WO2001088474A1

WO2001088474A1 - Interval measuring device and surface shape measuring device

Info

Publication number: WO2001088474A1
Application number: PCT/JP2001/003993
Authority: WO
Inventors: Hisashi Shiozawa; Jun Kawakami
Original assignee: Nikon Corporation
Priority date: 2000-05-15
Filing date: 2001-05-14
Publication date: 2001-11-22
Also published as: JP4665290B2; JP2001324308A

Abstract

A light flux from a light source (11) is reflected off a first and second reflection surfaces (15a, 16a), and a light beam incident onto a split beam splitter (17) is split into a measuring beam (M) and a reference beam (R) having mutually inverted phases to allow the beam (M) and the beam (R) to interfere with each other at a synthetic beam splitter (22). Then, a corner mirror (18) is moved at a moving stage (20) to change the optical path length of the beam (M) to thereby change the contrast of an interference beam. A distance between the reflection surfaces (15a, 16a) is determined from the contrast of the interference beam and the position of the stage (20). Accordingly, the interval between the reflection surfaces (15a, 16a) can be obtained without increasing the size of the device as a whole even when the distances from a polarization beam splitter (13) to the first and second reflection surfaces (15a, 16a) are long. Accordingly, an interval measuring device and a surface shape measuring device are provided that can measure the intervals between, and thicknesses or surface shapes of, optical elements, and are small-sized and excellent in flexibility.

Description

Description Interval measuring device and surface shape measuring device

The present invention relates to an interval measuring device for measuring the interval and thickness of an optical element using light interference and a surface shape measuring device for measuring a surface shape of an optical element and the like. Background art

As a surface shape measuring device, a device that measures the shape of a surface to be inspected such as an optical element, for example, a lens, using light interference has been conventionally used. These surface profile measuring devices include, for example, a Fizeo-lens having a reference surface formed of a curved surface having a known shape. The light beam parallel to the optical axis is spread in the normal direction by the Fize lens and hits the test surface of the test lens, and the light is reflected by the reference surface and the test surface to cause interference. In other words, interference is caused by using the air layer between the reference surface and the test surface as the optical path length difference, and the shape of the optical element and the like are measured based on interference fringes obtained as a result of the interference.

However, in the shape obtained by this method, since the distance between the reference surface and the test surface is not clear, even if the test surface has a shape that is uniformly enlarged or reduced along the normal, Can not grasp. Therefore, in order to measure the true shape, it is necessary to make known the distance from at least one location on the test surface from the reference surface. Therefore, there is a need for an interval measuring device for directly measuring the interval between the test surface and the reference surface in a non-contact manner.

As this kind of distance measuring apparatus, for example, an apparatus using a Michelson interferometer as shown in FIG. 6 is known. This distance measuring device is The optical system includes a light source 101 that emits measurement light having a spectrum spread with respect to a fixed center wavelength, an optical system 102, and a beam splitter 103. Reference numeral 2 includes a pinhole, a collimator lens, and the like (not shown). The measurement light emitted from the light source 101 is converted into a parallel light beam and is incident on the beam splitter 103. The beam splitter 103 has a function of reflecting a part of the incident light beam and transmitting the rest. As a result, a part of the light beam incident from the light source 101 is reflected to the two glasses 104 and 105 to be measured, and the remaining light beam is reflected by the reflection mirror 106. Transmitted to the side.

For the light beam reflected on the glass 104 and 105 side, the beam splitter of glass 104, the front side of glass 103 side, the back side of glass 104 and the beam splitter of glass 105ヅ The surface on the 103 side is a reflecting surface 104 a, 104 b, and 105 a, respectively. The reflection mirror 106 is attached to a moving stage (not shown), and is movable together with the moving stage in the direction of the arrow in FIG. The reflecting mirror 106 reflects the light beam transmitted through the beam splitter 103 and returns it to the beam splitter 103.

The light beam reflected by the glass 104 and 105 passes through the beam splitter 103 as measurement light and enters the light receiving element 107. On the other hand, the light beam reflected by the reflection mirror 106 is reflected by the beam splitter 103 as reference light and reaches the light receiving element 107. The measurement light and the reference light interfere with each other on the light receiving element 107. Then, the interference light is photoelectrically converted by the light receiving element 107 and output to the outside as an interference signal.

Fig. 7 shows the intensity of the interfering light incident on the light receiving element 10 とき when the coherence distance is much smaller than the measurement interval for the light source 101, and the The relationship with the position is shown. Where the measuring light is The optical path length of the optical path separated by the beam splitter 103 and reflected by the reflecting surface 104 a of the glass 104 and reaching the beam splitter 103 again is denoted by A 1. In addition, the measurement light is separated at the beam splitter 103, reflected by the reflecting surface 104b of the glass 104, and returned to the beam splitter 103 again. Let the length be A2. In addition, the measurement light is split by the beam splitter 103, reflected by the reflecting surface 105a of the glass 105, and returned to the beam splitter 103 by the optical path length A. Assume 3. In addition, the reference light is separated by the beam splitter 103, reflected by the reflecting mirror 106, and the optical path length of the optical path reaching the beam splitter 103 again is denoted by B.

Due to the beam splitter 103, the measurement light reflected by the reflecting surfaces 104a, 104b, and 105a is reflected by the reference mirror reflected by the reflection mirror 106 and the optical path length difference according to the optical path length difference. Interference can be observed. That is, interference light that changes in intensity between the measurement light and the reference light only when the optical path lengths A 1, A 2, A 3 and the optical path length Β are substantially equal is observed. Therefore, if the optical path length なる becomes substantially equal to the optical path length A 1 by shifting the position of the reflecting mirror 106, the intensity of the interference light entering the light receiving element 107 becomes as shown on the left side of FIG. Changes to When the optical path length B becomes substantially equal to the optical path length A 2, the intensity of the interference light incident on the light receiving element 107 changes as shown in the center of FIG. When the position of the reflecting mirror 106 is further shifted, and the optical path length B becomes substantially equal to the optical path length A3, the intensity of the interference light entering the light receiving element 107 changes as shown on the right side of FIG. .

In addition, until the measurement light and the reference light are separated and recombined in the beam splitter 103, the measurement light and the reference light are incident from, for example, a medium having a low refractive index and have a high refractive index. When the light is reflected at the boundary surface with the medium, for example, when the light is reflected at the reflecting surfaces 104a and 105a, the phase is inverted by 180 degrees, that is, a so-called phase jump occurs. In this case, the intensity distribution of the interference light is As in the case of the change in the intensity of the interference light of 104a and 105a with respect to the change of the intensity of the interference light of 104b in FIG. Then, based on the interference signal output from the light receiving element 107 corresponding to the intensity distribution of the interference light and the position of the reflection mirror 106 set on the moving stage, the thickness of the glass 104 and the glass 1 The intervals of 0 4 and 105 are determined.

