Distance measuring device and distance measurement method

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

[Technical field]

[0001] The present invention relates to a distance measurement device and a distance measurement method. [Background technology]

[0002] 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 reflected at the gas-liquid interface of the liquid film and re-entering the optical fiber is obtained. The light intensity of the light returning to the optical fiber attenuates according to the distance from the end face of the optical fiber that emits the measurement light to the gas-liquid interface of the liquid film. Therefore, by knowing the degree of attenuation of the light intensity, the distance from the end face of the optical fiber to the gas-liquid interface of the liquid film can be known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-77303 Summary of the Invention [Problem to be solved by the invention]

[0004] In technical fields where minute film thicknesses and minute distances are measured, the range of the measurement target is varied. However, in measurement methods that use light intensity, the range of the measurement target from which distance can be obtained is often limited due to reasons such as the susceptibility to disturbances.

[0005] Therefore, the present invention provides a distance measurement device and a distance measurement method that can obtain the distance in a desired measurement target range. [Means for solving the problem]

[0006] A distance measurement device according to one embodiment of the present invention comprises 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 includes an optical fiber end face that reflects reflected light that is the remainder of the measurement light, a spectroscopic unit that obtains the spectrum of interference light 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 unit that obtains the distance from the optical fiber end face to the measurement target surface using the spectrum of the interference light.

[0007] A distance measurement method according to another aspect of the present invention includes the steps of irradiating a surface to be measured with illumination light, which is a part 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 an optical fiber 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, which is return light that is reflected by the surface to be measured and then re-enters the optical fiber; and obtaining a distance from the end face of the optical fiber to the surface to be measured using the spectrum of interference light.

[0008] The distance measurement device and the distance measurement method obtain interference light 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 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.

[0009] 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 is the sum of a measurement target range in which distance measurement using the spectrum of the interference light is appropriate and a measurement target range in which distance measurement using the light intensity of the interference light is appropriate.

[0010] The distance acquisition unit in the distance measurement device of one embodiment may execute the following operations: acquiring a first candidate distance by a first candidate distance acquisition unit, acquiring a second candidate distance by a second candidate distance acquisition unit, and the distance output unit comparing the light intensity of the interference light with a threshold, 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, 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. According to this operation, it is possible to easily 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.

[0011] The distance acquisition unit in the distance measurement device of one embodiment may execute the following operations: the distance output unit compares the light intensity of the interference light with a threshold value, when the light intensity of the interference light is equal to or greater than the threshold value, the first candidate distance acquisition unit acquires a first candidate distance and outputs the first candidate distance as the distance from the end face of the optical fiber to the measurement target surface, and when the light intensity of the interference light is less than the threshold value, the second candidate distance acquisition unit acquires a second candidate distance and outputs the second candidate distance as the distance from the end face of the optical fiber 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 end face of the optical fiber to the measurement target surface.

[0012] The distance acquisition unit in the distance measurement device of one embodiment may include 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, and an evaluation value acquisition unit that acquires an error evaluation value that obtains a ratio of the error distance to 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.

[0013] The distance acquisition unit in the distance measurement device of one embodiment may execute the following operations: acquiring a first candidate distance by a first candidate distance acquisition unit, acquiring a second candidate distance by a second candidate distance acquisition unit, and the distance output unit comparing an error evaluation value with a threshold, 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, 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. This operation also makes it possible to easily 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.

