JPS59228105A - Film-thickness measuring device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Application] The present invention relates to a film thickness measuring device that measures film thickness based on the amount of light beams such as infrared rays absorbed by the film, and particularly relates to a film thickness measuring device that measures film thickness based on the amount of light beams such as infrared rays absorbed by the film. The present invention relates to a film thickness measuring device suitable for measuring the thickness of a film that is continuously running.

[Prior art]

In recent years, the fields of application of films, especially polymer films such as polyester films, have been expanding, and the demands on their quality have become stricter accordingly. There is a strong demand for uniformity of film thickness as a quality factor.

Therefore, thickness control based on online measurement is becoming necessary.

By the way, as a thickness measuring method capable of the above-mentioned online measurement, there have already been proposals such as Japanese Patent Laid-Open No. 53-31155. What is disclosed in JP-A No. 53-31155 is to measure infrared rays at the wavelength of the absorption peak of a film (absorption wavelength) and infrared rays at a wavelength that is hardly absorbed by the film (reference wavelength), which are measured by switching filters. This is an excellent two-color infrared thickness meter designed to pass the same optical path alternately, and is expected to provide stable continuous measurements, but it has the following problems. In other words, when the film thickness changes significantly or the temperature changes, the transmittance of the absorption wavelength and the reference wavelength do not change in the same way, resulting in film thickness measurement errors.As the thickness becomes thinner, the amount of absorption by the film decreases. Therefore, there is a problem that the measurement sensitivity and accuracy decrease, and there is also a problem that it is not sufficient to monitor thickness changes.

[Purpose of the invention]

In response to such a situation, the present inventor previously filed a
In No. 1506, we proposed the following method shown in FIG. 1 as a method for measuring the thickness of films ranging from thin films of 10 μm or less to thick films of several 100 μm with high accuracy and online. In the figure, P is a target film to be measured, for example, a polyethylene terephthalate (PET) film running during production.

S is the standard film, which has the same thickness t as the thickness set in the production conditions.
This film has the same composition as the target film of o.

1 is a light source, which emits a light beam I0 with a wavelength suitable for the target film.
(For example, in the case of PET film, the MK is designed to project an infrared beam with a wavelength of 5.8 μm whose absorption rate is approximately 1). 2 is a light beam■.

This is a projection system that splits the beam into a measurement beam Ip and a reference beam Is and guides the beam to a target film P and a reference film S.
This is a known optical system consisting of a half mirror 2b, and a reflection i:9-2c.

3 is a light receiving system that guides a reference beam I5 that has passed through the reference film S and a measurement beam E'p that has passed through the target film P to a photoelectric conversion section 41C (described later).

The photoelectric conversion unit 4 described above is composed of photodetectors 4a and 4b with good responsiveness such as In8b semiconductor, and detects both the received beams I'.
p, TI, , are converted into an assistant signal Ep and a reference signal Es, which are electric signals proportional to the amount of received light.

5 is a signal processing unit which processes both signals Ep and Es to obtain a thickness signal gt related to the thickness tK of the target film P, which calculates the ratio Ep/Es of both signals Ep + Es and calculates the ratio gp/Es. A logarithmic ratio calculation circuit 5a that calculates and outputs the logarithm Eg, and the output EI K thickness t of the reference film S
and an arithmetic circuit 5b that adds a predetermined value corresponding to o to obtain a thickness signal Et.

That is, the light beam■. At the same time, the target film P and the reference film S to be measured are irradiated with the transmitted light T.
p and I's are detected by the photodetectors 4a and 4b, and the light amount ratio I'p/I's K is measured.The corresponding ratio Ep/El is measured, and the thickness of the target film P is measured based on this ratio. It is something to do. Therefore, the thickness of the diagonal film P is detected as a variation from the reference film S, resulting in a high IP! It is possible to perform measurements that are consistent with degrees and also to be able to perform measurements that are robust against environmental changes such as fluctuations in the light source 1.

SUMMARY OF THE INVENTION The present invention is directed to - an apparatus for carrying out the above-mentioned method, and is aimed at a film thickness measuring apparatus with excellent environmental resistance and suitable for on-line measurement in busy manufacturing processes.

