JP2003240515A - Film thickness measuring method and manufacturing method for sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film thickness measuring method using optical interference, in which a high-precision measurement is possible with a single measuring instrument even if a measurement range for an object is wide. <P>SOLUTION: The film thickness of an object, which is to be measured, is acquired from an interference waveform which is acquired by spectroscopy, for each wavelength, of reflection light or transmission light from the object which is irradiated with light. The number of acquired extreme values of interference waveform or amplitude of the interference waveform is compared to a preset reference value, and depending on the result, one film-thickness calculation method is selected from among a plurality of different film-thickness calculation methods, for film thickness calculation. <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 method and a sheet manufacturing method based on the principle of optical interference.

[0002]

2. Description of the Related Art In a sheet such as a polymer film, the thickness uniformity is an important quality, and when the product has a non-uniform thickness, the user cannot handle it or convey it at a stage where it is used. It causes various troubles such as magnetic material application failure and vapor deposition failure. Therefore, in order to control the means for forming the sheet to manufacture products with excellent thickness uniformity, and for quality control and process control not to give the user products with poor thickness uniformity, the thickness of the sheet It is important to measure the profile.

The method for measuring the film thickness is based on the β
Many of them use absorption of rays and infrared rays,
None of these are suitable for highly accurate measurement. For more accurate measurement, a so-called optical interference method disclosed in, for example, JP-A-56-115905 and JP-A-63-163105 is adopted.

In the film thickness measuring method of the light interference method, a spectral spectrum due to an interference phenomenon when white light is reflected or transmitted by a film, an incident angle of white light, a film thickness of a film,
Utilizing that it depends on the refractive index, the reflected light or
The spectral spectrum of transmitted light is detected, and the film thickness is obtained from the spectrum.

At this time, in order to measure the film thickness with high accuracy, it is necessary to detect the extreme wavelength of the spectrum with high accuracy.

However, the spectroscopic range that can be set in the measuring device is limited, and the wavelength range in which the interference waveform can be captured as an electric signal is limited for each measuring device. Therefore, in each measuring device, the optimum spectral range that can obtain a sufficient interference waveform according to the measurement target is set,
It was difficult to secure a wide measurement range with one measuring instrument.

That is, the interval between the extreme values of the interference waveform varies depending on the film thickness of the sheet, and it may be difficult to detect a sufficient extreme value depending on the measurement target within the limited spectral range.

In particular, in order to remove the influence of light scattering inside the object to be measured, it is effective to calculate the film thickness from the interference waveform dispersed in the long wavelength region. Since the period of the waveform becomes large, it is difficult to sufficiently detect the extreme value of the interference waveform in the spectral range of the measuring device when the measurement target is thin.

Therefore, a film thickness measuring instrument having an optimum spectral range according to the thickness of the sheet to be measured is required,
It was impossible to measure a wide range with a single film thickness measuring device.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the conventional film thickness measuring instrument and realize a wide range of measurement with one measuring instrument.

Another object of the present invention is to enable the measurement of the film thickness of such a sheet in a wide range with one measuring device in the manufacturing process of a sheet such as a polymer film without changing the measuring device. Accordingly, it is to provide a method for manufacturing a sheet that can improve quality and yield.

[0012]

An object of the present invention is to irradiate a measurement object with light and to separate a reflected light or a transmitted light from the measurement object for each wavelength from an interference waveform to obtain a film thickness of the measurement object. A method for measuring the film thickness, wherein the number of extreme values of the obtained interference waveform or the amplitude of the interference waveform is compared with a preset reference value, and a plurality of different film thickness calculation methods are selected according to the result. It is achieved by a film thickness measuring method characterized in that the film thickness calculation is performed by selecting one of the above film thickness calculating methods.

Further, in the above, the plurality of film thickness calculation methods is a method of calculating the film thickness from each wavelength corresponding to a plurality of extreme values of the interference waveform, and the wavelength corresponding to the extreme value of the interference waveform is determined in advance. The method of calculating the film thickness from the order of interference that has been set, the method of calculating the film thickness from the order of interference estimated using the wavelength corresponding to the extreme value of the interference waveform and its extreme value, and the film thickness by curve fitting How to calculate, and
A film thickness measuring method, which is at least two methods selected from the method of calculating the film thickness based on the frequency analysis result of the interference waveform, is preferable.