[0014] The distance output unit in the distance measurement device of one embodiment may execute the following operations: the distance output unit compares the light intensity of the interference light with a threshold value, if the error evaluation value is equal to or greater than the threshold value, 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 error evaluation value is less than the threshold value, 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. Effect of the Invention

[0015] According to the present invention, a distance measurement device and a distance measurement method capable of obtaining a desired measurable range are provided. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating components of a distance measuring device according to an embodiment. [Diagram 2] Fig. 2(a) is a diagram showing a configuration in which the distance measurement device of the embodiment is applied to measuring a liquid film, and Fig. 2(b) is a diagram showing a configuration in which the distance measurement device of the embodiment is applied to measuring a distance to a measurement target. [Diagram 3] FIG. 3 is a diagram illustrating components of the computer shown in FIG. [Figure 4] FIG. 4 is a graph showing the relationship between the distance to the measurement target surface and the signal intensity. [Diagram 5] FIG. 5 is a flowchart showing a distance measuring method executed by the computer shown in FIG. [Figure 6] 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 the distance. [Figure 7] FIG. 7 is a diagram showing components of a distance measuring device according to a modified example. [Figure 8] FIG. 8 is a flowchart showing a distance measuring method executed by the computer shown in FIG. [Figure 9] FIG. 9 is a diagram showing components of a distance measurement device according to still another modified example. [Figure 10] FIG. 10 is a flowchart showing a distance measuring method performed by the distance measuring device of the modified example. [Figure 11] FIG. 11 is a graph showing the results of the example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted.

[0018] 1 is a diagram illustrating a schematic diagram of a distance measurement device 1. The distance measurement device 1 emits measurement light from one 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.

[0019] The distance measurement device 1 can be applied to, for example, a semiconductor manufacturing process. In the semiconductor manufacturing process, many processes involve the rotation of a wafer. When rotating a 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 also become important to prevent uneven contamination on the wafer surface and edge dripping of resist material. In other words, it is expected that the importance of wafer alignment will 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 there will be a need to measure vibrations caused by the rotation of the wafer.

[0020] Specifically, in the semiconductor manufacturing process, it is desirable to measure the inclination and flatness of the wafer on-site in processes such as forming a resist film (coating), polishing the wafer, and cleaning the wafer. In these processes, the distance measuring device 1 is used to measure the thickness of the resist film and the distance to the wafer, and the inclination 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 viewpoint 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 measuring device 1 can also be used to observe the bearing gap on-site.

[0021] The distance measurement device 1 and the distance measurement method have been developed as a result of extensive investigation into a method capable of meeting these needs.

[0022] 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.

[0023] First, the distance measurement device 1 obtains the thickness of the liquid film (hereinafter referred to as the "film thickness") illustrated in Fig. 2(a). In other words, the "measurement object 9" is the liquid 91, and the "distance to the measurement object surface" is the distance from the optical fiber end face 2a of the optical fiber 2 to the gas-liquid interface 91a (measurement object 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 aligned 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".

[0024] 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 a wafer surface. 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. This configuration makes it possible to measure the tilt movement and / or amplitude of the liquid film surface by continuous measurement at multiple points in real time.

[0025] Secondly, the distance measurement device 1 obtains the distance to an object 92 (hereinafter referred to as the "separation distance") as shown in Fig. 2(b). In other words, the "measurement target 9" is the object 92, and the "distance to the measurement target 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.

[0026] The distance measurement device 1 can arbitrarily select between two distance measurement modes depending on the installation mode with respect to the measurement target object 9. Therefore, there is no difference in 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).

[0027] Several lights used in the following description will be described. In the following description, "measurement light L1", "illumination light L2", "end surface reflected light L3", "return light L4", and "interference light L5" will be exemplified. The measurement light L1 is light generated by the light source unit 3 described later. The measurement light L1 includes a specific wavelength component including only a specific predetermined wavelength, and a white light component including multiple wavelengths and having substantially no bias in intensity for each wavelength. A portion of the measurement light L1 is emitted to the outside and the rest is reflected at the optical fiber end surface 2a. The light emitted to the outside is illumination light L2. The reflected light is end surface reflected light L3.

[0028] The illumination light L2 reaches the object 9 to be measured and is reflected by the gas-liquid interface 91a (see FIG. 2(a)) of the object 9 to be measured or the surface 92a (see FIG. 2(b)) of the object 92. A part or all of the reflected illumination 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.

