Objective lens telecentricity testing method and system

Abstract

The invention provides an objective telecentricity testing method and system, and the method relates to the technical field of semiconductor measurement, and the method comprises the steps: providing illumination light, and enabling the illumination light to be converged through an objective and to be incident to a testing mask plate located on a motion platform, the illumination light is reflected by the test mask and then is collected by the objective lens and reaches the camera to generate an image of the test mask; the focal plane position of the objective lens is obtained through an automatic focusing system, and then the vertical position of the moving table is adjusted, so that the test mask plate is located at the focal plane position of the objective lens; moving the motion platform according to a preset step length to calculate the defocusing amount of the test mask after each time of movement, and collecting space images at different defocusing amounts through a camera; comparing the space image with a standard image to obtain an imaging position deviation corresponding to each defocusing amount; acquiring a linear relation between the imaging position deviation and the defocusing amount; and calculating the telecentricity of the objective lens based on the linear relation. According to the invention, the telecentricity of the objective lens is accurately measured to verify the quality and performance of the optical element.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor equipment, and particularly to a method and system for testing the telecentricity of an objective lens. Background Art

[0002] The telecentricity detection of a wide-spectrum large numerical aperture (NA) objective lens is an important link in the practical application of the objective lens, which helps to ensure the performance and accuracy of the optical system and the quality and resolution of the image. In a traditional imaging optical system, the telecentricity is defined as the angle between the chief ray of the imaging light beam in a certain field of view and the optical axis. The telecentricity detection of a wide-spectrum large numerical aperture objective lens helps to ensure that each component (such as lenses, lenses, prisms, etc.) of the optical system can be accurately focused within different wavelength ranges, which helps to improve the performance of the optical system and ensure that the image quality and resolution reach the best state in multiple bands. For applications that require high-resolution imaging, such as semiconductor lithography and inspection equipment, microscopes, photography, and satellite remote sensing, the accuracy of the telecentricity of the objective lens is crucial. It determines the focal length and clarity of the imaging system, thus affecting the quality and resolution of the image. Especially in a wide-spectrum large numerical aperture objective lens, the telecentricity detection of the objective lens can be used to verify the quality and performance of optical components and ensure that they meet the design requirements. Therefore, there is an urgent need for a detection method to improve the telecentricity detection accuracy of the objective lens. Summary of the Invention

[0003] The present invention provides a method and system for testing the telecentricity of an objective lens to verify the quality and performance of optical components by accurately measuring the telecentricity of the objective lens.

[0004] To achieve the above object, in a first aspect, the present invention provides a method for testing the telecentricity of an objective lens. The method relates to the technical field of semiconductor measurement, and the method includes: providing illumination light, which is converged by the objective lens and incident on a test mask plate located on a moving stage. The illumination light is reflected by the test mask plate and then collected by the objective lens and reaches a camera to generate an image of the test mask plate. The test mask plate has a recognizable feature pattern;

[0005] Obtaining the focal plane position of the objective lens through an autofocus system, and then adjusting the vertical position of the moving stage so that the test mask plate is located at the focal plane position of the objective lens;

[0006] Moving the moving stage at a preset step size, calculating the defocus amount of the test mask plate after each movement, and collecting spatial images of the test mask plate at different defocus amounts through the camera. The defocus amount is the difference between the vertical position of the test mask plate after each movement and the focal plane position;

[0007] Compare the aerial image of the test reticle after each movement with the standard image of the test reticle to obtain the imaging position deviation corresponding to each defocus amount; obtain the linear relationship between the imaging position deviation and the defocus amount; calculate the telecentricity of the objective lens based on the linear relationship.

[0008] In a possible embodiment, the preset step size satisfies: 0.05*d ≤ ΔZ ≤ 0.5*d, where ΔZ is the preset step size and d is the depth of field of the objective lens.

[0009] In another possible embodiment, moving the moving stage by a preset step size includes: moving the moving stage step by step with the preset step size, and the value range of the defocus amount satisfies: -2*d ≤ ΔF ≤ 2*d, where ΔF is the defocus amount.

[0010] In other possible embodiments, the feature pattern includes a two-dimensional array structure pattern formed by arranging square units uniformly in a first direction and a second direction respectively.

[0011] In yet another possible embodiment, the square unit includes a light-transmitting area with a hollow center and a square-shaped light-shielding area surrounded by four sides.

