JPS627266B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric film thickness deposition method for controlling the thickness of a thin film when depositing it on a substrate, for example.

Currently, the following four methods are being considered as photoelectric film thickness control methods. These are monochromatic photometry, two-color photometry, wavelength scanning method, and ellipsometry. Monochromatic photometry is a method in which the spectral reflectance or spectral transmittance at the required film thickness is calculated in advance, and a thin film is formed until the detection signal at the wavelength that has the maximum or minimum value reaches the maximum or minimum. The device itself is small and easy to handle, so it is the most commonly used device.
It is difficult to detect the peak value of the detection signal, and the control accuracy cannot be said to be sufficient. In the two-color photometry method, the device itself is small and relatively easy to handle, and the measurement accuracy is good, but it generally requires two narrowband interference filters, and it is difficult to obtain a narrowband filter for the desired wavelength, and it is difficult to control the film thickness. It has the disadvantage that it cannot be chosen arbitrarily. The wavelength scanning method has very good measurement accuracy, but the equipment itself is large-scale.
The drawback is that setting the spectral sensitivity before forming the thin film is complicated and lacks stability. Ellipsometry is too sensitive and is easily influenced by the underlying substrate, is difficult to control for non-uniform films, and is extremely difficult to analyze for multilayer films.

The present invention provides a photoelectric film thickness control method with good stability and high accuracy, unlike the photoelectric film thickness control method which has the above-mentioned drawbacks.

The details will be explained below with reference to the drawings, taking as an example the control during vacuum deposition of a dielectric thin film.

FIG. 1 is a block diagram showing an embodiment of the present invention. Vapor deposition substrate 1 provided in metal bell gear 11
3 is installed on a substrate holder fixed to the base plate 12 to prevent the optical axis of the signal light A from shifting. Signal light A is modulated at 3KHz by a chopper 32 from a halogen lamp light source 31, and is then modulated by a lens 33.
The light is intermittently incident as parallel light. On the other hand, reference light B is 3KHz with a 180° phase difference from signal light A.
A chopper 32 extracts the modulated light from the lens 34 alternately with the signal light A. The signal light A reflected by the substrate 13 passes through the reference glass 20, and the reference light B is reflected by the reference glass 20 and alternately enters the high-speed scanning spectrometer 40. In this example, a TeO ₂ high-speed spectroscopic element 41 was used. The separated modulated light is converted into an electrical signal by a photomultiplier tube 42. The converted electrical signal is passed through a bandpass amplifier,
The signal is converted into a digital signal by an analog signal processing device 51 consisting of an analog data processor, a multi-contact potentiometer, a divider, and an A/D converter. The converted signal is input to digital signal processing device 60. The digital signal processing device 60 consists of a digital data processor, a storage circuit, a control circuit, a synchronization circuit, etc., inputs the detected signal value and its wavelength value to the electronic computer 70, and issues an analysis command. The electronic computer 70 determines the wavelength having the extreme value using the N-point comparison method, and when the required film thickness is reached, sends a vapor deposition stop command to the control device 80 to stop the vapor deposition. Note that the N-point comparison method described above is a method of finding the extreme value using f(x) at N points in a certain range [x ₁ , x _o ] of a continuous function such as spectral transmission characteristics. exists, then f at both ends
(x ₁ ) and f(x _o ), and the remaining f
(x), for example, f(x ₁ )>f
(x _o ), then f has a value larger than f(x ₁ )
(x _on ) and f(x _o-n+1 ) smaller than f(x ₁ ) continuously exist. At this time, a maximum value exists between (x _on +x ₁ )/2 and (x _o-n+1 +x ₁ )/2. This method uses both f(x _on ), f(x _o-n+1 ), and f(x ₁ ) and finally uses an interpolation method to numerically calculate the value of x having the maximum value. Moreover, when finding the minimum value, it can be obtained by finding a small value in the opposite way to the above.