[Structure and operation of the invention]

The present invention achieves the above object and is characterized by the following configuration.

That is, the present invention directs a light beam from the same light source to a target film to be measured and a predetermined reference film by a light projection system (and converts transmitted light from both films into electrical signals by a photoelectric conversion section). In the film thickness measuring device according to 5, which calculates the ratio and measures the thickness of the target film based on this ratio, a pair of heads are arranged facing each other with a gap for the target film to pass through, and , one head accommodates a reference conversion system that receives and photoelectrically converts transmitted light from the light source, the light projection system, and the reference film, and the other head houses a reference conversion system that receives transmitted light from the target film and converts it photoelectrically. This is a film thickness measuring device characterized by housing a measurement conversion system for conversion.

Note that the above-mentioned predetermined reference film is a film that generates a reference signal that compensates for the influence of factors other than the thickness of the target film on the measurement, as is clear from the above-mentioned principle.
Specifically, the film has the same optical properties as the target film, especially the light transmission properties for the light beam used. Therefore, a film having the same composition as the target film can be applied.

In addition, films with the same surface properties such as flatness have the same reflection properties, which is preferable. From these points of view, films of the same composition manufactured under the same manufacturing conditions are preferred. Note that the thickness of the reference film is appropriately selected depending on the purpose. In the online measurement described below, it is common to select a thickness close to the manufacturing conditions.

The details of the present invention described above will be explained based on an example suitable for continuous measurement in the manufacturing process of PET film.

FIG. 2 is a front view of the above embodiment, and FIG. 3 is a side view thereof.

As shown in the figure, in this embodiment, an upper head 200 of a film P to be measured is arranged with a lower head 300 thereof, and the film P is held by an upper arm 101 and a lower arm 102 of a common frame 100.

Therefore, the upper head 200 and the lower head 300 vibrate integrally in response to vibrations from the floor surface, etc., and there is no occurrence of deviation from the optical axis.

The interiors of the upper head 200 and the lower head 300 are constructed as shown in FIGS. 4 and 5.

FIG. 4 is a side sectional view of the upper head 200 and the lower head 300 on the optical axis plane, and FIG. 5 is a view taken along the line A--A in FIG. 3.

First, the configuration of the upper head 200 will be explained. Reference numeral 1 in the figure denotes a light source, which is attached to a predetermined position on the upper side of the upper case 201 as shown in the figure, and emits an infrared beam I0 vertically downward.

The light source 1 includes a light collecting cover 13 having a jacket structure, which forms a light collecting path 12 having a truncated cone shape with a predetermined length and a predetermined apex angle and a mirror surface, the lower side of which is a small-diameter emission aperture 11;
A reflective cover 15 having a jacket structure forming a reflective space 14 in which the surface connected to the paraboloid of revolution 9 is a mirror surface such as a spherical surface.
and a rod-shaped heating element 16 arranged laterally so as to pass through the focal point of the reflection space 14. The heating element 16 is a ceramic-coated sheathed electric heater, in which a thermocouple is embedded together with the heater wire, and the temperature is set to 5 K' so that the temperature can be controlled at a constant temperature. Further, air at a constant temperature is supplied to each jacket to stabilize the temperature of the light collecting path 12 and the reflection space 14. Therefore, the objective infrared beam at low temperature ■. can occur effectively and stably. In this example, when the temperature of the heating element 16 was set to 290°C, an infrared beam with a wavelength of 5.8 μm and a beam diameter of 8φ and an intensity equivalent to that of a tungsten lamp at 1500°C was obtained. Another advantage is that the beam diameter can be set freely, and even a thin beam can pass upward and have a high intensity. Moreover, it has the practical advantage of being cheaper than other light sources.

The infrared beam I0 emitted from the radiation aperture 11 is converted by the chopper device 60 into pulsed light having a predetermined period (500 Hz in this example). The chopper device 60 includes a rotating disk 62 in which predetermined through holes 61 are arranged at appropriate intervals on the same circumference.
It has a known configuration in which the motor 63 rotates at a constant speed. The motor 63 and the light shielding cover 64 are both attached and positioned to the surface plate 202 provided on the rear wall 201aK of the upper case 201 by an attachment member 651C.

