JP2025008158A - Distance measurement device and distance measurement method - Google Patents

Abstract

To obtain a desired measurable range.SOLUTION: A distance measuring device 1 includes: a light source unit 3 for generating measurement light L1; one optical fiber 2 that applies irradiation light L2 as one portion of the measurement light L1 to a measurement object surface 9a and includes an optical fiber end face 2a for reflecting end face reflection light L3 as the remainder of the measurement light L1; a spectroscope 51 for obtaining a spectrum of interference light L5 generated by interference between return light L4 and the end face reflection light L3 while the return light L4 impinges on the optical fiber 2 again after the irradiation light L2 is reflected on the measurement object surface 9a; and a computer 6 for obtaining distance 9H from the optical fiber end face 2a to the measurement object surface 9a by using the spectrum of the interference light L5.SELECTED DRAWING: Figure 1

Description

The present invention relates to a distance measurement device and a distance measurement method.

Patent Document 1 by the present inventors discloses a technique for obtaining the thickness of a liquid film using an optical fiber. In this technique, measurement light is emitted from an optical fiber toward a moving liquid film. Then, the light intensity of the light that is reflected at the liquid film gas-liquid interface and enters the optical fiber again is obtained. The light intensity of the light that returns to the optical fiber attenuates according to the distance from the end face of the optical fiber that emits the measurement light to the liquid film gas-liquid interface. Therefore, by knowing the degree of attenuation of the light intensity, the distance from the end face of the optical fiber to the liquid film gas-liquid interface can be known.

JP 2022-77303 A

In technical fields where minute film thicknesses and minute distances are measured, the range of the measurement target varies widely. However, with measurement methods that use light intensity, the measurement range from which distance can be obtained is often limited due to factors such as susceptibility to disturbances.

Therefore, the present invention provides a distance measurement device and a distance measurement method that can obtain the distance in a desired measurement range.

A distance measurement device according to one embodiment of the present invention includes a light source that generates measurement light, an optical fiber that irradiates a measurement target surface with illumination light that is a part of the measurement light and that includes an optical fiber end face that reflects reflected light that is the remainder of the measurement light, a spectroscopic section that obtains a spectrum of interference light that is generated by interference between the return light and the reflected light, which is return light that is reflected by the measurement target surface and then re-enters the optical fiber, and a distance acquisition section that obtains the distance from the optical fiber end face to the measurement target surface using the spectrum of the interference light.

A distance measurement method according to another embodiment of the present invention includes the steps of irradiating a surface to be measured with illumination light, which is a portion of the measurement light generated by a light source, and emitting the illumination light toward the object to be measured from an optical fiber including an end face of the optical fiber that reflects reflected light, which is the remainder of the measurement light; obtaining a spectrum of interference light that is generated by interference between the return light and the reflected light, which is return light that is reflected by the surface to be measured and then reenters the optical fiber; and obtaining the distance from the end face of the optical fiber to the surface to be measured using the spectrum of interference light.

The distance measurement device and distance measurement method obtain interference light that is generated by interference between reflected light generated at the end face of the optical fiber and return light that reenters the optical fiber due to reflection of the irradiated light generated at the measurement target surface. The distance measurement unit then obtains the distance from the end face of the optical fiber to the measurement target surface using the spectrum of the interference light. The spectrum of the interference light is less susceptible to disturbances than the light intensity of the interference light. Therefore, it is possible to obtain the distance in a measurement target range that is not suitable for distance measurement using the light intensity of the interference light.

The distance measurement device of one embodiment may further include a light intensity acquisition unit that acquires the light intensity of the interference light. The distance acquisition unit may include a first candidate distance acquisition unit that acquires a first candidate distance using the spectrum of the interference light, a second candidate distance acquisition unit that acquires a second candidate distance using the light intensity of the interference light, and a distance output unit that selects either the first candidate distance or the second candidate distance as the distance from the end face of the optical fiber to the measurement target surface. With this configuration, it is possible to obtain a wide measurement target range that combines the measurement target range in which distance measurement using the spectrum of the interference light is appropriate and the measurement target range in which distance measurement using the light intensity of the interference light is appropriate.

The distance acquisition unit in one embodiment of the distance measurement device may perform the following operations: an operation of acquiring a first candidate distance by a first candidate distance acquisition unit; an operation of acquiring a second candidate distance by a second candidate distance acquisition unit; an operation of the distance output unit comparing the light intensity of the interference light with a threshold value, and selecting the first candidate distance as the distance from the optical fiber end face to the measurement target surface if the light intensity of the interference light is equal to or greater than the threshold value; and an operation of selecting the second candidate distance as the distance from the optical fiber end face to the measurement target surface if the light intensity of the interference light is less than the threshold value. This operation makes it easy to select either the first candidate distance or the second candidate distance as the distance from the optical fiber end face to the measurement target surface.

The distance acquisition unit in one embodiment of the distance measurement device may perform the following operations: the distance output unit compares the light intensity of the interference light with a threshold; if the light intensity of the interference light is equal to or greater than the threshold, the first candidate distance acquisition unit acquires a first candidate distance and outputs the first candidate distance as the distance from the optical fiber end face to the measurement target surface; and if the light intensity of the interference light is less than the threshold, the second candidate distance acquisition unit acquires a second candidate distance and outputs the second candidate distance as the distance from the optical fiber end face to the measurement target surface. This operation also makes it possible to easily output either the first candidate distance or the second candidate distance as the distance from the optical fiber end face to the measurement target surface.

The distance acquisition unit in one embodiment of the distance measurement device may include an error distance acquisition unit that acquires an error distance indicating the uncertainty derived from the noise signal and superimposed on the second candidate distance based on the intensity of the noise signal output by the light intensity acquisition unit when the irradiation light is not emitted from the fiber end face, and an evaluation value acquisition unit that acquires an error evaluation value that obtains the proportion of the error distance in the second candidate distance. With this configuration, it is possible to select either the first candidate distance or the second candidate distance based on a threshold value of a viewpoint different from the light intensity.

