JPH04522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a reflective optical interference type film thickness measuring device using a condenser. In particular, the film thickness measuring device according to the present invention is suitable for measurement when the object to be measured is moving.

(Prior Art) Conventionally, a condenser lens is known as a condensing device for efficiently concentrating light.

On the other hand, there were methods that used absorption of beta rays and infrared rays to measure the thickness of films, etc., but as a method for measuring film thickness with higher precision,
2. Description of the Related Art An optical interference type film thickness measuring device using reflected light from an object to be measured (Japanese Unexamined Patent Application Publication No. 115905/1983, etc.) is known.

An optical interference type film thickness measurement device that uses reflected light is based on the principle that when parallel white light is reflected on a surface to be measured, the change in spectral intensity caused by the interference phenomenon depends on the film thickness of the object to be measured. The film thickness is measured by detecting the reflected light from the object to be measured and quantitatively detecting the intensity of the spectral light.

(Problem to be Solved by the Invention) When condensing light with a condenser lens, if the angle or position of the light incident on the condenser lens changes, the angle or position of the condensed light itself will change as well. There was a drawback that a photodetector placed afterwards could not capture the light.

Furthermore, in the conventional film thickness measuring device described above, quantitative detection of spectral intensity specifically means knowing the wavelength position of the bright or dark portion of the spectral intensity caused by an interference phenomenon. .

Therefore, in the optical interference method that uses reflected light, the reflected light from the measurement target is ignored regardless of whether the measurement target is stationary or moving, and regardless of whether the measurement target has wrinkles or fluctuations. It is necessary to know the spectral intensity by reliably receiving light and dividing it into spectra.

However, in order to accurately determine the spectral intensity, especially the wavelength position, using a spectrometer that uses a normal planar diffraction grating or prism, light must be incident on the spectrometer at a constant angle of incidence. In this case, if the parallelism or angle of incidence of the incident light is not even slightly accurate,
The result is that the spectral intensity cannot be obtained, or even if it is obtained, the wavelength position has a large error.

For the above reasons, in the conventional optical interference method that uses reflected light, it is necessary to reliably receive the reflected light from the measurement target surface and to always input the received light into the spectrometer in a constant and correct manner. There is.

Hereinafter, the drawbacks of the prior art will be detailed as follows.

a. If the object to be measured has wrinkles, the reflected light may not enter the light receiving section correctly, or may be completely removed from the light receiving section, making measurement impossible.

b When measuring without wrinkles using some kind of material, the material must be a flat plate without curvature (if it has curvature, the reflected light cannot be received correctly), but even in this case, the reflected light In order to receive light correctly, the surface to be measured requires highly accurate positioning.

c. When a reflective member is provided on the back side of the surface to be measured, it is practically impossible to completely contact the reflective member, and the interference to be detected is disturbed by the presence of an air layer or the like.

Especially when the object to be measured is moving, the above problems are compounded and it becomes increasingly difficult to overcome them.

(Means for Solving the Problems) The film thickness measuring device according to the present invention eliminates the drawbacks of the prior art described above. Film thickness can be measured even in-line (in-line).

In order to achieve the above object, the present invention provides an apparatus for making parallel white light incident on a measurement object at a fixed angle, and measuring the film thickness of the measurement object from the spectral intensity of the light reflected by the measurement object. A light-receiving part formed by inserting one end portions of a plurality of optical fibers into a hemispherical shell so that they are arranged densely and such that the perpendicular to one end surface of each optical fiber faces the center of curvature of the shell. and a light emitting section formed by bundling the other end portions of the plurality of optical fibers in parallel, and (b) parallel light forming means for converting the light coming out from the light emitting section into parallel light. A film characterized in that the light reflected by the object to be measured is received by a condensing device and guided to a parallel light forming means, and the parallel light coming out from the parallel light forming means is guided to a spectrometer to be separated into spectra. Provides a thickness measuring device.

In the present invention, both plastic and glass are currently in practical use as materials for the optical fiber used in the condensing device, but plastic is preferred from the viewpoint of flexibility and workability.

In addition, as a white light source of the film thickness measuring device in which the above condensing device is a component, a tungsten lamp,
Examples include xenon lamps and halogen lamps. The object to be measured by the film thickness measuring device is mainly a transparent thin plate-like object such as a glass plate or a polymer film, but any object through which white light can pass through to some extent may be used.

As the parallel light forming means of the film thickness measuring device, in addition to the combination of lenses, pinholes, and lenses as shown in the examples described later, it is also possible to use a reflecting mirror. Further, a prism, a diffraction grating, etc. can be used as a spectrometer.

Hereinafter, the film thickness measuring device of the present invention will be explained in detail using FIGS. 1 and 2.

