JP2015137886A - Depth measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a depth measuring instrument which is capable of appropriately measuring a depth of a microstructure as a measurement object even in the case of the microstructure having an extremely small diameter or width.SOLUTION: The depth measuring instrument includes a light source 10 which generates coherent light having a prescribed wavelength width, incidence/emission parts 22 and 25 which emit the coherent light toward a measurement object surface and on which the coherent light reflected by the measurement object surface impinges, a guiding optical system 20 which guides the coherent light from the light source 10 to the incidence/emission parts 22 and 25, an interference optical system 20 which causes the coherent light reflected by the measurement object surface and impinging on the incidence/emission parts 22 and 25 to interfere, and a detection unit 50 which detects interference light obtained by the interference optical system, per wavelength. The depth measuring instrument measures a depth of a microstructure formed on the measurement object surface. In the depth measuring instrument, the incidence/emission parts 22 and 25 are disposed so that an optical axis of the coherent light emitted to the measurement object surface is inclined relative to the measurement object surface.

Description

  The present invention relates to a depth measuring apparatus for measuring the depth of a fine structure provided on an object surface, for example, the depth of a fine hole or groove formed in a semiconductor substrate or the like by various etching processes.

  In the manufacturing process of a semiconductor integrated circuit, a low pressure is used to form a very fine hole (hole) such as TSV (= Through Silicon Via) or a very fine groove (trench) in a semiconductor substrate such as a silicon wafer. Etching using plasma or the like is performed. Usually, when performing etching processing, first, masking is performed with a resist film on a portion of the substrate where holes or grooves are not formed, and then etching processing is performed. As a result, only the unmasked portion is selectively scraped, so that it is possible to obtain holes or grooves of any shape by removing the resist film after processing. The depth of the hole or groove formed at this time depends on various conditions such as the etching time, the type of etching gas, and the gas pressure. Therefore, in order to set the depth of the hole or groove to the target depth, processing is performed. Control is performed to determine the end point of etching and adjust the conditions while monitoring the actual depth.

  As a device for optically measuring the depth of fine holes and grooves formed by etching, for example, a depth measuring device described in Patent Document 1 is known. This depth measuring apparatus uses, for example, a substrate processed by a plasma etching apparatus as a sample, and measures the distance between the bottom surface of the hole or groove and the surface of the sample, which change from moment to moment, thereby measuring the hole or groove. This device monitors depth in real time.

  FIG. 7 shows a schematic configuration of the depth measuring apparatus. The apparatus includes a light source 110, an introduction / interference optical system 120, a detection unit 150, a data processing unit 160, a control unit 170, and a display unit 180. The coherent light having a predetermined wavelength width emitted from the light source 110 is taken into the light source side optical fiber 121 provided in the introduction / interference optical system 120 and proceeds to the sample side optical fiber 122 via the fiber coupler 124. The sample S is emitted from the tip into the space, and is irradiated onto the sample S through the collimating lens 125 and the measurement window 133.

  The state of interference in the measurement target region of the sample S will be described with reference to an enlarged view in FIG. For example, when measuring the depth of a fine hole during etching, as shown in the figure, the reflected light 192a from the surface of the resist layer 192 on the substrate 191 and the surface of the substrate 191 due to light entering the resist layer 192 are used. The reflected light 191a and the reflected light 193a from the bottom surface of the fine hole which is the etched portion 193 are mainly generated.

  These reflected lights 191a, 192a, and 193a enter the end portion of the sample-side optical fiber 122 following the measurement window 133 and the collimator lens 125 in the opposite direction to the time of light irradiation. Then, the light reaches the detection unit 150 through the fiber coupler 124 and the detector-side optical fiber 123. As apparent from FIG. 7, the plurality of reflected lights 191a, 192a, and 193a have optical path differences from each other, and these reflected lights 191a, 192a, and 193a mainly pass through the sample-side optical fiber 122. Thus, interference occurs for each wavelength and becomes interference light.

  The interference light reaching the detection unit 150 is incident on a spectroscopic unit such as a diffraction grating 153 via a collimator lens 151 and a light amount adjustment unit 152 including a plurality of neutral density filters. Then, wavelength dispersion is performed by the spectroscopic means, and light having a plurality of wavelengths is simultaneously detected by an array detector 154 such as a CCD line sensor. A detection signal corresponding to each wavelength by the array detector 154 is input to the data processing unit 160. The data processing unit 160 creates a spectral spectrum in a predetermined wavelength range based on the detection signal, and fine holes based on the position of the peak on a signal (Fourier transformed signal) obtained by Fourier transforming the spectral spectrum. The depth of is calculated. Then, the calculation result is presented to the user by the display unit 180.