However, in the distance measuring apparatus having the above-described configuration, the Michelson-type interferometer is used as the basic configuration. Otherwise, interference light with varying intensity cannot be obtained. Therefore, for example, when the glasses 104 and 105 are arranged far from the beam splitter 103, the reflecting mirror 106 also needs to be separated from the beam splitter 103 as well. .

For example, when the glass 104 is formed as a Fizeau lens, the measurement light from the light source 101 is made incident on the glass 104 so as to be parallel to the optical axis of the glass 104. Then, a part of the measurement light is emitted along the normal direction from the reflecting surface 104 b of the glass serving as a reference surface, and the reflecting surface 105 a of the glass 105 serving as a test surface. And then re-enter the glass 104.

Here, the measurement light is made incident on the glass 104 in parallel with its optical axis, and the measurement light reflected on the glass 104 and 105 is made parallel to the optical axis to make the beam split. To return to 03, a null lens system consisting of multiple lenses is required. In this case, the optical path length in the null lens system becomes longer, so that the optical path length A becomes longer. Accordingly, the optical path length; B needs to be made longer. Accordingly, there has been a problem that the entire device becomes larger.

Further, in the interval measuring device having the above-described configuration, the optical path of the reference light can be accommodated in the housing to reduce the influence of air fluctuation and the influence of dust. However, the optical path of the measuring light is different in the shape and arrangement of the test object each time Therefore, it is difficult to accommodate the case. As a result, the measurement light is easily affected by air fluctuations, and the conditions of the reference light and the measurement light are different, and there is a problem that the measured value of the interval may include an error.

Further, in order to make each optical path length A l, A 2, A 3 equal to the optical path length B, according to the distance between the glass 104, 105 and the beam splitter 103, It is necessary to set the initial position and movable distance of the reflection mirror 106. For this reason, it is necessary to design the structure of the device in accordance with the shape and arrangement of the glass 104 and 105 to be measured, and there has been a problem that the versatility of the device has been significantly reduced. . Disclosure of the invention

The present invention has been made to solve such a problem existing in the conventional technology. The purpose is to provide a compact and highly versatile spacing measuring device that can measure the spacing and thickness of optical elements with high accuracy. Another object is to provide a compact and versatile surface profile measuring device that can reduce the influence of the shape and arrangement of the test object and measure the surface shape of the optical element with high accuracy. To provide. In the first invention, a light beam emitted from a light source is applied to a first surface, and the light beam transmitted through the first surface is applied to a second surface. An interval measuring device for determining an interval between the first and second surfaces based on reflected light from a second surface, wherein the reflected light from the first and second surfaces is converted into a first light beam and a second light beam. Splitting means for splitting the first light flux and the second light flux split by the splitting means; andinterfering at least the optical path length of the first light flux with the second light flux. An optical path length changing means for changing the optical path length before the light is transmitted, A length measuring means for determining a distance between the first and second surfaces based on a path length.

In this distance measuring device, the light reflected from the first and second surfaces is split into first and second light beams by a splitting means, and the first and second light beams are respectively measured light and reference light. Caused by interference means. Here, the optical path length of at least the first light beam is changed by the optical path length changing means. Then, for example, the optical path of the light beam reflected by the first surface and incident on the interference means as the first light beam and the light path of the light beam reflected on the second surface and incident on the interference means as the second light beam If the lengths are equal, the contrast of the interference light has a maximum value. Further, the optical path length of the light beam reflected by the first surface and incident on the interference means as the second light beam and the light path length of the light beam reflected by the second surface and incident on the interference means as the first light beam are different from each other. If they are equal, the contrast of the interference light takes the maximum value. Then, the distance between the first and second reflection surfaces is obtained by the length measuring means from the intensity distribution of the interference light of the first light flux and the second light flux that have interfered by the interference means and each optical path length.

Here, the optical path length of the first light beam and the second light beam is changed only between the splitting means and the interference means, and the other parts are the same. For this reason, the optical path length of each light beam can be set without being affected by the shape and arrangement of the test object, thereby reducing the size of the entire device and improving the versatility of the device. Can be done.

In a second aspect based on the first aspect, the length measuring means is configured to determine the optical information of the interference light based on the optical path length when the contrast of the interference light is maximized. It is characterized in that the distance between the first and second reflecting surfaces is obtained.

In this distance measuring device, the distance between the first and second surfaces is easier and higher than the optical path length of each light beam when the contrast of the interference light is maximized. Required for accuracy.

A third invention is the first invention or the second invention, wherein the interference means has a first interference having a phase inverted with respect to each other based on the first light flux and the second light flux. Light and a second interference light are generated, and the measuring step has a first detection means and a second detection means for separately detecting the first and the second interference light, respectively. It is assumed that.

In this interval measuring device, the interference light between the first light beam and the second light beam of the interference means can be used without waste.

A fourth invention is the third invention, wherein the length measurement means is configured to perform the first and second measurements based on a difference between a detection result of the first detection means and a detection result of the second detection means. The feature is that the distance between the two surfaces is obtained.

In this interval measuring device, the difference between the first and second interference lights whose phases have been inverted can be obtained, whereby the change of one of the interference signals can be substantially doubled. Therefore, the S / N ratio of the interference light can be improved, and the noise resistance can be improved. Therefore, the interval measurement can be performed with higher accuracy. A fifth invention is any one of the first to fourth inventions, wherein a light beam emitted from the light source is reflected or reflected between the light source and the first and second surfaces. The first and second surfaces, comprising: a light beam relay means for transmitting and reflecting or reflecting linearly polarized light in a direction orthogonal to a predetermined direction; and a conversion means for converting a linearly polarized light beam in a predetermined direction to a circularly polarized light beam. The reflected light from the light source is guided to the splitting means via the converting means and the light beam relaying means.

In this interval measuring device, the light beam emitted from the light source is provided as a circularly-polarized light beam to the first and second surfaces by the light beam relay means and the conversion means. Then, when this circularly polarized light beam is reflected by the first and second surfaces, the light beam becomes Is reversed. The light beams reflected from the first and second surfaces are converted into linearly polarized light orthogonal to the predetermined direction via a conversion unit. As a result, almost all of the light flux composed of the linearly polarized light in the orthogonal direction does not return to the light source side via the light beam relay means, but enters the splitting means. Therefore, when measuring the distance between the optical elements, The waste of reflected light can be significantly reduced.