The distance acquisition unit in one embodiment of the distance measurement device may perform the following operations: an operation of acquiring a first candidate distance by a first candidate distance acquisition unit; an operation of acquiring a second candidate distance by a second candidate distance acquisition unit; an operation of the distance output unit comparing an error evaluation value with a threshold value, and selecting the first candidate distance as the distance from the optical fiber end face to the measurement target surface if the error evaluation value is equal to or greater than the threshold value; and an operation of selecting the second candidate distance as the distance from the optical fiber end face to the measurement target surface if the error evaluation value is less than the threshold value. This operation also makes it easy to select either the first candidate distance or the second candidate distance as the distance from the optical fiber end face to the measurement target surface.

The distance output unit in one embodiment of the distance measurement device may perform the following operations: the distance output unit compares the light intensity of the interference light with a threshold; if the error evaluation value is equal to or greater than the threshold, the first candidate distance acquisition unit obtains a first candidate distance and outputs the first candidate distance as the distance from the optical fiber end face to the measurement target surface; and if the error evaluation value is less than the threshold, the second candidate distance acquisition unit obtains a second candidate distance and outputs the second candidate distance as the distance from the optical fiber end face to the measurement target surface. This operation also makes it possible to easily output either the first candidate distance or the second candidate distance as the distance from the optical fiber end face to the measurement target surface.

The present invention provides a distance measurement device and a distance measurement method that can obtain a desired measurable range.

FIG. 1 is a diagram showing components of a distance measuring device according to an embodiment. Fig. 2A is a diagram showing a configuration in which the distance measurement device according to the embodiment is applied to measurement of a liquid film, and Fig. 2B is a diagram showing a configuration in which the distance measurement device according to the embodiment is applied to measurement of a distance to a measurement target. FIG. 3 is a diagram illustrating components of the computer shown in FIG. FIG. 4 is a graph showing the relationship between the distance to the measurement target surface and the signal intensity. FIG. 5 is a flowchart showing a distance measuring method executed by the computer shown in FIG. Fig. 6(a) is a graph showing noise superimposed on the output signal of the photodetector, and Fig. 6(b) is a graph explaining the effect of the noise shown in Fig. 6(a) on distance. FIG. 7 is a diagram showing components of a distance measuring device according to a modified example. FIG. 8 is a flowchart showing a distance measuring method executed by the computer shown in FIG. FIG. 9 is a diagram showing components of a distance measurement device according to still another modified example. FIG. 10 is a flowchart showing a distance measuring method performed by the distance measuring device of the modified example. FIG. 11 is a graph showing the results of the example.

Below, the embodiment of the present invention will be described in detail with reference to the attached drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

Figure 1 is a diagram showing a schematic diagram of a distance measurement device 1. The distance measurement device 1 emits measurement light from a single optical fiber 2 toward a measurement object 9. The distance measurement device 1 obtains return light that is reflected by the measurement object 9 and returns to the optical fiber 2. The distance measurement device 1 then obtains the distance to the measurement object 9 using the return light.

The distance measurement device 1 can be applied, for example, to semiconductor manufacturing processes. Many processes in semiconductor manufacturing processes involve the rotation of wafers. When rotating the wafer, wafer alignment is important to suppress eccentricity and tilt of the wafer. Furthermore, as the integration density of semiconductor chips increases in the future, it is expected that it will become more important to prevent uneven contamination within the wafer surface and edge dripping of resist material. In other words, the importance of wafer alignment is expected to increase in the future. In this case, it is expected that measurement accuracy at the micrometer level, and even sub-micrometer level, will be required to evaluate wafer alignment. Furthermore, it is expected that a need will arise to measure vibrations associated with wafer rotation.

Specifically, in the semiconductor manufacturing process, it is desirable to measure the tilt and flatness of the wafer on-site during processes such as forming a resist film (coating), polishing the wafer, and cleaning the wafer. In these processes, the distance measurement device 1 is used to measure the thickness of the resist film and the distance to the wafer, and the tilt and flatness of the wafer are obtained based on the results. The results of measuring the distance to the wafer may also be used to check the positioning accuracy of the wafer. From the perspective of checking the positioning accuracy, the measurement target is not limited to semiconductor wafers, and may also be applied to fields such as magnetic disk substrates and precision machining. Furthermore, the distance measurement device 1 can also be used to observe the bearing gap on-site.

The distance measurement device 1 and distance measurement method were developed as a result of extensive research into a method that could meet these needs.

First, two examples of the "distance to the measurement object 9" are presented. The "distance" in this embodiment includes the "thickness" of the measurement object 9 illustrated in FIG. 2(a) and the "distance" to the measurement object 9 illustrated in FIG. 2(b). In the examples of FIG. 2(a) and FIG. 2(b), the light emitted from the optical fiber end face 2a and the reflected light are illustrated tilted with respect to the optical axis of the optical fiber 2. This is for convenience of explanation. The light emitted from the optical fiber end face 2a and the reflected light may be parallel to the optical axis of the optical fiber 2 or tilted. For example, the light emitted from the optical fiber end face 2a and the reflected light may be approximately parallel to the optical axis of the optical fiber 2. In other words, the light emitted from the optical fiber end face 2a and the reflected light may be approximately perpendicular to the optical fiber end face 2a.

First, the distance measurement device 1 obtains the thickness of the liquid film (hereinafter referred to as the "film thickness") as shown in FIG. 2(a). In other words, the "measurement object 9" is the liquid 91, and the "distance to the measurement target surface" is the distance from the optical fiber end face 2a of the optical fiber 2 to the gas-liquid interface 91a (measurement target surface 9a). When the bottom surface 101 of the flow path through which the liquid 91 flows and the optical fiber end face 2a are coincident with each other, the distance from the optical fiber end face 2a to the gas-liquid interface 91a is the distance 9H from the gas-liquid interface 91a to the liquid-solid interface 91b of the liquid 91, that is, the "film thickness".

An example of an application of the distance measurement device 1 to obtain the thickness of a liquid film may be, for example, a process of applying a resist liquid to the surface of a wafer. Another example of an application of the distance measurement device 1 to obtain the thickness of a liquid film may be the observation of liquid (water) adhering to a stationary blade in a gas turbine used for thermal power generation or the like. For example, the distance measurement device 1 of this embodiment is disposed at multiple locations on the inner surface of a generator turbine. With this configuration, it becomes possible to measure the tilt movement and/or amplitude of the liquid film surface by continuous measurement at multiple points in real time.

