Multi-magnification imaging system axis deviation detection system and method

Abstract

Embodiments of the present invention disclose a multi-magnification imaging system axis deviation detection system and method. The system includes an objective lens, multiple tube lenses, a tube lens switching structure, a Z-direction moving stage, a camera, a beam splitter, and a marking plate. The detection method is based on the reference beam and the defocus imaging of the object to be measured. The reflected beam of the beam splitter is used as the reference beam, combined with the defocus imaging method of the object to be measured. By the position changes of the reference spot and the imaging spot at different Z-direction positions of the camera, the optical axis tilt is measured to achieve the axis deviation measurement of the tube lens module with multiple magnification factors and the objective lens. Since the reflected beam of the beam splitter is used as the reference beam during the axis deviation measurement and correction is performed in the result, the measurement accuracy of the present invention is independent of the moving axis of the camera, eliminating the influence of the moving axis tilt of the camera and further improving the detection accuracy.

Description

Technical Field

[0001] The present invention relates to the field of industrial inspection, and particularly to the field of semiconductor imaging inspection. Background Art

[0002] In the field of industrial inspection, such as in the field of semiconductor imaging inspection, as Figure 1 shown, an imaging inspection system is composed of a large numerical aperture objective lens 4, multiple magnification tube lenses, a tube lens switching structure 30, a Z-direction moving stage 2, a camera 1, etc.; among them, the tube lens switching structure 30 moves horizontally to realize the switching of different tube lenses including a first tube lens 31, a second tube lens 32, a third tube lens 33, etc.; the camera 1 is installed on the Z-direction moving stage 2 and can move up and down and perform image plane focusing. When the system performs imaging inspection on a measured object 5 such as a wafer, the coaxiality deviation between the tube lens and the objective lens will affect the imaging quality and cause the deviation of the imaging field center in the image space, so precise control is required to minimize or avoid the coaxiality deviation.

[0003] For this reason, in an axial deviation measurement method in the prior art, the coaxiality between the tube lens and the objective lens is detected by relying on off-line three-coordinate calibration and the dimension chain transfer of mechanical parts. However, in the above method, due to factors such as equipment accuracy, assembly error, and dimension chain transfer error, the measurement error accumulates, so the coaxiality measurement accuracy is not high. Summary of the Invention

[0004] The main technical problem to be solved by the present invention is to improve the accuracy in the axial deviation measurement of the imaging system.

[0005] Accordingly, first, in an embodiment of the present invention, a method for detecting the axial deviation of a multi-magnification imaging system is provided; the method includes the following steps:

[0006] 1) Beam splitter setting:

[0007] A beam splitter is arranged on the image side of the tube lens, and the attitude of the beam splitter is calibrated by using a parallel reference beam until the spots formed by at least two beams emitted from it coincide on the camera.

[0008] 2) Measurement of the position of the first imaging spot: The camera is located at the first axial position, a marker plate for imaging measurement is placed on the object side of the objective lens, the illumination beam for objective lens imaging is turned on, and the absolute position of the objective lens imaging spot on the camera target surface is recorded as the first imaging spot position P11.

[0009] 3) Measurement of the position of the first reference spot: The camera is located at the first axial position, the parallel reference beam is turned on, and the absolute position of the spot formed by the parallel reference beam is recorded as the first reference spot position P10.

[0010] 4) Measurement of the position of the second imaging spot: The camera is located at the second axial position. A marking plate for imaging measurement is placed on the object side of the objective lens. The illumination beam for objective lens imaging is turned on, and the absolute position of the imaging spot of the objective lens on the camera target surface is recorded as the position P21 of the second imaging spot;

[0011] 5) Measurement of the position of the second reference spot: The camera is located at the second axial position. The parallel reference beam is turned on, and the absolute position of the spot formed by the parallel reference beam is recorded as the position P20 of the second reference spot;

[0012] 6) Calculation of the axial offset:

[0013] Record the axial movement distance ΔZ between the first axial position and the second axial position of the camera;

[0014] Calculate the change in the center distance M between the imaging spot position and the reference spot position at different axial positions of the camera, which is recorded as ΔM = (P11 - P10) - (P21 - P20);

[0015] According to tanα = ΔM / ΔZ, where α is the tilt angle of the tube lens optical axis after removing the influence of the tilt of the camera movement axis; calculate the value of α;

[0016] According to the formula tanα = ΔL / f, where f is the focal length of the tube lens, calculate the corresponding axial offset ΔL = f·tanα of the tube lens;

[0017] Among them, the execution order of the step 2) is any one of the following: before step 1), after step 1) and before step 6); the execution order of the step 4) is any one of the following: before step 1), after step 1) and before step 6).

