A two-dimensional dot-lattice grating in-plane displacement sensor with optical self-subdivision function

Abstract

The application belongs to the technical field of displacement sensors, and particularly relates to a two-dimensional dot matrix grating in-plane displacement sensor with an optical self-subdivision function, which comprises a laser, a collimating beam expander, an upper grating, a lower four-quadrant array grating, a four-quadrant detector and a subdivision circuit module. The collimating beam expander is arranged on the light path direction of the laser, the upper grating is arranged on the light path direction of the collimating beam expander, the lower four-quadrant array grating is arranged on the light path direction of the upper grating, the four-quadrant detector is arranged on the light path direction of the lower four-quadrant array grating, and the four-quadrant detector is electrically connected with the subdivision circuit module. The application realizes the in-plane displacement high-resolution detection function. Based on the optical self-imaging subdivision imaging effect, the optical subdivision with a change period of one half of the grating period is realized, the problem that the traditional double-layer grating displacement sensor cannot realize the optical subdivision is solved, and the displacement resolution is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of displacement sensors, and particularly relates to a two-dimensional dot array grating in-plane displacement sensor with optical self-subdivision function. BACKGROUND

[0002] Ultra-precision and high-stability two-dimensional displacement measurement plays an extremely important role in the development of the fields of semiconductor manufacturing, photolithography, chip processing and preparation. In recent years, photolithography and chip manufacturing technology have developed rapidly, and higher requirements have been put forward for technical indexes such as displacement measurement precision, stability and stroke. At present, mainstream displacement detection principles include a laser interference measurement method and a grating displacement measurement method using the single first-order diffraction light interference effect of a grating. Among them, the grating displacement sensor is widely used in integrated precision processing test equipment and systems such as photolithography machines and atomic force microscopes due to its advantage of being able to perform absolute position measurement. The principle of traditional grating displacement detection is based on the interference effect of multi-path diffraction light. Such a device adopts a spatial light interference technology and needs a large number of optical elements such as filter plates, beam splitters and mirrors, so that the system is complex, bulky and poor in stability. In addition, this method needs to use a two-dimensional displacement measurement mode combined by two one-dimensional displacement sensors. System assembly errors often have a great influence on the measurement accuracy in the process. Based on the optical self-imaging principle, a double-layer grating structure can successfully realize two-dimensional in-plane displacement measurement. This scheme can effectively simplify the optical path structure, improve the system stability and integration. However, compared with the traditional multi-order diffraction interference displacement sensor, this method cannot realize optical subdivision, so the resolution is poor under the same electronic subdivision multiple. SUMMARY

[0003] In view of the technical problems of the above-mentioned traditional grating displacement detection system being complex, bulky and poor in stability, and the double-layer grating structure being unable to realize optical subdivision, the application provides a two-dimensional dot array grating in-plane displacement sensor with optical self-subdivision function, which is simple in structure, small in size, strong in stability and high in resolution.

[0004] In order to solve the above technical problems, the technical scheme adopted by the application is as follows:

[0005] The two-dimensional dot array grating in-plane displacement sensor with optical self-subdivision function comprises a laser, a collimating expander, an upper grating, a lower four-quadrant array grating, a four-quadrant detector and a subdivision circuit module. The collimating expander is arranged on the light path direction of the laser. The upper grating is arranged on the light path direction of the collimating expander. The lower four-quadrant array grating is arranged on the light path direction of the upper grating. The four-quadrant detector is arranged on the light path direction of the lower four-quadrant array grating. The four-quadrant detector is electrically connected with the subdivision circuit module.

[0006] The upper layer grating is connected with the displacement object to be measured, and the lower layer four-quadrant array grating is connected with the four-quadrant detector.

[0007] The upper layer grating adopts a two-dimensional honeycomb hexagonal circular hole periodic structure distribution, the centers of each row or column of circular holes of the upper layer grating are on the same parallel line, the distance between adjacent parallel lines is the grating period length, and the circular holes on adjacent parallel lines are mutually externally tangent.

[0008] The lower layer four-quadrant array grating adopts a four-quadrant array circular hole two-dimensional plane grating, the lower layer four-quadrant array grating includes a first quadrant grating, a second quadrant grating, a third quadrant grating and a fourth quadrant grating, the first quadrant grating and the second quadrant grating are arranged side by side, and the third quadrant grating and the fourth quadrant grating are arranged side by side.