Further, in the above, a film thickness measuring method in which the film thickness calculating method is selected depending on whether the number or amplitude of the extreme values of the obtained interference waveform is less than the reference value or more than the reference value is preferable.

Further, in the above, when the film thickness is continuously measured, the reference value is composed of the upper limit value and the lower limit value, and the number or amplitude of the extreme values of the obtained interference waveform is Only if either less than the upper limit and greater than or equal to the upper limit during the current measurement or greater than or equal to the lower limit during the previous measurement and less than the lower limit during the current measurement,
A film thickness measuring method for selecting the film thickness calculating method is preferable.

Further, in the above, when the number of extreme values of the interference waveform is less than a preset value, the film thickness is calculated from the wavelength corresponding to the extreme value of the interference waveform and the predetermined order of interference. If the number of extreme values of the interference waveform is greater than or equal to the preset value, the film thickness is calculated from the wavelength corresponding to the extreme value of the interference waveform and the interference order estimated using the extreme value. A film thickness measuring method characterized by selecting the method described above is preferable.

Further, an object of the present invention is to provide a light irradiating means for irradiating the measurement object with light, and a light receiving means for receiving reflected light or transmitted light from the measurement object with respect to the light from the light irradiation means,
A spectroscopic unit that disperses the reflected light received by the light receiving unit for each wavelength, a signal conversion unit that converts the light dispersed by the spectroscopic unit into an electric signal according to its intensity, and the signal conversion unit. Detecting means for detecting the number of extreme values of the signal waveform of the electric signal or the amplitude of the signal waveform, and a plurality of different film thickness calculating methods according to the number or the amplitude of the extreme values of the signal waveform detected by the detecting means. It is achieved by a film thickness measuring device characterized in that it has a selecting means for selecting one of the film thickness calculating methods and a film thickness calculating means for calculating the film thickness by the selected film thickness calculating method.

When a sheet is manufactured by discharging resin from a die having a gap, the thickness of the sheet is measured using the above-mentioned film thickness measuring device, and the gap of the die is controlled based on the obtained measurement value. A method for producing a sheet is preferred.

Another object of the present invention is to obtain the film thickness of the object to be measured from the interference waveform obtained by irradiating the object to be measured with light and separating the reflected light or transmitted light from the object to be measured for each wavelength. A detecting step of detecting the number of extreme values of the interference waveform or the amplitude of the interference waveform, and a program for causing a computer to execute a plurality of values in accordance with the number or amplitude of the extreme values of the interference waveform detected by the detecting step. And a film thickness calculating step of calculating a film thickness by the selected film thickness calculating method, and a film thickness calculating step of calculating a film thickness by the selected film thickness calculating method. To be done.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention detects the number or amplitude of extreme values of an interference waveform obtained from a spectral spectrum of reflected light and determines a plurality of different film thicknesses according to the number or amplitude of detected extreme values. The optimum film thickness calculation method is selected from the calculation methods, the film thickness is calculated, and the film thickness d is determined. Here, the number of extreme values is the number of extreme values in the spectral range of the measuring device used.

The film thickness measuring method of the present invention will be described below with reference to the drawings.

FIG. 1 is a flowchart of a film thickness measuring method according to the present invention. The measuring procedure is step 1 for measuring a spectral intensity spectrum and step 2 for selecting a film thickness calculating method based on the measurement result of the spectral intensity spectrum. And the step 3 of calculating the film thickness by the film thickness calculating method selected in the step 2.

FIG. 2 is a schematic configuration diagram showing an example of the optical interference type film thickness measuring apparatus used in the film thickness measuring method of the present invention. The light source 21, the light projecting unit 22, the optical path changing unit 25, the spectroscopic unit 26, and the data. The processing device 27 is included. In the figure and the following description, a reflection-type optical interference type film thickness measuring device that uses reflected light 24 obtained by reflecting the incident light 23 by the measurement target 20 will be described, but a transmission type that uses transmitted light that has passed through the measurement target 20. The same applies when a film thickness measuring device is used.

