CN112577431B

CN112577431B - Grating ruler measuring device and measuring method

Info

Publication number: CN112577431B
Application number: CN201910935450.2A
Authority: CN
Inventors: 吴萍
Original assignee: Shanghai Micro Electronics Equipment Co Ltd
Current assignee: Shanghai Micro Electronics Equipment Co Ltd
Priority date: 2019-09-29
Filing date: 2019-09-29
Publication date: 2022-02-08
Anticipated expiration: 2039-09-29
Also published as: CN112577431A

Abstract

The invention provides a grating ruler measuring device and a measuring method, comprising the following steps: the reading head comprises a first reflecting unit and a second reflecting unit, the first reflecting unit and the second reflecting unit respectively comprise at least two first reflecting elements and at least one second reflecting element, a first light beam and a second light beam emitted by the light source are incident to the grating from the reading head, at least part of light spot positions on the grating are overlapped after diffraction or reflection of the grating and reflection of the first reflecting element and the second reflecting element, and the light spots are emitted along the same direction after diffraction of the grating. The invention can utilize the one-dimensional grating to realize two-dimensional position measurement, improve the optical subdivision multiple of the system, compensate the deviation of the measurement light spot caused by the vertical motion between the grating and the reading head, keep the measurement light spot having the best effective signal and obviously enlarge the vertical measurement range of the grating ruler measurement device.

Description

Grating ruler measuring device and measuring method

Technical Field

The present disclosure relates to measuring devices, and particularly to a grating ruler measuring device and a measuring method thereof.

Background

The nanometer measurement technology is the basis of the fields of nanometer processing, nanometer control, nanometer materials and the like. High-resolution and high-precision displacement sensors are required in the IC industry, precision machinery, micro-electro-mechanical systems and the like to achieve nanometer precision positioning.

With the rapid development of the integrated circuit towards large scale and high integration, the alignment precision requirement of the photoetching machine is higher and higher, and correspondingly, the precision of acquiring the six-degree-of-freedom position information of the workpiece table and the mask table is improved.

The interferometer has high measurement precision, can reach nanometer level, and is used for measuring the positions of a workpiece table and a mask table in a photoetching system. However, the measurement accuracy of the current interferometer almost reaches the limit, meanwhile, the measurement accuracy of the interferometer is greatly influenced by the surrounding environment, the measurement repetition accuracy is not high (even if the environment is good, the measurement repetition accuracy exceeds 1nm), and the traditional interferometer measurement device is difficult to meet the requirement of further improving the alignment accuracy. Therefore, a high-precision and high-stability picometer measurement scheme is urgently needed.

In contrast, the optical path of the grating ruler measuring device can be very small, usually several millimeters, and the optical path is independent of the measuring range, so that the measuring precision of the grating ruler measuring device is insensitive to the environmental influence, and the grating ruler measuring device has the characteristics of high measuring stability, simple structure and easiness in miniaturization, and occupies an important place in the field of nano measurement. Interferometers are gradually replaced in a new generation of photoetching systems, and the tasks of high-precision and high-stability picometer precision measurement are undertaken.

Patent US6762845B2 discloses a light beam rotation and translation self-calibration structure, which makes the light spot offset generated by the angle deflection of the measured mirror relative to the interferometer, and after multiple reflections, the reference light spot and the measurement light spot received by the interferometer always coincide, and the scheme can significantly increase the angle measurement range of the interferometer. The interferometer measurement device described in this patent is implemented by surface multiple reflections. There is no measurement application protocol for surface diffraction. Patent US9410796B2 discloses a grating displacement measuring device with high power subdivision, and the scheme adopts a two-dimensional grating to realize two-dimensional displacement measurement in the plane direction of the grating. The system adopts the two-dimensional grating, the light power utilization rate is low, and the displacement measurement in the direction vertical to the grating surface can not be carried out.

Disclosure of Invention

In order to solve the above problems, the present invention provides a grating ruler measurement apparatus and a measurement method thereof, so as to improve the optical resolution of grating ruler measurement and increase the vertical measurement range.

The invention provides a grating ruler measuring device, which comprises: the reading head comprises a first reflecting unit and a second reflecting unit, the first reflecting unit and the second reflecting unit respectively comprise at least two first reflecting elements and at least one second reflecting element, a first light beam and a second light beam emitted by the light source are incident to the grating from the reading head, at least part of light spot positions on the grating are overlapped after the light beams are diffracted or reflected by the grating and reflected by the first reflecting elements and the second reflecting elements, and the light beams are emitted along the same direction after being diffracted by the grating.

Optionally, the first reflection unit and the second reflection unit are symmetrically arranged with respect to a central axis of the grating in a horizontal direction.

Optionally, the first reflective element is configured to reversely reflect the diffracted light beams, the outgoing light beam and the incoming light beam of the first reflective element are parallel and opposite in direction, and the incoming light beam and the outgoing light beam are deviated from each other by a certain distance.

Optionally, the first reflective elements are paired in the horizontal positive and negative diffraction directions to multiply the horizontal optical subdivision number.

Optionally, the first reflecting element is a pyramid prism, a right-angle prism, a cat eye reflector, a dove prism or a roof prism.

Optionally, the second reflecting element is configured to reflect the diffracted light beam to the grating again after deviating a certain distance, and a spatial angle between two light beams having a spatial angle is unchanged, where the two light beams are reflected by the second reflecting element and then exit the light beams.