In Figure 1, 1 is a white light source, 2 is a condenser lens group, 3 is a pinhole, and lens group 2 is:
The pinhole 3 is arranged so that light from a light source 1 is focused onto the pinhole 3. 4 is a collimating lens, and the distance from the pinhole 3 is the focal length of the lens 4. 5 is a condenser; 7 is a lens for discriminating components emitted in the same direction;
8 is a pinhole for extracting components emitted in the same direction, and the distance between the lens 7 and the pinhole 8 is set to the focal length of the lens 7. Reference numeral 9 denotes a collimating lens whose distance from the pinhole 8 is equal to the focal length of the lens 9.
10 is a spectrometer such as a plane diffraction grating or a prism (in this example, a plane diffraction grating); 11 is an imaging lens; 12 is a linear image sensor for detecting spectral intensity; Deploy.

Note that the lens 7, pinhole 8, and collimating lens 9 constitute parallel light forming means.

FIG. 2 shows a detailed cross-sectional structure of the condensing device 5. As shown in FIG. In this figure, 13 is the measurement target, 14
1 is a film thickness measurement point, 15 is a light receiving part having a hemispherical shell having the film thickness measurement point 14 as the center of curvature, and a window 1 for allowing incident light beam 16, which is white parallel light, to enter.
7 and a plurality of optical fibers 18 are inserted and arranged in the shell toward the center of curvature of the shell, that is, toward the film thickness measurement point 14. The end surface of each of the plurality of optical fibers 18 is
It is cut vertically and polished, with the perpendicular of each end face facing the center of curvature. multiple optical fibers 18
The arrangement on the curved surface inside the light receiving section 15 should be as far as possible.
A dense and uniform distribution is desirable. Third
The figure schematically shows an example of this arrangement.The hexagon shown by 20 in the figure is taken as one unit, and no matter which optical fiber on the curved surface is selected, this hexagon can be approximately centered around it. It is arranged so that it exists.

Reference numeral 19 in FIG. 2 is a light emitting portion in which the other ends of the plurality of optical fibers 18 are vertically cut and polished, and the fibers are bundled in parallel and with their end surfaces aligned. FIG. 4 shows a view of the light emitting section 19 viewed from direction A.

(Function) Hereinafter, the function of the apparatus will be explained using FIG. 1 and FIG. 2.

The light emitted from the white light source 1 is focused onto the pinhole 3 as efficiently as possible by the lens group 2, and the collimating lens 4 converts the light emitted from the pinhole 3 into parallel light. The parallel light formed here is irradiated at a constant angle to the film thickness measurement point 14 through the entrance window 17 of the light receiving section 15 of the condensing device 5. When the irradiated parallel light is reflected by the surface to be measured, the spectral intensity changes due to an interference phenomenon. This change depends on the incident angle of the parallel light and the film thickness if the refractive index of the object to be measured is constant. Therefore, the film thickness can be determined by dividing the reflected light and quantitatively detecting the change in the intensity of this spectrum. I can do it.

When the incident light beam 16 and the measurement object 13 have a relationship as shown in FIG. 2, the reflected light is reflected in the regular reflection direction (direction 21) relative to the incident light. On the other hand, if the measurement object 13 has wrinkles or changes in position such as vertical movement or inclination, the direction of reflection may change or the reflected light may become diffused or convergent light instead of parallel light. It shows irregular behavior such as.

On the other hand, for example, as shown in FIG. 2, a light condensing device 5 has a plurality of optical fibers 18 arranged densely and uniformly over a range of ±45 degrees as shown by a broken line arrow 22 centered on the direction of an arrow 21. In the case of , even if the reflection direction fluctuates irregularly due to the wrinkles and positional fluctuations of the measurement object, it will be within ±
Within the 45 degree range, reflected light can be received with the same efficiency at any light receiving position.

The light thus received is transmitted through the optical fiber 18 and is emitted from the end face of the light emitting section 19.
It should be noted here that the direction of reflection of the reflected light flux varies irregularly due to wrinkles and positional variations at the measurement target point 14, so the location of the optical fiber that receives the reflected light,
The number of optical fibers and the amount of light received by each optical fiber change irregularly, and as a result, the shape of the light output from the light output section 19 also varies, and the position and amount of light from which the light is output among the bundle of multiple optical fibers is irregular. It will fluctuate. Further, in the case of plastic optical fibers, the light emitted from each optical fiber in the light emitting section 19 has a maximum opening of 60 degrees (dashed line arrow 24 in FIG. 1).

By the lens 7 placed next to the light emitting part 19, the light beams incident on the lens 7 in the same direction and at the same angle are condensed to one point on the surface of the pinhole 8 in the focal plane of this lens. There is.

Therefore, it can be said that the light that has reached different positions on the surface of the pinhole 8 is a light beam that has entered the lens 7 at different angles. In other words, the lens 7 discriminates the components of the light emitted from the light emitting section 19 in the same direction based on the position on the pinhole surface.