[0012] In other possible embodiments, the imaging position deviation includes the imaging position deviation Dx in the first direction and the imaging position deviation Dy in the second direction.

[0013] In still another possible embodiment, obtaining the linear relationship between the imaging position deviation and the defocus amount includes: performing mathematical fitting on the imaging position deviation Dx in the first direction and the defocus amount to establish a first linear relationship curve and obtaining the slope Kx of the first linear relationship curve; performing mathematical fitting on the imaging position deviation Dy in the second direction and the defocus amount to establish a second linear relationship curve and obtaining the slope Ky of the second linear relationship curve.

[0014] In other possible embodiments, calculating the telecentricity of the objective lens based on the linear relationship includes: calculating the telecentricity OBTE in the first direction based on the slope Kx of the first linear relationship curve x , OBTE x = arctan(Kx); calculating the telecentricity OBTE in the second direction based on the slope Ky of the second linear relationship curve y , OBTE y = arctan(Ky); calculating the telecentricity OBTE of the objective lens to be measured according to the telecentricity OBTE in the first direction x and the telecentricity OBTE in the second direction y :

[0015] OBTE = sqrt(OBTE x 2 + OBTE Y 2 )。

[0016] In other possible embodiments, the wavelength of the illumination light is consistent with the working wavelength of the objective lens.

[0017] In a second aspect, the present invention provides an objective lens telecentricity testing system, including an illumination system, a moving stage, a test mask, an objective lens, an autofocus system, a camera, and a processor;

[0018] The illumination system provides illumination light, which is converged by the objective lens and incident on the test mask, reflected, then collected by the objective lens and reaches the camera; the moving stage is used to carry and drive the test mask; the autofocus system is used to obtain the focal plane position of the objective lens and the defocus amount when the test mask is at different vertical positions; the processor controls the movement of the moving stage based on a preset step size to make the test mask at different vertical positions, and controls the camera to collect the spatial images of the test mask at different defocus amounts; the processor is further used to compare the spatial image of the test mask after each movement with the standard image of the test mask, obtain the imaging position deviation corresponding to each defocus amount, and obtain the linear relationship between the imaging position deviation and the defocus amount, and calculate the telecentricity of the objective lens based on the linear relationship.

[0019] Compared with the prior art, the present invention has the following beneficial effects: Utilizing the existing structural basis of the existing optical equipment including the objective lens to be tested, combined with its autofocus system to obtain the spatial images of the test mask at different defocus amounts, comparing the spatial image of the test mask after each movement with the standard image of the test mask to obtain the imaging position deviation corresponding to each defocus amount, then generating the linear relationship curves between the imaging position deviations in the first direction and the second direction and the defocus amount, and further calculating the telecentricity of the objective lens based on the slope of the linear relationship curve. The present invention can conveniently and accurately measure the telecentricity of the objective lens without modifying the structure of the existing optical equipment, so as to verify the quality and performance of the optical element. Description of the Drawings

[0020] Figure 1 It is a schematic diagram for defining the telecentricity of the objective lens;

[0021] Figure 2 It is a schematic diagram for testing the telecentricity of the objective lens provided by the embodiment of the present invention;

[0022] Figure 3Another schematic diagram of objective lens telecentricity test provided by an embodiment of the present invention;

[0023] Figure 4 A schematic flow chart of a method for testing telecentricity of an objective lens provided by an embodiment of the present invention;

[0024] Figure 5 A schematic diagram of a test mask pattern provided by an embodiment of the present invention;

[0025] Figure 6 It is a schematic diagram of the data relationship curve between the imaging position deviation Dx and the defocus amount.

[0026] Description of the symbols in the accompanying drawings:

[0027] Illumination system 10; motion stage 20; test mask 30; objective lens 40; automatic focusing system 50; camera 60; tube lens 70;

[0028] Light source 101 ; a rotating filter 102 ; an ND filter 103 ; a light homogenizing rod 104 ; a coupling lens group 1051 ; an aperture 1052 ; a relay lens group 1053 ; and a beam splitter 1054 . DETAILED DESCRIPTION

[0029] The following is an explanation of the terms used in this article.

[0030] (1) Objective telecentricity refers to the fact that the aperture diaphragm of the optical system is imaged at infinity by the lens in front of it, that is, the entrance pupil of the optical system is located at infinity, so the principal ray is parallel to the optical axis. As a result, when the object to be measured moves back and forth, only the image of the object to be measured is diffused and blurred, and its center of mass position coordinates are not affected.