[0009] The first quadrant grating and the second quadrant grating are separated by n+1 / 4 (n=0, 1, 2, 3…) grating periods in the transverse direction, and the third quadrant grating and the fourth quadrant grating are separated by n+1 / 4 (n=0, 1, 2, 3…) grating periods in the longitudinal direction.

[0010] The laser wavelength of the laser is 635 nm, the power of the laser is 1.2 mw, and the circuit subdivision multiple of the subdivision circuit module is 1000 times.

[0011] The grating circular hole diameter of the upper layer grating and the lower layer four-quadrant array grating is 450 nm, the grating duty cycle of the upper layer grating and the lower layer four-quadrant array grating is 0.5, the grating thickness of the upper layer grating and the lower layer four-quadrant array grating is 150 nm, the grating material of the upper layer grating and the lower layer four-quadrant array grating is AI, the grating period of the upper layer grating and the lower layer four-quadrant array grating is 900 nm, and the grating area of the upper layer grating is 10 mm*10 mm.

[0012] The grating area of the first quadrant grating, the second quadrant grating, the third quadrant grating and the fourth quadrant grating is 2.5 mm*2.5 mm.

[0013] The lower layer four-quadrant array grating is located within the effective self-imaging distance D of the upper layer grating, and the lower layer four-quadrant array grating is at a self-imaging half period or period position Z.

[0014]

[0015]

[0016] The d is the grating period of the upper layer grating and the lower layer four-quadrant array grating, the N is the number of grating periods, and the n is the diffraction order of a single period grating, and the N and n are integers 0, 1, 2, and the like.

[0017] A two-dimensional dot array grating in-plane displacement sensor measurement method with an optical self-subdivision function, comprising the following steps:

[0018] S1, the light emitted by the laser is collimated and expanded by the collimating expander, propagates along a straight line and directly enters the upper layer grating;

[0019] S2, the upper layer grating is attached to the displacement object to be measured and moves together with the displacement object to be measured in the plane;

[0020] S3, the light beam directly passes through the lower layer four-quadrant array grating, and the lower layer four-quadrant array grating is tightly attached to the four-quadrant detector;

[0021] S4, the four-quadrant detector collects the entire system light intensity transmittance signal when the upper layer grating and the lower layer four-quadrant array grating move relatively in the two-dimensional plane, and obtains two groups of four-way sinusoidal signals;

[0022] S5, each group of signals is composed of two-way sine and cosine signals with a phase difference of 90 degrees from each other, and is used for detecting the displacement in the X direction and the Y direction, respectively, the transverse direction is defined as the X direction, the longitudinal direction is defined as the Y direction, the first quadrant grating and the second quadrant grating generate the X direction signal, and the third quadrant grating and the fourth quadrant grating generate the Y direction signal;

[0023] S6, the two groups of signals are subdivided and modulated by the subdivision circuit module, and the in-plane displacement of the displacement object to be measured is measured.

[0024] Compared with the prior art, the present application has the beneficial effects that:

[0025] The present application is based on the optical self-imaging principle of the double-layer two-dimensional circular hole array grating structure, realizes the high-resolution detection function of in-plane displacement, and realizes the optical subdivision with a change period of one-half of the grating period based on the optical self-imaging subdivision imaging effect, that is, realizes two times of optical subdivision, solves the problem that the traditional double-layer grating displacement sensor cannot realize optical subdivision, and improves the displacement resolution; and the optical path of the present application is simple, without the need for optical elements such as mirrors, prisms, optical filters, beam splitters and the like, the optical path is simple, the system is stable, the anti-interference ability is strong, and it is beneficial to miniaturization, integration, high-resolution displacement detection application. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only exemplary, and for those skilled in the art, other drawings can be obtained from the provided drawings without creative labor.

[0027] The structures, proportions, sizes, etc. shown in the specification are only used to cooperate with the content disclosed in the specification, to be understood and read by those skilled in the art, and are not used to limit the implementation conditions of the present application, so they do not have technical significance. Any modification of structure, change of proportion relationship or adjustment of size, without affecting the effects and purposes that can be achieved by the present application, should still fall within the scope of the technical content disclosed by the present application.

