JPH09113228A - Film thickness meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a film thickness meter to measure the thickness of a thin film with a high accuracy and, at the same time, to simplify the optical system of the meter by obtaining intensity signals corresponding to individual CCD elements by fetching the light intensity distribution on CCD elements and A/D-converting the distribution, and then, comparing the signals with a threshold. SOLUTION: The intensity of the light which enters CCD elements 3 after the light is reflected by the front and rear surfaces of a cylindrical film 12 sensed by each element 3 is outputted in due time synchronously to a readout timing signal. The light intensity distribution on the elements 3 is obtained by inputting the output and readout timing signal of the element 3 to a synchronous A/D converter 5 after fetching the output and signal from a signal converter 4 and converting the light quantity data on the elements 3 into digital values indicating the intensities of the light. A threshold processor 6 compares a threshold set in a threshold storing means 10 with the intensity distribution and binarizes the distribution into binarized signals by judging whether or not the distribution exceeds the threshold. Then the processor 6 finds the distance between the peaks of the distribution indicated by means of an inter-peak computing means 7 and obtains the actual thickness of the film 12 by multiplying the distance by a coefficient stored in advance in means 11 for storing number of element/ film thickness converting coefficient by means of a multiplying means 8.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a film thickness meter for measuring the thickness of a transparent film.

[0002]

2. Description of the Related Art A method of irradiating a film with a laser beam and measuring the film thickness by using the optical path difference of the reflected light from the front surface and the back surface of the film makes it possible to measure the thickness of a transparent film from one side. This is very useful because the tubular film can be measured from the outside. Further, among the film thickness meters based on this principle, the film thickness meter using the semiconductor laser light emitting element for light emission and the CCD element for light reception has no moving parts, so that it is durable and easy to handle when used online for industrial purposes. Although the above is suitable, it is difficult to measure the thickness of 300 μm or less, and it has been desired to expand the thickness.

[0003]

The reason why it is difficult to measure a thin object is that the output of the CCD element is processed as an analog time-series signal that is not discretized. Therefore, a filter for removing the carrier wave of the CCD element is required and its application. This is because the waveform becomes dull. As a countermeasure against this, the laser light has been made thin so far, but when the spot diameter of this reflected light becomes about 10 times smaller than the size of each light receiving element which constitutes the CCD element, the CCD element is However, even if the optical path difference could be distinguished, the waveform was blunted by the effect of the filter, making measurement impossible and making a significant improvement difficult. Further, when calculating the thickness from the filtered CCD element signal in the thickness calculation, binarization using a threshold value is performed, and the difference in rising time is used as the thickness signal, so that the distribution shape of reflected light and its peak are calculated. There was a measurement error due to the relationship between height and threshold.

[0004]

A film in which a laser light source for detecting an optical path difference of laser light reflected from a front surface and a back surface of a transparent film as a difference in a light receiving position of a CCD element and the CCD element are integrated. In the thickness meter, the light intensity distribution on the CCD element is taken out as a time-series signal or in its entirety at the same time, and in the case of the time-series signal, A / D conversion is performed synchronously by the read-out signals of the CCD element generated at the same time, Further, when the whole is taken out in parallel at the same time, the output signals of the individual CCD elements are respectively A / D converted to obtain an intensity signal for each CCD element, and the intensity signal is preset. It is determined whether the value is larger or smaller than the value, a binary signal is obtained, and the distance between the centers of the two peaks due to the reflection from the front surface and the back surface that appears in the binary signal is obtained, and this distance is calculated as the CC value.
The difference between the optical paths of the reflected light from the front surface and the back surface on the D element is used, and the obtained distance between the centers is multiplied by a coefficient determined by measurement in advance to output the film thickness. As a result, the above problem can be solved by continuously measuring the film thickness by repeating this.

In the above process of the film thickness meter, the C
The autocorrelation function of the intensity signal for each of the CCD elements obtained from the output of the CD element is obtained, and the distance between the central peak and either of the peaks on both sides thereof is calculated to obtain the reflected light from the front surface and the back surface. And the optical path difference on the CCD element of
The above problem can be solved by multiplying by a coefficient determined in advance to determine the film thickness.

Further, in the above processing of the film thickness meter, the CC
By processing the intensity signal for each of the CCD elements obtained from the output of the D element, the time range in which the reflected light from the front surface and the back surface exists is recorded, and the signal of the signal is recorded in the next processing. It has been found that the time required for processing can be reduced by treating only a time range that is wider than the recorded time range by a preset range.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. FIG. 1 shows the entire configuration, FIG. 2 shows the intensity distribution of the amount of received light on each element of the CCD element, and FIGS. 3 to 5 show the contents of the signal being processed.
1 to 4 in FIG. 1 are parts constituting a commercially available laser type film thickness meter. In the present invention, the optical system, the laser light source, and the CC
It is used only for driving the D element. Laser light emitted from the laser light source 2 is reflected by the front surface and the back surface of the cylindrical film 12, and enters the CCD element 3 through different optical paths. Therefore, the CCD element 3 in which the light receiving element is arranged on a straight line
There are two intensity distributions of the light reflected from the front surface and the back surface. The light intensity distribution appearing on this CCD element is shown in FIG.
Shown in

