Vertical displacement measuring device and optical imaging system

Abstract

The invention discloses a vertical displacement measuring device and an optical imaging system, the vertical displacement measuring device comprises a grating projection module, a grating detection module and a processor, the grating detection module comprises a detection grating and a photoelectric detector, and the grating projection module forms a projection grating pattern and projects the projection grating pattern to a measured object; the projection grating pattern is reflected to the detection grating through the detected object, then forms a detection grating pattern through the detection grating and is imaged on the photoelectric detector, and the photoelectric detector receives the detection grating pattern and outputs corresponding detection information. The grating projection module and the detection grating can form different projection detection grating pairs, and the corresponding relations between the detection information corresponding to the different projection detection grating pairs and the vertical displacement of the detected object are different. And the processor determines the vertical displacement of the measured object according to the detection information combination formed by the detection information corresponding to the plurality of different projection detection grating pairs, so that the dimension of the detection information is increased, and the measuring range of the vertical displacement measurement of the object can be expanded.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, and in particular to a vertical displacement measuring device and an optical imaging system. Background Art

[0002] In order to ensure the working performance of the optical detection equipment, it is necessary to ensure that the observed sample is within the object depth of field of the objective lens. Therefore, a vertical displacement measurement device is required to detect the height information of the sample in real time and feed the measured height information back to the displacement stage to form a closed loop with the displacement stage. The displacement stage drives the sample to move, thereby adjusting the height of the sample's measured point in real time to ensure that the sample's measured point is always within the focal depth of the objective lens. Therefore, it is necessary to measure the vertical displacement of the sample with high precision.

[0003] In the prior art, optical triangulation is often used to measure the vertical displacement of a sample. Optical triangulation is a widely used off-axis optical measurement method. High-sensitivity and high-precision triangulation displacement measurement usually uses a striped grating-style graphic template. Based on the optical path principle of triangulation, the displacement of the object to be measured is amplified and mapped as a relative displacement change between two grating patterns. Usually, a striped grating pattern is projected onto the object to be measured, which is reflected by the object to be measured onto the detection grating in front of the detector, and then hits the detector after passing through the detection grating. The intensity of the light beam passing through the detection grating is similar to a sinusoidal function in its relationship to the displacement of the reflected grating pattern reflected by the object to be measured on the detection grating relative to the detection grating, and the displacement of the grating pattern is proportional to the change in the height of the object to be measured, thereby enabling high-precision vertical displacement measurement based on the detection of light intensity. However, the inherent periodicity of the grating pattern leads to the periodic characteristics between the light intensity and the relative displacement of the grating pattern, that is, when the reflected grating pattern is offset by a whole period component relative to the detection grating, the light intensity remains basically unchanged, and the change of the light intensity of the half-period is symmetrical with the change of the light intensity of the other half-period, resulting in the inability of this type of method to effectively measure the displacement exceeding half a period. The range of displacement measurement using a constant period grating can be extended by designing an encoded grating, but the decoding method to obtain the height is complex, and the measurement accuracy is only equivalent to the grating stripe width, and it is usually necessary to combine other methods to improve the accuracy. Summary of the invention

[0004] The main technical problem solved by the present invention is how to expand the measuring range of vertical displacement.

[0005] According to the first aspect, an embodiment provides a vertical displacement measuring device, including a grating projection module, a grating detection module and a processor, wherein the grating detection module includes a detection grating and a photoelectric detector;

[0006] The grating projection module is used to form a projection grating pattern and project the projection grating pattern onto the object to be measured; after the projection grating pattern is reflected by the object to be measured to the detection grating, it passes through the detection grating to form a detection grating pattern and is imaged on the photoelectric detector; the photoelectric detector is used to receive the detection grating pattern and output corresponding detection information;

[0007] Wherein, the detection information changes with the change of the vertical displacement of the object to be measured; the grating projection module and the detection grating can form different projection detection grating pairs, and the corresponding relationship between the detection information corresponding to different projection detection grating pairs and the vertical displacement of the object to be measured is different, and the projection detection grating pair refers to the combination of the projection grating pattern and the detection grating;

[0008] The processor is connected to the grating projection module and the grating detection module, and is used to control the grating projection module to project the projection grating pattern onto the object to be measured, and obtain detection information corresponding to multiple different projection detection grating pairs output by the photoelectric detector to form a detection information combination, and determine the vertical displacement of the object to be measured based on the detection information combination.

[0009] In some embodiments, the grating projection module is capable of forming a plurality of projection grating patterns with different grating parameters, and / or the detection grating includes a plurality of detection sub-gratings with different grating parameters, wherein the grating parameters are related to the correspondence between the detection information and the vertical displacement of the object being measured.

[0010] In some embodiments, if the grating projection module can form a plurality of projection grating graphics with different grating parameters, the processor is used to control the grating projection module to sequentially project a plurality of projection grating graphics with different grating parameters onto the object to be measured, or to simultaneously project a plurality of projection grating graphics with different grating parameters onto the object to be measured.

