A focusing calibration method and an exposure compensation method with an auto-focusing function

Abstract

The application discloses a focusing calibration method and an exposure compensation method with an automatic focusing function, determines the relationship between the movement amount of an AF mechanism and the change amount of a platform focal plane, and specifically comprises the following steps: arranging the AF mechanism below an exposure lens, moving a suction disc camera on the platform to be directly below the exposure lens, determining the optimal focal plane position Z of the platform through the suction disc camera m ; determining the relationship between the movement amount of the AF mechanism and the change amount of the platform focal plane, obtaining the relationship model between the focusing position of the AF mechanism and the change amount of the platform focal plane, thereby ensuring the accuracy of the focal plane compensation of the AF mechanism, eliminating the different influences of machining errors and movement errors and movement amounts on the focal plane, and preventing the phenomenon that the difference between the theoretical compensation surface and the actual compensation surface is different.

Description

Technical Field

[0001] This invention relates to the field of micro-optical equipment technology, and in particular to a focusing calibration method with automatic focusing function. Background Technology

[0002] The AF (auto focus) mechanism is an automatic focusing mechanism. The AF mechanism motion is the change in the relative translation distance of the right-angle wedge prism in the focusing module of the automatic focusing mechanism. In micro-optical equipment, the focusing motion mechanism is an important component to realize the automatic focusing function. It can change the focal plane position of the lens, so that the pattern on the carrier plate is clearly projected onto the platform surface.

[0003] A Chinese patent discloses an optical system for a direct-write lithography machine (authorization announcement number CN216351771U). The patent discloses that, depending on the system's structural layout, an upper right-angle wedge prism or a lower right-angle wedge prism can be fixed. Both wedge prisms can be driven by a driving device to translate along the plane containing the inclined surface. By translating the wedge prisms relative to each other, the distance the light beam travels in the prisms is changed, thereby changing the focal plane of the system.

[0004] However, due to manufacturing errors, motion errors, and varying effects of motion on the focal plane, the focusing motion mechanism can cause a difference between the theoretically compensated surface aberration and the actual surface aberration that needs to be compensated. This can lead to exposure not being at the optimal focal plane, thus affecting the exposure effect. Therefore, it is necessary to calibrate the relative relationship between the motion of the AF mechanism and the change in the focal plane of the platform to ensure the accuracy of the AF mechanism's focal plane compensation and thereby improve the exposure effect.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A focusing calibration method with autofocus function, characterized by comprising the following steps:

[0007] S1: Determine the relationship between the motion of the AF mechanism and the change in the focal plane of the platform, specifically including:

[0008] S101: Position the AF mechanism below the exposure lens, move the suction cup camera on the platform directly below an exposure lens, and use the suction cup camera to determine the optimal focal plane position Z of the platform at that location. m ;

[0009] S102: Control the focusing module of the AF mechanism to step a certain distance, repeat step s101, and obtain the optimal focal plane position Z in the z-direction of the platform under different positions of the focusing module of the AF mechanism. m This forms a set of AF mechanism positions S and optimal focal plane positions Z for a single exposure lens. mThe corresponding relationship data was obtained, and then the suction cup camera was moved to multiple exposure lenses respectively. Similarly, multiple sets of AF mechanism positions S and platform optimal focal plane positions Z were obtained. m The corresponding relationship data.

[0010] S103: The position S of the AF mechanism and the focal plane position Z of the platform are fitted using a cubic fitting method. m The correspondence;

[0011] S104: Based on the focal plane position Z of the platform m The range of variation determines the focal plane position Z of the platform under a single exposure lens. m median Z mid Then take multiple exposure shots of Z mid The average value Z avg Using the fitting method in step S103, the logic zero point y0 of the AF mechanism is obtained, which is the initial position of the focusing module of the AF mechanism.

[0012] S105: Move the platform to Z avg The position is adjusted so that multiple AF mechanisms are moved to the position of y0, thereby aligning the focal planes of multiple exposure lenses.

[0013] S106: Based on the calibration data from step S102, the relative average value Z of the platform focal plane position can be obtained. avg The change in x, the motion y of the AF mechanism relative to the logical zero point y0, and the one-to-one correspondence between the change in the focal plane of the platform x and the motion y of the AF mechanism.

[0014] S107: The relationship between the focal plane change x and the motion y of the AF mechanism is obtained by fitting a cubic term.

