment motion stage, an alignment camera, and a verticality test board; the industrial computer main control module is used to control the movement of the alignment motion stage so that the alignment motion stage is aligned with the verticality test board; the alignment camera is arranged on the alignment motion stage and moves with the alignment motion stage; the surface of the verticality test board is a reflection surface, a small square chrome-plated surface is superimposed on the central area of ​​the reflection surface, and a test mark is arranged on the surface, and the alignment camera is aligned with the test mark. The invention only requires the participation of hardware modules such as the alignment motion stage and the alignment camera in the whole process, and the motion adjustment is completed by the motion stage control module and the alignment module of the industrial computer main control system to complete the module motion control, and then the coordinates of the mark image are recognized by the machine vision recognition algorithm, thereby solving the problems of the traditional testing method.

Description

Technical Field

[0001] The present invention relates to the field of photolithography, and in particular to a Z-axis verticality calibration device and a calibration method for an alignment motion stage. Background Art

[0002] The alignment camera is an important part of the lithography equipment. The verticality of the Z-axis of its motion stage directly affects the accuracy and stability of pattern alignment. Traditional testing methods often have problems such as complex operation, low detection efficiency, and insufficient accuracy, which are difficult to meet the needs of high-precision semiconductor manufacturing. Therefore, it is of great significance to develop a fast and accurate test method for the verticality of the alignment motion stage of the lithography equipment.

[0003] The traditional methods for testing the verticality of the motion axis are as follows:

[0004] The entire process requires the use of hardware modules such as the mask motion stage, wafer motion stage, alignment motion stage and alignment camera.

[0005] The main disadvantages of the existing traditional test for the verticality of the motion stage are that the test process involves many motion stages, the operation is complicated and coupling errors are prone to occur. Summary of the invention

[0006] The main purpose of the present invention is to solve the technical problems in the prior art that the test process involves many moving stages, the operation is complicated and coupling errors are prone to occur. A device for measuring and calibrating the verticality of the Z-axis of an alignment moving stage comprises:

[0007] Industrial computer main control module, alignment motion stage, alignment camera, verticality test board;

[0008] The main control module of the industrial computer is used to control the movement of the alignment motion stage so that the alignment motion stage is aligned with the verticality test board;

[0009] The alignment camera is arranged on the alignment motion stage and moves with the alignment motion stage;

[0010] The surface of the verticality test plate is a reflective surface, a small square chrome-plated surface is superimposed in the central area of ​​the reflective surface, and a test mark is set on the surface of the chrome-plated surface, and the alignment camera is aligned with the test mark.

[0011] As a preferred technical solution, the measurement and calibration device also includes a mask stage, and the verticality test plate is arranged on the mask stage.

[0012] As a preferred technical solution, the measurement and calibration device also includes a wafer table, the wafer table is provided with a wafer table window, the alignment motion stage and the alignment camera are arranged below the wafer table, the verticality test board is arranged above the wafer table, and the alignment camera can observe the test mark on the verticality test board through the wafer table window.

[0013] As a preferred technical solution, the measurement and calibration device further includes a real image best focal plane finding module, and the real image best focal plane finding module is used to find the best real image focal plane of the test mark.

[0014] The calibration device further comprises a virtual image best focal plane searching module, and the virtual image best focal plane searching module is used to search for the best virtual image focal plane of the test mark.

[0015] A second aspect of the present invention provides a method for measuring and calibrating the verticality of the Z-axis of an alignment motion stage, the method comprising the following steps:

[0016] The main control module of the industrial computer controls the alignment motion stage to align with the test mark on the verticality test board;

[0017] Perform high point matching to find the best focal plane of the real image and obtain the real image coordinates after image matching;

[0018] Control the alignment motion stage, move the alignment camera, until the virtual image mark is found, perform low point matching, find the best focal plane of the virtual image, and obtain the virtual image coordinates after image matching;

[0019] Obtain the movement amount △L between the best focal plane of the real image and the best focal plane of the virtual image

[0020] According to the obtained real image coordinates and virtual image coordinates, the displacement s of the test mark is calculated;

[0021] Use the following formula to calculate the vertical deviation angle α of the Z axis of the alignment motion stage:

[0022]

[0023] In the process of finding the best focal plane of the virtual image and the best focal plane of the real image, it is necessary to determine whether the following conditions are met within the field of view of the alignment camera:

[0024] Only one mark is selected, the size and brightness of the mark are appropriate, and the camera is controlled and moved until the real or virtual image of the test mark is clear;

[0025] If the conditions are not met, the measuring and calibration device is adjusted. If the conditions are met, the best focal planes of the virtual image and the real image are found.

