A Measuring System and Method for the Outer Dimension of a Photomask Substrate

Abstract

The present invention discloses an optical mask substrate contour dimension measurement system and method, belonging to the field of semiconductor and display panel optical mask substrate manufacturing. The system includes: a sample transfer unit, a sample movement unit, and an optical measurement system; the sample transfer unit is used to transfer the optical mask substrate to be measured between the area to be inspected and the test area; the sample movement unit is used to cooperate with the optical measurement system to adjust the pitch angle, rotation angle, and height of the optical mask substrate to be measured; the optical measurement system is used to measure the contour dimensions of the optical mask substrate to be measured. The present invention provides an optical mask substrate contour dimension measurement system and method with high precision, high repeatability, non-destructive, and high cost performance.

Description

Technical Field

[0001] The present invention belongs to the field of manufacturing semiconductor and display panel photomask substrates, and more particularly, relates to a system and method for measuring the external dimensions of a photomask substrate. Background Art

[0002] As an important link in the semiconductor and display panel manufacturing processes, the photomask templates used in this process usually consist of a quartz substrate and a chromium film with high purity, high laser damage threshold, high ultraviolet transmittance, and low thermal expansion coefficient. At present, due to high foreign technical barriers and thresholds, domestic enterprises have started to research and develop photomask substrates, so it is crucial to accurately measure the photomask substrates.

[0003] According to the regulations in national standards, the external dimensions of a photomask substrate that need to be measured include side length, thickness, total thickness variation, apex angle, apex radius, chamfer straight edge length, size A (distance from the straight edge of the mark to the apex) and size B (depth of the mark) of the mark. Currently, these dimensions can be measured by contact measurement methods such as vernier calipers, height gauges, and profilometers, which are inexpensive and easy to operate, but have poor accuracy and are likely to damage the light-transmitting surface, resulting in the scrapping of the photomask substrate; using optical image measurement equipment, the cost is relatively low and the reliability is high, but large measurement errors are likely to occur during edge focusing, and the adaptability to samples is poor; using high-end optical measurement equipment has high accuracy and good sample adaptability, but the cost is too high and the efficiency is low. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement requirements in the prior art, the present invention provides a system and method for measuring the external dimensions of a photomask substrate with high accuracy, high repeatability, non-damage, and high cost performance.

[0005] To achieve the above object, according to one aspect of the present invention, a system for measuring the external dimensions of a photomask substrate is provided, including: a sample transfer unit, a sample movement unit, and an optical measurement system;

[0006] The sample transfer unit is configured to transfer the photomask substrate to be measured between the area to be inspected and the test area;

[0007] The sample movement unit is configured to cooperate with the optical measurement system to adjust the pitch angle, rotation angle, and height of the photomask substrate to be measured;

[0008] The optical measurement system is configured to measure the external dimensions of the photomask substrate to be measured.

[0009] In some alternative embodiments, the sample transfer unit includes: a loading and unloading stage and a grasping manipulator;

[0010] The sample loading and unloading stage is located in the area to be inspected and is used to place the optical mask substrate to be measured and the inspected optical mask substrate;

[0011] The grasping manipulator is used to grasp and move the optical mask substrate to be measured to the test area, and when the optical mask substrate to be measured needs to be turned over for measurement, it grasps and turns over the optical mask substrate to be measured, and after the measurement of the optical mask substrate to be measured is completed, it grasps the optical mask substrate to be measured and transfers it to the sample loading and unloading stage.

[0012] In some alternative embodiments, the sample movement unit includes: a sample claw disc and a sample displacement stage;

[0013] The grasping manipulator grasps and moves the optical mask substrate to be measured to the sample claw disc in the test area, and after detecting the optical mask substrate to be measured, clamps the optical mask substrate to be measured through the sample claw disc to prevent the optical mask substrate to be measured from falling;

[0014] The sample displacement stage can drive the sample claw disc to perform pitching, rotating and lifting movements, so as to cooperate with the optical measurement system to adjust the optical mask substrate to be measured to the target position.