Secondly, the distance measurement device 1 obtains the distance to the object 92 (hereinafter referred to as the "separation distance") as shown in FIG. 2(b). In other words, the "measurement object 9" is the object 92, and the "distance to the measurement object surface" is the distance 9H from the optical fiber end face 2a to the surface 92a of the object 92. An example of the object 92 is a silicon wafer.

The distance measurement device 1 can arbitrarily select between two distance measurement modes depending on the installation mode relative to the measurement object 9. Therefore, there is no difference in the configuration of the distance measurement device 1 between the mode for measuring the film thickness shown in FIG. 2(a) and the mode for measuring the separation distance shown in FIG. 2(b).

Several types of light used in the following explanation will be described. In the following explanation, "measurement light L1", "illumination light L2", "end surface reflected light L3", "return light L4", and "interference light L5" will be exemplified. Measurement light L1 is light generated by light source unit 3, which will be described later. Measurement light L1 includes a specific wavelength component that includes only a specific predetermined wavelength, and a white light component that includes multiple wavelengths and has substantially no bias in intensity for each wavelength. A portion of measurement light L1 is emitted to the outside, and the remainder is reflected at optical fiber end surface 2a. The light emitted to the outside is illumination light L2. The light that is reflected is end surface reflected light L3.

The irradiation light L2 reaches the measurement object 9 and is reflected by the gas-liquid interface 91a (see FIG. 2(a)) of the measurement object 9 or the surface 92a (see FIG. 2(b)) of the object 92. A part or all of the reflected irradiation light L2 enters the core 21 of the optical fiber 2 again from the optical fiber end face 2a. The light that enters the core 21 of the optical fiber 2 again from the optical fiber end face 2a is the return light L4. The return light L4 and the end face reflected light L3 interfere with each other within the core 21. The light that results from the interference between the return light L4 and the end face reflected light L3 is the interference light L5.

Refer back to FIG. 1. As shown in FIG. 1, the distance measurement device 1 has a light source unit 3, a light guide unit 4, an optical fiber 2, a light receiving unit 5, and a computer 6.

The light source unit 3 generates white light L11 and specific wavelength light L12 in response to a command received from the computer 6, and passes the white light L11 and specific wavelength light L12 to the light guide unit 4. The light guide unit 4 combines the received white light L11 and specific wavelength light L12 to generate measurement light L1, and passes the measurement light L1 to the optical fiber 2. The optical fiber 2 emits the measurement light L1 received from the light receiving unit 5 toward the measurement object 9. The optical fiber 2 receives the measurement light L1 reflected by the measurement object 9 as return light L4. The optical fiber 2 then passes the interference light L5, which includes the return light L4 and the end surface reflected light L3, to the light receiving unit 5. The light receiving unit 5 acquires information about the interference light L5 and passes the information to the computer 6. The computer 6 uses the information about the interference light L5 to obtain the distance 9H to the measurement object surface 9a.

The light source unit 3 generates measurement light L1. The light source unit 3 may switch between emitting and stopping measurement light L1 based on a command passed from the computer 6. The light source unit 3 is optically connected to the light guide unit 4. The light source unit 3 includes a white light source 31 and a laser light source 32. The white light source 31 generates white light L11 that includes multiple wavelengths and has substantially no bias in intensity for each wavelength. The laser light source 32 generates specific wavelength light L12 that includes only a predetermined specific wavelength.

The light guide unit 4 has a first coupler 41, a second coupler 42, and a third coupler 43. The light guide unit 4 has a function of transmitting light from the light source unit 3 to the optical fiber 2, and a function of transmitting light from the optical fiber 2 to the light receiving unit 5.

First, the function of passing light from the light source unit 3 to the optical fiber 2 will be described. The first coupler 41 is connected to the white light source 31 and the third coupler 43. The first coupler 41 passes the white light L11 received from the white light source 31 to the third coupler 43. The second coupler 42 is connected to the laser light source 32 and the third coupler 43. The second coupler 42 passes the specific wavelength light L12 received from the laser light source 32 to the third coupler 43. The third coupler 43 combines the white light L11 received from the first coupler 41 and the specific wavelength light L12 received from the second coupler 42. As a result of combining the white light L11 and the specific wavelength light L12, the measurement light L1 is generated. The third coupler 43 is connected to the optical fiber 2. The third coupler 43 passes the measurement light L1 to the optical fiber 2.

Next, the function of passing light from the optical fiber 2 to the light source unit 3 will be described. The third coupler 43 receives the interference light L5 from the optical fiber 2. The third coupler 43 passes the interference light L5 to each of the first coupler 41 and the second coupler 42. The first coupler 41 passes the interference light L5 to the spectroscope 51. The second coupler 42 passes the interference light L5 to the photodetector 52.

The optical fiber 2 has an optical fiber base end connected to the third coupler 43 of the light guide unit 4, and an optical fiber output end facing the measurement object 9. The optical fiber output end includes an optical fiber end face 2a (see FIG. 2(a) etc.).

The optical fiber end surface 2a shown in FIG. 2(a) etc. is perpendicular to the optical axis of the optical fiber 2. The optical fiber end surface 2a may be an inclined surface inclined with respect to the optical axis of the optical fiber 2.

The light receiving unit 5 has a spectroscope 51 (spectroscope section) and a photodetector 52 (light intensity acquisition section). The spectroscope 51 obtains the spectrum of the interference light L5. The spectrum of the interference light L5 indicates the light intensity for each wavelength contained in the interference light L5. The spectroscope 51 passes the spectrum of the interference light L5 to the computer 6. In the following description, the spectrum of the interference light L5 handled by the computer 6 is referred to as interference light spectrum data D1. The photodetector 52 obtains the light intensity of the interference light L5. The light intensity of the interference light L5 is the sum of the light intensities for each wavelength. The photodetector 52 passes the light intensity of the interference light L5 to the computer. In the following description, the light intensity of the interference light L5 handled by the computer 6 is referred to as interference light intensity data D2.

The computer 6 sends commands to the light source unit 3 to control the operation of the light source unit 3. The computer 6 obtains the distance 9H to the measurement target surface 9a based on the information received from the light receiving unit 5. The information received from the light receiving unit 5 is the interference light spectrum data D1 and the interference light intensity data D2.

