CN108286943B - Displacement measurement optical system applied to workbench of photoetching system - Google Patents
Displacement measurement optical system applied to workbench of photoetching system Download PDFInfo
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- CN108286943B CN108286943B CN201810035524.2A CN201810035524A CN108286943B CN 108286943 B CN108286943 B CN 108286943B CN 201810035524 A CN201810035524 A CN 201810035524A CN 108286943 B CN108286943 B CN 108286943B
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Abstract
The invention discloses a displacement measurement optical system applied to a workbench of a photoetching system.A first difference frequency interference device is used for generating difference frequency coherent light with the central wavelength of a first wavelength value, respectively transmitting two frequencies to a first reflector and a second reflector to form split light, and receiving interference light formed by converging two beams of light after returning; the second difference frequency interference device is used for generating difference frequency coherent light with the central wavelength being a second wavelength value, respectively transmitting two frequencies to the first reflector and the second reflector to form split light, and receiving interference light formed by converging two beams of light after returning; the first reflector is fixed in position, the second reflector can move along with the workbench, and the signal processing device calculates the displacement of the second reflector after the environmental factor disturbance is eliminated according to the interference image recorded by the two difference frequency interference devices. The displacement measurement optical system utilizes light with two light sources to realize displacement measurement based on an optical interference method, compensates the influence of environmental factors in the whole displacement area, and can improve the measurement precision compared with the prior art.
Description
Technical Field
The invention relates to the technical field of optical measurement, in particular to a displacement measurement optical system applied to a workbench of a photoetching system.
Background
At present, a nanoscale long-stroke two-dimensional worktable applied to a photoetching system is mostly used for grating displacement measurement and difference frequency laser interference displacement measurement, but in the long-stroke displacement measurement, the grating is required to have high line number and large length, the grating is difficult to etch, the contradiction that the measurement resolution and the measuring range can not be considered exists, the measurement precision and the etching precision of the grating have a direct relation, and the influence of the grating processing technology is large. In comparison, the displacement measurement based on the difference frequency laser interference has the remarkable characteristics of high resolution, high precision, high speed measurement, long stroke, multiple channels and the like, and is the best choice for the displacement measurement of the nanoscale long-stroke two-dimensional workbench.
However, the laser interference displacement measurement system has high requirements on environmental conditions, and environmental factors in the measurement process have considerable influence on the measurement. In the prior art, a temperature sensor, an air pressure sensor and a humidity sensor are used for detecting corresponding parameters in a measuring environment, refractive index and wavelength values are calculated by combining the environmental parameters, and then the refractive index and the wavelength values are input into a signal processing system in parallel with signals measured by the system for air refractive index compensation. However, due to the limitations of the measuring instrument and the method, for a long-stroke and moving workbench, the environmental parameters of the whole displacement area cannot be accurately detected, and the accurate compensation of the environmental influence cannot be realized.
Disclosure of Invention
In view of this, the present invention provides a displacement measurement optical system applied to a workbench of a lithography system, which is used for measuring the displacement of the workbench, and utilizes light of two light sources to realize displacement measurement based on an optical interference method, so as to compensate the influence of environmental factors in the whole displacement area, and improve the measurement accuracy.
In order to achieve the purpose, the invention provides the following technical scheme:
a displacement measurement optical system applied to a workbench of a photoetching system comprises a first difference frequency interference device, a second difference frequency interference device, a first reflecting mirror, a second reflecting mirror and a signal processing device;
the position of the first reflector is fixed, and the second reflector is connected with the workbench and can move along with the workbench;
the first difference frequency interference device is used for generating difference frequency coherent light with the central wavelength being a first wavelength value, respectively transmitting two frequency component lights to the first reflector and the second reflector, and receiving interference light formed by converging two beams of light after returning;
the second difference frequency interference device is used for generating difference frequency coherent light with the central wavelength being a second wavelength value, respectively transmitting two frequency component lights to the first reflector and the second reflector, and receiving interference light formed by converging two beams of light after returning;
the signal processing device is used for calculating a first optical path displacement described by a first wavelength value according to the interference image recorded by the first difference frequency interference device, calculating a second optical path displacement described by a second wavelength value according to the interference image recorded by the second difference frequency interference device, and calculating the displacement of the second reflecting mirror for eliminating the environmental factor disturbance according to the first optical path displacement and the second optical path displacement.
Optionally, a third mirror is further included;
the third reflector is fixed on the exposure system;
the first difference frequency interference device is further configured to transmit two frequency component lights with center wavelengths of first wavelength values to the first reflector and the third reflector, respectively, wherein the same frequency component light as that transmitted to the second reflector is transmitted to the third reflector, and the two beams of light are received and returned to join to form interference light;
the second difference frequency interference device is further configured to transmit two frequency component lights with center wavelengths of second wavelength values to the first reflector and the third reflector, respectively, wherein the same frequency component light as the frequency component light transmitted to the second reflector is transmitted to the third reflector, and the interference light formed by converging the two beams of light after returning is received;
the signal processing device is further configured to calculate a third optical path displacement amount described by a first wavelength value according to the interference image recorded by the first difference frequency interference device, calculate a fourth optical path displacement amount described by a second wavelength value according to the interference image recorded by the second difference frequency interference device, and calculate and eliminate environmental factor disturbance, light source stability disturbance and displacement of the second mirror, where the exposure system generates disturbance due to thermal expansion, according to actual displacement of the third mirror, the third optical path displacement amount and the fourth optical path displacement amount.
Optionally, further comprising an optic:
the optical mirror is located at the intersection of the emergent light beams of the first difference frequency interference device and the second difference frequency interference device, and is used for transmitting light with a central wavelength of a first wavelength value and reflecting light with the central wavelength of a second wavelength value.