[0011] In some embodiments, the grating projection module includes an illumination light source and a projection grating, and the light emitted by the illumination light source passes through the projection grating to form the projection grating pattern; the projection grating includes a plurality of projection sub-gratings with different grating parameters, and / or the detection grating includes a plurality of detection sub-gratings with different grating parameters.

[0012] In some embodiments, the projection grating includes a plurality of projection sub-gratings, and the detection grating includes a plurality of detection sub-gratings corresponding to the plurality of projection sub-gratings one by one, and the projection grating pattern formed by each of the projection sub-gratings is reflected by the measured object and then irradiated onto the corresponding detection sub-grating;

[0013] Wherein, the plurality of projection sub-gratings have different grating parameters and the plurality of detection sub-gratings have the same grating parameters;

[0014] Alternatively, the plurality of projection sub-gratings have the same grating parameters and the plurality of detection sub-gratings have different grating parameters;

[0015] Alternatively, the plurality of projection sub-gratings have different grating parameters and the plurality of detection sub-gratings have different grating parameters.

[0016] In some embodiments, the grating parameters include at least one of phase, period, transmission coefficient and duty cycle.

[0017] In some embodiments, if the detection grating includes a plurality of detection sub-gratings, the imaging surface of the photodetector is divided into a plurality of imaging areas corresponding to the plurality of detection sub-gratings one by one, each imaging area is used to receive a detection grating pattern formed by passing through the corresponding detection sub-grating, and the detection information output by the photodetector includes the detection information of each of the imaging areas;

[0018] Alternatively, a photodetector is provided corresponding to each of the detection sub-gratings, and each photodetector is used to receive the detection grating pattern formed through the corresponding detection sub-grating and output corresponding detection information.

[0019] In some embodiments, if the imaging surface of the photodetector is divided into a plurality of imaging areas corresponding one to the plurality of detection sub-gratings, the vertical displacement measuring device further includes a lens array, wherein the lens array is disposed on the optical path from the detection grating to the photodetector, and is used to converge the light passing through each of the detection sub-gratings onto the corresponding imaging area, so that the detection grating pattern formed by passing through each of the detection sub-gratings is imaged within the corresponding imaging area.

[0020] In some embodiments, the detection information changes with the change of reflection displacement, and the reflection displacement is the displacement of the reflection grating pattern reflected by the detected object onto the detection grating relative to the detection grating;

[0021] The processor determines the vertical displacement of the object under test according to the detection information combination, including: the processor determines the reflection displacement corresponding to the detection information combination according to the correspondence between the detection information combination and the reflection displacement, and calculates the vertical displacement of the object under test according to the determined reflection displacement; wherein the correspondence between the detection information combination and the reflection displacement is calibrated according to the correspondence between the detection information corresponding to each of the projection detection grating pairs and the reflection displacement.

[0022] In some embodiments, the correspondence between the detection information combination and the reflection displacement is periodic, and the processor determines the reflection displacement corresponding to the detection information combination according to the correspondence between the detection information combination and the reflection displacement within a period;

[0023] If there are more than one reflection displacements corresponding to the detection information combination in one cycle, the one-to-one corresponding part of the detection information combination and the reflection displacement in one cycle is used to determine the reflection displacement, or,

[0024] For a detection information combination corresponding to more than one reflection displacement, the corresponding vertical displacement is determined as a candidate vertical displacement according to the corresponding reflection displacements, and the candidate vertical displacement among the candidate vertical displacements that is closest to the historical vertical displacement obtained by the most recent N measurements is determined as the vertical displacement of the object under test, where N is an integer not less than 1.

[0025] In some embodiments, the processor is further configured to compare the currently measured vertical displacement of the measured object with the vertical displacement of the measured object measured last time to determine the rise and fall of the measured object.

[0026] According to the second aspect, an embodiment provides an optical imaging system, including an objective lens, a stage, and the vertical displacement measuring device of the above embodiment;

[0027] The carrier is used to carry the object to be measured;

[0028] The objective lens is used to image the object to be measured;

[0029] The vertical displacement measuring device is used to measure the vertical displacement of the measured object, and the processor is also used to control the relative movement of the stage and the objective lens according to the vertical displacement of the measured object, so that the measured object is located within the focal depth range of the objective lens.