[0015] In some alternative embodiments, the optical measurement system includes: a three-axis displacement stage, a white light source, a spectral confocal lens, a photoelectric sensor and a laser confocal probe;

[0016] The three-axis displacement stage is used to drive the white light source, the spectral confocal lens, the photoelectric sensor and the laser confocal probe to move in the horizontal and vertical directions;

[0017] The white light source is used to provide a measurement light source to irradiate the optical mask substrate to be measured;

[0018] The spectral confocal lens is composed of a light-emitting lens and a light-receiving lens. The light-emitting lens is used to disperse and converge white light into light beams of different wavelengths, so that the focal heights of light of different wavelengths in the vertical direction are different. Among them, the light with a shorter wavelength to a longer wavelength corresponds to the light focus distance from the light-emitting position from far to near. After the light beam is reflected by the surface of the optical mask substrate to be measured, it is coupled into the light-receiving lens;

[0019] The photoelectric sensor is used to convert the light coupled by the light-receiving lens into an electrical signal;

[0020] The laser confocal probe is used to measure the thickness of the optical mask substrate to be measured.

[0021] According to another aspect of the present invention, there is provided a method for measuring the external dimensions of an optical mask substrate, including:

[0022] Place the optical mask substrate to be measured on the sample transfer unit in the area to be inspected. The sample transfer unit clamps and moves the optical mask substrate to be measured to the sample motion unit in the test area;

[0023] When measuring the side length, apex angle, apex radius and chamfer straight edge length of the optical mask substrate to be measured, control the optical measurement system to move to the measurement position, and control the pitch, rotation and lifting of the sample motion unit so that the outer dimensions of the optical mask substrate to be measured are located at the measurement position. The optical measurement system scans the front profile of the optical mask substrate to be measured, collects data and then draws a front profile point cloud image. Calculate and generate the measurement results of the side length, apex angle, apex radius and chamfer straight edge length of the optical mask substrate according to the coordinates of each sampling point on the front profile point cloud image;

[0024] Measure the thickness of the optical mask substrate to be measured by the optical measurement system, and calculate the total thickness variation according to the measured thickness;

[0025] When measuring the dimensions A and B of the mark on the optical mask substrate to be measured, the sample transfer unit grabs the optical mask substrate from the sample motion unit, flips it 180° and then places it back on the sample motion unit so that the back of the optical mask substrate to be measured is placed in the test area. The sample motion unit drives the optical mask substrate to be measured, and after tilting to the target angle in cooperation with the optical measurement system, control the optical measurement system to scan the mark angle profile, collect data and then draw an angle profile point cloud image. Calculate and generate the measurement results of the outer dimensions of the optical mask substrate to be measured according to the coordinates of each sampling point on the angle profile point cloud image.

[0026] In some optional implementation manners, placing the optical mask substrate to be measured on the sample transfer unit in the area to be inspected, and the sample transfer unit clamps and moves the optical mask substrate to be measured to the sample motion unit in the test area includes:

[0027] Place the optical mask substrate to be measured on the sampling and loading platform, and the grasping manipulator clamps and moves the optical mask substrate to be measured to the sample claw disc on the sample displacement table in the test area;

[0028] After detecting the optical mask substrate to be measured, clamp the optical mask substrate by the sample claw disc to prevent the optical mask substrate to be measured from falling, and the grasping manipulator is removed from the test area.

[0029] In some optional implementation manners, after detecting the optical mask substrate to be measured, clamping the optical mask substrate by the sample claw disc to prevent the optical mask substrate to be measured from falling, and after the grasping manipulator is removed from the test area, the method further includes:

[0030] Calibrate the initial positions of the foci of each wavelength of the spectral calibration optical measurement system in the coordinate system of the three-axis displacement stage as the origin coordinates, and calibrate the position coordinates, pitch, and rotation angles of the sample displacement stage in the coordinate system of the three-axis displacement stage.

[0031] In some alternative embodiments, when measuring the side length, apex angle, apex radius, and chamfer straight edge length of the measured photomask substrate, control the optical measurement system to move to the measurement position, and control the pitch, rotation, and lifting of the sample displacement stage so that the outer dimensions of the measured photomask substrate are located at the measurement position. After the optical measurement system scans the front profile of the measured photomask substrate and collects data, a front profile point cloud image is drawn. Based on the coordinates of each sampling point on the front profile point cloud image and the calibrated origin coordinates, the position coordinates, pitch, and rotation angles of the sample displacement stage in the coordinate system of the three-axis displacement stage, calculate and generate the measurement results of the side length, apex angle, apex radius, and chamfer straight edge length of the photomask substrate.

