JP2005106706A - Instrument and method for measuring refractive index and thickness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quicken measurement for a thickness and a refractive index of a measured object using an optical interference method. <P>SOLUTION: The measured object 3 is irradiated with transmission light transmitted through a semi-transparent mirror 22 out of light source light, via a condenser lens 23. A peak of non-interfered light is detected by the first photoreceiver 5 while scanning a Z-stage 25, so as to obtain a moving amount Δz of the Z-stage between the first state light-converged on a front face of the measured object 3 and the second state light-converged on a rear face thereof. The first state is held, and the third state where intensity of the interference light gets maximum is detected by the second photoreceiver 4 while scanning an L-stage 39. The second state is held, and the fourth state where intensity of the interference light gets maximum is detected by the second photoreceiver 4 while scanning the L-stage 39. The refractive index and the thickness of the measured object 3 are found based on a moving amount ΔL of the L-stage between the third state and the fourth state, and based on the Δz hereinbefore. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus capable of measuring a refractive index and a thickness of an object to be measured sandwiched between interfaces of media having different refractive indexes of light, such as a refractive index and a thickness of a thin film.

Conventionally, a method and an apparatus capable of simultaneously measuring the refractive index and thickness of an object to be measured such as a thin film using an optical interference method are known (for example, see Patent Documents 1 to 5 below).
Japanese Patent Laid-Open No. 9-2108016 Japanese Patent Laid-Open No. 10-2855 JP-A-10-325795 JP-A-11-344313 JP 2001-4538 A

FIG. 5 shows a conventional example of an apparatus for measuring the refractive index and thickness of a medium using optical interferometry.
In the apparatus of this example, the low coherent light emitted from the light source 51 is branched into two by the beam splitter 52. One branched light is condensed by the condensing lens 53 and irradiated to the measurement object 54, and the other branched light is irradiated to the reference mirror 55. The inspection light reflected by the DUT 54 and the reference light reflected by the reference mirror 55 are combined by the beam splitter 52 to form interference light, and the light intensity of the interference light is detected by the light receiver 56. It is comprised so that. An object 54 to be measured is held on a Z stage 61 that can be finely moved, and a reference mirror 55 is held on an L stage 62 that can be finely moved. Further, the reference mirror 55 is fixed to a vibrator (not shown), and is configured such that vibration of a predetermined amplitude is applied at a predetermined frequency, and thereby the reference light is phase-modulated.

A method for measuring the refractive index and the thickness of the thin film-like object 54 using the apparatus having such a configuration will be described.
First, the measurement object 54 is set so that the thickness direction thereof is the optical axis direction, and light is emitted from the light source 51.
Then, one of the branched lights branched from the beam splitter 52 while the light from the light source 51 is condensed on the surface (referred to as the front surface) closer to the condensing lens 53 among the front and back surfaces of the measurement object 54. The optical path length from when (inspection light) is reflected from the front surface of the measurement object 54 to the light receiver 56 and the optical path from the other branched light (reference light) reflected by the reference mirror 55 to the light receiver 56 The positions of the DUT 54 and the reference mirror 55 are detected so that the lengths are equal (first position detection).
Furthermore, the light from the light source 51 condenses on the surface (referred to as the rear surface) far from the condensing lens 53 among the front and back surfaces of the object to be measured 54 and one branched light branched by the beam splitter 52. The optical path length from when (inspection light) is reflected from the front surface of the measurement object 54 to the light receiver 56 and the optical path from the other branched light (reference light) reflected by the reference mirror 55 to the light receiver 56 The positions of the DUT 54 and the reference mirror 55 are detected so that the lengths are equal (second position detection).
Specifically, the first position and the second position are detected as positions where the peak intensity of the interference light signal detected by the light receiver 56 is maximum.