[0026] The step of finding the best focal plane of the real image specifically includes:

[0027] Controlling the motion stage to move the camera downward at a predetermined speed while aiming the camera to continuously capture images;

[0028] After a clear real image mark is identified in the captured image, a colored frame is used to cover the area where the real image mark is located;

[0029] The motion stage is fine-tuned and the clarity of the image with the colored frame is analyzed in real time. When the image clarity reaches the preset standard, it is considered that the best focal plane of the real image has been found.

[0030] The step of finding the best focal plane of the virtual image specifically includes:

[0031] Controlling the motion stage to move the camera downward at a predetermined speed while aiming the camera to continuously capture images;

[0032] After a clear virtual image mark is identified in the captured image, a colored frame is used to cover the area where the virtual image mark is located;

[0033] Fine-tune the motion stage and analyze the clarity of the image with the colored box in real time. When the image clarity reaches the preset standard, it is considered that the best focal plane of the virtual image has been found.

[0034] The present invention has the following beneficial effects:

[0035] The present invention only requires the participation of hardware modules such as the alignment motion stage and the alignment camera in the entire process. The motion adjustment is completed by the motion stage control module and the alignment module of the industrial computer main control system, and the module motion control is completed. The marked image coordinates are then identified through the machine vision recognition algorithm to calculate the direction and angle of the vertical deflection of the alignment motion stage to complete the calibration. The operation is simple, the detection efficiency is high and the accuracy is high, which solves the problems of traditional testing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a Z-axis verticality calibration device for the existing alignment motion stage;

[0037] Figure 2 This is the flow chart of the existing Z-axis verticality calibration of the alignment motion table;

[0038] Figure 3 A diagram of a Z-axis verticality calibration device for an alignment motion stage provided in an embodiment of the present invention;

[0039] Figure 4 A diagram of another Z-axis verticality calibration device for an alignment motion stage provided in an embodiment of the present invention;

[0040] Figure 5 A schematic diagram of the Z-axis verticality calibration principle of the alignment motion stage provided in an embodiment of the present invention;

[0041] Figure 6 A software interface for measuring and calibrating the Z-axis verticality of an alignment motion stage provided in an embodiment of the present invention.

[0042] The reference numerals are as follows:

[0043] Alignment motion stage 1, alignment camera 2, wafer stage 3, wafer stage window 31, wafer 100, verticality test board 4, test mark 41, test mark virtual image 42, mask stage 5. DETAILED DESCRIPTION

[0044] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" or "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0045] like Figure 1-2 , the traditional solution for testing the verticality of the motion axis. The entire process requires the use of hardware modules such as the mask motion stage, wafer motion stage, alignment motion stage and alignment camera.

[0046] For ease of understanding, the specific process of the embodiment of the present invention is described below. Figure 3 The first embodiment of the Z-axis verticality calibration device for the alignment motion stage in the embodiment of the present invention comprises:

[0047] Industrial computer main control module, alignment motion stage, alignment camera, verticality test board;

[0048] The main control module of the industrial computer is used to control the movement of the alignment motion stage so that the alignment motion stage is aligned with the verticality test board;

[0049] The alignment camera is arranged on the alignment motion stage and moves with the alignment motion stage;

[0050] The surface of the verticality test plate is a reflective surface, a test mark is set on the reflective surface, and the alignment camera is aligned with the test mark.

[0051] The calibration device further comprises a mask stage, and the verticality test plate is arranged on the mask stage.

[0052] This method is to adjust the absolute verticality of the Z axis of the motion stage and calibrate it using a verticality test plate. Figure 3As shown in the figure, a small square chrome surface is superimposed on the central area of ​​the reflective surface of the verticality test plate, and a test mark is set on the chrome surface. Since the mark and the virtual image in the reflective surface are in an absolutely vertical relationship relative to the mask plane, the entire process does not require moving the mask stage and the wafer stage, and the Z-axis of the alignment motion stage can be calibrated to be absolutely vertical.