Optionally, the first difference frequency interference device includes:
the first light source is used for generating difference frequency coherent light with the central wavelength being a first wavelength value;
the first polarization beam splitter prism is used for respectively enabling two frequency components of the difference frequency coherent light generated by the first light source to enter the first reflecting mirror and the second reflecting mirror and converging the light returned by the first reflecting mirror and the second reflecting mirror;
the first optical receiver is connected with the signal processing device and used for receiving the converged interference light transmitted by the first polarization beam splitter prism;
the second difference frequency interference device includes:
a second light source for generating difference frequency coherent light having a center wavelength of a second wavelength value;
the second polarization beam splitter prism is used for respectively transmitting the two frequency components of the difference frequency coherent light generated by the second light source to the first reflecting mirror and the second reflecting mirror and converging the light returned by the first reflecting mirror and the second reflecting mirror;
and the second optical receiver is connected with the signal processing device and used for receiving the converged interference light transmitted by the second polarization beam splitter prism.
Optionally, a quarter-wave plate is arranged on an optical path between the first difference frequency interference device and the first reflecting mirror and an optical path between the first difference frequency interference device and the second reflecting mirror;
and quarter wave plates are arranged on the light path between the second difference frequency interference device and the first reflecting mirror and the light path between the second difference frequency interference device and the second reflecting mirror.
Optionally, the first difference frequency interference device includes:
the first light source is used for generating difference frequency coherent light with the central wavelength being a first wavelength value;
the first light splitting mirror is arranged on a light path between the first light source and the first polarization light splitting prism, and is used for splitting light emitted by the first light source into two beams of light with parallel propagation directions, and the two beams of light are incident to the first polarization light splitting prism;
the first polarization beam splitter prism is used for respectively enabling two frequency components of one beam of incident difference frequency coherent light to enter the first reflecting mirror and the second reflecting mirror, merging the light returning from the first reflecting mirror and the second reflecting mirror, respectively enabling two frequency components of the other beam of incident difference frequency coherent light to enter the first reflecting mirror and the third reflecting mirror, and merging the light returning from the first reflecting mirror and the third reflecting mirror;
the first optical receiver is connected with the signal processing device and used for receiving interference light which is propagated by the first polarization beam splitter prism and is formed by merging the return light of the first reflector and the return light of the second reflector;
the third optical receiver is connected with the signal processing device and used for receiving interference light which is transmitted by the first polarization beam splitter prism and is formed by merging the return light of the first reflector and the return light of the third reflector;
the second difference frequency interference device includes:
a second light source for generating difference frequency coherent light having a center wavelength of a second wavelength value;
the second beam splitter is arranged on a light path between the second light source and the second polarization beam splitter prism, and is used for splitting light emitted by the second light source into two beams of light with parallel propagation directions, and the two beams of light are incident to the second polarization beam splitter prism;
the second polarization beam splitter prism is used for respectively enabling two frequency components of one beam of incident difference frequency coherent light to enter the first reflecting mirror and the second reflecting mirror, converging the light returning from the first reflecting mirror and the second reflecting mirror, respectively enabling two frequency components of the other beam of incident difference frequency coherent light to enter the first reflecting mirror and the third reflecting mirror, and converging the light returning from the first reflecting mirror and the light returning from the third reflecting mirror;
a second optical receiver connected to the signal processing device, for receiving the interference light propagated by the second polarization beam splitter prism and obtained by combining the return light from the first reflecting mirror and the return light from the second reflecting mirror;
and the fourth light receiver is connected with the signal processing device and used for receiving the interference light which is transmitted by the second polarization beam splitter prism and is formed by merging the return light of the first reflector and the return light of the third reflector.
Optionally, quarter-wave plates are arranged on an optical path between the first difference frequency interference device and the first reflecting mirror, an optical path between the first difference frequency interference device and the second reflecting mirror, and an optical path between the first difference frequency interference device and the third reflecting mirror;
quarter-wave plates are arranged on the light path between the second difference frequency interference device and the first reflecting mirror, the light path between the second difference frequency interference device and the second reflecting mirror and the light path between the second difference frequency interference device and the third reflecting mirror.
Optionally, the light source comprises a laser source, an acousto-optic modulator, a first beam splitter, a second beam splitter, a reflector, a half wave plate and a polarizing beam splitter;
the laser source is used for emitting laser;
the acousto-optic modulator is used for dividing laser into one path of light with unchanged frequency to be incident to the first beam splitter, and the other path of light with frequency shift to be incident to the second beam splitter;
the second spectroscope and the reflector are sequentially arranged along a light path, and the reflector reflects light to the half-wave plate and then emits the light to the polarization spectroscope;
the first spectroscope and the polarization spectroscope are sequentially arranged along a light path, and the frequency-shifted light reflected by the second spectroscope is incident to the first spectroscope and is transmitted out through the first spectroscope;
the frequency-unchanged light reflected by the first beam splitter is combined with the frequency-shifted light transmitted by the first beam splitter to serve as reference light, and the light output by the polarization beam splitter serves as measurement light.
Optionally, the first wavelength value belongs to a red wavelength band, and the second wavelength value belongs to a blue wavelength band.
Optionally, a temperature sensor for measuring temperature and a humidity sensor for measuring humidity are disposed on an optical path between the second mirror and the third mirror and the difference frequency interference device.
According to the technical scheme, the displacement measurement optical system applied to the workbench of the photoetching system comprises a first difference frequency interference device, a second difference frequency interference device, a first reflecting mirror, a second reflecting mirror and a signal processing device.
