JP2003161605A - Film thickness measuring device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure the film thickness of an intermediate layer in a moving multi-layered film. <P>SOLUTION: A film thickness measuring device is provided with a stroboscopic light source 11 emitting stroboscopic light formed with a near infrared area, a bundled two-branch optical fiber 13 carrying reflected light from the multi- layered film with carrying light from the stroboscopic light source 11 to apply it to the moving multi-layered film on the line of the plant, a spectroscope 16 decomposing the reflected light obtained from this bundled two-branch optical fiber 13, a multi-channel detector 17 converting the reflected light decomposed into a spectrum with the spectroscope 16 into an electric signal, and a signal processing part 20 displaying as a membrane thickness profile by processing the electric signal obtained by the multi-channel detector 17. <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 film thickness measuring device and the like, and more particularly to a film thickness measuring device and the like for accurately measuring the film thickness of a moving film.

[0002]

2. Description of the Related Art In recent years, a multi-layer film in which films having different properties are stacked to form a multi-layer film has been widely used in accordance with diversified film requirements. Taking a film used for food packaging as an example, for example, an intermediate layer that has a structure composed of a three-layer film and requires a gas barrier property that is impermeable to water vapor and oxygen, and an outer layer that provides strength. It constitutes a multilayer film. In this intermediate layer, it is necessary to ensure a certain thickness or more in order to ensure this gas barrier property. On the other hand, if the thickness of the intermediate layer is too thick, the amount of material used increases and the cost increases. Therefore, for example, it is required to accurately measure the film thickness of the intermediate layer. If the thickness can be measured in a so-called in-line state where the film is moving on the factory line, it is possible to immediately improve yield and quality in film production.

Conventionally, several methods have been adopted to measure these film thicknesses. For example, there are infrared type multi-layer thickness gauges, β ray thickness gauges, contact type thickness gauges and the like. This infrared type multi-layer thickness gauge measures the thickness from a characteristic waveform by observing the absorption of infrared rays, and can measure even a moving film. Further, the β-ray thickness meter is suitable for measuring the basis weight of the entire film with high penetrating power and measuring the total layer thickness. In addition, with a contact type thickness meter, it is possible to measure the total layer thickness in the same manner.

[0004]

However, this infrared type multi-layer thickness gauge can measure only when all layers such as A layer / B layer / C layer are different.
In the case of a multi-layer thickness consisting of / B layer / A layer type, it is difficult to measure the respective thicknesses of both outer layers. In addition, in an apparatus using this infrared type multi-layer thickness gauge, there are many types in which an optical filter matching the wavelength peculiar to each composition component is incorporated, but this requires a different optical filter each time a multilayer film having different components is produced. There is a need to prepare. There is also a method of improving these and measuring the entire wavelength region in a very short time, but the cost of the device becomes very high.

Further, although the β-ray thickness gauge and the contact type thickness gauge can measure the total thickness of all layers,
The thickness of each layer cannot be measured. For example, a β-ray thickness meter could not be used as a thickness gauge for each layer except for special ones such as layers containing heavy metals.
In addition, since the β-ray thickness gauge handles radiation, there has been a problem that a great deal of labor is required for managing and operating the apparatus.

Furthermore, a reflection interference type multi-layer thickness gauge may be used. However, in the conventional reflection interference type multi-layer thickness gauge, the shake of the film is directly output as noise, and it is necessary to always keep the distance from the sensor to the film constant. Therefore, it cannot be used for in-line film thickness measurement in which the distance from the sensor to the film is not constant.

The present invention has been made to solve the above technical problems, and its object is to accurately measure the film thickness of a moving film. Another object is to easily and accurately measure the thickness of the intermediate layer, which is particularly difficult to measure.