First, the hardware configuration of the computer 6 will be described with reference to FIG. 3. The computer 6 has a processor 61, which is a CPU (Central Processing Unit), a main storage unit 62, a memory 63, an external communication unit 64, an operation unit 65, and an output unit 66. The computer 6 is composed of this hardware and software such as programs.

The processor 61 executes an operating system, application programs, etc. The main memory unit 62 is composed of a ROM (Read Only Memory) and a RAM (Random Access Memory). The memory 63 is a storage medium composed of a hard disk, a flash memory, etc. The memory 63 generally stores a larger amount of data than the main memory unit 62. The operation unit 65 is composed of a keyboard, a mouse, a touch panel, a microphone for voice input, etc. The output unit 66 is composed of a display, a printer, etc. For example, the computer 6 may display the distance 9H to the measurement target surface 9a, etc. on a display, etc.

The memory 63 stores in advance a program P1 for obtaining the distance 9H to the measurement target surface 9a and data necessary for processing. The program P1 for obtaining the distance 9H to the measurement target surface 9a causes the computer 6 to execute several functional elements for obtaining the distance 9H to the measurement target surface 9a. For example, the program P1 for obtaining the distance 9H to the measurement target surface 9a is loaded by the processor 61 or the main memory unit 62, and causes at least one of the processor 61, the main memory unit 62, the memory 63, the external communication unit 64, the operation unit 65, and the output unit 66 to operate.

As shown in FIG. 1, the processor 61 functions as a first candidate distance acquisition unit 6a, a second candidate distance acquisition unit 6b, and a distance output unit 6c by executing a program P1 that obtains a distance 9H to the measurement target surface 9a read from the memory 63.

The computer 6 calculates the first candidate distance data D3 obtained using the interference light spectrum data D1 and the second candidate distance data D4 obtained using the interference light intensity data D2. Then, the computer 6 selects either the first candidate distance data D3 or the second candidate distance data D4 as the distance 9H to the measurement target surface 9a using a predetermined judgment condition. The first candidate distance data D3 is suitable for measuring the distance 9H to the measurement target surface 9a, which is relatively short. The second candidate distance data D4 is suitable for measuring the distance 9H to the measurement target surface 9a, which is relatively long. In other words, the range of distances suitable for measurement differs from each other. Then, the first candidate distance data D3 or the second candidate distance data D4 is selected by judgment based on the predetermined judgment condition, so that the range of the distance 9H to the measurement target surface 9a output by the computer 6 is the combination of the range of distance measurement targeted by the first candidate distance data D3 and the range of distance measurement targeted by the second candidate distance data D4.

The first candidate distance acquisition unit 6a reads out the interference light spectrum data D1 from the memory 63. The first candidate distance acquisition unit 6a obtains the first candidate distance data D3 using the interference light spectrum data D1. Then, the first candidate distance acquisition unit 6a stores the first candidate distance data D3 in the memory 63.

As a method for obtaining the distance using the interference light spectrum data D1, for example, so-called interference spectroscopy may be used. The spectrum of the interference light L5 depends on the refractive index and distance of the medium through which the irradiation light L2 propagates. The medium through which the irradiation light L2 propagates is a liquid according to the example of FIG. 2(a), and is air according to the example of FIG. 2(b). The relationship between the distance 9H to the measurement target surface 9a and the spectrum of the interference light L5 is defined by the following formula (1).
d=Δm/2n×(λ1×λ2/(λ1-λ2))...(1)
d: first candidate distance data D3.
Δm: the number of peaks in the interference light spectrum.
n: refractive index of the medium.
λ1, λ2: wavelengths.

The second candidate distance acquisition unit 6b reads out the interference light intensity data D2 from the memory 63. The second candidate distance acquisition unit 6b acquires the second candidate distance data D4 using the interference light intensity data D2. The second candidate distance acquisition unit 6b then stores the second candidate distance data D4 in the memory 63. The method of acquiring the second candidate distance data D4 using the interference light intensity data D2 may be the method described in JP 2022-77303 A by the present inventors.

The distance output unit 6c obtains the first candidate distance data D3, the second candidate distance data D4, and the interference light intensity data D2 from the memory 63. The distance output unit 6c selects either the first candidate distance data D3 or the second candidate distance data D4 as the distance 9H to the measurement target surface 9a using a predetermined judgment condition. The distance output unit 6c stores the distance 9H to the measurement target surface 9a in the memory.

As a predetermined judgment condition, "Is the interference light intensity equal to or greater than the intensity threshold?" may be used. FIG. 4 shows the distance 9H to the measurement target surface 9a and the signal intensity output from the photodetector 52. In other words, the signal intensity output from the photodetector 52 is the interference light intensity. As shown in graph G4 of FIG. 4, the signal intensity (interference light intensity) weakens as the distance 9H to the measurement target surface 9a increases. A high signal intensity is advantageous from the viewpoint of S/N ratio, etc. However, in the range R1 where the signal intensity is high, the signal intensity changes significantly with an increase (or decrease) in the distance 9H to the measurement target surface 9a. In such a relationship, it is disadvantageous to calculate the distance 9H to the measurement target surface 9a based on the signal intensity. Therefore, in the range R1 where the absolute value of the signal intensity is large and the signal intensity is high with respect to an increase (or decrease) in the distance 9H to the measurement target surface 9a, the first candidate distance data D3 based on the interference light spectrum data D1 is selected as the distance 9H to the measurement target surface 9a. On the other hand, in a range such as range R2 where the absolute value of the signal strength is small and the signal strength is small relative to an increase (or decrease) in the distance 9H to the measurement target surface 9a, the second candidate distance data D4 based on the interference light intensity data D2 is selected as the distance 9H to the measurement target surface 9a.

That is, an intensity threshold _VTH is set for the signal intensity (interference light intensity). When the signal intensity is greater than the intensity threshold _VTH , first candidate distance data D3 based on the interference light spectrum data D1 is selected as the distance 9H to the measurement target surface 9a. On the other hand, when the signal intensity is less than the intensity threshold _VTH , second candidate distance data D4 based on the interference light intensity data D2 is selected as the distance 9H to the measurement target surface 9a.

