JPH0357407B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] This is a film thickness measuring device that measures the interference waveform of a transparent thin film created on a substrate using light interference.
By determining the wavelengths of any two peaks and the number of peaks between them, and calculating the film thickness from the measured values using a microcomputer, it is possible to fully automate the film thickness measurement.

[Industrial application field]

The present invention relates to a film thickness measuring device, and more particularly to an automatic film thickness measuring device that fully automatically measures the thickness of a transparent film formed on a substrate.

2. Description of the Related Art In recent semiconductor devices, such as magnetic bubble memory devices, storage densities have become more sophisticated as the amount of information increases. For this reason, the thickness of the magnetic garnet film formed on the substrate in magnetic bubble memory devices has gradually become thinner (less than 1 μm), and it has become necessary to precisely control the thickness, creating a need for a device that can accurately measure the film thickness. Ru.

[Conventional technology]

To measure the thickness of a transparent thin film 2 formed on a substrate 1 as shown in FIG.
The interference waveform is measured using the interference of L ₁ and L ₂ , the wavelength λ _i of any two peaks and the number of peaks between them are determined, and the film thickness h can be determined using the following calculation formula. .

F _i =√n ² _i −sin ² θ／λ _i θ=45゜ h=N/2｜F ₁ −F ₂ ｜N=(number of peaks)−1 Here, the refractive index n _i of the thin film is n _i =a+b/λ ² _i +c/λ ⁴ _i (Cauchy's formula).

Fig. 7 shows a conventional film thickness measuring device, where 4 is a light source, 5 is a pinhole, 6 is an objective lens, 7 is a sample, 8 is a condenser lens, 9 is a spectrometer, and 10 is a photomultiplier tube. , 11 indicate X-Y recorders, respectively. Film thickness measurement using this device involves scanning the wavelength by rotating the diffraction grating in the spectrometer 9 to obtain waveform 12.
After correcting the background from step 2 (this operation is performed automatically), the peak shape of the waveform curve is determined and whether or not to be adopted as data is determined, and the first and last peaks of this curve are determined. The film thickness was calculated by reading the wavelengths and using the number of peaks between these wavelengths.

[Problem that the invention seeks to solve]

Traditionally, all of the above work was done by the measurer.
If the waveform is distorted by noise or the like, the position of the peak becomes inaccurate, errors occur when reading the wavelength, and the analysis time becomes longer.

In view of these points, it is an object of the present invention to provide an automatic film thickness measuring device that is fully automatic, highly reliable, and capable of processing in a short time.

[Means for solving problems]

In order to solve the above problems, the present invention provides a means for detecting the swept wavelength of light of a spectrometer in which a sample to be measured is set at regular intervals, and a means for detecting at regular intervals the swept wavelength of light of a spectrometer in which a sample to be measured is set, means for reading the electric signal of the above, means for storing each wavelength-light intensity value pair, and a means for storing each wavelength-light intensity value pair by a pre-stored set of wavelength-light intensity values measured on a board, etc. means for correcting the values and drawing a reference line at the average position of the correction values; means for storing the correction values; and each curve on the positive side or negative side of the reference line of the light interference waveform curve based on the correction values. means for examining the shape of the curve and determining whether to adopt it as data; means for regressing to a quadratic curve (parabola) using the method of least squares from the data of the curve adopted by the means; and determining the roots of the parabola. , calculate the film thickness from the wavelength of the first and last peaks of the positive side curve and the value obtained by subtracting 1 from the number of peaks, and also from the negative side curve. The method is characterized in that it consists of a means for determining the film thickness by calculating the film thickness, and averaging both values to determine the film thickness of the thin film.

[Effect]

First, in order to obtain the sensitivity curve of a photomultiplier tube for correction, a substrate on which a thin film is not formed is set in the device, and the wavelength-output signal data set A() is measured. The light intensity values are stored in the storage means as a set, and then the thin film to be measured is set, and the wavelength-output signal data B is stored in the same manner.
() is taken, B() is corrected by A(), each wavelength-light intensity value is stored in a storage unit, and the film thickness can be calculated from these values by a microcomputer.