JP 2013-120063 A

  The above-mentioned conventional depth measuring apparatus does not cause a problem particularly when the diameter or width of the hole or groove to be measured is relatively large with respect to the spot diameter of the irradiation light. However, when the diameter or width of the hole or groove is very small, the reflected light from the bottom surface of the hole or groove becomes difficult to reach the introduction / interference optical system 120, and the light reaching the introduction / interference optical system is Reflected light from the periphery of the hole or groove (that is, the resist layer surface or the sample surface) becomes dominant. Therefore, if the light amount adjusting unit 152 or the array detector 154 is adjusted based on the intensity of the entire incident light to the detector, the amplitude of the interference light component reflecting the depth of the hole or groove becomes too small, and the measurement sensitivity is reduced. If the adjustment is made so that the sensitivity does not decrease, the upper limit of the amount of light that can be received by the detector (that is, the upper limit of the detector dynamic range) may be exceeded.

  The present invention has been made in view of these points, and the object of the present invention is to appropriately set the depth of the microstructure even when the diameter and width of the microstructure to be measured are very small. An object of the present invention is to provide a depth measuring apparatus capable of measuring.

A depth measuring apparatus according to the present invention, which has been made to solve the above problems, is a depth measuring apparatus that measures the depth of a microstructure formed on a measurement target surface,
a) a light source that generates coherent light having a predetermined wavelength width;
b) an incident / exit section that emits the coherent light toward the measurement target surface and on which the coherent light reflected by the measurement target surface is incident;
c) an introduction optical system for guiding the coherent light from the light source to the incident / exit section;
d) an interference optical system that interferes with the coherent light reflected on the measurement target surface and incident on the incident / exit section;
e) a detection unit for detecting the interference light obtained by the interference optical system for each wavelength;
Have
The incident / exit section is arranged such that the optical axis of the coherent light emitted to the measurement target surface is inclined with respect to the measurement target surface.

  When light is irradiated onto a silicon substrate or the like having a fine structure on the surface, most of the reflected light from the periphery of the fine structure travels in the same direction, that is, the regular reflection direction, whereas the light from the bottom of the fine structure The reflected light travels with a spread like light that has passed through the pin spot due to diffraction when emitted from the fine structure. Therefore, the traveling direction of the reflected light from the peripheral portion is more susceptible to the incident angle of the coherent light to the sample than the traveling direction of the reflected light from the bottom surface.

  In the conventional depth measuring apparatus, since the coherent light is vertically incident on the surface to be measured as shown in FIG. 7, the specular reflection component from the peripheral portion follows the same path as the incident light, and enters and exits ( In the case of the example in FIG. 7, the light is incident on the collimating lens 125 and the end of the sample-side optical fiber 122. On the other hand, in the depth measuring apparatus according to the present invention, the specular reflection component from the peripheral part is opposite to the incident light across the optical axis by irradiating the coherent light with an inclination to the surface to be measured. Therefore, the amount of light incident on the incident / exit section can be greatly reduced as compared with the conventional case. On the other hand, since the outgoing direction of the reflected light from the bottom surface of the fine structure is not easily affected by the incident angle, the incident light quantity to the incident / exit portion does not change greatly. As described above, in the depth measuring apparatus according to the present invention, the reflected light from the peripheral portion of the fine structure can be reduced intensively, so that the reflected light amount from the peripheral portion and the reflected light amount from the bottom surface of the fine structure are the same amount. The interference light extinction ratio (ratio between the peak and valley values of the interference light) can be improved and highly accurate depth measurement can be performed.

  As described above, according to the depth measurement apparatus of the present invention, the amount of reflected light received from the peripheral portion of the fine structure is reduced intensively by irradiating coherent light with an inclination to the surface to be measured. Therefore, even when the diameter or width of the structure to be measured is fine, the extinction ratio can be improved and highly accurate depth measurement can be performed.

The schematic block diagram of the depth measuring apparatus which concerns on one Embodiment of this invention. The schematic diagram which shows the state of the reflected light at the time of the measurement in the depth measuring apparatus of the said embodiment. The schematic diagram which shows the state of the reflected light at the time of the measurement in the conventional depth measuring apparatus. The schematic diagram which shows the measurement conditions in a test example. The figure which shows the spectrum obtained by the test example. The figure which shows the waveform obtained by Fourier-transforming the said spectrum. The schematic block diagram of the conventional depth measuring apparatus.

