JPH0754802Y2 - Contact type profilometer - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type surface profile measuring instrument for measuring the surface profile of a measured object by following it with a probe (stylus). In addition, the displacement of the probe can be detected with high accuracy.

[0002]

2. Description of the Related Art In order to measure the surface shape of metal or glass,
Conventionally, a contact-type profilometer has been used. This conventional contact-type surface profile measuring instrument is provided with a probe such as a diamond at one end of a movable arm that can be swung by a horizontal axis, and the probe is in contact with the surface to be measured. Trace it. A flat reflecting mirror is provided at the other end of the movable arm that has a probe at one end, and displacement due to the shape of the surface is
Detect using a Michelson type interferometer. Thereby, the shape of the surface can be measured.

However, the conventional contact-type surface profile measuring instrument described above cannot be used for general purposes. That is, in order to perform general-purpose measurement using the above-mentioned conventional device, the distance from the horizontal axis to one end where the probe is provided is the distance from this horizontal axis to the other end where the plane reflecting mirror is provided. Need to be larger than. Therefore, the displacement of the other end of the movable arm, which is directly involved in the measurement of the surface shape of the object to be measured, becomes smaller than the displacement of the probe that follows the surface shape, and this surface shape is reduced and detected. It becomes a matter. As a result, high precision detection becomes difficult.

In Japanese Patent Publication No. 4-5922, a corner cube is provided at the other end of a movable arm, which has three reflecting surfaces orthogonal to each other and emits light rays in a direction parallel to and parallel to the incident direction. , An apparatus for detecting the displacement of a corner cube associated with the displacement of a probe according to the surface shape of an object to be measured by an interferometer.

According to this device, one interference fringe changes with respect to the displacement of the corner cube by a quarter wavelength, so that it is possible to obtain twice the sensitivity. Further, the probe may tilt depending on the surface shape of the object to be measured. In such a case, in the above-mentioned conventional device, the movable arm body provided with the probe also tilts, so that it is reflected by the plane reflecting mirror. However, there is a disadvantage that the surface shape of the object to be measured cannot be measured because the generated light flux is not returned to a predetermined optical path. In the device described in the above publication, such inconvenience is eliminated, and the light flux reflected by the corner cube is not affected by the tilt of the movable arm and the lateral movement on the predetermined optical path. You can return to. Therefore, general-purpose use becomes possible.

[0006]

[Problems to be Solved by the Invention] With the recent development of processing technology, the surface shape of metal or glass is
The emergence of a measuring device capable of measuring on the order of (10 ⁻⁹ m) has come to be desired. In the conventional device described above or the device described in the above-mentioned publication, in order to obtain resolution on the order of nm, it is necessary to further subdivide one cycle of the interference fringes and electrically detect it. Noise is easily received, and it is difficult to put it into practical use. Further, in the device described in the above publication, in order to perform general-purpose measurement, it is necessary to take a large distance from the horizontal axis of the movable arm to one end where the probe is provided, as in the conventional device described above. Since the displacement of the probe is reduced and detected, highly accurate measurement is still difficult. Furthermore, since a Michelson-type interferometer is used as the detection means for detecting the displacement of the plane reflecting mirror provided at the other end of the movable arm or the corner cube, it is easily affected by disturbance such as vibration, Was an obstacle to measuring on the order of.

The contact type surface profile measuring instrument of the present invention was devised in view of the above circumstances.

[0008]

A contact type surface profile measuring instrument of the present invention is movable relative to an object to be measured and is displaced according to the surface profile of the object to be measured, a light source means, and a light source means. Optical for splitting the light beam emitted from the light source means into a reference light and a measuring light for measuring the displacement of the measuring means, and for amplifying the optical path length of the measuring light which changes with the displacement of the measuring means. And means for calculating the surface shape of the object to be measured based on the optical path length.