[0031] (2) Objective telecentricity refers to the degree to which the object side of an optical system is non-telecentric, and is represented by the angle between the principal ray at the edge of the objective field of view and the optical axis. Figure 1 As shown in (a), the telecentricity of a strictly telecentric objective lens is 0, which means that the entrance pupil is located at infinity on the image side, making the chief ray completely parallel to the optical axis in the object side (the dotted line is the direction of the optical axis). Figure 1 As shown in (b), the two solid lines below the objective lens (the black frame in the figure) are the main light rays at the edge of the objective lens field of view, and the dotted line is the direction of the optical axis. Assuming that the telecentricity of the objective lens of the optical system is α and the height of the object to be measured is ΔZ, then in the image of the object to be measured collected at this time, the coordinate change of the center of mass position of the object to be measured caused by the non-telecentricity is: Δx = Δz·tanα.

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings as understood by those of ordinary skill in the art to which the present invention pertains. The words such as "including" used herein mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0033] As Figure 2 shown, an objective telecentricity testing system provided by an embodiment of the present invention includes: an illumination system 10, a moving stage 20, a test mask 30, an objective lens 40, an autofocus system 50, a camera 60, and a processor 70 (not shown in the figure), wherein:

[0034] The moving stage 20 is used to carry and drive the test mask 30;

[0035] The illumination system 10 provides illumination light, and the illumination light is converged by the objective lens 40 and incident on the test mask 30 located on the moving stage 20. After being reflected by the test mask 30, the illumination light is collected by the objective lens 40 and reaches the camera 60 to generate an image of the test mask 30;

[0036] The autofocus system 50 is used to obtain the focal plane position of the objective lens 40 and the defocus amount when the test mask 30 is at different vertical positions;

[0037] The processor 70 controls the movement of the moving stage based on a preset step size to make the test mask at different vertical positions, and controls the camera to collect the spatial images of the test mask at different defocus amounts;

[0038] The processor 70 is further used to compare the spatial image of the test mask 30 after each movement with the standard image of the test mask 30, obtain the imaging position deviation corresponding to each defocus amount, and obtain the linear relationship between the imaging position deviation and the defocus amount, and calculate the telecentricity of the objective lens based on the linear relationship.

[0039] In a possible embodiment, as Figure 3As shown, the above-mentioned illumination system 10 may specifically include a light source 101, a rotary filter 102, an ND filter 103, a light homogenizing rod 104, a coupling lens group 1051, a diaphragm 1052, a relay lens group 1053, and a beam splitter 1054. Optionally, the objective lens 40 may be a wide-spectrum objective lens, the moving stage 20 may be a Z-axis electric moving platform, and the camera 60 may be a area array CCD camera. A tube lens 70 may also be provided above the wide-spectrum objective lens.

[0040] Combined with Figure 3 Regarding the objective lens telecentricity test system shown, the optical path of the illumination system 10 is as follows: After the light source 101 of the wide-spectrum laser emits a coherent light beam, it passes through the rotary filter 102 for filtering, that is, selecting the transmission band, then passes through the ND filter 103 to adjust the intensity, is homogenized by the light homogenizing rod 104, passes through the coupling lens group 1051, the diaphragm 1052, and the relay lens group 1053, reaches the beam splitter 1054, and enters the wide-spectrum objective lens 40 to illuminate the test reticle 30 placed on the moving stage 20. The test reticle 30 is adjusted to the best focal plane through the autofocus system 50, and the vertical position of the test reticle 30 at this time is recorded. Then, the test reticle 30 is vertically moved step by step by the moving stage 20 at a preset step size to perform measurements within the defocus range of -2*d to 2*d of the test reticle 30, where d is the depth of field of the objective lens. After each movement, the Z-axis position of the test reticle 30 and the formed image pass through the wide-spectrum objective lens 40, and then pass through the tube lens and are imaged on the camera 60. The camera 60 takes pictures of the test reticle 30 at each measurement position (corresponding to different defocus amounts), so as to obtain the spatial image of the test reticle 30 at different defocus amounts.

[0041] The embodiment of the present invention also provides an objective lens telecentricity test method, as Figure 4 shown, including the following steps:

[0042] S401, provide illumination light, the illumination light is converged by the objective lens and incident on the test reticle located on the moving stage, the illumination light is reflected by the test reticle and collected by the objective lens and reaches the camera to generate an image of the test reticle, and the test reticle has a recognizable feature pattern.