As an example, the range of distances for which the first candidate distance data D3 is used may be 1 μm or more and less than 100 μm. The range of distances for which the second candidate distance data D4 is used may be 100 μm or more. In this case, the signal intensity (interference light intensity) at which the second candidate distance data D4 is 100 μm is set as the intensity threshold _VTH .

In addition, a part of the distance range in which the first candidate distance data D3 is adopted and a part of the distance range in which the second candidate distance data D4 is adopted may overlap. For example, it is possible to use either the first candidate distance data D3 or the second candidate distance data D4 in the range of 50 μm or more and less than 100 μm. In this case, the signal strength at which the second candidate distance data D4 is 50 μm is adopted as the first intensity threshold, and the signal strength at which the second candidate distance data D4 is 100 μm is adopted as the second intensity threshold. Then, when the second candidate distance data D4 obtained by measurement is equal to or greater than the first intensity threshold, the first candidate distance data D3 is adopted. When the second candidate distance data D4 obtained by measurement is less than the second intensity threshold, the second candidate distance data D4 is adopted. When the second candidate distance data D4 obtained by measurement is less than the first intensity threshold and equal to or greater than the second intensity threshold, either the first candidate distance data D3 or the second candidate distance data D4 is selected. For example, if the second candidate distance data D4 is less than the first intensity threshold and greater than or equal to the second intensity threshold, it may be determined in advance whether the first candidate distance data D3 or the second candidate distance data D4 is to be selected.

<Method of Obtaining Distance 9H to Measurement Target Surface 9a>
Next, a method for obtaining the distance 9H to the measurement target surface 9a, which is executed by the computer 6, will be described with reference to FIG.

First, the irradiation light L2 is emitted toward the measurement target surface 9a (S11). This step S11 is performed by the computer 6, the light source unit 3, the light guide unit 4, and the optical fiber 2.

Next, the interference light spectrum data D1 and the interference light intensity data D2 are obtained (S12). This step S12 is performed by the optical fiber 2, the light guide unit 4, the light receiving unit 5, and the computer 6. As a result of step S12, the interference light spectrum data D1 and the interference light intensity data D2 are stored in the memory 63.

Next, first candidate distance data D3 is obtained (S13). This step S13 is performed by the processor 61 constituting the first candidate distance acquisition unit 6a and the memory 63 storing the interference light intensity data D2. As a result of step S13, the first candidate distance acquisition unit 6a stores the first candidate distance data D3 in the memory 63.

Next, second candidate distance data D4 is obtained (S14). This step S14 is performed by the processor 61 constituting the second candidate distance acquisition unit 6b and the memory 63 storing the interference light spectrum data D1. As a result of step S14, the second candidate distance acquisition unit 6b stores the second candidate distance data D4 in the memory 63.

Next, either the first candidate distance data D3 or the second candidate distance data D4 is selected as the distance 9H to the measurement target surface 9a (S15). This step S15 is performed by the processor 61 constituting the distance output unit 6c, and the memory 63 storing the first candidate distance data D3, the second candidate distance data D4, and the interference light intensity data D2. As a result of step S15, the distance output unit 6c stores the selected candidate distance in the memory 63 as the distance 9H to the measurement target surface 9a.

<Action and effect>
Conventionally, there are several methods for measuring minute distances. For example, examples of methods for measuring minute distances include an ultrasonic echo method, an optical method based on time of flight, an optical method based on confocal, and an electrical method based on eddy current or capacitance. However, these methods have their own unique characteristics. The ultrasonic echo method is good at measuring relatively long distances (in meters), but is not good at measuring minute distances (in micrometers) or at high speed. The optical method based on time of flight is advantageous for measuring relatively long distances (in meters), but is disadvantageous for measuring minute distances (in micrometers). The optical method based on confocal can be used to measure relatively short distances (in micrometers), but has issues with nano-order resolution. In addition, there is also an issue that it is disadvantageous in zero point correction and high-speed measurement. The electrical method based on eddy current or capacitance is capable of measuring relatively short distances (in micrometers) and has a proven track record. However, it has an issue of being easily affected by disturbances in the measurement space, and calibration work is essential to suppress the effects of disturbances on the measurement results.

Therefore, the distance measuring device 1 of the present embodiment has a measurement range of relatively short distances (in micrometers), which is a weakness of the above-mentioned method. The measurement target range of the distance measuring device 1 of the present embodiment is, for example, 10 nm or more and less than 100 μm. Furthermore, the measurement target range of the distance measuring device 1 of the present embodiment can be, for example, 10 nm or more and less than 1 mm. Furthermore, the distance measuring device 1 does not require zero point correction or calibration, and can also measure at high speed. For example, the sampling frequency of the distance measuring device 1 of the present embodiment can be, for example, 100 kHz. In short, the distance measuring device 1 of the present embodiment can monitor minute displacements on the spot. The distance measuring device 1 of the present embodiment can obtain the inclination of a measurement target 9 by measuring the distance at multiple points for one measurement target 9. Furthermore, since distance information can be obtained at high speed, it can also be used to measure the vibration of the measurement target 9.

In other words, the distance measurement device 1 includes a light source unit 3 that generates measurement light L1, an optical fiber 2 that irradiates the measurement target surface 9a with irradiation light L2, which is a part of the measurement light L1, and includes an optical fiber end face 2a that reflects end face reflected light L3, which is the remainder of the measurement light L1, a spectroscope 51 that obtains the spectrum of interference light L5 that is generated by interference between the return light L4 and the end face reflected light L3, which is return light L4 that is reflected by the measurement target surface 9a and then re-enters the optical fiber 2, and a computer 6 that obtains the distance 9H from the optical fiber end face 2a to the measurement target surface 9a using the spectrum of interference light L5.

The distance measurement method includes step S11 of irradiating the measurement target surface 9a with irradiation light L2, which is a part of the measurement light L1 generated by the light source unit 3, and emitting the irradiation light L2 toward the measurement target 9 from an optical fiber 2 including an optical fiber end face 2a that reflects the end face reflected light L3, which is the remainder of the measurement light L1; step S12 of obtaining a spectrum of interference light L5, which is return light L4 that is reflected by the measurement target surface 9a and then re-enters the optical fiber 2, and is generated by interference between the return light L4 and the end face reflected light L3; and steps S13 to S17 of obtaining a distance 9H from the optical fiber end face 2a to the measurement target surface 9a using the spectrum of interference light L5.