The first difference frequency interference device generates difference frequency coherent light with the center wavelength being a first wavelength value, the two frequency component lights are respectively emitted to the first reflecting mirror and the second reflecting mirror, and the interference light formed by converging the two beams of light after returning is received; the second difference frequency interference device generates difference frequency coherent light with the center wavelength of a second wavelength value, the two frequency components are respectively emitted to the first reflecting mirror and the second reflecting mirror, and the two beams of light are received and then converged to form interference light. The first reflector is fixed and used as a reference mirror, and the second reflector is connected with the workbench and can move along with the workbench. The signal processing device calculates a first optical path displacement described by a first wavelength value according to an interference image recorded by the first difference frequency interference device, calculates a second optical path displacement described by a second wavelength value according to an interference image recorded by the second difference frequency interference device, and calculates the displacement of the second reflector for eliminating the environmental factor disturbance, namely the displacement of the workbench according to the first optical path displacement and the second optical path displacement.
The displacement measurement optical system utilizes the difference frequency coherent light with two different wavelengths to measure the displacement, calculates the displacement according to the optical path displacement measured by the two wavelengths, compensates the influence of environmental factors on the displacement measurement in the whole displacement area, and improves the measurement precision compared with the prior art.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a displacement measurement optical system applied to a stage of a lithography system according to an embodiment of the present invention;
FIG. 2 is a schematic view of a displacement measurement optical system applied to a stage of a lithography system according to another embodiment of the present invention;
FIG. 3 is a schematic diagram of a displacement measurement optical system applied to a stage of a lithography system according to another embodiment of the present invention;
FIG. 4 is a schematic diagram of a displacement measurement optical system for a stage of a lithography system according to another embodiment of the present invention;
fig. 5 is a schematic view of a light source according to an embodiment of the invention.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, an embodiment of the present invention provides a displacement measurement optical system for a stage of a lithography system, including a first difference frequency interference device 10, a second difference frequency interference device 11, a first mirror 12, a second mirror 13, and a signal processing device 14.
The first reflecting mirror 12 is fixed in position, the second reflecting mirror 13 is arranged on the workbench, connected with the workbench and capable of moving along with the workbench, the first reflecting mirror 12 is used as a reference mirror, and the second reflecting mirror 13 is used as a measuring mirror.
The first difference frequency interference device 10 is configured to generate difference frequency coherent light with a center wavelength being a first wavelength value, transmit two frequency component lights to the first reflecting mirror 12 and the second reflecting mirror 13, respectively, and receive interference light formed by returning and converging two light beams. Wherein the two frequency components are coherent light.
The second difference frequency interference device 11 is configured to generate difference frequency coherent light with a center wavelength of a second wavelength value, respectively emit two frequency component lights to the first reflecting mirror 12 and the second reflecting mirror 13, and receive interference light formed by converging two light beams after returning. Wherein the two frequency components are coherent light.
The signal processing device 14 is configured to calculate a first optical path displacement amount described by a first wavelength value according to the interference image recorded by the first difference frequency interference device 10, calculate a second optical path displacement amount described by a second wavelength value according to the interference image recorded by the second difference frequency interference device 11, and calculate a displacement of the second mirror 13, which is a displacement of the stage, for eliminating the environmental factor disturbance according to the first optical path displacement amount and the second optical path displacement amount.
The measurement principle of the displacement measurement optical system is as follows: if it is assumed that the center wavelength of the difference frequency coherent light generated by the first difference frequency interference device 10 is λ1The center wavelength of the difference frequency coherent light generated by the second difference frequency interference device 11 is λ2The refractive indexes of the air corresponding to the optical system measuring arms (i.e. the optical path between the second reflector 13 and the first difference frequency interference device 10 and the optical path between the second reflector 13 and the second difference frequency interference device 11) are nλ1m、nλ2m. The first optical path displacement L measured by the first beat frequency interference device 10λ1mA second optical path displacement L measured by a second difference frequency interference device 11λ2mRespectively expressed as:
Lλ1m＝nλ1mL，Lλ2m＝nλ2mL； (1)
where L represents the actual displacement of the measuring arm (i.e. the displacement of the second mirror 13).
The geometrical length L of the measuring arm can be derived from the above equation:
wherein, K (lambda)i)、g(λi) (i ═ 1 or 2) is the wavelength λiFunction of pwmRepresenting the water vapor pressure in the measurement arm.
It can be seen that the displacement of the measuring wall is calculated according to equation (2), where temperature, pressure and CO2The disturbing influence of the environmental factors such as concentration on the measurement displacement is eliminated, only the influence of the pressure of the residual water vapor is not eliminated, and the influence of the pressure of the water vapor is small and can be compensated through measurement by a temperature sensor and a humidity sensor. Therefore, the displacement measurement optical system is applied to the displacement measurement optical system of the workbench of the photoetching system, displacement measurement is realized by using two kinds of wavelength light based on an optical interference method, and the disturbance influence of some environmental factors is compensated in the whole displacement area. The accuracy of the displacement measurement can be improved.
In the optical system of this embodiment, referring to fig. 1, in order to design the optical path and layout the optical elements, an optical mirror 15 is further included for guiding the difference frequency coherent light emitted by the first difference frequency interference device 10 and the second difference frequency interference device 11 to propagate to the first reflecting mirror 12 and the second reflecting mirror 13.
In specific implementation, as shown in fig. 1, the light emitting direction of the first difference frequency interference device 10 is perpendicular to the light emitting direction of the second difference frequency interference device 11, and the optical mirror 15 is located at the intersection of the light beams emitted from the first difference frequency interference device 10 and the second difference frequency interference device 11, and is used for transmitting the light with the first wavelength value at the center wavelength and reflecting the light with the second wavelength value at the center wavelength to realize guided light propagation.
In particular, the optic 15 mayUsing a dichroic mirror which makes the center wavelength a first wavelength value lambda1Is transmitted so that the central wavelength is a second wavelength value lambda2Is reflected out. The light emitting direction of the first difference frequency interference device 10 is perpendicular to the light emitting direction of the second difference frequency interference device 11, and the optical mirror 15 is disposed at an angle of 45 degrees with respect to the light emitting direction.