The steps in FIG. 1 will be described in detail below.

Step 1 is executed by the optical interference type film thickness measuring device shown in FIG. That is, the white light 23 emitted from the light source 21 and collimated by the light projecting unit 22 has a constant incident angle θ.
And is incident on the measurement target 20. The incident light is reflected (or transmitted) by the measurement target, but at that time, the intensity of each wavelength component changes due to the interference phenomenon. The reflected light 24 enters the spectroscope 26 through the optical path conversion unit 25, is converted into an electric signal and is input to the data processing device 27, and the intensity for each wavelength, that is, the spectral intensity spectrum can be measured. The subsequent steps may be performed using the spectrum measured in step 1 as it is, but the spectrum absorption characteristics of each optical system of the optical interference type film thickness measurement apparatus shown in FIG. It is preferable to carry out the subsequent steps after obtaining the spectral spectrum in which

In step 2, a film thickness calculation method is selected from a plurality of different film thickness calculation methods based on the measurement result of the spectral intensity spectrum in step 1. As a plurality of different film thickness calculation methods, (1) the number or the amplitude of the extreme values of the spectral intensity spectrum is compared with a preset reference value, and the plurality of extreme values of the interference waveform are calculated according to the comparison result. A method of calculating the film thickness from each corresponding wavelength, (2) A method of calculating the film thickness from the wavelength corresponding to the extreme value of the interference waveform and the predetermined order of interference, (3) A method of calculating the film thickness from the wavelength corresponding to the extreme value and the estimated order of interference, (4) a method of calculating the film thickness by curve fitting, and (5) a film based on the frequency analysis result of the interference waveform. At least two methods selected from the methods for calculating the thickness are preferable.

The method of selecting the film thickness calculation method is not particularly limited, but the film thickness calculation method depends on whether the number or amplitude of the extreme values of the obtained interference waveform is less than the reference value or more than the reference value. Is preferably selected. You may select from two film thickness calculation methods using one reference value, and you may select from three or more film thickness calculation methods using two or more reference values.

For example, if the number of extreme values of the interference waveform obtained as the reference value is used and the number of extreme values of the interference waveform is less than a preset value, the wavelength corresponding to the extreme value of the interference waveform and the If the method of calculating the film thickness from the determined order of interference is selected and the number of extreme values of the interference waveform is greater than or equal to the preset value, the wavelength corresponding to the extreme value of the interference waveform and its extreme value It is preferable to select the method of calculating the film thickness from the order of interference estimated by using, because high-precision measurement can be performed even when the measurement range of the measurement target is wide.

Step 2 while continuously measuring the film thickness
When selecting the film thickness calculation method of, as the reference value,
When the upper limit value and the lower limit value are set, and the number or amplitude of the extreme values of the obtained interference waveform is less than the upper limit value during the previous measurement and greater than or equal to the upper limit value during the current measurement, and the previous measurement It is preferable that the film thickness calculation method is selected only when the time is equal to or more than the lower limit value and the current measurement is less than the lower limit value. When the measurement is performed continuously, the spectral intensity spectrum also changes continuously. that time,
When the characteristics of the spectral intensity spectrum change around the reference value, the film thickness calculation method is frequently switched. Since it is unavoidable that some measurement error occurs due to the switching of the film thickness calculation method, if the switching is performed frequently, the measurement accuracy may decrease. By setting two values, the upper limit value and the lower limit value, as the reference value, and by doing the above, even if the number or amplitude of extreme values slightly changes around the reference value, the film thickness calculation method can be switched. Does not occur. As a result, frequent switching of the film thickness calculation method can be prevented, and the measurement accuracy can be improved.

In step 3, the film thickness is calculated using the film thickness calculation method selected in step 2.

The respective film thickness calculation methods will be described in detail below.

(Film Thickness Calculation Method 1) A method of calculating the film thickness from each wavelength corresponding to a plurality of extreme values of the interference waveform is performed by detecting the wavelengths of two adjacent extreme values of the interference waveform. First, the wavelengths λ _m and λ _{m + 1} that give the extreme values that are adjacent to each other in the spectrum measured in step ₁ are determined.