[0029] Referring again to Fig. 1, the distance measurement device 1 includes a light source unit 3, a light guide unit 4, an optical fiber 2, a light receiving unit 5, and a computer 6.

[0030] 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 passes the interference light L5 including the return light L4 and the end face 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 obtains a distance 9H to the measurement object surface 9a using the information about the interference light L5.

[0031] The light source unit 3 generates a measurement light L1. The light source unit 3 may switch between emitting and stopping the measurement light L1 based on a command sent 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 a plurality of 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.

[0032] The light-guiding unit 4 has a first coupler 41, a second coupler 42, and a third coupler 43. The light-guiding 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.

[0033] First, the function of transferring 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 transfers 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 transfers 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 transfers the measurement light L1 to the optical fiber 2.

[0034] Next, a function of transferring 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 transfers the interference light L5 to each of the first coupler 41 and the second coupler 42. The first coupler 41 transfers the interference light L5 to the spectrometer 51. The second coupler 42 transfers the interference light L5 to the photodetector 52.

[0035] The optical fiber 2 has an optical fiber base end connected to the third coupler 43 of the light-guiding 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.).

[0036] 2(a) and the like is perpendicular to the optical axis of the optical fiber 2. The optical fiber end surface 2a may be an inclined surface that is inclined with respect to the optical axis of the optical fiber 2.

[0037] 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.

[0038] 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 a distance 9H to the measurement target surface 9a based on information received from the light receiving unit 5. The information received from the light receiving unit 5 is interference light spectrum data D1 and interference light intensity data D2.

[0039] 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 a program.

[0040] 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.

[0041] 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 storage unit 62, and causes at least one of the processor 61, the main storage unit 62, the memory 63, the external communication unit 64, the operation unit 65, and the output unit 66 to operate.

[0042] 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 a measurement target surface 9a read from a memory 63.

[0043] 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 the distance suitable for each is different. 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.

[0044] 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.

[0045] 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 of the medium through which the irradiation light L2 propagates and the distance. 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: number of peaks in the interference light spectrum. n: refractive index of the medium. λ1, λ2: Wavelength.

[0046] 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 obtains the second candidate distance data D4 using the interference light intensity data D2. Then, the second candidate distance acquisition unit 6b stores the second candidate distance data D4 in the memory 63. As a method for obtaining the second candidate distance data D4 using the interference light intensity data D2, the method described in JP 2022-77303 A by the present inventors may be applied.

[0047] 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 one of 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.

[0048] 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. That is, the signal intensity output from the photodetector 52 is the interference light intensity. As shown in the graph G4 of FIG. 4, the signal intensity (interference light intensity) decreases as the distance 9H to the measurement target surface 9a increases. A high signal intensity is advantageous from the viewpoint of the S / N ratio, etc. However, in the range R1 where the signal intensity is high, the signal intensity changes significantly with respect to 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 high 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 intensity is small and the signal intensity 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.

[0049] In other words, the signal strength (interference light strength) is compared to the intensity threshold V TH Set the signal strength threshold V TH If the signal intensity is greater than the intensity threshold V TH If it is smaller, 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.

[0050] As an example, the range of distances for which the first candidate distance data D3 is adopted may be 1 μm or more and less than 100 μm. The range of distances for which the second candidate distance data D4 is adopted 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 equal to or greater than the intensity threshold V TH is set as:

[0051] Also, 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 intensity at which the second candidate distance data D4 is 50 μm is adopted as the first intensity threshold, and the signal intensity 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, when the second candidate distance data D4 is less than the first intensity threshold and equal to or greater than 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.

[0052] <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.

[0053] 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.

[0054] 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 guiding 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] <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, each of these methods has its 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 a problem with nano-order resolution. In addition, there is also a problem 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 good track record. However, it has a problem that it is easily affected by disturbances in the measurement space, and calibration work is essential to suppress the effects of disturbances on the measurement results.