[0043] In a possible embodiment, the wavelength of the illumination light is the same as the working wavelength of the objective lens.

[0044] S402, obtain the focal plane position of the objective lens through the autofocus system, and then adjust the vertical position of the moving stage so that the test reticle is located at the focal plane position of the objective lens;

[0045] S403. Move the stage at a preset step size, calculate the defocus amount of the test reticle after each movement, and collect the spatial images of the test reticle at different defocus amounts through the camera. The defocus amount is the difference between the vertical position of the test reticle after each movement and the focal plane position.

[0046] In a possible embodiment, the preset step size can be selected according to actual needs. Generally, the value of the preset step size satisfies: 0.05*d ≤ ΔZ ≤ 0.5*d, where ΔZ is the preset step size and d is the depth of field of the objective lens.

[0047] S404. Compare the spatial image of the test reticle after each movement with the standard image of the test reticle to obtain the imaging position deviation corresponding to each defocus amount.

[0048] In a possible embodiment, the feature pattern in the test reticle includes a two-dimensional array structure pattern formed by uniformly arranging square units in the first direction and the second direction respectively. The square unit includes a light-transmitting area with a hollow center and a square-shaped light-shielding area surrounded by four sides. Exemplarily, as Figure 5 shown, the feature pattern is a 4mm × 4mm two-dimensional square array structure. The square unit in the square array structure is a square structure with a side length of 40μm and an edge width of 4μm, and the square units are evenly distributed. Through this two-dimensional square array structure, by comparing the image taken by the camera with the standard reticle pattern, the position deviation Dx in the first direction and the position deviation Dy in the second direction can be directly obtained, and at the same time, the imaging resolution of the camera can be ensured.

[0049] S405. Obtain the linear relationship between the imaging position deviation and the defocus amount.

[0050] In a possible embodiment, perform mathematical fitting on the imaging position deviation Dx in the first direction and the defocus amount to establish a first linear relationship curve and obtain the slope Kx of the first linear relationship curve; perform mathematical fitting on the imaging position deviation Dy in the second direction and the defocus amount to establish a second linear relationship curve and obtain the slope Ky of the second linear relationship curve. Exemplarily, the first direction can be the X direction in the plane coordinate system, and the second direction can be the Y direction in the plane coordinate system.

[0051] S406. Calculate the telecentricity of the objective lens based on the linear relationship.

[0052] Combined with Figure 3For example, first turn on the light source, use a rotating filter to change the illumination light source to the required illumination wavelength range, place the test reticle on the Z-axis electric moving platform, turn on the autofocus function, obtain the optimal focal plane position, and place the test reticle at the optimal focal plane position of the detection system; then, with a step size of 0.1 times the depth of field, vertically move the test reticle through the Z-axis electric moving platform, and calculate the defocus amount of the test reticle after each movement. At each measurement position (corresponding to different defocus amounts), take a planar array imaging camera photo of the test reticle to collect the spatial images of the test reticle at different defocus amounts through the camera. Compare the spatial images obtained at different defocus amounts with the standard image of the reticle respectively, and measure the imaging position deviations Dx and Dy in the X and Y directions. For example, the data relationship between Dx and the defocus amount is shown in Table 1.

[0053]

[0054]

[0055] After that, respectively fit the first linear relationship curve between the imaging position deviation Dx and the defocus amount, and the second linear relationship curve between the imaging position deviation Dy and the defocus amount. Exemplarily, the first linear relationship curve between Dx and the defocus amount is as Figure 6 shown. Finally, based on the slope Kx of the first linear relationship curve, calculate the telecentricity OBTE x in the first direction, OBTE x = arctan(Kx); based on the slope Ky of the second linear relationship curve, calculate the telecentricity OBTE y in the second direction, OBTE y = arctan(Ky); according to the telecentricity OBTE x in the first direction and the telecentricity OBTE y in the second direction, calculate the telecentricity OBTE of the objective lens to be measured: OBTE = sqrt(OBTE x 2 + OBTE Y 2 ).

[0056] In summary, the embodiment of the present invention utilizes the existing structure of an existing optical device including an objective lens to be measured, and combines an autofocus system to obtain a spatial image of a test mask at different defocus amounts. By comparing the spatial image of the test mask after each movement with the standard image of the test mask, the imaging position deviation corresponding to each defocus amount is obtained, and then a linear relationship curve between the imaging position deviations in the first direction and the second direction and the defocus amount is generated. Furthermore, based on the slope of the linear relationship curve, the telecentricity of the objective lens is calculated. The present invention can conveniently and accurately measure the telecentricity of the objective lens without modifying the structure of the existing optical device, so as to verify the quality and performance of the optical element.

