Automatic focusing device and focusing method

Abstract

The automatic focusing device and focusing method provided in the present application change the position of the conjugate plane of the automatic focusing device by moving the positions of the projection mask and the detection mask, compensate for the displacement caused by the change of the conjugate plane, and change the focal plane position of the automatic focusing device without changing the measurement accuracy. Compared with the existing range-increasing solutions, this method achieves a larger range, higher accuracy, and less impact of image quality degradation.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to an automatic focusing device and a focusing method. Background Art

[0002] Since semiconductor wafer inspection equipment requires high detection accuracy, the magnification of the objective lens continues to increase and the depth of field gradually decreases, the impact of the distance change between the objective lens and the wafer cannot be ignored. In order to keep the wafer at the correct working distance, an automatic focusing device is required to measure the distance change between the objective lens and the wafer quickly and accurately in real time.

[0003] With the improvement of semiconductor technology, the wafer pattern structure is becoming more and more complex, especially for 3D NAND wafers with more structural levels, the autofocus device needs to have sufficient measurement range to achieve focusing within a larger range, while ensuring that the measurement accuracy remains unchanged, and the resolution of the autofocus device cannot be reduced due to the increase in range. In addition, due to reasons such as objective lens chromatic aberration, system optical magnification error, and module-to-module adjustment error, there will be a certain difference between the focal plane of the autofocus device and the focal plane of the system imaging.

[0004] Existing solutions to the above problems include: (1) increasing the mask period and increasing the measurement range. This method will lead to reduced resolution and measurement accuracy; (2) adding a lens group at the front end of the autofocus device and adjusting the lens in the lens group to achieve the purpose of adjusting the focal plane. If the focal plane distance adjusted by this method is too large, it will greatly change the image quality and reduce the measurement accuracy of the autofocus device; (3) using software methods to compensate for the distance difference between the focal plane of the autofocus device and the imaging focal plane of the system and adjust the focal plane. This method will reduce the measurement range of the autofocus device. Summary of the invention

[0005] In view of this, the present invention provides an automatic focusing device and a focusing method to achieve the effect of increasing the measurement range.

[0006] To solve the above problems, this application adopts the following technical solutions:

[0007] One of the purposes of the present application is to provide a focusing method for an automatic focusing device, comprising the following steps:

[0008] Moving the projection mask along the direction of the optical axis;

[0009] Moving the detection mask along the direction of the optical axis;

[0010] The projection mask is moved along a direction perpendicular to the optical axis.

[0011] In some embodiments, the step of moving the projection mask along the direction of the optical axis specifically includes the following steps: controlling the projection mask to move along the direction of the optical axis by a manual translation stage or an electric translation stage.

[0012] In some embodiments, the displacement of the projection mask along the direction of the optical axis can be obtained by converting the square of the ratio of the focal length of the focusing lens group of the automatic focusing device to the focal length of the objective lens.

[0013] In some of the embodiments, whether the projection mask is displaced into place is determined based on the clarity of the mask image at the imaging focal plane of the automatic focusing device.

[0014] In some embodiments, in the step of moving the detection mask along the direction of the optical axis, the detection mask is controlled to move along the direction of the optical axis by a manual translation stage or an electric translation stage.

[0015] In some embodiments, the projection mask, the imaging focal plane of the autofocus device and the detection mask are in a conjugate relationship.

[0016] In some embodiments, the step of moving the projection mask along a direction perpendicular to the optical axis specifically includes the following steps: controlling the projection mask to move along a direction perpendicular to the optical axis by a manual translation stage or an electric translation stage.

[0017] In some embodiments, the moving direction and the moving position of the projection mask are determined according to the focal plane position of the automatic focusing device.

[0018] In some embodiments, the movement amount △x of the projection mask along the direction perpendicular to the optical axis is △x=G*△z*NA, △x is the movement amount, △z is the focal plane movement amount, G is the magnification, NA is the incident angle of light of the automatic focusing device, and the magnification G=the size of the projection mask / the size of the mask image on the object plane.