[0030] According to the vertical displacement measuring device and optical imaging system of the above-mentioned embodiment, a grating projection module, a grating detection module and a processor are included. The grating detection module includes a detection grating and a photodetector. The grating projection module and the detection grating can form different projection detection grating pairs, and the corresponding relationship between the detection information corresponding to different projection detection grating pairs and the vertical displacement of the measured object is different. The processor determines the vertical displacement of the measured object according to the detection information combination composed of the detection information corresponding to a plurality of different projection detection grating pairs. Since the corresponding relationship between the detection information corresponding to different projection detection grating pairs and the vertical displacement of the measured object is different, the vertical displacement of the measured object is determined by using the detection information combination, which increases the dimension of the detection information and can expand the range of vertical displacement measurement of the object. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of a vertical displacement measuring device according to an embodiment;

[0032] Figure 2 It is a structural schematic diagram of a vertical displacement measuring device according to another embodiment;

[0033] Figure 3 is a schematic diagram of a projection grating or a detection grating according to an embodiment;

[0034] Figure 4 is a schematic diagram of a projection grating and a detection grating of an embodiment;

[0035] Figure 5 Two different sets of projection gratings and detection gratings in one embodiment, and the relationship between the corresponding detection information and the vertical displacement;

[0036] Figure 6 for Figure 5 The relationship between the detection information combination composed of the detection information corresponding to the two different projection gratings and detection gratings and the vertical displacement;

[0037] Figure 7 Two different sets of projection gratings and detection gratings in another embodiment, and the relationship between the corresponding detection information and the vertical displacement;

[0038] Figure 8 for Figure 7 The relationship between the detection information combination composed of the detection information corresponding to the two different projection gratings and detection gratings and the vertical displacement;

[0039] Fig. 9 It is a structural schematic diagram of a vertical displacement measuring device according to another embodiment;

[0040] Fig.10 A schematic structural diagram of an optical imaging system according to an embodiment. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. Wherein similar elements in different embodiments adopt associated similar element numbers. In the following embodiments, many detailed descriptions are for making the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different situations, or can be replaced by other elements, materials, methods. In some cases, some operations related to the present application are not shown or described in the specification, this is to avoid the core part of the present application being overwhelmed by too much description, and 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 according to the description in the specification and the general technical knowledge in the art.

[0042] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various implementations. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a required sequence, unless otherwise specified that a certain sequence must be followed.

[0043] The serial numbers of the components in this document, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings).

[0044] It can be understood that "vertical displacement" refers to the displacement of an object in the vertical direction, and vertical refers to the direction perpendicular to the horizontal direction or the surface of the object. Usually, the objective lens images the object above the object, and the vertical displacement of the object reflects its height information and the distance between the objective lens and the objective lens. By moving the objective lens up and down, the distance between the objective lens and the object can be adjusted so that the object is within the focal depth of the objective lens. The vertical displacement here can be a relative displacement, that is, the distance relative to a predetermined 0 displacement point, and the positive and negative signs can be used to distinguish the direction. For example, a positive displacement indicates that it is above the 0 displacement point, and a negative displacement indicates that it is below the 0 displacement point, etc.

[0045] The present invention provides a vertical displacement measuring device with a larger measuring range, which can extend the measuring range of a vertical displacement measuring method based on grating projection, by adding different projection detection grating pairs, analyzing detection information formed by a plurality of different projection detection grating pairs, and combining the detection information to determine the vertical displacement, thereby extending the measuring range of the vertical displacement, while still maintaining its measurement accuracy, and realizing vertical displacement measurement in a larger range, wherein the measuring range is extended by no less than two times.

[0046] Please refer to Figure 1 The vertical displacement measuring device in some embodiments of the present invention includes a grating projection module 10, a grating detection module 20 and a processor 30, which are described in detail below.

[0047] The grating projection module 10 is used to form a projection grating pattern and project the projection grating pattern onto the object 80 to form an image on the object 80. The grating projection module 10 can be a projection light source (such as an LED projector) and can project different projection grating patterns under the control of the processor 30. Figure 2 As shown, the grating projection module 10 may also include an illumination light source 11 (for example, a light source that can emit uniform white light) and a projection grating 12. The illumination light source 11 emits uniform light, which is irradiated onto the projection grating 12, and the projection grating pattern is formed after passing through the projection grating 12.

[0048] The grating detection module 20 includes a detection grating 22 and a photodetector 21. After the projected grating pattern is reflected by the object to be measured 80 to the detection grating 22, it passes through the detection grating 22 to form a detection grating pattern and is imaged on the photodetector 21; the photodetector 21 is used to receive the detection grating pattern and output corresponding detection information. Among them, the detection information is information that can reflect the changes in the detection grating pattern, which can be light intensity, voltage signal, etc. The grating detection module 20 can be a grating sensor, etc., which integrates the detection grating 22 and the photodetector 21. The detection grating 22 and the photodetector 21 can also be two independently arranged devices, wherein the photodetector 21 can be a specific photodiode or a camera, etc.

[0049] After being reflected by the object 80 to be measured, the projected grating pattern carries the vertical displacement information of the object 80 to be measured. The reflection grating pattern reflected or imaged by the object 80 to be measured on the detection grating 22 overlaps with the detection grating 22, so that the detection information obtained after passing through the detection grating 22 carries the vertical displacement information of the object 80 to be measured, so that the detection information changes with the change of the vertical displacement of the object 80 to be measured, and the vertical displacement of the object 80 to be measured can be measured using the detection information.