[0032] In some alternative embodiments, the thickness of the measured photomask substrate is obtained by taking points on the measured photomask substrate by a laser confocal probe in the optical measurement system, and the total thickness variation is calculated based on the measured thickness.

[0033] In some alternative embodiments, when measuring the dimensions A and B of the marks on the measured photomask substrate, the gripper manipulator grabs the measured photomask substrate from the sample chuck and flips it 180° and then places it back on the sample chuck again, so that the back of the measured photomask substrate is placed in the test area. The sample displacement stage drives the measured photomask substrate, and after tilting to the target angle in cooperation with the optical measurement system, control the optical measurement system to scan the mark angle profile and collect data, and then draw a mark angle profile point cloud image. Based on the coordinates of each sampling point on the mark angle profile point cloud image and the calibrated origin coordinates, the position coordinates, pitch, and rotation angles of the sample displacement stage in the coordinate system of the three-axis displacement stage, calculate and generate the measurement results of the dimensions A and B of the marks on the measured photomask substrate.

[0034] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0035] (1) Through the sample transfer unit, the sample motion unit, and the optical measurement system, it is possible to achieve high-precision, high-repeatability, non-destructive, and cost-effective measurement of the outer dimensions of the photomask substrate.

[0036] (2) The optical plane measurement system composed of a white light source, a spectral confocal lens, and a photoelectric sensor, and the laser confocal probe for height measurement constitute the optical measurement system, and the sample displacement stage equipped with a sample chuck and capable of pitching, rotating, and lifting has the advantages of high precision, high repeatability, and high cost performance.

[0037] (3) The sample jaw plate equipped with sensors can clamp the sample to prevent it from falling after detecting the sample, and will not cause damage to the sample. Description of the Drawings

[0038] Figure 1 is a schematic diagram of a system for measuring the external dimensions of a photomask substrate provided by an embodiment of the present invention;

[0039] Figure 2 is a schematic diagram of a method for measuring the external dimensions of a photomask substrate provided by an embodiment of the present invention;

[0040] Among them, 1 - feeding and sampling stage; 2 - grasping manipulator; 3 - sample jaw plate; 4 - sample displacement stage; 5 - three-axis displacement stage; 6 - white light source; 7 - spectral confocal lens; 8 - photoelectric sensor; 9 - laser confocal probe; 10 - photomask substrate. Detailed Embodiment

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] The technical solution adopted by the present invention is as follows: An optical mask substrate external dimension measurement system includes a sample transfer unit composed of a feeding and sampling stage 1 and a grasping manipulator 2, a sample motion unit composed of a sample chuck 3 and a sample displacement stage 4, and an optical measurement system composed of a three-axis displacement stage 5, a white light source 6, a spectral confocal lens 7, a photoelectric sensor 8, and a laser confocal probe 9. The optical mask substrate to be measured is placed on the feeding and sampling stage 1, and the grasping manipulator 2 picks up the optical mask substrate to be measured and moves it to the sample chuck 3 on the sample displacement stage 4 in the test area; the sample displacement stage 4 can perform pitching, rotation, and lifting motions. After the sensor on the sample chuck 3 detects the optical mask substrate to be measured, it clamps the optical mask substrate to prevent it from falling; An optical plane measurement system composed of a white light source 6, a spectral confocal lens 7, and a photoelectric sensor 8, and a laser confocal probe 9 for height measurement are installed on the three-axis displacement stage 5. These two constitute the optical measurement system, and the optical measurement system can move in horizontal and vertical directions. When measuring the side length, apex angle, apex radius, and chamfer straight edge length of the optical mask substrate, the optical measurement system is controlled by the measurement software to scan the front contour of the optical mask substrate to be measured, collect data, and then draw a point cloud image; the thickness of the optical mask substrate to be measured is measured by the laser confocal probe 9 in the optical measurement system, and the total thickness change is calculated based on the measured thickness; when measuring the dimensions A and B of the mark on the optical mask substrate to be measured, the grasping manipulator 2 picks up the optical mask substrate from the sample chuck 3, flips it 180°, and then places it back on the sample chuck 3, so that the back of the optical mask substrate to be measured is placed in the test area. The sample displacement stage 4 drives the optical mask substrate to be measured, and after tilting it to the target angle in cooperation with the optical measurement system, the measurement software controls the optical measurement system to scan the mark angle contour, collect data, and then draw a point cloud image; finally, the software calculates and generates the measurement result of the external dimensions of the optical mask substrate to be measured based on the coordinates of each sampling point on the point cloud image.