[0008]

Based on the above object, the present invention obtains an interference waveform by irradiating a film moving on a factory line with a strobe light source for ensuring a wavelength in the near infrared region. This makes it possible to measure the thickness of the intermediate layer, which is generally difficult to measure. That is, the film thickness measuring apparatus to which the present invention is applied emits the strobe light from the light emitting means for emitting strobe light in the near infrared region and the film moving on the manufacturing line. And a light receiving means for receiving the reflected light from each layer of the film by the strobe light projected by the light projecting means,
And a measuring unit for measuring the thickness of the film forming the film based on the reflected light received by the light receiving unit.

Here, the film thickness measuring device constituted by each of these means is characterized in that it is possible to secure a light amount having a dynamic range of 5000 or more, and the intermediate layer having a reflectance smaller than that of the film surface. However, it is preferable in that the interference waveform can be observed. Further, as the film to be measured in the present invention, generally a large effect is obtained when a multilayer film in which a plurality of layers whose film thickness is difficult to measure is used as the measured object, for example, a film of a single layer Even when the present invention is used for measurement, a great effect can be obtained.

Further, the film thickness measuring apparatus to which the present invention is applied, has a strobe light source for emitting strobe light in the near infrared region, and conveys the light from the strobe light source to irradiate the object to be measured. At the same time, an optical fiber that carries the reflected light from this DUT, a spectroscope that decomposes the reflected light obtained from this optical fiber into a spectrum, and the reflected light that is decomposed into a spectrum by this spectroscope into an electrical signal. It is characterized by including a multi-channel detector for conversion and a signal processing unit for processing an electric signal obtained by the multi-channel detector.

Here, this optical fiber is characterized in that it has a sensor portion at one end where a plurality of fibers on the light emitting side and the light receiving side are bundled and which is brought close to the object to be measured.

On the other hand, in the film thickness measuring method to which the present invention is applied, the web-like film moving in a fixed direction is irradiated with strobe light in the near-infrared region and the light reflected from the film is measured. The power spectrum is analyzed from the interference waveform, and the film thickness of the layers constituting the film is measured from this power spectrum.

Here, the stroboscopic light irradiation in the near-infrared region is characterized by performing stroboscopic irradiation for one irradiation time of 10 to 50 μs (μ seconds) depending on the moving speed of the film. For example, it is excellent in that it is possible to appropriately measure the thickness of each layer of a film that is moving and has a smaller difference in refractive index. Further, the analysis of the power spectrum can be characterized by being analyzed through a measuring instrument having a dynamic range of 5000 or more.

From another point of view, the present invention is a film thickness measuring method for measuring the film thickness of an intermediate layer of a multilayer film, wherein an optical fiber is provided while the multilayer film is moving on a production line. This multi-layer film is intermittently irradiated with light in the near-infrared region using, and the reflected light from the multi-layer film is extracted via an optical fiber, and the multi-layer film is constructed from the interference waveform of the extracted reflected light. It is characterized in that the film thickness of the intermediate layer is measured.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the accompanying drawings. FIG. 1 is a diagram showing the overall configuration of a film thickness measuring apparatus to which this embodiment is applied. The film thickness measuring device shown in FIG.
And the signal processing unit 20. This measuring unit 10
A strobe light source 11 that emits light by a strobe that secures a wavelength in the near-infrared region to provide intermittent light, a condensing optical system 12 that condenses the light emitted from the strobe light source 11 by an aspheric lens, A bundle-type two-branch optical fiber 13 that conveys the light condensed by the optical system 12 to irradiate the multilayer film which is an object to be measured, and also conveys the reflected light from the multilayer film, the bundle type It is obtained through a sensor unit 14 provided at a branching portion of the two-branching optical fiber 13 and provided with a light projecting terminal and a light receiving terminal, for example, a filter 15, which is an interference filter for dimming the stroboscopic line spectrum of 560 nm or less, Spectroscope 16 for decomposing the reflected light into a spectrum, and a multi-channel demultiplexer for converting the reflection light decomposed into a spectrum by the spectroscope 16 into an electric signal. It has a Kuta 17. Incidentally, like the condensing optical system 12, the strobe light source 11 and the bundle type 2
If a lens is inserted between the branch optical fiber 13 and the light that spreads from the light source is collimated, it is possible to widen the distance between the light source and the optical fiber.