A sixth invention is any of the first invention to the fifth invention, wherein an environment adjusting means for maintaining an environment of each optical path from the splitting means to the interference means substantially constant is provided. It is characterized by the following.

In this distance measuring device, the reflected light from the first and second surfaces has a common optical path up to the division means, so that it is less susceptible to disturbances such as air fluctuations and dust. However, since each optical path from the splitting means to the interference means is independent, it is easily affected by disturbance. Therefore, the accuracy of the interval measurement can be improved by reducing the disturbance received by each optical path by the environmental adjustment means.

According to a seventh aspect of the present invention, a surface shape measurement light beam from a light source is irradiated onto a predetermined reference surface and a test surface of a measurement object, and the test object is reflected based on the reflected light beam reflected from the reference surface and the test surface. A surface shape measuring apparatus provided with a surface shape measuring means for obtaining a shape of a surface, characterized by comprising an interval measuring means for measuring an interval between the reference surface and the test surface.

In this surface shape measuring device, the distance between the reference surface and the surface to be measured is determined with higher precision by the distance measuring means, and the shape of the surface to be measured is determined based on the determined distance between the reference surface and the surface to be measured. It can be obtained with higher accuracy by the surface shape measuring means.

The eighth invention irradiates a surface shape measurement light beam from a light source onto a predetermined reference surface and a test surface of a measurement object, and generates a reflected light beam reflected from the reference surface and the test surface. A surface shape measuring device provided with a surface shape measuring means for obtaining the shape of the surface to be measured based on the distance measuring device, comprising: a space measuring device for measuring a space between the reference surface and the surface to be measured; Wherein the reference surface and the surface to be inspected are the first and second reflecting surfaces, wherein the distance measuring device is any one of the first to sixth inventions. Device.

In this surface profile measuring device, the interval measuring device does not increase in size, it is possible to suppress the entire surface profile measuring device from increasing in size, and it is also possible to measure the surface profile of an optical element or the like with higher accuracy. It becomes possible.

A ninth invention is the seventh or the eighth invention, wherein the reference surface and the surface shape measurement light flux between the surface to be measured and the surface shape measurement means are arranged in an optical path of the light beam for surface shape measurement. And a distance measuring optical means for guiding the distance measuring light beam to the reference surface and the test surface substantially parallel to the optical axis of the surface shape measuring light beam.

In this surface shape measuring device, in the optical path of the surface shape measuring light beam, the interval measuring light beam is guided to the reference surface and the test surface in a state parallel to the surface shape measuring light beam. For this reason, in the optical path of the light beam for measuring the surface shape, the distance between the reference surface and the test surface can be measured with higher accuracy and reliability. This makes it possible to easily and more accurately measure the surface shape of the test object. According to a tenth aspect, in the ninth aspect, the interval measuring optical unit includes an optical path switching unit that switches an optical path between the surface shape measuring light beam and the interval measuring light beam. It is assumed that.

In this surface shape measuring device, the light beam for surface shape measurement or the light beam for distance measurement is selected by switching by the optical path switching means, and is applied to the reference surface and the surface to be measured. Accordingly, it is possible to avoid that the light beam for interval measurement is guided to the surface shape measuring means at the time of measuring the surface shape, and that the light flux for surface shape measurement is guided to the distance measuring means at the time of measuring the distance. Therefore, surface shape measurement and interval measurement Constant accuracy can be kept high.

An eleventh invention is the ninth invention, wherein the interval measuring optical means is disposed so as to be detachable in an optical path of the surface shape measuring light beam, and the distance measuring optical beam is substantially completely removed. It is characterized by comprising movable reflecting means for reflecting.

In this surface profile measuring device, all the light beams for distance measurement from the light source are guided into the optical path of the light beam for surface shape measurement, and all the light reflected on the reference surface and the test surface is incident on the distance measuring means. Therefore, when measuring the distance between the reference surface and the surface to be measured, the light beam for distance measurement can be used without waste.

FIG. 1 is a schematic configuration diagram showing an interval measuring device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an optical path length in the interval measuring device shown in FIG. 1 ₍ FIG. 3 is a characteristic diagram of interference light incident on a light receiving element of the interval measuring device shown in FIG. 1).

FIG. 4 is a schematic configuration diagram showing an interval measuring device according to a second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a surface shape measuring device according to a third embodiment and a modification of the present invention.

FIG. 6 is a schematic configuration diagram showing an example of a conventional interval measuring device.

FIG. 7 is a characteristic diagram of the interference light incident on the light receiving element of the interval measuring device shown in FIG. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode of the embodiment of the present invention will be described with reference to the drawings. As will be described, the scope of the present invention is not limited to these embodiments.

(First Embodiment)

An outline of an interval measuring device according to a first embodiment of the present invention will be described with reference to FIGS.

The distance measuring device includes a light source 11, a parallel optical system 12 that converts light emitted from the light source 11 into a parallel light beam, and a parallel light beam from the parallel optical system 12 reflected to the measurement target side. The beam splitter 13 is provided.

As the light source 11, a white light source that emits white light, a super luminescent diode (SLD) that emits low coherent light, or the like is used. It is desirable to select the coherent length from several meters to several ten meters. In the vicinity of the light source 11, a polarizing beam splitter 13 as a light beam relay means is arranged. The polarization beam splitter 13 reflects linearly polarized light in a predetermined direction and transmits linearly polarized light in a direction orthogonal to the predetermined direction. A quarter-wave plate 14 as a conversion means is placed near the polarized beam splitter 13, and the linearly polarized light in the predetermined direction is transmitted when passing through the quarter-wave plate 14. Then, the light is converted into circularly polarized light around a predetermined direction.

The measurement object in Fig. 1 consists of two glasses 15 and 16 arranged side by side so that their own optical axes coincide with the parallel beam reflected by the polarizing beam splitter 13 is there. In the glass 15 near the polarizing beam splitter 13, the back surface facing the glass 16 constitutes a first reflecting surface 15 a, and the luminous flux from the polarizing beam splitter 13 is formed. Reflects part and transmits the rest. In the glass 16, the surface facing the glass 15 constitutes a second reflection surface 16 a, and reflects a light beam transmitted through the glass 15. When reflecting on the first and second reflecting surfaces 15a and 16a, a predetermined direction The direction of the surrounding circularly polarized light is reversed and becomes circularly polarized light around the opposite direction.