As described above, the light intensity sensed by each of the elements on the CCD element 3 is output by the normal CCD element 3 in synchronism with the reading timing signal. This output and the read timing signal of the CCD element 3 are taken out from the signal converter 4 and input to the synchronous A / D converter 5.
In the synchronous A / D converter 5, each light receiving CCD shown in FIG. 2 is based on the read timing signal from the CCD element 3.
The light amount data on the element 3 is converted into a digital value indicating each intensity. Therefore, the light intensity distribution on the CCD element 3 shown in FIG. 2 can be obtained without being affected by the carrier wave at the time of reading the CCD element 3. Here, for ease of viewing, this waveform is illustrated in the form of a solid line in FIG. Now that the waveform is digitized,
Subsequent processing can be easily realized by computer software. Of course, it can also be realized by using hardware.

The waveform processing method will be described below. The waveform is converted into a film thickness using the thickness calculating means indicated by 6 to 11. The threshold value processing device 6 compares the intensity distribution with a threshold value 17 which is set in the threshold value recording means 10 and which is set to an appropriate value by an experiment, and judges whether or not the intensity distribution is exceeded. And obtain the result as a rectangular wave as shown in FIG. Of course, the threshold value may not be determined in advance, and it is also possible to perform the calculation on the spot from the waveform for each time using an index such that the ratio of the data on the threshold value is constant. Next, a method of measuring the distance between the peaks of the intensity distribution indicated by the peak-to-peak calculation means 7 will be described. Based on the data of FIG. 4, the time difference between the centers of the mountains represented by the reflected lights 15 and 16 of FIG. 3 is calculated. For that purpose, for example, the number of elements from the left end to the rising edge and the falling edge shown in the order of 18, 19, 20, 21 is calculated, and is calculated as X1, X2, X.
3 and X4, the calculation can be performed by (X3 + X4-X1-X2) / 2. Next, the actual film thickness can be obtained by multiplying the distance by a coefficient for converting the difference in the number of CCD elements 3 stored in the recording unit 11 preset by the multiplying unit 8 into the film thickness. The thickness thus obtained can be output and displayed outside by the output means 9. After this, the same measurement is repeated to enable continuous film thickness measurement.

Next, another embodiment will be described. CCD device 3 which should have a film thickness when realizing the above film thickness meter
Taking the autocorrelation function of the light intensity signal shown in FIG. 3 to measure between the upper two peaks, the result is shown in FIG. 5, and the location of the first peak excluding the 0 part is the distance between the two peaks. . This means was replaced with 6, 7 and 10 in FIG. 1 to construct a film thickness meter.

Another embodiment will be described. When the time for the film thickness calculation is not sufficient, the waveform selection device 12 is inserted between the synchronous AD converter 5 and the threshold value processing device 6 as shown in FIG. The element number represented by X1 and the element number represented by X4 are recorded, and in the next calculation, the recorded value and the reflected light existing area extension length recording means 14 are not calculated from the end element. Predetermined variation range δ saved
Using, the processing time can be shortened by taking out only the range of X1−δ and X4 + δ and making it the target of the above film thickness calculation. X1 is determined by the positional relationship between the sensor 1 and the film 12 to be measured, but does not change significantly between measurements. Therefore, the fluctuation range δ can be set to an appropriate value in advance.

By using the film thickness meter described above, the thickness of the inflation film in the circumferential direction can be measured in correspondence with the accurate position on the film. At this time, the sensor 1 shown in FIG. 7 is rotationally moved, and the interface is installed so that the angle at that time is detected by the rotary encoder 23 and taken in. With this configuration, the sensor 1 is first rotated clockwise at an appropriate speed, the film thickness is measured by the film thickness meter 22 according to the present invention at each appropriate angle, and recorded in the recording means 24. Therefore, the recording position in the recording means 24 corresponds to the position where the film thickness is measured. When the measurement for one rotation is completed, the sensor 1 is rotated counterclockwise at the same speed to perform the measurement, and the measurement is recorded in the recording means 25. The number of data to be acquired is the same in both clockwise and counterclockwise directions. It depends on the required angular resolution in the rotation direction.
It was divided into 56. Of course, it is not necessary that the numbers of data at the time of measurement match if the numbers in the recording means 24 and 25 match the resolution. However, more than the number satisfying the required angular resolution is required.