That is, as shown in FIG. 3, when a film having a thickness d and a refractive index n is irradiated with white light at an incident angle θ, a light ray I reflected on the front surface and a light ray II reflected on the back surface are

[0034]

[Equation 1]

An optical optical path difference Δ represented by (1) is generated to cause interference. Therefore, when the reflected light is dispersed, a spectral spectrum with a dark part (valley) and a bright part (mountain) is obtained as shown in FIG. 4, and the wavelength that gives the extreme value is an integer m called the order of interference. It is expressed by the following equation.

[0036]

[Equation 2]

[0037] (Minimum condition) (2)

[0038]

[Equation 3]

(Maximum Condition) (3) That is, considering that the phase of the light beam I is inverted, the light beam I and the light beam II have opposite phases at a wavelength where Δ is m times the wavelength. The spectrum has a minimum, and Δ is the wavelength (m
At a wavelength that becomes +1/2) times, the light rays I and II have the same phase and the spectrum becomes maximum. In the following, for simplification, the case of the wavelength λ _m giving the minimum is described, but the same applies to the wavelength λ _{m + 1/2} giving the maximum.

From equation (2), the wavelengths λ _m and λ of the adjacent valleys are
_{If m + 1} (λ _m > λ _{m + 1} ) is detected, as described above,

[0041]

[Equation 4]

(5) Therefore, delete m from the two expressions,

[0043]

[Equation 5]

(6) Becomes

This calculation method is suitable because the accuracy of film thickness measurement can be increased when the film thickness of the object to be measured is large.

(Film Thickness Calculation Method 2) The method of calculating the film thickness from the wavelength corresponding to the extreme value of the interference waveform and the predetermined order of interference is to detect the wavelength giving the extreme value of the interference waveform. In both cases, the order of interference is determined in advance, and the film thickness is calculated from the interference order and the wavelength giving the extreme value of the interference waveform. First, the wavelength giving the extreme value from the spectrum measured in step 1 Determine λ _m . As described above, when the film thickness d, the refractive index n, and the incident angle θ,

[0047]

[Equation 6]

(2) Have a relationship.

This calculation method is suitable when the film thickness of the object to be measured is thin and the number of extreme values of the interference waveform that can be detected in the spectral range of the film thickness measuring device is small. If the film thickness is thin,
The order of the wavelength giving the extreme value on the long wavelength side among the wavelengths giving the extreme value of the obtained interference waveform can be determined in advance from the film thickness and the spectral range of the film thickness measuring device. From the predetermined interference order and the wavelength that gives the extreme value of the interference waveform, the film thickness d
Is

[0050]

[Equation 7]

(4) It is calculated by the equation (4).

According to this method, the film thickness can be determined even when either _one of the two adjacent extreme wavelengths λ _m and λ _{m + 1} cannot be detected, and when the measurement target is thin. Even if it is difficult to detect the extreme value of the interference waveform, such as when performing spectroscopy in the long wavelength region or in the long wavelength region, if the wavelength of a single peak or valley can be detected, the film thickness can be measured with high accuracy. .

(Thickness Calculation Method 3) The method of calculating the film thickness from the wavelength corresponding to the extreme value of the interference waveform and the order of interference estimated using the extreme value is the wavelength giving the extreme value of the interference waveform. After detecting, the estimated film thickness is obtained using the extreme value, and the film thickness is calculated from the order of the interference estimated from the obtained estimated film thickness and the wavelength giving the extreme value of the interference waveform. 1
The wavelength λ that gives the extreme value from the spectrum measured in
Determine _m .

Next, the estimated film thickness d _E is determined. Estimated film thickness d _E
As a method of determining, the estimated value of the approximate value d _P of the known film thickness itself is used. That is,

[0055]

[Equation 8]

(7) Further, as another method of determining the estimated film thickness d _E , a method of calculating the film thickness from each wavelength corresponding to a plurality of extreme values of the interference waveform, that is, the formula (6) is used. There is a method of using the calculated film thickness. That is,

[0057]

[Equation 9]

(8) As another method for determining the estimated film thickness d _E , there is a method based on the measurement values at one or more adjacent measurement points. That is, the K film thickness measurement values at that measurement point are calculated as d _N-1 , d _N-2 , d _N-3 ,
... When d _NK

[0059]

[Equation 10]

The value estimated by (9) is used. Here, a _{1 to} a _K are linear prediction coefficients.