That is, as shown in FIG. 6, the L stage 62 is scanned with the Z stage 61 fixed at the initial position “P ₀ = 0 μm”, and the interference light signal of the inspection light and the reference light detected by the light receiver 56 is detected. The L stage position “L (P ₀ )” when the peak is obtained and the peak intensity at that time are measured. The initial position of the Z stage 61 is preferably set so that the focal point of the condenser lens 53 is located in the vicinity of either one of the front and back surfaces of the object to be measured 54.
Thereafter, the Z stage 61 is finely moved and fixed at the position of “P ₁ = P ₀ +1 μm”, and in this state, the L stage 62 is scanned again to measure the intensity of the interference light signal, and a peak is obtained. The L stage position “L (P ₁ )” and the peak intensity at that time are measured. In this way, while finely moving and fixing the Z stage 61 and scanning of the L stage 62 are repeated alternately, the peak intensity of the interference light signal is measured, and the place where the peak intensity becomes maximum is the first position and the second position. Detect as the position of.
Therefore, for example, when the minimum distance (resolution) at which the Z stage can be finely moved is 1 μm and the thickness of the DUT 54 (the distance between the front and back surfaces) is 5 mm, the scanning of the L stage 62 is performed 5000 times or more. It will be.

  By detecting the first position and the second position in this manner, the movement amount Δz of the Z stage 61 from the first position to the second position and the movement amount Δ of the L stage 62 are detected. Since L is obtained, the refractive index and thickness of the object to be measured can be obtained simultaneously from the value of Δz and the value of ΔL (see, for example, Patent Document 4 [0007] to [0012] above). .

  By the way, in such a measuring method, there was dissatisfaction that it took time for the measurement. That is, in order to find the state where the light source light is condensed on each of the front and back surfaces of the object to be measured whose thickness is unknown, it is necessary to scan the L stage 62 every time the Z stage 61 is finely moved. The measurement was not quick.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a measuring apparatus and a measuring method capable of speeding up the measurement of the thickness and refractive index of an object to be measured using an optical interference method. .

  In order to solve the above problems, a refractive index and thickness measuring apparatus according to the present invention includes a light source, a semi-transparent mirror that reflects part of light from the light source and transmits part of the light, and transmitted light of the semi-transparent mirror. The light is reflected by the semi-transparent mirror, the light collecting means for collecting the light and irradiating the object to be measured, the first detecting means for detecting the intensity of the non-interference light including the inspection light reflected by the object to be measured. Branching means for branching light including reference light and inspection light reflected by the object to be measured into a first branching optical path and a second branching optical path having an optical path length varying unit; and the first branching And a light combining means for combining the light having passed through the optical path and the light having passed through the second branch optical path to generate interference light, and a second detection means for detecting the intensity of the interference light. Features.

Branching means for branching light including reference light reflected by the semi-transparent mirror and inspection light reflected by the measurement object before reaching the first branch optical path and leading to the first detection means; Can be provided.
Alternatively, the optical path length of the second branch optical path can be adjusted to a non-interference region in which the light passing through the first branch optical path and the light passing through the second branch optical path do not generate interference light, The detecting means may also serve as the first detecting means.
Alternatively, a means capable of blocking either one of the first branch optical path and the second branch optical path may be provided, and the second detection means may also serve as the first detection means.

The present invention is also a method for measuring the refractive index and thickness of an object to be measured using the measuring apparatus of the present invention, wherein light from the light source that has passed through the semi-transparent mirror is used as the light collecting means. The intensity of the non-interfering light is detected by the first detecting means while irradiating the object to be measured via the first detecting means while changing the distance between the light collecting means and the object to be measured. A first state in which light transmitted through the semi-transparent mirror is collected on the light source side front surface of the object to be measured, and a second state in which the light is condensed on a rear surface far from the light source of the object to be measured. Respectively, and obtaining a change amount Δz of the distance between the light collecting means and the object to be measured between the first state and the second state;
By detecting the intensity of the interference light detected by the second detection means while changing the optical path length of the second branch optical path while maintaining the first state, Detecting a third state where the intensity is maximum;
By detecting the intensity of the interference light detected by the second detection means while changing the optical path length of the second branch optical path while maintaining the second state, Detecting a fourth state where the intensity is maximum;
Obtaining a change amount ΔL of the optical path length of the second branch optical path between the third state and the fourth state;
A method for measuring the refractive index and thickness, comprising the step of determining the refractive index and thickness of the object to be measured using the values of Δz and ΔL.

  According to the present invention, the number of stage scans required to obtain Δz and ΔL can be greatly reduced, so that the measurement can be speeded up.