[0059] Therefore, the distance measurement device 1 of the present embodiment has a measurement range of a relatively short distance (in micrometers), which is a weakness of the above-mentioned method. The measurement target range of the distance measurement 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 measurement device 1 of the present embodiment can be, for example, 10 nm or more and less than 1 mm. Moreover, the distance measurement device 1 does not require zero point correction or calibration, and can also perform high-speed measurement. For example, the sampling frequency of the distance measurement device 1 of the present embodiment can be, for example, 100 kHz. In short, the distance measurement device 1 of the present embodiment can monitor minute displacements on the spot. The distance measurement 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.

[0060] In other words, the distance measurement device 1 comprises a light source unit 3 that generates measurement light L1, an optical fiber 2 that includes an optical fiber end face 2a that irradiates irradiation light L2, which is a part of the measurement light L1, onto the measurement target surface 9a and reflects end face reflected light L3, which is the remainder of the measurement light L1, a spectrometer 51 that obtains the spectrum of interference light L5 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 enters the optical fiber 2 again, 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.

[0061] The distance measurement method includes step S11 of irradiating a measurement target surface 9a with irradiation light L2, which is a part of measurement light L1 generated by a 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 end face reflected light L3, which is the remainder of the measurement light L1; step S12 of obtaining a spectrum of interference light L5 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 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.

[0062] The distance measurement device 1 and the distance measurement method obtain an interference light L5 generated by interference between the end face reflected light L3 generated at the optical fiber end face 2a and the return light L4 that is caused by the reflection of the irradiation light L2 generated at the measurement target surface 9a and enters the optical fiber 2 again. The distance measurement device 1 and the distance measurement method obtain a 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 a distance in a measurement target range that is not suitable for distance measurement using the light intensity of the interference light L5.

[0063] 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.

[0064] The distance output unit 6c of the distance measurement device 1 selects a 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 a threshold, and selects a 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.

[0065] In other words, the computer 6 executes an operation of acquiring first candidate distance data D3 by the first candidate distance acquisition unit 6a, an operation of acquiring second candidate distance data D4 by the second candidate distance acquisition unit 6b, an operation of the distance output unit 6c comparing the light intensity of the interference light with a threshold 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 light intensity of the interference light is equal to or greater than the threshold, 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 light intensity of the interference light is less than the threshold. According to this operation, either the first candidate distance or the second candidate distance can be easily selected as the distance from the optical fiber end face 2a to the measurement object 9.

[0066] <Modification> The above has described an example of the distance measurement device and the distance measurement method according to the present invention. The distance measurement device and the distance measurement method may be implemented in various forms without being limited to the above example.

[0067] In the above embodiment, when selecting the first candidate distance data D3 and the second candidate distance data D4, a determination condition using the interference light intensity data D2 and the intensity threshold V TH was set. The determination condition may have other contents.

[0068] As shown in FIG. 6(a), a predetermined noise is superimposed on the signal output from the photodetector 52. As this noise, for example, noise caused by the dark current generated by the photodetector 52 can be exemplified. That is, it can be said that the noise is the signal output from the photodetector 52 when no light is incident on the photodetector 52. This noise causes variations in the interference light intensity. For example, as shown in FIG. 6(b), a noise amplitude (±ΔV) is superimposed on the output signal of the photodetector 52. The noise amplitude (±ΔV) may be assumed to be, for example, plus or minus 5% with respect to the maximum value (VMAX) of the output signal of the photodetector 52. Now, assuming that the maximum value (VMAX) of the output signal of the photodetector 52 is 1V, the noise amplitude (±ΔV) is 0.1V. When this noise amplitude (±ΔV) is converted into a distance, it becomes a noise distance (±ΔL). That is, when 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 measured value fluctuates within the range of -ΔL < L < ΔL.