Among these, the measuring means has a movable arm and a probe which is provided at one end of the movable arm and follows the surface of the object to be measured in contact with the surface. or,
The optical means includes a first polarization beam splitter and a first reflecting mirror for splitting the light flux emitted from the light source means into the reference light and the measurement light traveling along a substantially common optical path, and other movable arm members. A corner cube that is provided at the end and that displaces the measurement light and sends it out in the direction opposite to the incident direction, a quarter-wave plate that transmits the measurement light emitted from the corner cube and the reference light, and a quarter-wave plate A second reflecting mirror that reflects the measurement light emitted from the wave plate in a backward direction, a third reflecting mirror that reflects the reference light that has passed through the ¼ wavelength plate in a backward direction, and the third reflection mirror. Reference light reflected by the mirror and backward and reflected by the first polarizing beam splitter, and measurement light reflected by the second reflecting mirror and backward and transmitted through the first polarizing beam splitter through the corner cube. To It has first and a reflecting member for reflecting toward the polarization beam splitter.

Further, the detecting means converts the interference intensity between the reference light and the measuring light into an electric signal and calculates the surface shape of the object to be measured from the phase difference between the electric signals.

Then, after the reference light is reflected by the first reflecting mirror and then reciprocated twice between the third reflecting mirror and the reflecting member,
Take the optical path entering the detection means. The measurement light is emitted from the first polarization beam splitter, then reciprocated between the second reflection mirror and the reflection member twice, and then emitted from the first polarization beam splitter to enter the detection means. Characterized by taking an optical path.

[0012]

Since the contact-type surface profile measuring device of the present invention is constructed as described above, the displacement of the corner cube due to the surface profile of the object to be measured is quadrupled as a change in the optical path length of the measuring light. Amplified and measured. Therefore, measurement on the order of nm is possible. Moreover, it is not necessary to increase the size of the corner cube, and since it is not easily affected by disturbance, reliable measurement can be performed.

[0013]

Embodiments Next, the illustrated embodiments will be described. Figure 1
Reference numeral 4 shows a first embodiment of the present invention. The contact type surface shape measuring instrument of the present invention comprises a measuring means 2 for measuring the surface shape of an object 1 to be measured, a light source means 3, and a light beam emitted from the light source means 3 for reference light and displacement of the measuring means 2. The optical means 4 is divided into two parts, the measuring light to be measured and the optical path length of the measuring light is amplified, and the interference intensity between the reference light and the measuring light emitted from the optical means 4 is detected and converted into an electric signal. rear,
The detection means 5 calculates the surface shape of the DUT 1 based on the phase difference between the electric signals.

The measuring means 2 is, as shown in FIGS.
An object to be measured 1 is attached to one end (left end in FIGS. 1 and 2) of an arm 7 which is a movable arm and is swingably provided around a horizontal axis 6.
A probe 8 (sillus) that can be freely contacted is provided on the surface of. At the other end (right end in FIGS. 1 and 2) of the arm 7, a corner cube 16 which will be described later and is included in the optical means 4 is provided. The arm 7 is movable by a drive mechanism (not shown) while the probe 8 is in contact with the surface of the DUT 1. Therefore, the probe 8 follows the surface and the arm 7
Are displaced according to the shape of the surface.

The above-mentioned light source means 3 is, in this embodiment,
A laser with a single frequency is used. Light source means 3
This laser is separate from the measuring means 2 and the optical means 4, and an isolator 9 and a half-wave plate 10 are arranged between the end of the laser and the optical means 4, and Between the isolator 9 and the wave plate 10,
A polarization maintaining fiber 11 for guiding the light beam emitted by the laser is provided. In this way, by providing the light source means 3 separately from the other means, the volume of the measuring system (measuring means 2, optical means 4) can be reduced, and the influence of heat generated by the light source means 3 is small. You can Although not shown, a collimator lens and the like are actually provided in addition to the above components.

The isolator 9 is provided to prevent the luminous flux emitted from the laser from returning toward the laser (block the returning light). 1/2 wave plate 1
0 is used to radiate the laser and guide the light beam guided by the polarization maintaining fiber 11 into linearly polarized light having an inclination of 45 degrees with respect to the paper surface in FIG.

The light beam linearly polarized by the action of the half-wave plate 10 passes through a first beam splitter 22 constituting a detecting means 5 described later and enters the optical means 4.

