Three-DOF heterodyne grating interferometer displacement measurement system

Abstract

A three-DOF (Degree of Freedom) heterodyne grating interferometer displacement measurement system comprises a dual-frequency laser, a grating interferometer, a measurement grating, receivers and an electronic signal processing component; the grating interferometer comprises a polarizing beam splitter, a reference grating and dioptric elements; the measurement system realizes displacement measurement on the basis of grating diffraction, the optical Doppler Effect and the optical beat frequency principle. Three linear displacements can be output by the system when the grating interferometer and the measurement grating perform a three-DOF linear relative motion. The measurement system can reach sub-nanometer and higher resolution and precision, and can simultaneously measure three linear displacements. The measurement system has the advantages of being environmentally insensitive, high in measurement precision, small in size, light in weight, and is capable of improving the overall performances of an ultra-precision stage of a lithography machine as a position measurement system for this stage.

Claims

1. A three-DOF (Degrees Of Freedom) heterodyne grating interferometer displacement measurement system, characterized in that it comprises: a dual-frequency laser (1), a grating interferometer (2), a measurement grating (3), four receivers (4) and an electronic signal processing component (5), wherein the grating interferometer (2) comprises: a polarizing beam splitter (21), a reference grating (22), a first dioptric element, and a second dioptric element; wherein each of the reference grating (22) and the measurement grating (3) adopts a two-dimensional reflection grating; the dual-frequency laser (1) emits a dual-frequency orthogonal polarized laser light which is split into a transmitted light and a reflected light after being provided to the polarizing beam splitter (21) through an optical fiber coupling, wherein the transmitted light is a reference light, and the reflected light is a measurement light; after the reference light is incident onto the reference grating (22), four beams of diffracted and reflected reference light are generated, and the four beams of diffracted and reflected reference light are deflected through the first dioptric element to form four beams of parallel reference light, which return to the polarizing beam splitter (21) and transmit therethrough; after the measurement light is incident onto the measurement grating (3), four beams of diffracted and reflected measurement light are generated, and the four beams of diffracted and reflected measurement light are deflected through the second dioptric element to form four beams of parallel measurement light, which return to the polarizing beam splitter (21) and are reflected by the polarizing beam splitter (21); four beams of transmitted reference light and four beams of reflected measurement light are incorporated with each other respectively to form four paths of measurement optical signals; the four paths of measurement optical signals are transmitted to the four receivers (4) through optical fibers to be processed so as to form four paths of measurement electrical signals, respectively, and the four paths of measurement electrical signals are transmitted to the electronic signal processing component (5) to be processed; meantime, the dual-frequency laser (1) also outputs a beam of reference electrical signal to the electronic signal processing component (5); when the measurement grating (3) conducts three-DOF linear movements, i.e., movements in x direction, y direction and z direction, with respect to the grating interferometer (2), the electronic signal processing component (5) outputs three-DOF linear displacements, and the displacements of the three-DOF movements are calculated by
k.sub.x=.sub.x/4,
k.sub.y=.sub.y/4,
k.sub.z=/4(1+cos ),
x=k.sub.x(),
y=k.sub.y(), and
z=k.sub.z(+++), where , , and are the reading values of an electronic signal processing component (5), .sub.x and .sub.y are grating constants in the x and y directions of the measurement grating (3) and the reference grating (22), is the wavelength of the laser light, and is a grating diffraction angle of the measurement grating (3) and the reference grating (22).

2. The three-DOF heterodyne grating interferometer displacement measurement system according to claim 1, characterized in that each of the first dioptric element and the second dioptric element adopts a dioptric prism (23) composed of two right angle prisms located on xoy plane and two right angle prisms located on xoz plane.

3. The three-DOF heterodyne grating interferometer displacement measurement system according to claim 1, characterized in that each of the first dioptric element and the second dioptric element adopts a lens (24).

4. The three-DOF heterodyne grating interferometer displacement measurement system according to claim 1, characterized in that the receivers (4) and the electronic signal processing component (5) are integrated into an integral structure (6), wherein, the four paths of measurement optical signals and a path of reference electrical signal output from the dual-frequency laser are input to the integral structure (6) to be processed, and then the displacements of the three-DOF linear movements, i.e., movements in x direction, y direction and z direction, are output.

5. The three-DOF heterodyne grating interferometer displacement measurement system according to claim 2, characterized in that the receivers (4) and the electronic signal processing component (5) are integrated into an integral structure (6), wherein, the four paths of measurement optical signals and a path of reference electrical signal output from the dual-frequency laser are input to the integral structure (6) to be processed, and then the displacements of the three-DOF linear movements, i.e., movements in x direction, y direction and z direction, are output.

6. The three-DOF heterodyne grating interferometer displacement measurement system according to claim 3, characterized in that the receivers (4) and the electronic signal processing component (5) are integrated into an integral structure (6), wherein, the four paths of measurement optical signals and a path of reference electrical signal output from the dual-frequency laser are input to the integral structure (6) to be processed, and then the displacements of the three-DOF linear movements, i.e., movements in x direction, y direction and z direction, are output.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the first kind of heterodyne grating interferometer displacement measurement system of the present invention.

(2) FIG. 2 is a schematic diagram of a second kind of heterodyne grating interferometer displacement measurement system of the present invention.

(3) FIG. 3 is a schematic diagram of the internal structure of the first kind of grating interferometer of the present invention of the present invention.

(4) FIG. 4 is a schematic diagram of the internal structure of the second kind of grating interferometer of the present invention.