[0018] In the above method for detecting the axial offset of a multi-magnification imaging system, in one embodiment, in the step of setting the beam splitter, the step of calibrating the attitude of the beam splitter includes:

[0019] Set a reference reflection element on the mechanical reference plane on the image side of the tube lens;

[0020] Set the beam splitter between the camera and the reference reflection element, and irradiate the parallel reference beam into the beam splitter;

[0021] The beam splitter splits the parallel reference beam into at least two beams;

[0022] One beam passes through the beam splitter - reference reflection element - beam splitter - camera, and the other beam passes through the beam splitter - camera; the two beams form two spots on the camera;

[0023] Adjust the attitude of the beam splitter so that the two light spots coincide on the camera. At this time, the attitude of the beam splitter relative to the reference reflection element has been adjusted to be parallel.

[0024] In one embodiment of the multi-magnification imaging system axis deviation detection method described above, it further includes a step of calibrating the parallel reference beam:

[0025] A calibration reflection element is arranged on the side of the mechanical reference plane on the image side of the tube mirror, and the reflection surface of the calibration reflection element is perpendicular to the mechanical reference plane on the image side of the tube mirror;

[0026] The beam emitted by the parallel light generator irradiates the surface of the calibration reflection element and returns to the parallel light generator after reflection;

[0027] According to the measurement reading of the parallel light generator, adjust the attitude of the parallel light generator so that the beam emitted by the parallel light generator is perpendicular to the reflection surface of the calibration reflection element;

[0028] At this time, the emitted beam is calibrated as the parallel reference beam.

[0029] In one embodiment of the multi-magnification imaging system axis deviation detection method described above, the beam splitter is a cube beam splitter prism, and the cube beam splitter prism splits the parallel reference beam into two paths.

[0030] In one embodiment of the multi-magnification imaging system axis deviation detection method described above, the first interface, the second interface and the third interface of the cube beam splitter prism are high-transmission surfaces coated with an anti-reflection film, the fourth interface is a reflection surface coated with a reflection film, and the fifth interface is a semi-transparent and semi-reflective surface coated with a beam-splitting film.

[0031] Secondly, in one embodiment of the present invention, a multi-magnification imaging system axis deviation detection system is provided, which includes an objective lens, a plurality of tube lenses, a tube lens switching structure, a Z-direction moving stage, a camera, a beam splitter and a marking plate; the tube lens switching structure carries the plurality of tube lenses and is used for moving horizontally to realize the switching of different tube lenses; the camera is installed on the Z-direction adjustment structure and can move up and down and focus on the image plane; the beam splitter is arranged between the image side of the tube lens and the object side of the camera, and after attitude calibration, the light spots formed by at least two beams generated by the parallel reference beam on the camera coincide; the marking plate is used to be placed on the object side of the objective lens and form an imaging light spot on the camera; the objective lens, the plurality of tube lenses, the tube lens switching structure, the Z-direction moving stage, the camera, the beam splitter and the marking plate cooperate to realize the multi-magnification imaging system axis deviation detection method described above.

[0032] In one embodiment of the above-mentioned multi-magnification imaging system axis deviation detection system, it further includes a reference reflection element, which is arranged on the mechanical reference plane on the image side of the tube mirror; and is used for: when the reference beam is split into at least two beams by the beam splitter, one of the beams passes through the beam splitter - reference reflection element - beam splitter - camera, and the other beam passes through the beam splitter - camera; the two beams form two light spots on the camera; adjust the attitude of the beam splitter so that the two light spots coincide on the camera, and at this time the attitude of the beam splitter relative to the reference reflection element has been adjusted to be parallel.

[0033] In one embodiment of the above-mentioned multi-magnification imaging system axis deviation detection system, it further includes a collimated light generator and a calibration reflection element. The collimated light generator and the calibration reflection element are respectively arranged on the side of the beam splitter, and the reflecting surface of the calibration reflection element is perpendicular to the mechanical reference plane on the image side of the tube mirror; and is used for: the beam emitted by the collimated light generator irradiates the surface of the calibration reflection element and returns to the collimated light generator after reflection; according to the measurement reading of the collimated light generator, adjust the attitude of the collimated light generator so that the beam emitted by the collimated light generator is perpendicular to the reflecting surface of the calibration reflection element; at this time, the emitted beam is calibrated as the parallel reference beam.

[0034] In one embodiment of the above-mentioned multi-magnification imaging system axis deviation detection system, the beam splitter is a cube beam splitter prism.