Infrared beam I coming out of the Chi-type tube mount R60. enters the projection system 2 and is split into a measurement beam Ip and a reference beam I@. That is, the light projecting system 2 includes a lens barrel block 21 that forms a vertical optical path with a mirror surface of a cylindrical curved surface passing through the lens barrel block 21 in the vertical direction, and a horizontal optical path that is also cylindrical and has a mirror surface that is perpendicular to the vertical optical path; A vertical optical path 645 is formed by a filter unit 22 which is removably screwed into the vertical optical path entrance 9 and a holding unit 23 which is removably fitted from the left side of the horizontal optical path.
Half me' arranged to intersect at an angle of degrees, −
2b, and is divided into a vertical measurement beam Ip and a horizontal reference beam Is by a half mirror 2b.

In this example, the filter of the filter unit 22 is a bandpass filter with a transmission center wavelength of 5.8 μm. Reference numeral 24 in the figure denotes a beam diameter setting unit for setting the diameter of the measurement beam 8, which is composed of a ring with an appropriate diameter, and is mounted at the exit VCm of the vertical optical path. Lens barrel block 2
1 is positioned by fixing it to the knock-bin assembly K via the surface plate 2 (13Vc sizing plate 204) on the rear wall 201a of the upper case 201. Therefore, assembly is very simple and , the main optical path is covered by a lens barrel to eliminate the influence of environmental conditions such as external light.

A reference system that generates the aforementioned reference signal Eg is connected to the horizontal optical path of the lens barrel block 21.

That is, a predetermined reference film S is placed at the exit of the horizontal optical path.
The holder S, which is set with , is screwed on. As the reference film S, a film having the same composition and thickness as the target film and the same thickness under the manufacturing conditions was used, specifically, a PET film.

The reference beam I's transmitted through the reference film S is converted into a reference signal F's K by the following reference conversion system. That is, at the exit of the horizontal optical path of the lens barrel pull 21, a lens holder 31 consisting of a cylindrical body of a predetermined length with six mirror surfaces on the inner surface is removably set by aligning knock pins, and a condensing lens 3b consisting of a germanium convex lens is attached. is fixed to the lens holder 31 by screwing the fixing ring 32,
It constitutes the aforementioned light receiving system.

Then, the reference beam I's focused by the lens 3b
is input to an infrared photodetector 4bK placed at the focal position of the lens 3b, and is converted into a reference signal E8K. lens 3
The optical path from b to the photodetector 4P is surrounded by a cylindrical cover 41b whose inner surface is a mirror surface, so as not to be affected by environmental conditions such as external light. Note that 1R8-3118 manufactured by Fujitsu ■ was used as the photodetector 4b. 42 in the figure. b is a heatsink for the photodetector 4b, and 43b is a circuit unit housing a temperature control circuit of 1R8-3118 using the photodetector 4bK, a p-small circuit, and a preamplifier. The positioning of the photodetector 4h is exactly the same as that of the lens barrel block 21, and the explanation thereof will be omitted.

Reference numeral 205 in the figure denotes a partition plate of a partition wall that divides each upper head 200 tVt heat generation source into a small chamber, and is provided to separate the light source unit WL1 and the photodetector 4b.

Then, each compartment was individually air-purged with air whose temperature and humidity were controlled at a constant temperature, and the same air was used to purge the lower part of the @moon block 21 and the optical path before and after the γ-domain film S, and the measurement conditions were In particular, it is aimed at stabilizing the temperature and humidity. Note that 206 in FIG. 1 is a front cover plate of the -E section head 200.