Referring to fig. 2, the first difference frequency interference device 10 in the present embodiment specifically includes:
a first light source 100 for generating difference frequency coherent light having a center wavelength of a first wavelength value;
a first polarization beam splitter prism 101 for respectively making two frequency components of the difference frequency coherent light generated by the first light source 100 incident on the first reflecting mirror 12 and the second reflecting mirror 13, and merging the light returned by the first reflecting mirror 12 and the second reflecting mirror 13;
and a first optical receiver 102, connected to the signal processing device 14, for receiving the merged interference light propagated by the first polarization splitting prism 101.
The second difference frequency interference device 11 specifically includes:
a second light source 110 for generating difference frequency coherent light having a center wavelength of a second wavelength value;
a second polarization beam splitter prism 111 for respectively making the two frequency components of the difference frequency coherent light generated by the second light source 100 incident on the first reflecting mirror 12 and the second reflecting mirror 13, and merging the light returned by the first reflecting mirror 12 and the second reflecting mirror 13;
and a second optical receiver 112, connected to the signal processing device 14, for receiving the merged interference light propagated by the second polarization splitting prism 111.
In addition, a quarter-wave plate 16 is arranged on the light path between the first difference frequency interference device 10 and the first reflecting mirror 12 and on the light path between the first difference frequency interference device 10 and the second reflecting mirror 13; a quarter-wave plate 16 is arranged on the light path between the second difference frequency interference device 11 and the first reflecting mirror 12 and on the light path between the second difference frequency interference device 11 and the second reflecting mirror 13.
In the first difference frequency interference device 10The first light source 100 generates a first wavelength λ having a center wavelength1The difference frequency coherent light comprises two frequency components, one of which is a light beam lambda1mAs measuring light, another frequency component light as reference light lambda1rThe two frequency components are in optical coherence, parallel and orthogonal polarization states. Wherein the frequency component is a light lambda1cThe light is guided to enter the first reflector 12 through the first polarization beam splitter prism 101, and returns to the original path after being reflected, wherein the light passes through the quarter-wave plate 16 twice to enable the polarization state of the light to rotate by 90 degrees, and the light returns to the diagonal plane of the first polarization beam splitter prism 101 and is transmitted out; frequency component light lambda1mThe light is guided to enter the second reflecting mirror 13 through the first polarization beam splitter prism 101, and the light returns to the original path after being reflected, wherein the light passes through the quarter-wave plate 16 twice, the polarization state is rotated by 90 degrees, and the light returns to the diagonal plane of the first polarization beam splitter prism 101 and is reflected; the two returned lights are combined to form interference light, which is received by the first optical receiver 102.
In the second difference frequency interference device 11, the second light source 110 generates the second wavelength λ having the center wavelength2The difference frequency coherent light comprises two frequency components, one of which is a light beam lambda2mAs measuring light, another frequency component light as reference light lambda2rThe two frequency components are in optical coherence, parallel and orthogonal polarization states. Wherein the frequency component is a light lambda2cThe light is guided to enter the first reflector 12 through the second polarization beam splitter prism 111, and returns to the original path after being reflected, wherein the light passes through the quarter-wave plate 16 twice to enable the polarization state of the light to rotate by 90 degrees, and the light returns to the diagonal plane of the second polarization beam splitter prism 111 to be transmitted; frequency component light lambda2mThe light is guided to enter the second reflecting mirror 13 through the second polarization beam splitter prism 111, and the light returns to the original path after being reflected, wherein the light passes through the quarter-wave plate 16 twice, the polarization state is rotated by 90 degrees, and the light returns to the diagonal plane of the second polarization beam splitter prism 111 and is reflected out; the two returned lights are combined to form interference light, which is received by the second light receiver 112.
In the displacement measurement optical system applied to the workbench of the lithography system described in the above embodiment, the dual light source method is adopted to successfully eliminate the influence of atmospheric environmental factors on the measurement, but at the same time, the influence of the uncertainty of the measured value of the optical path displacement amount on the measurement is amplified, and the influence is mainly caused by the instability of the light source wavelength. In addition, for the photoetching system, an etched object is arranged on the workbench, and the displacement of the workbench, namely the displacement of the etched object, is measured through the displacement measuring optical system so as to control the photoetching position. However, when the exposure system is displaced due to thermal expansion, the exposure system is displaced relative to the stage, and the displacement measurement optical system provided in the above embodiment measures only the stage position, and cannot capture the displacement of the exposure system due to disturbance of factors such as thermal expansion, which may cause deviation between the lithography position and the ideal position. In view of this, another embodiment of the present invention provides a displacement measurement optical system applied to a stage of a lithography system, in which a compensation arm is applied to compensate for an influence of uncertainty of a measured value of an optical path displacement of a measurement arm, specifically, while measuring a geometric length of the measurement arm, the geometric length of the compensation arm is measured to obtain uncertainty of the measured value of the optical path displacement of the measurement arm due to instability of a wavelength of a light source, and an offset of an exposure system due to disturbance of thermal expansion and other factors is compensated for an error.
Referring to fig. 3, the displacement measuring optical system of the present embodiment includes a first difference frequency interference device 20, a second difference frequency interference device 21, a first reflector 22, a second reflector 23, a third reflector 27, and a signal processing device 24.
The position of the first reflector 22 is fixed, the second reflector 23 is arranged on the workbench and connected with the workbench and can move along with the workbench, the etched object is arranged on the workbench, the third reflector 27 is fixed on the exposure system, the first reflector 12 is used as a reference mirror, the second reflector 13 is used as a measuring mirror, and the actual displacement of the third reflector 27 in the measuring process is known.