  A depth measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of a depth measurement apparatus according to the present embodiment, and FIGS. 2 and 3 are schematic diagrams illustrating a state of reflected light during depth measurement.

  This depth measuring apparatus uses a silicon substrate disposed in a vacuum chamber 31 of an etching apparatus as a sample S, and the depth of fine holes and fine grooves formed on the upper surface of the sample S (measurement target surface in the present invention). In general, the apparatus includes a light source 10, an introduction / interference optical system 20, a measurement unit 30, an optical system driving unit 40, a detection unit 50, a data processing unit 60, a control unit 70, and a display unit 80. Yes. The introduction / interference optical system 20 serves as both the introduction optical system and the interference optical system in the present invention.

  The data processing unit 60, the control unit 70, and the display unit 80 may be integrated with the depth measurement device, but are realized by an external computer connected to the depth measurement device via a network or the like. It may be. When an external computer is used, functions as the data processing unit 60, the control unit 70, and the display unit 80 may be exhibited by executing control / processing software installed in the computer in advance. it can.

  The light source 10 is a light source that emits light having a low wavelength coherence and high emission intensity and having a wavelength width necessary for measuring a desired depth, for example, a super luminescence having a center wavelength of 830 nm and a full width at half maximum of 40 nm. A cent diode (SLD) can be used.

  The introduction / interference optical system 20 includes a light source side optical fiber 21, a sample side optical fiber 22, a detector side optical fiber 23, a fiber coupler 24, and a collimating lens 25. The measurement light emitted from the light source 10 is taken into the light source side optical fiber 21 of the introduction / interference optical system 20, travels through the sample side optical fiber 22 via the fiber coupler 24, and proceeds to the measurement unit 30. The measurement light emitted from the end portion of the sample-side optical fiber 22 passes through the collimator lens 25 and is irradiated onto the sample S through the measurement window 33 provided in the vacuum chamber 31 of the measurement unit 30. The end portion of the sample-side optical fiber 22 and the collimating lens 25 correspond to the incident / exiting portion in the present invention. Further, the sample S is placed on the upper surface of the sample placing portion 32 provided in the vacuum chamber 31, and the upper surface corresponds to the sample placing surface in the present invention.

  Of the reflected light from the sample S, the light reflected in the direction of the measurement window 33 follows the measurement window 33 and the collimating lens 25 in the opposite direction to the time of irradiation of the measurement light and enters the end of the sample-side optical fiber 22. Then, the reflected lights having different optical path differences interfere with each other inside the sample-side optical fiber 22. The light that has passed through the sample-side optical fiber 22 reaches the detection unit 50 via the fiber coupler 24 and the detector-side optical fiber 23. Then, the light is dispersed for each wavelength by the diffraction grating 53 through the collimating lens 51 and the light amount adjusting unit 52, and then detected in parallel for each wavelength by the array detector 54 such as a CCD line sensor. These detection signals are sent to the data processing unit 60 through predetermined signal processing, and are used to calculate the depth of the etched portion on the sample surface by a method described later.

  The depth measurement apparatus according to this embodiment is characterized in that the optical axis of the measurement light emitted from the introduction / interference optical system 20 is inclined with respect to the sample surface. In order to realize this, in the present embodiment, the end surface of the sample-side optical fiber 22 and the collimating lens 25 are coincident with each other in the central axis, and the central axis is relative to the upper surface of the sample mounting portion 32 of the vacuum chamber 31. It is arranged to be inclined.

  An example of the state of the measurement light and the reflected light from the sample at this time is shown in FIG. For comparison, FIG. 3 shows an example of the state of the measurement light and the reflected light from the sample in the conventional depth measurement apparatus.

  In these examples, the sample S includes a substrate 91 as an object to be etched, a resist layer 92 made of an etching protection resist applied thereon, and an etched portion 93 where the substrate 91 is exposed without being applied with a resist. And have. Further, the spot diameter of the incident spot light on the sample S is adjusted so as to have a size straddling the etched portion 93 on the sample S and the surrounding resist layer 92. Thereby, on the sample S, reflected light 91a from the substrate surface, reflected light 92a from the resist layer surface, and reflected light 93a from the etched portion are generated. Of these, the reflected light 93a from the etched portion travels with a spread like light that has passed through the pin spot due to the diffraction phenomenon when emitted from the fine holes or grooves that are the etched portion 93. On the other hand, the reflected light 91a from the substrate surface and the reflected light 92a from the resist layer surface are scattered in various directions, but the reflected light in the regular reflection direction is particularly dominant. Therefore, the intensity distribution of the reflected light 91a from the substrate surface and the reflected light 92a from the resist layer surface in the space between the sample S and the introduction / interference optical system 20 is compared with the intensity distribution of the reflected light 93a from the etched portion. Therefore, the dependency on the incident angle of the measurement light is high.

