CN110966939A - Interferometric measuring device, measuring method and photoetching equipment - Google Patents
Interferometric measuring device, measuring method and photoetching equipment Download PDFInfo
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- CN110966939A CN110966939A CN201811141969.5A CN201811141969A CN110966939A CN 110966939 A CN110966939 A CN 110966939A CN 201811141969 A CN201811141969 A CN 201811141969A CN 110966939 A CN110966939 A CN 110966939A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
- G01B9/02017—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations
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Abstract
The invention discloses an interference measurement device, a measurement method and a photoetching device. The object that awaits measuring moves along first direction, and perpendicular to first direction and be located the relative both sides of the object that awaits measuring and be equipped with first reflection unit and second reflection unit, this interferometric device includes: the polarization light splitting unit is used for splitting light rays emitted by the light source into measuring light and reference light; the measuring light path unit is used for reflecting the measuring light at least once on the reflecting surface of the first reflecting unit when the measuring light passes through; a reference light path unit which reflects the reference light at least once at the second reflecting unit when the reference light passes; and the beam combining unit is used for combining the measuring light and the reference light into one beam to generate interference. According to the technical scheme, the reference light is introduced to the other side of the object to be measured, so that the reference light carries frequency change information opposite to the measurement light, the light subdivision is doubled, the accurate displacement measurement of the object to be measured is realized, the measurement light and the reference light do not have a common-path part before interference, errors caused by polarization frequency aliasing are effectively avoided, and the measurement accuracy is improved.
Description
Technical Field
Embodiments of the present invention relate to optical measurement technologies, and in particular, to an interferometric measuring device, a measuring method, and a lithographic apparatus.
Background
With the rapid development of modern industry, displacement measurement becomes very important, and the requirements on the speed and the precision of displacement measurement, such as the measurement of micro-deformation displacement of a machine tool under a bearing condition, the precise positioning of a workpiece table and a mask table of a photoetching machine, and the like, are very high. The optical interference displacement measurement has high test sensitivity and precision, and is widely applied. Among them, the most commonly used optical interferometric displacement measuring devices include michelson interferometric measuring devices and heterodyne laser interferometric measuring devices.
The Michelson interference measurement is the most classical optical interference displacement measurement method, the technology is mature and reliable after long-term research and development, and the resolution ratio after circuit subdivision can reach 1 nm. However, the measurement accuracy is directly related to the stability of the wavelength of the light source, so that the requirements on the environment where the light source and the light path are located are high, and the measurement range is greatly limited due to the existence of sinusoidal errors. The heterodyne laser interference measuring device is commonly called as a double-frequency laser interferometer and has the characteristics of large measuring range and extremely high resolution and precision.
In the traditional dual-frequency laser interferometer structure, incident light is divided into two beams, one beam is used as reference light, and the other beam is used as measuring light, wherein only the measuring light is in contact with an object to be measured, and the reference light is not in contact with the object to be measured, so that displacement information to be measured cannot be carried all the time, the reference light is not fully utilized, and the measuring precision of the dual-frequency laser interferometer is not high enough; in addition, in the existing dual-frequency laser interferometer structure, in order to double optical subdivision, a long common path part is added to reference light and measurement light, and the polarization frequency aliasing caused by the long common path part increases the nonlinear error of the interferometer, so that the measurement repeatability of the interferometer is reduced.
Disclosure of Invention
The embodiment of the invention provides an interference measurement device, a measurement method and photoetching equipment, which are used for realizing accurate displacement measurement of an object to be measured and effectively improving the measurement precision.
In a first aspect, an embodiment of the present invention provides an interferometric measuring device, in which an object to be measured moves along a first direction, and a first reflection unit and a second reflection unit are disposed at two opposite sides of the object to be measured, perpendicular to the first direction, the interferometric measuring device including:
the polarization splitting unit is used for splitting light rays emitted by the light source into measurement light in a first polarization direction and reference light in a second polarization direction, and the first polarization direction is vertical to the second polarization direction;
the measuring light path unit is positioned on one side of the first reflection unit, which is far away from the object to be measured, and the measuring light is reflected at least once on the reflection surface of the first reflection unit when passing through the measuring light path unit;
the reference light path unit is positioned on one side of the second reflection unit, which is far away from the object to be detected, and the reference light is reflected at least once by the second reflection unit when passing through the reference light path unit;
and the beam combining unit is used for combining the measuring light output by the measuring light path unit and the reference light output by the reference light path unit into one beam to generate interference.