The light reflected by the glasses 15 and 16 is incident on the quarter-wave plate 14 and is converted into linearly polarized light in a direction orthogonal to the predetermined direction. The light reflected by the glasses 15 and 16 that have passed through the 1Z 4 wavelength plate 14 travels to the polarization beam splitter 13. Here, since the polarization beam splitter 13 transmits only the linearly polarized light in the orthogonal direction, most of the light reflected by the glasses 15 and 16 is a polarization beam splitter. It is configured to proceed to the split beam splitter 17 that transmits the light 13 and forms the splitting means.

The split beam splitter 17 splits the light incident from the polarizing beam splitter 13 into a measurement light M forming a first light flux and a reference light R forming a second light flux. In other words, the split beam splitter 17 transmits a part of the reflected light incident from the polarization beam splitter 13 as the reference light R, and reflects the rest as the measurement light M in the orthogonal direction. . On the optical axis of the measurement light M reflected by the split beam splitter 17, a corner mirror 18 that bends the measurement light M is arranged. A corner mirror 19 similar to the corner mirror 18 is arranged on the optical axis of the reference light R passing through the split beam splitter 17.

The corner mirror 18 is attached to a moving stage 20 as an optical path length changing means, and is movable in the direction of the arrow in FIG. In the vicinity of the moving stage 20, a stage position sensor 20a (not shown) for detecting the position of the moving stage 20 is provided. The measurement light M bent by the corner mirror 18 is reflected by the reflection mirror 21a and is incident on the synthetic beam splitter 22 which is an interference means. On the other hand, the corner mirror 19 is fixed in a stationary state, and the reference beam R bent at the corner mirror 19 is reflected by the reflecting mirror 21 b. To enter the combined beam splitter.

The synthesized beam splitter 22 causes the measurement light M and the reference light: R to interfere with each other to generate first and second interference lights whose phases are inverted, and divides them into two directions. Output function. On the other hand, the first interference light is a combination of the measurement light M 1 transmitted through the combined beam splitter 22 and the reference light R 1 reflected by the combined beam splitter 22. The first interference light is incident on a first light receiving element 23 as first detecting means. Here, the measurement light M 1 in the first interference light passes through the synthesized beam splitter 22, so that no phase inversion occurs. Further, the reference light R 1 in the first interference light is reflected by the combined beam splitter 22. At this time, the phase of the reference light R 1 is inverted because the reference light R 1 is incident from a medium having a low refractive index and is reflected at a boundary surface of a medium having a high refractive index.

The other second interference light is a combination of the measurement light M 2 reflected by the combined beam splitter 22 and the reference light R 2 transmitted through the combined beam splitter 22. The second interference light is incident on a second light receiving element 24 as second detecting means. Here, the measurement light M 2 in the second interference light is reflected by the combined beam splitter 22, but is incident from a medium having a high refractive index and is reflected at a boundary surface of a medium having a low refractive index. Therefore, phase inversion does not occur. Further, since the reference light R2 in the second interference light passes through the combined beam splitter 22, the phase is not inverted. As a result, the phase of R 1 is inverted in the first interference light, while the phase of R 2 is not inverted in the second interference light; The intensities of the interference light as optical information and the intensities of the second interference light incident on the second light receiving element 24 as optical signals have respective phases inverted from each other. The output signal of the stage position sensor 20a is input to the main control system 25 constituting the length measuring means. The main control system 25 includes a first reflection surface 15a and a second reflection surface 16a based on the output signals of the respective light receiving elements 23 and 24 and the stage position sensor 20a. To find the interval. The main control system 25 controls the operation of the entire interval measuring device.

Light source 1 1 、 Parallel optical system 1 2 、 Beam split 13 、 Beam split 7、22 、 Corner 1-18、1 9 、 Reflection mirror 2 1a 、 2 1b and light receiving element 23 and 24 are housed in a housing 30 which is an environmental control means. Under the control of the main control system 25, an environment such as temperature and humidity is kept constant in the housing 30.

Next, a description will be given of a measurement principle when the distance between the first reflection surface 15a and the second reflection surface 16a is measured by the distance measurement device shown in FIG.

The light emitted from the light source 11 is converted into a parallel light beam by the parallel optical system 12 and is incident on the polarization beam splitter 13. The polarizing beam splitter 13 reflects the parallel light beam incident from the parallel optical system 12 through the quarter-wave plate 14 to the glass 15 and 16 sides.

The first reflecting surface 15a of the glass 15 and the second reflecting surface 16a of the glass 16 transmit the parallel light beam incident from the polarizing beam splitter 13 side through the 1/4 wavelength plate 14 Then, it is reflected to the polarized beam splitter 13 side. The light reflected by the glasses 15 and 16 passes through the polarization beam splitter 13 and reaches the split beam splitter 17.

The split beam splitter 17 splits the light reflected by the glasses 15 and 16 into the reference light R and the measurement light M, and divides the reference light R into a corner mirror 19 and the measurement light M into a corner mirror 1 1 Make each incident on 8. The corner mirror 18 bends the measuring light M and makes it incident on the reflecting mirror 21a. The reflecting mirror 21a reflects the measuring light M and makes it incident on the composite beam splitter 22. The corner mirror 19 bends the reference beam R and makes it incident on the reflection mirror 21 b. The reflection mirror 21 b reflects the reference light R and makes it enter the combined beam splitter 22.

The composite beam splitter 22 transmits a part of the measurement light M incident from the reflection mirror 21a to the first light receiving element 23 side, and transmits the remainder of the measurement light M to the second light receiving element. 2 Reflect to the 4 side. On the other hand, the combined beam splitter 22 transmits a part of the reference light R incident from the reflection mirror 21b to the first light receiving element 23, and transfers the rest of the reference light R to the second light receiving element. Reflect it toward 24. Therefore, the combined light of the measurement light M 1, M 2 and the reference light: R 1, R 2 is incident on each of the light receiving elements 23, 24. However, the first interference light incident on the first light receiving element 23 and the second interference light incident on the second light receiving element 24 are, as described above, the reference lights R l and R of the components. Since the phases of 2 are opposite to each other, the phase of the intensity of the interference light is inverted.

The reference light R actually incident on the composite beam splitter 22 includes a plurality of light beams that have passed through different paths due to reflection and transmission. Here, when measuring the distance between the first reflecting surface 15a and the second reflecting surface 16a, the reflected beam is reflected by the reflecting surface 15a and the polarized beam splitter 13 and the split beam Light beam passing through the mirror 17, the corner mirror 19 and the reflecting mirror 21 b, and the polarizing beam splitting transmitted through the glass 15 and reflected by the reflecting surface 16 a. The split beam 17, the corner mirror 19, and the luminous flux through the reflection mirror 21 b are used. Hereinafter, for the sake of simplicity, the optical path from the light source 11 to the composite beam splitter 22 in these two light fluxes is referred to as the R optical path, and the optical path length is referred to as r.