[0015] As a further aspect of the present invention: in step S101, the method for determining the focal plane position of the platform using the suction cup camera is specifically as follows:

[0016] a) The exposure lens projects circular markers onto the suction cup camera. The suction cup camera collects the average grayscale gradient g of the projected image above, below, left, and right of each marker. The g value reflects the degree of focus of the projected image. The higher the g value, the closer it is to the focal plane.

[0017] b) Control the platform to move in the z-direction, and repeat step a) with the suction cup camera to obtain a set of g values ​​at different z-direction heights. Perform a second fitting on the g values ​​at different z-direction heights of the platform to obtain the relationship model between z and g.

[0018] c) Based on the obtained relational model, solve for the focal plane z value when the g value reaches its maximum, and use this as the optimal focal plane position Z for the suction cup camera at this location. m Since the suction cup camera and the platform move synchronously, this position also serves as the optimal focal plane position Z for the platform.m .

[0019] As a further aspect of the present invention: in step S103, the fitting formula used is: Where: a3, a2, and a1 are calibration coefficients, and l is a constant term.

[0020] As a further aspect of the present invention: in step S104, the median Z of the multiple exposure lenses is... mid The average value Z avg After substituting into the fitting formula in step S103, the formula for calculating the logic zero y0 is obtained;

[0021]

[0022] Take the median Z mid To ensure the zoom module of the AF mechanism can achieve the maximum vertical adjustment range; take the average value Z. avg This is to ensure that all exposure lenses have a consistent focal plane at the zero point, while also ensuring that the focal plane of all exposure lenses can achieve the maximum adjustment range.

[0023] As a further aspect of the present invention: in step S107, the fitting formula for the relationship between the focal plane change x and the AF mechanism change y is: y = ax 3 +bx 2 +cx 1 +L, then the relationship between the focal plane change x and the focusing position Y of the AF mechanism relative to the logic zero point y0 is: Y = ax 3 +bx 2 +cx 1 +L0, where L0=y0+L, a is the calibrated first-order coefficient, b is the calibrated second-order coefficient, c is the calibrated third-order coefficient, and L is the constant term.

[0024] An exposure compensation method includes the following steps:

[0025] S1: The focusing calibration method with autofocus function is adopted;

[0026] S2: Real-time surface scanning;

[0027] S3: Process the scanned surface data;

[0028] S4: Perform AF compensation on the scanned surface.

[0029] As a further aspect of the present invention: in step S2, the specific method for real-time surface scanning is as follows:

[0030] S201: Move the platform to the starting position, fix the displacement sensor to an initial position on the crossbeam, and start scanning the surface profile of the loading plate on the platform.

[0031] S202: By moving the platform in the y-direction and moving the displacement sensor in the x-direction via the crossbeam, the z-direction change of the surface of the loading plate on the platform can be measured in real time. The displacement sensor records the surface data of the loading plate until the entire surface of the loading plate is scanned, and multiple columns of raw scan data can be obtained.

[0032] As a further aspect of the present invention: the specific method for processing the scanned surface data in step S3 is as follows:

[0033] S301: The scan data obtained in step S2 is filtered once using the average sliding method to obtain filtered data;

[0034] S302: Perform outlier removal on the filtered data. Based on the set outlier threshold, determine whether a data point is an outlier. If it is, take the two most recent data points that meet the threshold and perform interpolation to obtain new data, thus obtaining the data after outlier removal.

[0035] S303: The average sliding method is used to perform secondary filtering on the data after removing outliers to obtain the final surface data.

[0036] As a further aspect of the present invention: In step S4, the specific method for performing AF compensation on the scanned surface is as follows:

[0037] S401: The surface shape difference after scanning and processing by the displacement sensor needs to be compensated by the AF mechanism. Different points have different heights, and this height is the amount of change of the focal plane of the actual scanning point of the carrier plate.

[0038] S402: Substitute the above focal plane change into the relationship model between the AF mechanism focusing position Y and the platform focal plane change x in step S107, and calculate the AF mechanism focusing position Y corresponding to each compensation point as a compensation instruction.

[0039] S403: Sends compensation commands to the AF mechanism, controlling it to move to the corresponding position to achieve compensation of the focus plane.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] By determining the relationship between the motion of the AF mechanism and the change in the focal plane of the platform, a model is obtained to show the relationship between the focusing position of the AF mechanism and the change in the focal plane of the platform. This ensures the accuracy of the AF mechanism's focal plane compensation, eliminates the different effects of processing errors, motion errors, and motion on the focal plane, and prevents the phenomenon of differences between the theoretically compensated surface shape difference and the actual surface shape difference that needs to be compensated.