[0035] According to the method and / or system of the above embodiment, based on the reference beam and the defocused imaging of the object to be measured, using the reflected beam of the beam splitter as the reference beam, combined with the defocused imaging method of the object to be measured, by the position changes of the reference light spot and the imaging light spot at different Z-axis positions on the camera, measure the optical axis tilt, and realize the axis deviation measurement of the tube mirror module and the objective lens with multiple magnification factors; because the reflected beam of the beam splitter is used as the reference beam during axis deviation measurement and the axis deviation of the Z moving axis is corrected in the result, the measurement accuracy of the present invention is independent of the moving axis of the camera, eliminating the influence of the moving axis tilt of the camera and further improving the detection accuracy.

[0036] According to the method and / or system of the above embodiment, further, first use the reference reflection element to adjust the attitude of the beam splitter so that the splitting angle of the beam splitter relative to the tube mirror axis can be ensured to be in a parallel state, ensuring the accuracy and precision of the position of the beam splitter, and further ensuring the accuracy of the axis deviation measurement of the present invention.

[0037] According to the method and / or system of the above embodiment, further, use the collimated light generator and the calibration reflection element to calibrate the parallel reference light incident on the beam splitter, ensuring the accuracy of the parallel performance of the parallel reference beam, and further ensuring the accuracy of the axis deviation measurement of the present invention.

[0038] For the method and / or system according to the above embodiments, further, a cube beam splitter prism is selected as the beam splitter, which has a simple structure, is easy to debug, and is convenient for measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of an imaging detection system;

[0040] Figure 2 It is a schematic diagram of the principle of the defocus imaging axis deviation measurement method in the present invention;

[0041] Figure 3 It is a schematic diagram of the light spot of the defocus imaging axis deviation measurement method in the present invention;

[0042] Figure 4 It is a schematic diagram of the prism attitude calibration process of an embodiment of the present invention;

[0043] Figure 5 It is a schematic diagram after the prism attitude calibration of an embodiment of the present invention is completed;

[0044] Wherein: camera 1, camera target surface 10, imaging light spot 100, first axial position 11, second axial position 12, Z-axis moving stage 2, tube lens 3, tube lens switching structure 30, first tube lens 31, second tube lens 32, third tube lens 33, objective lens 4, object to be measured 5, cube beam splitter prism 6, prism optical axis 60, first interface 61, second interface 62, third interface 63, fourth interface 64, fifth interface 65, reference reflecting flat crystal 71, calibration reflecting flat crystal 72, aperture 8, parallel reference light beam 90. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The present invention will be further described in detail below in conjunction with the accompanying drawings through specific embodiments. Similar elements in different embodiments are labeled with related similar device numbers. In the following embodiments, many detailed descriptions are provided to enable a better understanding of the present application. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other devices, materials, or methods. In some cases, some operations related to the present application are not shown or described in the specification, which is to avoid the core part of the present application being overwhelmed by excessive descriptions. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the descriptions in the specification and the general technical knowledge in the art.

[0046] In addition, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can also be reordered or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean a necessary sequence, unless it is stated otherwise that a certain sequence must be followed.

[0047] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any sequential meaning. And the "connection" and "coupling" mentioned in this application, unless otherwise specified, both include direct and indirect connection (coupling).

[0048] In the embodiment of the present invention, a defocus imaging axis deviation measurement method is adopted. The principle is described in combination with Figure 2 , Figure 3 As shown, when the tube lens axis deviates, it introduces an inclination of the image-side optical axis. When the camera measures at different Z-axis positions, the position of the imaging spot 100 on the camera target surface 10 will shift. The imaging spot when the camera is at the second axial position 12 has a shift of ΔX in position relative to the imaging spot when the camera is at the first axial position 11.

[0049] The measurement method is summarized as follows: the camera moves slightly along the Z-axis movement axis, and the defocus amount is denoted as ΔZ; the translation amount ΔX of the imaging spot on the camera target surface is obtained, and tanθ = ΔX / ΔZ is calculated, where θ is the optical axis inclination angle.

[0050] The optical axis inclination angle has a direct relationship with the axis deviation amount of the tube lens. Assuming the focal length of the tube lens is f and the axis deviation amount is ΔL, then tanθ = ΔL / f; therefore, by measuring θ, the axis deviation amount ΔL of the tube lens can be calculated as ΔL = f·tanθ.