The optical means 4 includes a first polarization beam splitter 12 for separating the above-mentioned linear polarization into two linear polarizations orthogonal to each other, and the first polarization beam splitter 12
A first reflection that reflects one light flux (reference light) that has traveled straight in the direction of the first polarization beam splitter 12 so as to be parallel to another light flux (measurement light) that has an optical path that is bent perpendicularly to the incident direction. Of the mirror 13, the quarter-wave plate 14 and the third reflecting mirror 15 arranged on the optical path of the reference light reflected by the first reflecting mirror 13, and the arm 7 constituting the measuring means 2. The corner cube 16 which is provided at the other end and which displaces the measurement light reflected by the first polarization beam splitter 12 and emits it in the direction opposite to the incident direction, and the measurement light emitted from the corner cube 16 are After passing through the quarter-wave plate 14, the light is reflected in the reverse direction of the optical path .
A second reflecting mirror 17, the first polarization beam splitter 1
And a right-angle prism 21 which is a reflecting member, which is provided at a position above 2, and which shifts a light flux emitted from the first polarization beam splitter 12 and directed upwards to be parallel to the incident light flux by displacing the light flux in a direction perpendicular to the incident direction. Composed of.

More specifically, the first polarization beam splitter 12 has one luminous flux which is a reference light which travels straight in the same direction as the incident direction and a vertical direction (downward in FIG. 1) perpendicular to the incident direction. It bends and separates into another light flux which becomes the measurement light directly involved in the surface shape measurement of the DUT 1. Further, the first reflecting mirror 13 reflects the light flux serving as the reference light so as to travel in parallel and in the same direction with respect to the other light flux serving as the measurement light, separated by a minute distance.

The corner cube 16 has three reflecting surfaces 18, 19 and 20 which are a first, a second and a third, changes the incident measuring light in the direction perpendicular to the incident direction and emits it in the direction opposite to the incident direction. Let A metal coating is applied to each of the reflecting surfaces 18, 19 and 20.

The first reflecting mirror 13 and the corner cube 16
Between 1 and 2, in order from the first reflecting mirror 13 side,
A four-wave plate 14 and a third reflecting mirror 15 are arranged.
Among these, the quarter-wave plate 14 changes the polarization state of the transmitted light flux, and is commonly used for the measurement light and the reference light. Therefore, the number of parts constituting the optical means 4 is reduced, and when passing through the quarter-wave plate,
The change in optical path length due to the temperature change can be eliminated, which contributes to highly reliable measurement. Third reflector 1
Reference numeral 5 reflects the reference light transmitted through the quarter-wave plate 14 so as to reverse the optical path up to that point. This third
The reflecting mirror 15 is fixed to a fixed member (not shown) above the corner cube 16, and a flat reflecting mirror can be used.

On the opposite side of the quarter-wave plate 14 from the corner cube 16, a fixed member (not shown) is provided with a second reflection member .
The mirror 17 is fixed. The second reflecting mirror 17, the measurement light emitted from the corner cube 16, as to reverse the optical path up to it, but to reflect the third reflecting mirror 1
Similar to 5 , a plane reflecting mirror is used.

Further, a right-angle prism 21 which is a reflecting member is provided above the first polarization beam splitter 12. The right-angle prism 21 displaces an incident light flux in a direction perpendicular to the incident direction and returns the light flux to be parallel to the incident light flux. As the reflecting member, other members such as the corner cube and the like can be used in addition to the right-angle prism 21.

Since the optical means 4 is constructed as described above, the light beam which has emitted the laser and has passed through the isolator 9 and the polarization maintaining fiber 11 constitutes the half-wave plate 10 and the detection means 5. It is incident on the first polarization beam splitter 12 via the first beam splitter 22.

Of the two light beams which are incident on the first polarization beam splitter 12 and are separated into two linearly polarized lights which are orthogonal to each other, the light beam whose polarization direction is parallel to the paper surface of FIG. The light is transmitted and is bent by the first reflecting mirror 13 perpendicularly to the incident direction. This light flux acts as the reference light.

A light beam whose polarization direction is perpendicular to the plane of the paper in FIG. 1 is reflected by the first polarization beam splitter 12 and bent in a direction perpendicular to the incident direction, which is a parallel optical path separated from the reference light by a small distance. I take the. This light flux acts as the measurement light to measure the displacement of the arm 7.

The distance between the reference light and the measurement light is extremely small, parallel to each other, and in the same direction (vertically downward in FIG. 1).
Proceed to. In this way, since the distance between the reference light and the measurement light is extremely small, they can be regarded as a common optical path. Therefore,
Hardly affected by vibration and heat.