Position the pinhole 8 on the lens 7 as shown in Figure 1.
Of the light discriminated as above, extracting only the component vertically incident on the lens 7, that is, the component vertically emitted from each optical fiber, and extracting the other emitted components on the central axis. It will be removed.

The collimating lens 9 collimates the light selectively extracted by the lens 7 and the pinhole 8 to form incident light to the plane diffraction grating 10 .

With the parallel light forming means composed of the above lens 7, pinhole 8, and collimating lens 9,
In the light emitting section 19, even if the position of the optical fiber from which the light is emitted varies irregularly, parallel light that always enters the plane diffraction grating 10 at a constant angle is obtained. Furthermore, since only the vertical component of the light emitted from any optical fiber is extracted, a substantially constant amount of parallel light can always be obtained.

The parallel light incident on the plane diffraction grating 10 is divided into light beams that are emitted at different angles within the same plane depending on the wavelength. When these light beams are received by the lens 11, they are focused at different positions on the focal plane of the lens 11.

Moreover, the angle of incidence of each light beam on the lens 11 corresponds to the wavelength, and furthermore, since the angle of incidence changes within the same plane, the light beam of each wavelength is on a straight line on the focal plane of the lens 11. The light will be focused on.

Therefore, by placing a linear image sensor 12 on the focal plane of the lens 11 and detecting light of each wavelength, the wavelength position of the bright or dark area caused by the interference phenomenon is determined. Similar to a film thickness meter, the film thickness of the object to be measured can be calculated using spectroscopic analysis.

The film thickness measuring device according to the present invention
Regardless of movement, when the reflected light fluctuates irregularly due to factors such as wrinkles, vertical movement, and tilt changes of the object to be measured, for example, when measuring the thickness of film or glass with curvature, etc. Can adapt.

(Example) Hereinafter, an example of the present invention will be shown using FIGS. 1 and 2.

As light source 1, a long-life halogen lamp (150W) was used. After the light from the light source is focused onto the pinhole 3 by the lens group 2, the lens 4
A light projection system, an optical axis, and an entrance window 17 on the light receiving section 15 were provided so that parallel light was formed and the angle of incidence on the surface to be measured was 30 degrees. The size of the entrance window was 8 mm in diameter, so that the measurement spot was also a parallel light beam with 8 mm in diameter. The outer shape of the shell of the light receiving part is
A hemisphere with a diameter of 50 mm, an inner diameter of 40 mm, and a wall thickness of 5 mm was shaped with the bottom surface cut off by 5 mm, and this was placed at a position 5 mm from the measurement target. Optical fiber used 18
was made of plastic because it has a diameter of 1 mm and a length of 30 cm, has a large acceptance angle, and is easy to work with. Specular reflection direction for an incident angle of 30 degrees (arrow 21)
600 optical fibers were arranged in an area within ±45 degrees around , as shown in Figure 3. The angle of incidence is preferably around 30 degrees, which was used in this example, because it allows a wide fixed angle range centered on the specular reflection direction (excluding overlap with the entrance window).

The light emitting section 19 is made by bundling optical fibers 18 with a diameter of about 30 mm, and distinguishes and distinguishes the light emitted from the light emitting section 19.
Lens 7 for extraction has aperture φ=38.1mm, focal length f=38.1mm, pinhole 8 has aperture φ=0.4mm,
The lens 9 used had an aperture φ of 20.0 mm and a focal length f of 25 mm.

The specifications of these optical components are determined from the parallelism, size, amount of light, etc. of the formed light beam. In particular, as the collimating lens 9, it is desirable to use a lens corrected for aberrations including spherical aberration in order to obtain highly accurate parallel light.

The planar diffraction grating 10 used as a spectrometer was a 52 mm x 52 mm square planar diffraction grating with a blaze wavelength of 500 mm, a groove count of 1200/mm, and a planar diffraction grating that had sufficient wavelength resolution and spectral characteristics, and had adjacent orders in the necessary wavelength range. Any spectrometer may be used as long as there is no overlap between them. The lens 11 is selected to have a diameter that can receive the necessary wavelength range from the separated light, and a focal length that allows the wavelength range to be detected to be imaged within a predetermined detector. .

The linear image sensor 12 has a 2048-bit
A CCD type image sensor was used. Generally, there are two types of image sensors: MOS type and CCD type, but it is preferable to use a CCD type image sensor because the light amount accumulation time for all bits is the same. The wavelength range used is
In view of the spectral characteristics of the light source, plane diffraction grating, and image sensor, it is preferably between 450 and 850 μm.

Measurement results using the apparatus of this example are shown in FIGS. 5 to 9.