[0043] Embodiment

[0044] As Figure 1 shown is a schematic diagram of an optical mask substrate external dimension measurement system provided by an embodiment of the present invention, including a sample transfer unit, a sample motion unit, and an optical measurement system;

[0045] The sample transfer unit is used to transfer the optical mask substrate to be measured between the area to be inspected and the test area;

[0046] The sample motion unit is used to adjust the pitching angle, rotation angle, and height of the optical mask substrate to be measured in cooperation with the optical measurement system;

[0047] The optical measurement system is used to measure the external dimensions of the optical mask substrate to be measured.

[0048] In an embodiment of the present invention, the above-mentioned sample transfer unit mainly includes a sample loading and unloading stage 1 and a grasping manipulator 2. The sample loading and unloading stage 1 is located in the area to be inspected and is used to place the optical mask substrate to be measured and the inspected optical mask substrate, facilitating the operator to pick and place samples. The grasping manipulator 2 is used to grasp the optical mask substrate to be measured and move it to the sample chuck 3 in the test area, and when the optical mask substrate to be measured needs to be turned over for measurement, grasp and turn over the optical mask substrate to be measured; after the measurement of the optical mask substrate to be measured is completed, grasp the optical mask substrate to be measured and transfer it to the sample loading and unloading stage 1.

[0049] In an embodiment of the present invention, the above-mentioned sample movement unit mainly includes a sample chuck 3 and a sample displacement stage 4. After the sensor on the sample chuck 3 detects the optical mask substrate to be measured, it clamps it to prevent it from falling. The sample displacement stage 4 can perform pitching, rotating and lifting movements, and cooperate with the optical measurement system to adjust the optical mask substrate to be measured to the correct target position.

[0050] In an embodiment of the present invention, the above-mentioned optical measurement system mainly includes a three-axis displacement stage 5, a white light source 6, a spectral confocal lens 7, a photoelectric sensor 8 and a laser confocal probe 9, and the functions of each part are as follows:

[0051] The three-axis displacement stage 5 is used to drive the white light source 6, the spectral confocal lens 7, the photoelectric sensor 8 and the laser confocal probe 9 to move in the horizontal and vertical directions;

[0052] The white light source 6 is used to provide a measurement light source to irradiate the sample 10 to be measured, and its wavelength range is the visible light spectrum, that is, 380nm to 780nm;

[0053] The spectral confocal lens 7 is composed of a light-emitting lens and a light-receiving lens. The light-emitting lens is used to disperse and converge the white light into light beams of different wavelengths. The focal heights of light of different wavelengths in the vertical direction are different. The focal point of short-wavelength light is far from the light-emitting position, and the focal point of long-wavelength light is close to the light-emitting position. After the light beam is reflected by the surface of the optical mask substrate 10, it is coupled into the light-receiving lens;

[0054] In an embodiment of the present invention, the short wavelength refers to a wavelength of 380nm, and the long wavelength refers to a wavelength of 780nm. That is, the focal distance of the light corresponding to the wavelength from short to long from the light-emitting position is from far to near.

[0055] The photoelectric sensor 8 is used to convert the light coupled by the light-receiving lens into an electrical signal;

[0056] The laser confocal probe 9 is used to measure the thickness of the optical mask substrate to be measured.

[0057] A method for measuring the outer dimension of a photomask substrate provided by an embodiment of the present invention. This method controls a three-axis displacement stage to drive an optical measurement system through measurement software, scans, samples points, and collects data on the contour of the outer dimension of the photomask substrate to be measured, and then draws a point cloud image. The outer dimension of the photomask substrate is calculated based on the coordinate relationship of each point on the point cloud image. As Figure 2 shown, the method for measuring the outer dimension of a photomask substrate using this system is as follows:

[0058] Place the photomask substrate 10 to be measured on the loading and unloading stage 1, and the grasping manipulator 2 picks it up and moves it to the sample chuck 3 of the sample displacement stage 4 in the test area;

[0059] After the sensor on the sample chuck 3 detects the photomask substrate to be measured, it clamps the photomask substrate to prevent it from falling, and the grasping manipulator 2 moves away from the test area, and the optical measurement system is ready to start measurement;