The reference light is changed from linearly polarized light to circularly polarized light by passing through the quarter-wave plate 14 after being reflected by the first reflecting mirror 13. Further, this reference light is transmitted to the third reflecting mirror 15
It reflects at and reverses the optical path up to that point. At this time, the reflected reference light is converted into linearly polarized light.

Further, the reference light is reflected by the first reflecting mirror 13, and then by the first polarizing beam splitter 12, and travels upward in FIG. Since the right-angle prism 21 is provided above the first polarization beam splitter 12, the reference light is displaced by the right-angle prism 21 in the direction perpendicular to the incident direction and is emitted in parallel with the incident light beam.

The reference light emitted from the rectangular prism 21 enters the first polarization beam splitter 12 and reciprocates in the optical path from the first polarization beam splitter 12 to the third reflecting mirror 15 . On this return path, the reference light is 1/4
Since the light that has passed through the wave plate 14 becomes linearly polarized light parallel to the incident direction thereof, it is reflected by the first reflecting mirror 13 and then passes through the first polarizing beam splitter 12 to constitute the detecting means 5. Incident on the beam splitter 22. After all, the reference light is first reflected by the first reflecting mirror 13 and then reciprocates twice in the optical path from the third reflecting mirror 15 to the rectangular prism 21. The light beam traveling from the first beam splitter 22 to the first polarization beam splitter 12 and the reference light in the opposite direction to this light beam are spatially displaced.

On the other hand, the measurement light exits the first polarization beam splitter 12 and then enters a corner cube 16 provided at the other end of the arm 7 constituting the measuring means 2. Since the reflecting surfaces 18, 19 and 20 of the corner cube 16 are metal-coated as described above, the polarization state of the light reflected by the corner cube 16 is not disturbed.

The corner cube 16 is shown in FIG.
As shown in (B), the first, second, and third reflecting surfaces 18, 1
It has 9 and 20. Since these anti-slope surfaces are orthogonal to each other, as shown in FIG.
There are a total of 6 areas S1 to S6 obtained by dividing each of 9 and 20 into two. Light incident on the area S1 in a state substantially perpendicular to the corner cube 16 (black circle in FIG. 3A)
Is reflected by the first reflecting surface 18, passes through the region S2, and exits from the region S4. Further, the light incident on the area S2 in a state substantially perpendicular to the corner cube 16 (white circle in FIG. 3A)
Exits from the area S5 via the area S1. And
The right-angle prism 21, which is a reflecting member in the present invention, shifts the light flux incident on the corner cube 16 in the direction perpendicular to the plane on which the corner cube 16 is displaced. It is incident on different areas. As a result, in the present invention, the optical path length of the measurement light can be amplified four times without making the corner cube 16 large.

The first to third reflecting surfaces 18 to 2 as described above.
The measurement light incident on the corner cube 16 having 0 is
The optical path deviated from the third reflecting mirror 15 is taken and
The light passes through the four-wave plate 14 and is reflected by the second reflecting mirror 17 .

Before passing through the quarter-wave plate 14, the measurement light is linearly polarized light whose polarization direction is perpendicular to the paper surface due to the metal coating, but Circularly polarized light is obtained by passing through the four-wave plate 14. Further, after being reflected by the second reflecting mirror 17 , it travels backward through the optical path up to that point, passes through the quarter-wave plate 14, and is converted into linearly polarized light whose polarization direction is parallel to the paper surface. It is incident on 16.

The measurement light incident on the corner cube 16 again is reflected by the three first to third reflecting surfaces 18 to 20 and then emitted toward the first polarization beam splitter 12, as described above. . At this time, since the measurement light is linearly polarized light whose polarization direction is parallel to the paper surface, it passes through the first polarization beam splitter 12 and is reflected by the rectangular prism 21. Then, the polarization direction is displaced in the direction perpendicular to the paper surface, and becomes parallel to the incident measuring light. After that, the measurement light travels along the optical path from the first polarization beam splitter 12 to the second reflecting mirror 17 .
Proceed as described above.

After the third reflection by the corner cube 16, after passing through the quarter-wave plate 14, this measurement light changes from linearly polarized light whose polarization direction is parallel to the paper surface to circularly polarized light,
When reflected by the second reflecting mirror 17 and returned, it is converted into linearly polarized light whose polarization direction is perpendicular to the paper surface, and reflected by the first polarization beam splitter 12. As described above, in the present invention, the measurement light is reflected by the corner cube 16 four times, and the corner cube 1 corresponding to the surface shape of the DUT 1 is measured.
The displacement amount of 6 can be amplified and measured four times as a change in the optical path length of the measurement light. Moreover, it is not necessary to upsize the corner cube 16.