Optionally, the second reflecting element is an integral element, and includes a translation reflector, a pyramid prism, a right-angle prism, a cat-eye reflector, a dove prism, or a roof prism.

Optionally, the second reflecting element is a combination of two independent elements to reflect the two light beams respectively, so that a spatial included angle of the two light beams after being reflected by the second reflecting element is unchanged.

Optionally, the second reflecting element includes a translational mirror group, a pyramid prism group, a right-angle prism group, a cat-eye reflector group, a dove prism group or a roof prism group.

Optionally, the grating is a one-dimensional grating or a two-dimensional grating, and diffraction of the first light beam and the second light beam on the grating has diffraction light intensity at least in a positive and negative diffraction direction.

Optionally, the grating ruler measuring device further includes: the light detection unit is used for detecting the emergent diffraction light beams and transmitting the light beams to the light signal processing unit for analysis and processing.

Optionally, a light-incident optical fiber is disposed between the light source and the reading head, a light-emitting optical fiber is disposed between the reading head and the optical detection unit, and the light-incident optical fiber, the light-emitting optical fiber and the reading head are integrated into an optical fiber type micro structure.

Optionally, the grating ruler measuring device further includes: and the beam angle controller is used for controlling the directions of the first beam and the second beam so that the first beam and the second beam are incident to the grating in parallel.

Optionally, the beam angle controller comprises a wedge, a pair of wedge, a diffraction grating or a birefringent element.

Optionally, the light source is a coherent light source or an incoherent light source.

Optionally, the coherent light source is a single-frequency light source or a dual-frequency light source.

Optionally, the first light beam and the second light beam are light beams in the same polarization state, light beams with a certain polarization included angle, or the polarization states of the first light beam and the second light beam are orthogonal.

Optionally, the first light beam and the second light beam are unpolarized light beams.

The invention also provides a grating ruler measuring method, which adopts the grating ruler measuring device and comprises the following steps:

the light source emits a first light beam and a second light beam which are incident to the grating by the reading head;

and controlling the relative positions of the first reflecting element and the second reflecting element to enable the first light beam and the second light beam to be emitted along the same direction, wherein the positions of light spots on the grating are at least partially overlapped before emission.

Optionally, the first light beam and the second light beam are incident simultaneously, and the incident positions of the first light beam and the second light beam on the grating are different.

Optionally, the exit position and the incident position of the first light beam and the second light beam on the grating are different.

Optionally, after the first light beam enters the grating, an n-order diffracted light beam is generated, and is reversely reflected to the grating by the first reflection unit, and then exits along the first direction after the n-order diffraction is generated; after the second light beam is incident to the grating, a + m-order diffraction light beam is generated and is reversely reflected to the grating through a second reflection unit, and the + m-order diffraction light beam is emitted along a first direction; and controlling the relative positions of the first reflecting element and the second reflecting element to enable the emergent beam diffracted by the first light beam to be overlapped with the emergent beam diffracted by the second light beam to form a horizontal displacement signal.

Optionally, after the first light beam enters the grating, a-n-order diffracted light beam is generated, and is reversely reflected to the grating by the first reflection unit, and exits along the second direction after + n-order diffraction; after the second light beam is incident to the grating, a + m-order diffraction light beam is generated, is reversely reflected to the grating through the second reflection unit and the first reflection unit, and is emitted along a second direction after being diffracted at the + m-order; and controlling the relative positions of the first reflecting element and the second reflecting element to enable the emergent beam diffracted by the first light beam to be overlapped with the emergent beam diffracted by the second light beam to form a vertical displacement signal.

Optionally, the first reflection unit and the second reflection unit each include two first reflection elements and one second reflection element, and when m is equal to n, an interference signal including a phase change in a horizontal direction is formed in the first direction, and then a displacement value in the horizontal direction is:

wherein p is the pitch of the grating, m is the diffraction order, m is + -1, + -2, + -3 …,

the phase of the direction of the outgoing interference beam is changed in the first direction.

Optionally, when m is equal to n, an interference signal including a vertical phase change is formed in the second direction, and the vertical displacement value is:

wherein, lambda is the laser wavelength, p is the grating pitch of the grating, m is the diffraction order, m is +/-1, +/-2, +/-3 …, theta is the m-order diffraction angle formed after the light beam vertically enters the grating,

the phase of the outgoing interfering beam is varied for the second direction.

Optionally, when the grating is vertically displaced, the second reflecting element translates the light beam to offset the light beam deviations generated by the reflection of the first reflecting element, so as to implement displacement compensation.

Optionally, the light beam generated by the reverse retroreflection of the first reflecting element is deviated in the same dimension, and the light beam translation of the second reflecting element is set to be deviated in the same dimension as the light beam generated by the reverse retroreflection of the first reflecting element; if the beam deviation generated by the reverse retroreflection of the first reflecting element is orthogonal, the beam translation of the second reflecting element and the beam deviation generated by the reverse retroreflection of the first reflecting element, which is the first time the beam enters through the grating, are arranged in the same dimension.

Optionally, when the light beam translation of the second reflecting element and the light beam deviation generated by the reverse retro-reflection of the first reflecting element are in the same dimension, the emergent light beam of the second reflecting element is reversed relative to the incident light beam and translated for a certain distance, and the sum of the angles between the incident light beam and the reflected light beam is zero or an integral multiple of 360 degrees.