The first difference frequency interference device 20 is configured to generate difference frequency coherent light with a center wavelength of a first wavelength value, respectively emit two frequency component lights to the first reflector 22 and the second reflector 23, and receive interference light formed by converging two light beams after returning; and also respectively emitting two frequency component lights with the central wavelength of the first wavelength value to the first reflector 22 and the third reflector 27, wherein the two frequency component lights which are the same as the frequency component light emitted to the second reflector 23 are emitted to the third reflector 27, and the two beams of lights are received and returned to be merged to form interference light. Wherein, two frequency component lights of the difference frequency coherent light with the central wavelength as the first wavelength value are coherent light.
The second difference frequency interference device 21 is configured to generate difference frequency coherent light with a central wavelength of a second wavelength value, respectively emit two frequency component lights to the first reflecting mirror 22 and the second reflecting mirror 23, and receive interference light formed by converging two light beams after returning; and is further configured to respectively emit two frequency component lights with a central wavelength of a second wavelength value to the first reflector 22 and the third reflector 27, where the same frequency component light as that emitted to the second reflector 23 is emitted to the third reflector 27, and the two beams of light are received and returned to join to form interference light. Wherein, the two frequency component lights of the difference frequency coherent light with the center wavelength as the second wavelength value are coherent light.
The signal processing device 24 is configured to calculate a first optical path displacement amount described by a first wavelength value according to the interference image recorded by the first difference frequency interference device 20, and calculate a second optical path displacement amount described by a second wavelength value according to the interference image recorded by the second difference frequency interference device 21.
The signal processing device 24 is further configured to calculate a third optical path displacement amount described by the first wavelength value according to the interference image recorded by the first difference frequency interference device 20, calculate a fourth optical path displacement amount described by the second wavelength value according to the interference image recorded by the second difference frequency interference device 21, where the third optical path displacement amount and the fourth optical path displacement amount are the optical path displacement amounts of the third mirror 27,
the signal processing device 24 calculates the displacement of the second reflecting mirror 23 for eliminating the disturbance of the environmental factor, the disturbance of the light source stability, and the disturbance of the exposure system due to thermal expansion, according to the actual displacement of the third reflecting mirror 27, the third optical path displacement amount, and the fourth optical path displacement amount. .
The measurement principle of the displacement measurement optical system is as follows: according to measurementUncertainty Δ L of arm, optical path displacement measurement valueλ1m、ΔLλ1mRespectively expressed as:
wherein elaser1、elaser2Respectively representing the fluctuation errors of the first light source and the second light source.
The influence of the uncertainty of the measured value of the optical path displacement on the measurement is as follows:
a compensation arm is formed by the light path between the third reflector 27 and the difference frequency interference device, and the third optical path displacement S is obtained by measurementλ1cAnd a fourth optical path displacement amount Sλ2cUncertainty Δ S of measured value of optical path displacementλ1c、ΔSλ2cExpressed as:
ΔSλ1c＝nλ1cS-Sλ1c＝Sλ1c·elaser1； (6)
ΔSλ2c＝nλ2cS-Sλ2c＝Sλ2c·elaser2； (7)
wherein n isλ1c、nλ2cWhich represents the refractive index of air corresponding to the light of the two wavelengths in the compensating arm (i.e., the optical path between the third mirror 27 and the first beat frequency interference device 20, and the optical path between the second mirror 23 and the second beat frequency interference device 21), and S represents the actual displacement of the compensating arm (i.e., the displacement of the third mirror 27).
The light fluctuation error obtained by the above equation is:
and (3) integrating the formula (1), the formula (5), the formula (8) and the formula (9), wherein the compensated measurement arm displacement measurement value is as follows:
further, according to the Edlen formula, the refractive index of the compensation arm is expressed as:
nλic-1＝K(λi)·D(tc,pc,xc)-pwc·g(λi)，i＝0or 1。 (11)
wherein, tc、pc、xcAnd pwcRespectively representing the temperature, pressure and CO of air of the compensating arm2Concentration and water vapor pressure. Substituting equation (11) into equation (10) and approximating as follows:
equation (10) is rewritten as:
further, a light path between the third reflector 27 and the difference frequency interference device is used to form a compensation arm, the actual displacement is S, the third reflector 27 is fixed on the exposure system, and when the exposure system is displaced by Delta S due to thermal expansion, the measurement value of the displacement of the measurement arm is Lc＝LmS/(Sm+ Δ S) that compensates for the error in the displacement of the second mirror due to the displacement of the third mirror, and also compensates for the displacement of the exposure system due to thermal expansion.
Therefore, the embodiment is applied to the displacement measurement optical system of the workbench of the lithography system, eliminates the influence of environmental factors on interferometer measurement through a double-light-source measurement method, and compensates the influence of uncertainty of the optical path displacement measurement value through the compensation arm, thereby compensating the measurement error caused by light source wavelength fluctuation and thermal expansion of the exposure system. The method can greatly improve the precision of displacement measurement, can be applied to a photoetching system, can greatly improve the precision of displacement measurement of a long-stroke two-dimensional worktable, and is beneficial to improving the photoetching precision in the photoetching system.
In this embodiment, for the purpose of designing the optical path and arranging the optical elements, an optical mirror 25 is further included for guiding the difference frequency coherent light emitted by the first difference frequency interference device 20 and the second difference frequency interference device 21 to propagate to the first mirror 22, the second mirror 23 and the third mirror 27.
In specific implementation, referring to fig. 3, the light emitting direction of the first difference frequency interference device 20 is perpendicular to the light emitting direction of the second difference frequency interference device 21, and the optical mirror 25 is located at the intersection of the light beams emitted from the first difference frequency interference device 20 and the second difference frequency interference device 21, and is used for transmitting the light with the first wavelength value at the center wavelength and reflecting the light with the second wavelength value at the center wavelength to realize guided light transmission.