In a second aspect, an embodiment of the present invention further provides an interferometric method, which is performed by the above interferometric apparatus, and includes:
dividing light rays emitted by a light source into measurement light in a first polarization direction and reference light in a second polarization direction by a polarization light splitting unit, wherein the first polarization direction is vertical to the second polarization direction;
transmitting the measuring light through a measuring light path unit, wherein the measuring light is reflected at least once on a reflecting surface of the first reflecting unit when passing through the measuring light path unit;
transmitting the reference light through a reference light path unit, wherein the reference light is reflected at least once on a reflecting surface of the second reflecting unit when passing through the reference light path unit;
and combining the measuring light output by the measuring light path unit and the reference light output by the reference light path unit into one beam through a beam combining unit to generate interference.
In a third aspect, an embodiment of the present invention further provides a lithographic apparatus, including any one of the interferometric measuring devices described above.
The embodiment of the invention provides an interference measurement device, an object to be measured moves along a first direction, a first reflection unit and a second reflection unit are arranged on two opposite sides of the object to be measured and are perpendicular to the first direction, the interference measurement device comprises: the polarization splitting unit is used for splitting light rays emitted by the light source into measurement light in a first polarization direction and reference light in a second polarization direction, and the first polarization direction is vertical to the second polarization direction; the measuring light path unit is positioned on one side of the first reflection unit, which is far away from the object to be measured, and the measuring light is reflected at least once on the reflection surface of the first reflection unit when passing through the measuring light path unit; the reference light path unit is positioned on one side of the second reflection unit, which is far away from the object to be detected, and the reference light is reflected at least once in the second reflection unit when passing through the reference light path unit; and the beam combining unit is used for combining the measuring light output by the measuring light path unit and the reference light output by the reference light path unit into one beam to generate interference. Dividing light emitted by a light source into measurement light in a first polarization direction and reference light in a second polarization direction by a polarization light splitting unit; the measuring light is reflected at least once on the reflecting surface of the first reflecting unit when passing through the measuring light path unit; the reference light is reflected at least once by the second reflecting unit when passing through the reference light path unit; the measuring light and the reference light are combined into one beam through the beam combining unit to generate interference, the reference light is introduced to the other side of the object to be measured to enable the other side to carry frequency change information opposite to the measuring light, on the premise that the frequency aliasing effect is not increased, the light subdivision is doubled, the accurate displacement measurement of the object to be measured is achieved, the measuring light and the reference light do not have a common-path part before interference, errors caused by polarization frequency aliasing can be effectively avoided, and the measuring accuracy is effectively improved.
Drawings
FIG. 1 is a schematic structural diagram of an interferometric measuring device according to an embodiment of the invention;
FIG. 2 is a schematic diagram of another interferometric device according to an embodiment of the invention;
FIG. 3 is a schematic diagram of the beam splitting of a polarization beam splitter prism;
FIG. 4 is a schematic structural diagram of another interferometric measuring device provided in an embodiment of the present invention;
FIG. 5 is a schematic structural diagram of another interferometric device provided in an embodiment of the invention;
FIG. 6 is a schematic structural diagram of another interferometric measuring device provided in an embodiment of the present invention;
fig. 7 is a schematic flow chart of an interferometric method according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It should be noted that the terms "upper", "lower", "left", "right", and the like used in the description of the embodiments of the present invention are used in the angle shown in the drawings, and should not be construed as limiting the embodiments of the present invention. In addition, in this context, it is also to be understood that when an element is referred to as being "on" or "under" another element, it can be directly formed on "or" under "the other element or be indirectly formed on" or "under" the other element through an intermediate element. The terms "first," "second," and the like, are used for descriptive purposes only and not for purposes of limitation, and do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The specific meanings of the above terms in the present invention can be understood in specific cases by those skilled in the art.
Fig. 1 is a schematic structural diagram of an interferometric measuring device according to an embodiment of the present invention, which can be used to measure a displacement of an object 10 to be measured, where the object 10 to be measured moves along a first direction, and a first reflection unit 11 and a second reflection unit 12 are disposed on two opposite sides of the object 10 to be measured, perpendicular to the first direction, and the interferometric measuring device includes: a polarization splitting unit 20, configured to split light emitted from the light source 30 into measurement light a with a first polarization direction and reference light b with a second polarization direction, where the first polarization direction is perpendicular to the second polarization direction; the measuring light path unit 40 is positioned on one side of the first reflection unit 11, which is far away from the object to be measured 10, and the measuring light a is reflected at least once on the reflection surface of the first reflection unit 11 when passing through the measuring light path unit 40; the reference light path unit 50 is positioned on one side of the second reflection unit 12, which is far away from the object to be measured 10, and the reference light b is reflected at least once by the second reflection unit 12 when passing through the reference light path unit 50; and a beam combining unit 60 for combining the measuring light a output by the measuring optical path unit 40 and the reference light b output by the reference optical path unit 50 into one beam to generate interference.