[0019] In some embodiments, before moving the projection mask or the detection mask, the displacement of the projection mask or the detection mask required for different focal plane positions of the automatic focusing device may be calibrated in advance.

[0020] In some of the embodiments, the autofocus device is a coaxial autofocus device or an off-axis autofocus device.

[0021] The second object of the present application is to provide an automatic focusing device, comprising:

[0022] A first control unit, used for controlling the projection mask to move along the direction of the optical axis;

[0023] A second control unit, used for controlling the detection mask to move along the direction of the optical axis;

[0024] The third control unit is used to control the projection mask to move along a direction perpendicular to the optical axis.

[0025] In some embodiments, the first control unit controls the projection mask to move along the direction of the optical axis through a manual translation stage or an electric translation stage.

[0026] In some embodiments, the displacement of the projection mask along the direction of the optical axis can be obtained by converting the square of the ratio of the focal length of the focusing lens group of the automatic focusing device to the focal length of the objective lens.

[0027] In some of the embodiments, whether the projection mask is displaced into place is determined based on the clarity of the mask image at the imaging focal plane of the automatic focusing device.

[0028] In some embodiments, the second control unit may control the detection mask to move along the direction of the optical axis via a manual translation stage or an electric translation stage.

[0029] In some embodiments, the projection mask, the imaging focal plane of the autofocus device and the detection mask are in a conjugate relationship.

[0030] In some embodiments, the third control unit may control the projection mask to move along a direction perpendicular to the optical axis via a manual translation stage or an electric translation stage.

[0031] In some embodiments, the moving direction and the moving position of the projection mask are determined according to the focal plane position of the automatic focusing device.

[0032] In some embodiments, the movement amount △x of the projection mask along the direction perpendicular to the optical axis is △x=G*△z*NA, △x is the movement amount, △z is the focal plane movement amount, G is the magnification, NA is the incident angle of the light of the automatic focusing device, and the magnification G=the size of the projection mask / the size of the mask image on the object plane.

[0033] In some embodiments, when moving the projection mask or the detection mask, the first control unit, the second control unit and the third control unit may calibrate in advance the displacement of the projection mask or the detection mask required for different focal positions of the automatic focusing device.

[0034] In some of the embodiments, the autofocus device is a coaxial autofocus device or an off-axis autofocus device.

[0035] This application adopts the above technical solution, and its beneficial effects are as follows:

[0036] The automatic focusing device and focusing method provided in the present application change the position of the conjugate plane of the automatic focusing device by moving the positions of the projection mask and the detection mask, compensate for the displacement caused by the change of the conjugate plane, and change the focal plane position of the automatic focusing device without changing the measurement accuracy. Compared with the existing range-increasing solutions, this method achieves a larger range, higher accuracy, and less impact of image quality degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 A schematic diagram of the structure of a coaxial autofocusing device provided in an embodiment of the present application.

[0039] Figure 2 It is a schematic diagram of the structure of the off-axis automatic focusing device provided in an embodiment of the present application.

[0040] Figure 3 It is a flowchart of the steps of a focusing method of an automatic focusing device provided by an embodiment of the present invention.

[0041] Figure 4 It is a schematic diagram of the structure of an automatic focusing device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0043] In the description of the present application, it should be understood that the terms "upper", "lower", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0044] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0045] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0046] See also Figure 1 , is a schematic structural diagram of a coaxial autofocusing device provided in an embodiment of the present application, which includes a light source 110, a first focusing lens group 120, a projection mask 130, a beam splitter 140, an objective lens 150, a second focusing lens group 160, a detection mask 170 and a detector 180. The first focusing lens group 120 includes a 1st lens, ... an Nth lens, N is greater than or equal to 1, the second lens 160 includes a 1′ lens, ... an Mth lens, M is greater than or equal to 1, the projection mask 130 is arranged between the lenses of the first focusing lens group 120, and the detection mask 170 is arranged between the lenses of the second focusing lens group 160. The laser beam emitted by the light source 110 passes through the 1st lens, the projection mask 130, and the Nth lens in sequence and then enters the beam splitter 140. The beam splitter 140 reflects the incident light beam and is focused on the surface of the wafer to be tested by the objective lens 150 and stimulates the wafer to be tested to generate reflected light. The reflected light then enters the beam splitter 140 through the objective lens. The beam splitter 140 transmits the incident reflected light and then passes through the 1′ lens, the detection mask 170 and the Mth lens in sequence and is detected by the detector 180, thereby realizing the detection of the semiconductor wafer on the stage 190.