As a special case, when the film thickness of the sheet changes gently and the detection error of the wavelength λ _m giving the extreme value of the spectrum at each measurement point is small, a ₁ = 1. 0, a ₂ = ... = a _K = 0,

[0062]

[Equation 11]

(10) That is, the film thickness measurement value at the closest measurement point may be used as the estimated film thickness value.

As another method of determining the estimated film thickness d _E , there is a method of determining it on the basis of the measured values at the adjacent measurement points and the estimated film thickness at the adjacent measurement points.
That is, when the measured value at the adjacent measurement point is d _N-1 and the estimated film thickness at the adjacent measurement point is d _E ′,

[0065]

[Equation 12]

The value estimated by (11) is used. Here, b is a first-order lag coefficient and 0 <b <1.

Next, the interference order m corresponding to the wavelength λ _m giving the determined extreme value is determined. The wavelength λ _m , the interference order m, and the film thickness d have the relationship of the equation (2). When the estimated film thickness d _E is used instead of the film thickness d,

[0068]

[Equation 13]

M _E satisfying (12) is a good approximation value of m if d _E is a good approximation value of d. Therefore, we solved the above equation for m _E

[0070]

[Equation 14]

(13) m _E is obtained according to (13), and m _E is determined by rounding m _E to an integer value.

Using the interference order m thus determined, the film thickness is calculated. That is,

[0073]

[Equation 15]

(4) The film thickness is calculated by

At this time, if λ _m is detected to be large by Δλ, the error of the film thickness d obtained by the above equation is proportional to Δλ / λ _m, and the film thickness obtained by the equation (6) has the conventional value. Error Δ
It is sufficiently smaller than λ / (λ _m −λ _{m + 1} ). Therefore, even if the contrast decreases due to birefringence and the accuracy of detecting the peaks or valleys of the spectral spectrum deteriorates,
Highly accurate film thickness measurement is possible.

Also in the case of this method, the film thickness can be determined even when either _one of the two adjacent extreme wavelengths λ _m and λ _{m + 1} cannot be detected. Therefore, even if it is not possible to detect the wavelengths of adjacent peaks or troughs in the spectrum, the contrast decreases due to birefringence, but if the wavelength of a single peak or trough can be detected, the film with high accuracy can be obtained. Thickness can be measured.

Among the methods for determining the estimated film thickness d _E , the method using the measurement values at adjacent measurement points, that is, the method using the equation (9) or the equation (10) or the equation (11), The measuring method at the measured point is not particularly limited. That is, the measuring method at the adjacent measuring points may be the value measured by the conventional method using the formula (6) or the value measured by the method of the present invention. Especially in the latter case, the film thickness is measured by determining the estimated film thickness at the Nth adjacent measurement point by using the film thickness measurement method at the N-1th measurement point measured using this film thickness measurement method. This measurement method may be repeated, such as performing the measurement, determining the next N + 1th estimated film thickness from the film thickness measurement value at the Nth measurement point, and measuring the film thickness.

The invention is applicable not only to the measurement of the thickness profile of a sheet having a different thickness depending on the measurement location, but also to the measurement of the same measurement point whose thickness gradually changes with time. Any measuring method can be used. In this case, in the estimated film thickness determination method using the above equations (9) and (10), instead of using the film thickness measurement values at adjacent measurement points, the film thickness measurement values at the previous time may be used. .

This calculation method is suitable because the accuracy of film thickness measurement can be increased when the film thickness of the object to be measured is large.