The distance measurement device 1 and the distance measurement method obtain interference light L5 that is generated by interference between end face reflected light L3 generated at the optical fiber end face 2a and return light L4 that is re-entered into the optical fiber 2 due to reflection of the irradiation light L2 generated at the measurement target surface 9a. The distance measurement device 1 and the distance measurement method then obtain the distance 9H from the optical fiber end face 2a to the measurement target surface 9a using the spectrum of the interference light L5. The spectrum of the interference light L5 is less susceptible to disturbances than the light intensity of the interference light L5. Therefore, the distance measurement device 1 and the distance measurement method can obtain the distance in a measurement target range that is not suitable for distance measurement using the light intensity of the interference light L5.

The distance measurement device 1 further includes a photodetector 52 that obtains the light intensity of the interference light L5. The computer 6 includes a first candidate distance acquisition unit 6a that obtains a first candidate distance using the spectrum of the interference light L5, a second candidate distance acquisition unit 6b that obtains a second candidate distance using the light intensity of the interference light L5, and a distance output unit 6c that selects either the first candidate distance or the second candidate distance as the distance 9H from the optical fiber end face 2a to the measurement target surface 9a. With this configuration, it is possible to obtain a wide measurement target range that combines the measurement target range in which distance measurement using the spectrum of the interference light L5 is appropriate and the measurement target range in which distance measurement using the light intensity of the interference light L5 is appropriate.

The distance output unit 6c of the distance measurement device 1 selects the first candidate distance as the distance 9H from the optical fiber end face 2a to the measurement target surface 9a when the light intensity of the interference light L5 is equal to or greater than the threshold, and selects the second candidate distance as the distance 9H from the optical fiber end face 2a to the measurement target surface 9a when the light intensity of the interference light L5 indicated by the light intensity of the interference light L5 is less than the threshold. With this configuration, it is possible to easily select either the first candidate distance or the second candidate distance as the distance 9H from the optical fiber end face 2a to the measurement target surface 9a.

In other words, the computer 6 executes the following operations: the first candidate distance acquisition unit 6a acquires first candidate distance data D3; the second candidate distance acquisition unit 6b acquires second candidate distance data D4; the distance output unit 6c compares the light intensity of the interference light with a threshold value, and if the light intensity of the interference light is equal to or greater than the threshold value, selects the first candidate distance data D3 as the distance from the optical fiber end face 2a to the measurement object 9; and if the light intensity of the interference light is less than the threshold value, selects the second candidate distance data D4 as the distance from the optical fiber end face 2a to the measurement object 9. This operation makes it easy to select either the first candidate distance or the second candidate distance as the distance from the optical fiber end face 2a to the measurement object 9.

<Modification>
While the distance measurement device and the distance measurement method according to the present invention have been described above by way of example, the distance measurement device and the distance measurement method are not limited to the above examples and may be embodied in various forms.

In the above embodiment, when selecting the first candidate distance data D3 and the second candidate distance data D4, the judgment condition is set using the interference light intensity data D2 and the intensity threshold value _VTH . However, the judgment condition may be different.

6(a), a certain noise is superimposed on the signal output from the photodetector 52. For example, the noise may be caused by a dark current generated by the photodetector 52. In other words, the noise is the signal output from the photodetector 52 when no light is incident on the photodetector 52. This noise causes variation in the intensity of the interference light. For example, as shown in FIG. 6(b), a noise amplitude (±ΔV) is superimposed on the output signal from the photodetector 52. The noise amplitude (±ΔV) may be assumed to be, for example, plus or minus 5% of the maximum value (VMAX) of the output signal from the photodetector 52. Now, if the maximum value (VMAX) of the output signal from the photodetector 52 is 1V, the noise amplitude (±ΔV) is 0.1V. This noise amplitude (±ΔV) is converted into a distance to become a noise distance (±ΔL). In other words, if the distance indicated by the true signal component is L, and the noise distance (±ΔL) is superimposed on the distance L indicated by the true signal component, the measurement value fluctuates in the range of -ΔL<L<ΔL.

The proportion of noise intensity in the interference light intensity is used as the error evaluation value. The proportion of noise intensity in the interference light intensity increases as the measured distance becomes shorter. In other words, as the proportion of noise intensity in the interference light intensity increases, the reliability of the distance based on the light interference intensity also decreases. Therefore, if the proportion of noise intensity in the interference light intensity (error evaluation value) is equal to or greater than a threshold value, the first candidate distance data D3 is selected as the distance 9H to the measurement target surface 9a. If this error evaluation value is less than the threshold value, the second candidate distance data D4 is selected as the distance 9H to the measurement target surface 9a.

As an example, the noise threshold N _TH may be set to 0.2 (20% ₎ , which corresponds to a distance of 100 μm.

Figure 7 is an example of a distance measurement device 1A that selects the candidate distance described above. The distance measurement device 1A has a light source unit 3, a light guide unit 4, an optical fiber 2, a light receiving unit 5, and a computer 6A. Of these, the details of the light source unit 3, the light guide unit 4, the optical fiber 2, and the light receiving unit 5 are the same as in the embodiment. In other words, the processing performed by the computer 6A in the modified distance measurement device 1A differs from that in the embodiment.

The computer 6A realizes several functional components by executing a program P1, which obtains a distance 9H to a measurement target surface 9a of a modified example, by a processor 61. The computer 6A has a first candidate distance acquisition unit 6a, a second candidate distance acquisition unit 6b, a noise distance acquisition unit 6d (error distance acquisition unit), a noise evaluation value acquisition unit 6e, and a distance output unit 6f. Of these, the details of the first candidate distance acquisition unit 6a and the second candidate distance acquisition unit 6b are the same as those in the embodiment, so detailed explanations are omitted.

The noise distance acquisition unit 6d obtains noise intensity data D6 from the memory 63. The noise distance acquisition unit 6d converts the noise intensity into noise distance data D7. The noise distance acquisition unit 6d stores the noise distance data D7 in the memory 63.