On the other hand, the measurement light M actually incident on the composite beam splitter 22 also includes a plurality of light beams that have passed through different paths due to reflection and transmission. Here, the distance between the first reflecting surface 15a and the second reflecting surface 16a was measured. In this case, the reflected beam is reflected by the reflecting surface 15a and the light beam passing through the polarizing beam splitter 13 and the beam splitter 17 and the corner mirror 18 and the reflecting mirror 21a and the glass 15 The transmitted light is reflected by the reflecting surface 16a and reflected by the polarizing beam splitter, and the light beam passing through the beam splitter 17, the beam splitter 17, the corner mirror 18 and the reflecting mirror 21a is used. Hereinafter, for the sake of simplicity, the light path from the light source 11 to the combined beam splitter 22 in these two light beams is referred to as the M light path, and the light path length is referred to as m.

When the distance between the first reflecting surface 15a and the second reflecting surface 16a is D, the light beam reflected by the reflecting surface 15a is divided by a beam splitter 17 The optical path of the reference beam R that reaches the composite beam splitter 22 via the Namira 19 and the reflecting mirror 21b and the light beam reflected by the reflecting surface 16a pass through the same optical path. The reference beam that reaches the combined beam splitter 22; the difference from the optical path of R is 2D. Similarly, the measurement light beam reflected by the reflecting surface 15a reaches the combined beam splitter 22 via the split beam splitter 17, the corner mirror 18 and the reflecting mirror 21a. The difference between the optical path of M and the optical path of the measurement light M, in which the light beam reflected by the reflecting surface 16a reaches the combined beam splitter 22 via the same optical path, is 2D.

In the present embodiment, the reference beam R and the measurement beam M are caused to interfere with each other by the combined beam splitter 22 to generate interference light whose intensity changes according to the position of the corner mirror 18. Here, the optical path length r of the reference light R is fixed, whereas the optical path length m of the measurement light M is variable by the moving stage 20. When the optical path length m is substantially equal to the optical path length r by the moving stage 20 (m = r), as shown in Fig. 2, the light is radiated from the light source 11 and is reflected by the first reflecting surface 15a of the glass 15 The light L 15r is reflected and reaches the combined beam splitter 22 via the split beam splitter 17, the corner mirror 19 and the reflecting mirror 21b, and the light L 11r emitted from the light source 11 is Reflected on reflective surface 15a, min The split beam split ヅ 17, the corner mirror 818, and the light L 15ml that reaches the composite beam split ヅ Y22 via the reflecting mirror 21a are as shown in the dashed box in Fig. 2. Then, the optical path lengths are almost equal. For this reason, in each of the light receiving elements 23 and 24, an interference signal whose intensity changes due to interference is obtained. In addition, the light emitted from the light source 11 is reflected by the second reflecting surface 16a of the glass 16 and passes through the split beam splitter 17, the corner mirror 19, and the reflection mirror 21b. The light L 16r reaching the composite beam splitter 22 and the light emitted from the light source 11 and reflected by the second reflecting surface 16 a of the glass 16, the split beam splitter 17 and the corner mirror 18 As shown in the broken line frame in FIG. 2, the optical path length is substantially equal to the light L 16 ml that reaches the beam splitter 22 via the reflection mirror 21a. Therefore, in each of the light receiving elements 23 and 24, an interference signal whose intensity changes due to interference is obtained. Therefore, in the vicinity where the optical path length m and the optical path length: 等しく are equal, the first light receiving element 23 outputs the central waveform in FIG. 3 to the main control system 25 as an interference signal.

On the other hand, when the optical path length m is shorter than the optical path length r by about 2 D (m <r), the light is radiated from the light source 11 and is reflected by the first reflecting surface 15a of the glass 15 to form a split beam splitter. The optical path length of the light L15r that reaches the composite beam splitter 22 via the mirror 17 and the corner mirror 19 and the reflection mirror 21b, and the light path length of the glass 16 emitted from the light source 11 Light reflected by the reflecting surface 16a of 2 and passing through the split beam splitter 17, the corner mirror 18 and the reflecting mirror 2 la to reach the composite beam splitter 22 L 16m2 optical path length Are almost equal to each other. Therefore, in each of the light receiving elements 23 and 24, an interference signal whose intensity changes due to interference is obtained. Therefore, when the optical path length m is about 2D shorter than the optical path length r, the first light receiving element 23 outputs the waveform on the left side of FIG. 3 to the main control system 25 as an interference signal.

If the optical path length m is about 2 D longer than the optical path length r (m> r), the light source 11 The beam is radiated and reflected by the second reflecting surface 16 a of the glass 16, and passes through the split beam splitter 17, the corner mirror 19, and the reflecting mirror 2 lb to form the composite beam splitter 2 2 And the optical path length of the light L 16r, and the light radiated from the light source 11 and reflected by the i-th reflection surface 15 a of the glass 15, and the divided beams The optical path length of the light L 15m3 reaching the composite beam splitter 22 via the reflection mirror 21a is almost equal. Therefore, in each of the light receiving elements 23 and 24, a interference signal whose intensity changes due to interference is obtained. Therefore, when the optical path length m is about 2D longer than the optical path length r, the first light receiving element 23 outputs the waveform on the right side in FIG. 3 to the main control system 25 as an interference signal.

On the other hand, the second light receiving element 24 outputs to the main control system 25 an interference signal whose phase is inverted from that of the first light receiving element 23. In other words, the second light receiving element 24 outputs an interference signal obtained by inverting the intensity of the interference signal shown in FIG. 3 by the center value CV. The main control system 25 outputs the light receiving elements 23 and 24 respectively. Find the difference signal of the interfering signals. By obtaining the difference signal, the change in the intensity of the interference signal can be doubled, the SZN ratio can be improved, and the offset can be canceled. The main control system 25 estimates the maximum value or the minimum value of the envelope in the difference signal by interpolation or the like.