In the present invention, by having a microcomputer perform wavelength-output signal correction and film thickness calculation, fully automatic, highly reliable, and high-speed thin film measurement is possible.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.

As shown in the figure, this embodiment uses a wavelength marker 20 as a means for detecting the swept wavelength of light at regular intervals.
1, and a photomultiplier tube 2 as a means for reading an electrical signal of light at that wavelength when a signal at that wavelength is received from the spectroscope.
02, the photomul 202 and the wavelength marker 20
A/D converter 2 that A/D converts the signal of 1
1 and 22, a microcomputer 24 connected to the A/D converters 21 and 22 via an interface 23, and a display 25 and a printer 26 connected to the microcomputer. The microcomputer 24 has a CPU 241, RAM 242, and ROM 2.
43, the RAM 242 has a means for storing the wavelength-light intensity values measured on the sample as a pair, and the CPU 241 stores the wavelength-light intensity values measured on a board, etc. that have been stored in advance. means for correcting each wavelength-light intensity value of the sample as a set and drawing a reference line at the average position of the correction values, and examining the shape of each light interference waveform curve based on the correction values, A means for determining whether or not to be adopted as data, a means for regressing to a quadratic curve (parabola) using the least squares method from the data of the curves on the positive and negative sides of the reference line, and a means for determining the root of the parabola and 1/ 2 as the peak wavelength of the curve, calculate the film thickness from the wavelength of the first and last peak of the positive curve, and the value obtained by subtracting 1 from the number of peaks, and then calculate the film thickness in the same way from the negative curve. and averages both values to determine the thickness of the thin film.

The film thickness measurement procedure of this embodiment configured as described above will be explained next.

First, in order to obtain a photosensitive sensitivity curve for correction, a substrate on which a thin film is not formed is set in the apparatus and the spectrometer 20 is operated. As the spectrometer 20 operates, a signal is output from the wavelength marker 201 at regular intervals of the swept wavelength. This signal is input to the A/D converter 22, converted to a digital value, and sent to the microcomputer 24 via the interface 23.
is output to the CPU 241 of. I received this
The CPU 241 transmits the output signal of the photomultiplier 202 at that time to the A/D converter 21 and the interface 2.
Read through 3. This operation is repeated as the wavelength is swept, and the wavelength-output signal data set A() is
is stored in the RAM 242. In this case, a correction curve A( ) as shown in FIG. 2 is obtained.

Next, a thin film sample to be measured is set, and wavelength-output signal data B() is obtained in the same manner. In this case, for example, a curve B( ) as shown in FIG. 3 is obtained.
Here, [B()/{A()×(1+C×)}]×
d (where c and d are constants), convert B() to A()
This is corrected and stored in the RAM 242. The constant C is used to correct the fact that when the waveform of B() is corrected by A(), it may become a curve upward to the right or downward to the right with respect to the reference line. For example, in the case of an upward slope, if C is set to a positive value, the larger the value, the stronger the correction will be, and B()
Decrease the value of Therefore, B(), which increases as B becomes larger, is lowered. Further, when B( ) is downward to the right, if C is set to a certain negative value, the correction strength becomes weaker as C becomes larger, and in both cases, the inclination with respect to the reference line is corrected. The magnitude of the value of C is determined experimentally from the measured value. Further, d is a magnification that enlarges the value corrected as described above to a value that is easy to calculate, and the magnitude of this value is determined empirically.

Next, the average value of the waveform obtained by dividing the sum of B() by the number of measurement points (N points) is subtracted from B(), [B′()=B()−{ _N 〓 ^I=1 B()}/ N] Draw a reference line at the average position of the correction values. In this case the fourth
A curve B'() as shown in the figure is obtained. Add this to RAM
242. From this data, CPU241
The film thickness h is calculated in . The calculation procedure is shown in the flowchart of FIG.