(Film Thickness Calculation Method 4) A method for determining the film thickness by curve fitting is obtained by curve fitting the spectral spectrum measured in step 1 to a function of the film thickness and the interference waveform using the least square method or the like. The film thickness value corresponding to the interference waveform is detected. The relationship between the film thickness d and the interference waveform y is

[0081]

[Equation 16]

It can be expressed by (14). Here, n is the refractive index and λ is the wavelength. By curve-fitting the spectrum to the equation (14), each coefficient of the equation (14) is determined, and the equation (14) is determined.
The film thickness d, which is one of the coefficients of, is also determined.

(Film Thickness Calculation Method 5) The frequency of the interference waveform is analyzed, and the film thickness is calculated based on the analysis result. The interference waveform signal y, which is a function of wavelength, is converted into a function signal G of wave number.

[0084]

[Equation 17]

After conversion to (15), the known function such as fast Fourier transform or autocorrelation function is applied to the converted function signal G of wave number to perform spectrum calculation, and the maximum spectrum is obtained from the obtained spectrum data. The frequency f of the wavenumber function signal G having the spectrum intensity is obtained, and the wavenumber function signal G is calculated from the frequency f.
Find the most probable adjacent extreme wavenumber interval P in
The film thickness d is obtained by substituting the wave number interval P (= 1 / λ _m −1 / λ _{m + 1} ) by the formula (16) obtained by modifying the formula (6).

[0086]

[Equation 18]

(16) The case of producing a sheet by applying the film thickness measuring method according to the present invention will be described below.

FIG. 5 is a schematic diagram of a general sheet manufacturing facility.

The polymer extruded by the extruder 53 is
The sheet is expanded by a die 54 in the width direction perpendicular to the paper surface of FIG. 5 and extruded into a sheet 51.
The film is stretched in the lateral direction and wound up by the winder 56.

In the method for producing this sheet, the stretching machine 5 is used.
A thickness gauge 58 (for example, one having a measuring unit as shown in FIG. 2) using the film thickness measuring method of the present invention is installed between the No. 2 and the winder 56, and the thickness profile of the sheet in the width direction is set. To measure. The lip gap of the die 54 is controlled by the control means 59 so that the width-direction thickness profile has a desired shape.

The sheets thus manufactured are generally shipped in various thicknesses. However, the conventional film thickness calculation method has an optimum spectral range according to the thickness of the sheet to be measured. It was necessary to change to a film thickness measuring device.

The sheet manufactured in this manner generally has birefringence, but depending on the conditions of the manufacturing process, the size of the birefringence in the width direction of the sheet and the location in the width direction of the main axis direction. Therefore, the degree of distortion of the spectral spectrum due to birefringence may also vary depending on the location in the width direction of the sheet, and in conventional film thickness measurement methods that do not switch the measurement method according to the obtained interference waveform. In a place where the distortion of the spectrum is large, the measurement error of the film thickness becomes large, and the accuracy of the measured thickness profile deteriorates. As a result, since the measured thickness profile does not represent the actual film thickness profile,
It cannot be used for control, or even if the measured thickness profile is controlled to have the desired shape, the thickness profile of the manufactured sheet will be different from the desired shape.

Therefore, in the sheet manufacturing method of the present invention, the width direction thickness profile of the sheet is measured by using the above-described film thickness measuring method of the present invention, and the measured thickness profile has a desired shape. To control. Thereby, the film thickness can be measured with high accuracy even if the spectrum is distorted, and thus the thickness profile can be formed into a desired shape.

Further, the manufactured sheet is evaluated from the thickness profile in the width direction of the sheet measured by the film thickness measuring method of the present invention, and when the sheet is out of a certain standard, the sheet is not considered as a product. Thus, it is possible to prevent the defective products from being continuously manufactured by keeping the quality of the sheet shipped to the customer at a certain level or more and adjusting / correcting the process that causes the sheet.

[0095]

EXAMPLES Now, examples in which the film thickness is measured by using the present invention will be described.