The present invention will be described in detail below. FIG. 1 is a schematic configuration diagram showing a first embodiment of the measuring apparatus of the present invention. In the figure, reference numeral 1 denotes a light source, and 3 denotes an object to be measured.
The light source light is preferably low coherence light, and the light source 1 is preferably one that can emit light having a wide bandwidth, such as SLD (super-luminescent diode) or LED (light An emitting diode (light emitting diode) is preferably used.
The object to be measured 3 is a layer sandwiched between the interfaces of media having different light refractive indexes, such as a thin plate or a thin film, and is capable of transmitting light from the light source and can be regarded as an optically uniform layer. The
The DUT 3 is held and fixed so that the optical axis direction of the light source light coincides with the thickness direction. One of the front and back surfaces of the DUT 3 on the light source 1 side (hereinafter referred to as the front surface) may form the outermost surface, and a layer that transmits light source light may be provided on the front surface. Good. Further, the other surface (hereinafter referred to as a rear surface) of the device under test 3 may form the outermost surface, and a layer having a refractive index different from that of the device under test 3 may be provided on the rear surface. If the value of the product of the thickness of the object to be measured and the refractive index is smaller than the coherence length of the broadband light source 1 to be used, the thickness of the object to be measured 3 becomes difficult to measure due to the resolution. On the other hand, if the thickness is too thick, the difference between the amount of reflected light when the focal point is located on the front surface of the object to be measured and the amount of reflected light when the focal point is located on the rear surface becomes large. Is about 10 μm to 2 mm.

In the apparatus of the present embodiment, the light emitted from the light source 1 is configured to reach the measurement unit 20 through the first optical fiber 11, the circulator 2, and the second optical fiber 12 in order.
The circulator 2 has three ports, to which a first optical fiber 11, a second optical fiber 12, and a third optical fiber 13 are connected. In the circulator 2, light passes from the first optical fiber 11 to the second optical fiber 12, and light also passes from the second optical fiber 12 to the third optical fiber 13. Is configured not to return.
As the first optical fiber 11, the second optical fiber 12, and the third optical fiber 13, a general transmission optical fiber is used, and a silica-based glass fiber is preferably used.

  In the measurement unit 20, the collimator 21, the quarter wavelength plate 24, the semi-transparent mirror 22, and the condensing lens (condensing means) 23 are arranged so that their optical axes coincide with each other, and along the optical axis direction. And is fixed on a Z stage 25 that can be moved finely.

In the measurement unit 20, the light emitted from the second optical fiber 12 is collimated by the collimator 21 and then enters the semi-transparent mirror 22.
The semi-transparent mirror 22 has a characteristic of reflecting a part of incident light and transmitting a part of the incident light. The transmitted light of the semi-transparent mirror 22 is collected by a condenser lens 23, and the collected light is measured. 3 is irradiated. Then, the reflected light of the object to be measured 3 (hereinafter also referred to as inspection light) passes through the condensing lens 23 and passes through the semi-transparent mirror 22, and then enters the second optical fiber 12 through the collimator 21. It is configured.
On the other hand, the reflected light of the semi-transparent mirror 22 (hereinafter also referred to as reference light) is incident on the second optical fiber 12 through the collimator 21.

As the semi-transparent mirror 22, for example, one having a configuration in which a dielectric multilayer film is deposited on a glass substrate can be used. The reflectance and transmittance of the semi-transparent mirror 22 are not particularly limited. However, if the transmittance is too low, the intensity of reflected light (inspection light) from the object to be measured 3 is too weak and the measurement accuracy is greatly degraded. Become. Therefore, the reflectance of the semi-transparent mirror 22 is preferably about 3% to 20%, although it depends on the reflectance on the front surface and the rear surface of the DUT 3.
The quarter-wave plate 24 is not essential, but if it is provided, the polarization plane of the light incident on the first optical fiber 11 from the light source 1 and emitted from the second optical fiber 12 to the measuring unit 20; Since the polarization planes of the light reflected by the semi-transparent mirror 22 and the DUT 3 and incident on the second optical fiber 12 are orthogonal to each other, the configuration of the circulator 2 can be simplified. It is preferable to provide between the collimator 21 and the semi-transparent mirror 22. The quarter wave plate 24 and the semi-transparent mirror 22 can be provided integrally.