[0042] By employing an autofocus calibration method, the surface of the carrier plate is scanned in real time, and the scanned surface data is processed to obtain the change in focal plane at the compensation point. This change is then substituted into the relationship model between the focusing position of the AF mechanism and the change in the focal plane of the platform as a compensation command. Finally, the compensation command is sent to the AF mechanism to control it to move to the corresponding position, so that any point on the carrier plate is exposed at the focal plane position, thereby improving the exposure effect. Attached Figure Description

[0043] Figure 1 This is a flowchart illustrating the exposure compensation method.

[0044] Figure 2 This is a front view of the surface profile of the carrier plate scanned by the displacement sensor on the crossbeam.

[0045] Figure 3 This is a top view of the scan points on the carrier plate.

[0046] Figure 4 This is a schematic diagram showing the focusing changes of the AF mechanism.

[0047] Figure 5 This is a schematic diagram of circular markers.

[0048] Figure 6 This is a schematic diagram illustrating the relationship between different z-axis heights and g values ​​of the platform.

[0049] Figure 7 A top view of the surface of the carrier plate scanned by the motion sensor.

[0050] Figure 8 This is a schematic diagram of surface data processing.

[0051] Figure 9 This is a diagram illustrating the relative positions of the compensation points and the scanning points.

[0052] Figure 10 This is a schematic diagram of the actual surface shape relative to the theoretical focal plane.

[0053] In the diagram: 1. Displacement sensor; 2. Crossbeam; 3. Carrier plate; 4. Platform; 5. Scanning point; 6. Exposure lens; 7. AF mechanism; 8. Suction cup camera. Detailed Implementation

[0054] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] Example 1

[0056] A focusing calibration method with autofocus function includes the following steps:

[0057] S1: Determine the relationship between the motion of AF mechanism 7 and the change in focal plane of platform 4, specifically including:

[0058] S101: Position the AF mechanism 7 below the exposure lens 6, move the suction cup camera 8 on platform 4 directly below the exposure lens 6, and determine the optimal focal plane position Z of platform 4 at that position using the suction cup camera 8. m ,like Figure 4 As shown, specifically:

[0059] a) Exposure lens 6 projects a circular marker onto suction cup camera 8, such as Figure 5 As shown, the suction cup camera 8 collects the average grayscale gradient g of the projected image from the top, bottom, left, and right of each marker point. The g value reflects the degree of focus of the projected image; the higher the g value, the closer it is to the focal plane.

[0060] b) Control platform 4 to move in the z-direction, and suction cup camera 8 repeats step a) to obtain a set of g values ​​at different z-direction heights. Perform a second-order fitting on the g values ​​of platform 4 at different z-direction heights to obtain a relationship model between z and g. This model can be expressed as: g = a g z 2 +b g z 1 +c g ,like Figure 6 As shown;

[0061] c) Based on the obtained relational model, solve for the focal plane z value when the g value reaches its maximum, and use this as the optimal focal plane position Z for the suction cup camera at this location. m , where z m =-b g / (2a g This position, which is the center axis of the curve, is also considered the optimal focal plane position Z of platform 4 because the suction cup camera 8 and platform 4 move synchronously. m .

[0062] S102: Control the focusing module of the AF mechanism 7 to step a certain distance, repeat step s101, and obtain the optimal focal plane position Z of platform 4 in the z-direction under different positions of the focusing module of the AF mechanism 7. m This forms a set of single-exposure lenses with AF mechanism position 7 (S) and platform position 4 (Z) optimal focal plane position. m Corresponding relationship data:

[0063] S <![CDATA[S0]]> <![CDATA[S1]]> <![CDATA[S2]]> <![CDATA[S3]]> …… <![CDATA[S n-2 ]]> <![CDATA[S n-1 ]]> <![CDATA[S n ]]> <![CDATA[Z m ]]> <![CDATA[Z0]]> <![CDATA[Z1]]> <![CDATA[Z2]]> <![CDATA[Z3]]> …… <![CDATA[Z n-2 ]]> <![CDATA[Z n-1 ]]> <![CDATA[Z n ]]>

[0064] Then, the suction cup camera 8 is moved under multiple exposure lenses 6 respectively. Similarly, multiple sets of AF mechanism 7 positions S and platform 4 optimal focal plane positions Z are obtained. m The corresponding relationship data.