[0050] The grating projection module 10 and the detection grating 22 can form different projection detection grating pairs, and the corresponding relationship between the detection information corresponding to different projection detection grating pairs and the vertical displacement of the object 80 under test is different, wherein the projection detection grating pair refers to a combination of a projection grating pattern and a detection grating.

[0051] Specifically, the grating projection module 10 can form a plurality of projection grating patterns with different grating parameters, and / or the detection grating 22 includes a plurality of detection sub-gratings with different grating parameters. The grating parameters here are related to the correspondence between the detection information and the vertical displacement of the object to be detected, and can be any one or more parameters that can affect the correspondence between the detection information and the vertical displacement of the object to be detected, including at least one of phase, period, transmission coefficient and duty cycle.

[0052] If the grating projection module 10 is capable of forming a plurality of projection grating patterns with different grating parameters, the processor 30 is used to control the grating projection module 10 to sequentially project a plurality of projection grating patterns with different grating parameters onto the object to be measured 80, or to simultaneously project a plurality of projection grating patterns with different grating parameters onto the object to be measured 80.

[0053] There are many ways to implement the grating projection module 10 to form a plurality of projection grating patterns with different grating parameters. In some embodiments, the grating projection module 10 is a projection light source, and forms a plurality of projection grating patterns with different grating parameters under the control of the processor 30. In other embodiments, the grating projection module 10 includes an illumination light source 11 and a projection grating 12, and the projection grating 12 includes a plurality of projection sub-gratings 12a with different grating parameters, such as Figure 3 The light emitted by the illumination light source 11 can be irradiated on all projection sub-gratings 12a at the same time, thereby simultaneously projecting multiple projection grating patterns with different grating parameters onto the object 80 to be measured, or it can be irradiated on only one projection sub-grating 12a, and then the illumination light source 11 and the projection grating 12 are controlled to move relative to each other, so that the light emitted by the illumination light source 11 is irradiated on another projection sub-grating 12a, thereby sequentially projecting multiple projection grating patterns with different grating parameters onto the object 80 to be measured. The projection sub-gratings 12a can also be arranged in other ways, such as up and down arrangement, and are not limited to Figure 3 Arrangement shown.

[0054] If the detection grating 22 includes a plurality of detection sub-gratings with different grating parameters, it can also be as follows Figure 3 In the arrangement shown or other arrangements, the light beam emitted by the object 80 to be measured passes through multiple detection sub-gratings to form multiple detection grating patterns, and the processor 30 obtains corresponding multiple detection information through the photodetector 21.

[0055] In some embodiments, the projection grating 12 includes a plurality of projection sub-gratings, and the detection grating 22 includes a plurality of detection sub-gratings corresponding to the plurality of projection sub-gratings one by one, and the projection grating pattern formed by each projection sub-grating is reflected by the measured object 80 and then irradiated onto the corresponding detection sub-grating. The plurality of projection sub-gratings have different grating parameters and the plurality of detection sub-gratings have the same grating parameters, or the plurality of projection sub-gratings have the same grating parameters and the plurality of detection sub-gratings have different grating parameters, or the plurality of projection sub-gratings have different grating parameters and the plurality of detection sub-gratings have different grating parameters, thereby forming a plurality of projection detection grating pairs with different corresponding relationships between the detection information and the vertical displacement of the measured object 80.

[0056] like Figure 4 As shown, the projection grating 12 includes n projection sub-gratings, and the detection grating 22 includes n detection sub-gratings corresponding to the n projection sub-gratings one by one. The projection grating pattern formed by each projection sub-grating is reflected by the object to be measured 80 to the reflection grating pattern PF on the corresponding detection sub-grating, and after passing through the detection sub-grating, n detection grating patterns PD1, PD2...PDn are formed and imaged on the photodetector 21.

[0057] By setting a plurality of projection sub-gratings and a plurality of detection sub-gratings corresponding to the plurality of projection sub-gratings one by one, the projection grating pattern formed by each projection sub-grating is reflected by the measured object 80 and then irradiated onto the corresponding detection sub-grating, so that the detection information of different projection detection grating pairs can be obtained at the same time, thereby improving the efficiency and real-time performance of the vertical displacement measurement.

[0058] The processor 30 is connected to the grating projection module 10 and the grating detection module 20, and is used to control the grating projection module 10 to project the projection grating pattern onto the object to be measured 80, and obtain the detection information corresponding to multiple different projection detection grating pairs output by the photodetector 21 to form a detection information combination, and determine the vertical displacement of the object to be measured 80 according to the detection information combination, thereby obtaining the vertical position information or height information of the object to be measured 80.

[0059] Specifically, a correspondence between the detection information combination and the vertical displacement can be established in advance, and the vertical displacement of the measured object 80 can be determined by the detection information combination according to the correspondence when measuring. The correspondence can be represented by a curve in space, for example. The correspondence can be fitted by actually collecting data, or it can be calculated by simulation software.

[0060] Since the correspondence between the detection information corresponding to different projection detection grating pairs and the vertical displacement of the measured object 80 is different, the dimension of the correspondence between the detection information and the vertical displacement is increased, thereby expanding the range of vertical displacement measurement of the object and realizing vertical displacement measurement over a large range.