It will be appreciated that the first direction is either the positive or negative direction of the x-axis and the light source 30 may be a laser, such as a he-ne laser. The polarization beam splitting unit 20 has a light-transmitting polarization direction, light rays with the polarization direction parallel to the light-transmitting polarization direction are transmitted, light rays with the polarization direction perpendicular to the light-transmitting polarization direction are reflected, the light source can emit light rays with two polarization directions, the light rays pass through the polarization beam splitting unit 20 and are divided into measurement light with a first polarization direction and reference light with a second polarization direction, and the first polarization direction is perpendicular to the second polarization direction. The measurement light path unit 40 is configured to transmit measurement light a, the reference light path unit 50 is configured to transmit reference light b, the measurement light a and the reference light b are reflected by the first reflection unit 11 and the second reflection unit 12 at least once during transmission, when the object to be measured 10 is displaced, the measurement light a and the reference light b have equal values and opposite frequency shifts according to the doppler effect, when the measurement light a and the reference light b carrying displacement information are transmitted to the beam combining unit 60 to interfere, and the displacement information of the object to be measured 10 can be obtained by measuring the interference information. The beam combining unit 60 may be a beam splitter.
According to the interference measurement device provided by the embodiment of the invention, light rays emitted by a light source are divided into measurement light in a first polarization direction and reference light in a second polarization direction through a polarization light splitting unit; the measuring light is reflected at least once on the reflecting surface of the first reflecting unit when passing through the measuring light path unit; the reference light is reflected at least once by the second reflecting unit when passing through the reference light path unit; the measuring light and the reference light are combined into one beam through the beam combining unit to generate interference, the reference light is introduced to the other side of the object to be measured to enable the other side to carry frequency change information opposite to the measuring light, on the premise that the frequency aliasing effect is not increased, the light subdivision is doubled, the accurate displacement measurement of the object to be measured is achieved, the measuring light and the reference light do not have a common-path part before interference, errors caused by polarization frequency aliasing can be effectively avoided, and the measuring accuracy is effectively improved.
Alternatively, the frequencies of the measurement light and the reference light are different.
It is understood that the measurement results of the single-frequency interferometer are affected by internal factors (e.g., electronic noise, long-term drift, etc.) as well as external factors (e.g., environmental changes, such as temperature, atmospheric pressure, refractive index, etc.) of the light source. By setting the frequency difference between the measurement light and the reference light, a high-precision dual-frequency interferometer can be formed. Specifically, an axial magnetic field of about 0.03 tesla may be applied to a he-ne laser, which produces two different frequencies of left-handed and right-handed circularly polarized light due to the zeeman splitting effect and the frequency pulling effect, the difference between the frequencies being about 1.5 MHz. The two linearly polarized lights are formed by 1/4 wave plates and are divided into two paths by the beam splitter. One path of light is converted into a reference beam with the frequency of f1-f2 after passing through a polaroid, and the other path of light is divided into two paths after passing through a polarization beam splitter: one path becomes a beam containing only f1, and the other path becomes a beam containing only f 2. The light beam with frequency f1 and the light beam with frequency f2 output by the helium neon laser can be used as measuring light and reference light respectively.
Optionally, the measurement light is reflected twice on the reflection surface of the first reflection unit, and the reference light is reflected twice on the reflection surface of the second reflection unit.
Illustratively, an optical eight-segment structure or an optical four-segment structure may be formed below by taking the case where the measurement light frequency is f1, the reference light frequency is f2, and the measurement light and the reference light are reflected twice by the first reflection unit and the second reflection unit, respectively. It should be noted that the following description is exemplary and should not be construed as limiting the invention, and other embodiments are possible based on the concept and drawings of the embodiments of the invention and are within the scope of the embodiments of the invention.
Fig. 2 is a schematic structural diagram of another interferometric measuring device according to an embodiment of the present invention. Referring to fig. 2, the interferometric measuring device provided in this embodiment can implement optical subdivision, and optionally, the measurement optical path unit 40 includes a first double-sided mirror 41, and the measurement light is reflected on the reflection surface of the first reflection unit 11, the first reflection surface of the first double-sided mirror 41, the second reflection surface of the first double-sided mirror 42, and the reflection surface of the first reflection unit 11 respectively; the reference light path unit 50 includes a second double-sided mirror 51, and the reference light is reflected by the reflection surface of the second reflection unit 12, the first reflection surface of the second double-sided mirror 51, the second reflection surface of the second double-sided mirror 51, and the reflection surface of the second reflection unit 12, respectively.