Specifically, the optical mirror 25 may be a dichroic mirror that makes the center wavelength a first wavelength value λ1Is transmitted so that the central wavelength is a second wavelength value lambda2Is reflected out. The light emission direction of the first difference frequency interference device 20 is perpendicular to the light emission direction of the second difference frequency interference device 21, and the optical mirror 25 is disposed at an angle of 45 degrees to the light emission direction.
Referring to fig. 4, the first difference frequency interference device 20 in this embodiment includes:
a first light source 200 for generating difference frequency coherent light having a center wavelength of a first wavelength value;
a first beam splitter 203, disposed on the light path between the first light source 200 and the first polarization beam splitter 201, for splitting the light emitted from the first light source 200 into two beams of light with parallel propagation directions, and making the two beams of light incident on the first polarization beam splitter 201;
a first polarization beam splitter 201 for making the two frequency components of one beam of the incident difference-frequency coherent light beam enter the first reflecting mirror 22 and the second reflecting mirror 23, respectively, and joining the light returning from the first reflecting mirror 22 and the second reflecting mirror 23, making the two frequency components of the other beam of the incident difference-frequency coherent light beam enter the first reflecting mirror 22 and the third reflecting mirror 27, respectively, and joining the light returning from the first reflecting mirror 22 and the third reflecting mirror 27;
a first light receiver 202 connected to the signal processing device 24 for receiving the interference light propagated by the second polarization beam splitter 201 and combined with the return light from the first mirror 22 and the return light from the second mirror 23;
a third optical receiver 204. And is connected to the signal processing device 24 for receiving the interference light propagated by the first polarization splitting prism 201 and combined by the return light from the first reflector 22 and the return light from the third reflector 27.
The second difference frequency interference device 21 includes:
a second light source 210 for generating difference frequency coherent light having a center wavelength of a second wavelength value;
the second beam splitter 213 is disposed on the light path between the second light source 210 and the second polarization beam splitter 211, and is configured to split the light emitted by the second light source 210 into two beams of light with parallel propagation directions, and the two beams of light are incident on the second polarization beam splitter 211;
a second polarization beam splitter prism 211 for respectively making the two frequency components of one beam of the incident difference-frequency coherent light incident on the first reflecting mirror 22 and the second reflecting mirror 23, merging the return light from the first reflecting mirror 22 and the second reflecting mirror 23, respectively making the two frequency components of the other beam of the incident difference-frequency coherent light incident on the first reflecting mirror 22 and the third reflecting mirror 27, and merging the return light from the first reflecting mirror 22 and the return light from the third reflecting mirror 27;
a second light receiver 212, connected to the signal processing device 24, for receiving the interference light propagated by the second polarization beam splitter 211 and combined with the return light from the first reflecting mirror 22 and the return light from the second reflecting mirror 23;
and a fourth light receiver 214 connected to the signal processing device 24 and configured to receive the interference light propagated by the second polarization splitting prism 211 and combined with the return light from the first mirror 22 and the return light from the third mirror 27.
In addition, a quarter-wave plate 26 is disposed on the optical path between the first difference frequency interference device 20 and the first reflecting mirror 22, on the optical path between the first difference frequency interference device 20 and the second reflecting mirror 23, and on the optical path between the first difference frequency interference device 20 and the third reflecting mirror 27.
A quarter-wave plate 26 is arranged on the light path between the second difference frequency interference device 21 and the first reflecting mirror 22, on the light path between the second difference frequency interference device 21 and the second reflecting mirror 23, and on the light path between the first difference frequency interference device 21 and the third reflecting mirror 27.
In the first difference frequency interference device 20, the first light source 200 generates the first wavelength λ as the center wavelength1The difference frequency coherent light comprises two frequency components, one of which is a light beam lambda1mAs measuring light, another frequency component light as reference light lambda1rThe two frequency components are in optical coherence, parallel and orthogonal polarization states. The first beam splitter 203 splits each frequency component light into two beams propagating in parallel, and the two beams are incident on the first polarization splitting prism 201.
In the second difference frequency interference device 21, the second light source 210 generates the second wavelength λ having the center wavelength2The difference frequency coherent light comprises two frequency components, one of which is a light beam lambda2mAs measuring light, another frequency component light as reference light lambda2rThe two frequency components are in optical coherence, parallel and orthogonal polarization states. The second beam splitter 213 splits each frequency component light into two beams propagating in parallel, and enters the first polarization beam splitter prism 211.
In the above embodiments, in order to make the two measuring optical paths have the same measuring environment, the optical mirror uses a dichroic mirror to combine the reference light, the measuring light and the compensating light output by the difference frequency interference device, respectively, so as to ensure the common optical path property thereof.
Further, a temperature sensor for measuring temperature and a humidity sensor for measuring humidity are arranged on an optical path between the second reflecting mirror and the third reflecting mirror and the difference frequency interference device. The temperature and humidity changes in the measuring light path and the compensation light path are detected by the temperature sensor and the humidity sensor so as to compensate the influence of the water vapor pressure on the light beam measurement.
In the above embodiments, referring to fig. 5, the light source includes a laser source 30, an acousto-optic modulator 31, a first beam splitter 32, a second beam splitter 33, a reflector 34, a half-wave plate 35 and a polarization beam splitter 36;
the laser source 30 is used for emitting laser;
the acousto-optic modulator 31 is configured to split laser light into one path of light with unchanged frequency, which is incident to the first beam splitter 32, and another path of light with frequency shift, which is incident to the second beam splitter 33;
the second beam splitter 33 and the reflector 34 are sequentially arranged along a light path, and the reflector 34 reflects light to the half-wave plate 35 and then enters the polarization beam splitter 36;
the first beam splitter 32 and the polarization beam splitter 36 are sequentially arranged along a light path, and the frequency-shifted light reflected by the second beam splitter 33 enters the first beam splitter 32 and is transmitted out through the first beam splitter 32;
the frequency-unchanged light reflected by the first beam splitter 32 is combined with the frequency-shifted light transmitted by the first beam splitter 32 as reference light, and the light output by the polarization beam splitter 36 is used as measurement light.