[0061] In some embodiments, the detection information changes with the change of the reflection displacement, and the reflection displacement is the displacement of the reflection grating pattern reflected by the detected object 80 on the detection grating 22 relative to the detection grating 22. The processor 30 determines the vertical displacement of the detected object 80 according to the detection information combination, including: the processor 30 determines the reflection displacement corresponding to the detection information combination according to the corresponding relationship between the detection information combination and the reflection displacement, and calculates the vertical displacement of the detected object 80 according to the determined reflection displacement; wherein the corresponding relationship between the detection information combination and the reflection displacement is calibrated according to the corresponding relationship between the detection information corresponding to each projection detection grating pair and the reflection displacement.

[0062] Among them, the corresponding relationship between the detection information corresponding to each projection detection grating pair and the reflection displacement can also be fitted through actual acquisition data or obtained by simulation calculation using simulation software. By integrating the corresponding relationship between the detection information corresponding to each projection detection grating pair and the reflection displacement, multiple detection information corresponding to each reflection displacement can be known, thereby obtaining the corresponding relationship between the reflection displacement and the combination of detection information. After obtaining the reflection displacement, the vertical displacement of the measured object 80 can be calculated according to the optical triangulation method.

[0063] Usually, the relationship between each detection information and the reflection displacement is a sinusoidal function and is periodic. The relationship between the detection information combination and the reflection displacement is also periodic. In some cases, within the same period, there may be a detection information combination corresponding to more than one reflection displacement, resulting in the reflection displacement determined based on the detection information combination being non-unique.

[0064] In order to uniquely determine the reflection displacement, in some embodiments, the processor 30 determines the reflection displacement corresponding to the detection information combination based on the correspondence between the detection information combination and the reflection displacement within a cycle; if there is a detection information combination corresponding to more than one reflection displacement within a cycle, the part of the detection information combination and the reflection displacement within a cycle that corresponds one to one is taken to determine the reflection displacement, or, for the detection information combination corresponding to more than one reflection displacement, the corresponding vertical displacement is determined as the candidate vertical displacement according to the corresponding reflection displacements, and the candidate vertical displacement among the candidate vertical displacements that is closest to the historical vertical displacement obtained by the most recent N measurements is determined as the vertical displacement of the object 80 under test, where N is an integer not less than 1.

[0065] When the vertical displacement of the measured object 80 is determined by using the historical vertical displacements obtained by the most recent N measurements, the processor 30 will record the N historical vertical displacements including the vertical displacement measured this time during measurement, and use them in the next measurement. When N is 1, it is sufficient to determine the actual vertical displacement of the measured object 80. In order to improve stability, N can be greater than or equal to 2, and the candidate vertical displacement closest to the N historical vertical displacements is taken as the vertical displacement of the measured object 80.

[0066] In this embodiment, the reflection displacement is determined by taking the part of the detection information combination corresponding to the reflection displacement in one cycle, or the vertical displacement of the object to be measured is determined by using the historical vertical displacement obtained by the most recent N measurements, so that the vertical displacement of the object to be measured can be correctly measured even when there are more than one reflection displacements corresponding to the detection information combination in one cycle. Among them, the method of taking the part of the detection information combination corresponding to the reflection displacement in one cycle to determine the reflection displacement can be used in the scenario where the processor 30 has low computing processing power; the method of using the historical vertical displacement obtained by the most recent N measurements to determine the vertical displacement of the object to be measured, even if a certain detection information combination corresponds to different vertical displacements in the same cycle, the specific vertical displacement of the object to be measured can be determined according to the historical vertical displacement, so that all detection information combinations in one cycle can be used, and a larger range of measurements can be performed, which can be used in scenarios where a larger measurement range is required and the processor 30 has a higher processing power.

[0067] In some embodiments, the processor 30 is further configured to compare the currently measured vertical displacement of the measured object 80 with the vertical displacement of the measured object 80 measured last time to determine the rise and fall of the measured object 80. When the vertical displacement of the measured object 80 is determined using the historical vertical displacements obtained from the most recent N measurements, the vertical displacement measured last time can be directly obtained from the N historical vertical displacements.

[0068] The following is an explanation with a specific example, where the detection information is light intensity. Figure 5 In one embodiment, the projection grating 12 includes a projection sub-grating 1 and a projection sub-grating 2, the two projection sub-gratings have a phase difference of π / 4 and a period of P, the detection grating 22 includes a detection sub-grating 1 and a detection sub-grating 2, the two detection sub-gratings have the same period (both P) and the same phase, the projection sub-grating 1 and the detection sub-grating 1 form a projection detection grating pair 1, and the projection sub-grating 2 and the detection sub-grating 2 form a projection detection grating pair 2. The corresponding relationship between the light intensity and the reflection displacement of the two projection detection grating pairs is as follows: Figure 5As shown in Figure (b), it can be seen that the correspondence between the light intensity and the reflected displacement of a single projection detection grating pair is a sinusoidal function. In one cycle, the same light intensity corresponds to two reflected displacements. Therefore, only the correspondence of half a cycle can be used to measure the vertical displacement, that is, the range is 0.5P.