Optionally, with continued reference to fig. 2, the measurement optical path unit 40 further includes a first polarization beam splitter 42, a first quarter-wave plate 43, and a second polarization beam splitter 44; the measurement light a is reflected by the first polarization beam splitter 42, enters the reflection surface of the first reflection unit 11 through the first quarter-wave plate 43, is reflected by the reflection surface of the first reflection unit 11, passes through the first quarter-wave plate 43, is transmitted by the first polarization beam splitter 42, is reflected by the first reflection surface and the second reflection surface of the first double-sided reflector 41, is transmitted by the second polarization beam splitter 44, enters the reflection surface of the first reflection unit 11 through the first quarter-wave plate 43 again, is reflected by the reflection surface of the first reflection unit 11, passes through the first quarter-wave plate 43, is reflected by the second polarization beam splitter 44, and reaches the beam combining unit 60; the reference optical path unit 50 further includes a third polarizing beam splitter 52, a second quarter wave plate 53, and a fourth polarizing beam splitter 54; the reference light b is reflected by the third polarization beam splitter 52, enters the reflection surface of the second reflection unit 12 through the second quarter-wave plate 53, is reflected by the reflection surface of the second reflection unit 12, passes through the second quarter-wave plate 53, is transmitted by the third polarization beam splitter 52, is reflected by the first reflection surface and the second reflection surface of the second double-sided mirror 51, is transmitted by the fourth polarization beam splitter 54, enters the reflection surface of the second reflection unit 12 through the second quarter-wave plate 53 again, is reflected by the reflection surface of the second reflection unit 12, passes through the second quarter-wave plate 53, is reflected by the fourth polarization beam splitter 54, and reaches the beam combining unit 60.
The measurement optical path unit 40 and the reference optical path unit 50 may use the same optical device, and the interferometric measuring device is substantially symmetrical in the measurement direction. The first double-sided mirror 41 may be a pyramid prism for returning the measurement light in the original direction and being offset from the original light by a distance. The first and second pbs 42, 44 can be polarization beam splitters or polarization beam splitting prisms, preferably polarization beam splitting prisms, which facilitate device assembly. The polarization beam splitter prism is an optical element for separating horizontal polarization and vertical polarization of light, and fig. 3 is a beam splitting diagram of the polarization beam splitter prism. Referring to fig. 3, the polarization beam splitter prism is an optical element that uses the property that when a light ray is incident at the brewster angle, the transmittance of parallel polarized light (P light) is 1 and the transmittance of perpendicular polarized light (S light) is less than 1, so that after the light ray passes through the multilayer film structure multiple times at the brewster angle, the P polarized component is completely transmitted and most of the S polarized component is reflected (at least 90% or more). It will be appreciated that when P-polarized light passes twice through the quarter wave plate it becomes S-polarized light and vice versa.
The measurement light a incident to the first polarization beam splitter 42 is S-polarized light, the S-polarized light is reflected, passes through the first quarter wave plate 43 and enters the reflection surface of the first reflection unit 11, is reflected by the reflection surface of the first reflection unit 11 and then passes through the first quarter wave plate 43 again, and is then converted into P-polarized light, so that the measurement light a is transmitted when passing through the first polarization beam splitter 42 again, is reflected twice by the first double-sided reflector 41 without changing the polarization state, passes through the second polarization beam splitter 44 for transmission, passes through the first quarter wave plate 43 for two times, is converted into S-polarized light again, is reflected by the second polarization beam splitter 44, and finally reaches the beam combining unit 60. The optical path of the reference light b is similar and will not be described again.
Optionally, the measurement optical path unit and/or the reference optical path unit further includes a first mirror, and the first mirror is configured to enable the measurement light emitted from the measurement optical path unit and the reference light emitted from the reference optical path unit to reach the beam combining unit.
Illustratively, with continuing reference to fig. 2, in the present embodiment, the beam combining unit 60 is located on the output optical path of the reference optical path unit 50, and the measurement optical path unit 40 includes a first mirror 45 for reflecting the measurement light a to the beam combining unit 60. It should be understood that the beam combining unit 60 may also be located on the output optical path of the measurement optical path unit 40, and a first mirror is disposed on the reference optical path unit 50, or both the measurement optical path unit 40 and the reference optical path unit 50 are disposed with a first mirror, which is not limited in this embodiment of the present invention.
With reference to fig. 2, optionally, the measurement light a is the transmission light of the polarization beam splitting unit 20, the reference light b is the reflection light of the polarization beam splitting unit 20, the interferometric measuring device further includes a first one-half wave plate 70 and a second reflecting mirror 80, the first one-half wave plate 70 is located on the transmission light path of the polarization beam splitting unit 20, and the measurement light a is transmitted to the measurement light path unit 40 after passing through the first one-half wave plate 70; the second reflecting mirror 80 is located on the reflected light path of the polarization beam splitting unit 20, and the reference light b is reflected to the reference light path unit after passing through the second reflecting mirror 80.
It is understood that since the transmitted light of the polarization splitting unit 20 is P-polarized light and the measurement light a is S-polarized light, the first one-half wave plate 70 is disposed to convert the transmitted P-polarized light of the polarization splitting unit 20 into S-polarized light to form the measurement light a. Since the reflected light is S-polarized light but cannot be directly incident on the reference optical path unit 50, the second mirror 80 needs to be provided.