[0053] The single alignment module is set symmetrically on the left and right, and different alignment methods have different loading methods. For a single alignment module, the installation position is on the air-floating platform mounting frame. The relative positions of the alignment motion stage, alignment camera, mask plate, and mask stage are as follows: Figure 3 As shown in FIG. 1 , due to processing and installation tolerances and other reasons, there may be problems with the verticality of the alignment module on the Z axis.

[0054] The calibration principle of this method is as follows: For the alignment motion stage, Figure 5 It is shown that when the alignment motion stage is aligned with the real image mark, the center of the field of view is at point O0 on the W1 plane. When the alignment motion stage moves downward to make the focus mark mirrored on the best focal plane, the center of the field of view is at point O1 on the W2 plane. Due to the existence of the motion stage deflection angle α, the position of the virtual image of the mark point in the field of view is offset after the alignment motion stage moves, and the displacement is s. The downward movement of the alignment motion stage is △L, and the length of q1q2 is equal to the displacement s. This displacement is readable in the alignment motion stage control system. The deflection angle of the Z axis of the alignment motion stage relative to the standard Z axis can be obtained from the triangular relationship formed by these two known quantities.

[0055] See also Figure 4 , which is different from the first embodiment, the Z-axis verticality of the back alignment motion stage can also be measured and calibrated. The measurement and calibration device also includes a wafer stage, the wafer stage is provided with a wafer stage window, the alignment motion stage and the alignment camera are arranged below the wafer stage, the verticality test board is arranged above the wafer stage, and the alignment camera can observe the test mark on the verticality test board through the wafer stage window.

[0056] A second aspect of the present invention provides a method for measuring and calibrating the verticality of the Z-axis of an alignment motion stage, the method comprising the following steps:

[0057] The main control module of the industrial computer controls the alignment motion stage to align with the test mark on the verticality test board;

[0058] Perform high point matching to find the best focal plane of the real image and obtain the real image coordinates after image matching;

[0059] Control the alignment motion stage, move the alignment camera, until the virtual image mark is found, perform low point matching, find the best focal plane of the virtual image, and obtain the virtual image coordinates after image matching;

[0060] Obtain the movement amount △L between the best focal plane of the real image and the best focal plane of the virtual image

[0061] According to the obtained real image coordinates and virtual image coordinates, the displacement s of the test mark is calculated;

[0062] Use the following formula to calculate the vertical deviation angle α of the Z axis of the alignment motion stage:

[0063]

[0064] In the process of finding the best focal plane of the virtual image and the best focal plane of the real image, it is necessary to determine whether the following conditions are met within the field of view of the alignment camera:

[0065] Only one mark is selected, the size and brightness of the mark are appropriate, and the camera is controlled and moved until the real or virtual image of the test mark is clear;

[0066] If the conditions are not met, the measuring and calibration device is adjusted. If the conditions are met, the best focal planes of the virtual image and the real image are found.

[0067] The step of finding the best focal plane of the real image specifically includes:

[0068] The motion stage is controlled to move the camera downward at a predetermined speed, while aiming the camera to continuously capture images; after a real image mark is identified in the captured image, a colored frame is used to cover the area where the real image mark is located; the motion stage is fine-tuned and the clarity of the image with the colored frame is analyzed in real time. When the image clarity reaches a preset standard, it is considered that the best focal plane of the real image has been found.

[0069] The step of finding the best focal plane of the virtual image specifically includes:

[0070] The motion stage is controlled to move the camera downward at a predetermined speed, while aiming the camera to continuously capture images; after a virtual image mark is identified in the captured image, a colored frame is used to cover the area where the virtual image mark is located; the motion stage is fine-tuned and the clarity of the image with the colored frame is analyzed in real time. When the image clarity reaches a preset standard, it is considered that the best focal plane of the virtual image has been found.

[0071] In the process of fine-tuning the motion stage and analyzing the image clarity in real time, the colored boxes provide a clear area range, making the evaluation work more focused and efficient. The algorithm can focus on analyzing the image changes within the box, so as to find the moment when the image clarity reaches the preset standard more quickly.