Next, the lower head 300 will be explained. lower head 300
K is the measurement beam I'p transmitted through the film P to be measured
It houses an engineering measurement conversion system that receives light and converts it into an electric signal Ep. The light receiving system consists of a block body 33 made of a cylindrical body, a condensing lens 3a made of a germanium convex lens built into a receiving part that enlarges the optical path of the block body 33, and a screw thread attached to the end of the optical path of the block body 33. It consists of a condensing unit 34 having a conical condensing path with a mirror surface, and a mask unit 35 attached to the entrance side of the condensing unit 340 for adjusting the size of the measurement beam. A surface plate 302 provided at the rear of the case 301 is attached via a sizing pin 303, and is arranged so that the optical axis of the light receiving system coincides with the optical axis of the measurement beam Ip from the upper head 200. .

The light receiving aperture of the condensing unit 34 has a projection aperture of the measurement beam Ip, that is, 1.5 to 1.5 of the aperture of the beam diameter setting unit 240.
It has tripled. A mask unit 35 shown in FIG. 5 is attached to the light receiving port. Mask unit 35
As shown in the figure, a liner (35a) with a predetermined width perpendicular to the running direction of the target film P, mask plates 35b with a predetermined transmittance provided on both sides thereof, and a shielding plate 35 that blocks light.
It consists of c. For the mask plate 3Fib, a PET film having a predetermined thickness, specifically, approximately the same thickness as the target film, was used.

It should be noted that all optical paths of the block main body 33 directly hit by the measurement beam ■'p are mirror surfaces.

The photoelectric conversion unit that converts the measurement beam I'p from the light receiving system described above into an electrical signal EpVc has exactly the same configuration as the photoelectric conversion unit for the reference beam I's described above.

That is, lR8- placed at the focal position of the lens 3a.
Photoelectric detector 4a using 3118 and cylindrical cover 41a
, a radiator 42α, and a circuit unit 43a,
It is attached and positioned to a surface plate 302 by a sizing block 304.

In addition, 305 in the figure is the aforementioned partition plate, and the partition plate 305
Each chamber divided by 1 is air purged with the same type of air as that used for the construction barge of the upper head 200. Furthermore, the optical path of the light receiving system for the measurement beam I'p mentioned above is similarly air purged.

306 in the figure is a front cover plate.

By the way, in front of the measurement beam Ip of the upper head 200 and the lower head 300, that is, on the upstream side in the running direction of the film, there is a measurement beam t extending in the width direction of the film P to be measured.
Two air outlet ports 111 which are sufficiently longer than the diameter of p are provided (an air curtain boot 110 is provided), which blows air under the same conditions as the air purge described above onto both sides of the film P to be measured, and blocks the accompanying airflow. It looks like this.

Based on the above configuration, this embodiment has the following effects.

It is divided into two parts, an upper head 200 and a lower head 300. The upper head 200 houses a light source 1, a light projection system 2%, and a reference system, and the lower head 300K houses a measurement conversion system.
K, both heads become compact, and it is very easy to adjust the optical axis of the optical system. Since both heads are held on the same stand, it has excellent vibration resistance.

Also, the upper head 200 and the lower head 300 #cIc
.

Each heat source was divided into small rooms and air purged with air whose temperature and humidity were controlled to a constant level, making it possible to largely eliminate the influence of the measurement atmosphere. Furthermore, an air curtain unit 110 is disposed upstream of the measurement section, and the film PK to be measured is
The measurement conditions were stabilized by blocking the accompanying airflow and allowing air under certain conditions to accompany the film. In this example, which uses infrared rays that are sensitive to the atmosphere, stability of the measurement atmosphere is extremely important.

If both the upper head 200 and the lower head 300 have a sealed structure, the insides of both are all blackened by black coating, etc., so that the influence of disturbance light such as external light is almost eliminated.

Furthermore, since the main part of the optical path is entirely constituted by a lens barrel, there is less light loss due to the optical path and less influence from the above-mentioned disturbance light.

Since the rod-shaped heating element 17 is provided so that the light source l passes laterally through the focal point of the reflective surface in the cavity, which is a combination of a reflective surface consisting of a paraboloid of revolution and a condensing surface consisting of a conical surface, the light source 17 is black. Similar to body cavity radiation, infrared radiation can be effectively generated as described above. Since the obtained infrared rays are mixed light with random directions and phases, even if the angle of the target film P with respect to the measurement beam IpK changes due to the waving phenomenon of the running target film P, the scattered light is averaged out. ,
This has the advantage of having a small impact. Note that since a thermocouple or the like is embedded in the heating element 17 to control the temperature at 51C, the obtained infrared rays are stabilized.