Fig. 4 is a schematic structural diagram of another interferometric measuring device according to an embodiment of the present invention. Referring to fig. 4, optionally, the measurement light a is the reflected light of the polarization splitting unit 20, the reference light b is the transmitted light of the polarization splitting unit 20, the interference measurement apparatus further includes a second half-wave plate 71 and a third mirror 81, and the measurement light a reaches the measurement light path unit 40 after being reflected by the polarization splitting unit 20; the third reflecting mirror 81 is located on the transmission light path of the polarization beam splitting unit 20, the second half-wave plate 71 is located on the reflection light path of the third reflecting mirror 81, and the reference light b is transmitted to the reference light path unit 50 after passing through the second half-wave plate 71.
It is understood that since the transmitted light of the polarization splitting unit 20 is P-polarized light and the reference light is S-polarized light, the second half-wave plate 71 is arranged to convert the transmitted P-polarized light of the polarization splitting unit 20 into S-polarized light, thereby forming the reference light b. Since the transmitted light cannot be directly incident on the reference light path unit 50, the third reflecting mirror 81 needs to be provided.
In the present embodiment, if the object 10 to be measured moves to the right by Δ x in the measurement direction, the measurement light a generates a frequency shift of Δ f, and then the reference light b generates a frequency shift of- Δ f. Since the measuring light a and the reference light b respectively travel to and fro on the object 10 to be measured twice, the subdivision numbers of the measuring light a and the reference light b are both four subdivisions, so that the subdivision number of the whole device is twice of the four subdivisions, and is eight subdivisions.
According to the doppler effect, the total phase change magnitude is:
from the above formula (1):
where the coefficient 8 represents an 8 subdivision. n is the refractive index, v is the object motion velocity, f is the frequency, and c is the speed of light, it being understood that since the frequencies of f1 and f2 are at 1014Hz, and the frequency difference between f1 and f2 is about 1.5MHz, so f1 or f2 can be directly used instead of f. The phase is the integral of the frequency multiplied by 2 pi over time and represents the total phase change caused by the displacement of the object to be measured. That is, the optical path length changes by one λ for every λ/8 change in position, i.e., optical octal subdivision is achieved. The embodiment separates the light paths of the measuring light and the reference light, reduces the nonlinear error caused by frequency aliasing while realizing light subdivision and doubling, and effectively improves the measuring precision.
Fig. 5 is a schematic structural diagram of another interferometric measuring device according to an embodiment of the present invention. Referring to fig. 5, the interferometric measuring device provided in this embodiment can implement optical four-subdivision, and optionally, the measurement optical path unit 40 includes a first double-sided mirror 41, the reference optical path unit 50 includes a second double-sided mirror 51, the first reflecting unit 11 includes a third double-sided mirror, and the second reflecting unit 12 includes a fourth double-sided mirror; the first reflecting surface 111 of the third double-sided mirror is parallel to the first reflecting surface 411 of the first double-sided mirror 41, the second reflecting surface 112 of the third double-sided mirror is parallel to the second reflecting surface 412 of the first double-sided mirror 41, and the measuring light a is reflected by the first reflecting surface 411 of the first double-sided mirror 41, the first reflecting surface 111 of the third double-sided mirror, the second reflecting surface 112 of the third double-sided mirror, and the second reflecting surface 412 of the first double-sided mirror 41 in sequence; the first reflecting surface 121 of the fourth double-sided mirror is parallel to the first reflecting surface 511 of the second double-sided mirror 51, the second reflecting surface 122 of the fourth double-sided mirror is parallel to the second reflecting surface 512 of the second double-sided mirror 51, and the reference light b is reflected by the first reflecting surface 511 of the second double-sided mirror 51, the first reflecting surface 121 of the fourth double-sided mirror, the second reflecting surface 122 of the fourth double-sided mirror, and the second reflecting surface 512 of the second double-sided mirror 51 in this order.
Optionally, the measurement optical path unit and/or the reference optical path unit further includes a first mirror, and the first mirror is configured to enable the measurement light emitted from the measurement optical path unit and the reference light emitted from the reference optical path unit to reach the beam combining unit.
Illustratively, with continuing reference to fig. 5, in the present embodiment, the beam combining unit 60 is located on the output optical path of the reference optical path unit 50, and the measurement optical path unit 40 includes a first mirror 45 for reflecting the measurement light a to the beam combining unit 60. It should be understood that the beam combining unit 60 may also be located on the output optical path of the measurement optical path unit 40, and a first mirror is disposed on the reference optical path unit 50, or both the measurement optical path unit 40 and the reference optical path unit 50 are disposed with a first mirror, which is not limited in this embodiment of the present invention.