[0072] As an embodiment, a low-magnification camera (for example, 5x) is generally used to first find a suitable mark, the camera is moved so that the mark is in the center of the field of view, and then a high-magnification camera (for example, 10x) is used to focus clearly. At this time, it is considered that the best focal plane of the real image has been preliminarily found; then the test mark is covered with a colored frame and the image algorithm is used to identify and confirm the best focal plane of the real image, that is, the low-magnification camera searches for the mark, and the high-magnification camera focuses to find the best focal plane.

[0073] The specific steps of finding the best focal plane of the present invention may be:

[0074] initialization:

[0075] Set the initial speed v 0 Control the motion stage to move the camera downward. Set the fine-tuning step length Δz and the color change threshold ΔC. Set the image clarity threshold T and the color stability standard S C .

[0076] Shooting and identification:

[0077] The camera continuously captures images. Virtual or real markers are identified in the image and the area is covered with a colored box.

[0078] Color histogram analysis:

[0079] Calculate the color histogram H for the area covered by the colored box for each shot i (where i is the number of shots).

[0080] Define a color change ΔH i,i-1 , which is used to measure the difference in color histogram between two consecutive shots.

[0081] Image clarity assessment:

[0082] The image clarity is calculated using the clarity evaluation function S(I).

[0083]

[0084] Among them, G x and G y are the gradients of image I in the x and y directions respectively, ROI (Region of Interest) is the area within the colored box, and N is the total number of pixels within the ROI.

[0085] Gradient G x and G y It can be calculated by an edge detection operator, such as the Sobel operator.

[0086] Multimodal Optimization:

[0087] Create a multi-objective optimization problem, the objectives include maximizing the image clarity S(I i ) and minimize the color change ΔH i,i-1 , while ensuring color stability (i.e. color change does not exceed ΔC).

[0088] A weighting factor α and β is introduced to balance the importance of clarity and color stability:

[0089] F(I i)=α·S(I i )-β·max(0,ΔH i，i-1 -ΔC)

[0090] When the color change is less than or equal to ΔC, the color term does not incur a penalty; otherwise, a penalty is incurred according to the excess amount.

[0091] Fine-tuning and real-time analysis:

[0092] Initially, assume that the current optimal value F best =F(I 0 ).

[0093] Enter the fine-tuning loop, each time the motion stage moves Δz, a new image I is captured new , and calculate F(I new ).

[0094] If F(I new )>F best , then update F best =F(I new ) and continue to make fine adjustments in the same direction.

[0095] If F(I new ) does not significantly improve or reaches the preset maximum number of fine-tuning times, try reverse fine-tuning or reduce the fine-tuning step size.

[0096] Monitor color stability and clarity to ensure both are within acceptable ranges.

[0097] End: When F(I i ) for multiple times without significant improvement, and the image clarity and color stability meet the requirements, the best focal plane is considered to have been found. Stop fine-tuning and lock the position of the motion stage.

[0098] The difference of color histograms can be calculated using various distance metrics, such as Bhattacharyya distance and histogram intersection.

[0099] The weighting factors α and β need to be adjusted according to the specific application scenario to balance the importance of clarity and color stability.

[0100] The algorithm of this embodiment combines image clarity evaluation and color histogram analysis to optimize the process of finding the best focal plane by comprehensively considering image quality and color stability.

[0101] See Figure 6 The calibration method of the present invention is specifically as follows:

[0102] 1. When aiming the camera to search for a mark, the following conditions must be met: 1) There is only one mark in the field of view; 2) The selected mark must be of appropriate size and brightness.

[0103] 2. Move the camera until the real image mark is clear.

[0104] 3. After meeting the above two points, use Figure 6 The green border in the upper left corner covers the mark in the field of view, then click Set TopPosition to match the high point and find the best focal plane of the real image.

[0105] 4. Move the camera downward until the virtual image mark is found. This process also needs to meet the requirements of points 1 and 2. Record the moving distance ΔL of the alignment motion stage. Figure 6 The green border in the upper left corner covers the mark in the field of view, then click Set BottomPosition to match the low point and find the best focal plane of the virtual image.