Optionally, after the first light beam and the second light beam are emitted in the same direction, the light detection unit detects the emitted diffracted light beam and transmits the detected diffracted light beam to the optical signal processing unit for analysis and processing.

Optionally, the first light beam and the second light beam are transmitted from the light source to the reading head through the light-entering optical fiber, and transmitted from the reading head to the optical detection unit through the light-exiting optical fiber.

Compared with the prior art, the invention has the following beneficial effects:

1. two-dimensional position measurement can be realized by using the one-dimensional grating, and the optical subdivision multiple of the system is improved;

2. the device can compensate the deviation of the measuring light spot caused by the vertical movement between the grating and the reading head, keep the measuring light spot to have the best effective signal and enlarge the vertical measuring range of the grating ruler measuring device.

Drawings

Fig. 1 is a schematic structural diagram of a grating ruler measurement apparatus according to a first embodiment;

fig. 2a and fig. 2b are schematic measurement diagrams of a grating ruler measurement apparatus according to a first embodiment;

fig. 3a to 3d are schematic structural diagrams of a first reflective element in a grating ruler measurement apparatus according to an embodiment;

fig. 4 is a schematic structural diagram of a second reflective element in the grating scale measuring apparatus according to the first embodiment;

fig. 5a and 5b are schematic diagrams illustrating a measurement principle of increasing a vertical measurement range in the grating ruler measurement device according to the second embodiment;

fig. 6a and 6b are schematic structural diagrams of a second reflective element in the grating ruler measuring apparatus according to the second embodiment;

fig. 7 is a measurement schematic diagram of a grating scale measurement apparatus according to a third embodiment;

fig. 8 is a light spot distribution on the surface of the grating in the grating scale measuring apparatus provided in the third embodiment;

fig. 9 is a flowchart of a grating scale measuring method according to the third embodiment.

100-a read head; 200-a grating; 300-a light detection unit; 400-an optical signal processing unit; 500-beam angle controller; 600-a light source;

110. 111, 112, 113-first reflective element; 120. 121, 130, 131, 140, 141, 123-second reflective element; 610-a first light beam; 611-a second light beam; 621. 631, 632-incident beam; 612. 613, 622, 633, 634-exit beam; a 180-cube corner prism; 181-right angle prism; 182-cat eye reflector; 183-dove prism; 1821-a lens; 1822-a concave mirror; 184. 185-a combined structure of second reflective elements; 1841. 1842, 1843, 1851, 1852, 1853-mirrors.

Detailed Description

The grating ruler measuring device and the measuring method of the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and drawings, it being understood, however, that the concepts of the present invention may be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. The drawings are in simplified form and are not to scale, but are provided for convenience and clarity in describing embodiments of the invention.

The terms "first," "second," and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other sequences than described or illustrated herein. Similarly, if the method described herein comprises a series of steps, the order in which these steps are presented herein is not necessarily the only order in which these steps may be performed, and some of the described steps may be omitted and/or some other steps not described herein may be added to the method. Although elements in one drawing may be readily identified as such in other drawings, the present disclosure does not identify each element as being identical to each other in every drawing for clarity of description.

Example one

Fig. 1 is a schematic structural diagram of a grating scale measuring device provided in this embodiment, and as shown in fig. 1, the grating scale measuring device provided in this embodiment includes: the optical pickup head 100 includes a first reflection unit and a second reflection unit, each of the first reflection unit and the second reflection unit includes at least two first reflection elements and at least one second reflection element, a first light beam and a second light beam emitted from the light source 600 are incident to the grating 200 from the pickup head 100, at least a part of light spots on the grating 200 are overlapped after being diffracted by the grating 200 and reflected by the first reflection elements and the second reflection elements, and are emitted along the same direction after being diffracted by the grating 200, and the light detection unit 300 detects the emitted diffracted light beam and outputs the light beam to the optical signal processing unit 400.

For example, in this embodiment, each of the first reflection unit and the second reflection element includes two first reflection elements and one second reflection element, and in other embodiments of the present invention, the number and arrangement of the first reflection elements and the second reflection elements in the second reflection element may also adopt other manners. Fig. 2a and 2b are schematic measurement diagrams of the grating scale measuring apparatus of this embodiment, and referring to fig. 2a and 2b, the first reflection unit and the second reflection unit are symmetrically arranged in a horizontal direction (X direction) with respect to a central axis of the grating 200. Specifically, the first

reflective elements

110 and 111 of the first reflective unit and the first

reflective elements

112 and 113 of the second reflective unit are symmetrically disposed in the horizontal direction, and the second reflective element 120 of the first reflective unit and the second reflective element 121 of the second reflective unit are symmetrically disposed in the horizontal direction.

The first reflecting element is used for reversely reflecting the diffracted light beams, the transmission directions of the light beams entering and exiting the first reflecting element are parallel and opposite, and the incident light beams and the emergent light beams deviate from a certain distance. The first reflective elements, which are paired in the horizontal plus-minus diffraction direction to multiply the horizontal optical subdivision number, can be, for example, a pyramid prism 180, a right-angle prism 181, a cat-eye reflector 182, a dove prism 183, or a roof prism (not shown in the drawings), as shown in fig. 3a to 3 d. Illustratively, as shown in fig. 3c, the first reflective element is a cat-eye reflector 182, the cat-eye reflector 182 is composed of a lens 1821 and a concave mirror 1822, the spherical center of the concave mirror 1822 is disposed at the principal point of the lens 1821, the lens 1821 is focused on the reflective surface of the concave mirror 182, the incident light beam 621 is converged on the concave mirror 1822 by the lens 1821, and is reflected by the concave mirror 1822, and the emergent light beam 622 is still parallel to the original incident light beam 621 after passing through the lens 1821, but the direction is opposite, and the incident light beam 621 deviates a certain distance from the emergent light beam.