With reference to fig. 5, optionally, the measurement light a is the transmission light of the polarization beam splitting unit 20, the reference light b is the reflection light of the polarization beam splitting unit 20, the interferometric measuring device further includes a first one-half wave plate 70 and a second reflecting mirror 80, the first one-half wave plate 70 is located on the transmission light path of the polarization beam splitting unit 70, and the measurement light a is transmitted to the measurement light path unit 40 after passing through the first one-half wave plate 70; the second reflecting mirror 80 is located on the reflected light path of the polarization beam splitting unit 20, and the reference light b is reflected to the reference light path unit after passing through the second reflecting mirror 80.
It is understood that since the transmitted light of the polarization splitting unit 20 is P-polarized light and the reflected light is S-polarized light, the P-polarized light is converted into S-polarized light by the first one-half wave plate 70 since the P-polarized light and the S-polarized light cannot interfere with each other.
It should be noted that the first quarter wave plate 70 may also be disposed on the reflected light path of the second reflecting mirror 80 to convert the S-polarized light into the P-polarized light.
Fig. 6 is a schematic structural diagram of another interferometric measuring device according to an embodiment of the present invention. Referring to fig. 6, optionally, the measurement light a is the reflected light of the polarization splitting unit 20, the reference light b is the transmitted light of the polarization splitting unit 20, the interference measurement apparatus further includes a second half-wave plate 71 and a third mirror 81, and the measurement light a reaches the measurement light path unit 40 after being reflected by the polarization splitting unit 20; the third reflecting mirror 81 is located on the transmission light path of the polarization beam splitting unit 20, the second half-wave plate 71 is located on the reflection light path of the third reflecting mirror 81, and the reference light b is transmitted to the reference light path unit 50 after passing through the second half-wave plate 71.
It is understood that since the transmitted light of the polarization splitting unit 20 is P-polarized light and the reflected light is S-polarized light, the P-polarized light is converted into S-polarized light by the second half wave plate 71 since the P-polarized light and the S-polarized light cannot interfere with each other.
The second half wave plate 71 may be disposed on the reflection optical path of the polarization splitting unit 20 to convert the S-polarized light into the P-polarized light. Since the transmitted light cannot be directly incident on the reference light path unit 50, the third reflecting mirror 81 needs to be provided.
In the present embodiment, if the object 10 to be measured moves to the right by Δ x in the measurement direction, the measurement light a generates a frequency shift of Δ f, and then the reference light b generates a frequency shift of- Δ f. Since the measuring light a and the reference light b respectively travel to and fro on the object 10 to be measured once, the subdivision numbers of the measuring light a and the reference light b are both two subdivisions, so that the subdivision number of the whole device is two times that of the two subdivisions, and is four subdivisions.
According to the doppler effect, the total phase change magnitude is:
from the above formula (2):
where the coefficient 4 represents a 4 subdivision. n is the refractive index, v is the object motion velocity, f is the frequency, and c is the speed of light, it being understood that since the frequencies of f1 and f2 are at 1014Hz, and the frequency difference between f1 and f2 is about 1.5MHz, so f1 or f2 can be directly used instead of f. The phase is the integral of the frequency multiplied by 2 pi over time and represents the total phase change caused by the displacement of the object to be measured. That is, the optical path length changes by one λ for every λ/4 change in position, i.e., optical four subdivision is achieved. The embodiment separates the light paths of the measuring light and the reference light, reduces the nonlinear error caused by frequency aliasing while realizing light subdivision and doubling, and effectively improves the measuring precision.
With continuing reference to fig. 4 and 6, optionally, the interferometric measuring device further includes a measuring light protection unit 46 located on the measuring light path from the measuring light path unit 40 to the beam combining unit 60, the measuring light protection unit 46 being configured to eliminate interference of environmental changes on the measuring light a; and a reference light protection unit 56 located on the reference light path from the polarization beam splitting unit 20 to the reference light path unit 50, wherein the reference light protection unit 56 is used for eliminating interference of environmental changes to the reference light b.
Optionally, the measuring light protection unit comprises any one of a glass column, a glass tube or an aluminum tube; the reference light protection unit includes any one of a glass column, a glass tube, or an aluminum tube.
Between the polarization beam splitting unit 20 and the third reflecting mirror 81The optical path between the first reflector 45 and the beam combining unit 60 may have a large optical path due to the large size of the object 10 to be measured, and if the two optical paths are exposed outside, the environment may affect the two optical paths. In order to reduce or avoid the problem, the two optical paths are static, and therefore, the measuring light protection unit 46 and the reference light protection unit 56, which are made of the same material and have the same length, for example, may be glass strips, so that the light reflected by the polarization splitting unit 20 and the first reflecting mirror 45 respectively passes through the glass strips directly and is incident on the third reflecting mirror 81 and the beam combining unit 60 respectively. After the glass strip is added, on one hand, the influence of air disturbance and atmospheric pressure change on the light path can be completely avoided, and on the other hand, the thermal expansion coefficient and the refractive index temperature coefficient of the glass are both 10-6The magnitude of the change in ambient temperature is very slow, about 0.5 ℃/h, and is obtained from the OPD ═ l.DELTA.T (n β + gamma), where OPD represents the optical path difference, β represents the coefficient of thermal expansion of the glass, gamma represents the temperature coefficient of refractive index of the glass, and L represents the distance traveled by the light, and the change in ambient temperature after the addition of the glass strip is very small.