In this way, the reference light and the measurement light emitted from the first polarization beam splitter 12 enter the detecting means 5. In the present invention, the reference light and the measurement light emitted from the first polarization beam splitter 12 by the action of the rectangular prism 21 are converted into the first polarization beam splitter 1
It is spatially separated from the light incident on the beam 2 and other leaked light. Therefore, it is possible to eliminate the adverse effects of leaked light and the like due to the unavoidable manufacturing error of each component, and it is possible to measure with a small error. In order to further suppress the error, the position between the first beam splitter 22 and the detecting means 5, and the first beam splitter 22 and the polarization maintaining fiber 11
A spatial filter is provided at a position between and.

In the present embodiment, the detecting means 5 is constructed as shown in FIG. In FIG. 4, 22 is a first beam splitter, and this first beam splitter 22 reflects the reference light and the measurement light perpendicularly to the incident direction. Reference numeral 23 is a second beam splitter, which divides the reference light and the measurement light into two with the same amplitude.

Around the second beam splitter 23, in a state rotated by 45 degrees with respect to the incident direction of the incident light,
Second and third polarization beam splitters 24 and 25 are provided. Then, behind the second and third polarization beam splitters 24 and 25, as shown in FIG.
Fourth photoelectric conversion elements 26 to 29 are provided. A quarter wavelength plate 30 is provided between the second polarization beam splitter 22 and the third polarization beam splitter 25, and the interference intensity is obtained via the third polarization beam splitter 25. The phase of the electric signal is different by 90 degrees.

Further, although not shown, an arithmetic unit for calculating the surface shape of the DUT 1 based on the electric signal is provided. In the actual case, this computing device uses a computer such as a microcomputer

Since the detecting means 5 is constructed as described above, the reference beam and the measuring beam emitted from the first polarization beam splitter 12 have their paths vertically bent by the first beam splitter 22, and the second beam is reflected by the second beam splitter 22. The beam splitter 23 splits the beam into two with the same amplitude.

Each of the second beam splitters 23 has two
Of the split reference light and measurement light, one set of reference light and measurement light enters the second polarization beam splitter 24 and interferes with them. Then, the first and second photoelectric conversion elements 26, 27 provided behind the second polarization beam splitter 24.
Converts the interference intensity into an electric signal. The electric signal obtained by the first photoelectric conversion element 26 and the electric signal obtained by the second photoelectric conversion element 27 have a phase of 1
80 degrees different. These electric signals are input to the computer, which is the above-mentioned arithmetic unit, and the calculation of halving the sum of these electric signals is performed to obtain the DC component of the interference intensity. Further, this computer subtracts the DC component from any electric signal to obtain an output signal.

On the other hand, the other of the light beams divided into two parts with the same amplitude by the second beam splitter 23 has the main axis perpendicular to or parallel to the plane of the paper, and is a quarter of the above.
The light enters the third polarization beam splitter 25 through the wave plate 30 and interferes with it. Hereinafter, the output signal is obtained in the same manner as in the case of the second polarization beam splitter 24 described above.

The phases which are obtained in the above-described manner are 9
The computer calculates the surface shape of the DUT 1 from each output signal which is a sine signal wave different by 0 degree. still,
The reason why the surface shape is calculated using two output signals whose phases are different from each other by 90 degrees is to detect the displacement direction of the corner cube 16.

Since the contact surface measuring instrument of the present invention is constructed and operates as described above, the corner cube 16 is not increased in size and is not greatly affected by disturbance, and it is more accurate and reliable. Higher measurement is possible. Particularly, in the present invention, since the laser constituting the light source means 3 is provided separately from the other means, the influence of the heat generated from the light source means 3 is less likely to occur and the measurement with less error can be performed. .

Next, FIG. 5 shows a second embodiment of the present invention. In the present embodiment, the probe 8 is provided at the lower end of the arm 7 which is a movable arm, and the corner cube 16 is provided at the upper end, and the arm 7 can only be raised and lowered. Then, the DUT 1 is placed on the moving stage 31 of the XY driving device. When performing the measurement, the probe 8 is brought into contact with the surface of the DUT 1 by moving the arm 7 up and down, and the moving stage 31 is moved in the XY directions. Other configurations and operations are similar to those of the above-described first embodiment.