The second reflecting element is used for reflecting the diffracted light beams to the grating again after deviating a certain distance, the second reflecting element does not require that the reflected light beams entering the second reflecting element are completely parallel to the incident light beams, only the included angle alpha 1 between the diffracted light beams of the two incident light beams and the incident light beams before entering the second reflecting element is required to be ensured, and after the diffracted light beams pass through the second reflecting element, the included angle of the emergent light beams is the same and is also alpha 1. As shown in fig. 4, the spatial angle between the incident light beams 631 and 632 is α 1, and after passing through the second reflecting element 123, the spatial angle between the emergent

light beams

633 and 634 is still α 1, that is, the spatial angle between the two light beams having a spatial angle after being reflected by the second reflecting element is not changed. The characteristics of the second reflecting element in the grating ruler measuring device are as follows: after the included angle of the two incident light beams is ensured to pass through the second reflecting element, the included angle of the emergent light beam is unchanged, and the emergent light beam is ensured to deviate a certain distance relative to the incident light beam. The second reflecting element can be two independent elements in the grating ruler measuring device, each element independently ensures that emergent light and incident light are parallel, so that an included angle between the two light beams is ensured to be unchanged, for example, the second reflecting element comprises a translation reflector group, a pyramid prism group, a right-angle prism group, a cat eye reflector group, a dove prism group or a roof prism group and the like; the second reflecting element can also be a reflecting element, and only the included angle between the two light beams is ensured to be unchanged. For example, the second reflecting element includes a translation mirror, a pyramid prism, a right-angle prism, a cat-eye reflector, a dove prism, a roof prism, or the like.

In this embodiment, an incident optical fiber is disposed between the light source and the reading head, an outgoing optical fiber is disposed between the reading head and the optical detection unit, and the first light beam and the second light beam are incident from the light source to the reading head through the incident optical fiber and are emitted from the reading head to the optical detection unit through the outgoing optical fiber. The light-in optical fiber, the light-out optical fiber and the reading head are integrated into an optical fiber type microstructure, and the grating ruler measuring device has the advantages that the measuring convenience is improved, and the application range is expanded.

In addition, referring to fig. 1, the grating scale measuring apparatus provided in this embodiment further includes: and a beam angle controller 500, configured to control directions of the first light beam and the second light beam emitted by the light source 600, so that the first light beam and the second light beam are incident on the grating 200 in parallel. The beam angle controller 500 includes a wedge, a pair of wedge, a diffraction grating, a birefringent element.

As shown in fig. 9, the grating scale measuring method provided in this embodiment includes the following steps:

s01: the light source emits a first light beam and a second light beam which are incident to the grating by the reading head;

s02: and controlling the relative positions of the first reflecting element and the second reflecting element to enable the first light beam and the second light beam to be emitted along the same direction, wherein the positions of light spots on the grating are at least partially overlapped before being emitted.

Specifically, step S01 is first performed, and the light source 600 emits a first light beam 610 and a second light beam 611 and is incident on the grating 200 from the read head 100. The light source 600 may be a coherent light source or an incoherent light source, the first light beam 610 and the second light beam 611 may be single-frequency light beams with the same wavelength, for example, two laser beams may be directly split from the same laser by an optical energy distribution element, or may also be dual-frequency light beams with slightly different wavelengths, the dual-frequency light beam implementation scheme may be to use a free space dual-frequency laser, separate two polarization states by a polarization beam splitter prism, control the two light beams to exit in parallel, and then control the polarization state of one of the two light beams by a polarization device, such as a half wave plate, two quarter wave plates, an optical rotator, and the like; or a dual-frequency laser adopting optical fiber transmission, in which a single-frequency laser forms two beams with certain frequency difference through acousto-optic frequency shift or other frequency shift modulation methods, and the two beams are coupled through an optical fiber and then provided to the reading head 100. The first light beam 610 and the second light beam 611 are light beams in the same polarization state, or the first light beam 610 and the second light beam 611 have a certain polarization angle, or the first light beam 610 and the second light beam 611 have orthogonal polarization states, or the first light beam 610 and the second light beam 611 are light beams in non-polarization state. The first light beam 610 and the second light beam 611 may be frequency stabilized laser beams or non-frequency stabilized laser beams.

Said first beam 610 and said second beam 611 are incident on the grating 200 from the read head 100 at a distance. The first light beam 610 and the second light beam 611 may be parallel light beams or non-parallel light beams. When the first light beam 610 and the second light beam 611 are not parallel, the light beam direction can be controlled by the light beam angle controller 500, so that the first light beam 610 and the second light beam 611 enter the grating 200 in parallel, and the diffracted light beams of the first light beam 610 and the second light beam 611 are emitted in parallel during phase detection. The first light beam 610 and the second light beam 611 are incident simultaneously, and the incident positions of the first light beam 610 and the second light beam 611 on the grating 200 are different. The grating 200 is a one-dimensional grating or a two-dimensional grating, and the diffraction of the first light beam 610 and the second light beam 611 on the grating 200 has diffraction light intensity at least in the positive and negative diffraction directions.