In a specific embodiment, the first wavelength value belongs to the red wavelength band and the second wavelength value belongs to the blue wavelength band.
Specifically, the first wavelength value is 0.6328 μm, and the generated two-frequency component light has a 3MHz frequency shift. An Agilent5517C laser may be used in particular.
The second light source adopts the light source with the structure, the laser source outputs horizontal polarized light with the wavelength of 0.4131 mu m, the light source used by the exposure system can be selected, and the measuring light lambda with unchanged frequency is formed by the acousto-optic modulator2mReference light λ with a sum frequency shift of 20MHz2r。
In a specific embodiment, referring to fig. 2 and 4, the polarization splitting prism is spliced by a first prism having a parallelogram cross section and a second prism having a right trapezoid cross section, and a first side surface of the first prism is attached to an inclined surface of the second prism. One side surface of the first prism, which is opposite to the first side surface, is a reflecting surface.
The present invention provides a displacement measurement optical system for a stage of a lithography system. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (9)
1. A displacement measurement optical system applied to a workbench of a photoetching system is characterized by comprising a first difference frequency interference device, a second difference frequency interference device, a first reflecting mirror, a second reflecting mirror and a signal processing device;
the position of the first reflector is fixed, and the second reflector is connected with the workbench and can move along with the workbench;
the first difference frequency interference device is used for generating difference frequency coherent light with the central wavelength being a first wavelength value, respectively transmitting two frequency component lights to the first reflector and the second reflector, and receiving interference light formed by converging two beams of light after returning;
the second difference frequency interference device is used for generating difference frequency coherent light with the central wavelength being a second wavelength value, respectively transmitting two frequency component lights to the first reflector and the second reflector, and receiving interference light formed by converging two beams of light after returning;
the signal processing device is used for calculating and obtaining a first optical path displacement described by a first wavelength value according to the interference image recorded by the first difference frequency interference device, calculating and obtaining a second optical path displacement described by a second wavelength value according to the interference image recorded by the second difference frequency interference device, and calculating the displacement of the second reflecting mirror for eliminating the environmental factor disturbance according to the first optical path displacement and the second optical path displacement,the environmental factors include temperature, pressure and CO2Concentration;
the device also comprises a third reflector; the third reflector is fixed on the exposure system;
the first difference frequency interference device is further configured to transmit two frequency component lights with center wavelengths of first wavelength values to the first reflector and the third reflector, respectively, wherein the same frequency component light as that transmitted to the second reflector is transmitted to the third reflector, and the two beams of light are received and returned to join to form interference light;
the second difference frequency interference device is further configured to transmit two frequency component lights with center wavelengths of second wavelength values to the first reflector and the third reflector, respectively, wherein the same frequency component light as the frequency component light transmitted to the second reflector is transmitted to the third reflector, and the interference light formed by converging the two beams of light after returning is received;
the signal processing device is further used for calculating a third optical path displacement described by a first wavelength value according to the interference image recorded by the first difference frequency interference device, calculating a fourth optical path displacement described by a second wavelength value according to the interference image recorded by the second difference frequency interference device, and calculating and eliminating environmental factor disturbance, light source stability disturbance and displacement of the second reflector of the exposure system, wherein the displacement is disturbed by thermal expansion according to actual displacement of the third reflector, the third optical path displacement and the fourth optical path displacement;
specifically, the displacement Lc of the second reflector is obtained by calculation according to the following formula:
2. A displacement measuring optical system as applied to a stage of a lithography system as recited in claim 1, further comprising an optical mirror:
the optical mirror is located at the intersection of the emergent light beams of the first difference frequency interference device and the second difference frequency interference device, and is used for transmitting light with a central wavelength of a first wavelength value and reflecting light with the central wavelength of a second wavelength value.
3. Displacement measuring optical system to be applied to a stage of a lithography system according to claim 1,
the first difference frequency interference device includes:
the first light source is used for generating difference frequency coherent light with the central wavelength being a first wavelength value;
the first polarization beam splitter prism is used for respectively enabling two frequency components of the difference frequency coherent light generated by the first light source to enter the first reflecting mirror and the second reflecting mirror and converging the light returned by the first reflecting mirror and the second reflecting mirror;
the first optical receiver is connected with the signal processing device and used for receiving the converged interference light transmitted by the first polarization beam splitter prism;
the second difference frequency interference device includes:
a second light source for generating difference frequency coherent light having a center wavelength of a second wavelength value;
the second polarization beam splitter prism is used for respectively transmitting the two frequency components of the difference frequency coherent light generated by the second light source to the first reflecting mirror and the second reflecting mirror and converging the light returned by the first reflecting mirror and the second reflecting mirror;
and the second optical receiver is connected with the signal processing device and used for receiving the converged interference light transmitted by the second polarization beam splitter prism.
4. The displacement measuring optical system of claim 3, wherein a quarter-wave plate is disposed on the optical path between the first difference frequency interference device and the first mirror and on the optical path between the first difference frequency interference device and the second mirror;
and quarter wave plates are arranged on the light path between the second difference frequency interference device and the first reflecting mirror and the light path between the second difference frequency interference device and the second reflecting mirror.