[0047] See also Figure 2 , is a schematic structural diagram of an off-axis autofocusing device provided by another embodiment of the present application, which includes a light source 210, a projection mask 220, a first focusing lens group 230, an objective lens, a second focusing lens group 240, a detection mask 250 and a detector 260. The first focusing lens group 230 includes a 1st lens, ... an Nth lens, N is greater than or equal to 1, and the second lens 240 includes a 1st' lens, ... an Mth lens, M is greater than or equal to 1. The laser beam emitted by the light source 210 passes through the projection mask 220, the 1st lens, and the Nth lens in sequence, and then enters the objective lens, and is focused on the surface of the wafer to be tested by the objective lens, and excites the wafer to be tested to generate reflected light. The reflected light passes through the objective lens and then passes through the 1st' lens, the Mth lens and the detection mask 250 in sequence, and is detected by the detector 260, thereby realizing the detection of semiconductor wafers.

[0048] Understandably, through Figure 1 and Figure 2The provided autofocus device can realize the detection of semiconductor wafers. However, with the improvement of semiconductor technology, the wafer graphic structure is becoming more and more complex. Especially for wafers with more structural levels such as 3D NAND wafers, the autofocus device is required to have a sufficient measurement range and achieve focusing within a larger range. At the same time, the measurement accuracy must be guaranteed to remain unchanged. The resolution of the autofocus device cannot be reduced due to the increase in range. The current autofocus device cannot meet the above requirements. The present application achieves the effect of increasing the measurement range by moving the projection mask and the detection mask to change the focal plane position of the autofocus device. The technical solution is described in detail below.

[0049] See also Figure 3 , which is a step flow chart of the focusing method of the automatic focusing device provided in an embodiment of the present application, includes the following steps S310 to S330, and the implementation method of each step is described in detail below.

[0050] Step S310: moving the projection mask along the direction of the optical axis.

[0051] In this embodiment, the step of moving the projection mask along the direction of the optical axis specifically includes the following steps: controlling the projection mask to move along the direction of the optical axis by a manual translation stage or an electric translation stage.

[0052] In this embodiment, the displacement of the projection mask along the direction of the optical axis can be obtained by converting the square of the ratio of the focal length of the focusing lens group of the automatic focusing device to the focal length of the objective lens.

[0053] It should be noted that the focal plane position is the position where the output value of the automatic focusing device is 0, that is, the output value of the automatic focusing device is 0 when the target imaging position is reached. For a given automatic focusing device, its current focal plane position and imaging focal plane position are determined. The distance between the focal plane and the imaging focal plane can be calculated based on the focal plane position and the imaging focal plane position, and then converted based on the magnification relationship, that is, the square of the ratio of the focal length of the focusing lens of the automatic focusing device to the focal length of the objective lens, the displacement of the projection mask along the optical axis can be obtained.

[0054] In this embodiment, whether the projection mask is displaced into place can be determined according to the clarity of the mask image at the imaging focal plane of the automatic focusing device.

[0055] Specifically, the clarity of the mask image at the imaging focal plane is observed by a detector or a camera to determine whether the projection mask has been displaced into place. When the mask image at the imaging focal plane is clearly visible, the projection mask is displaced into place; otherwise, the projection mask is further controlled to move back and forth along the direction of the optical axis by a manual translation stage or an electric translation stage until the mask image at the imaging focal plane is clearly visible.

[0056] Step S320: moving the detection mask along the direction of the optical axis.