In Fig. 5, a reference line is drawn so that the corrected data B'() is located approximately in the center of the waveform (a
figure). Next, set R=0 and cut off the negative part (Figure b). Next, it is determined whether the shape of the waveform is to be read and adopted as data (Figure c). The determination criterion is that if the curve of each data set does not intersect with the reference line at two points (corresponding to numbers 1 and 5 in figure c), this data set is rejected. Next, the positive part is regressed to a parabola using the least squares method (Figure d). Next, find the peak position from 1/2 of the sum of the roots of the quadratic equation (e
figure). Next, the wavelengths of the first and last peaks λ ₁ , λ ₂ , N
= (number of peaks between λ ₁ and λ ₂ ) −1 is determined (Figure f).
Next, the film thickness is calculated using the above formula, and this film thickness is set as _h1 . Next, to calculate the negative part, B′()
=-B'() and R=1. Return this and calculate it in the same way as the positive part, and use it as the membrane pressure _h2 .
Next, h=h ₁ +h ₂ /2 is calculated and the film thickness h is output.

In this way, according to this embodiment, once the thin film sample to be measured is set and the apparatus is started, all subsequent work is done by the apparatus itself, eliminating mistakes that occur during conventional manual data analysis. , high reliability can be obtained. In addition, even if the waveform is deformed due to noise, etc., it has the effect of canceling out the error when regressing to the quadratic curve. Therefore, it is possible to suppress the repetition accuracy to 1% or less (3% with the conventional method), and further improve measurement analysis. The time is about half that of the conventional method.

Note that the data value of the photomal sensitivity curve hardly changes if the measurement conditions are kept constant, so store this data A() in advance in a file memory (for example, magnetic tape) and read it out during calculation. It can also be processed. In this way, the operation of measuring the substrate every time can be omitted, and the measurement time can be further shortened.

〔Effect of the invention〕

As described above, according to the present invention, the thickness of a thin film can be automatically measured quickly and accurately with an extremely simple configuration, and is extremely useful in practice.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a diagram showing the sensitivity curve of the photomultiplier, Fig. 3 is a diagram showing the optical interference waveform of the thin film to be measured, and Fig. 4 is a diagram showing the waveform of Fig. 3. Figure 5 shows the waveform corrected using the sensitivity curve in Figure 2.
The figure is a flowchart showing the software of the microcomputer, and Figure 6 is an illustration of light interference.
FIG. 7 is a diagram showing a conventional film thickness measuring device. In FIG. 1, 20...spectroscope, 201...wavelength marker, 202...photometer, 21, 22...A/
D converter, 23...interface, 24...
Microcomputer, 241...CPU, 242
...RAM, 243...ROM, 25...CRT, 26...
It's a printer.

Claims (1)

[Scope of Claims] 1 a) Means for detecting at regular intervals the swept wavelength of light of a spectrometer in which a sample to be measured is set; b) When receiving a signal at that wavelength, an electric signal of light at that wavelength c) Means for storing each wavelength-light intensity value pair; d) Correcting the value of c) with a pre-stored wavelength-light intensity value pair measured on a board, etc. , means for drawing a reference line at the average position of the correction values; e) means for storing the value calculated in step d); f) one of the positive or negative side curves of the reference line of the optical interference waveform curve based on the correction values; g) means for regressing the curve data adopted in step f) to a quadratic curve (parabola) using the method of least squares, h) Means for finding the root of the parabola in g) above and setting 1/2 of it as the peak wavelength of the curve, i) Subtracting 1 from the wavelength of the first and last peaks of the positive curve and the number of peaks between these wavelengths; An automatic film thickness measuring device characterized by comprising means for determining the film thickness from the obtained value, further determining the film thickness in the same manner from the negative side curve, and averaging both to determine the film thickness of the thin film. .