Here, when the optical path length m is substantially equal to the optical path length r, the position of the moving stage 20 when the difference between the interference signals takes the maximum value or the minimum value is X 0. Further, when the optical path length m is about 2 D shorter than the optical path length r, the position of the moving stage 20 when the difference between the interference signals takes the maximum value or the minimum value is XI. Further, when the optical path length m is shorter than the optical path length r by about 2 D, the position of the moving stage 20 when the difference between the interference signals takes the maximum value or the minimum value is X 2. The main control system 25 calculates | X 1 + X 2 | / 2 or calculates 1 X 0 — XII or | X 0 — X 2 I In this way, the distance between the first and second reflecting surfaces 15a and 16a, that is, the distance is obtained.

The interval measuring device according to the first embodiment configured as described above has the following effects. '

(a) In this distance measuring apparatus, the light beams reflected on the first reflecting surface 15a and the second reflecting surface 16a are made incident on the split beam splitter 17 and the split beam splitter 17a. The configuration is such that the reference light R and the measurement light M are split at 17. Then, the reference light R and the measurement light M are caused to interfere with each other by the combined beam splitter 22. For this reason, even if the distance between the polarizing beam splitter 13 and the glass 15 and 16 is long, the influence of the fluctuation of the air received by the measuring light M and the reference light R during this period becomes common, so that the first Further, the distance between the second reflecting surfaces 15a and 16a can be measured with higher accuracy.

(b) In this distance measuring apparatus, the optical path of the measuring light M adjusted by the moving stage 20 and the corner mirror 18 to obtain the distance between the first and second reflecting surfaces 15a and 16a. The length m can be set arbitrarily regardless of the distance from the polarizing beam splitter 13 to the glasses 15 and 16. Therefore, even if the distance from the polarizing beam splitter 13 to the glass 15 or 16 becomes long, the distance measuring device can be made not only large but also small. .

(c) In this distance measuring device, the configuration inside the housing 30 can be shared regardless of the distance from the polarizing beam splitter 13 to the glass 15 or 16 (for this reason, the distance measuring device The versatility can be increased, the production efficiency can be improved, and the cost can be reduced.

(d) The distance measuring device includes first and second light receiving elements 23, 24, and both light receiving elements 23, 24 output interference signals whose phases are inverted from each other. The difference between the two interference signals is determined. Therefore, for example, the intensity change due to the interference between the reference light R and the measurement light M can be amplified almost twice and extracted as compared with the case where only one light receiving element 23 is used. Can be improved. Therefore, the distance between the first and second reflecting surfaces 15'a and 16a can be measured with higher accuracy. In addition, light beams transmitted or reflected by the divided beam splitter 17 and the combined beam splitter 22 can be illuminated without any loss, so that there is no waste. further,

(e) In this distance measuring device, the difference between the optical path lengths r and m between the reference light R and the measurement light M when the intensity of the interference signal output from each of the light receiving elements 23 and 24 becomes maximum or minimum. , The distance between the first and second reflecting surfaces 15a and 16a is obtained. Here, the optical path length r of the reference light; R is fixed, and the optical path length m of the measurement light M can be easily and accurately determined by detecting the position of the moving stage 20. Therefore, the distance between the first and second reflecting surfaces 15a and 16a can be easily and accurately determined.

(f) In this distance measuring device, the light source 11 emits linearly polarized light in a predetermined direction, and a polarizing beam splitter 13 and a quarter-wave plate 14 are disposed between the light sources 11 and 16. Have been. As a result, almost all of the parallel light beams from the parallel optical system 12 can be supplied to the glasses 15 and 16, and almost all of the light beams reflected by the glass 15 and 16 can be split into split beam splits. We can lead to evening 17 without waste. Therefore, more light beams can be made incident on the first and second light receiving elements 23 and 24, and the distance between the first and second reflecting surfaces 15a and 16a can be measured with higher accuracy. can do.

(g) In this distance measuring device, most of its configuration is housed in a housing 30 in which the environment is kept constant. For this reason, the influence of the fluctuation of the air, etc., received by the measurement light M and the reference light R can be significantly reduced. The distance between the second reflecting surfaces 15a and 16a can be measured with higher accuracy.

(Second embodiment)

In the first embodiment, the basic configuration of the distance measuring device is configured by a Mach-Wender interferometer, but it can be configured by a Michelson-type interferometer as shown in FIG.

In FIG. 4, elements common to those in FIG. 1 are denoted by common reference numerals. This distance measuring device includes a light source 11, a parallel optical system 12, a polarizing beam splitter 13, and a 1Z 4 wavelength plate 14 similar to those in the first embodiment, and glass 15, 16. The light beam is incident on the light source. The luminous flux reflected by the first reflecting surface 15a of the glass 15 and the second reflecting surface 16a of the glass 16 passes through the polarizing beam splitter 13 to constitute a splitting unit and an interference unit. Beam splitting. Beam split ヅヅ 4 1 1 1 1 1 1 1 1 1 4 4 4 4 4 4 1 1 1 1 1 1 1 4 4 1 4 4 4 4 1 1 1 1 1 1 It has the function of entering the mirror 43.

The movable reflecting mirror 42 is fixed to the moving stage 20 so as to move similarly to the corner mirror 18 of the first embodiment. M is reflected toward the beam splitter 41. The fixed reflection mirror 43 is fixed, and reflects the reference light R incident from the beam splitter 41 again to the beam splitter 41. The beam splitter 41 transmits a part of the measurement light M incident from the reflection mirror 42 side to the light receiving element 44 side and receives a part of the reference light R incident from the reflection mirror 43 side. The element 44 reflects light to the 4 side.

Therefore, the interference light of the measurement light M and the reference light R enters the light receiving element 44. The light receiving element 4 4 is an interference signal corresponding to the intensity of the incident light. Signal to the main control system 25.

In this interval measuring device, the beam splitter 41 splits the measurement light M and the reference light R and causes the measurement light M and the reference light R to interfere with each other. Here, before the measurement light M and the reference light ': R interfere with each other, the position of the movable reflection mirror 142 is shifted by the moving stage 20 to change the optical path length of the measurement light M. As a result, an interference signal similar to that of FIG. 3 of the first embodiment can be obtained. When an interference signal similar to that shown in FIG. 3 is obtained, the main control system 25 obtains the interval between the reflecting surfaces 15a and 16a from the maximum value or the minimum value in the envelope of the interference signal. Then, the main control system 25 finds the maximum value or the minimum value by interpolating the interference signal, and determines the distance between the glass 15 and 16 from the position of the moving stage 20 as in the first embodiment. Ask.

The interval measuring apparatus according to the second embodiment having the above-described configuration has the following effects in addition to the same effects as those of the first embodiment.

(h) In this interval measuring apparatus, the beam splitter 41 separates the measuring light M and the reference light: R from each other and causes the measuring light M and the reference light R to interfere with each other. For this reason, the combined beam splitter 22 and the like become unnecessary, and the size of the apparatus can be further reduced.