[0057] In this embodiment, the step of moving the detection mask along the direction of the optical axis specifically includes the following steps: controlling the detection mask to move along the direction of the optical axis by a manual translation stage or an electric translation stage.

[0058] It can be understood that in the process of moving the detection mask along the direction of the optical axis, it is necessary to ensure that the projection mask, the imaging focal plane of the automatic focusing device and the detection mask are in a conjugate relationship. When the position of the projection mask can be determined, the displacement of the detection mask along the optical axis can be determined.

[0059] It can be understood that since the projection mask, the imaging focal plane and the detection mask are in a conjugate relationship, the position of the imaging focal plane of the automatic focusing device is changed by moving the projection mask and the detection mask, thereby expanding the imaging focus range without affecting the imaging quality.

[0060] Step S330: moving the projection mask along a direction perpendicular to the optical axis.

[0061] In this embodiment, the step of moving the projection mask along a direction perpendicular to the optical axis specifically includes the following steps: controlling the projection mask to move along a direction perpendicular to the optical axis by a manual translation stage or an electric translation stage.

[0062] It can be understood that in the process of moving the projection mask and the detection mask along the optical axis, the focal plane position of the automatic focusing device will move. By moving the projection mask in a direction perpendicular to the optical axis, the focal plane displacement and the mask image displacement caused by triangulation can be compensated.

[0063] In this embodiment, during the process of moving the projection mask along a direction perpendicular to the optical axis, the moving direction and the moving position can be determined by monitoring the focal plane position of the automatic focusing device.

[0064] For example: when the projection mask is translated upward perpendicular to the optical axis, it is found that the focal plane position is far away from the target position, which proves that the moving direction is wrong, and the projection mask should be moved downward. When the focal plane position reaches the target position, the projection mask moves into place; when the projection mask is translated downward perpendicular to the optical axis, it is found that the focal plane position is far away from the target position, which proves that the moving direction is wrong, and the projection mask should be moved upward. When the focal plane position reaches the target position, the projection mask moves into place. The above are just a list of possible situations. In practice, the moving direction and moving position can be determined by monitoring the focal plane position of the automatic focusing device.

[0065] In this embodiment, the movement amount △x of the projection mask along the direction perpendicular to the optical axis is G*△z*NA, △x is the movement amount, △z is the focal plane movement amount, G is the magnification, NA is the incident angle of light of the automatic focusing device, and the magnification G=the size of the projection mask / the size of the mask image on the object plane.

[0066] Furthermore, in executing the above steps S310 to S330, when moving the projection mask or the detection mask, the displacement of the projection mask or the detection mask required for different focal plane positions of the automatic focusing device may be calibrated in advance.

[0067] For example, in executing the above steps S310 to S330, the movement amount of the projection mask along the optical axis and along the axis perpendicular to the optical axis, and the movement amount of the detection mask along the optical axis are determined and recorded according to the above steps when the focal plane moves 1um. When the focal plane needs to move 1um, the projection mask and the detection mask are quickly moved according to the calibration value to achieve fast zooming.

[0068] It should be noted that the moving range of the projection mask and the detection mask is related to the focal plane moving range of the automatic focusing device and the system imaging performance. When the adjustment range is designed to be too large, the MTF, telecentricity, distortion and other indicators of the automatic focusing device will deteriorate, and the projection mask image at the detection mask will be distorted due to the above problems, affecting the measurement accuracy. Therefore, it is necessary to adjust the moving range according to the focal plane moving direction, position and imaging state during the movement process, and comprehensively optimize the system MTF, telecentricity, distortion and other performances under different focal plane states so that they are all within the index range, so that the above-mentioned mask displacement is large When the imaging quality is maintained at a good level while increasing the range of the automatic focusing device.

[0069] In this embodiment, the above adjustment method is adopted. Under a certain focal plane, the measurement range of the automatic focusing device is ±2um, and the range of the focal plane position that can be changed by moving the mask is ±18um, so the total range of the automatic focusing device is ±20um.