A polyester film A having a thickness of about 6 μm and a refractive index of 1.65 and a polyester film B having a thickness of about 0.7 μm and a refractive index of 1.65 have a measuring section shown in FIG. Was measured using. However, the reflected light from the film is dispersed in the range of 1100 to 2300 nm,
When the number of extrema of the spectral intensity spectrum of the reflected light from the film is less than three in the spectral range, the film thickness is calculated according to the wavelength corresponding to the extremal value of the spectral intensity spectrum and the most of the spectral intensity spectrum in advance. The interference order of the extreme value of the valley on the long wavelength side is 1
If the number of extrema of the spectral intensity spectrum is three or more, the wavelength corresponding to the extremal value of the spectral intensity spectrum is determined. , And the film thickness is calculated from the interference order estimated using the extreme value. 110 reflected light from the film
As a result of spectral analysis in the range of 0 to 2300 nm, the spectral intensity spectrum shown in FIG. 6 was obtained. As shown in FIG. 6, the number of extreme values of the spectral intensity spectrum is 1 for a film of about 0.7 μm.
One could be detected, and six could be detected with a film of about 6 μm.
In addition, with the conventional measuring instrument, it was not possible to measure with a single measuring instrument, with respect to samples in which the number of extreme values of the spectral intensity spectrum is greatly different.

The results of measuring the film thickness using the present invention from the spectral intensity spectrum shown in FIG. 6 are shown below.

First, in the polyester film A, since the number of extreme values of the spectral intensity spectrum shown in FIG. 6 is 6, the film thickness calculation method is to determine the wavelength corresponding to the extreme value of the spectral intensity spectrum and its extreme value. The film thickness calculation method for calculating the film thickness is selected from the interference order estimated using the number. The wavelengths corresponding to the peaks and valleys of the six extreme values of the spectral intensity spectrum of the polyester film A are detected, and the estimated film thickness is calculated for the detected extreme values from the wavelengths of the adjacent extreme values. Next, the interference order is calculated based on the calculated estimated film thickness, the actual interference order is estimated from the calculated interference order, and the estimated interference order and the wavelength corresponding to each extremum of the spectral intensity spectrum are calculated. The film thickness is calculated from The results are shown in Table 1.

[0099]

[Table 1]

As shown in Table 1, the film thickness calculation result is about 5.
A stable measurement result of 9 μm is shown, and an average value of 5.954 μm is the film thickness calculation result.

Since the number of extreme values of the spectral intensity spectrum shown in FIG. 6 is 1 for the polyester film B, the film thickness calculation method uses the wavelength of the extreme value of the spectral intensity spectrum and the predetermined interference order. The method for calculating the film thickness is selected. Only one extreme value of the spectral intensity spectrum of the polyester film B can be detected, and this extreme value is on the mountain side.
Since the order of the extreme value on the valley side on the longest wavelength side of the spectral intensity spectrum is previously determined to be 1, the order of this extreme value on the mountain side is determined to be 1.5. The film thickness is calculated from the determined order and the wavelength of the extreme value. The results are shown in Table 2.

[0102]

[Table 2]

As shown in Table 2, the film thickness is 0.664 μm.
Can be asked.

[0104]

As described above, according to the film thickness measuring method of the present invention, the film thickness can be measured with high accuracy even when the measurement target is in a wide range. Therefore, the thickness profile of the sheet is accurately measured by the sheet manufacturing method of the present invention,
By controlling this to a desired shape, the thickness profile can be controlled for products with a wide range of thickness, and the quality of the manufactured sheet is improved. Further, by accurately measuring the thickness profile of the sheet by the method for producing a sheet of the present invention and performing quality control using this, it is possible to prevent defective products from flowing out to the customer and cause defects. By correcting the process, it is possible to prevent further manufacturing of defective products, and as a result, it becomes possible to reduce the cost of the sheet.

[Brief description of drawings]

FIG. 1 is a flowchart of a film thickness measuring method according to an embodiment of the present invention.

FIG. 2 is a diagram showing an optical interference type film thickness measuring device according to an embodiment of the present invention.

FIG. 3 is a principle diagram of film thickness measurement using optical interference.

FIG. 4 is a diagram showing a spectral intensity spectrum in film thickness measurement using optical interference.

FIG. 5 is a diagram showing an overall schematic configuration of a sheet manufacturing facility according to an embodiment of the present invention.

FIG. 6 is a measurement result of a width-direction film thickness profile of a sheet according to an example of the present invention.