[0051] However, in the above defocus imaging axis deviation measurement method, the axis deviation of the tube lens will be coupled with the inclination of the detector's movement axis, which will introduce a large measurement error. Therefore, the measurement result is greatly affected by the inclination of the detector's movement axis.

[0052] Therefore, further, in the embodiments of the present invention, a multi-magnification imaging system axis deviation detection system is proposed. The system includes: an objective lens, a plurality of tube lenses, a tube lens switching structure, a Z-direction moving stage, a camera, a beam splitter, and a marking plate; the tube lens switching structure carries a plurality of tube lenses with different magnifications and is used to move horizontally to realize the switching of tube lenses with different magnifications; the camera is installed on the Z-direction moving stage to move up and down and focus the image plane; the beam splitter is arranged between the image side of the tube lens and the object side of the camera, and the beam splitter is calibrated in attitude until the spots formed by at least two beams generated by the parallel reference beam coincide on the camera target surface; the marking plate is used to be placed on the object side of the objective lens and form an imaging spot on the camera; a diaphragm is arranged between the tube lens and the objective lens to control the light quantity, reduce stray light and glare, thereby improving the image contrast and clarity.

[0053] Meanwhile, in the embodiments of the present invention, a multi-magnification imaging system axis deviation detection method is proposed, which is applicable to an imaging detection system, such as a semiconductor imaging detection system, and includes the following steps:

[0054] 1) Beam splitter setting: Set the beam splitter on the image side of the tube lens, and calibrate the attitude of the beam splitter with a parallel reference beam until the spots formed by at least two beams emitted by it coincide on the camera, and the calibration is completed;

[0055] 2) Imaging spot position measurement: The camera is located at the first axial position. Place a marking plate for imaging measurement on the object side of the objective lens, turn on the illumination beam for the objective lens to image, and the absolute position of the objective lens imaging spot on the camera target surface is recorded as the imaging spot position P1.

[0056] 3) Reference spot position measurement: The camera is located at the first axial position, turn on the parallel reference beam, and the absolute position of the spot formed by the parallel reference beam on the camera target surface is recorded as the reference spot position P0;

[0057] 4) Axis deviation calculation:

[0058] The camera moves axially by ΔZ; calculate the change in the center distance M between the imaging spot position P1 and the reference spot position P0 at different camera axial positions, which is recorded as ΔM;

[0059] According to tanα = ΔM / ΔZ, where α is the tilt angle of the tube lens optical axis after removing the influence of the tilt of the camera moving axis; calculate the value of α; according to the formula tanα = ΔL / f, where f is the focal length of the tube lens, calculate the corresponding axis deviation of the tube lens;

[0060] Among them, the execution order of step 2) is any one of the following: before step 1), after step 1) and before step 4).

[0061] The camera referred to in the embodiments of the present invention uses a camera that only includes the camera body without a lens.

[0062] Embodiment 1:

[0063] Please refer to Figure 4 As shown, the multi-magnification imaging system axis deviation detection system in this example includes: a camera 1, a beam splitter, a collimator (not shown in the figure), and a reflection element; wherein the reflection element includes a reference reflection flat crystal 71 and a calibration reflection flat crystal 72. The beam splitter uses a cube beam splitter prism 6, which has a simple structure and is easy to perform beam splitting operations. The first interface 61, the second interface 62, and the third interface 63 of the cube beam splitter prism 6 are high-transmission surfaces coated with an antireflection film, the fourth interface 64 is a reflection surface coated with a reflection film, and the fifth interface 65 is a semi-transparent and semi-reflecting surface coated with a beam splitting film.

[0064] The multi-magnification imaging system axis deviation detection method in this example is applicable to semiconductor imaging detection and specifically includes the following steps:

[0065] The first step: Calibration of the parallel reference beam of the collimator

[0066] Place the calibration reflection flat crystal 72 on the side of the image-side mechanical reference plane of the tube lens 3, and the reflection surface of the calibration reflection flat crystal is perpendicular to the image-side mechanical reference plane of the tube lens 3; at this time, do not place the cube beam splitter prism; the parallel reference beam 90 emitted by the collimator irradiates the reflection surface of the calibration reflection flat crystal 72 and returns to the collimator after reflection; according to the measurement reading of the collimator, adjust the attitude of the collimator so that the parallel reference beam 90 emitted by the collimator is perpendicular to the reflection surface of the calibration reflection flat crystal 72. At this time, the calibration of the parallel reference beam 90 is completed.