[0070] The focusing method of the automatic focusing device provided in the above embodiment of the present application is not limited to Figure 1 Coaxial autofocus device or Figure 2 The off-axis automatic focusing device in the present invention can also be used in other automatic focusing devices including a projection mask and a detection mask, as long as the positions of the projection mask and the detection mask are moved, they are within the protection scope of the present application.

[0071] The focusing method of the automatic focusing device provided in the present application changes the position of the conjugate plane of the automatic focusing device by moving the positions of the projection mask and the detection mask, compensates for the displacement caused by the change of the conjugate plane, and changes the focal plane position of the automatic focusing device without changing the measurement accuracy. Compared with the existing range-increasing scheme, this method achieves a larger range, higher accuracy, and less impact of image quality degradation.

[0072] See also Figure 4 The present application also provides an automatic focusing device, including a first control unit 410, a second control unit 420 and a third control unit 430. The first control unit 410, the second control unit 420 and the third control unit 430 can be set separately or integrated into a processor. The form is not limited. The specific implementation method is described in detail below.

[0073] The first control unit 410 is used to control the projection mask to move along the direction of the optical axis.

[0074] In this embodiment, the first control unit 410 controls the projection mask to move along the direction of the optical axis through a manual translation stage or an electric translation stage.

[0075] In this embodiment, the displacement of the projection mask along the direction of the optical axis can be obtained by converting the square of the ratio of the focal length of the focusing lens group of the automatic focusing device to the focal length of the objective lens.

[0076] It should be noted that the focal plane position is the position where the output value of the automatic focusing device is 0, that is, the output value of the automatic focusing device is 0 when the target imaging position is reached. For a given automatic focusing device, its current focal plane position and imaging focal plane position are determined. The distance between the focal plane and the imaging focal plane can be calculated based on the focal plane position and the imaging focal plane position, and then converted based on the magnification relationship, that is, the square of the ratio of the focal length of the focusing lens of the automatic focusing device to the focal length of the objective lens, the displacement of the projection mask along the optical axis can be obtained.

[0077] In this embodiment, whether the projection mask is displaced into place can be determined according to the clarity of the mask image at the imaging focal plane of the automatic focusing device.

[0078] Specifically, by observing the clarity of the mask image at the imaging focal plane, it is determined whether the projection mask has been displaced into place. When the mask image at the imaging focal plane is clearly visible, the projection mask has been displaced into place; otherwise, the projection mask is further controlled to move back and forth along the direction of the optical axis by a manual translation stage or an electric translation stage until the mask image at the imaging focal plane is clearly visible.

[0079] The second control unit 420 is used to control the detection mask to move along the direction of the optical axis.

[0080] In this embodiment, the second control unit 420 controls the detection mask to move along the direction of the optical axis through a manual translation stage or an electric translation stage.

[0081] It can be understood that in the process of moving the detection mask along the direction of the optical axis, it is necessary to ensure that the projection mask, the imaging focal plane of the automatic focusing device and the detection mask are in a conjugate relationship. When the position of the projection mask can be determined, the displacement of the detection mask along the optical axis can be determined.

[0082] It can be understood that since the projection mask, the imaging focal plane and the detection mask are in a conjugate relationship, the position of the imaging focal plane of the automatic focusing device is changed by moving the projection mask and the detection mask, thereby expanding the imaging focus range without affecting the imaging quality.

[0083] The third control unit 430 is used to control the projection mask to move along a direction perpendicular to the optical axis.

[0084] In this embodiment, the step of moving the projection mask along a direction perpendicular to the optical axis specifically includes the following steps: controlling the projection mask to move along a direction perpendicular to the optical axis by a manual translation stage or an electric translation stage.

[0085] It can be understood that in the process of moving the projection mask and the detection mask along the optical axis, the focal plane position of the automatic focusing device will move. By moving the projection mask in a direction perpendicular to the optical axis, the focal plane displacement and the mask image displacement caused by triangulation can be compensated.

[0086] In this embodiment, during the process of moving the projection mask along a direction perpendicular to the optical axis, the moving direction and the moving position can be determined by monitoring the focal plane position of the automatic focusing device.