In addition to the above embodiments, the core solution of the present invention can be combined with basically any conventional laser interferometer including a reference optical path and a measurement optical path to form a laser interferometer with double-path sharing and double optical subdivision.
Fig. 7 is a schematic flow chart of an interferometric method according to an embodiment of the present invention. Referring to fig. 7, the interferometric method is performed by any of the interferometric devices described above, comprising:
step 110, dividing the light emitted by the light source into measurement light in a first polarization direction and reference light in a second polarization direction by the polarization beam splitting unit, wherein the first polarization direction is perpendicular to the second polarization direction.
And 120, transmitting the measuring light through the measuring light path unit, wherein the measuring light is reflected at least once on the reflecting surface of the first reflecting unit when passing through the measuring light path unit.
Step 130, transmitting the reference light through the reference light path unit, wherein the reference light is reflected at least once on the reflecting surface of the second reflecting unit when passing through the reference light path unit.
Step 140, combining the measuring light output by the measuring light path unit and the reference light output by the reference light path unit into one beam through the beam combining unit to generate interference.
According to the interference measurement method provided by the embodiment of the invention, light emitted by a light source is divided into measurement light in a first polarization direction and reference light in a second polarization direction by a polarization light splitting unit; the measuring light is reflected at least once on the reflecting surface of the first reflecting unit when passing through the measuring light path unit; the reference light is reflected at least once by the second reflecting unit when passing through the reference light path unit; the measuring light and the reference light are combined into one beam through the beam combining unit to generate interference, the reference light is introduced to the other side of the object to be measured to enable the other side to carry frequency change information opposite to the measuring light, on the premise that the frequency aliasing effect is not increased, the light subdivision is doubled, the accurate displacement measurement of the object to be measured is achieved, the measuring light and the reference light do not have a common-path part before interference, errors caused by polarization frequency aliasing can be effectively avoided, and the measuring accuracy is effectively improved.
An embodiment of the present invention further provides a lithographic apparatus including any one of the interferometric measuring devices provided in the above embodiments. Since the lithographic apparatus provided by the embodiment of the present invention includes the interferometric measuring device provided in any of the above embodiments, the same and corresponding advantages as those of the interferometric measuring device are achieved, and details are not repeated here.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (13)
1. An interference measuring device, characterized in that, the object to be measured moves along a first direction, perpendicular to the first direction and located the relative both sides of the object to be measured are provided with first reflection unit and second reflection unit, this interference measuring device includes:
the polarization splitting unit is used for splitting light rays emitted by the light source into measurement light in a first polarization direction and reference light in a second polarization direction, and the first polarization direction is vertical to the second polarization direction;
the measuring light path unit is positioned on one side of the first reflection unit, which is far away from the object to be measured, and the measuring light is reflected at least once on the reflection surface of the first reflection unit when passing through the measuring light path unit;
the reference light path unit is positioned on one side of the second reflection unit, which is far away from the object to be detected, and the reference light is reflected at least once by the second reflection unit when passing through the reference light path unit;
and the beam combining unit is used for combining the measuring light output by the measuring light path unit and the reference light output by the reference light path unit into one beam to generate interference.
2. Interferometry device according to claim 1, wherein the frequencies of the measurement light and the reference light are different.
3. The interferometry device according to claim 1, wherein the measurement light is reflected twice on the reflective surface of the first reflection unit, and the reference light is reflected twice on the reflective surface of the second reflection unit.
4. The interferometry apparatus according to claim 3, wherein the measurement light path unit comprises a first double-sided mirror, and the measurement light is reflected on a reflection surface of the first reflection unit, a first reflection surface of the first double-sided mirror, a second reflection surface of the first double-sided mirror, and a reflection surface of the first reflection unit, respectively;
the reference light path unit comprises a second double-sided reflector, and the reference light is reflected on a reflecting surface of the second reflecting unit, a first reflecting surface of the second double-sided reflector, a second reflecting surface of the second double-sided reflector and a reflecting surface of the second reflecting unit respectively.