In this way, the inspection light and the reference light are incident on the second optical fiber 12 from the measurement unit 20, and the light including both the optical signal of the inspection light and the optical signal of the reference light is the second optical fiber 12, The circulator 2 and the third optical fiber 13 are sequentially passed to reach the interference unit 30.
In the present embodiment, a branch is provided in the middle of the third optical fiber 13, and a part of the optical signal propagating through the third optical fiber 13 passes through the fifth optical fiber 15 and passes through the first optical fiber 13. It is configured to be incident on a first light receiver 5 as a detecting means.

  The interference unit 30 includes a collimator 31, a beam splitter 32, a first mirror 35, and an output from the third optical fiber 13 within the beam splitter 32 provided on the optical path of the outgoing light from the third optical fiber 13. A second mirror 36 having an optical axis perpendicular to the optical path of the incident light, and a collimator 37 in a positional relationship facing the second mirror 36 with the beam splitter 32 interposed therebetween are provided.

In the interference unit 30, after the light emitted from the third optical fiber 13 is converted into parallel light by the collimator 31, the beam splitter (branching unit and combining unit) 32 first straightly travels the first branch optical path 33. The light is branched to a second branch optical path 34 that is orthogonal to the incident direction.
The light traveling through the first branch optical path 33 is reflected by the first mirror 35, and the reflected light is incident on the beam splitter 32 in parallel with the first branch optical path 33.
On the other hand, the light traveling through the second branch optical path 34 is reflected by the second mirror 36, and the reflected light is incident on the beam splitter 32 in parallel with the second branch optical path 33.
The beam splitter 32 is configured to linearly propagate the reflected light from the second mirror 36 and change the traveling direction of the reflected light from the first mirror 35 in a direction orthogonal to the incident direction. Thus, the reflected light of the first mirror 35 and the reflected light of the second mirror are combined. The two combined lights generate interference light, and the interference light is incident on the fourth optical fiber 14 via the collimator 37. The interference light transmitted through the fourth optical fiber 14 is incident on a second light receiver 4 as second detection means, and the light intensity of the interference signal is detected.

The first mirror 35 and the second mirror 36 preferably have a high reflectance, and a total reflection mirror is preferably used.
In the present embodiment, each of the first mirror 35 and the second mirror 36 includes two total reflection mirrors such that the reflection surface is on the inner side and the angle formed by the two total reflection mirrors is 90 degrees. The light emitted from the beam splitter 32 is configured to be incident on one reflection surface of the optical element at an incident angle of 45 degrees. That is, light incident on the first mirror 35 from the beam splitter 32, light reflected by the first mirror 35 toward the beam splitter 32, and light incident on the second mirror 36 from the beam splitter 32 The light that is reflected by the second mirror 36 and travels toward the beam splitter 32 passes through separate optical paths that are parallel to each other.
By using such an optical element, a mechanical angle error during the movement of the second stage 39 that can be finely moved, which will be described later, can be converted into a parallel movement of light in the second branch optical path 34. The variation in the amount of interference light coupled to the fourth optical fiber 14 due to the movement of the stage 39 can be reduced.

The first mirror 35 is fixed on a first stage 38 (optical path length correcting means) that can advance and retreat along the optical axis direction of the first branch optical path 33, and thereby the first splitter 35 is connected to the first splitter 35 from the beam splitter 32. The distance to one mirror 35 can be adjusted.
The second mirror 36 is fixed on a second stage 39 (optical path length variable means, hereinafter also referred to as “L stage”) that can be finely moved along the optical axis direction of the second branch optical path 34. Yes. The second stage (L stage) 39 is configured to vibrate at a predetermined frequency and a predetermined amplitude, and is capable of moving back and forth at a fine interval in the optical axis direction of the second branch optical path 34 while continuing the vibration. .

A method for measuring the refractive index and thickness of the DUT 3 using the apparatus having such a configuration will be described with reference to FIG.
First, in the first state where the focus when the low-coherence light from the light source 1 is collected by the condenser lens 23 is located on the front surface of the object to be measured 3, and the light from the light source 1 is collected by the condenser lens 23. The second state where the focal point when the light is condensed is located on the rear surface of the DUT 3 is detected.
Specifically, the Z stage 25 is scanned while emitting light from the light source 1 and irradiating the object to be measured 3 with the light transmitted through the semi-transparent mirror 22 via the condenser lens 23. At this time, the light incident on the first light receiver 5 includes the reference light and the inspection light in a state where they do not interfere with each other. Such light is referred to as non-interfering light in this specification. Such non-interfering light corresponds to a direct current component (DC component).