[0065] S103: The position S of AF mechanism 7 and the focal plane position Z of platform 4 are fitted using a cubic fitting method. m The corresponding relationship is fitted using the following formula: Where: a3, a2, and a1 are calibration coefficients, and l is a constant term.

[0066] S104: Based on the focal plane position Z of platform 4 m The range of variation determines the position Z of the 4 focal planes on the 6th exposure lens platform. m median Z mid Z mid =(Z min +Z max ) / 2, then take multiple exposures of lens 6 Z mid The average value Z avg Take the median Z mid To ensure that the zoom module of AF mechanism 7 can achieve the maximum vertical adjustment range, the average value Z is taken. avg To ensure the consistency of the focal plane at the zero point of all exposure lenses 6, and to guarantee that the focal plane of all exposure lenses 6 can achieve the maximum adjustment range, the fitting method in step S103 is used to calculate the median Z of multiple exposure lenses 6. mid The average value Z avg After substituting into the fitting formula in step S103, the formula for calculating the logic zero y0 is obtained;

[0067]

[0068] The logic zero point y0 of AF mechanism 7 is obtained, which is the initial position of the focusing module of AF mechanism 7.

[0069] S105: Move Platform 4 to Z avg The position is adjusted so that the focal planes of the multiple exposure lenses 6 are aligned to the same position by moving multiple AF mechanisms 7 to the position of y0.

[0070] S106: Based on the calibration data from step S102, the relative average value Z of the focal plane position of platform 4 can be obtained. avg The change in x, the motion y of AF mechanism 7 relative to the logic zero point y0, and the correspondence between the change in focal plane x of platform 4 and the motion y of AF mechanism 7 are mapped one-to-one:

[0071] y <![CDATA[S0-y0]]> <![CDATA[S1-y o ]]> <![CDATA[S2-y0]]> <![CDATA[S3-y0]]> …… <![CDATA[S n-2 -y0]]> <![CDATA[S n-1 -y0]]> <![CDATA[S n -y0]]> x <![CDATA[Z0-Z avg ]]> <![CDATA[Z1-Z avg ]]> <![CDATA[Z2-Z avg ]]> <![CDATA[Z3-Z avg ]]> …… <![CDATA[Z n-2 -WITH avg ]]> <![CDATA[Z n-1 -WITH avg ]]> <![CDATA[Z n -WITH avg ]]>

[0072] S107: The relationship between the focal plane change x and the motion y of the AF mechanism 7 was obtained by fitting a cubic term. The fitting formula is: y = ax 3 +bx 2 +cx 1+L, then the relationship between the focal plane change x and the focusing position Y of the AF mechanism 7 relative to the logic zero point y0 is: Y = ax 3 +bx 2 +cx 1 +L0, where L0=y0+L, a is the calibrated first-order coefficient, b is the calibrated second-order coefficient, c is the calibrated third-order coefficient, and L is the constant term.

[0073] Example 2

[0074] An exposure compensation method includes the following steps:

[0075] S1: Use the focusing calibration method with autofocus function.

[0076] S2: Real-time surface scanning:

[0077] S201: Move platform 4 to the starting position, fix displacement sensor 1 to an initial position on crossbeam 2, and begin scanning the surface profile of the loading plate 3 on the platform 4, such as... Figure 2 As shown;

[0078] S202: By moving platform 4 in the y-direction and by moving displacement sensor 1 in the x-direction via crossbeam 2, the z-direction change of the surface profile of the carrying plate 3 on platform 4 can be measured in real time. Displacement sensor 1 records the surface profile data of carrying plate 3, such as... Figure 3 As shown, the scanning continues until the entire surface of carrier plate 3 is scanned.

[0079] The specific scanning process is as follows: Figure 7 As shown: First, platform 4 moves to the starting position, then platform 4 moves forward to the ending position, and displacement sensor 1 records the surface shape data of carrier plate 3. Next, displacement sensor 1 moves forward a certain distance, and finally platform 4 moves in the reverse direction back to the starting position, and displacement sensor 1 records the surface shape data of carrier plate 3. Repeating the above motion trajectory, multiple columns of raw scan data can be obtained. Let its coordinates be (x... n y n , z n ).

[0080] S3: Process the scanned surface data:

[0081] S301: The scan data obtained in step S2 is filtered once using an average sliding method to obtain filtered data. Taking a column of original scan data in step S202 as an example: the original data can be regarded as: (x1, y1, y2) n d n ), d n The z-axis height data of the carrier plate 3 is scanned by displacement sensor 1. The x and y coordinates are not processed, only the dn data is processed.