[0087] For example: when the projection mask is translated upward, it is found that the focal plane position is far away from the target position, which proves that the moving direction is wrong and the projection mask should be moved downward. When the focal plane position reaches the target position, the projection mask moves into place; when the projection mask is translated downward, it is found that the focal plane position is far away from the target position, which proves that the moving direction is wrong and the projection mask should be moved upward. When the focal plane position reaches the target position, the projection mask moves into place. The above are just a list of possible situations. In practice, the moving direction and moving position can be determined by monitoring the focal plane position of the automatic focusing device.

[0088] In this embodiment, the movement amount △x of the projection mask along the direction perpendicular to the optical axis is G*△z*NA, △x is the movement amount, △z is the focal plane movement amount, G is the magnification, NA is the incident angle of light of the automatic focusing device, and the magnification G=the size of the projection mask / the size of the mask image on the object plane.

[0089] Furthermore, in executing the operation of the control unit, when moving the projection mask or the detection mask, the displacement of the projection mask or the detection mask required for different focal plane positions of the automatic focusing device may be calibrated in advance.

[0090] For example, in executing the operation of the above-mentioned control unit, the movement amount of the projection mask along the optical axis and along the axis perpendicular to the optical axis, and the movement amount of the detection mask along the optical axis are determined and recorded according to the above steps when the focal plane moves 1um. When the focal plane is to move 1um, the projection mask and the detection mask are quickly moved according to the calibration value to achieve fast zooming.

[0091] It should be noted that the moving range of the projection mask and the detection mask is related to the focal plane moving range of the automatic focusing device and the system imaging performance. When the adjustment range is designed to be too large, the MTF, telecentricity, distortion and other indicators of the automatic focusing device will deteriorate, and the projection mask image at the detection mask will be distorted due to the above problems, affecting the measurement accuracy. Therefore, it is necessary to adjust the moving range according to the focal plane moving direction, position and imaging state during the movement process, and comprehensively optimize the system MTF, telecentricity, distortion and other performances under different focal plane states so that they are all within the index range, so that the above-mentioned mask displacement is large When the imaging quality is maintained at a good level while increasing the range of the automatic focusing device.

[0092] In this embodiment, the above-mentioned adjustment device is used. At a certain focal plane, the measurement range of the automatic focusing device is ±2um, and the range of the focal plane position that can be changed by moving the mask is ±18um, so the total range of the automatic focusing device is ±20um.

[0093] The automatic focusing device provided in the above embodiments of the present application is not limited to Figure 1 Coaxial autofocus device or Figure 2 The off-axis automatic focusing device in the present invention can also be used in other automatic focusing devices including a projection mask and a detection mask, as long as the positions of the projection mask and the detection mask are moved, they are within the protection scope of the present application.

[0094] The autofocus device provided in the present application changes the position of the conjugate plane of the autofocus device by moving the positions of the projection mask and the detection mask, compensates for the displacement caused by the change of the conjugate plane, and changes the focal plane position of the autofocus device without changing the measurement accuracy. Compared with the existing range-increasing scheme, this method achieves a larger range, higher accuracy, and less impact of image quality degradation.

[0095] The above are only preferred embodiments of the present application, and only specifically describe the technical principles of the present application. These descriptions are only for explaining the principles of the present application and cannot be interpreted in any way as limiting the scope of protection of the present application. Based on the explanation here, any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application, and other specific implementation methods of the present application that can be associated with by technicians in this field without creative work, should be included in the scope of protection of the present application.

Claims

1. A focusing method of an automatic focusing device, characterized in that: The steps include: Moving the projection mask along the direction of the optical axis; Moving the detection mask along the direction of the optical axis; The projection mask is moved along a direction perpendicular to the optical axis.

2. The focusing method of the automatic focusing device according to claim 1, characterized in that: The steps of moving the projection mask and moving the detection mask specifically include: controlling the movement of the projection mask or the detection mask by a manual translation stage or an electric translation stage.