(Third embodiment)

An outline of a surface shape measuring apparatus according to a third embodiment of the present invention will be described with reference to FIG.

The surface shape measuring device shown in FIG. 5 has a Fizeau interferometer 51 as a surface shape measuring means, a null lens system 52, and a Fizeau lens 53. The Fizeau type interferometer 51 has a built-in laser light source 54 as a light source for generating a surface shape measuring light beam Ls composed of, for example, He-Ne laser light.

The null lens system 52 includes the luminous flux Ls and the luminous flux Ls emitted from the interferometer 51. And returns the light flux Ls returning to the interferometer 51 to be parallel to the normal of the Fizeau lens 53. The light beam Ls having passed through the null lens system 52 enters the Fizeau lens 53.

The Fizeau lens 53 has a reference surface 53a, and the reference surface 53a is disposed so as to face a test surface 55 of a measurement object formed of an optical element such as a lens or a mirror. Have been. The Fizeau lens 53 has a function of reflecting a part of the light beam Ls incident from the null lens system 52 side on the reference surface 53a and transmitting the rest. The light beam Ls transmitted through the Fizelens 53 travels in the normal direction of the reference surface 53 a of the lens 53, is reflected by the surface 55 to be measured of the measurement object, and returns along the same optical path. ing.

The surface shape measuring device further incorporates the distance measuring unit of the first embodiment housed in the housing 30 as a distance measuring unit 56 of the distance measuring means. The interval measuring light beam L d emitted from the interval measuring unit 56 is incident on a dichroic mirror 57 as an interval measuring optical unit. The dichroic mirror 57 is always disposed between the null lens system 52 and the interferometer 51. The dichroic mirror 57 bends the distance measuring light beam Ld so that its optical axis is parallel to the surface shape measuring light beam Ls, and converts the distance measuring light beam Ld into a null lens system 52. It functions so as to be made incident on the Fize lens 53 and the surface 55 to be measured via the FZ lens.

This surface shape measuring device is a device that determines the relative distance between the reference surface 53 a of the Fizeau lens 53 and the test surface 55 and measures the shape of the test surface 55. In other words, the light Ls for surface shape measurement emitted from the Fizeau interferometer 51 passes through the dichroic mirror 57 and enters the null lens system 52. Null lens system 52 is for measuring the surface shape incident from the interferometer 51 side The light beam Ls is transmitted through the Fizeau lens 53. The Fizeau lens 53 reflects a part of the surface shape measuring light beam Ls incident from the null lens system 52 and returns it to the null lens system 52 side. The light beam Ls for surface shape measurement transmitted through the Fizeau lens 53 spreads in the normal direction, is reflected by the surface 55 to be measured, passes through the Fizen lens 53, and returns to the null lens system 52.

The null lens system 52 returns the surface shape measuring light beam Ls reflected from the reference surface 53 a and the test surface 55 to the interferometer 51. The surface shape measuring light beam Ls reflected by the reference surface 53a and the surface shape measuring light beam Ls reflected by the test surface 55 enter the interferometer 51 through the same optical path. . Therefore, these reflected light beams Ls for surface shape measurement interfere with each other, and interference fringes are generated in the interferometer 51. In the interferometer 51, the interference fringes are converted into electric signals by a light-receiving element (not shown), and the shape data of the surface to be detected is obtained based on the electric signals. On the other hand, the distance measuring light beam L d emitted from the distance measuring unit 56 is reflected by the dichroic mirror 57 and travels in parallel with the optical axis of the surface shape measuring light beam Ls, and passes through the null lens system 52. Reaching the reference surface 53 a and the surface 55 to be measured <The light beam L for distance measurement is reflected by the reference surface 53 a and the surface 55 to be measured similarly to the light beam L s for surface shape measurement, and the null lens system 5 The light passes through 2 and enters the dichroic mirror 57. The dichroic mirror 57 reflects the distance measurement light beam Ld that has advanced from the null lens system 52 side and makes the light beam enter the distance measurement unit 56. The distance measurement unit 56 internally performs the same processing as in the first embodiment to determine the distance between the reference surface 53 a and the test surface 55. As a result, if the radius of curvature of the reference surface 53 a of the Fizeau lens 53 is known, the curvature of the surface 55 to be measured is obtained by adding the results of the surface shape measurement and the distance measurement to the radius of curvature. The value of the radius is also required with higher accuracy.

Both the surface shape measurement light beam Ls and the distance measurement light beam Ld reflected from the test surface 55 and the reference surface 53a advance to the dichroic mirror 57c. Here, when, for example, a He—Ne laser is used for the surface shape measuring light beam Ls, the wavelength is 633 nm. In this case, it is desirable to use LSD light having a wavelength of 680 nm for the distance measurement light beam Ld. By doing so, the two light beams Ls and Ld can be sufficiently separated, and the aberrations generated by the null lens system 52 and the like can be reduced because their wavelengths are relatively close.

The following effects can be obtained with the surface shape measuring device having such a configuration. (I) In this surface shape measuring device, the distance measuring device according to the first embodiment is incorporated as a distance measuring unit 56. Have been. Therefore, taking into account the measurement result of the distance between the test surface 55 and the reference surface 53a at the distance measurement unit 56, the shape of the test surface 55 is further improved by the Fizeau interferometer 51. It will be possible to measure with high accuracy.

(Modified example)

The above embodiments can be variously modified as follows, for example.

(1) In the third embodiment, the dichroic mirror 571 is always arranged in the optical path of the surface shape measuring light beam Ls from the Fizeau interferometer 51 to perform the interval measurement and the surface shape measurement. You can do both at the same time. On the other hand, for example, as shown by a dashed line in FIG. 5, for example, a shirt 61 is provided as an optical path switching means that appears and disappears in the optical path of the surface shape measuring light beam Ls, and the distance measuring light beam Ls is provided. A shirt 62 may be provided as an optical path switching means that appears and disappears in the optical path of Ld, so that the optical paths of the surface shape measuring light beam Ls and the distance measuring light beam Ld may be switched as appropriate.

In this case, when measuring the distance between the reference surface 53a and the surface 55 to be inspected, the shirt 61 is inserted into the optical path of the surface shape measuring light beam Ls and the distance measuring light beam Ld Evacuate the shirt from the optical path of the The distance measurement light beam Ld from the point 56 is guided to the reference surface 53a and the surface 55 to be measured. When the shirt 61 is retracted, the shutter 62 is inserted into the optical path of the distance measuring light beam L d, and the surface shape measuring light beam L s from the Fizeau type 1 interferometer 51 is referred to as the reference surface 53 a. And the test surface 55. In this case, the light beam Ld for distance measurement is not guided into the interferometer 51, and the light beam Ls for surface shape measurement is not guided into the distance measurement unit 56. And the accuracy of the interval measurement can be kept high.