The sensor portion 14 is sufficiently end face-treated, and is set so that the distance to the multilayer film is at the optimum position (for example, 5 mm). The spectroscope 16 uses a high-efficiency grating (diffraction grating), and employs a bright one of F2 or more. In the present embodiment, one having a resolution of 200 to 400 lines / mm and a wavelength range of 300 to 1000 nm is adopted. Further, the multi-channel detector 17 has a PD (Photo Detector) 1024 channels for photoelectrically converting the entire spectral wavelength region of the dispersed light, and 0.5 to 3.5 per channel.
It has a resolution of nm. The analog signal from the multi-channel detector 17 is A / D converted into a digital signal, which is processed by the signal processing unit 20. The analog signal from this multi-channel detector 17 is converted into A / D.
The converted data requires a dynamic range of 5000 or more (described later).

Further, the signal processing unit 20 for processing the obtained electric signal is a Kaiser conversion mechanism 21 for converting the wavelength into a unit of wave number, and a fast Fourier transform (FFT) process from the obtained wave number data. ) To output a power spectrum which is a continuous spectrum, and a power spectrum analysis mechanism 23 which removes noise from the power spectrum and detects, for example, three peak positions by morphology processing. The output from the power spectrum analysis mechanism 23 of the signal processing unit 20 is organized by a personal computer (PC) and displayed on the display as a film thickness profile which is information on the film thickness. In the Fourier transform mechanism 22, there is no problem even if the Fourier transform is not fast.

The multilayer film to be measured in the present embodiment has a three-layer structure of 15 to 25 μm, and when the apparatus adopted in this embodiment is used,
Usually, a film having a thickness of up to about 50 μm, theoretically up to about 100 μm can be measured. In the case of a three-layer structure, it is composed of an intermediate layer that requires a gas barrier property that does not pass water vapor and oxygen, and two outer layers that provide strength. In the intermediate layer, it is necessary to ensure a gas barrier property, so that it is necessary to secure a certain thickness or more, and in order to suppress the cost, it is necessary to avoid an excessive thickness. Further, this thickness measurement is required to be performed in a so-called in-line state in which the web-shaped multilayer film is moving in a certain direction on the factory line. Even if a defect is found by measurement after manufacturing, it is difficult to recover from the defect, but it is possible to quickly deal with the defect by performing the measurement in an in-line state.

In this multilayer film, the film thickness of each layer is set in consideration of the balance between gas barrier property and strength. In a general packaging film, for example, the total thickness is 10
.About.50 .mu.m and intermediate layer 1 to 40 .mu.m. Further, although this multilayer film is a transparent body, it may be transparent as long as reflected light can be obtained, and may have turbidity such as white turbidity. Further, if there is no absorption of a specific wavelength, even if a color such as a black film is contained, it can be an object to be measured. That is, even if the film is not a completely transparent film, it can be measured with a colored film as long as the effect of light absorption is not great.

The multilayer film, which is the object to be measured to which this embodiment is applied, preferably has a thickness of 2 to 3 layers in order to avoid complication of data and difficulty of analysis. For example, as the two layers, the case where the film thickness of the coating film coated on the film is measured and the like can be mentioned. The three-layer film measurement is particularly suitable for measurement of an A / B / A type three-layer structure in which the outer layers (A layers) on both sides sandwiching the intermediate layer (B layer) have the same film thickness. Further, as the object to be measured, a single layer film can be used instead of the multilayer film. When the measurement method of the present embodiment is applied to a single-layer film, it is possible to obtain a highly accurate measurement result compared with the conventional one, and the device is simple and inexpensive, and the type of film is different. It is also excellent in that it can be measured without using any radiation and does not use radiation.