[0067] The second step: Calibration of the prism attitude

[0068] Please combine Figure 4 and Figure 5 As shown, place the reference reflection flat crystal 71 on the upper mechanical reference plane of the tube lens 3, and place the cube beam splitter prism 6 between the camera 1 and the reference reflection flat crystal 71. The calibrated parallel reference beam 90 emitted by the collimator irradiates into the cube beam splitter prism 6; the parallel reference beam 90 is split into two paths by the cube beam splitter prism 6. One path of the beam passes through the second interface 62 - the fifth interface 65 - the third interface 63 - the reference reflection flat crystal - the third interface 63 - the fifth interface 65 - the first interface 61 - the camera; the other path of the beam passes through the second interface 62 - the fifth interface 65 - the fourth interface 64 - the fifth interface 65 - the first interface 61 - the camera; the two paths of the beam form two light spots on the camera.

[0069] Adjust the attitude of the cube beam splitter prism 6 so that the two light spots coincide on the target surface of the camera 1. At this time, the attitude of the cube beam splitter prism 6 relative to the reference reflection flat crystal 71 has been adjusted to be parallel. The coincident light spot is denoted as P0 and serves as the subsequent measurement reference light spot.

[0070] If the Z-axis movement axis of the camera is inclined, when the camera 1 moves along the Z-axis, the position of the light spot P0 changes on the camera target surface. Therefore, through the change of the position of P0 during the Z-axis movement of the camera, the inclination of the Z-axis movement axis of the camera can be characterized, and reference deduction can be carried out in subsequent measurements. After deducting the position change, the calculation is performed, and the influence of the inclination of the Z-axis movement axis is corrected, ensuring that this inclination will not affect the measurement result of the tube lens axis deviation, and further improving the detection accuracy.

[0071] Step 3: Defocus imaging measurement

[0072] Remove the reference reflecting flat crystal 71;

[0073] Place a marking plate for measurement (not shown in the figure) on the object side of the objective lens 4. The marking plate has appropriate markings, such as crosshairs, star holes, or round holes, etc., for imaging measurement; retain the cube beam splitter prism 6 with the attitude adjusted; at the same time, turn on the parallel reference beam 90 and the illumination beam for objective lens imaging (not shown in the figure);

[0074] When the camera 1 is at the first axial position 11, the absolute position of the objective lens imaging light spot on the camera target surface is recorded as the first imaging light spot P11; the absolute position of the parallel reference beam light spot on the camera target surface is recorded as the first reference light spot P10;

[0075] The camera 1 axially moves ΔZ to the second axial position 12. The absolute position of the objective lens imaging light spot on the camera target surface is recorded as the second imaging light spot P21, and the absolute position of the parallel reference beam light spot on the camera target surface is recorded as the second reference light spot P20;

[0076] Step 4: Axis deviation calculation

[0077] The change in the distance M between the objective lens imaging light spot and the reference light spot at different Z-axis positions is recorded as ΔM. Take ΔM = (P11 - P10) - (P21 - P20); then tanα = ΔM / ΔZ, where α is the tube lens optical axis inclination angle after removing the influence of the camera movement axis inclination.

[0078] According to the formula tanα = ΔL / f, calculate the corresponding axis deviation ΔL = f·tanα of the tube lens.

[0079] The axis deviation detection method and system of the multi-magnification imaging system in this example measure the axis deviation of the tube lens and the objective lens based on the reference beam and the defocus imaging method. The reflected beam of the cube beam splitter prism is used as the reference beam, and the defocus imaging method is combined to measure the optical axis inclination, realizing the axis deviation measurement of the tube lens module and the objective lens with multiple magnification factors. Moreover, because the reflected beam of the cube beam splitter prism is used as the reference beam during axis deviation measurement, the measurement accuracy is independent of the camera movement axis, eliminating the influence of the camera movement axis inclination and further improving the detection accuracy.

[0080] Embodiment 2:

[0081] The difference between this example and the first embodiment mainly lies in the different order of execution steps as follows:

[0082] The first step: Defocus imaging measurement

[0083] Place a marking plate for measurement (not shown in the figure) on the object side of the objective lens 4. The marking plate is provided with appropriate markings, such as crosshairs or star holes, etc., for imaging measurement; turn on the illumination beam for the objective lens imaging (not shown in the figure);

[0084] When the camera 1 is located at the first axial position 11, the absolute position of the objective lens imaging spot on the camera target surface is recorded as the first imaging spot P11;

[0085] The camera moves axially by ΔZ to the second axial position 12, and the absolute position of the objective lens imaging spot on the camera target surface is recorded as the second imaging spot P21;