[Explanation of symbols]

20: Measurement target 21: Light source 22: Projector 23: Incident light 24: Reflected light 25: Optical path changing unit 26: Spectroscopic unit 27: Data processing device 51: Sheet 52: Stretching device 53: Extruder 54: Base 55: Cooling roll 56: Winding machine 57: Transport roll 58: Thickness gauge 59: Control means

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Claims (8)

[Claims] 1. A film thickness measuring method for obtaining a film thickness of an object to be measured from an interference waveform obtained by irradiating the object to be measured with light and dispersing reflected light or transmitted light from the object to be measured for each wavelength.
The number of extreme values of the obtained interference waveform or the amplitude of the interference waveform is compared with a preset reference value, and one film thickness calculation method is selected from a plurality of different film thickness calculation methods according to the result. A film thickness measuring method, characterized in that a film thickness calculation is performed. 2. A method of calculating a film thickness from respective wavelengths corresponding to a plurality of extreme values of an interference waveform, wherein the plurality of film thickness computing methods is determined in advance as a wavelength corresponding to an extreme value of the interference waveform. The method of calculating the film thickness from the interference order, the method of calculating the film thickness from the wavelength corresponding to the extreme value of the interference waveform and the interference order estimated using the extreme value, and the method of calculating the film thickness by curve fitting And at least two methods selected from the method of calculating the film thickness based on the result of frequency analysis of the interference waveform. 3. The film thickness calculation method according to claim 1, wherein the film thickness calculation method is selected depending on whether the number or amplitude of the extreme values of the obtained interference waveform is less than the reference value or more than the reference value. Measuring method. 4. When continuously measuring a film thickness, the reference value is composed of an upper limit value and a lower limit value, and the number or amplitude of extreme values of the obtained interference waveform is less than the upper limit value in the previous measurement. Therefore, the film thickness calculation method should be selected only when the current measurement is greater than or equal to the upper limit value, the previous measurement is greater than or equal to the lower limit value, and the current measurement is less than or equal to the lower limit value. The film thickness measuring method according to claim 1, which is performed. 5. When the number of extreme values of the interference waveform is less than a preset value, a method of calculating the film thickness from the wavelength corresponding to the extreme value of the interference waveform and the predetermined order of interference is provided. If the number of extreme values of the interference waveform is selected or more than the preset value, the method of calculating the film thickness from the wavelength corresponding to the extreme value of the interference waveform and the order of interference estimated using the extreme value is selected. It selects, The film thickness measuring method in any one of Claims 1-4 characterized by the above-mentioned. 6. A light irradiating means for irradiating a measuring object with light, a light receiving means for receiving reflected light or transmitted light from the measuring object with respect to the light from the light irradiating means, and the reflected light received by the light receiving means. A spectroscopic unit that disperses for each wavelength, a signal conversion unit that converts the light dispersed by this spectroscopic unit into an electric signal according to its intensity, and an extreme value of the signal waveform of the electric signal obtained by this signal conversion unit. A film thickness calculating method from among a plurality of different film thickness calculating methods according to the number or the amplitude of the signal waveform and the number or amplitude of the extreme values of the signal waveform detected by the detecting means. A film thickness measuring device comprising: a selecting device for selecting and a film thickness calculating device for calculating a film thickness according to the selected film thickness calculating method. 7. When a resin is discharged from a die having a gap to manufacture a sheet, the thickness of the sheet is measured using the film thickness measuring device according to claim 6, and the die is based on the obtained measurement value. A method for manufacturing a sheet, comprising controlling the gap between the sheets. 8. A program for causing a computer to execute a step of obtaining a film thickness of an object to be measured from an interference waveform obtained by irradiating the object to be measured with light and dispersing reflected light or transmitted light from the object to be measured for each wavelength. And a detection step of detecting the number of extreme values of the interference waveform or the amplitude of the interference waveform,
Depending on the number or amplitude of extreme values of the interference waveform detected in the detection step, a selection step of selecting one film thickness calculation method from a plurality of different film thickness calculation methods, and a selected film thickness calculation method. A film thickness calculating step of calculating a film thickness.