These data are shown as measurement results 30 and 31 from the original angle shown by the dotted line of the correct angle-thickness relationship 29 as shown in FIG. 8 when the sensor contacts the blown film and rotates. As you can see, they are offset from each other by the same angle. Recording means 24 and 2
The thickness data stored in 5 is the cross-correlation function calculation means 26.
And a waveform as shown in FIG. 9 is obtained. If there is no rotational movement of the inflation film due to the rotation of the sensor 1, the waveforms of the measurement results 30 and 31 applied to the recording means 24 and 25 agree, and the cross-correlation function of FIG. 9 should have a peak in the center. Is. When there is a shift as in FIG. 8, the peak of the cross-correlation function in FIG. 9 shifts from the center, and this shift indicates the waveform shift of the measurement results 30, 31. Since the measurement results 30 and 31 deviate back and forth, 1/2 of the detected deviations are the actual deviations. Finally, the data stored in the recording means 24 to 25 is corrected by the device data shifter 27 that shifts the data by the shift calculated by the cross-correlation function calculating means 26, and the thickness corresponding to the angle is output to the output device 28. Write out and get the output shown in FIG. Note that the data for one rotation can be shifted without omission by replenishing the portion before or after the data that has become blank due to the data shifting operation, which has protruded backward or forward by this shifting operation. According to the above-described embodiment, it is possible to perform the film movement correction by detecting the thickness of the relatively thin film and measuring the movement in the circumferential direction, which have been difficult until now.

[0014]

EFFECTS OF THE INVENTION Even if the same laser light source and CCD light receiving element as in the prior art are used, it is possible to measure thinner objects than before, and high-precision measurement is possible. Further, when measuring the same thickness, a thicker laser beam can be used, and the optical system can be simplified. The film thickness meter according to the present method is particularly effective when measuring an inflation film that can be measured only from one side.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a film thickness meter of the present invention.

FIG. 2 is a light intensity distribution on the CCD device of FIG.

FIG. 3 is a digitized light intensity distribution of the signal of FIG.

FIG. 4 is a binarized light intensity distribution of FIG.

5 is an autocorrelation function of the light intensity distribution of FIG.

FIG. 6 is an overall configuration diagram of a film thickness meter having a calculation range narrowing function of the present invention.

FIG. 7 is an overall configuration diagram for measuring a film thickness distribution in the circumferential direction of an inflation film of the present invention.

FIG. 8 shows the influence of film movement due to the contact movement of the film thickness meter of FIG.

FIG. 9 is a cross-correlation function of the waveform of FIG.

FIG. 10 is a relation angle-thickness relationship output obtained in FIG. 7.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 sensor 2 laser light source 3 CCD element 4 signal converter 5 synchronous AD converter 6 threshold processing device 7 peak-to-peak calculation means 8 multiplication means 9 calculation result output means 10 threshold value storage means 11 element number film thickness conversion coefficient Storage means 12 Film to be measured 13 Reflected light existing area recording means 14 Reflected light existing area extended length recording means 15 Reflected light from film surface 16 Reflected light from film back surface 17 Threshold 18 Surface reflected light intensity distribution rise 19 Surface reflected light Intensity distribution fall 20 Back surface reflected light intensity distribution rising 21 Back surface reflected light intensity distribution falling 22 Film thickness gauge 23 according to the present invention 23 Angle measuring device 24 Recording means for clockwise thickness distribution 25 Measurement of counterclockwise thickness distribution Means 26 Cross-correlation function computing means 27 Data shifter 28 Output device 29 Correct angle A relationship between the thickness (estimated) 30 of the angle and the thickness of the measurement results 31 counterclockwise angle and thickness of the clockwise measurement result 32 shift amount calculation results

Claims (3)

[Claims] 1. A film thickness meter in which a laser light source for detecting an optical path difference of laser light reflected from a front surface and a back surface of a transparent film as a difference between light receiving positions of a CCD element and the CCD element are integrated, The light intensity distribution on the CCD element is taken out as a time-series signal or the whole is taken out at the same time, and in the case of the time-series signal, it is synchronously A / D-converted by the read-out signals of the CCD element which are generated at the same time, and the whole is put in parallel. In the case of taking out simultaneously, the output signals of the individual CCD elements are respectively A / D converted to obtain an intensity signal for each CCD element, and whether the intensity signal is larger than a preset threshold value or not. It is judged whether it is small or not, and a binary signal is obtained, and the distance between the centers of the two peaks appearing in the binary signal due to reflection from the front surface and the back surface is obtained, and this distance is determined from the front surface and the back surface on the CCD element Reflected light A film thickness meter having a system configuration in which the obtained distance between centers is used as a road difference and is multiplied by a coefficient determined in advance to output the thickness of a film, and the above is repeated for one cycle. 2. The autocorrelation function of the intensity signal for each of the CCD elements obtained from the output of the CCD element according to claim 1, wherein an autocorrelation function of the center signal and either of the peaks on both sides thereof are obtained. A film thickness meter in which the distance is defined as the optical path difference of the reflected light from the front surface and the back surface on the CCD element and the coefficient is multiplied to obtain the film thickness. 3. The time range in which the reflected light from the front surface and the back surface exists in the processing of the intensity signal for each of the CCD elements obtained from the output of the CCD element according to claim 1 or 2. In the next processing, the film thickness meter reduces the time required for processing by processing only a time range that is wider than the recorded time range of the signal by a preset range.