Here, as the strobe light source 11 used in the film thickness measuring apparatus according to the present embodiment, a strobe which covers a near infrared region, which is an infrared ray having a short wavelength and being close to visible light, is used. 1 flash per second,
Strobe emission time of 1 flash is 10 to 50 μs (μ
Seconds). For example, if the film to be measured (multilayer film) is moving at a line speed of 10 m / min, the strobe light emission time is 50 μs, the film movement distance is 8.3 μm, and the strobe light emission time is 20 μs. The moving distance of the film becomes 3.3 μm. Line speed is a
If the speed is doubled, the moving distance of the film in each stroboscopic light emission time is also a times. Depending on the accuracy you want to obtain as data at the time of measurement, the moving speed of the film,
It is possible to select the optimal strobe emission time in consideration of the light amount and the like.

As the near infrared region used for the strobe light source 11, a wavelength of about 500 to 1000 nm, preferably 600 to 1000 nm is selected. Furthermore, the dynamic range of the measuring unit 10 is 50 as the irradiation light amount.
It is necessary to have a strong irradiation light amount that can secure 00 or more, preferably 10,000 or more. When using other light sources,
For example, a strong halogen light source has a problem that the entrance is melted by heat when light is input to the optical fiber (bundle type two-branching optical fiber 13). Similarly, a light source composed of continuous light of halogen or xenon generally has the problem of this heat, and it is difficult to make it into a device. In addition, if you use a halogen light source for long time exposure and measure the film thickness, due to the influence of heat,
A slight change in film thickness occurs on the film. For example, the interface refractive index difference of the intermediate layer is often as small as about 0.01, and a minute change in the film thickness causes noise, making it difficult to detect the interference signal of the intermediate layer. Therefore, in the present embodiment, as the measuring unit 10, the strobe light source 11 that is an intermittent irradiation with little influence of heat even if it is a high output type is adopted.

By using the strobe light source 11,
It becomes possible to emit a strong irradiation light amount. For example, when measuring the film thickness of a moving film, if the measurement time (data acquisition time) is lengthened, the film thickness at a specific portion of the film cannot be accurately measured. This is because when the data acquisition time becomes long, the film length required for the data acquisition time becomes long, and the film thickness measurement data of the film to be measured overlap with each other. That is,
If the take-in time becomes long, not the film thickness data at a specific location, but the data with different film thicknesses are superimposed in a long film length, and only a low precision value can be obtained, or the film thickness of the intermediate layer is completely lost. It becomes impossible to measure. On the other hand, in order to shorten the data acquisition time and measure,
It is necessary to irradiate strong light, but it is difficult to emit this strong light with a conventional halogen lamp or the like. In the present embodiment, by using the strobe light source 11, it is possible to instantaneously emit strong light, and it is possible to satisfy the amount of light required for short-time measurement, and at the same time, there is a thermal problem between the light source and the optical fiber. Can be avoided. It should be noted that data acquisition is preferably short, and normally only the time during which the strobe light source 11 is lit is sufficient. However, if it is difficult to synchronize the strobe emission time and the data acquisition time, the strobe light source is used. You may include not only the shining time but the fixed time before and after that.

FIGS. 2A to 2C are views showing the structure of the bundle type two-branch optical fiber 13. The bundle-type two-branch optical fiber 13 to which this embodiment is applied uses silica glass as the material of the optical fiber, and has a length of about 3 m, 20 optical fibers of 10 on the light-projecting side and 10 on the light-receiving side (φ 70 μm).
(m / piece) constitutes a bundle structure of φ0.5 mm. The bundle structure is, for example, 15 on the light emitting side.
It is also possible to use 30 and 30 optical fibers on the light receiving side. Also, as the material of the optical fiber,
Approximately 80 optical fibers with a diameter of 3 mm and a diameter of 250 μm as the outgoing light side (sensor section 14 side) are used as the filter 15 side of the light receiving side using multi-component glass.
A preferable result can be obtained even by using a bundle structure in which about 20 μm optical fibers are used.