[0082] like Figure 8 As shown, when the filter width is m, m / 2 more data points will be scanned before and after.

[0083] Due to the measurement accuracy issue of displacement sensor 1, each measurement data is not the true value. Therefore, it is necessary to use an average sliding method to take it as the true value. The data is processed by sliding once, and the sliding area is the valid data.

[0084] The sliding zone is calculated as follows:

[0085] Because the sliding process requires averaging multiple points, a buffer of half a filter width needs to be added before and after the sliding process. The value in the buffer is the data from the invalid region.

[0086] The buffer is calculated as: e j = (d1+d2+…+d j ) / j

[0087] S302: Perform outlier removal on the filtered data. Based on a set outlier threshold, determine whether a data point is an outlier. If so, take the two most recent data points that meet the threshold and perform interpolation to obtain new data. This process removes outliers.

[0088] like Figure 8 As shown, the judgment is made when: |e i -d i |<γ, then f i =d i γ is the abnormal threshold;

[0089] When: |e i -d i If |>γ, then the two most recent data that meet the threshold are interpolated to obtain new data.

[0090] For example: e r e r+k e is a non-outlier value. r+1 e r+2 ....e r+k-1 If it is an outlier, then the new location is:

[0091] S303: The data after outlier removal is subjected to secondary filtering using an average sliding method to obtain the final surface data. Secondary sliding processing:

[0092] like Figure 8 As shown, the same sliding process yields new sliding data h. i Then the 3-sided shape data of the carrier board is updated to: (x1, y n hn h is the height of the actual scanning point 5 on the carrier plate 3.

[0093] S4: Perform AF compensation on the scanned surface.

[0094] S401: The surface shape difference after scanning and processing by displacement sensor 1 needs to be compensated by AF mechanism 7. Different points have different heights, and this height is the amount of change of the focal plane of the actual scanning point 5 of the carrier plate 3.

[0095] like Figure 9 As shown, the corresponding point that needs to be compensated is determined, and it is determined whether the corresponding point is the scanning point 5. If it is not the scanning point 5, the data of the compensation point is fitted by the double interpolation method to obtain the focusing distance k, which is the change in the focal plane of the compensation point.

[0096] S402: Substitute the aforementioned focal plane change into the relationship model between the focusing position Y of AF mechanism 7 and the focal plane change x of platform 4 in step S107, and calculate the focusing position Y of AF mechanism 7 corresponding to each compensation point, as a compensation command, such as... Figure 10 As shown.

[0097] S403: Sends the compensation command to the AF mechanism 7, controls it to move to the corresponding position, realizes the compensation of the focal plane, and makes any point on the carrier plate 3 exposed under the focal plane position, thereby improving the exposure effect.

[0098] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A focusing calibration method with an auto-focusing function, characterized in that, The method comprises the following steps: S1: determining the relationship between the AF mechanism movement and the platform focal plane change, specifically comprising: S101: Set the AF mechanism below the exposure lens, move the suction cup camera on the platform to a position directly below the exposure lens, and determine the optimal focal plane position Z of the platform through the suction cup camera m ; S102: Control the focusing module of the AF mechanism to step a certain distance, repeat step s101, and obtain the optimal focal plane position Z in the z-direction of the platform under different positions of the focusing module of the AF mechanism. m This forms a set of AF mechanism positions S and optimal focal plane positions Z for a single exposure lens. m The corresponding relationship data was obtained, and then the suction cup camera was moved to multiple exposure lenses respectively. Similarly, multiple sets of AF mechanism positions S and platform optimal focal plane positions Z were obtained. m Corresponding relationship data; S103: adopt cubic term fitting mode to fit the corresponding relationship between AF mechanism position S and platform focal plane position Z m ; S104: Based on the focal plane position Z of the platform m The range of variation determines the focal plane position Z of the platform under a single exposure lens. m The median z mid Then take multiple exposure shots of z mid The average value Z avg Using the fitting method in step S103, the logic zero point y0 of the AF mechanism is obtained, which is the initial position of the focusing module of the AF mechanism. S105: move the platform to the position of Z avg and move the plurality of AF mechanisms to the position of y0, thereby adjusting the focal planes of the plurality of exposure lenses to be consistent. S106: The variation x of the platform focal plane position relative to the average value Z can be obtained according to the calibration data of step S102, and the movement amount y of the AF mechanism relative to the logical zero point y0, so that the platform focal plane variation x and the AF mechanism movement amount y data are one-to-one corresponding. avg S106: The variation x of the platform focal plane position relative to the average value Z can be obtained according to the calibration data of step S102, and the movement amount y of the AF mechanism relative to the logical zero point y0, so that the platform focal plane variation x and the AF S107: fitting the corresponding relationship between the focal plane change x and the AF mechanism movement y by using a cubic term fitting method.