[0106] 5. Click Top Match and Bottom Match successively to obtain the coordinates of the real and virtual image markers after image matching, and identify the displacement s of the markers;

[0107] 6. Click Calculate and use Formula 1 to get the vertical deviation angle α of the Z axis of the alignment motion stage.

[0108] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring and calibrating the verticality of the Z-axis of an alignment motion stage, characterized in that: The calibration device used in the calibration method comprises: Industrial computer main control module, alignment motion stage, alignment camera, verticality test board, mask stage, wafer stage, real image best focal plane search module, virtual image best focal plane search module; The main control module of the industrial computer is used to control the movement of the alignment motion stage so that the alignment motion stage is aligned with the verticality test board; The alignment camera is arranged on the alignment motion stage and moves with the alignment motion stage; The verticality test plate is arranged on the mask stage, the surface of the verticality test plate is a reflective surface, a small square chrome-plated surface is superimposed in the center area of ​​the reflective surface, and a test mark is arranged on the surface of the chrome-plated surface, and the alignment camera is aligned with the test mark; The wafer stage is provided with a wafer stage window, the alignment motion stage and the alignment camera are arranged below the wafer stage, the verticality test board is arranged above the wafer stage, and the alignment camera can observe the test mark on the verticality test board through the wafer stage window; The real image best focal plane search module is used to find the best real image focal plane of the test mark; The virtual image best focal plane search module is used to find the best virtual image focal plane of the test mark; The calibration method comprises the following steps: The main control module of the industrial computer controls the alignment motion stage to align with the test mark on the verticality test board; Perform high point matching to find the best focal plane of the real image and obtain the real image coordinates after image matching; Control the alignment motion stage, move the alignment camera, until the virtual image mark is found, perform low point matching, find the best focal plane of the virtual image, and obtain the virtual image coordinates after image matching; Obtain the movement amount △L between the best focal plane of the real image and the best focal plane of the virtual image According to the obtained real image coordinates and virtual image coordinates, the displacement s of the test mark is calculated; Use the following formula to calculate the vertical deviation angle α of the Z axis of the alignment motion stage:

2. A method for measuring and calibrating the verticality of the Z-axis of an alignment motion stage according to claim 1, characterized in that: The step of searching for the best focal plane of the real image or the best focal plane of the virtual image comprises: initialization: Set the initial speed v0 to control the motion stage to move the camera downward; set the fine-tuning step Δz and the color change threshold ΔC; set the image clarity threshold T and the color stability standard S C ; Shooting and identification: The camera continuously captures images; virtual or real markers are identified in the image and the area is covered with a colored box; Color histogram analysis: Calculate the color histogram H for the area covered by the colored box for each shot i , where i is the number of shots; Define a color change ΔH i,i-1 , used to measure the difference in color histogram between two consecutive shots; Image clarity assessment: The image clarity is calculated using the clarity evaluation function S(I); Among them, G x and G y are the gradients of image I in the x and y directions, ROI is the area within the colored box, N is the total number of pixels within the ROI; the gradient G x and G y It is calculated using edge detection operator; Multimodal Optimization: Create a multi-objective optimization problem, the objectives include maximizing the image clarity S(I i ) and minimize the color change ΔH i,i-1 , while ensuring color stability, that is, the color change does not exceed ΔC; A weighting factor α and β is introduced to balance the importance of clarity and color stability: F(I i )=α·S(I i )-β·max(0,ΔH i，i-1 -ΔC) When the color change is less than or equal to ΔC, the color term does not incur a penalty; otherwise, a penalty is imposed based on the amount of excess; Fine-tuning and real-time analysis: Initially, assume that the current optimal value F best =F(I0); Enter the fine-tuning loop, each time the motion stage moves Δz, a new image I is captured new , and calculate F(I new ); If F(I new )>F best , then update F best =F(I new ) and continue to fine-tune in the same direction; If F(I new ) If there is no significant improvement or the preset maximum number of fine-tuning times is reached, try reverse fine-tuning or reduce the fine-tuning step size; Monitor color stability and clarity to ensure both are within acceptable ranges; End: When F(I i ) for multiple consecutive times without significant improvement, and the image clarity and color stability meet the requirements, it is considered that the best focal plane has been found; stop fine-tuning and lock the position of the motion stage.

Images