This bundle structure is protected by a protection tube as shown in FIG. As shown in FIG. 2A, the light projecting side optical fiber from the condensing optical system 12 side and the light receiving side optical fiber from the filter 15 side are combined to form a protection tube on the sensor section 14 side. That is, the protection tube extending from the sensor unit 14 side is branched into two, that is, the filter 15 side and the condensing optical system 12 side.

The end surface on the side of the sensor unit 14 has a bundle structure of φ0.5 mm and a light receiving side optical fiber of φ70 μm and a light projecting side light of φ70 μm in a bundle structure of φ0.5 mm as shown in FIG. The fibers are randomly arranged. These optical fibers have an NA value indicating the spread of light of about 0.2, and suppress the spread of the light projecting range and the light receiving range to about 11 °. On the end surface on the filter 15 side, as shown by the arrow B-B in FIG. 2C, the light-receiving side optical fibers of φ70 μm are arranged in a line, and the reflected light is reflected by the filter 15 and the spectroscope 1.
It is input to the multi-channel detector 17 via 6.

Next, a method of calculating the film thickness of the multilayer film will be described. 3A and 3B are diagrams for explaining the method of calculating the film thickness of the multilayer film adopted in the present embodiment, and the film thickness measurement by the optical interference method is performed.
Now, as shown in FIG. 3A, a film 1 having a refractive index n1 and a film thickness d1, a film 2 having a refractive index n2 and a film thickness d2, and a film thickness d3 having a refractive index d3.
An attempt is made to measure the film thickness of a multi-layer film consisting of three films, film 3 of 3. As shown in FIG. 3A, from the strobe light source 11 to the optical fiber (bundle type two-branch optical fiber 1
The incident light emitted via 3) is reflected at each interface of the multilayer film composed of three layers, and
The signal is converted into an electric signal by the multi-channel detector 17 via the (bundle type two-branch optical fiber 13).

That is, the incident light is incident on the film surface of the film 1 (the interface between the air and the film 1), the interface between the film 1 and the film 2, and the film 2 and the film 3.
The reflected light is reflected by the interface between the two and the interface between the film 3 and the air. Since light is a wave, these reflection components interfere with each other. Considering that the incident light is vertically incident on the multilayer film by the sensor unit 14, this interference is weakened depending on the optical film thickness nd obtained by multiplying the refractive index n and the film thickness d and the wavelength λ. Or strengthen each other.

Here, since the maximum value and the minimum value of the interference light are alternately generated, if the wavelength of the maximum value is λ _2m and the wavelength of the minimum value is λ _{2m + 1} , 2m = 4 · n · d It is expressed as / λ _2m 2m + 1 = 4 · n · d / λ _{2m + 1} . From these, it can be understood that when the order m is eliminated, nd = λ _2m · λ _{2m +} 1/4 (λ _2m −λ _{2m + 1} ), and the optical film thickness nd is derived from the maximum and minimum of interference. Here, when the refractive index n is known, the film thickness d can be obtained.

FIG. 3B shows the power spectrum after signal processing, where the horizontal axis shows the frequency and the vertical axis shows the power spectrum. P1 is the power spectrum due to the film thickness d1, P2 is the power spectrum due to the film thickness d1 + d2, P
Reference numeral 3 is a power spectrum based on the film thickness d1 + d2 + d3, and P1, P2, and P3 are respectively represented by frequency × resolution (nm). This resolution depends on the measurement wavelength region.

Here, assuming that the correction coefficients obtained from the known measurement values of the film thickness are k1, k2, and k3, each film thickness is obtained as follows. d1 = P1 × k1 d2 = (P2-P1) × k2 d3 = (P3-P2) × k3 In this way, for example, the width (film thickness) d2 of the intermediate layer can be calculated. It is possible to display the above as a film thickness profile.