[0028] Figure 1 It is a schematic diagram of the overall structure of the present application.

[0029] Figure 2 It is a schematic diagram of the structure of the upper grating of the present application.

[0030] Figure 3 It is a two-dimensional in-plane simulation result graph of the upper grating of the present application.

[0031] Figure 4 It is a simulation result graph of the upper grating of the present application along the Z direction out of the plane.

[0032] Figure 5 It is a schematic diagram of the structure of the lower four-quadrant array grating of the present application.

[0033] Figure 6 It is a four-quadrant detector output four-quadrant in-plane displacement signal graph of the present application.

[0034] Figure 7 It is a single-quadrant transmission light intensity FDTD displacement simulation result graph when the upper grating of the present application moves along the X direction by two grating period distances.

[0035] Wherein: 1 is a laser, 2 is a collimating expander, 3 is an upper grating, 4 is a lower four-quadrant array grating, 401 is a first quadrant grating, 402 is a second quadrant grating, 403 is a third quadrant grating, 404 is a fourth quadrant grating, 5 is a four-quadrant detector, and 6 is a subdivision circuit module. DETAILED DESCRIPTION

[0036] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application but not all the embodiments. The description is only used to further explain the features and advantages of the present application but not limit the claims of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of the present application.

[0037] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are used to illustrate the present application but not to limit the scope of the present application.

[0038] The terms "first", "second" are only used for description purpose and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0039] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connection" and "connecting" should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, and can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0040] The specific parameters of the embodiment are as follows: the laser wavelength of the laser 1 is 635 nm, the power of the laser 1 is 1.2 mw, the circuit subdivision multiple of the subdivision circuit module 6 is 1000 times. The grating hole diameter of the upper grating 3 and the lower four-quadrant array grating 4 is 450 nm, the grating duty cycle of the upper grating 3 and the lower four-quadrant array grating 4 is 0.5, the grating thickness of the upper grating 3 and the lower four-quadrant array grating 4 is 150 nm, the grating material of the upper grating 3 and the lower four-quadrant array grating 4 is Al, the grating period of the upper grating 3 and the lower four-quadrant array grating 4 is 900 nm, and the grating area of the upper grating 3 is 10 mm*10 mm. The grating area of the first quadrant grating 401, the second quadrant grating 402, the third quadrant grating 403 and the fourth quadrant grating 404 is 2.5 mm*2.5 mm.

[0041] In the embodiment, as Figure 1As shown, the light emitted by laser 1 is collimated and expanded by collimator and beam expander 2, then propagates in a straight line and directly incident on the upper grating 3. Wherein, as... Figure 2 As shown, the upper grating 3 adopts a two-dimensional honeycomb hexagonal circular aperture periodic structure. The centers of the circular apertures in each row and column of the upper two-dimensional honeycomb hexagonal circular aperture periodic structure grating 3 are on the same parallel line, and the distance between adjacent parallel lines is the grating period length. The basic periodic unit is a hexagonal honeycomb structure. The beam moves in the two-dimensional plane with the displacement of the object under test. Subsequently, the beam passes directly through the lower four-quadrant array grating 4, which is a four-quadrant array circular aperture two-dimensional planar grating composed of four two-dimensional linear circular aperture arrays spaced n+1 / 4 (n=0,1,2,3…) times the grating period. The basic periodic unit is a rectangular structure. Then, as the object under test moves along the in-plane X or Y direction, the overall transmitted subdivided light intensity signal of the system is collected by the four-quadrant detector 5. The output signal diagram of the four quadrants of the grating's two-dimensional in-plane displacement is shown in the figure. Figure 6 As shown, quadrants 1 and 2 detect two sine and cosine signals with a phase difference of 90° between them for X-axis displacement; quadrants 3 and 4 detect two sine and cosine signals with a phase difference of 90° between them for Y-axis displacement. Finally, the two sets of two sine and cosine signals with a phase difference of 90° between them are processed by the subsequent circuit subdivision module 6 to obtain displacement detection values ​​with a certain resolution. Figure 7 The figure shows the scanning simulation results when the plane is displaced along the X-axis. The scanning displacement length is the length of two grating periods. The obtained transmitted light intensity achieves light intensity signal subdivision with a variation period of half the grating period (i.e., achieving twice the optical subdivision).