Next, step S02 is executed to control the relative positions of the first reflective element and the second reflective element, so that the first light beam and the second light beam are emitted in the same direction and the spot positions on the grating 200 overlap at least partially before being emitted. Specifically, first, after the first light beam 610 enters the grating, a-n-order diffracted light beam is generated, and is reversely reflected back to the grating 200 by the first reflection unit, and then exits along the first direction after the-n-order diffraction is generated; the second light beam 611 enters the grating 200 to generate a + m-order diffracted light beam, and the + m-order diffracted light beam is reflected back to the grating 200 by the second reflecting unit and exits along the first direction after being diffracted by the + m-order. Controlling the relative positions of a first reflecting element and a second reflecting element in a first reflecting unit and a second reflecting unit to enable an emergent beam diffracted by the first beam to be overlapped with an emergent beam diffracted by the second beam to form a horizontal displacement signal;

then, after the first light beam 610 enters the grating 200, a-n-order diffracted light beam is generated, is reversely reflected to the grating 200 by the first reflection unit, and exits along a second direction after + n-order diffraction; after the second light beam enters the grating 200, a + m-order diffracted light beam is generated, is reversely reflected to the grating through the second reflecting unit and the first reflecting unit, and is emitted along a second direction after being diffracted at the + m-order. And controlling the relative positions of the first reflecting element and the second reflecting element in the first reflecting unit and the second reflecting unit to enable the emergent beam diffracted by the first beam to be overlapped with the emergent beam diffracted by the second beam to form a vertical displacement signal.

Referring to fig. 2a and 2b, taking the first reflection unit including two

first reflection elements

110 and 111 and one second reflection element 120, and the second reflection unit including two

first reflection elements

112 and 113 and one second reflection element 121 as an example, a process of acquiring a horizontal displacement signal and a vertical displacement signal will be described. The first light beam 610 and the second light beam 611 are incident on the grating 200 at any non-littrow angle, in this embodiment, the first light beam 610 and the second light beam 611 are incident perpendicularly to the grating 200 in parallel, as shown in fig. 2a, the first light beam 610 generates an-n-order diffracted light beam after being incident on the grating 200, and is reflected to the grating 200 by the first reflecting element 110, the-n-order diffracted light beam is generated on the grating 200, and is reflected to the grating 200 by the second reflecting element 120, so as to generate an-n-order diffracted light beam, which is reversely reflected to the grating 200 by the first reflecting element 111, and is emitted along the direction of the light beam 612 after being diffracted at the-n order. Meanwhile, the second light beam 611 is incident on the grating 200 to generate + m-order diffraction, the diffracted light beams are reversely reflected back to the grating 200 through the first reflecting element 112, the second reflecting element 121 and the first reflecting element 113 and generate + m-order diffraction, and when the positions of the first reflecting

element

110, 111, 112, 113 and the second reflecting

element

120, 121 are specially designed, the-n-order quartic diffracted light beams of the second light beam 611 and the + m-order quartic diffracted light beams of the first light beam 610 can be superposed on the surface of the grating 200 and are emitted along the direction of the light beam 612 to form a horizontal displacement signal.

The first light beam 610 enters the grating 200 to generate an n-th order diffracted light beam, and is reflected to the grating 200 by the first reflecting element 110, the n-th order diffracted light beam is generated on the grating 200, is reflected to the grating 200 by the second reflecting element 120, and is emitted along the direction of the light beam 613 after the n-th order diffracted light beam is generated; after the second light beam 611 enters the grating 200, a + m-order diffracted light beam is generated, and exits along the direction of the light beam 613 after passing through the first reflecting element 113, the second reflecting element 121, the first reflecting element 112, and the first reflecting element 111. When the positions of the first

reflective elements

110, 111, 112, 113 and the second

reflective elements

120, 121 are specially designed, the diffracted beams of the first light beam 610 and the diffracted beams of the second light beam 611 can be overlapped and emitted along the direction of the light beam 613, and the interference signal includes a vertical displacement signal. It should be noted that the exit positions of the first light beam 610 and the second light beam 611 on the grating 200 after the first light beam 610 and the second light beam 611 are diffracted and reflected by the first reflecting element, the second reflecting element and the grating 200 are different from the incident positions of the first light beam 610 and the second light beam 611 which are incident to the grating 200 for the first time.

Then, after the first light beam 610 and the second light beam 611 exit in the same direction, the light detection unit 300 detects the exiting diffracted light beam and transmits the detected diffracted light beam to the optical signal processing unit 400 for analysis processing. Specifically, when m is equal to n, an interference signal including a phase change in the horizontal direction is formed in the direction of the light beam 612. Phase change of X horizontal displacement information contained in beam 612

The expression of (a) is:

wherein p is the pitch of the grating, m is the diffraction order, m is + -1, + -2, + -3 …

Similarly, when m is equal to n, an interference signal containing a vertical phase change is formed along the direction of the light beam 613. Phase variation of vertical displacement information contained in beam 613

The expression of (a) is:

wherein λ is the laser wavelength, p is the grating pitch of the grating, m is the diffraction order, m is ± 1, ± 2, ± 3 …, θ is the m-order diffraction angle formed after the light beam vertically enters the grating (refer to fig. 2a), and Δ X is the horizontal displacement value.