[0086] The second step: Collimator parallel reference beam calibration

[0087] Place a calibration reflecting flat crystal 72 on the side of the mechanical reference plane of the image side of the tube lens 3, and the reflecting surface of the calibration reflecting flat crystal 72 is perpendicular to the mechanical reference plane of the image side of the tube lens 3; at this time, do not place the cube beam splitter prism; the parallel reference beam 90 emitted by the collimator (not shown in the figure) irradiates the reflecting surface of the calibration reflecting flat crystal 72 and returns to the collimator after reflection; according to the measurement reading of the collimator, adjust the attitude of the collimator so that the parallel reference beam 90 emitted by the collimator is perpendicular to the reflecting surface of the calibration reflecting flat crystal 72. At this time, the calibration of the parallel reference beam 90 is completed.

[0088] The third step: Prism attitude calibration

[0089] Please refer to Figure 4 and Figure 5 As shown, place a reference reflecting flat crystal 71 on the mechanical reference plane above the tube lens 3, and place a cube beam splitter prism 6 between the camera 1 and the reference reflecting flat crystal 71. The calibrated parallel reference beam 90 emitted by the collimator irradiates into the cube beam splitter prism 6; the parallel reference beam 90 is divided into two paths by the cube beam splitter prism 6. One path of the beam passes through the second interface 62 - the fifth interface 65 - the third interface 63 - the reference reflecting flat crystal 71 - the third interface 63 - the fifth interface 65 - the first interface 61 - the camera; the other path of the beam passes through the second interface 62 - the fifth interface 65 - the fourth interface 64 - the fifth interface 65 - the first interface 61 - the camera; the two paths of the beam form two spots on the camera.

[0090] Adjust the attitude of the cubic beam-splitting prism 6 so that the two light spots coincide on the camera target surface 10 of the camera 1. At this time, the attitude of the cubic beam-splitting prism 6 relative to the reference reflecting flat crystal 71 has been adjusted to be parallel. The coincident light spot is denoted as P0 and serves as the subsequent measurement reference light spot.

[0091] If the Z-axis moving axis of the camera is tilted, when the camera 1 moves along the Z-axis, the position of the light spot P0 changes on the camera target surface. Therefore, through the change of the position of P0 during the Z-axis movement of the camera, the tilt of the Z-axis moving axis of the camera can be characterized, and reference subtraction is performed in subsequent measurements. The calculation after subtracting this position change corrects the influence of the tilt of the Z-axis moving axis and avoids the influence of this tilt on the measurement result of the tube lens axis offset.

[0092] Fourth step: Imaging measurement of the reference light spot

[0093] Remove the reference reflecting flat crystal 71;

[0094] Retain the cubic beam-splitting prism 6 with the attitude adjusted, and at the same time turn on the parallel reference beam 90;

[0095] When the camera 1 is at the first axial position, the absolute position of the light spot of the parallel reference beam 90 on the camera target surface is denoted as the first reference light spot P10;

[0096] The camera axially moves ΔZ to the second axial position, and the absolute position of the light spot of the parallel reference beam 90 on the camera target surface is denoted as the second reference light spot P20;

[0097] Fifth step: Axis offset calculation

[0098] The change in the distance M between the imaging light spot of the objective lens and the reference light spot at different Z-axis positions is denoted as ΔM. Take ΔM = (P11 - P10) - (P21 - P20); then tanα = ΔM / ΔZ, where α is the tilt angle of the tube lens optical axis after removing the influence of the tilt of the camera moving axis.

[0099] According to the formula tanα = ΔL / f, calculate the corresponding axis offset ΔL = f·tanα of the tube lens.

[0100] The method and system for detecting the axis offset of the multi-magnification imaging system in this example measure the axis offset of the tube lens and the objective lens based on the reference beam and the defocus imaging method. The reflected beam of the cubic beam-splitting prism is used as the reference beam, and the defocus imaging method is combined to measure the tilt of the optical axis, realizing the measurement of the axis offset of the tube lens module and the objective lens with multiple magnification factors. And because the reflected beam of the cubic beam-splitting prism is used as the reference beam during the axis offset measurement, the measurement accuracy is independent of the camera moving axis, eliminating the influence of the tilt of the camera moving axis and further improving the detection accuracy.

[0101] Example three:

[0102] Based on the above embodiments, in this example, the calibrated reflection unit and the reference reflection unit are combined, that is, the two adopt an integrated structure. The calibrated reflection flat crystal 72 and the reference reflection flat crystal 71 are perpendicular to each other and integrated into an L-shaped reflection flat crystal. In this way, when setting, one arm of the L-shaped reflection flat crystal is directly set on the image-side mechanical reference plane of the tube lens 3 as the reference reflection flat crystal 71. At this time, the other arm is perpendicular to the image-side mechanical reference plane of the tube lens 3 as the calibrated reflection flat crystal 72. The position adjustment of the two relative to the image-side mechanical reference plane of the tube lens 3 is completed at one time and is more accurate.