The intensity of such non-interference light is such that when the front surface of the DUT 3 is located at the focal point of the condenser lens 23 (first state) and when the rear surface is located at the focal point of the condenser lens 23 (second state). Shows a peak.
For example, in the first state, as shown in FIGS. 7A and 7B, the focal point of the condensing lens 23 is located on the front surface of the DUT 3. In this state, as shown in FIG. 7 (a), the light emitted from the second optical fiber 12 reaches the front surface of the device under test 3 and is reflected by the front surface of the device under test 3; As shown in FIG. 4, since the light is condensed on the end face of the second optical fiber 12, it is efficiently coupled to the second optical fiber 12. Therefore, the intensity of the non-interfering light (DC component) incident on the first light receiver 5 is maximized. Similarly in the second state, that is, when the focal point of the condensing lens 23 is located on the rear surface of the object 3 to be measured, the second optical fiber 12 is also efficiently coupled.
On the other hand, as shown in FIGS. 8A and 8B, when the front surface of the DUT 3 is located closer to the condenser lens 23 than the focal point of the condenser lens 23, as shown in FIG. As shown in FIG. 8B, after the light emitted from the second optical fiber 12 is reflected by the front surface of the object 3 to be measured, the light is focused on the end surface of the second optical fiber 12 before being condensed as shown in FIG. Will reach. For this reason, the reflected light is not condensed on the end face of the second optical fiber 12 and is not coupled to the second optical fiber 12. Accordingly, the intensity of non-interfering light (DC component) incident on the first light receiver 5 is reduced.
9A and 9B, when the front surface of the DUT 3 is located farther from the condenser lens 23 than the focal point of the condenser lens 23, as shown in FIG. As shown in FIG. 9, after the light emitted from the second optical fiber 12 is reflected by the front surface of the object 3 to be measured, the light is collected before reaching the end surface of the second optical fiber 12 as shown in FIG. It will shine. Then, since the reflected light reaches the end face of the second optical fiber 12 in a spread state, it is not coupled to the second optical fiber 12. Accordingly, the intensity of non-interfering light (DC component) incident on the first light receiver 5 is reduced.

Accordingly, the position (P = A) of the Z stage 25 when the first state is obtained by measuring the light intensity with the first light receiver 5 while scanning the Z stage 25, and the second state. It is possible to detect the position (P = B) of the Z stage 25 when.
From this, the amount of change in the distance between the condenser lens 23 and the object to be measured 3 between the first state (P = A) and the second state (P = B), that is, from the first state. The amount of movement (Δz) of the Z stage 25 up to the second state is obtained.

Next, the Z stage 25 is fixed at a position (P = A) where the first state is obtained. In this state, if the distance from the reflecting surface of the semi-transparent mirror 22 to the front surface of the object to be measured 3 is X, the optical path between the first branch optical path 33 and the second branch optical path 34 branched by the beam splitter 32. The position of the first stage 38 is set so that the length difference is substantially equal to X. Specifically, the difference between the distance from the beam splitter 32 to the first mirror 35 and the distance from the beam splitter 32 to the second mirror 36 may be set to be substantially equal to X.
Then, while scanning the second stage (L stage) 39 while vibrating at a constant frequency and constant amplitude, the light intensity of the interference signal is measured by the second light receiver 4, and the peak intensity of the interference signal is maximized. The third state is detected (first scan of the L stage). Thereby, the position (L (P _A )) of the second stage 39 when the third state is obtained can be detected.

Next, the Z stage 25 is fixed at a position (P = B) where the second state is obtained. Then, while continuing to vibrate the second stage 39, while scanning the second stage 39, the light intensity of the interference signal is measured by the second light receiver 4, and the peak intensity of the interference signal is maximized. 4 is detected (second scanning of the L stage). Thereby, the position (L (P _B )) of the second stage 39 where the fourth state is obtained can be detected.
Then, the change amount ΔL of the optical path length of the second branch optical path between the third state and the fourth state, that is, the second stage (L from the third state to the fourth state) The amount of movement (ΔL) of the stage 39 is obtained.