[0069] Depend on Figure 5 Figure (b) in the figure can obtain the corresponding relationship between the light intensity combination and the reflection displacement of the light intensity composition corresponding to the two projection detection grating pairs, such as Figure 6 As shown in Figure (a), light intensity 1 is the light intensity corresponding to the projection detection grating pair 1, and light intensity 2 is the light intensity corresponding to the projection detection grating pair 2. Figure 6 Figure (b) in the figure is a top view of Figure (a). It can be seen that the corresponding relationship between the light intensity combination and the reflection displacement is periodic, with a period of P. Within a period, the light intensity combination and the reflection displacement are one-to-one corresponding. Outside a period, there are repeated values ​​due to periodicity, making it impossible to confirm the reflection displacement. Therefore, the reflection displacement is determined based on the corresponding relationship between the light intensity combination and the reflection displacement within a period, that is, using Figure 6 The solid or dotted part of Figure (a) is used to determine the reflection displacement. At this time, the range is P, which is twice the range of a single projection detection grating pair.

[0070] Please refer to Figure 7 In another embodiment, the projection sub-grating 1 and the projection sub-grating 2 have different periods, which are P and 1.3P respectively. The detection sub-grating 1 is the same as the projection sub-grating 1, and the detection sub-grating 2 is the same as the projection sub-grating 2. The corresponding relationship between the light intensity and the reflection displacement of the two projection detection gratings is as follows: Figure 7 As shown in Figure (b), the measuring ranges are 0.5P and 0.65P respectively.

[0071] Depend on Figure 7 Figure (b) in the figure can obtain the corresponding relationship between the light intensity combination and the reflection displacement of the light intensity composition corresponding to the two projection detection grating pairs, such as Figure 8 As shown in Figure (a), Figure 8 Figure (b) is a top view of Figure (a). It can be seen that within a period, there is a situation where the reflection displacement corresponding to the light intensity combination is not unique. Figure 8 At the intersection of the curves in Figure (b) (such as point A), the light intensity combination corresponds to two reflection displacements. In this case, the reflection displacement cannot be determined, so the measurement range needs to avoid these intersections, which limits the measurement range to a certain extent. Figure 8 The solid curve portion is used to determine the reflection displacement, while the dotted curve portion is discarded, so that the light intensity combination and the reflection displacement are uniquely corresponding. In this case, there is still a range of about 1.6P, which is more than twice the maximum range of 0.65P that can be achieved by a single projection detection grating pair.

[0072] It is also possible not to limit the measurement range, but to record the historical vertical displacements obtained from the most recent N measurements during the measurement. Figure 8 The intersection of the curves in Figure (b) is determined based on the corresponding reflection displacements as candidate vertical displacements. Among these candidate vertical displacements, the candidate vertical displacement closest to the historical vertical displacement obtained by the most recent N measurements is determined as the vertical displacement of the object 80 under test. Figure 8 The curve in , assuming that the periods of projection sub-grating 1 and projection sub-grating 2 are P1 and P2 respectively, then the range is the least common multiple of P1 and P2, which greatly expands the measurement range. When P1 and P2 are closer, the extended range is larger relative to the range of a single projection detection grating pair.

[0073] The above two groups of examples are only simple illustrations. In actual use, the projection grating 12 and / or detection grating 22 used can be composed of more sub-gratings with different grating parameters. By using multiple projection detection gratings to perform comprehensive analysis on the corresponding light intensities, the range of grating-based vertical displacement measurement can be greatly and flexibly expanded.

[0074] In some embodiments, if the detection grating 22 includes a plurality of detection sub-gratings, a photodetector 21 is provided corresponding to each detection sub-grating, and each photodetector 21 is used to receive the detection grating pattern formed by the corresponding detection sub-grating and output corresponding detection information, that is, Figure 4 The detection grating patterns PD1, PD2...PDn are imaged on different photodetectors 21 respectively.

[0075] Alternatively, the imaging surface of the photodetector 21 (e.g., a specific photodiode or a target surface of a camera) is divided into a plurality of imaging areas corresponding to a plurality of detection sub-gratings, each imaging area is used to receive a detection grating pattern formed by passing through a corresponding detection sub-grating, and the detection information output by the photodetector 21 includes the detection information of each imaging area. In this case, there may be only one photodetector 21, i.e. Figure 4 The detection grating patterns PD1, PD2 ... PDn are imaged on different areas of the same photodetector 21. This solution allows all detection grating patterns to converge into a smaller range, saving space, and can be used in scenarios where the size of the grating detection module 20 is required or there is only one photodetector 21.