As described above, in the present embodiment, since the film thickness measurement by the optical interference method is adopted, the measurement result is stable, and it is strong against the vibration of the object to be measured. The thickness of a web-shaped multilayer film moving in one direction can be appropriately measured. Further, the measurement can be performed without contacting the multilayer film, and the position setting of the sensor unit 14 becomes easy. Further, in an intermediate layer having a small difference in refractive index of, for example, about 0.01 or less, a subtle change in film thickness causes noise, and it is generally difficult to detect an interference signal. Infrared strobe light source 11
By irradiating strong light in a short time by using, it is possible to cope with a minute difference in refractive index. Furthermore, the ease of detection of the interference waveform is determined by the magnitude of the reflectance, and the reflection of the intermediate layer is about 1/500 lower than that of the film surface, and thus detection of the interference waveform is generally difficult. . However, in the present embodiment, the dynamic range of the measuring unit 10 is set to 5
000 or more, preferably about 10,000,
It is possible to solve these problems.

[0033]

As described above, according to the present invention,
It is possible to accurately measure the film thickness of a moving film.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a film thickness measuring apparatus to which this embodiment is applied.

2A to 2C are diagrams showing a configuration of a bundle-type two-branch optical fiber 13. FIG.

3 (a) and 3 (b) are diagrams for explaining a method for calculating the film thickness of a multilayer film adopted in the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Measuring part, 11 ... Strobe light source, 12 ... Condensing optical system, 13 ... Bundle type two-branch optical fiber, 14 ... Sensor part, 15 ... Filter, 16 ... Spectroscope, 17 ... Multi-channel detector, 20 ... Signal processing Part, 21 ... Kaisai transformation mechanism, 22 ... Fourier transformation mechanism, 23 ... Power spectrum analysis mechanism

Continued front page    F term (reference) 2F065 AA30 BB13 BB15 BB17 BB22                       CC02 CC31 DD06 DD11 FF41                       FF51 FF56 GG08 LL02 LL03                       LL04 LL22 LL42 LL67 QQ16                       QQ25 QQ28 QQ29

Claims (8)

[Claims] 1. A light emitting means for emitting strobe light in the near-infrared region, a light projecting means for projecting the strobe light from the light emitting means onto a film moving on a manufacturing line, and the projecting means. Light receiving means for receiving the reflected light from each layer of the film by the strobe light projected by the light means, and measuring the thickness of the film forming the film based on the reflected light received by the light receiving means A film thickness measuring device, comprising: 2. The film thickness measuring device according to claim 1, wherein the film thickness measuring device can secure a light amount having a dynamic range of 5000 or more. 3. A strobe light source that emits strobe light in the near-infrared region, transports light from the strobe light source to irradiate an object to be measured, and transports reflected light from the object to be measured. An optical fiber, a spectroscope that decomposes the reflected light obtained from the optical fiber into a spectrum, a multi-channel detector that converts the reflected light decomposed into a spectrum by the spectroscope into an electric signal, and the multi-channel detector And a signal processing unit for processing the electric signal obtained by 4. The film according to claim 3, wherein the optical fiber is provided with a sensor unit at one end where a plurality of fibers on the light emitting side and the light receiving side are bundled and which is in proximity to the object to be measured. Thickness measuring device. 5. A web-like film moving in a fixed direction is irradiated with strobe light in the near-infrared region, and a power spectrum is analyzed from an interference waveform of light reflected from the film, A film thickness measuring method, which comprises measuring the film thickness of a layer constituting the film from a power spectrum. 6. The stroboscopic light irradiation in the near-infrared region is performed by stroboscopic irradiation for one irradiation time of 10 to 50 μs according to the moving speed of the film. Film thickness measurement method. 7. The film thickness measuring method according to claim 5, wherein the power spectrum is analyzed through a measuring instrument having a dynamic range of 5000 or more. 8. A film thickness measuring method for measuring a film thickness of an intermediate layer of a multilayer film, comprising: a light in a near infrared region using an optical fiber while the multilayer film is moving on a production line. Intermittently irradiating the multilayer film, reflected light from the multilayer film is taken out through an optical fiber, and the film of the intermediate layer constituting the multilayer film from the interference waveform of the extracted reflected light A method for measuring film thickness, which comprises measuring the thickness.