Furthermore, since the measurement beam transmitted through the target film P is received by an inverted cone-shaped condensing unit 34 with an aperture 1.5 to 3 times the beam diameter, the above-mentioned waving of the target film P can be avoided. By reducing the effects of this phenomenon, measurements became stable.

In addition, a mask unit 35 having a mask plate 35b having an appropriate light transmittance and a slit 35a on the front surface of the electric light unit 34 is provided.
By providing this, it was possible to improve the detection resolution by the slit effect while maintaining the level of the amount of light received by the photodetector 4a at a level that does not significantly reduce the S/N ratio. Also, regarding dynamic properties, the number I required for online measurement is
I) For thickness changes greater than T(y), the mask unit 35 acts as a spatial filter, and a detection IE with an 8/N ratio is possible.Specifically, the slit 35a (D
A thickness change of several tens of Hz could be effectively detected using the mask unit 351C, which had a width of 2 m, a width of 5 fi on both sides of the mask plate 35b including a slit of 35 g, and a length of ism. Note that the mask plate 35b at this time has the same thickness as the target film as described above, so the mask plate 35b
The amount of transmitted light is approximately half that of the slit 35a.

Although the present invention has been described above based on examples, the present invention is not limited to such examples. It is sufficient to synchronize with the lower head and transfer it in the middle direction (51C), and this can be easily realized using a known configuration for X-ray thickness gauges.

In this case, because of the above-mentioned configuration, it is only necessary to pay attention to the optical axis deviation of the measurement system when moving, and the above-mentioned waving phenomenon of the target film and optical axis deviation have a large influence on measurement errors.
Since they are equivalent, there is an advantage that the influence of optical axis deviation is small.

In addition, in cases where it is difficult to stabilize the temperature condition with only the air purge described in the example, such as when there is a high temperature heater etc. near the measurement point in the manufacturing process and the measurement atmosphere fluctuates greatly, it is possible to use a jacket structure for the partition wall, side wall, etc. It is best to stabilize the temperature using a refrigerant such as water.

As described above, the present invention is suitable for on-line measurement of film thickness during manufacturing processes, and is very useful as it can be implemented in various ways.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the principle of the present invention, Fig. 2 is an overall front view of the embodiment, Fig. 3 is an overall side view of the house, Fig. 4 is a front sectional view of the main parts, and Fig. 5 The figures are a cross-sectional view taken along the line A-A in FIG. 4, and an explanatory diagram of the mask unit in FIG. 6 ('!).

Claims (1)

[Claims] 1. Guide a light beam from the same light source to a target film to be measured and a predetermined reference film by a projection system, and
The transmitted light from both films is converted into an electric signal by a photoelectric converter, the ratio is determined, and the thickness of the target film is measured based on this ratio. A pair of heads are arranged facing each other with a gap between the reservoirs. One head houses the light source 1 curved projection system and a reference conversion system that receives the transmitted light from the reference film and converts it into electricity, and the other head receives the transmitted light from the M11y film and converts it into charge. A film thickness measuring device characterized by housing a measuring conversion system for measuring the thickness of a film. 2. The film thickness measuring device according to claim 1, wherein the heads between the two are disposed opposite to each other on a common mount. 3. Film thickness measurement according to claim 1 or 2, wherein each head is divided into small chambers by partition walls for each light source and heat source of the photoelectric conversion section, and is air purged with air at a constant temperature and humidity. Device. 4. The film according to claim 1, 2, or 3, wherein the light receiving aperture of the measurement conversion system is 1.5 to 3 times the projection aperture of the projection system onto the target film. Thickness measuring device. 5. The upstream side K of the light receiving port of the measurement conversion system and the projection port for the target film of the light projecting system in the running direction of the target film.
, a film thickness measuring device according to claim 1, 2, 3, or 4, which has an air curtain block that blocks the accompanying airflow of the target film.