(2) In the third embodiment, the dichroic mirror 571 is always arranged in the optical path of the surface shape measuring light beam Ls from the Fizeau interferometer 51 to perform the interval measurement and the surface shape measurement. You can do both at the same time. On the other hand, as shown by a two-dot chain line in FIG. 5, for example, the dichroic mirror 57 is changed to a total reflection mirror 65 as movable reflection means, and the total reflection mirror 65 is used for measuring a surface shape. The light beam Ls may be arranged so as to be insertable into and removable from the optical path.

In this case, when measuring the distance between the reference surface 53a and the test surface 55, a total reflection mirror 65 is inserted into the optical path of the light beam Ls for measuring the surface shape, and the distance measurement unit is measured. The light beam Ld for distance measurement from the point 56 is guided to the reference surface 53 a and the test surface 55. On the other hand, when measuring the surface shape, the total reflection mirror 65 is retracted from the optical path of the surface shape measurement light beam Ls, and the surface shape measurement light beam Ls from the Fizeau interferometer 51 is used as a reference surface. It leads to 53 a and the test surface 55. In this case, in addition to the effects of the above embodiments, the interval measurement light beam L d can be used without waste.

(3) In the first embodiment, two light receiving elements 23 and 24 are provided to output an interference signal whose phase is inverted to improve the S / N ratio. However, the S / N ratio is improved. When it is not necessary, only one light receiving element 23 may be provided to output an interference signal as in the second embodiment. In the first and second embodiments, the polarizing beam splitter 13 and the quarter-wave plate 14 are arranged between the light source 11 and the glasses 15 and 16. The four-wavelength plate 14 may be omitted, and the polarization beam splitter 13 may be changed to a normal beam splitter.

では In the third embodiment, the interval measuring device according to the first embodiment is incorporated, but the interval measuring device according to the second embodiment may be incorporated.

において In the first embodiment, the two corner mirrors 18 and 19 may be movably disposed together. In this case, the difference between the optical path lengths of the reference light R and the measurement light M is obtained from the positions of both corners 18 and 19, and the first and second reflecting surfaces 1 are determined based on the difference in the optical path lengths. Find the interval of 5 a, 1 6 a,

In the third embodiment, a beam splitter may be used instead of the dichroic mirror 57. Industrial applicability

As is apparent from the above description, the present invention can be used for accurately measuring the distance, thickness, and the like of an optical element, and for accurately measuring the surface shape of an optical element and the like.

Claims

The scope of the claims

1. While irradiating a light beam emitted from a light source to a first surface, irradiating the second surface with the light beam transmitted through the first surface, reflection from the first surface and the second surface An interval measuring device for determining an interval between the first and second surfaces based on light,

Splitting means for splitting the reflected light from the first and second surfaces into a first light flux and a second light flux;

Interference means for causing the first light flux and the second light flux split by the splitting means to interfere with each other;

Light path length changing means for changing at least the light path length of the first light beam before causing the light path length to interfere with the second light beam;

An interval measuring device, comprising: a length measuring unit that obtains the interval between the first and second surfaces based on optical information of the interference light interfered by the interfering unit and the optical path length.

2. The distance measuring apparatus according to claim 1, wherein the length measuring means is based on the optical path length when the contrast of the interference light is maximized as optical information of the interference light. A distance between the first and second reflection surfaces.

3. The distance measuring apparatus according to claim 1 or 2, wherein the interference unit is configured to control the first light flux and the second light flux whose phases are inverted with respect to each other based on the first light flux and the second light flux. In addition to generating interference light and second interference light, the length measuring means has first detection means and second detection means for detecting the first and second interference lights separately. Interval measuring device.

4. The distance measuring apparatus according to claim 3, wherein the length measuring means is configured to perform a measurement based on a difference between a detection result of the first detecting means and a detection result of the second detecting means. The distance between the first and second surfaces based on the distance.

5. The distance measuring device according to any one of claims 1 to 4, wherein the light is emitted from the light source between the light source and the first and second surfaces. A light beam relay means for transmitting or reflecting the linearly polarized light in a direction orthogonal to a predetermined direction, and a converting means for converting the linearly polarized light beam in a predetermined direction to a circularly polarized light beam. An interval measuring device, wherein reflected light from the first and second surfaces is guided to the division means via the conversion means and the light beam relay means.

6. The distance measuring apparatus according to any one of claims 1 to 5, wherein an environment of each optical path from the splitting means to the interference means is kept almost constant. An interval measuring device comprising means.

7. A light beam for surface shape measurement from a light source is applied to a predetermined reference surface and the surface to be measured of the object to be measured, and the shape of the surface to be measured is obtained based on the light beam reflected from the reference surface and the surface to be measured A surface shape measuring apparatus provided with a surface shape measuring means, comprising: a distance measuring means for measuring a distance between the reference surface and the test surface.

8. A light beam for surface shape measurement from a light source is applied to a predetermined reference surface and the surface to be measured of the object to be measured, and the shape of the surface to be measured is obtained based on the reflected light beam reflected from the reference surface and the surface to be measured. A surface shape measuring apparatus including a surface shape measuring unit, comprising: a distance measuring unit configured to measure a distance between the reference surface and the surface to be measured, wherein the distance measuring unit is configured to measure the reference surface and the surface to be measured. 7. A surface shape measuring device comprising the interval measuring device according to any one of claims 1 to 6 as first and second reflecting surfaces.

9. The surface shape measuring apparatus according to claim 7, wherein the surface shape measuring light flux between the reference surface and the surface to be measured and the surface shape measuring means. And an interval measuring optical means for guiding the interval measuring light beam to the reference surface and the test surface substantially parallel to the optical axis of the surface shape measuring light beam. Surface shape measuring device.

10. The surface shape measuring device according to claim 9, wherein the optical device for measuring a distance includes an optical path switching means for switching an optical path between the light beam for measuring the surface shape and the light beam for measuring the distance. Characteristic surface shape measuring device.

11. The surface shape measuring device according to claim 9, wherein the gap measuring optical unit is disposed so as to be detachable in an optical path of the surface shape measuring light beam, and substantially removes the space measuring light beam. A surface shape measuring device comprising movable reflecting means for total reflection.