[0076] In a specific implementation, the vertical displacement measuring device may include a lens array, which is arranged on the optical path from the detection grating 22 to the photodetector 21, and is used to converge the light passing through each detection sub-grating on the imaging area corresponding to the photodetector 21, so that the detection grating pattern formed by each detection sub-grating is imaged in its corresponding imaging area.

[0077] Please refer to Fig. 9 In some embodiments, the vertical displacement measuring device further includes a first reflector 40, a second reflector 50, a first telecentric lens 60, and a second telecentric lens 70. The first reflector 40 is disposed on the optical path of the outgoing light of the grating projection module 10, and is used to reflect the outgoing light of the grating projection module 10 onto the object to be measured 80. The first telecentric lens 60 is disposed on the optical path of the reflected light of the first reflector 40, and is used to converge the reflected light of the first reflector 40 and project it onto the object to be measured 80. The second telecentric lens 70 is disposed on the optical path of the reflected light of the object to be measured 80, and is used to converge the reflected light of the object to be measured 80. The second reflector 50 is disposed on the optical path of the outgoing light of the second telecentric lens 70, and is used to reflect the outgoing light of the second telecentric lens 70 onto the detection grating 22. Among them, the first telecentric lens 60 and the second telecentric lens 70 can be double telecentric lenses.

[0078] In this embodiment, by setting the first reflector 40 and the second reflector 50, the structure of the vertical displacement measuring device is made more compact; by setting the first telecentric lens 60 and the second telecentric lens 70, the light beam is more concentratedly irradiated onto the object to be measured 80 and the detection grating 22, and the perspective error can be eliminated, which is beneficial to reducing the error of vertical displacement measurement.

[0079] The present invention also provides an optical imaging system, which can be an optical detection system, a photolithography machine, etc. Fig.10 The optical imaging system in some embodiments includes an objective lens 1, a stage 2, and a vertical displacement measuring device 3 in any embodiment of the present invention.

[0080] The stage 2 is used to carry the object 80 to be measured. The stage 2 can move under the control of the processor 30 in the vertical displacement measuring device 3, thereby driving the object 80 to be measured to move.

[0081] The objective lens 1 is used to image the measured object 80. The objective lens 1 can move under the control of the processor 30 in the vertical displacement measuring device 3.

[0082] The vertical displacement measuring device 3 is used to measure the vertical displacement of the measured object 80, and the processor 30 is also used to control the relative movement of the stage 2 and the objective lens 1 according to the vertical displacement of the measured object 80, so that the measured object 80 is located within the focal depth range of the objective lens 1. Specifically, one of the stage 2 and the objective lens 1 can be controlled to move, or both can be controlled to move.

[0083] Those skilled in the art will appreciate that all or part of the functions of the various methods in the above-mentioned embodiments can be implemented by hardware or by computer programs. When all or part of the functions in the above-mentioned embodiments are implemented by computer programs, the program can be stored in a computer-readable storage medium, and the storage medium can include: read-only memory, random access memory, disk, optical disk, hard disk, etc., and the program is executed by a computer to implement the above-mentioned functions. For example, the program is stored in the memory of the device, and when the program in the memory is executed by the processor, all or part of the above-mentioned functions can be implemented. In addition, when all or part of the functions in the above-mentioned embodiments are implemented by computer programs, the program can also be stored in a storage medium such as a server, another computer, disk, optical disk, flash disk or mobile hard disk, and can be downloaded or copied and saved in the memory of the local device, or the system of the local device is updated, and when the program in the memory is executed by the processor, all or part of the functions in the above-mentioned embodiments can be implemented.

[0084] The above specific examples are used to illustrate 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, according to the concept of the present invention, some simple deductions, modifications or substitutions can be made.

Claims

1. A vertical displacement measuring device, characterized in that: It includes a grating projection module, a grating detection module and a processor, wherein the grating detection module includes a detection grating and a photoelectric detector; The grating projection module is used to form a projection grating pattern and project the projection grating pattern onto the object to be measured; after the projection grating pattern is reflected by the object to be measured to the detection grating, it passes through the detection grating to form a detection grating pattern and is imaged on the photoelectric detector; The photoelectric detector is used to receive the detection grating pattern and output corresponding detection information; Wherein, the detection information changes with the change of the vertical displacement of the object to be measured; the grating projection module and the detection grating can form different projection detection grating pairs, and the corresponding relationship between the detection information corresponding to different projection detection grating pairs and the vertical displacement of the object to be measured is different, and the projection detection grating pair refers to the combination of the projection grating pattern and the detection grating; The processor is connected to the grating projection module and the grating detection module, and is used to control the grating projection module to project the projection grating pattern onto the object to be measured, and obtain detection information corresponding to multiple different projection detection grating pairs output by the photoelectric detector to form a detection information combination, and determine the vertical displacement of the object to be measured based on the detection information combination.

2. The vertical displacement measuring device according to claim 1, characterized in that: The grating projection module can form a plurality of projection grating patterns with different grating parameters, and / or the detection grating includes a plurality of detection sub-gratings with different grating parameters, wherein the grating parameters are related to the corresponding relationship between the detection information and the vertical displacement of the object to be measured.