[0042] Furthermore, the two-dimensional in-plane simulation results of the upper grating 3 are shown in the figure below. Figure 3 As shown, the simulated pattern range within the FDTD is presented as a centrally symmetrical two-dimensional array module. The simulation results show that the simulation yields excellent in-plane self-imaging of the honeycomb-shaped hexagonal circular aperture periodic structure grating.

[0043] Furthermore, the simulation results of the upper grating 3 being out-of-plane along the X-axis are shown in the figure below. Figure 4 As shown, the simulation results were obtained using a 2D xz-plane detector in FDTD. From the simulation results, it can be concluded that within the Talbot self-imaging range of the upper two-dimensional honeycomb hexagonal circular aperture periodic structure grating 3 in the out-of-plane direction, the circular aperture spot distribution pattern presents as a staggered inverted triangle.

[0044] Furthermore, such as Figure 5As shown, the first quadrant grating 401 and the second quadrant grating 402 are separated by n+1 / 4 (n=0, 1, 2, 3…) grating periods in the lateral direction, and the third quadrant grating 403 and the fourth quadrant grating 404 are separated by n+1 / 4 (n=0, 1, 2, 3…) grating periods in the longitudinal direction.

[0045] Based on the optical self-imaging effect of the upper grating, in order to ensure good signal output, the lower four-quadrant array grating 4 is located within the effective self-imaging distance D of the upper grating 3, and the lower four-quadrant array grating 4 needs to be at the self-imaging half-period or period position Z.

[0046]

[0047]

[0048] Wherein: d is the grating period of the upper grating 3 and the lower four-quadrant array grating 4, N is the number of grating periods, n is the diffraction order of a single period grating, and N and n are both integers 0, 1, 2…

[0049] In this embodiment, the self-imaging effect in the grating diffraction phenomenon is used to measure the in-plane displacement of the displacement object to be measured by using a two-dimensional point array grating in-plane displacement measurement system with optical self-subdivision function, to realize high-resolution optical signal subdivision with a change period of half of the grating period (i.e. two times of optical subdivision), which is the core of two-dimensional displacement measurement of the present application, and the resolution S of the system displacement measurement in which can be expressed as:

[0050]

[0051] In the formula, S1 is the optical resolution, which is determined by the optical signal period L; and S2 is the electrical resolution, which is determined by the subdivision multiple M of the subdivision circuit. As can be seen from the formula, by using a high-resolution optical subdivision period signal with a change period of half of the grating period (i.e. two times of optical subdivision), combined with subsequent electronic subdivision, higher resolution displacement detection of the entire system can be realized under simple electronic subdivision conditions.

[0052] Taking the parameters given in this embodiment as an example: from Figure 7 As can be seen, when the periods of the upper grating 3 and the lower four-quadrant array grating 4 are both 900 nm, the output signal period is 450 nm, i.e. the optical sensitivity is 450 nm, and the optical self-subdivision with a change period of half of the grating period (i.e. two times of optical subdivision) is realized. As can be seen from formula (3), when the optical signal resolution S1 becomes 2 times of the self-imaging period resolution, the overall resolution S of the measurement system inThe resolution is doubled to the original 2 times. When the circuit subdivision multiple is 1000 times, the overall resolution of the system is improved from 0.9 nm to 0.45 nm.

[0053] The above only describes the preferred embodiments of the present application in detail, but the present application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application, and all the changes shall be included in the protection scope of the present application.