5. The interferometry device according to claim 4, wherein the measurement optical path unit further comprises a first polarization beam splitter, a first quarter wave plate, a second polarization beam splitter;
the measuring light is reflected by the first polarization beam splitter, enters the reflection surface of the first reflection unit through the first quarter-wave plate, is reflected by the reflection surface of the first reflection unit, passes through the first quarter-wave plate, is transmitted by the first polarization beam splitter, is reflected by the first reflection surface and the second reflection surface of the first double-sided reflector, is transmitted by the second polarization beam splitter, enters the reflection surface of the first reflection unit through the first quarter-wave plate again, passes through the first quarter-wave plate after being reflected by the reflection surface of the first reflection unit, is reflected by the second polarization beam splitter, and reaches the beam combination unit;
the reference light path unit further comprises a third polarization beam splitter, a second quarter wave plate and a fourth polarization beam splitter;
the reference light is reflected by the third polarization beam splitter, enters the reflection surface of the second reflection unit through the second quarter-wave plate, is reflected by the reflection surface of the second reflection unit, passes through the second quarter-wave plate, is transmitted by the third polarization beam splitter, is reflected by the first reflection surface and the second reflection surface of the second double-sided reflector, is transmitted by the fourth polarization beam splitter, enters the reflection surface of the second reflection unit through the second quarter-wave plate again, passes through the second quarter-wave plate after being reflected by the reflection surface of the second reflection unit, is reflected by the fourth polarization beam splitter, and reaches the beam combination unit.
6. The interferometry device according to claim 3, wherein the measurement optical path unit comprises a first double-sided mirror, the reference optical path unit comprises a second double-sided mirror, the first reflection unit comprises a third double-sided mirror, and the second reflection unit comprises a fourth double-sided mirror;
the first reflecting surface of the third double-sided reflector is parallel to the first reflecting surface of the first double-sided reflector, the second reflecting surface of the third double-sided reflector is parallel to the second reflecting surface of the first double-sided reflector, and the measuring light is reflected on the first reflecting surface of the first double-sided reflector, the first reflecting surface of the third double-sided reflector, the second reflecting surface of the third double-sided reflector and the second reflecting surface of the first double-sided reflector in sequence;
the first reflecting surface of the fourth double-sided reflector is parallel to the first reflecting surface of the second double-sided reflector, the second reflecting surface of the fourth double-sided reflector is parallel to the second reflecting surface of the second double-sided reflector, and the reference light is reflected by the first reflecting surface of the second double-sided reflector, the first reflecting surface of the fourth double-sided reflector, the second reflecting surface of the fourth double-sided reflector and the second reflecting surface of the second double-sided reflector in sequence.
7. The interferometry device according to claim 4 or 6, wherein the measurement optical path unit and/or the reference optical path unit further comprises a first mirror for allowing the measurement light emitted from the measurement optical path unit and the reference light emitted from the reference optical path unit to reach the beam combining unit.
8. The interferometry device according to claim 1, wherein the measurement light is a transmission light of the polarization beam splitting unit, the reference light is a reflection light of the polarization beam splitting unit, and further comprising a first one-half wave plate and a second mirror, wherein the first one-half wave plate is located on the transmission light path of the polarization beam splitting unit, and the measurement light is transmitted to the measurement light path unit after passing through the first one-half wave plate;
the second reflecting mirror is located on a reflection light path of the polarization beam splitting unit, and the reference light is reflected to the reference light path unit after passing through the second reflecting mirror.
9. The interferometry device according to claim 1, wherein the measurement light is a reflected light of the polarization beam splitting unit, the reference light is a transmitted light of the polarization beam splitting unit, and further comprising a second half-wave plate and a third mirror, wherein the measurement light reaches the measurement light path unit after being reflected by the polarization beam splitting unit;
the third reflector is located on a transmission light path of the polarization beam splitting unit, the second half-wave plate is located on a reflection light path of the third reflector, and the reference light is transmitted to the reference light path unit after passing through the second half-wave plate.
10. The interferometry device of claim 1, further comprising:
the measuring light protection unit is positioned on a measuring light path between the measuring light path unit and the beam combining unit and is used for eliminating the interference of environmental change on the measuring light;
and the reference light protection unit is positioned on a reference light path between the polarization beam splitting unit and the reference light path unit and is used for eliminating the interference of environmental change on the reference light.
11. The interferometry device according to claim 10, wherein the measuring light protecting unit comprises any one of a glass column, a glass tube or an aluminum tube;
the reference light protection unit includes any one of a glass column, a glass tube, or an aluminum tube.
12. An interferometric measuring method performed by an interferometric measuring device according to any one of claims 1 to 11, comprising:
dividing light rays emitted by a light source into measurement light in a first polarization direction and reference light in a second polarization direction by a polarization light splitting unit, wherein the first polarization direction is vertical to the second polarization direction;
transmitting the measuring light through a measuring light path unit, wherein the measuring light is reflected at least once on a reflecting surface of the first reflecting unit when passing through the measuring light path unit;
transmitting the reference light through a reference light path unit, wherein the reference light is reflected at least once on a reflecting surface of the second reflecting unit when passing through the reference light path unit;
and combining the measuring light output by the measuring light path unit and the reference light output by the reference light path unit into one beam through a beam combining unit to generate interference.
13. A lithographic apparatus comprising an interferometric device according to any of claims 1 to 11.
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