According to the analysis of the above measurement principle, the relationship between the horizontal (X direction) and vertical (Z direction) displacements to be measured and the measurement phase of the reading head is as follows:

displacement value Δ X in the horizontal direction:

vertical displacement value Δ Z:

example two

The present embodiment provides a grating ruler measuring apparatus and a method, different from the first embodiment, in the present embodiment, the grating ruler measuring apparatus can utilize the second reflective element to implement vertical displacement compensation. Namely, the deviation of the measuring light spot caused by the vertical movement between the grating and the reading head can be compensated by the displacement of the second reflecting element through the translation of the light beam so as to offset the deviation of the light beam generated by the reflection of the first reflecting element, thereby keeping the measuring light spot to have the optimal effective signal and enlarging the vertical measuring range of the grating ruler measuring device.

Specifically, as shown in fig. 5a and 5b, the light beam generated by the reverse retroreflection of the first reflective element 110 and the first reflective element 111 is shifted in the same dimension, the light beam translation of the second reflective element 130 is set in the same dimension as the light beam generated by the reverse retroreflection of the first reflective element 110 and the first reflective element 111, and the light beam translation of the second reflective element 130 makes the light beam shifts generated by the reverse retroreflection of the first reflective element 110 and the second reflective element 111 cancel each other out, so as to implement the vertical displacement compensation; similarly, the beam translation of the second reflective element 131 is arranged to be offset in the same dimension as the beams generated by the reverse retroreflection of the first reflective element 112 and the first reflective element 113.

When the light beam generated by the reverse retro-reflection of the first reflective element is shifted in the same dimension, in order to realize the same-dimension light beam translation of the second reflective element to compensate for the vertical displacement, the emergent light beam of the second reflective element 130 is reversed and translated for a distance relative to the incident light beam, and the sum of the angles between the incident light beam and the reflected light beam is zero or an integral multiple of 360 degrees. For example, the second reflective element 130 can adopt the combined structure 184 shown in fig. 6a, where the combined structure 184 includes a mirror 1841, a mirror 1842 and a mirror 1843, the light beam 621 enters the mirror 1841, is reflected by an angle α counter-clockwise, reflected by an angle β counter-clockwise, and finally exits by an angle γ clockwise along the direction of the light beam 622, where α, β and γ are defined as an angle formed by the incident light beam turning toward the exiting light beam, the counter-clockwise direction is a negative value, and the clockwise direction is a positive value. In fig. 6a, the rotation angle α is a negative value, the angle β is a negative value, the angle γ is a positive value, and α + β + γ is equal to 0. The second reflective element 130 can also adopt the combined structure 185 shown in fig. 6b, where the combined structure 185 includes a mirror 1851, a mirror 1852 and a mirror 1853, the light beam 621 enters the mirror 1851, is reflected to the mirror 1852 by rotating α clockwise, then reflected to the mirror 1853 by rotating β clockwise, and finally exits along the direction of the light beam 622 by rotating γ clockwise, and α + β + γ is 360 °. In other embodiments of the present invention, the second reflective element 130 can be combined in other ways as long as the sum of the angles of the outgoing beam relative to the incoming beam is 0 degree or an integer multiple of 360 degrees.

By providing the second

reflective elements

130, 131, measurement spot deviations due to vertical movement between the grating 200 and the read-head 100 can be avoided. Specifically, referring to fig. 5a, the first light beam 610 and the second light beam 611 enter the grating 200 at any non-littrow angle, and when the grating 200 moves from the position shown by the original solid line to the position shown by the dashed line along the direction perpendicular to the grating, the first light beam 610 does not change the position of the light beam 612 that outputs the horizontal displacement signal after passing through the first reflecting element 110, the second reflecting element 130, and the first reflecting element 111; after the second light beam 611 passes through the first reflective element 113, the second reflective element 131, and the first reflective element 112, the light beam 612 outputting the horizontal displacement signal does not change position. Thus, the beam 612 does not deviate as the grating 200 moves vertically relative to the readhead 100, i.e., the horizontal displacement signal measurement is not affected by the vertical movement of the grating 200. Referring to fig. 5b, when the grating 200 moves from the original position shown by the solid line to the position shown by the dashed line along the vertical grating 200, the first light beam 610 outputs the light beam 613 including the vertical displacement signal to the dashed line after being acted by the first reflecting element 110 and the second reflecting element 130; after the second light beam 611 passes through the first reflective element 113, the second reflective element 131, the first reflective element 112, and the first reflective element 111, the position of the light beam 613 outputting the vertical displacement signal is also changed to the dotted line. Thus, when the grating 200 is moved vertically relative to the readhead 100, the diffracted beams of the first beam 610 and the second beam 611 included in the beam 613 still coincide, and the position of the beam 613 deviates, maintaining the measurement spot with the best effective signal.