In Figure 5, a polyethylene terephthalate (PET) film 13 of 4.2 μm (measured by a contact type electronic micrometer) is used as the measurement object, and the film is measured by ±3 mm from a position 5 mm from the light receiving part 15.
This figure shows a comparison of spectral intensities when moving in parallel (optical fibers are omitted from the figure). Figure 6a is when the film is translated +3 mm, Figure 6b is when the film is in the normal position, Figure 6c is
3 shows the results when the film was translated by -3 mm. However, the spectral intensity shown in this example is based on the spectral intensity actually detected from the light source.
It shows the results of detecting only changes in spectral intensity caused by interference phenomena by normalizing with the spectral characteristics unique to devices such as planar diffraction gratings and image sensors.

As a result, although some light intensity fluctuations remained due to manufacturing errors in the condensing device 5 or optical system errors, the spectral intensity of almost the same pattern was obtained at all positions, and the same film thickness of 4.2 μm was obtained.

Figures 7 and 8 are similar to Figure 5.
By using a 4.2 μm PET film 13 and tilting it 5 mm from the light receiving part 15 by ±20 degrees around the film thickness measurement point, the receiving position of the reflected light is adjusted to C, N, S, in the figure. This shows a case where the spectral intensities are compared when W and E are changed.

In this case, tilting the film causes a relative change in the angle of incidence, which affects the spectral intensity and film thickness, but the results obtained by measurement are almost in line with theory. It was confirmed that the influence was small and that measurements could be made within the error range of the incident angle change.

(Effects of the Invention) a. Even if the reflected light from the object to be measured changes, the condensing device 5 can reliably receive the light as long as it is within the range where the optical fibers are arranged.

Moreover, (a) the end faces of each optical fiber were cut and polished vertically, and each end face was placed facing the film thickness measurement point.

(b) By making the distribution of optical fibers uniform and dense, it is possible to receive light with constant and high efficiency at any light receiving position.

b The reflected light from the measurement object fluctuates by the parallel light forming means consisting of the lens 7, pinhole 8, and collimating lens 9, and the light emitting part 19 of the condensing device
Even if the position of the optical fiber that emits light fluctuates irregularly, parallel light of a constant angle and a substantially constant amount of light can always be incident on the spectroscope.

c With the configurations a and b above, even if the reflection direction of the reflected light beam changes irregularly due to wrinkles or fluctuations in the measurement target, it is possible to always obtain a nearly constant pattern and constant spectral intensity at a constant position. can.

With the above configuration, the film thickness can be measured with high accuracy even if the reflected light varies due to wrinkles or variations in the measurement target. Further, even for a measurement target that does not have wrinkles or fluctuations, the film thickness can be measured without highly accurate positioning.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the film thickness measuring device according to the present invention, Fig. 2 is a diagram showing a cross section of an embodiment of the condensing device used in the present invention, and Fig. 3 is a diagram showing the optical fiber of the condensing device. 4 is a diagram showing the light emitting part of the condensing device. FIG. 5 is a diagram explaining the case where the object to be measured is vertically moved in parallel. FIGS. 6 a, b, and c are
A diagram showing the spectral intensity patterns in cases a, b, and c in Figure 5, respectively. Figure 7 is a side view explaining the position of reflected light when the measurement target is tilted. Figure 8 is a diagram showing the position of the reflected light when the measurement target is tilted. Figure 9 is a plan view explaining the position of reflected light when W, N, C, S, and E are tilted.
It is a figure which shows the pattern of the spectral intensity when it comes to N, C, S, and E. 1: white light source, 2: condenser lens group, 4,
11: Collimating lens, 7, 9: Lens,
3, 8: Pinhole, 5: Concentrator, 10: Planar diffraction grating, 12: Linear image sensor, 13:
Measurement object (film), 14: Film thickness measurement point, 1
5: Light receiving section, 16: Incident light flux, 17: Incident window, 1
8: Optical fiber, 19: Light output part, 20: Unit hexagon.

Claims (1)

[Scope of Claims] 1. An apparatus for making parallel white light incident on a measurement object at a fixed angle and measuring the film thickness of the measurement object from the spectral intensity of the light reflected by the measurement object, which includes: a. a light-receiving portion formed by inserting one end portions of a plurality of optical fibers into a shell in such a way that one end portions of a plurality of optical fibers are arranged in a dense manner and the perpendicular to one end surface of each optical fiber faces the center of curvature of the shell; a light condensing device comprising a light emitting part formed by bundling the other ends of the optical fibers in parallel, and b a parallel light forming means for converting the light emitted from the light emitting part into parallel light, and reflecting the light from the object to be measured. A film thickness measuring device characterized in that light is received by a condensing device and guided to a parallel light forming means, and the parallel light coming out from the parallel light forming means is guided to a spectrometer to be separated into spectra.