[0103] The above uses specific examples to elaborate on the present invention, which is only used to help understand the present invention and is not intended to limit the present invention. For those skilled in the art of the present invention, according to the idea of the present invention, several simple deductions, deformations or substitutions can also be made. For example, the beam splitter can also adopt other types of beam splitters, as long as one of the beams of light can be kept perpendicular to the mechanical surface of the tube lens and can be irradiated to the camera for the purpose of monitoring and calibrating the movement axis of the camera. For the method for detecting the axis deviation of the multi-magnification imaging system of the present invention, those skilled in the art can also change or adjust the execution order in the specific execution steps according to the specific situation, and still be able to achieve the purpose of the present invention.

Claims

1. A method for detecting axis deviation of a multi-magnification imaging system; comprising the following steps: 1) Beam splitter settings: A beam splitter is arranged on the opposite side of the tube image, and a parallel reference beam is used to calibrate the attitude of the beam splitter until the light spots formed by at least two beams emitted by the beam splitter overlap on the camera; 2) Measurement of the first imaging light spot position: The camera is located at the first axial position, a marking plate for imaging measurement is placed on the object side of the objective lens, the illumination beam of the objective lens imaging is turned on, and the absolute position of the objective lens imaging light spot on the camera target surface is counted as the first imaging light spot position P11; 3) First reference light spot position measurement: the camera is located at the first axial position, the parallel reference beam is turned on, and the absolute position of the light spot formed by the parallel reference beam is recorded as the first reference light spot position P10; 4) Second imaging spot position measurement: the camera is located at the second axial position, a marking plate for imaging measurement is placed on the object side of the objective lens, the illumination beam of the objective lens imaging is turned on, and the absolute position of the objective lens imaging spot on the camera target surface is counted as the second imaging spot position P21; 5) Second reference light spot position measurement: the camera is located at the second axial position, the parallel reference beam is turned on, and the absolute position of the light spot formed by the parallel reference beam is recorded as the second reference light spot position P20; 6) Calculation of axis offset: Record the axial movement distance ΔZ between the first axial position and the second axial position of the camera; Calculate the change in the center distance M between the imaging spot position and the reference spot position under different camera axial positions, which is calculated as ΔM=(P11-P10)-(P21-P20); According to tanα=ΔM / ΔZ, where α is the inclination angle of the optical axis of the tube lens after removing the influence of the camera motion axis inclination; Calculate the value of α; According to the formula tanα=ΔL / f, where f is the focal length of the tube lens, the corresponding axis offset ΔL= f·tanα of the tube lens is calculated; The execution order of step 2) is any one of the following: before step 1), after step 1) and before step 6); the execution order of step 4) is any one of the following: before step 1), after step 1) and before step 6).

2. The method for detecting axis deviation of a multi-magnification imaging system according to claim 1, characterized in that: In the beam splitter setting step, the step of calibrating the beam splitter posture includes: A reference reflective element is arranged on the image-side mechanical reference plane of the tube lens; The beam splitter is arranged between the camera and the reference reflective element, and the parallel reference beam is irradiated into the beam splitter; The beam splitter splits the parallel reference beam into at least two beams; One path of the light beam passes through a beam splitter-reference reflective element-beam splitter-camera, and the other path of the light beam passes through a beam splitter-camera; the two paths of the light beam form two light spots on the camera; The posture of the beam splitter is adjusted so that the two light spots overlap on the camera. At this time, the posture of the beam splitter relative to the reference reflective element has been adjusted to be parallel.

3. The method for detecting axis deviation of a multi-magnification imaging system according to claim 2, characterized in that: The method also includes the step of calibrating the parallel reference beam: A calibration reflective element is arranged on the image side mechanical reference plane of the tube lens, wherein the reflective surface of the calibration reflective element is perpendicular to the image side mechanical reference plane of the tube lens; The light beam emitted by the parallel light generator is irradiated onto the surface of the calibration reflective element, and then returns to the parallel light generator after being reflected; According to the measurement indication of the parallel light generator, the posture of the parallel light generator is adjusted so that the outgoing light beam of the parallel light generator is perpendicular to the reflective surface of the calibration reflective element; At this time, the outgoing light beam is calibrated as the parallel reference light beam.