In the present embodiment, the light emitted from the third optical fiber 13 includes reflected light (reference light) from the semi-transparent mirror 22 and reflected light (inspection light) from the object to be measured 3. Therefore, regarding the light intensity of the two branched lights (the propagating light of the first branching optical path 33 and the propagating light of the second branching optical path 34) branched by the beam splitter 32, both the peak derived from the reference light and the inspection The peak derived from light is included, and the deviation of the two peaks on the time axis corresponds to the distance X from the reflecting surface of the semi-transparent mirror 22 to the front surface of the object 3 to be measured.
Therefore, in a state where the optical path length difference between the first branch optical path 33 and the second branch optical path 34 is substantially equal to the X, the interference light intensity obtained by combining the two branch lights is maximized. By detecting this, it is possible to detect a state (third state) in which the reference light and the inspection light (reflected light from the front surface) interfere with each other.
Thereafter, the first stage 38 is fixed, the focus of the light source light is moved onto the rear surface of the object 3 to be measured, and the state in which the interference light intensity detected by the light receiver 4 is maximized is detected. A state (fourth state) in which the reference light and the inspection light (reflected light from the rear surface) interfere with each other can be detected.

From the values of the movement amount (Δz) of the Z stage 25 and the movement amount (ΔL) of the second stage (L stage) 39 obtained in this way, the phase refractive index n and the thickness t of the DUT 3 are measured. Can be derived as follows.
That is, the numerical aperture of the condenser lens 23 for condensing the low-coherence light on the device under test 3 is S, the phase refractive index of the device under test 3 is n, and the refractive index wavelength dispersion amount of the device under test 3 is Δn. And When approximated by the chromatic dispersion amount Δn << 1, the phase refractive index n of the DUT 3 is expressed by the following mathematical formula (1).
The chromatic dispersion amount Δn in the formula (1) is expressed by the following formula (2) using the ΔL and Δz and the constants a and b. Here, the constants a and b are experimentally obtained. When the DUT 3 is solid, a is 0.0241 and b is 1.69. When the DUT 3 is liquid, a is a. Is 0.0460, and b is 1.53.
Further, the thickness t of the device under test 3 is expressed by the following formula (3) using the phase refractive index n, the wavelength dispersion amount Δn of the device under test 3 obtained here, and the ΔL and Δz. .

Thus, according to the present embodiment, the phase refractive index n and the thickness t of the device under test 3 can be simultaneously measured in a non-contact and non-destructive manner by the measurement method using the optical interference method.
According to the present embodiment, Δz can be obtained by simply scanning the Z stage 25 once while measuring the intensity of non-interfering light with the first light receiver 5.
Then, the Z stage 25 is fixed at a position where the first state is obtained, the L stage is scanned once, the Z stage 25 is fixed at a position where the second state is obtained, and the L stage is operated once. Since ΔL can be obtained simply by scanning, the number of scans required to obtain Δz and ΔL can be greatly reduced as compared with the conventional case.
Therefore, it is possible to shorten the measurement time that has been spent for many scans so far, and to speed up the measurement of the thickness and refractive index of the object to be measured.

FIG. 3 is a schematic block diagram showing a second embodiment of the measuring apparatus of the present invention. The apparatus of this embodiment differs greatly from the first embodiment in that a branch is not provided in the middle of the third optical fiber 13, and the second stage (L stage) 39 is connected to the second branch. The optical path 34 is configured to be adjustable longer than in the first embodiment.
When fixing the optical path length of the first branch optical path 33 and increasing the optical path length of the second branch optical path 34, if the optical path length of the second branch optical path 34 falls outside a specific range (non-interference area), When the light that has passed through the first branch optical path 33 and the light that has passed through the second branch optical path 34 are combined by the beam splitter 32, interference light cannot be generated. In the present embodiment, the optical path length of the second branch optical path 34 is configured to be adjustable to this non-interference area.
That is, if the distance from the reflecting surface of the semi-transparent mirror 22 to the front surface of the device under test 3 is X, the phase refractive index of the device under test 3 is n, and the thickness is t, the optical path length of the first branch optical path 33 and the first When the difference between the optical path lengths of the two branch optical paths 34 is equal to X and equal to X + nt, an interference state between the reference light and the inspection light is obtained, so that the first branch optical path is prevented from becoming such an interference state. By adjusting the optical path length of 33 and the optical path length of the second branch optical path 34, the light combined by the beam splitter 32 becomes non-interfering light.
Therefore, if the difference between the optical path length of the first branch optical path 33 and the optical path length of the second branch optical path 34 is set to be smaller than X or larger than X + nt (non-interference area), the beam splitter The light combined at 32 becomes non-interfering light. Before measurement, X can be measured, but n and t are unknown. Therefore, the optical path length of the first branch optical path 33 and the optical path length of the second branch optical path 34 are set to be smaller than X. It may be configured so that it can be set sufficiently large to be surely larger than X + nt.

The method for measuring the refractive index and thickness of the DUT 3 using the apparatus having such a configuration is substantially the same as that in the first embodiment, except that the first state and the second state are different. In the step of detecting Δz by detection, light is emitted from the light source 1 in a state where the optical path length of the second branch optical path 34 is adjusted to the non-interference area by moving the second stage (L stage) 39 backward. Thus, the intensity of non-interfering light is measured by the second light receiver 4.
That is, since the two branched lights combined by the beam splitter 32 do not interfere with each other, the light is emitted from the light source 1, and the light to be measured 3 is irradiated onto the object 3 to be measured through the condenser lens 23. When the Z stage 25 is scanned, the second light receiver 4 can detect the intensity peak of non-interfering light. Thereby, the position (P = A) of the Z stage 25 when the first state is obtained and the position (P = B) of the Z stage 25 when the second state is obtained can be detected. , Δz is obtained.
Thereafter, the second stage (L stage) 39 is advanced to return the optical path length of the second branch optical path 34 to the same level as in the first embodiment, and then the same procedure as in the first embodiment. ΔL can be obtained.
Then, from the obtained Δz and ΔL, the phase refractive index n and the thickness t of the DUT 3 can be obtained.

  According to this embodiment, the same operational effects as those of the first embodiment can be obtained, and in particular, the second light receiver 4 can move the second stage 39 to a specific range to cause non-interfering light. Can be detected, so that there are advantages such as a small number of parts and a small loss of light to be measured.

  FIG. 4 is a schematic configuration diagram showing a third embodiment of the measuring apparatus of the present invention. The apparatus of this embodiment differs greatly from the first embodiment in that a branch is not provided in the middle of the third optical fiber 13 and a shutter that blocks the optical path on the first branch optical path 33. 6 is provided. The shutter 6 can be freely opened and closed.

The method for measuring the refractive index and thickness of the DUT 3 using the apparatus having such a configuration is substantially the same as that in the first embodiment, except that the first state and the second state are different. In the step of detecting and obtaining Δz, light is emitted from the light source 1 with the shutter 6 closed and the first branch optical path 33 blocked, and the intensity of non-interfering light is measured by the second light receiver 4. It is a point to do.
That is, since the light that has passed through the first branched light path 33 is not incident on the second light receiver 4, only the light that has passed through the second branched light path 34, that is, non-interfering light, is incident on the second light receiver 4. The Therefore, when the Z stage 25 is scanned while emitting light from the light source 1 and irradiating the object to be measured 3 with the light transmitted through the semi-transparent mirror 22 via the condenser lens 23, the second light receiver 4 does not interfere. The peak of light intensity can be detected. Thereby, the position (P = A) of the Z stage 25 when the first state is obtained and the position (P = B) of the Z stage 25 when the second state is obtained can be detected. Δz is obtained.
Thereafter, after the shutter 6 is opened to release the blocking state of the first branch optical path 33, ΔL can be obtained in the same procedure as in the first embodiment.
Then, from the obtained Δz and ΔL, the phase refractive index n and the thickness t of the DUT 3 can be obtained.

According to the present embodiment, the same operational effects as the first embodiment can be obtained, and in particular, the second light receiver 4 is non-interfering by blocking the first branch optical path 33 with the shutter 6. Since the light can be detected, there are advantages that the apparatus is not enlarged and the loss of the light to be measured is small.
The shutter 6 may be provided on one of the first branch optical path 33 and the second branch optical path 34.

The present invention can be applied to the measurement of the thickness and refractive index distribution of the coating material on the surface, and the thickness measurement of those that are not completely solid.
It is particularly suitable for objects that need to be measured non-destructively and non-contactly, such as confirmation of the cured state of the resin and measurement of the buffer layer between the glass of the liquid crystal screen.

It is a schematic block diagram which shows 1st Embodiment of the measuring apparatus of this invention. It is a flow sheet which shows one embodiment of the measuring method of the present invention. It is a schematic block diagram which shows 2nd Embodiment of the measuring apparatus of this invention. It is a schematic block diagram which shows 3rd Embodiment of the measuring apparatus of this invention. It is a schematic block diagram which shows the example of the conventional measuring apparatus. It is a flow sheet which shows the example of the conventional measuring method. It is explanatory drawing of the measuring method which concerns on this invention. It is explanatory drawing of the measuring method which concerns on this invention. It is explanatory drawing of the measuring method which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source, 3 ... To-be-measured object, 4 ... 2nd light receiver (2nd detection means),
5 ... 1st light receiver (1st detection means), 6 ... Shutter (blocking means)
22 ... Semi-transparent mirror, 23 ... Condensing lens (condensing means),
25 ... Z stage,
32 ... Beam splitter (branching means / multiplexing means),
33 ... 1st branch optical path, 34 ... 2nd branch optical path,
38 ... 1st stage (optical path length correction means),
39. Second stage (optical path length variable means, L stage).

Claims (5)

A light source, a semi-transparent mirror that reflects part of the light from the light source and transmits part of the light,
Condensing means for condensing the transmitted light of the semi-transparent mirror and irradiating the object to be measured;
First detection means for detecting the intensity of non-interference light including inspection light reflected by the object to be measured;
Branch means for branching light including reference light reflected by the semi-transparent mirror and inspection light reflected by the object to be measured into a first branch optical path and a second branch optical path provided with an optical path length variable means When,
A multiplexing unit that combines the light that has passed through the first branch optical path and the light that has passed through the second branch optical path to generate interference light;
An apparatus for measuring refractive index and thickness, comprising second detection means for detecting the intensity of the interference light.   Branching means for branching light including reference light reflected by the semi-transparent mirror and inspection light reflected by the object to be measured before branching to the first branch optical path and leading to the first detection means; The refractive index and thickness measuring apparatus according to claim 1, wherein the measuring apparatus is provided.   The optical path length of the second branch optical path can be adjusted to a non-interference area where the light passing through the first branch optical path and the light passing through the second branch optical path do not generate interference light, 2. The refractive index and thickness measuring apparatus according to claim 1, wherein the detecting means also serves as the first detecting means.   A means capable of blocking either one of the first branch optical path and the second branch optical path is provided, and the second detection means also serves as the first detection means. Item 1. The refractive index and thickness measuring device according to Item 1. A method for measuring the refractive index and thickness of an object to be measured using the measuring apparatus according to claim 1,
While irradiating the object to be measured with the light passing through the semi-transparent mirror from the light source through the light collecting means, and changing the distance between the light collecting means and the object to be measured, A first state in which the light transmitted through the semi-transparent mirror is collected on the light source side front surface of the device under test by detecting the intensity of the non-interfering light with the first detection means; and Each of the second states collected on the rear surface far from the light source of the object to be measured is detected, and the condensing means and the object to be measured between the first state and the second state are detected. A step of obtaining a change amount Δz of the distance between,
By detecting the intensity of the interference light detected by the second detection means while changing the optical path length of the second branch optical path while maintaining the first state, Detecting a third state where the intensity is maximum;
By detecting the intensity of the interference light detected by the second detection means while changing the optical path length of the second branch optical path while maintaining the second state, Detecting a fourth state where the intensity is maximum;
Obtaining a change amount ΔL of the optical path length of the second branch optical path between the third state and the fourth state;
A method for measuring the refractive index and thickness, comprising the step of determining the refractive index and thickness of the object to be measured using the values of Δz and ΔL.

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