Claims

1. A two-dimensional dot-matrix grating in-plane displacement sensor with optical self-distribution function, characterized in that: The system includes a laser (1), a collimating beam expander (2), an upper grating (3), a lower four-quadrant array grating (4), a four-quadrant detector (5), and a subdivision circuit module (6). The laser (1) has a collimating beam expander (2) in its optical path direction. The collimating beam expander (2) has an upper grating (3) in its optical path direction. The upper grating (3) has a lower four-quadrant array grating (4) in its optical path direction. The lower four-quadrant array grating (4) has a four-quadrant detector (5) in its optical path direction. The four-quadrant detector (5) is electrically connected to the subdivision circuit module (6). The upper grating (3) adopts a two-dimensional honeycomb hexagonal circular hole periodic structure. The center of each row or column of circular holes in the upper grating (3) is on the same parallel line. The distance between adjacent parallel lines is the grating period length. The circular holes on adjacent parallel lines are externally tangent to each other. The lower quadrant array grating (4) adopts a two-dimensional planar grating with a four-quadrant array circular aperture. The lower quadrant array grating (4) includes a first quadrant grating (401), a second quadrant grating (402), a third quadrant grating (403), and a fourth quadrant grating (404). The first quadrant grating (401) and the second quadrant grating (402) are arranged side by side, and the third quadrant grating (403) and the fourth quadrant grating (404) are arranged side by side. The first quadrant grating (401) and the second quadrant grating (402) are separated by n+1 / 4 grating periods in the lateral distance, n=0,1,2,3…, and the third quadrant grating (403) and the fourth quadrant grating (404) are separated by n+1 / 4 grating periods in the longitudinal distance, n=0,1,2,3….

2. The two-dimensional dot-matrix grating in-plane displacement sensor with optical self-division function according to claim 1, characterized in that: The upper grating (3) is attached to the object to be measured and the lower quadrant array grating (4) is attached to the quadrant detector (5).

3. A two-dimensional dot-matrix grating in-plane displacement sensor with optical self-division function according to claim 1, characterized in that: The laser wavelength of the laser (1) is 635nm, the power of the laser (1) is 1.2mw, and the subdivision factor of the subdivision circuit module (6) is 1000 times.

4. A two-dimensional dot-matrix grating in-plane displacement sensor with optical self-division function according to claim 1, characterized in that: The diameter of the grating circular hole of the upper grating (3) and the lower four-quadrant array grating (4) is 450nm, the grating duty cycle of the upper grating (3) and the lower four-quadrant array grating (4) is 0.5, the grating thickness of the upper grating (3) and the lower four-quadrant array grating (4) is 150nm, the grating material of the upper grating (3) and the lower four-quadrant array grating (4) is AI, the grating period of the upper grating (3) and the lower four-quadrant array grating (4) is 900nm, and the grating area of ​​the upper grating (3) is 10mm*10mm.

5. A two-dimensional dot-matrix grating in-plane displacement sensor with optical self-division function according to claim 1, characterized in that: The grating areas of the first quadrant grating (401), the second quadrant grating (402), the third quadrant grating (403), and the fourth quadrant grating (404) are all 2.5mm*2.5mm.

6. A two-dimensional dot-matrix grating in-plane displacement sensor with optical self-division function according to claim 1, characterized in that: The lower quadrant array grating (4) is located at the effective self-imaging distance of the upper grating (3). D Within this range, the lower quadrant array grating (4) is located at a self-imaging half-cycle or periodic position. Z Place; The d The grating period is the grating period of the upper grating (3) and the lower four-quadrant array grating (4). N The number of grating periods, the m For the diffraction order of a single periodic grating, the N , m All are integers 0, 1, 2, ...

7. A method for measuring a two-dimensional dot-matrix grating in-plane displacement sensor with optical self-distribution function according to any one of claims 1-6, characterized in that: Includes the following steps: S1. The light emitted by the laser is collimated and expanded by the collimator and beam expander, and then propagates in a straight line and directly incident on the upper grating. S2. The upper grating is attached to the object to be measured and moves together with the object in the plane. S3. The beam passes directly through the lower four-quadrant array grating, and the lower four-quadrant array grating is tightly attached to the four-quadrant detector. S4. The four-quadrant detector collects the light intensity transmittance signal of the entire system when the upper grating and the lower four-quadrant array grating move relative to each other in the two-dimensional plane, and obtains two sets of four sinusoidal signals. S5. Each signal consists of two sine and cosine signals with a phase difference of 90°, which are used to detect displacement in the X and Y directions respectively. The lateral direction is defined as the X direction and the longitudinal direction is defined as the Y direction. The first quadrant grating and the second quadrant grating generate the signal in the X direction, and the third quadrant grating and the fourth quadrant grating generate the signal in the Y direction. S6. The two sets of signals are subdivided and modulated by the subdivision circuit module to measure the in-plane displacement of the object to be measured.

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