4. The method for detecting axis deviation of a multi-magnification imaging system according to claim 2 or 3, characterized in that: The beam splitter is a cubic beam splitter prism, which splits the parallel reference beam into two paths.

5. The method for detecting axis deviation of a multi-magnification imaging system according to claim 3, characterized in that: The parallel light generator is a parallel light tube.

6. The method for detecting axis deviation of a multi-magnification imaging system according to claim 3, characterized in that: The calibration reflective element and the reference reflective element are reflective flat crystals.

7. The method for detecting axis deviation of a multi-magnification imaging system according to claim 2 or 3, characterized in that: The marking plate carries markings suitable for imaging measurement, including but not limited to crosshairs, star holes or circular holes.

8. The method for detecting axis deviation of a multi-magnification imaging system according to claim 4, characterized in that: The first interface, the second interface and the third interface of the cubic beam splitter prism are high-transmittance surfaces coated with anti-reflection films, the fourth interface is a reflective surface coated with a reflective film, and the fifth interface is a semi-transparent and semi-reflective surface coated with a beam splitting film.

9. The method for detecting axis deviation of a multi-magnification imaging system according to claim 6, characterized in that: The calibration reflective element and the reference reflective element are integrated into an L-shaped reflective flat crystal, and two arms of the L-shape are perpendicular to each other.

10. A multi-magnification imaging system axis deviation detection system, characterized in that: It includes an objective lens, multiple tube lenses, a tube lens switching structure, a Z-axis motion stage, a camera, a beam splitter and a marking plate; the tube lens switching structure carries the multiple tube lenses and is used to move in the horizontal direction to achieve switching of different tube lenses; the camera is installed on the Z-axis adjustment structure and can move up and down and focus the image plane; the beam splitter is arranged between the image side of the tube lens and the object side of the camera, and is calibrated through posture so that the spots formed on the camera by at least two beams generated by parallel reference beams overlap; the marking plate is used to be placed on the object side of the objective lens and form an imaging spot on the camera; the objective lens, the multiple tube lenses, the tube lens switching structure, the Z-axis motion stage, the camera, the beam splitter and the marking plate cooperate to implement the axis deviation detection method of the multi-magnification imaging system as described in claim 1.

11. The multi-magnification imaging system axis deviation detection system according to claim 10, characterized in that: It also includes a reference reflective element, which is arranged on the image-side mechanical reference plane of the tube lens; and is used for: when the reference light beam is split into at least two light beams by the beam splitter, one of the light beams passes through the beam splitter-reference reflective element-beam splitter-camera, and the other light beam passes through the beam splitter-camera; the two light beams form two light spots on the camera; the posture of the beam splitter is adjusted so that the two light spots overlap on the camera, and at this time, the posture of the beam splitter relative to the reference reflective element has been adjusted to be parallel.

12. The multi-magnification imaging system axis deviation detection system according to claim 11, characterized in that: It also includes a parallel light generator and a calibration reflective element, wherein the parallel light generator and the calibration reflective element are respectively arranged on the side of the beam splitter, and the reflective surface of the calibration reflective element is perpendicular to the image side mechanical reference surface of the tube lens; Used to: irradiate the outgoing light beam of the parallel light generator to the surface of the calibration reflective element, and return to the parallel light generator after reflection; adjust the posture of the parallel light generator according to the measurement indication of the parallel light generator, so that the outgoing light beam of the parallel light generator is perpendicular to the reflective surface of the calibration reflective element; at this time, the outgoing light beam is calibrated as the reference light beam.

13. The multi-magnification imaging system axis deviation detection system according to claim 11 or 12, characterized in that: The beam splitter is a cubic beam splitter prism.

14. The multi-magnification imaging system axis deviation detection system according to claim 12, characterized in that: The parallel light generator is a parallel light tube.

15. The multi-magnification imaging system axis deviation detection system according to claim 12, characterized in that: The calibration reflective element and the reference reflective element are reflective flat crystals.

16. The multi-magnification imaging system axis deviation detection system according to claim 13, characterized in that: The first interface, the second interface and the third interface of the cubic beam splitter prism are high-transmittance surfaces coated with anti-reflection films, the fourth interface is a reflective surface coated with a reflective film, and the fifth interface is a semi-transparent and semi-reflective surface coated with a beam splitting film.

17. The multi-magnification imaging system axis deviation detection system according to claim 15, characterized in that: The calibration reflective element and the reference reflective element are integrated into an L-shaped reflective flat crystal, and two arms of the L-shape are perpendicular to each other.

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