The noise evaluation value acquisition unit 6e acquires the interference light intensity data D2 and the noise intensity data D6 from the memory 63. The noise evaluation value acquisition unit 6e acquires the noise evaluation value data D8 using the interference light intensity data D2 and the noise intensity data D6. The noise evaluation value may be, for example, a value obtained by dividing the noise intensity by the interference light intensity. The noise evaluation value acquisition unit 6e stores the noise evaluation value data D8 in the memory 63.

The distance output unit 6f obtains the noise threshold _NTH , the noise evaluation value data D8, the first candidate distance data D3, and the second candidate distance data D4 from the memory 63. The distance output unit 6f determines whether the noise evaluation value data D8 is equal to or greater than the noise threshold _NTH . If the noise evaluation value data D8 is equal to or greater than the noise threshold _NTH , the distance output unit 6f selects the first candidate distance data D3 as the distance 9H to the measurement target surface 9a. If the noise evaluation value data D8 is less than the noise threshold _NTH , the distance output unit 6f selects the second candidate distance data D4 as the distance 9H to the measurement target surface 9a.

<Method of Obtaining Distance 9H to Measurement Target Surface 9a>
A method for obtaining the distance 9H to the measurement target surface 9a, which is a modified example, will be described with reference to Fig. 8. The method for obtaining the distance 9H to the measurement target surface 9a, which is a modified example, is also executed by the computer 6A in the same manner as the method for obtaining the distance 9H to the measurement target surface 9a of the embodiment.

First, noise intensity data D6 is obtained (S20). This step S21 is performed by the light receiving unit 5 and the computer 6. The computer 6 issues a command to the light source unit 3 to stop emitting the measurement light L1. The computer 6 then stores the signal output from the light receiving unit 5 in the memory 63 as noise intensity data D6.

Next, the irradiation light L2 is emitted toward the measurement target surface 9a (S21). Then, the interference light spectrum data D1 and the interference light intensity data D2 are obtained (S22). These steps S21 and S22 are the same as steps S11 and S12 in the embodiment, so a detailed description is omitted.

Next, first candidate distance data D3 is obtained (S23). Then, second candidate distance data D4 is obtained (S24). These steps S23 and S24 are the same as steps S13 and S14 in the embodiment, so detailed explanations are omitted.

Next, noise distance data D7 is obtained (S25). This step S25 is performed by the processor 61 constituting the noise distance acquisition unit 6d and the memory 63 that stores the noise intensity data D6. As a result of step S25, the noise distance acquisition unit 6d stores the noise distance data D7 in the memory 63.

Next, noise evaluation value data D8 is obtained (S26). This step S26 is performed by the processor 61 constituting the noise evaluation value acquisition unit 6e and the memory 63 storing the noise distance data D7 and the first candidate distance data D3. As a result of step S26, the noise evaluation value acquisition unit 6e stores the noise evaluation value data D8 in the memory 63.

Next, either the first candidate distance data D3 or the second candidate distance data D4 is selected as the distance 9H to the measurement target surface 9a (S27). This step S27 is performed by the processor 61 constituting the distance output unit 6c, and the memory 63 storing the first candidate distance data D3, the second candidate distance data D4, and the noise evaluation value data D8. As a result of step S27, the distance output unit 6c stores the selected candidate distance in the memory 63 as the distance 9H to the measurement target surface 9a.

<Effects>

The computer 6 includes a noise distance acquisition unit 6d that acquires an error distance indicating the uncertainty derived from the noise signal and superimposed on the second candidate distance based on the intensity of the noise signal output by the photodetector 52 when the irradiation light L2 is not emitted from the fiber end face, and a noise evaluation value acquisition unit 6e that acquires an error evaluation value that obtains the proportion of the error distance in the second candidate distance. The distance output unit 6c selects the first candidate distance as the distance 9H from the optical fiber end face 2a to the measurement target surface 9a when the error evaluation value is less than a threshold value, and selects the second candidate distance as the distance 9H from the optical fiber end face 2a to the measurement target surface 9a when the error evaluation value is equal to or greater than the threshold value. With this configuration, it is easy to select either the first candidate distance or the second candidate distance as the distance 9H from the optical fiber end face 2a to the measurement target surface 9a.

In other words, the computer 6 of the modified example executes an operation of obtaining the first candidate distance data D3 by the first candidate distance acquisition unit 6a, an operation of obtaining the second candidate distance data D4 by the second candidate distance acquisition unit 6b, an operation of the distance output unit 6f comparing the noise evaluation value data D8 with the noise threshold _NTH and selecting the first candidate distance data D3 as the distance from the optical fiber end face 2a to the measurement object 9 if the noise evaluation value data D8 is equal to or greater than _the noise threshold _NTH , and an operation of selecting the second candidate distance data D4 as the distance from the optical fiber end face 2a to the measurement object 9 if the noise evaluation value data D8 is less than the noise threshold NTH. This operation also makes it easy to select either the first candidate distance data D3 or the second candidate distance data D4 as the distance from the optical fiber end face 2a to the measurement object 9.

As another modified example, the distance measurement device 1B shown in FIG. 9 is exemplified. As shown in FIG. 9, the light source unit 3B can be configured with only a white light source 31 and without a laser light source 32.

<Modification of distance output unit>
In the embodiment, the first candidate distance data D3 and the second candidate distance data D4 are calculated, and either the first candidate distance data D3 or the second candidate distance data D4 is selected as the distance by a judgment process using either the light intensity or the noise evaluation value. For example, the distance output unit 6f may obtain the distance by a process different from this. Specifically, as shown in FIG. 10, the distance output unit 6f first judges whether the value based on the interference light spectrum data D1 or the value based on the interference light intensity data D2 is better by a judgment process using the light intensity (S31). At this time, the first candidate distance acquisition unit 6a and the second candidate distance acquisition unit 6b have not calculated the first candidate distance data D3 and the second candidate distance data D4, respectively. When the judgment process of the distance output unit 6f judges that the value based on the interference light spectrum data D1 is better (S31: YES), the first candidate distance acquisition unit 6a calculates the first candidate distance data D3 (S32) and outputs the first candidate distance data D3 as the distance to the measurement target surface (S33). Furthermore, when the distance output unit 6f judges that the value based on the interference light intensity data D2 is good (S31: NO), the second candidate distance acquisition unit 6b calculates second candidate distance data D4 (S34) and outputs the second candidate distance data D4 as the distance to the measurement target surface (S35). Even with this operation, it is possible to obtain a wide measurement target range that combines the measurement target range in which distance measurement using the spectrum of the interference light L5 is appropriate and the measurement target range in which distance measurement using the light intensity of the interference light L5 is appropriate.