In each of the above-mentioned embodiments, a laser having a single frequency is used as the light source means 3, but instead of this, the frequency is slightly different and the polarization directions are orthogonal to each other. A frequency laser can also be used.
In this case, the detecting means 5 is adapted to the laser of these two frequencies.

Further, the contact type surface profile measuring device of the present invention is
As described above, the measurement light is reflected by the corner cube 16 four times to amplify the displacement of the corner cube 16 according to the surface shape of the DUT 1 to 4 times the sensitivity. By changing the measuring means, optical means, etc. of the device which has been used to the one of the present invention, it is possible to obtain a highly accurate resolution at a low cost.

[0049]

Since the contact type surface profile measuring instrument of the present invention is constructed and operates as described above, it is possible to perform highly accurate measurement such as nm order. In addition, since it is not easily affected by disturbance such as heat and highly reliable measurement can be performed, it has a great practical effect.

[Brief description of drawings]

FIG. 1 is a diagram showing the overall configuration of the present invention.

FIG. 2 is a side view showing a measuring unit.

FIG. 3 is a view showing an upper surface and a side surface of a corner cube.

FIG. 4 is a diagram showing a detection means.

FIG. 5 is a diagram showing a main part of a second embodiment of the present invention.

[Explanation of symbols]

1 Object to be Measured 2 Measuring Means 3 Light Source Means 4 Optical Means 5 Detecting Means 6 Horizontal Axis 7 Arms 8 Probes 9 Isolators 10 1/2 Wave Plates 11 Polarization Preserving Fibers 12 First Polarizing Beam Splitters 13 First Reflecting Mirrors 14 1/4 Wave Plate 15 Third Reflecting Mirror 16 Corner Cube 17 Second Reflecting Mirror 18 First Reflecting Surface 19 Second Reflecting Surface 20 Third Reflecting Surface 21 Right Angle Prism 22 First Beam Splitter 23 Second beam splitter 24 Second polarization beam splitter 25 Third polarization beam splitter 26 First photoelectric conversion element 27 Second photoelectric conversion element 28 Third photoelectric conversion element 29 Fourth photoelectric conversion element 30 1/4 Wave plate 31 Moving stage

Claims (1)

[Scope of utility model registration request] 1. A measuring unit which is movable relative to an object to be measured and which is displaced according to the surface shape of the object to be measured, a light source unit, and a light beam emitted from the light source unit, which is a reference beam and the measuring unit. Optical means for dividing the measuring light for measuring the displacement and amplifying the optical path length of the measuring light that changes with the displacement of the measuring means, and the surface of the object to be measured based on this optical path length The measuring means includes a movable arm and a probe that is provided at one end of the movable arm and follows the surface of the object to be measured in contact with the surface of the object to be measured. The optical means splits the light flux emitted from the light source means into the reference light and the measurement light traveling along a substantially common optical path, a first polarizing beam splitter and a first reflecting mirror, and the movable arm. Is provided at the other end of the Corner cube that sends out in the direction opposite to the incident direction, the measurement light emitted from this corner cube, and the quarter-wave plate that transmits the reference light, and the measurement emitted from this quarter-wave plate. A second reflecting mirror that reflects light so as to go backward, a third reflecting mirror that reflects the reference light that has passed through the quarter-wave plate so as to go backward, and a third reflecting mirror that reflects and goes backward. Then, the reference light reflected by the first polarizing beam splitter, and the measuring light reflected by the second reflecting mirror and passing backward through the corner cube and passing through the first polarizing beam splitter, And a reflection member for reflecting the light toward the polarization beam splitter, the detection means converts the interference intensity of the reference light and the measurement light into an electric signal, and determines the surface shape of the object to be measured from the phase difference of the electric signal. To calculate, The reference light is reflected by the first reflecting mirror and then reciprocates twice between the third reflecting mirror and the reflecting member, and then takes an optical path that enters the detecting means. The contact type surface profile measuring device characterized in that after the light is emitted from the splitter, the optical path length is amplified by making two round trips between the second reflecting mirror and the reflecting member, and then the optical path entering the detecting means is taken. .