EXAMPLE III

In this embodiment, on the basis of the second embodiment, by setting the beam offset generated by the reverse retro-reflection of the first reflective element in the orthogonal dimension, the light spots form a symmetrical compact layout on the grating surface. Referring to fig. 7, the first

reflective elements

110 and 113 reflect light beams along the Y direction, the second

reflective elements

140 and 141 reflect light beams along the Y direction, and the first

reflective elements

111 and 112 reflect light beams along the X direction. The first light beam 610 and the second light beam 611 enter the grating 200 at any non-littrow angle, the first light beam 610 exits along the light beam 612 after being acted by the first reflecting element 110, the second reflecting element 140 and the first reflecting element 111, the second light beam 611 exits along the light beam 612 after being acted by the first reflecting element 113, the second reflecting element 141 and the first reflecting element 112, and the phase of the horizontal displacement information contained in the light beam 612 changes. Further, the first light beam 610 exits along the light beam 613 after being reflected by the first reflecting element 110, the second reflecting element 140, the first reflecting element 111, and the second reflecting element 112, the second light beam 611 exits along the light beam 613 after being diffracted by the first reflecting element 113, the second reflecting element 141, and the grating 200, and the phase of the vertical displacement information included in the light beam 613 varies. Fig. 8 shows the distribution of the spots on the surface of the grating 200 in this embodiment, and as shown in fig. 8, the first

reflective elements

110 and 113 and the first

reflective elements

111 and 112 are arranged to deflect the beams generated by the reverse retroreflection in the orthogonal dimension, so that the spots are arranged compactly and symmetrically.

In this embodiment, the beam offset generated by the reverse retroreflection of the first reflective element is not in the same dimension, as shown in fig. 7, the beam offset generated by the reverse retroreflection of the first

reflective elements

110 and 113 and the beam offset generated by the reverse retroreflection of the first

reflective elements

111 and 112 are in orthogonal dimensions, and in order to implement vertical displacement compensation, the beam translation of the second reflective element 140 and the beam offset generated by the reverse retroreflection of the first reflective element 110 are set to be in the same dimension, that is, the second

reflective elements

140 and 141 reflect the beams in the Y direction. The second

reflective elements

140 and 141 may be a pyramid prism, a right-angle prism set, a dove prism set, a roof prism set, or the like.

In other embodiments of the present invention, the arrangement of the second

reflective elements

130 and 131 when the beam offset generated by the reverse retroreflection of the first reflective element is in the same dimension and the arrangement of the second

reflective elements

140 and 141 when the beam offset generated by the reverse retroreflection of the first reflective element is in the orthogonal dimension may be combined to perform a combined design.

In summary, the present invention provides a grating ruler measurement apparatus and a measurement method, including: the reading head comprises a first reflection unit and a second reflection unit, the first reflection unit and the second reflection unit respectively comprise at least two first reflection elements and at least one second reflection element, a first light beam and a second light beam emitted by the light source are incident to the grating from the reading head, the light spot positions on the grating are at least partially overlapped after being diffracted or reflected by the grating and reflected by the first reflection elements and the second reflection elements, the light beams are emergent along the same direction after being diffracted or reflected by the grating, and the light detection unit detects the emergent diffracted light beams and transmits the emergent diffracted light beams to the light signal processing unit. The invention can utilize the one-dimensional grating to realize two-dimensional position measurement, improve the optical subdivision multiple of the system, compensate the deviation of the measurement light spot caused by the vertical motion between the grating and the reading head, keep the measurement light spot having the best effective signal and obviously enlarge the vertical measurement range of the grating ruler measurement device.

It should be noted that, in the present specification, all the embodiments are described in a related manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the structural embodiment, since it is substantially similar to the method embodiment, the description is relatively simple, and for the relevant points, reference may be made to the partial description of the method embodiment.

The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.

Claims

1. A grating ruler measuring device is characterized by comprising: the reading head comprises a first reflecting unit and a second reflecting unit, the first reflecting unit and the second reflecting unit respectively comprise at least two first reflecting elements and at least one second reflecting element, a first light beam and a second light beam emitted by the light source are incident to the grating from the reading head, are diffracted or reflected by the grating and reflected by the first reflecting elements and the second reflecting elements, at least partially overlap at the positions of light spots on the grating, and are diffracted by the grating and emitted along the same direction;

the first reflection unit and the second reflection unit are symmetrically arranged relative to the central axis of the grating in the horizontal direction;

the first reflecting element is used for reversely reflecting the diffracted light beams, an emergent light beam of the first reflecting element is parallel to and opposite to an incident light beam, and the incident light beam and the emergent light beam deviate from a certain distance;

the second reflecting element is used for reflecting the diffracted light beams to the grating again after deviating a certain distance, and the spatial angle of the emergent light beams of the two light beams with a spatial angle after being reflected by the second reflecting element is unchanged.

2. A grating ruler measurement device according to claim 1 wherein the first reflective elements are paired in the horizontal positive and negative diffraction directions to multiply the horizontal optical subdivision.

3. The device of claim 1, wherein the first reflective element is a cube-corner prism, a right-angle prism, a cat-eye reflector, a dove prism, or a roof prism.

4. The device according to claim 1, wherein the second reflective element is a single element comprising a translating mirror, a cube-corner prism, a right-angle prism, a cat-eye reflector, a dove prism or a roof prism.

5. The device of claim 1, wherein the second reflective element is a combination of two independent elements to reflect the two light beams respectively, so that the spatial angle of the two light beams reflected by the second reflective element is not changed.

6. The apparatus according to claim 5, wherein the second reflective element comprises a translational mirror set, a pyramid prism set, a right angle prism set, a cat-eye reflector set, a dove prism set, or a roof prism set.

7. A grating ruler measurement device according to claim 1 wherein the grating is a one-dimensional or two-dimensional grating, and the diffraction of the first and second beams on the grating has a diffraction intensity in at least positive and negative diffraction directions.

8. The grating ruler measuring device of claim 1, further comprising: the light detection unit is used for detecting the emergent diffraction light beams and transmitting the light beams to the light signal processing unit for analysis and processing.