2. The focusing calibration method with auto-focusing function according to claim 1, wherein, In step S101, the method for determining the platform focal plane position by the chuck camera is specifically: a) The exposure lens projects a circular marker point on the chuck camera, and the chuck camera collects the average value g of the gray scale change gradient of the projected pattern at each marker point up and down and left and right. The g value reflects the focusing degree of the projected pattern, and the higher the g value, the closer to the focal plane position; b) Control the platform to move in the z direction, and repeat step a) to obtain a group of g values at different z direction heights. The g values of the platform at different z direction heights are subjected to quadratic fitting to obtain a relationship model of z and g; c) According to the relationship model, the value of focal plane z is solved when the value of g reaches the maximum, which is the best focal plane position Z of the chuck camera at this position m Since the chuck camera and the platform are synchronous, this position is also the best focal plane position Z of the platform m .

3. The focusing calibration method with auto-focusing function according to claim 1, wherein, In step S103, the fitting formula used is: wherein a3, a2, a1 are calibration coefficients, and l is a constant term.

4. The focusing calibration method with auto-focusing function according to claim 3, wherein, In step S104, the median value Z of the plurality of exposure lenses is calculated mid The average value Z of the median values Z of the plurality of exposure lenses is calculated avg After being brought into the fitting formula of step S103, the logical zero point y0 calculation formula is obtained as Take the median Z mid In order to ensure that the zoom module of the AF mechanism can get the maximum adjustment range up and down; take the average Z avg In order to ensure that all exposure lenses have consistent focal surfaces at zero position, and at the same time ensure that all exposure lenses can get the maximum adjustment range.

5. The focusing calibration method with auto-focusing function according to claim 4, wherein, In step S107, the fitting formula for the relationship between the focal plane change x and the AF mechanism change y is: y = ax 3 +bx 2 +cx 1 +L, then the relationship between the focal plane change x and the focusing position Y of the AF mechanism relative to the logic zero point y0 is: Y = ax 3 +bx 2 +cx 1 +L0, where L0=y0+L, a is the calibrated first-order coefficient, b is the calibrated second-order coefficient, c is the calibrated third-order coefficient, and L is the constant term.

6. An exposure compensation method characterized by, The method comprises the following steps: S1: using the focusing calibration method with automatic focusing function according to any one of claims 1-5; S2: real-time surface scanning; S3: processing the scanned surface data; S4: AF compensation for the scanned surface.

7. The exposure compensation method according to claim 6, wherein In step S2, the real-time surface scanning method is specifically: S201: move the platform to the starting position, fix the displacement sensor at an initial position on the cross beam, and start scanning the surface of the load plate on the platform table; S202: by moving the platform in the y direction and moving the displacement sensor in the x direction through the cross beam, the z direction change of the load plate surface on the platform table can be measured in real time. The displacement sensor records the load plate surface data until the entire load plate surface is scanned, and a plurality of columns of original scanning data can be obtained.

8. The exposure compensation method of claim 7, wherein, In step S3, the method for processing the scanned surface data is specifically: S301: using the average sliding method to perform first filtering processing on the scanning data obtained in step S2 to obtain first filtered data; S302: removing abnormal points from the first filtered data, and determining whether the data point is an abnormal point according to the set abnormal threshold. If it is, the nearest two data points meeting the threshold are taken for interpolation processing to obtain new data, and the data after removing the abnormal points is obtained; S303: using the average sliding method to perform second filtering processing on the data after removing the abnormal points to obtain the final surface data.

9. The exposure compensation method of claim 8, wherein, In step S4, the method for AF compensation for the scanned surface is specifically: S401: the displacement sensor scans the surface difference after processing, which needs to be compensated by the AF mechanism. Different point positions have different heights, and the height is the actual scanning point focal plane change of the load plate; S402: substituting the above focal plane change into the relationship model between the AF mechanism focusing position Y and the platform focal plane change x in step S107 to calculate the corresponding AF mechanism focusing position Y of each compensation point position as the compensation instruction; S403: send the compensation instruction to the AF mechanism to control it to move to the corresponding position to realize the compensation of the focal plane.

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