High-speed spectrometer 40 using TeO ₂ high-speed spectroscopic element 41
It is possible to perform spectroscopy in the visible wavelength region of 400 to 700 nm by scanning the frequency of the high frequency oscillator 52 of 100 to 47 MHz.
At this time, it is possible to perform spectroscopy at 31 wavelengths at intervals of about 10 nm, and by switching, it is possible to select 9 of these points and measure the spectral reflectance. It takes about 0.25 seconds for one scan, and the signal is averaged about 100 times per point, and the S/N is
improving the ratio. and 9 by electronic computer.
The point comparison method was used to calculate the extreme values and their wavelengths, and the time required for this was approximately 0.7 seconds. In other words, the extreme value of the spectral reflectance and its wavelength can be calculated at a rate of about 1 time/second.

The control obtained in this way is
The accuracy is high because it uses the point comparison method.
It also has good stability.

In manufacturing the red-enhanced reflection filter shown in Figure 2, which has a three-layer structure of TiO ₂ -SiO ₂ -TiO ₂ and has a reflection peak at 670 nm, measurements were taken at nine points from 600 nm to 680 nm, taking into account moisture absorption after the thin film was formed. Substrate temperature 390℃
When vapor deposition was performed with a reflection peak of 640 nm, the reflection peak was shifted by about 30 nm after being taken out into the air due to moisture absorption, and a reflection peak was obtained at 670 nm.

The curve in FIG. 2 shows the spectral characteristics after vapor deposition, and the curve shows the spectral characteristics after being taken out into the air.

The accuracy at this time was that vapor deposition was possible within an error range of 25 nm or less.

By the way, according to the present invention, it is also possible to perform vapor deposition while evaluating the entire spectral characteristics.

For example, in a cyan filter with a 12-layer structure made of TiO ₂ -SiO ₂ in Fig. 3, curves A and B
It is also possible to simultaneously monitor the extreme values of ripples that occur at short wavelengths, such as in TiO ₂ -SiO ₂ two-layer and five-layer structures, etc. It is possible to simultaneously monitor the extreme values of ripples that occur at short wavelengths, such as in TiO 2 -SiO 2 two-layer and five-layer structures. It is also possible to calculate extreme values and their wavelengths. Therefore, the film thickness can be easily controlled by utilizing the large change in the ripple extreme value. In addition, when depositing the final layer (12th layer) of curve C, by adding the measured values in the wavelength range of 400 to 560 nm and performing deposition until the added value becomes the minimum, it is possible to achieve a method with less ripple and a half-value wavelength. A stable filter can be obtained.

FIG. 3 shows the reflection peak at 651.6 nm, which was obtained by vapor deposition at a substrate temperature of 390° C., and after the wavelength shift by taking it out in the air, the reflection peak was 602 nm at half the wavelength of 680 nm. Note that nd=λ/4 for the 1st to 11th layers, nd=λ/8λ= for the 12th layer
It is 651.6nm.

As explained above, according to the present invention, the spectral transmittance or spectral reflectance of the substrate is measured at at least three wavelengths, and the extreme value and the wavelength having the extreme value are calculated and determined. Since the film thickness is controlled, highly accurate and stable control can be performed.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
3 and 3 are diagrams showing the spectral characteristics of the filter produced according to the present invention. DESCRIPTION OF SYMBOLS 11... Metal bell gear, 12... Base plate, 13... Evaporation substrate, 20... Reference glass, 3
1... Light source, 32... Chiyotsupa, 33, 34...
Lens, 40... High-speed scanning spectrometer, 41...
TeO ₂ high-speed spectroscopic element, 42...Photoelectron intensifier, 5
1... Analog signal processing device, 52... High frequency oscillator, 60... Digital signal processing device, 70...
...Electronic computer, 80...Control device.

Claims (1)

[Claims] 1 Detect the spectral transmittance or spectral reflectance of the thin film formed on the thin film forming substrate at three or more wavelengths intermittently, and use the detected transmittance or reflectance value to determine the spectral transmittance or spectral reflectance. In a film thickness control method comprising means for calculating the wavelength having the maximum value or minimum value of reflectance and detecting the thickness of the thin film, the detection wavelength range is set to a wavelength including the wavelength having the maximum value or the minimum value. A film thickness control method characterized by: