JP2003185416A - Method and apparatus for measurement of film thickness thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for the measurement of the film thickness of a thin film wherein the film thickness of a scattering or absorptive thin film can be measured by solving the problem that the coupling efficiency of light from a low-coherence light source to a fiber is low, that the utilization efficiency of the light is unsatisfactory, and that the scattering or absorptive thin film is hard to measure although it is desired that, in the method and the apparatus for the measurement of the film thickness of an interference film by using the light from the low-coherence light source, the fiber is used in the apparatus, that the apparatus is assembled easily and that the apparatus is operated stably. <P>SOLUTION: A semiconductor laser which is modulated at a high frequency of 0.8 to 3 GHz is used as the light source, the coupling efficiency of its output light to the fiber is increased, and the film thickness of the scattering or absorptive thin film can be measured. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for non-destructively and non-contactlessly measuring and displaying the thickness of a thin film.

[0002]

2. Description of the Related Art The need to measure non-destructively a thin film applied / formed on an object by various methods such as application, painting, printing, coating, laminating, vapor deposition, deposition, pasting, transfer, generation and growth. It often occurs in various fields of industrial, distribution, and general consumer economic activities, such as management of production processes thereof, quality control of products, and identification, identification, and authentication of jewelry formed of thin films such as pearls. Further, non-destructive film thickness of the thin film formed on the outer surface or the inner surface of the tubular or tubular body,
Process control by non-contact continuous measurement and treatment and diagnosis related to the film thickness immediately below the surface of living tissue having a layer structure in dentistry, ophthalmology, dermatology, etc., for example, enamel (or enamel) of human or animal teeth Often the need for non-destructive measurement of the thickness of the will occur.

An independent single sheet thin film such as a film, paper or plastic sheet can be measured with a micrometer or other mechanical film thickness meter.
Such a mechanical film thickness measuring method cannot be applied to a thin film formed on an object as described above, a thin film on the surface of a tubular or tubular body, or the like. For a thin film formed on an object, an ellipsometer is used when the thin film is relatively transparent. However, ellipsometer measurement is complicated and time-consuming, and is not suitable for general purposes such as process control, quality control, and discrimination.

When the thickness of the thin film is 100 μm or more and the required resolution is 10 μm or more, a simpler low coherence interferometer has been used instead of the ellipsometer. First, FIG. 7 is a diagram showing the principle of a conventional low coherence interferometer using optical propagation in space. In FIG. 7, when the relative intensity of the incident light 3 emitted from the light source 1 and incident on the half mirror 2 is 1, the transmitted light 4 and the upward reflected light 5 each have a relative intensity of about 0.5. Occurs. The transmitted light 4 is reflected by the surface of the DUT 6 and enters the half mirror 2 again. On the other hand, the upward reflected light 5 is reflected by the reflecting mirror 7 and enters the half mirror 2 again.
The respective reflected lights re-incident on the half mirror 2 interfere on the half mirror 2 to generate two interference lights 8 and 9.
One interference light 8 goes to the photodetector 10, and the other interference light 9 goes to the light source 1. The above constitutes a so-called Michelson interferometer.

The optical path from the half mirror 2 to the object 6 to be measured is arranged on one arm 11 of the interferometer, and from the half mirror 2 to the reflecting mirror 7.
The optical path up to is called the other arm 12 of the interferometer. When the coherence of the light source is good, when the length of one arm is fixed and the length of the other arm is slowly changed, the two reflected lights that re-enter the half mirror 2 interfere with each other. As shown in FIG. 8, the intensities of the interference lights 8 and 9 of the book change sinusoidally. When one interference light becomes strong, the other interference light becomes weak. The output current from the photodetector 10 changes sinusoidally when the length of one arm changes according to the change in the intensity of the interference light 8. In FIG. 7, arm 1
The case where the optical path length of 2 is changed is shown. A reflecting mirror 7 is attached to the tip of the displacement device 13 for changing the optical path length of the arm 12.

The principle of the above-mentioned conventional thin film thickness meter using the low coherence interferometer will be described. A light source of low coherence, that is, a light source of short coherence length is selected as the light source 1 of the interferometer for measuring the film thickness. Light sources with a short coherence length include so-called super luminescent diodes (hereinafter referred to as SLD) and halogen lamps. If the coherence length is short, the interference light that changes sinusoidally with respect to the change in the length of one arm of the interferometer, and thus the sinusoidal output current from the detector 10, is generated as shown in FIG. The maximum value is taken at the center point M of the envelope on the horizontal axis when the lengths of both arms (Fig. 7) are equal, and the sinusoidal change of the narrow range (current (optical input)) before and after that takes place. 10 to several tens of cycles). Therefore, the position of the reflecting mirror 7 that gives the maximum value of the envelope of the sinusoidal change in the output current of the photodetector can be used for position measurement by interference. The narrower the half-width of the envelope is, the smaller the resolvable distance can be.

When the film thickness of a thin film is measured by an interferometer, since there are step changes in the refractive index on the front surface and the back surface, respectively, there are two reflection points. If the resolvable distance of each of these two reflection points is smaller than the film thickness itself, the above-mentioned position measurement can be applied twice, and the difference between each position is defined as the optical film thickness of the thin film. You can The optical film thickness refers to the mechanical film thickness to be measured multiplied by the refractive index of the thin film. Therefore, when the refractive index of the thin film is known, the actual mechanical thickness of the film to be measured can be obtained by dividing the optical film thickness by the refractive index. However, if the refractive index of the thin film is not known, it is necessary to measure the refractive index of the thin film independently. In this way, for the method of independently obtaining the optical film thickness and the refractive index, for example, Optics Lette
rs, Volume 20, Issue 21, pages 2258 (November 1995)
"Determination by GJ Tearney et al.
of the refractive Index of highly scattering human
tissue by optical doherence tomography "(hereinafter referred to as Reference 1), also Optics Letters, Volume 21, 23
Issue, p. 1942 (December 1996)
"Simultaneous measurement of thick" by T. Fukano et al.
nesses and refractive Indices of multiple layers "
(Hereinafter referred to as Document 2), and Japanese Patent Laid-Open No. 2001-1416.
52, the inventor, Masamitsu Haruna, "A known method by optical interferometry is a method for simultaneously measuring the refractive index and thickness of an object to be measured and a device therefor".

The interferometer type film thickness measuring device which relies on the light propagation in the space in the prior art as described above requires a high degree of skill and a long time for arranging, setting and adjusting the optical components. In addition, there is a problem with respect to long-term stability after completion of the device, and there is a problem that adjustment is required by a skilled person every time the device is used after the device is manufactured. This is because in an interferometer that relies on light propagation in space, the placement, setting, and adjustment of one optical component of the mirror, beam splitter, etc. are interrelated with the placement, setting, and adjustment of other optical components. , N (N-where N is approximately the number of parts in the adjustment time required for adjusting each part to complete the arrangement and adjustment of the entire device).
1) Double adjustment time is required. Also, regarding the stability, the stability of each component is calculated as follows:
This is because the double stability is required.

If the arrangement, setting and adjustment of one optical component do not correlate with the arrangement, setting and adjustment of other optical components, the time required to complete the arrangement and adjustment of the entire apparatus is Generally, the adjustment time required for adjusting each component is approximately the number of component times, and the stability of the entire device is the stability of each component as it is.
As described above, in order to separate and independently arrange, set, adjust, and stabilize each optical component, the optical propagation between the optical components depends on the spatial propagation, and the optical fiber depends on the spatial propagation. It should be independent of light propagation.

FIG. 10 shows a conventional interferometer film thickness measuring device in which the film thickness measuring device using the interferometer by the light propagating in the space shown in FIG. 7 is made into a fiber. The fiber is shown by a thick solid line. The components in FIG. 10 that perform the same functions as the components in FIG. 7 are assigned the same numbers as the corresponding components in FIG. 7. The half mirror 2 in FIG. 7 is replaced with the fiber directional coupler 2 in FIG. The function of the fiber directional coupler 2 is the same as that of the half mirror 2 in FIG. 7, and the light entering from the terminal 21 of the directional coupler goes out from the terminals 22 and 24 in the same amount, but from the terminal 23. I won't go out. Light entering terminal 22 exits at ends 21 and 23 in equal amounts, but not at terminal 24. The light entering from the terminal 24 exits from the ends 21 and 23 in equal amounts, but does not exit from the terminal 22. The lenses 16 and 26 as optical elements for projection are for converting divergent light emitted rightward from the fiber ends of the respective arms into parallel light, and the DUT 6 and the reflecting mirror 7 are respectively provided with , The distances to the fiber ends and the lenses 16 and 26 are matched to the focal lengths of the respective lenses so that parallel rays are incident. As shown by 14 and 15 in FIG. 10, each arm has a spatial propagation path.

In the conventional fiberized interferometer film thickness measuring device shown in FIG. 10, the arrangement, setting and adjustment of each optical component are also required for the assembly of the system of the interferometer type film thickness measuring device using a large number of optical parts. Be independent. Also, their assembly is performed by simply connecting the respective parts with fiber connectors. Therefore, no expert is required, and the assembly work is extremely shortened. Also, the stability of the device is significantly improved for the reasons described above. However, with this conventional device, the space propagation path 14 immediately before the DUT 6 and the space propagation path 15 immediately before the reflecting mirror 7 for changing the length of the arm 12 of the interferometer cannot be removed. Reference numeral 13 is a spatial propagation path 1 immediately before the reflecting mirror 7.
5 is a reflecting mirror moving mechanism to which a reflecting mirror 7 for changing the propagation length of 5 is attached.

[0012]

In the conventional fiberized interferometer film thickness measuring apparatus of FIG. 10, in order to project the measurement light on the object to be measured in a non-contact manner and to change the arm distance of the interferometer. Requires a space propagation path 14 immediately before the DUT 6 and a space propagation path 15 immediately before the reflecting mirror 7 for changing the length of the arm 12 of the interferometer. Therefore, the shortcomings of the prior art caused by the existence of the spatial propagation path, namely, the complexity of the assembly and adjustment work of the device, and the inclusion of the spatial propagation path interferometer which is sensitive to the disturbance from the surrounding environment are included. The resulting instability of the device was not resolved.

Further, as the light source, SLDs and halogen lamps having a low coherence have conventionally been used in order to keep the resolvable distance small. However, since these light sources have a low spatial coherence, when they are made into fibers, the coupling efficiency from the light sources to the fibers becomes extremely poor, and the power level of light that can be used for interferometric measurement becomes extremely low. Therefore, the S / N ratio of the sinusoidal detection current output obtained as a result of the interference is lowered, and the film thickness resolution to be obtained is lowered. Particularly when the thin film to be measured is not a transparent body but a medium having a scattering property or an absorbing property, it is fatal that the power level of the measurement light is low, and in that case, the measurement becomes impossible.

As described above, in the fiberized interferometer type film thickness measuring device, a fiber, a low coherence SLD or a halogen lamp light source necessary for high resolution interferometric film thickness measurement is coupled to the fiber. There was a problem in that the efficiency was extremely reduced due to the use of fibers, and the film thickness decomposing ability resulting therefrom was reduced.

[0015]

In the fiberized interferometer film thickness measuring device of the present invention, first, in order to facilitate the assembly and adjustment work of the interferometer included in the device and to improve the stability of the device, the interference By making the fiber length of some of the fibers that make up the meter variable, the spatial propagation path that was necessary to make the arm length of the interferometer variable was eliminated. As a result, the thus constructed fiberized interferometer film thickness measuring device of the present invention is shown in FIG. In FIG. 1, spatial propagation paths other than the extremely short spatial propagation path 14 immediately before the DUT 6 necessary for projecting the measurement light onto the DUT (for example, the spatial propagation path 15 immediately before the reflecting mirror 7 in FIG. 10). ) Are all fiberized.

As a method of varying the physical length of the fiber itself described above, a long fiber wound around a piezoelectric element or a magnetostrictive element is inserted into at least one arm of the interference type, and A variable voltage (for piezoelectric element) or variable current (for magnetostrictive element) is applied. As a result, the spatial propagation path 14 immediately before the DUT is measured.
Everything except fiber is made into fiber. It aims at facilitating the assembly and stabilizing the operation of the film thickness measuring interferometer.

The thin film thickness measuring apparatus of the present invention comprises a semiconductor laser as a light source modulated at a predetermined high frequency of the order of gigahertz, and a measurement optical path arm and a non-measurement optical path arm for guiding the low coherence light emitted by the semiconductor laser. And an interferometer having two arms, wherein the non-measurement optical path arm is an optical path that substantially consists of optical fibers (hereinafter simply referred to as “fibers”) and does not include a spatial propagation optical path. The arm is from only the optical fiber except for the spatial propagation optical path of a predetermined length from the end face of the optical fiber for projecting the low coherence light emitted by the semiconductor laser onto the surface of the thin film to be measured of the measured object. It is characterized by The thin film thickness measuring method of the present invention comprises a step of modulating a semiconductor laser as a light source at a predetermined high frequency of the order of gigahertz to generate low coherence light, the low coherence light being measured by an interferometer, an optical path arm and a non-measurement step. Leading to two arms of the optical path arm, wherein the non-measurement optical path arm is an optical path that substantially consists of optical fibers (hereinafter simply referred to as “fiber”) and does not include a spatial propagation optical path. The arm is from only the optical fiber except for the spatial propagation optical path of a predetermined length from the end face of the optical fiber for projecting the low coherence light emitted by the semiconductor laser onto the surface of the thin film to be measured of the measured object. In addition, the film thickness of the thin film to be measured is measured by the interferometer. In addition, in the fiber interferometer film thickness measuring device of the present invention, a pulsed semiconductor laser is used, and the excitation current thereof is subjected to high frequency modulation, so that the semiconductor laser of the semiconductor laser is compared with the SLD and the like used in the prior art. While utilizing the better spatial coherency that it possesses, it also achieves the reduction in temporal coherency (necessary to improve film thickness resolution) that can be realized by modulation. As a result, even at the time of forming a fiber, it is possible to maintain a highly efficient coupling of the light source to the fiber,
Coupled with the realization of low temporal coherency, sensitivity and resolution for film thickness are simultaneously improved.

Further, a long fiber wound around a piezoelectric element or a magnetostrictive element for varying the length of the arm of the interferometer is provided on both arms of the interferometer, and the long fibers are driven in opposite phases. , The range of measurable film thickness is expanded.

Further, by moving only the lens for irradiating the object to be measured with light, it is possible to simultaneously measure the optical film thickness and the refractive index necessary for measuring the film thickness of unknown refractive index with a single device. A method has been proposed. As a result, the measurement head portion including the space propagation path immediately before the object to be measured can be integrated, and by holding the tip end in contact with the object to be measured, stable film thickness measurement can be performed more easily.

Combined with the improvements of the above-mentioned components, the assembling is easy, the sensitivity and the film thickness resolution are improved, the measurable film thickness range is widened, and the film thickness and the refractive index can be measured at the same time in a stable operation. A new fiberized interferometer film thickness measuring device can be realized.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below.

FIG. 1 shows a first embodiment of the present invention. Corresponding elements that perform the same functions as the constituent elements of the conventional example shown in FIG. 6 or FIG. 10 in the constituent elements of FIG. 1 have the same reference numerals as those of the constituent elements of FIG. 6 or FIG. The duplicated description thereof will be omitted here.

A semiconductor laser is used as the light source 1.
As the semiconductor laser 1, a type of semiconductor laser that is capable of high-speed modulation, has a small junction capacitance and other stray capacitances, has a short device lead wire, and has a low inductive reactance, which is used in an optical LAN or the like. A DC power supply 101 is passed through such a semiconductor laser through a bias tee 100 represented by an equivalent circuit shown in the drawing.
And a sinusoidal high frequency voltage from the high frequency power supply 102 of about 0.8 GHz to 3 GHz is applied. Generally, such a semiconductor laser capable of high frequency modulation repeats at the frequency of the applied high frequency voltage even if the degree of modulation is about 10% to 20% because of the non-linearity of the electron distribution existing at the junction. It outputs pulsed light with a pulse width of tens of picoseconds. Due to this pulsed laser oscillation, the density of the electron distribution in the above-mentioned junction changes abruptly within a short time within the pulse width. Therefore, the refractive index of the junction also changes abruptly, and the oscillated light undergoes frequency modulation with a large degree of modulation. It is generally known that the spectrum of frequency modulation spreads over a wide frequency band.
As a result, in DC excitation, a laser that oscillates in a substantially single-chip longitudinal mode oscillates in many longitudinal modes, and a wide spectrum can be obtained. In addition, about the above.
At a modulation frequency of 8 GHz or less, the light intensity changes substantially faithfully to the modulation waveform, and the pulsed light output is not obtained. Further, at a modulation frequency of about 3 GHz or higher, the light output cannot follow the modulation waveform, becomes a constant output, and does not become a pulsed light output. On the other hand, laser oscillation has a high spatial coherence, which is different from that of ordinary semiconductor lasers, unlike halogen lamps and SLDs. Therefore, it has both low coherence and high spatial coherence that cannot be obtained with halogen lamps and SLDs.
The most suitable light source for interference film thickness measurement is obtained by the modulated semiconductor laser.

Of the two arms of the interferometer, the arm that changes the length of the fiber is the non-measuring optical path arm 12 in this embodiment, and the fiber 18 that is the main element constituting the arm 12 is used.
Is as long as several tens of meters. This is a cylinder 1 of, for example, a cylindrical piezoelectric element (poled by a known method) such as lead zirconate titanate (so-called PZT).
A piezoelectric fiber length varying device 19 wound while applying a constant tension and preferably a constant reverse bias voltage to 91.
Is. The piezoelectric element excitation power source 2 is connected to the piezoelectric element cylinder 191.
Apply excitation voltage from zero. The excitation voltage may be a constant voltage (DC) or a voltage that changes with a desired waveform at a desired frequency (AC). Piezoelectric fiber length variable device 19
An example of the above configuration is shown in FIG. In FIG. 2, the long fiber 18 is wound around the cylindrical piezoelectric element 191 a number of times, and appropriate electrodes installed on the piezoelectric element, that is, in this embodiment, gold plating is applied on the entire surfaces of the inner wall and the outer wall of the cylinder shown in FIG. Between the electrodes 193 and 194 provided in
From the low-frequency AC power supply 202, or these voltages are applied at the same time through the illustrated filter circuit (L + C). This allows the cylinder 19
The diameter of 1 is changed constantly or periodically, and the fiber is tensioned to change the length of the fiber constant or periodically. In the structure of FIG. 2, an ordinary fiber having a clad diameter of 125 mm is used, and when the cylindrical piezoelectric element has a tube thickness of 5 mm, the applied voltage is 100 V and the fiber 10
An elongation of 1 mm per m was obtained.

As described above with reference to FIG. 9, in the low coherence interferometer according to the present invention, an interference waveform appears only in the vicinity of a state where both arms of the interferometer are equal in length. Therefore, in the present embodiment in which the non-measurement optical path arm 12 includes a long fiber, the fiber length that constitutes the majority of the measurement optical path arm 11 in order to balance the length with this long fiber of the arm 12 is the non-measurement optical path. The length of the long fiber of the arm 12 must be the length obtained by subtracting the spatial propagation path length 14 immediately before the DUT 6 (converted into the in-fiber optical propagation path). Therefore, the fiber 17 of the measuring optical path arm 11 of FIG. 1 is made to include a long fiber 199 wound around an air core.

The piezoelectric fiber length varying device 19 described above.
As a result, the length of one arm 12 of the interferometer becomes variable, so that the length of the arm 12 of the interferometer in the prior art fiber interferometer shown in FIG. The spatial propagation path 15 of is no longer needed. Therefore, in the present invention, the highly reflective coating 25 is directly applied to the end surface of the end of the fiber forming the arm 12, and this is used as the reflecting mirror of the arm 12 of the interferometer. As a result, the spatial propagation path 15 as shown in FIG. 10 can be eliminated, and the device can be easily assembled (the length of the spatial propagation path 15 and the verticality of the mirror and the light beam need not be adjusted).
This can contribute to the improvement of the stability of the interferometer (the calibration of the above-mentioned length and the deviation between the angle of the mirror and the direction of movement is unnecessary).

The piezoelectric fiber length varying device described above is
This may be replaced with a magnetostrictive fiber length varying device using a magnetostrictive body such as an alfero alloy or a rare earth intermetallic compound (so-called terphenol). An example thereof is shown in FIG. FIG. 11 shows a magnetostrictive body 600 formed in a rod shape (a) or a toroidal shape (b).
Electric conductor winding 5 shown by the thin wire in the figure for applying a magnetic field to
00 and a fiber 18 shown by a thick line are wound together. In the case of the piezoelectric fiber length variable device, the method of considering the winding method while applying tension when winding the fiber, the method of applying the DC bias of the polarity that makes the magnetostrictive body 600 thin at that time, the method of applying the DC bias during operation, etc. Is the same as.

Next, the measuring operation of the thin film thickness measuring apparatus using interference according to the first embodiment of the present invention shown in FIG. 1 will be described. The length of one arm 12 of the interferometer is changed by sweeping the voltage from the piezoelectric element excitation power source 20 applied to the piezoelectric fiber length varying device 19. When the long fiber 18 wound around the piezoelectric element 191 of the piezoelectric fiber length varying device 19 is sufficiently long and the insertion voltage width from the power source 20 is also sufficiently large, the change in the optical length of the arm 12 is determined from the measured optical film thickness. Can also be large. Therefore, the change in the length of the arm 12 can be made larger than the optical film thickness of the film 69 of the DUT 6. Then, since there are two surfaces 6A and 6B of the film 69 as the reflection surfaces of the DUT 6 at the terminal end of the light beam of the arm 11, the interference intensity with respect to the change in the length of the arm 12 is set in this way. The waveform changes occur at two places as shown in FIG. The measured object 6 is the surface 6 of the measured thin film 69.
The A and the back surface 6B are held by a goniometer type two-degree-of-freedom angle fine adjustment device 690 for adjusting the A and the back surface 6B substantially perpendicularly to the optical axis of the light projected from the lens 16 of the arm 11.

The horizontal axis of FIG. 3 represents the mechanical length of the arm 12, that is, in the normal sense, by replacing the object 6 to be measured with a reflecting mirror in advance and moving this by a predetermined distance. Since it can be calibrated as a change in the actual length, the horizontal axis in FIG. 3 can be shown as the mechanical length of the arm 12. The interval between two interference peaks on the scale of such a horizontal axis is represented by L. Further, since the interference peaks at the above two positions occur due to the round trip of light in the thin film 69, these two peaks
Interval L between interference peaks (scaled by mechanical distance)
Is the optical length of the thin film 69, that is, the optical thickness of the thin film 69 (value obtained by multiplying the mechanical thickness of the thin film by the refractive index of the thin film) To.
It is 1/2 of pt. Therefore,

[0030]

[Equation 1]

It is expressed as That is, the distance L measured at the peak interval of intensity change in FIG. 3 is not 1/2 of the mechanical film thickness of the thin film to be measured, but 1/2 of the optical film thickness Topt of the thin film.

When the refractive index n of the thin film 69 of the DUT 6 is known, the mechanical film thickness T of the thin film to be obtained from the measured optical film thickness Topt is the optical length and the mechanical film thickness described above. Depending on the relationship with the chief

[0033]

[Equation 2]

Is given by As described above, the film thickness T of the thin film 69 is obtained when the refractive index n is known.

When the refractive index n of the thin film 69 of the DUT 6 is unknown, the refractive index n of the DUT 6 must be measured independently of the optical film thickness Topt measured above. As described above, as methods for obtaining the optical film thickness Topt and the refractive index n independently of each other, as described above, there are Document 1, Document 2, and JP-A-9-218016.

In the present invention, as a simpler and more stable method, the following method with a small number of moving parts is used. By the method described above, the optical film 69 of the DUT 6 is measured.
It is assumed that the thickness Topt has already been obtained. This T
The fiber 17 of the arm 11 during the measurement of the opt, the lens 16 which is the optical projection optical means, the moving helicoid 160 for moving the lens in the optical axis direction, the object 6 to be measured, and the object 6 to be measured in the plane of the thin film 69 to be measured. 2 around the two orthogonal axes X and Y
Goniometer type adjustment device 69 for fine adjustment of posture
The arrangement of the mutual positions of 0 and 0 is shown in FIG. In this state, the distance between the end face of the fiber 17 and the lens 16 is kept at the focal length f of the lens, and the light emitted from the lens 16 is parallel light, which results in the parallel light as shown in FIG. In addition, two peaks are obtained on the interference intensity change. In this state, the distance g between the end surface of the fiber 17 and the DUT 6 is, for example, 4 to 5 times the focal length f of the lens 16, that is,

[0037]

[Equation 3]

It is fixed at a predetermined distance g within the range of. Next, with the distance g fixed once, the lens 16
Move only in the direction of the object to be measured. As a result, the light emitted from the lens 16 is not parallel light, and the DUT 6
Since the reflected light from both the front surface 6A and the back surface 6B of the thin film 69 is diverged, most of the light does not return to the fiber 17. As a result, the interference peak disappears. [Formula 3] is
This is a condition for obtaining an image on the front surface 6A and the back surface 6B of the measured thin film 69 with respect to the movement of the lens with one lens 16.

Further, the lens 16 is attached to the thin film 6 of the DUT 6.
As it is moved in the direction of 9, the converged light flux forms an image on the back surface 6B of the measured thin film 69 as shown in FIG. 4 (b). In order to show the state of image formation on the back surface 6B in more detail,
FIG. 4 (d) shows an enlarged view of FIG. 4 (b). The condensed light beam is
The surface 6A of the thin film 69 due to the refractive index of the measured thin film 69.
Refract at. The incident angle and the refraction angle of the light beam are refracted so as to satisfy the law of refraction. The moving distance from the initial state of the lens 16 at this time is defined as a. Here, the back surface 6 of the thin film
The incident light on B and the reflected light have a confocal relationship with each other, and a large part of the reflected light returns to the fiber 17,
One peak appears on the interference intensity pattern in the interferometer. At this time, since no image is formed on the surface 6A and the confocal state is not satisfied, the interference peak due to the reflected light from the surface does not appear. That is, two peaks from the back surface and the front surface do not appear at the same time, and only one peak appears as described above.

Further, when the lens 16 is moved in the direction of the object to be measured, the converged light flux eventually forms an image on the surface 6A of the thin film to be measured 69, as shown in FIG. 4C. At this time, as in the case of imaging on the back surface 6B, a large part of the reflected light returns to the fiber 17, and one peak appears on the interference intensity pattern in the interferometer. Lens 16 here
The moving distance from the state of FIG. 4C is b. Lens focal length f, the above distances, a, b, c, g and
It will be understood from the image formation relational expression of the lens and the law of refraction that the following various expressions are established between the refractive index n and the like of the thin film 69 with reference to FIG.

In FIG. 4B, c is the distance from the lens 16 to the intersection of the extended line (broken line) of the convergent incident light flux on the thin film 69 to be measured into the film 69. From the imaging formula of the lens,

[0042]

[Equation 4]

Is satisfied. Also, as is clear from the figure,

[0044]

[Equation 5]

There is a relationship of Surface 6A of thin film to be measured 69
For the refraction that occurs in, from the law of refraction, the following [Equation 6]
Is established.

[0046]

[Equation 6]

By deleting c from [Equation 4], [Equation 5] and [Equation 6], the following [Equation 7] is obtained.

[0048]

[Equation 7]

The rightmost side of [Equation 7] is a known quantity.
From [Equation 2] above

[0050]

[Equation 8]

It is Topt is a known quantity that has already been measured. From [Equation 6], [Equation 7], and [Equation 8]

[0052]

[Equation 9]

[0053]

[Equation 10]

Since d is a known quantity according to [Equation 7],
The film thickness T and the refractive index n of the thin film 69 are calculated by [Equation 9] and [Equation 10].
Will be obtained independently. During this measurement
The distance g between the fiber output end and the object to be measured is kept constant. In FIG. 4C, the position of the lens is further advanced by b shown in the figure, and an image is formed on the surface 6A of the thin film to be measured, and a peak appears in the interference intensity pattern. The image of 6A can be confirmed.
An imaging relationship by a lens similar to [Equation 4] is established between the value of b and the values of a, f, and g used previously. At this time, the distance between the end surface of the fiber 17 and the lens 16, the distance between the lens 16 and the surface 6A of the thin film to be measured,
Is almost twice the focal length f of the lens 16.

During the above measurement, the distance g between the fiber output end and the object to be measured was kept constant as described above. The range of g in which such measurement is possible is sufficient if g satisfies [Equation 3] and does not need to be a strictly defined value. Therefore, an adjustable and fixed frame structure (which does not block the projected light) is attached to the fiber output end, and the tip of the frame structure is lightly touched on the measured object to perform the measurement. Setting is simple and stable measurement is possible.

Next, a second embodiment will be described with reference to FIG. 5 in the case where the thin film to be measured is a cylindrical thin film having a radius smaller than the focal point f of the lens or a spherical shell-like curved thin film. . Examples of the cylindrical thin film include a thin tube itself or a thin film formed on the outer surface thereof, and examples of the spherical shell thin film include a pearl growth layer. In these cases, the case where the thin film to be measured is flat is shown in FIG.
(A), (b), (c) and (d) are shown in FIG.
It replaces (b), (c), and (d). In FIG. 4A, the distance between the fiber 17 and the lens 16 at the time of measuring Topt is matched with the focal length f of the lens, but in the case of a spherical thin film, as shown in FIG. Is a value h near twice the focal length f, that is,

[0057]

[Equation 11]

In particular, the spherical object to be measured may be set so that two peaks are generated on the interference intensity pattern. The subsequent measurement process is shown in (b), (c), and 4 in FIG.
Since the processes in (b), (c), and (d) of FIG. 5 are similar to those in (d), f in [Expression 4] to [Expression 7] may be replaced with h, and finally, , [Equation 8] to [Equation 9] can be applied as they are, and the film thickness T and the refractive index n of the spherical thin film can be measured independently.

The layout of the third embodiment is shown in FIG. In this embodiment, the piezoelectric fiber length variable devices 19A and 19B having the same characteristics are installed on both the arm 11 and the arm 12, respectively. Piezoelectric fiber length variable device 19A, 19
Excitation voltages from excitation power supplies 20A and 20B are applied to B, respectively. Whether DC is applied, low frequency AC voltage is applied, or they are superimposed and applied,
In any case, they may be applied independently or a common voltage may be applied. In particular, if a common voltage is applied so that their waveforms act in opposite phases on both piezoelectric elements, the difference in the length of both arms at the same voltage can be used to change the length of a single fiber shown in FIG. It can be changed twice as much as in the case of the device, and the measurable film thickness range can be expanded. Further, when the same voltage is applied, it goes without saying that the same effect can be obtained even if one power source is used and the direction of application to each piezoelectric element is reversed.

While the present invention has been particularly described with respect to the embodiments and various aspects thereof, it is generally familiar to those skilled in the art that various modifications and variations thereof can be made without departing from the spirit and purpose of the invention. It will be understood by some people.

[0061]

As described above, according to the present invention,
It is possible to use all the optical propagation paths of the interferometer other than the optical space propagation path immediately before the thin film to be measured as fibers.
Further, by using the high frequency modulation semiconductor laser as the low coherence light source, it is possible to improve the utilization efficiency of the light source output, even though the optical propagation path is made almost fiber. Moreover, the film thickness and refractive index of the object to be measured can be measured by operating a single movable part of a single device. Further, these measuring methods and measuring devices are not limited to the planar thin film, and can be applied to the measurement of spherical, cylindrical, and various other curved thin films. As a result, it can be applied to a thin film formed on another object, or a thin film having a tube shape or a curved surface. Moreover, this film thickness measuring device is easy to assemble, does not require adjustment by a specialist every time it is used, has excellent stability, and can measure the film thickness stably. Therefore, the industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is an optical layout diagram of a film thickness measuring apparatus according to a first embodiment and a light source excitation power supply circuit.

FIG. 2 is a perspective view of a piezoelectric fiber length varying device used in the first embodiment and a circuit diagram of its excitation application unit.

FIG. 3 is a diagram showing changes in the interference intensity waveform with respect to the arm length of the interferometer in the first embodiment.

FIG. 4 is a diagram of various optical arrangement states of a space propagating portion immediately before an object to be measured, for explaining the measurement principle of the first embodiment.

5A and 5B are diagrams of various optical arrangement states of a space propagating unit immediately before an object to be measured for explaining the measurement principle of the second embodiment.

FIG. 6 is an optical layout diagram of a film thickness measuring device according to a third embodiment.

FIG. 7 is an optical layout diagram showing the principle of a conventional space propagation optical path type film thickness measuring device.

FIG. 8 is a diagram showing a change in interference intensity from both arms with respect to displacement of one reflecting mirror when a coherence light source is used in a conventional space propagation type interferometer.

FIG. 9 is a diagram showing a change in interference intensity from both arms with respect to displacement of one reflecting mirror when a low coherence light source is used in a conventional space propagation type interferometer.

FIG. 10 is an optical layout diagram of a conventional fiberized film thickness measuring device.

11A and 11B are perspective views showing two examples of the magnetostrictive device used in the embodiment of the present invention, where FIG. 11A shows a cylindrical structure, and FIG. 11B shows a toroidal structure. is there.

[Explanation of symbols]

1 light source, semiconductor laser 2 half mirror 3 incident light 4 transmitted light 5 reflected light 6 DUT 6A Surface of thin film to be measured 6B Back side of thin film to be measured 7 Reflector 8, 9 Interference light 10 Photodetector 11,12 Interferometer arm 13 Displacement device 14, 15 Spatial propagation path 16, 26 lens 17 fiber 18 long fiber 19, 19A, 19B Piezoelectric fiber length variable device 20, 20A, 20B Piezoelectric element excitation power supply 21, 22, 23, 24 Terminals of directional coupler 25 Highly reflective coating 69 membrane 100 Bias Tee 101 DC power supply 102 high frequency power supply 191 Piezoelectric element 193 and 194 electrodes 201 DC power supply 500 electric conductor winding 600 magnetostrictive body

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F064 AA01 BB07 CC02 CC04 DD01                       EE01 FF01 GG02 GG17 GG22                       GG24 GG63 GG64 HH01 HH05                       JJ03 KK01                 2F065 AA30 CC31 DD03 DD11 DD15                       FF51 GG06 LL02 NN06 NN08

Claims (22)

[Claims] 1. An interferometer having a semiconductor laser as a light source modulated at a predetermined high frequency on the order of gigahertz, and two arms, a measurement optical path arm and a non-measurement optical path arm for guiding low coherence light emitted by the semiconductor laser. And the non-measurement optical path arm is an optical path that is substantially composed of only optical fibers (hereinafter simply referred to as “fiber”) and does not include a spatial propagation optical path, and the measurement optical path arm is the low optical path emitted by the semiconductor laser. The thin film is characterized by comprising only an optical fiber except for a spatial propagation optical path of a predetermined length from the end face of the optical fiber for projecting coherence light to the surface of the thin film to be measured of the object to be measured to the surface of the thin film to be measured. Film thickness measuring device. 2. A reflecting mirror in which at least the measurement optical path arm of the interferometer includes a piezoelectric type fiber length varying device in which a fiber is wound around a piezoelectric element, and an end face of an optical fiber of the non-measurement optical path arm is highly reflective coated. The film thickness measuring device for a thin film according to claim 1, wherein: 3. An interferometer, both arms of which include a piezoelectric type fiber length variable device in which fibers are wound around a piezoelectric element, and an end face of an optical fiber of the non-measurement optical path arm is a reflecting mirror having a high reflection coating. The thin film thickness measuring device according to claim 1, wherein. 4. A reflection in which at least a pre-measurement optical path arm of the interferometer includes a magnetostrictive fiber length varying device in which a fiber is wound around a magnetostrictive body, and an end face of an optical fiber of the non-measurement path arm is highly reflective coated. It is a mirror, The film thickness measuring device of the thin film of Claim 1 characterized by the above-mentioned. 5. An interferometer, wherein both arms of the interferometer include a magnetostrictive fiber length varying device in which a fiber is wound around a magnetostrictive body, and the end face of the optical fiber of the non-measurement optical path arm is a reflecting mirror having a high reflection coating. The film thickness measuring device for a thin film according to claim 1, wherein: 6. The thin film thickness measuring device according to claim 4, wherein the magnetostrictive body has a substantially cylindrical shape, and a fiber is wound around the cylindrical surface. 7. The thin film thickness measuring apparatus according to claim 4, wherein the magnetostrictive body is substantially toroidal, and a fiber is wound around the toroidal surface. . 8. Fixing means for fixing the relative spatial positional relationship between the end face of the fiber of the measurement optical path arm and the surface of the thin film to be measured, and space propagation of a predetermined length from the end face of the fiber to the surface of the thin film to be measured. 8. The thin film thickness measuring apparatus according to claim 1, further comprising: a moving unit that moves the projection optical unit placed on the optical path along the spatial propagation optical path. 9. The thin film to be measured is an arbitrary flat surface or curved surface, and the posture of the measured object is finely adjusted so that the normal line of the flat surface or curved surface substantially coincides with the optical axis of the spatial propagation optical path. 9. The thin film thickness measuring device according to claim 1, further comprising a holder for holding the thin film. 10. The thin film thickness measuring device according to claim 8, wherein the curved surface of the thin film to be measured is cylindrical, spherical or irregular. 11. The predetermined high frequency is 0.8 to 3
11. The thin film thickness measuring device according to claim 1, wherein the film thickness measuring device is in the gigahertz range. 12. A step of modulating low-coherence light by modulating a semiconductor laser as a light source at a predetermined high frequency of the order of gigahertz, and two low-coherence lights of a measurement optical path arm and a non-measurement optical path arm of an interferometer. The step of guiding the non-measurement optical path arm is an optical path that substantially consists of optical fibers (hereinafter simply referred to as “fiber”) and does not include a spatial propagation optical path, and the measurement optical path arm is the semiconductor laser. Of the low coherence light emitted from the optical fiber for projecting the low coherence light onto the surface of the thin film to be measured of the object to be measured, except for the spatial propagation optical path of a predetermined length from the end surface of the thin film to be measured to the surface of the thin film to be measured. A method for measuring the thickness of a thin film, wherein the thickness of the thin film to be measured is measured by. 13. At least the measurement optical path arm of the interferometer includes a piezoelectric type fiber length variable device in which a fiber is wound around a piezoelectric element, and the fiber length is significantly changed by the piezoelectric action, and the non-measurement optical path arm The method for measuring the film thickness of a thin film according to claim 12, wherein a stable non-measurement optical path arm length is always maintained by using a reflecting mirror whose end face of the optical fiber is highly reflective coated. 14. A mirror, wherein both arms of the interferometer include a piezoelectric type fiber length variable device in which fibers are wound around a piezoelectric element, and an end face of an optical fiber of the non-measurement optical path arm is a reflecting mirror having a high reflection coating, 13. The thin film thickness measuring method according to claim 12, wherein the film thickness of the thin film to be measured is measured by the interferometer by significantly changing the fiber lengths of both arms by a piezoelectric action. 15. At least the measurement optical path arm of the interferometer includes a magnetostrictive fiber length varying device in which a fiber is wound around a magnetostrictive body, and the fiber length is significantly changed by the magnetostrictive action, and the non-measurement is performed. 13. The thin film thickness measuring device according to claim 12, wherein a stable non-measurement optical path arm length can be maintained at all times by using a reflecting mirror having a highly reflective coating on the end surface of the optical fiber of the optical path arm. 16. The non-measurement optical path arm, wherein both arms of the interferometer include a magnetostrictive fiber length varying device in which fibers are wound around a magnetostrictive body, and the fiber length is significantly changed by the magnetostrictive action. 13. The method for measuring the film thickness of a thin film according to claim 12, wherein a stable non-measuring optical path arm length is always maintained by using a reflecting mirror having an end face of the optical fiber with high reflection coating. 17. The method for measuring the film thickness of a thin film according to claim 15, wherein the magnetostrictive body has a substantially cylindrical shape, and a fiber is wound around the cylindrical surface. 18. The method for measuring the film thickness of a thin film according to claim 15, wherein the magnetostrictive body has a substantially toroidal shape, and a fiber is wound around the toroidal surface. . 19. A step of fixing the relative spatial positional relationship between the end surface of the fiber of the measurement optical path arm and the surface of the thin film to be measured by a fixing means, and a predetermined length from the end surface of the fiber to the surface of the thin film to be measured. 19. The method for measuring the film thickness of a thin film according to claim 12, further comprising a step of moving the projection optical means placed on the spatial propagation optical path along the spatial propagation optical path. 20. The posture adjusting holder for adjusting the posture of the object to be measured so that the thin film to be measured is an arbitrary flat surface or curved surface, and the normal line of the flat surface or curved surface is substantially aligned with the optical axis of the spatial propagation optical path. 20. The method for measuring the film thickness of a thin film according to claim 12, further comprising a step of finely adjusting and holding with. 21. The method for measuring the thickness of a thin film according to claim 20, wherein the curved surface of the thin film to be measured has a cylindrical shape, a spherical shell shape, or an amorphous shape. 22. The predetermined high frequency is 0.8 to 3
The thin film thickness measuring method according to any one of claims 12 to 21, which is in a range of gigahertz.