3. The focusing method of the automatic focusing device according to claim 1 or 2, characterized in that: In the step of moving the projection mask along the direction of the optical axis, the displacement of the projection mask along the direction of the optical axis can be obtained by converting the square of the ratio of the focal length of the focusing lens group of the automatic focusing device to the focal length of the objective lens.

4. The focusing method of the automatic focusing device according to claim 1, characterized in that: In the step of moving the projection mask along the direction of the optical axis, it is determined whether the projection mask has been displaced into place according to the clarity of the mask image at the imaging focal plane of the automatic focusing device.

5. The focusing method of the automatic focusing device according to claim 1 or 2, characterized in that: In the step of moving the detection mask along the direction of the optical axis, the projection mask, the imaging focal plane of the automatic focusing device and the detection mask are in a conjugate relationship.

6. The focusing method of the automatic focusing device according to claim 1 or 2, characterized in that: The step of moving the projection mask along a direction perpendicular to the optical axis specifically includes: determining the moving direction and moving position of the projection mask according to the focal plane position of the automatic focusing device.

7. The focusing method of the automatic focusing device according to claim 6, characterized in that: The movement amount △x of the projection mask along the direction perpendicular to the optical axis is G*△z*NA, where △x is the movement amount, △z is the focal plane movement amount, G is the magnification, NA is the incident angle of light of the automatic focusing device, and the magnification G=size of the projection mask / size of the mask image on the object plane.

8. The focusing method of the automatic focusing device according to claim 1, characterized in that: Before moving the projection mask or the detection mask, the displacement of the projection mask or the detection mask required for different focal plane positions of the automatic focusing device may be calibrated.

9. The focusing method of the automatic focusing device according to claim 1, characterized in that: The automatic focusing device is a coaxial automatic focusing device or an off-axis automatic focusing device.

10. An automatic focusing device, characterized in that: include: A first control unit, used for controlling the projection mask to move along the direction of the optical axis; A second control unit, used for controlling the detection mask to move along the direction of the optical axis; The third control unit is used to control the projection mask to move along a direction perpendicular to the optical axis.

11. The automatic focusing device according to claim 10, characterized in that: The first control unit and the second control unit and the second control unit may control the movement of the projection mask or the detection mask through a manual translation stage or an electric translation stage.

12. The automatic focusing device according to claim 10 or 11, characterized in that: In controlling the projection mask to move along the direction of the optical axis, the displacement of the projection mask along the direction of the optical axis can be obtained by converting the square of the ratio of the focal length of the focusing lens group of the automatic focusing device to the focal length of the objective lens.

13. The automatic focusing device according to claim 10, characterized in that: When the projection mask is controlled to move along the direction of the optical axis, it can be determined whether the projection mask has been displaced into place according to the clarity of the mask image at the imaging focal plane of the automatic focusing device.

14. The automatic focusing device according to claim 10 or 11, characterized in that: When the detection mask is controlled to move along the direction of the optical axis, the projection mask, the imaging focal plane of the automatic focusing device and the detection mask are in a conjugate relationship.

15. The automatic focusing device according to claim 10 or 11, characterized in that: When the projection mask is controlled to move in a direction perpendicular to the optical axis, the moving direction and the moving position of the projection mask can be determined according to the focal plane position of the automatic focusing device.

16. The automatic focusing device according to claim 15, characterized in that: The movement amount of the projection mask in the direction perpendicular to the optical axis △x=G*△z*NA, △x is the movement amount, △z is the focal plane movement amount, G is the magnification, NA is the incident angle of the light of the automatic focusing device, and the magnification G=the size of the projection mask / the size of the mask image on the object plane.

17. The automatic focusing device according to claim 10, characterized in that: When moving the projection mask or the detection mask, the first control unit, the second control unit and the third control unit may calibrate in advance the displacement of the projection mask or the detection mask required for different focal plane positions of the automatic focusing device.

18. The automatic focusing device according to claim 10, characterized in that: The automatic focusing device is a coaxial automatic focusing device or an off-axis automatic focusing device.

Images