  In the conventional depth measuring apparatus, as shown in FIG. 3, since the measurement light is irradiated perpendicularly to the sample S, most of the reflected light 91a from the substrate surface and the reflected light 92a from the resist layer surface are collimated lenses. 25 is incident. As a result, as described above, there is a problem that the ratio of the interference light component in the total amount of light received by the array detector 54 is reduced, and the measurement accuracy is lowered.

  On the other hand, in the depth measuring apparatus according to the present embodiment, as shown in FIG. 2, since the measurement light is irradiated with being inclined with respect to the sample S, the collimating lens 25 is compared with the conventional example of FIG. The amount of reflected light 91a from the incident substrate surface and reflected light 92a from the resist layer surface can be reduced. At this time, the amount of reflected light 93a from the etched portion that is incident on the collimating lens 25 also decreases, but the reflected light 91a and the resist layer surface from the substrate surface rather than the reflected light 93a from the etched portion as described above. Since the reflected light 92a from the surface is more dependent on the incident angle of the measuring light, the amount of reflected light 93a from the etched portion is reduced by the reflected light 91a from the substrate surface and the reflected light 92a from the resist layer surface. This is sufficiently smaller than the amount of decrease. As a result, the ratio of the interference light component in the total amount of light received by the array detector 54 can be increased, and the measurement accuracy can be improved.

  The depth measurement apparatus according to the present embodiment includes an optical system driving unit 40 that can change the relative position between the introduction / interference optical system 20 and the sample mounting unit 32, and is controlled by the control unit 70. The introduction / interference optical system 20 can be rotated and / or translated by the optical system driving unit 40.

  The ratio of the interference light component that reflects the depth of the etched portion 93 includes the reflected light 93a from the etched portion incident on the introduction / interference optical system 20, the reflected light 91a from the substrate surface, and the reflected from the resist layer surface. It becomes the highest when the intensity ratio with the light 92a is 1: 1. Therefore, it is desirable to adjust the optical system driving unit 40 so that the intensity ratio approaches the above value.

  When the incident angle of the measurement light is constant, the longer the distance from the sample S to the introduction / interference optical system 20 (specifically, the distance from the sample S to the collimating lens 25), the longer the introduction / interference optical system. The amount of reflected light 91a incident on the substrate surface 20 and the amount of reflected light 92a reflected from the resist layer surface decreases (that is, the incident angle dependency of the amount of received light of these reflected light 91a and 92a increases as the distance increases. growing). On the other hand, when the distance from the sample S is constant, the amount of the reflected light 91a and 92a incident on the introduction / interference optical system 20 decreases as the incident angle of the measurement light is increased. The amount of the reflected light 93a also decreases. Therefore, if a sufficient distance (for example, 50 mm or more) is provided between the sample S and the introduction / interference optical system 20, and the measurement light is incident on the sample S with a minimum incident angle (for example, 1 ° or less), The received light intensity of the reflected light 91a from the substrate surface and the reflected light 92a from the resist layer surface can be effectively reduced while maintaining the received light intensity of the reflected light 93a from the etched portion.

  The driving amount of the introduction / interference optical system 20 by the optical system driving unit 40 may be instructed directly by the user using an input means or the like (not shown), but the data based on the received light intensity in the array detector 54 It is desirable that the processing unit 60 calculates an appropriate driving amount, and the control unit 70 instructs the optical system driving unit 40 to drive the introduction / interference optical system 20 according to the calculation result.

  If the amount of incident light on the array detector 54 exceeds the dynamic range even if the optical system driving unit 40 is adjusted to reduce the reflected light 91a from the substrate surface and the reflected light 92a from the resist layer surface, the light amount adjustment is performed. The amount of incident light is adjusted by the unit 52. The light amount adjustment unit 52 reduces the intensity of the entire reflected light introduced into the detection unit 50 by inserting or removing a dimming element such as an ND filter on the optical path. In the present embodiment, as described above, the ratio of the interference light component in the entire reflected light introduced into the detection unit 50 is higher than in the conventional case, so that the amount of light incident on the array detector 54 is adjusted so that it falls within the dynamic range. Even when the portion 52 is adjusted, it is possible to prevent the conventional measurement accuracy from being lowered.