3. The vertical displacement measuring device according to claim 2, characterized in that: If the grating projection module can form a plurality of projection grating graphics with different grating parameters, the processor is used to control the grating projection module to sequentially project a plurality of projection grating graphics with different grating parameters onto the object to be measured, or to simultaneously project a plurality of projection grating graphics with different grating parameters onto the object to be measured.

4. The vertical displacement measuring device according to claim 2 or 3, characterized in that: The grating projection module includes an illumination light source and a projection grating, and the light emitted by the illumination light source forms the projection grating pattern after passing through the projection grating; the projection grating includes a plurality of projection sub-gratings with different grating parameters, and / or the detection grating includes a plurality of detection sub-gratings with different grating parameters.

5. The vertical displacement measuring device according to claim 4, characterized in that: The projection grating includes a plurality of projection sub-gratings, and the detection grating includes a plurality of detection sub-gratings corresponding to the plurality of projection sub-gratings one by one, and the projection grating pattern formed by each of the projection sub-gratings is reflected by the measured object and then irradiated onto the corresponding detection sub-grating; Wherein, the plurality of projection sub-gratings have different grating parameters and the plurality of detection sub-gratings have the same grating parameters; Alternatively, the plurality of projection sub-gratings have the same grating parameters and the plurality of detection sub-gratings have different grating parameters; Alternatively, the plurality of projection sub-gratings have different grating parameters and the plurality of detection sub-gratings have different grating parameters.

6. The vertical displacement measuring device according to any one of claims 2 to 5, characterized in that: The grating parameters include at least one of phase, period, transmission coefficient and duty cycle.

7. The vertical displacement measuring device according to any one of claims 2 to 6, characterized in that: If the detection grating includes a plurality of detection sub-gratings, the imaging surface of the photodetector is divided into a plurality of imaging areas corresponding to the plurality of detection sub-gratings one by one, each imaging area is used to receive a detection grating pattern formed by passing through the corresponding detection sub-grating, and the detection information output by the photodetector includes the detection information of each of the imaging areas; Alternatively, a photodetector is provided corresponding to each of the detection sub-gratings, and each photodetector is used to receive the detection grating pattern formed through the corresponding detection sub-grating and output corresponding detection information.

8. The vertical displacement measuring device according to claim 7, characterized in that: If the imaging surface of the photodetector is divided into a plurality of imaging areas corresponding one to the plurality of detection sub-gratings, the vertical displacement measuring device further comprises a lens array, wherein the lens array is arranged on the optical path from the detection grating to the photodetector, and is used to converge the light passing through each of the detection sub-gratings onto the corresponding imaging area, so that the detection grating pattern formed by passing through each of the detection sub-gratings is imaged within the corresponding imaging area.

9. The vertical displacement measuring device according to claim 1, characterized in that: The detection information changes with the change of the reflection displacement, and the reflection displacement is the displacement of the reflection grating pattern reflected by the measured object on the detection grating relative to the detection grating; The processor determines the vertical displacement of the object under test according to the detection information combination, including: the processor determines the reflection displacement corresponding to the detection information combination according to the correspondence between the detection information combination and the reflection displacement, and calculates the vertical displacement of the object under test according to the determined reflection displacement; wherein the correspondence between the detection information combination and the reflection displacement is calibrated according to the correspondence between the detection information corresponding to each of the projection detection grating pairs and the reflection displacement.

10. The vertical displacement measuring device according to claim 9, characterized in that: The corresponding relationship between the detection information combination and the reflection displacement is periodic, and the processor determines the reflection displacement corresponding to the detection information combination according to the corresponding relationship between the detection information combination and the reflection displacement within a period; If there are more than one reflection displacements corresponding to the detection information combination in one cycle, the one-to-one corresponding part of the detection information combination and the reflection displacement in one cycle is used to determine the reflection displacement, or, For a detection information combination corresponding to more than one reflection displacement, the corresponding vertical displacement is determined as a candidate vertical displacement according to the corresponding reflection displacements, and the candidate vertical displacement among the candidate vertical displacements that is closest to the historical vertical displacement obtained by the most recent N measurements is determined as the vertical displacement of the object under test, where N is an integer not less than 1.

11. The vertical displacement measuring device according to any one of claims 1 to 10, characterized in that: The processor is further used to compare the currently measured vertical displacement of the measured object with the vertical displacement of the measured object measured last time, so as to determine the lifting and lowering of the measured object.

12. An optical imaging system, characterized in that: It comprises an objective lens, a stage and a vertical displacement measuring device as claimed in any one of claims 1 to 11; The carrier is used to carry the object to be measured; The objective lens is used to image the object to be measured; The vertical displacement measuring device is used to measure the vertical displacement of the measured object, and the processor is also used to control the relative movement of the stage and the objective lens according to the vertical displacement of the measured object, so that the measured object is located within the focal depth range of the objective lens.

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