(5) The reference numbers in the drawings comprise: 1dual-frequency laser, 2grating interferometer, 3measurement grating, 4receiver, 5electronic signal processing component, 6integral structure, 21polarizing beam splitter, 22reference grating, 23dioptric prism, 24lens.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(6) Hereinafter, the structure, principle and specific implementing mode of the present invention will be further detailed in connection with the accompanying drawings.

(7) With reference to FIG. 1, FIG. 1 is a schematic diagram of the first kind of heterodyne grating interferometer displacement measurement system of the present invention. As shown in FIG. 1, the three-DOF heterodyne grating interferometer displacement measurement system comprises a dual-frequency laser 1, a grating interferometer 2, a measurement grating 3, receivers 4 and an electronic signal processing component 5, and the measurement grating 3 is a two-dimensional reflection grating.

(8) With reference to FIG. 3, FIG. 3 is a schematic diagram of the internal structure of the first kind of grating interferometer of the present invention. The grating interferometer 2 comprises a polarizing beam splitter 21, a reference grating 22, a first dioptric element and a second dioptric element; the reference grating 22 is a two-dimensional reflection grating; and, each of the first dioptric element and the second dioptric element adopts a dioptric prism 23 composed of two right angle prisms located on the xoy plane and two right angle prisms located on the xoz plane.

(9) The principle of the measurement system will be described in conjunction with FIG. 1 and FIG. 3. The dual-frequency laser 1 emits dual-frequency orthogonal polarized laser light which is split into transmitted light and reflected light after being incident onto the polarizing beam splitter 21 through an optical fiber coupling 8, wherein the transmitted light is reference light, and the reflected light is measurement light; after the reference light is incident onto the reference grating 22, four beams of diffracted and reflected reference light are generated, and the four beams of diffracted and reflected reference light are deflected through the dioptric prism 23 to form four beams of parallel reference light, which return to the polarizing beam splitter 21 and transmit therethrough; after the measurement light is incident onto the measurement grating 3, four beams of diffracted and reflected measurement light are generated, the four beams of diffracted and reflected measurement light are deflected through the dioptric prism 23 to form four beams of parallel measurement light, which return to the polarizing beam splitter 21 and are reflected by the polarizing beam splitter 21; the four beams of transmitted reference light and the four beams of reflected measurement light are incorporated with each other respectively to form four paths of measurement optical signals, which are transmitted to the four receivers 4, respectively, through optical fibers to be processed so as to form four paths of measurement electrical signals, respectively, and the four paths of measurement electrical signals are transmitted to the electronic signal processing component 5 to be processed; meantime, the dual-frequency laser 1 also outputs a beam of reference electrical signal to the electronic signal processing component 5; when the measurement grating 3 conducts three-DOF linear movements, i.e., movements in x direction, y direction and z direction (the movement in z direction is a minute movement, where the movement range is about 1 mm), with respect to the grating interferometer 2, the electronic signal processing component 5 outputs three-DOF linear displacements.

(10) The expressions of the displacements of the three-DOF movements are: x=k.sub.x(), y=k.sub.y(), z=k.sub.z(+++), k.sub.x=.sub.x/4, k.sub.y=.sub.y/4 and k.sub.z=/4(1+cos ), where , , and are the reading values of an electronic signal processing card, .sub.x and .sub.y are the grating constants, is the wavelength of the laser light, is the grating diffraction angle, taking .sub.x=.sub.y=1 m, =632.8 nm, the phase resolution of , , and is 2/1024, the measurement resolution of x, y and z of the heterodyne grating interferometer are 0.49 nm, 0.49 nm and 0.18 nm, respectively.

(11) With reference to FIG. 2, FIG. 2 is a schematic diagram of the second kind of heterodyne grating interferometer displacement measurement system of the present invention. As shown in FIG. 2, the receivers 4 and the electronic signal processing component 5 are integrated into an integral structure 6, wherein, the four paths of measurement optical signals and a path of reference electrical signal output from the dual-frequency laser are input to the integral structure 6 to be processed, and then the displacements of the three-DOF linear movements, i.e., movements in x direction, y direction and z direction, are output. The adoption of this kind of integral structure 6 of the measurement system can effectively reduce the number of systematic components, improve anti-jamming capability of the system, and improve system integration.

(12) With reference to FIG. 4, FIG. 4 is a schematic diagram of the internal structure of the second kind of grating interferometer of the present invention. In the internal structure of the grating interferometer, as shown in FIG. 4, each of the first dioptric element and the second dioptric element adopts lens 24. Compared to the dioptric prism 23, the lens 24 features such advantages as simple structure, being easy to process and being convenient to install.

(13) The measurement system and structure scheme described in the above embodiments can implement simultaneous measurements of three-linear-DOF displacements, and the measurement system features a short measurement light path, a low environmental sensitivity, an easy-to-process measurement signal, and a resolution and accuracy reaching up to the subnanometer scale or even higher. Meanwhile, the grating interferometer measurement system also features such advantages as a simple structure, a small volume, a light weight, being easy to install, and being convenient to apply, etc. Compared to a laser interferometer measurement system, the measurement system of the present invention applied to the displacement measurement of the ultra-precise workpiece stage of a photoetching machine can, based on meeting measurement demands, effectively reduce the volume and weight of the workpiece stage, greatly enhance dynamic performance of the workpiece stage, and make the whole performance of the workpiece stage be enhanced comprehensively. The three-DOF heterodyne grating interferometer displacement measurement system can also be applied to the precise measurement of multi-DOF displacements of the workpiece stage of precision machine tools, three-coordinate measuring machines, and semiconductor testing equipment, etc.