9. The grating ruler measuring device of claim 8, wherein an incident optical fiber is disposed between the light source and the reading head, an outgoing optical fiber is disposed between the reading head and the optical detecting unit, and the incident optical fiber, the outgoing optical fiber and the reading head are integrated into an optical fiber type micro structure.

10. The grating ruler measuring device of claim 1, further comprising: and the beam angle controller is used for controlling the directions of the first beam and the second beam so that the first beam and the second beam are incident to the grating in parallel.

11. A grating ruler measurement device according to claim 10 wherein the beam angle controller comprises a wedge, a pair of wedge, a diffraction grating or a birefringent element.

12. The device of claim 1, wherein the light source is a coherent light source or an incoherent light source.

13. The device of claim 12, wherein the coherent light source is a single-frequency light source or a dual-frequency light source.

14. The device according to claim 1, wherein the first and second light beams are light beams of the same polarization state; or the first light beam and the second light beam are light beams with a certain polarization included angle; or the first and second light beams are orthogonal in polarization state.

15. The device of claim 1, wherein the first and second beams are unpolarized beams.

16. A grating ruler measurement method, characterized in that the grating ruler measurement device of any one of claims 1-15 is adopted, comprising the following steps:

controlling the relative positions of a first reflecting element and a second reflecting element, wherein the first light beam and the second light beam are diffracted or reflected by the grating and are emitted along the same direction after being reflected by the first reflecting element and the second reflecting element, and at least part of light spot positions on the grating are overlapped before being emitted;

the first reflection unit and the second reflection unit are symmetrically arranged relative to the central axis of the grating in the horizontal direction, and diffracted light beams of the first light beam and the second light beam are deflected for a certain distance after passing through the first reflection element and the second reflection element and then reversely retroreflected.

17. The grating scale measuring method according to claim 16, wherein the first light beam and the second light beam are incident simultaneously, and incident positions of the first light beam and the second light beam on the grating are different.

18. The grating scale measuring method according to claim 17, wherein the exit position and the entrance position of the first light beam and the second light beam on the grating are different.

19. The grating ruler measurement method of claim 18, wherein the first light beam is incident on the grating to generate an n-order diffracted light beam, and the n-order diffracted light beam is reflected back to the grating by the first reflection unit and exits along a first direction after being diffracted by the n-order diffraction; after the second light beam is incident to the grating, a + m-order diffraction light beam is generated and is reversely reflected to the grating through a second reflection unit, and the + m-order diffraction light beam is emitted along a first direction; and controlling the relative positions of the first reflecting element and the second reflecting element to enable the emergent beam diffracted by the first light beam to be overlapped with the emergent beam diffracted by the second light beam to form a horizontal displacement signal.

20. The grating ruler measurement method of claim 19, wherein the first light beam is incident on the grating to generate an n-th order diffracted light beam, which is reflected back to the grating by the first reflection unit, and exits along the second direction after being diffracted by n + th order; after the second light beam is incident to the grating, a + m-order diffraction light beam is generated, is reversely reflected to the grating through the second reflection unit and the first reflection unit, and is emitted along a second direction after being diffracted at the + m-order; and controlling the relative positions of the first reflecting element and the second reflecting element to enable the emergent beam diffracted by the first light beam to be overlapped with the emergent beam diffracted by the second light beam to form a vertical displacement signal.

21. The grating scale measuring method according to claim 20, wherein the first reflection unit and the second reflection unit each include two first reflection elements and one second reflection element, and when m-n is obtained, an interference signal including a phase change in a horizontal direction is formed in the first direction, and then a displacement value in the horizontal direction is:

the phase of the outgoing interfering beam is varied in a first direction.

22. The grating scale measuring method according to claim 21, wherein when m is equal to n, an interference signal including a vertical phase change is formed in the second direction, and the vertical displacement value is:

for emitting the phase of the interfering beam in a second directionThe bit changes.

23. The grating ruler measurement method of claim 16, wherein when the grating is vertically displaced, the second reflection element translates the light beam to offset the light beam deviations generated by the reflection of the first reflection element, so as to realize displacement compensation.

24. The grating ruler measurement method according to claim 23, wherein the beam deviation generated by the reverse retroreflection of the first reflective element is in the same dimension, and the beam translation of the second reflective element is set to be in the same dimension as the beam deviation generated by the reverse retroreflection of the first reflective element; if the beam deviation generated by the reverse retroreflection of the first reflecting element is orthogonal, the beam translation of the second reflecting element and the beam deviation generated by the reverse retroreflection of the first reflecting element, which is the first time the beam enters through the grating, are arranged in the same dimension.

25. The method according to claim 24, wherein when the beam translation of the second reflective element and the beam deviation generated by the backward reflection of the first reflective element are set to be in the same dimension, the emergent beam of the second reflective element is backward and translated a distance relative to the incident beam, and the sum of the angles between the incident beam and the reflected beam is zero or an integer multiple of 360 degrees.

26. The grating scale measuring method according to claim 16, wherein the grating scale measuring apparatus further comprises: the optical detection unit and the optical signal processing unit, the grating ruler measurement method further comprises: after the first light beam and the second light beam are emitted along the same direction, the light detection unit detects the emitted diffracted light beam and transmits the light beam to the light signal processing unit for analysis and processing.

27. The grating scale measuring method according to claim 26, wherein the first light beam and the second light beam are incident from the light source to the reading head through an incident optical fiber, and exit from the reading head to the optical detection unit through an exit optical fiber.