[0069] Therefore, the ratio of the noise intensity to the interference light intensity is used as an error evaluation value. The ratio of the noise intensity to the interference light intensity increases as the measured distance becomes shorter. That is, when the ratio of the noise intensity to the interference light intensity increases, the reliability of the distance based on the light interference intensity also decreases. Therefore, when the ratio (error evaluation value) of the noise intensity to the interference light intensity is equal to or greater than the threshold, the first candidate distance data D3 is selected as the distance 9H to the measurement target surface 9a. When this error evaluation value is less than the threshold, the second candidate distance data D4 is selected as the distance 9H to the measurement target surface 9a.

[0070] As an example, the noise threshold N TH may be set to 0.2 (20%). TH When converted to distance, this is equivalent to 100 μm.

[0071] 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. Among 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 those of the embodiment. That is, the distance measurement device 1A of the modification differs from the process of the embodiment in the process performed by the computer 6A.

[0072] The computer 6A realizes several functional components by executing a program P1 for obtaining a distance 9H to a measurement target surface 9a of the 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. Among these, the details of the first candidate distance acquisition unit 6a and the second candidate distance acquisition unit 6b are the same as those of the embodiment, and therefore detailed description thereof will be omitted.

[0073] The noise distance acquisition unit 6d acquires the 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.

[0074] 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 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.

[0075] The distance output unit 6f receives the noise threshold value N TH The distance output unit 6f obtains noise evaluation value data D8, first candidate distance data D3, and second candidate distance data D4. The distance output unit 6f calculates the noise evaluation value data D8 based on the noise threshold N TH The distance output unit 6f judges whether the noise evaluation value data D8 is equal to or greater than the noise threshold value N TH If the noise evaluation value data D8 is greater than or equal to the noise threshold value N TH If it is less than this, the second candidate distance data D4 is selected as the distance 9H to the measurement target surface 9a.

[0076] <Method of obtaining distance 9H to measurement target surface 9a> A method for obtaining a distance 9H to a measurement target surface 9a according to a modified example will be described with reference to Fig. 8. The method for obtaining a distance 9H to a measurement target surface 9a according to a modified example is also executed by a computer 6A in the same manner as the method for obtaining a distance 9H to a measurement target surface 9a according to the embodiment.

[0077] 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. Then, the computer 6 stores the signal output from the light receiving unit 5 in the memory 63 as the noise intensity data D6.

[0078] 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 detailed description will be omitted.

[0079] 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 description will be omitted.

[0080] 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 storing 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.

[0081] 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.

[0082] 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.

[0083] <Action and effect>

[0084] 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 ratio of the error distance to the second candidate distance, and 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, 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. This configuration also makes it 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.

[0085] In other words, the computer 6 of the modified example performs an operation of obtaining the first candidate distance data D3 by the first candidate distance obtaining unit 6a, obtaining the second candidate distance data D4 by the second candidate distance obtaining unit 6b, and outputting the noise evaluation value data D8 and the noise threshold value N TH The noise evaluation value data D8 is compared with the noise threshold value N TH If the noise evaluation value data D8 is greater than or equal to the noise threshold value N TH and if it is less than that, select 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 possible to easily 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.

[0086] As another modified example, a distance measurement device 1B shown in Fig. 9 is exemplified. As shown in Fig. 9, the light source unit 3B may be configured with only a white light source 31 and may not include a laser light source 32.

[0087] <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.

[0088] In the modified example, the computer 6 executes an operation of comparing the light intensity of the interference light with a threshold value, an operation of obtaining first candidate distance data D3 by the first candidate distance acquisition unit 6a and outputting the first candidate distance data D3 as the distance from the optical fiber end face 2a to the measurement object 9 when the light intensity of the interference light is equal to or greater than the threshold value, and an operation of obtaining second candidate distance data D4 by the second candidate distance acquisition unit 6b and outputting the second candidate distance data D4 as the distance from the optical fiber end face 2a to the measurement object 9 when the light intensity of the interference light is less than the threshold value. This operation also makes it possible to easily 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.

[0089] <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 shows the movement amount of the electric stage, and the vertical axis shows 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. [Explanation of symbols]

[0090] 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

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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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