[0057] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. An objective telecentricity testing method, characterized in that, Including: Providing illumination light, which is converged by an objective lens and incident on a test reticle located on a stage. The illumination light is reflected by the test reticle and then collected by the objective lens and reaches a camera to generate an image of the test reticle. The test reticle has recognizable characteristic patterns; Obtaining the focal plane position of the objective lens through an auto-focusing system, and then adjusting the vertical position of the stage so that the test reticle is located at the focal plane position of the objective lens; Moving the stage in a preset step, calculating the defocus amount of the test reticle after each movement, and collecting the spatial images of the test reticle at different defocus amounts through the camera. The defocus amount is the difference between the vertical position of the test reticle after each movement and the focal plane position; Comparing the spatial image of the test reticle after each movement with the standard image of the test reticle to obtain the imaging position deviation corresponding to each defocus amount; Obtaining the linear relationship between the imaging position deviation and the defocus amount; Calculating the telecentricity of the objective lens based on the linear relationship.

2. The objective telecentricity testing method according to claim 1, characterized in that, The preset step satisfies: 0.05*d ≤ ΔZ ≤ 0.5*d, where ΔZ is the preset step and d is the depth of field of the objective lens.

3. The objective telecentricity testing method according to claim 2, characterized in that, Moving the stage step by step with the preset step, and the value range of the defocus amount satisfies: -2*d ≤ ΔF ≤ 2*d, where ΔF is the defocus amount.

4. The objective telecentricity testing method according to claim 1, characterized in that, The characteristic patterns include a two-dimensional array structure pattern formed by square units arranged uniformly along a first direction and a second direction respectively.

5. The objective telecentricity testing method according to claim 4, characterized in that, The square unit includes a light-transmitting area with a hollow center and a frame-shaped light-shielding area surrounded by four sides.

6. The objective telecentricity testing method according to claim 4 or 5, characterized in that, The imaging position deviation includes the imaging position deviation Dx in the first direction and the imaging position deviation Dy in the second direction.

7. The objective telecentricity testing method according to claim 6, characterized in that, The obtaining the linear relationship between the imaging position deviation and the defocus amount includes: Performing mathematical fitting on the imaging position deviation Dx in the first direction and the defocus amount to establish a first linear relationship curve and obtaining the slope Kx of the first linear relationship curve; Performing mathematical fitting on the imaging position deviation Dy in the second direction and the defocus amount to establish a second linear relationship curve and obtaining the slope Ky of the second linear relationship curve.

8. The objective telecentricity testing method according to claim 7, characterized in that, The calculating the telecentricity of the objective lens based on the linear relationship includes: Calculate the telecentricity OBTE in the first direction based on the slope Kx of the first linear relationship curve x , OBTE x = arctan(Kx); Calculate the telecentricity OBTE in the second direction based on the slope Ky of the second linear relationship curve y , OBTE y = arctan(Ky); Based on the telecentricity OBTE in the first direction x and the telecentricity OBTE in the second direction y calculate the telecentricity OBTE of the objective lens to be measured: OBTE = sqrt(OBTE x 2 + OBTE Y 2 )。 9. The objective telecentricity testing method according to claim 1, characterized in that, The wavelength of the illumination light is consistent with the working wavelength of the objective lens.

10. An objective telecentricity testing system, characterized in that, Including an illumination system, a stage, a test reticle, an objective lens, an auto-focusing system, a camera, and a processor; The illumination system provides illumination light, which is converged by the objective lens and incident on the test reticle, reflected and then collected by the objective lens and reaches the camera. The stage is used to carry and drive the test reticle; The auto-focusing system is used to obtain the focal plane position of the objective lens and the defocus amount when the test reticle is at different vertical positions; The processor controls the movement of the stage based on a preset step to make the test reticle at different vertical positions, and controls the camera to collect the spatial images of the test reticle at different defocus amounts. The processor is further configured to compare the aerial image of the test reticle after each movement with the standard image of the test reticle to obtain the imaging position deviation corresponding to each defocus amount, and acquire the linear relationship between the imaging position deviation and the defocus amount, and calculate the telecentricity of the objective lens based on the linear relationship.

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