The reflected light from the sample S is detected for each wavelength by the array detector 54 as described above, and a spectral spectrum indicating the relationship between the wavelength and the signal intensity is created by the data processing unit 60 based on the detection signal. Further, the data processing unit 60 performs a process of extracting an interference light component from the spectrum, creates an interference spectrum, converts the horizontal axis from a wavelength to a wave number, and performs a Fourier transform so that each horizontal axis A graph representing the distance between the reflecting surfaces is obtained. In the sample S of FIG. 2, since the etched portion 93 is etched to some extent, the interference light obtained by the introduction / interference optical system 20 includes:
[I] Resist layer 92 upper surface−substrate 91 upper surface;
[Ii] The top surface of the substrate 91-the bottom surface of the etched portion 93;
[Iii] Interference light derived from the combination of three types of reflecting surfaces, that is, the upper surface of the resist layer 92 and the bottom surface of the etched portion 93 is included. Therefore, peaks appear at three positions corresponding to the optical distances [i], [ii], and [iii] in the signal waveform after Fourier transform. Therefore, the peak position indicating the longest distance among these is specified as the distance from the upper surface of the resist layer 92 corresponding to the above [iii] to the bottom surface of the etched portion 93, and thereby the fine portion which is the etched portion 93. Determine the depth of the hole or microgroove.

  The depth measurement as described above is repeatedly performed at predetermined time intervals during the execution of the etching process on the sample S in the vacuum chamber 31, and the hole depth that changes momentarily as the etching progresses is real time. Is calculated and displayed on the display unit 80.

  The depth measuring apparatus according to the present invention has been described with reference to one embodiment of the present invention, but the present invention is not limited to the above embodiment, and is appropriately modified within the scope of the present invention. It is obvious that additions and changes are included in the scope of the claims of the present application.

  For example, in the above-described embodiment, the depth measuring apparatus according to the present invention monitors the depths of the fine holes and fine grooves formed in the sample S to be processed placed in the vacuum chamber 31 of the etching apparatus. Although it was set as an apparatus, it is not restricted to this, The apparatus for monitoring the processing condition of the said material in the processing of various materials, or inspecting the depth of the hole and groove | channel provided in the workpiece surface after the process It is good.

  In the above-described embodiment, the introduction / interference optical system 20 is driven by the optical system driving unit 40 in order to adjust the incident angle of the measurement light, but a mechanism for driving the sample mounting unit 32 is provided. The sample side may be moved.

  In the above embodiment, the optical system driving unit 40 drives the introduction / interference optical system 20 under the control of the control unit 70, thereby adjusting the distance to the sample S and the incident angle of the measurement light. However, instead of this, the distance and angle may be adjusted by the user manually moving the introduction / interference optical system 20. Moreover, it is good also as a structure which does not set it as the structure which can adjust the said distance and angle, and always performs depth measurement from a fixed distance and angle. In this case, the distance from the introduction / interference optical system 20 (specifically, the center of the collimating lens 25) to the measurement target surface is set to 50 mm or more, and the incident angle of the measurement light to the measurement target surface is set to 1 ° or less. desirable.

  The best incident angle is the angle at which the extinction ratio of the interference wave is maximized. Therefore, it is desirable to adjust the incident angle at which the extinction ratio is maximized by moving the introduction / interference optical system 20 by the optical system driving unit 40 or manually to increase the incident angle from 0 degree. Similarly, it is desirable that the distance from the sample is adjusted to a distance that maximizes the extinction ratio by moving the introduction / interference optical system 20 by the optical system driving unit 40 or manually.

  Hereinafter, test examples performed for confirming the effect of the depth measuring apparatus according to the present invention will be described. FIG. 4 is a diagram showing measurement conditions in this test example. In this test example, a silicon substrate 91 (without a masking film) having a micro hole 94 having a diameter of 10 μm and a depth of 75 μm formed on the surface is used as a sample, and various incident angles θ of measurement light irradiated on the sample from the SLD light source It changed and the depth measurement of the said fine hole 94 was performed. The distance from the center of the collimating lens 25 to the measurement target surface was 120 mm, the spot diameter of the measurement light was 100 μm, and irradiation was performed so that the irradiation spot straddled the fine hole 94 and its peripheral part. The reflected light from the sample was dispersed by a spectroscope and then received by an array detector (quantization bit number: 10 bits).