[0060] Calibrate the initial position of the focus of each wavelength of the spectrum of the optical measurement system in the coordinate system of the three-axis displacement stage as the origin coordinate, and calibrate the position coordinate, pitch, and rotation angle of the sample displacement stage 4 in the coordinate system of the three-axis displacement stage;

[0061] Control the optical measurement system to move to the measurement position through the measurement software, and control the pitch, rotation, and lifting of the sample displacement stage 4 so that the outer dimension to be measured is located at the measured position. The optical measurement system scans the front contour of the photomask substrate 10 to be measured, collects data, and then draws a front contour point cloud image. The software will calculate and generate the measurement results of the side length, vertex angle, vertex radius, and chamfer straight edge length of the photomask substrate to be measured based on the coordinates of each sampling point on the front contour point cloud image;

[0062] The thickness of the photomask substrate 10 to be measured is obtained by sampling points with a laser confocal probe 9 in the optical measurement system, and the total thickness variation is calculated based on the measured thickness;

[0063] When measuring the marked dimensions A and B of the photomask substrate 10 to be measured, the grasping manipulator 2 grabs the photomask substrate 10 from the sample chuck 3, flips it 180°, and then places it back on the sample chuck 3 again, so that the back of the photomask substrate 10 is placed in the test area. The sample displacement stage 4 drives the photomask substrate 10 to be measured, and after tilting it to a specific target angle in cooperation with the optical measurement system, the measurement software controls the optical measurement system to scan the marked angle contour, collect data, and then draw a marked angle contour point cloud image; the software will calculate and generate the measurement results of the marked dimensions A and B of the photomask substrate 10 to be measured based on the coordinates of each sampling point on the marked angle contour point cloud image.

[0064] It should be noted that according to the needs of implementation, each step / component described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0065] Those skilled in the art can easily understand that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the external dimensions of a photomask substrate based on a photomask substrate external dimension measurement system, characterized in that, the photomask substrate external dimension measurement system includes: a sample transfer unit, a sample movement unit and an optical measurement system. The sample transfer unit is used to transfer the measured photomask substrate between the area to be inspected and the test area; the sample movement unit is used to cooperate with the optical measurement system to adjust the pitch angle, rotation angle and height of the measured photomask substrate; the optical measurement system is used to measure the external dimensions of the measured photomask substrate. The method includes: Placing the measured photomask substrate on the sample transfer unit in the area to be inspected, and the sample transfer unit clamps and moves the measured photomask substrate to the sample movement unit in the test area; When measuring the side length, apex angle, apex radius and chamfer straight edge length of the measured photomask substrate, controlling the optical measurement system to move to the measurement position, and controlling the pitch, rotation and lifting of the sample movement unit so that the external dimensions of the measured photomask substrate are located at the measured position. The optical measurement system scans the front contour of the measured photomask substrate and collects data, and then draws a front contour point cloud image. According to the coordinates of each sampling point on the front contour point cloud image, the measurement results of the side length, apex angle, apex radius and chamfer straight edge length of the photomask substrate are calculated; Measuring the thickness of the measured photomask substrate by the optical measurement system, and calculating the total thickness change amount according to the measured thickness; When measuring the dimensions A and B of the mark on the measured photomask substrate, the sample transfer unit grabs the measured photomask substrate from the sample movement unit, flips it 180° and then places it back on the sample movement unit again, so that the back of the measured photomask substrate is placed in the test area. The sample movement unit drives the measured photomask substrate, and after tilting it to the target angle in cooperation with the optical measurement system, controls the optical measurement system to scan the mark angle contour and collect data, and then draws an angle contour point cloud image. According to the coordinates of each sampling point on the angle contour point cloud image, the measurement results of the external dimensions of the measured photomask substrate are calculated.

2. The method according to claim 1, characterized in that, the step of placing the measured photomask substrate on the sample transfer unit in the area to be inspected, and the sample transfer unit clamps and moves the measured photomask substrate to the sample movement unit in the test area includes: Placing the measured photomask substrate on the sampling and conveying stage, and the grabbing manipulator clamps and moves the measured photomask substrate to the sample claw plate on the sample displacement stage in the test area; After detecting the measured photomask substrate, clamping the measured photomask substrate by the sample claw plate to prevent the measured photomask substrate from falling, and the grabbing manipulator moves away from the test area.