In the modified example, the computer 6 performs the following operations: compares the light intensity of the interference light with a threshold value; obtains first candidate distance data D3 by the first candidate distance acquisition unit 6a when the light intensity of the interference light is equal to or greater than the threshold value, and outputs the first candidate distance data D3 as the distance from the optical fiber end face 2a to the measurement object 9; and obtains second candidate distance data D4 by the second candidate distance acquisition unit 6b when the light intensity of the interference light is less than the threshold value, and outputs the second candidate distance data D4 as the distance from the optical fiber end face 2a to the measurement object 9. This operation also makes it easy to select either the first candidate distance data D3 or the second candidate distance data D4 as the distance from the optical fiber end face 2a to the measurement object 9.

<Example>
As an example, the distance to the measurement object 9 illustrated in FIG. 2(b) was measured. The measurement object 9 was a glass plate, and the glass plate was placed on an electric stage driven by a stepping motor. Then, a command was given to the electric stage to move it a predetermined distance, and the distance between the glass plate and the optical fiber end face 2a after the movement was measured. FIG. 11 is a graph showing the measurement results. The horizontal axis indicates the movement amount of the electric stage, and the vertical axis indicates the output of the distance measurement device 1. This measurement employs a method of obtaining the distance using the spectrum of interference light. As shown in graph G10, it was confirmed that the movement amount of the electric stage and the output value of the distance measurement device 1 matched well.

1...distance measurement device, 2...optical fiber, 2a...optical fiber end face, 6...computer (distance acquisition section), 6a...first candidate distance acquisition section, 6b...second candidate distance acquisition section, 6c, 6f...distance output section, 6e...evaluation value acquisition section, 9...measurement object, 9a...measurement object surface, 91a...air-liquid interface (measurement object surface), L1...measurement light, L2...irradiation light, L3...end face reflected light, L4...return light, L5...interference light.

Claims (8)

a light source that generates measurement light;
an optical fiber including an end face of the optical fiber that irradiates a surface to be measured with irradiation light that is a part of the measurement light and reflects reflected light that is the remainder of the measurement light;
a spectroscopic unit for obtaining a spectrum of interference light generated by interference between the return light and the reflected light, the return light being reflected by the measurement target surface and then entering the optical fiber again, the interference light being a return light;
a distance acquisition unit that acquires the distance from the end face of the optical fiber to the measurement target surface by using the spectrum of the interference light. a light intensity acquiring unit for acquiring the light intensity of the interference light,
The distance acquisition unit is
a first candidate distance acquisition unit that acquires a first candidate distance using a spectrum of the interference light;
a second candidate distance acquisition unit that acquires a second candidate distance using the light intensity of the interference light;
The distance measurement device according to claim 1 , further comprising: a distance output unit that outputs either the first candidate distance or the second candidate distance as a distance from the optical fiber end face to the measurement target surface. The distance acquisition unit is
an operation of obtaining the first candidate distance by the first candidate distance obtaining unit;
an operation of obtaining the second candidate distance by the second candidate distance obtaining unit;
The distance measurement device of claim 2, wherein the distance output unit performs the following operations: comparing the light intensity of the interference light with a threshold value, and selecting the first candidate distance as the distance from the optical fiber end face to the measurement target surface if the light intensity of the interference light is greater than or equal to the threshold value; and selecting the second candidate distance as the distance from the optical fiber end face to the measurement target surface if the light intensity of the interference light is less than the threshold value. The distance acquisition unit is
an operation of the distance output unit comparing the light intensity of the interference light with a threshold;
an operation of obtaining the first candidate distance by the first candidate distance acquisition unit when the light intensity of the interference light is equal to or greater than a threshold value, and outputting the first candidate distance as a distance from the end face of the optical fiber to the measurement target surface;
The distance measurement device of claim 2, further comprising: when the light intensity of the interference light is less than a threshold value, the second candidate distance acquisition unit obtains the second candidate distance and outputs the second candidate distance as the distance from the optical fiber end face to the measurement target surface. The distance acquisition unit is
an error distance acquisition unit that acquires an error distance indicating an uncertainty derived from a noise signal and superimposed on the second candidate distance, based on the intensity of the noise signal output by the light intensity acquisition unit when the irradiation light is not emitted from the fiber end face;
The distance measurement device according to claim 2 , further comprising: an evaluation value acquisition unit that acquires an error evaluation value that obtains a ratio of the error distance to the second candidate distance. The distance acquisition unit is
an operation of obtaining the first candidate distance by the first candidate distance obtaining unit;
an operation of obtaining the second candidate distance by the second candidate distance obtaining unit;
The distance measurement device of claim 5, wherein the distance output unit performs the following operations: comparing the error evaluation value with a threshold value, and selecting the first candidate distance as the distance from the optical fiber end face to the measurement target surface if the error evaluation value is greater than or equal to the threshold value; and selecting the second candidate distance as the distance from the optical fiber end face to the measurement target surface if the error evaluation value is less than the threshold value. The distance output unit is
an operation of the distance output unit comparing the light intensity of the interference light with a threshold;
an operation of obtaining the first candidate distance by the first candidate distance obtaining unit and outputting the first candidate distance as a distance from the optical fiber end face to the measurement target surface when the error evaluation value is equal to or greater than a threshold value;
The distance measurement device of claim 5, further comprising: when the error evaluation value is less than a threshold value, the second candidate distance acquisition unit acquires the second candidate distance and outputs the second candidate distance as the distance from the optical fiber end face to the measurement target surface. a step of irradiating a surface of a measurement object with irradiation light, which is a part of measurement light generated by a light source, and emitting the irradiation light toward the measurement object from an optical fiber including an optical fiber end face that reflects reflected light, which is the remainder of the measurement light;
obtaining a spectrum of interference light generated by interference between the return light and the reflected light, the return light being reflected by the measurement target surface and then entering the optical fiber again;
and obtaining a distance from the end face of the optical fiber to the measurement target surface using the spectrum of the interference light.

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