5. Displacement measuring optical system to be applied to a stage of a lithography system according to claim 1,
the first difference frequency interference device includes:
the first light source is used for generating difference frequency coherent light with the central wavelength being a first wavelength value;
the first light splitting mirror is arranged on a light path between the first light source and the first polarization light splitting prism, and is used for splitting light emitted by the first light source into two beams of light with parallel propagation directions, and the two beams of light are incident to the first polarization light splitting prism;
the first polarization beam splitter prism is used for respectively enabling two frequency components of one beam of incident difference frequency coherent light to enter the first reflecting mirror and the second reflecting mirror, merging the light returning from the first reflecting mirror and the second reflecting mirror, respectively enabling two frequency components of the other beam of incident difference frequency coherent light to enter the first reflecting mirror and the third reflecting mirror, and merging the light returning from the first reflecting mirror and the third reflecting mirror;
the first optical receiver is connected with the signal processing device and used for receiving interference light which is propagated by the first polarization beam splitter prism and is formed by merging the return light of the first reflector and the return light of the second reflector;
the third optical receiver is connected with the signal processing device and used for receiving interference light which is transmitted by the first polarization beam splitter prism and is formed by merging the return light of the first reflector and the return light of the third reflector;
the second difference frequency interference device includes:
a second light source for generating difference frequency coherent light having a center wavelength of a second wavelength value;
the second beam splitter is arranged on a light path between the second light source and the second polarization beam splitter prism, and is used for splitting light emitted by the second light source into two beams of light with parallel propagation directions, and the two beams of light are incident to the second polarization beam splitter prism;
the second polarization beam splitter prism is used for respectively enabling two frequency components of one beam of incident difference frequency coherent light to enter the first reflecting mirror and the second reflecting mirror, converging the light returning from the first reflecting mirror and the second reflecting mirror, respectively enabling two frequency components of the other beam of incident difference frequency coherent light to enter the first reflecting mirror and the third reflecting mirror, and converging the light returning from the first reflecting mirror and the light returning from the third reflecting mirror;
a second optical receiver connected to the signal processing device, for receiving the interference light propagated by the second polarization beam splitter prism and obtained by combining the return light from the first reflecting mirror and the return light from the second reflecting mirror;
and the fourth light receiver is connected with the signal processing device and used for receiving the interference light which is transmitted by the second polarization beam splitter prism and is formed by merging the return light of the first reflector and the return light of the third reflector.
6. The displacement measuring optical system for a stage of a lithography system according to claim 5, wherein a quarter-wave plate is disposed on an optical path between the first difference frequency interference device and the first mirror, on an optical path between the first difference frequency interference device and the second mirror, and on an optical path between the first difference frequency interference device and the third mirror;
quarter-wave plates are arranged on the light path between the second difference frequency interference device and the first reflecting mirror, the light path between the second difference frequency interference device and the second reflecting mirror and the light path between the second difference frequency interference device and the third reflecting mirror.
7. The displacement measuring optical system applied to the workbench of lithography system according to any of claims 3-6, wherein the light source comprises a laser source, an acousto-optic modulator, a first beam splitter, a second beam splitter, a mirror, a half wave plate and a polarizing beam splitter;
the laser source is used for emitting laser;
the acousto-optic modulator is used for dividing laser into one path of light with unchanged frequency to be incident to the first beam splitter, and the other path of light with frequency shift to be incident to the second beam splitter;
the second spectroscope and the reflector are sequentially arranged along a light path, and the reflector reflects light to the half-wave plate and then emits the light to the polarization spectroscope;
the first spectroscope and the polarization spectroscope are sequentially arranged along a light path, and the frequency-shifted light reflected by the second spectroscope is incident to the first spectroscope and is transmitted out through the first spectroscope;
the frequency-unchanged light reflected by the first beam splitter is combined with the frequency-shifted light transmitted by the first beam splitter to serve as reference light, and the light output by the polarization beam splitter serves as measurement light.
8. The displacement measuring optical system as claimed in claim 1, wherein the first wavelength value belongs to a red wavelength band and the second wavelength value belongs to a blue wavelength band.
9. The optical displacement measuring system applied to a stage of a lithography system according to claim 1, wherein a temperature sensor for measuring temperature and a humidity sensor for measuring humidity are disposed on an optical path between the second and third mirrors and the difference frequency interference device.
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| CN1260474A (en) * | 1999-01-08 | 2000-07-19 | 惠普公司 | Structure of double wavelength heterodyne interferometer for compensating air disturbance |
| CN103697807A (en) * | 2013-12-13 | 2014-04-02 | 清华大学 | Double-frequency laser displacement and angle interferometer |
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| JP4939765B2 (en) * | 2005-03-28 | 2012-05-30 | 株式会社日立製作所 | Displacement measuring method and apparatus |
| CN101413783B (en) * | 2008-07-23 | 2012-06-27 | 中国航空工业第一集团公司北京长城计量测试技术研究所 | Double-frequency laser interferometry apparatus |
| CN202853565U (en) * | 2012-06-29 | 2013-04-03 | 上海理工大学 | Acousto-optic heterodyne ineterferometer light path device |
| CN103743708B (en) * | 2013-12-11 | 2015-11-11 | 浙江理工大学 | The method of Laser synthesizing wavelength interferometry air refraction fluctuation |
| CN106643478B (en) * | 2017-03-03 | 2018-05-15 | 中国科学院长春光学精密机械与物理研究所 | A kind of displacement measurement optical system |
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| CN1260474A (en) * | 1999-01-08 | 2000-07-19 | 惠普公司 | Structure of double wavelength heterodyne interferometer for compensating air disturbance |
| CN103697807A (en) * | 2013-12-13 | 2014-04-02 | 清华大学 | Double-frequency laser displacement and angle interferometer |
| CN107192336A (en) * | 2017-05-26 | 2017-09-22 | 浙江大学 | Displacement measurement system and method during dual wavelength superhet interference large-range high-precision real |
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