3. The method according to claim 2, characterized in that, after detecting the measured photomask substrate, clamping the measured photomask substrate by the sample claw plate to prevent the measured photomask substrate from falling, and after the grabbing manipulator moves away from the test area, the method further includes: Calibrate the initial positions of the foci of each wavelength of the spectral calibration optical measurement system in the coordinate system of the three-axis displacement stage as the origin coordinates, and calibrate the position coordinates, pitch, and rotation angles of the sample displacement stage in the coordinate system of the three-axis displacement stage.

4. The method according to claim 3, wherein, when measuring the side length, apex angle, apex radius, and chamfer straight-edge length of the measured photomask substrate, control the optical measurement system to move to the measurement position, and control the pitch, rotation, and lifting of the sample displacement stage so that the external dimensions of the measured photomask substrate are located at the measured position. After the optical measurement system scans the front contour of the measured photomask substrate and collects data, a front contour point cloud image is drawn. According to the coordinates of each sampling point on the front contour point cloud image and the calibrated origin coordinates, the position coordinates, pitch, and rotation angles of the sample displacement stage in the coordinate system of the three-axis displacement stage, calculate and generate the measurement results of the side length, apex angle, apex radius, and chamfer straight-edge length of the photomask substrate.

5. The method according to claim 4, wherein, The thickness of the measured photomask substrate is obtained by taking points on the measured photomask substrate by the laser confocal probe in the optical measurement system, and the total thickness change is calculated based on the measured thickness.

6. The method according to claim 5, wherein, when measuring the dimensions A and B of the mark on the measured photomask substrate, the gripping manipulator grabs the measured photomask substrate from the sample chuck and flips it 180° and then places it back on the sample chuck, so that the back of the measured photomask substrate is placed in the test area. The sample displacement stage drives the measured photomask substrate, and after tilting to the target angle in cooperation with the optical measurement system, control the optical measurement system to scan the mark angle contour and collect data, and then draw a mark angle contour point cloud image. According to the coordinates of each sampling point on the mark angle contour point cloud image and the calibrated origin coordinates, the position coordinates, pitch, and rotation angles of the sample displacement stage in the coordinate system of the three-axis displacement stage, calculate and generate the measurement results of the dimensions A and B of the mark on the measured photomask substrate.

7. The method according to claim 1, wherein, the sample transfer unit includes: a sampling and loading stage and a gripping manipulator; the sampling and loading stage is located in the area to be inspected and is used to place the measured photomask substrate and the inspected photomask substrate; the gripping manipulator is used to grab and move the measured photomask substrate to the test area, and when the measured photomask substrate needs to be turned over for measurement, grab and turn over the measured photomask substrate, and after the measurement of the measured photomask substrate is completed, grab the measured photomask substrate and transfer it to the sampling and loading stage.

8. The method according to claim 7, wherein, the sample motion unit includes: a sample chuck and a sample displacement stage; the gripping manipulator grabs and moves the measured photomask substrate to the sample chuck in the test area, and after detecting the measured photomask substrate, clamps the measured photomask substrate through the sample chuck to prevent the measured photomask substrate from falling; the sample displacement stage can drive the sample chuck to perform pitch, rotation, and lifting movements, so as to cooperate with the optical measurement system to adjust the measured photomask substrate to the target position.

9. The method according to claim 8, wherein, the optical measurement system comprises: a three-axis displacement stage, a white light source, a spectral confocal lens, a photoelectric sensor, and a laser confocal probe; the three-axis displacement stage is configured to drive the white light source, the spectral confocal lens, the photoelectric sensor, and the laser confocal probe to move in horizontal and vertical directions; the white light source is configured to provide a measurement light source to irradiate the light mask substrate to be measured; the spectral confocal lens consists of an outgoing light lens and a light-receiving lens, the outgoing light lens is configured to disperse and converge white light into light beams of different wavelengths, so that the focal heights of light of different wavelengths in the vertical direction are different, wherein, the light focus corresponding to the wavelength from short to long is from far to near from the outgoing position, and the light beam is coupled into the light-receiving lens after being reflected by the surface of the light mask substrate to be measured; the photoelectric sensor is configured to convert the light coupled by the light-receiving lens into an electrical signal; the laser confocal probe is configured to measure the thickness of the light mask substrate to be measured.

Images