  The spectrum obtained as described above is shown in FIG. In each of these spectrums, the horizontal axis is the wavelength [μm], and the vertical axis is the input value of the array detector (that is, the incident light quantity to the detector). (A)-(e) of the figure shows the measurement results when the incident angle θ of the measurement light is 0 °, 0.08 °, 0.17 °, 0.25 °, and 0.35 °, respectively. ing. At this time, the amount of attenuation in the light amount adjusting unit was set to −30 db. Further, (f) in the figure shows the measurement results when the incident angle θ is set to 0.35 °, which is the same as (e) in the figure, and the attenuation in the light amount adjusting unit is set to −20 db. As apparent from FIGS. 5A to 5E, the amount of reflected light decreases as the incident angle of the measuring light increases, whereas the interference by the reflected light from the surface of the substrate 91 and the bottom of the hole 94 occurs. The extinction ratio of the light component (portion enclosed by an ellipse in the figure), that is, the ratio of the peak and valley values of the interference light is large. Further, in FIG. 5F, the peak height of the entire reflected light is approximately the same as that shown in FIG. 5A by adjusting the attenuation, but the extinction ratio of the interference light component is shown in FIG. You can see that it is getting bigger. This is because the amount of reflected light from the surface of the substrate 91 is greatly reduced to approach the amount of reflected light from the bottom of the fine hole 94 and the extinction ratio of the interference light is improved. This is because the dynamic range can be used effectively. In this embodiment, the amount of light incident on the array detector 54 is adjusted by the light amount adjusting unit 52, but the same effect can be obtained by increasing the exposure time of the array detector 54.

  FIGS. 6A to 6F show waveforms obtained by extracting an interference light component from the spectral spectra of FIGS. 5A to 5F and converting the horizontal axis into wave numbers, and then performing Fourier transform. Yes. The horizontal axis of the figure indicates the depth [μm] of the fine hole 94, and a peak (location indicated by an arrow in the figure) derived from the interference light component appears at a position of 75 μm. In (f) of the figure, the peak of 75 μm is higher than in (a) of the figure, and it can be seen that the detection of the peak is easy.

DESCRIPTION OF SYMBOLS 10 ... Light source 20 ... Introduction / interference optical system 21 ... Light source side optical fiber 22 ... Sample side optical fiber 23 ... Detector side optical fiber 25 ... Collimator lens 30 ... Measurement part 31 ... Vacuum chamber 32 ... Sample mounting part 33 ... Measurement Window 40 ... Optical system drive unit 50 ... Detection unit 52 ... Light amount adjustment unit 53 ... Diffraction grating 54 ... Array detector 60 ... Data processing unit 70 ... Control unit 91 ... Substrate 92 ... Resist layer 93 ... Etched portion 91a ... Substrate surface Reflected light 92a ... Reflected light from resist layer surface 93a ... Reflected light from etched portion

Claims (4)

A depth measurement device for measuring the depth of a microstructure formed on a measurement target surface,
a) a light source that generates coherent light having a predetermined wavelength width;
b) an incident / exit section that emits the coherent light toward the measurement target surface and on which the coherent light reflected by the measurement target surface is incident;
c) an introduction optical system for guiding the coherent light from the light source to the incident / exit section;
d) an interference optical system that interferes with the coherent light reflected on the measurement target surface and incident on the incident / exit section;
e) a detection unit for detecting the interference light obtained by the interference optical system for each wavelength;
Have
The depth measuring apparatus, wherein the incident / exit section is arranged so that an optical axis of the coherent light emitted to the measurement target surface is inclined with respect to the measurement target surface.   The depth according to claim 1, wherein a distance from the incident / exit section to the measurement target surface is 50 mm or more, and an incident angle of coherent light to the measurement target surface is 1 ° or less. measuring device. Furthermore,
f) a sample mounting surface for mounting a sample having the measurement target surface;
g) an incident angle adjusting unit that adjusts an incident angle of coherent light with respect to the measurement target surface by changing a relative position between the incident / exiting unit and the sample mounting surface;
The depth measuring device according to claim 1, wherein: Furthermore,
h) control means for controlling the incident angle adjustment unit;
Have
The depth measuring apparatus according to claim 3, wherein the control unit determines a change amount of the relative position based on an amount of received light in the detection unit.

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