JPS58140605A - Controlling method of thickness of optical thin film - Google Patents

Abstract

PURPOSE:To obtain prescribed film thickness with high accuracy in controlling of the optical film thickness of vapor deposited thin films by passing monochromatic light through the thin films during vapor deposition of the thin films and measuring the inverse proportional value of transmittance. CONSTITUTION:An evaporating source material 3 placed on the inner side of an opening/closing device 2 is heated in a vacuum vessel 1. Monochromatic light is projected from a light projector 6 to the substrate 5 to be deposited in a circular cover 4 and the light passed through the substrate 5 is fed to a measuring mechanism 7. The incident light in the mechanism 7 is passed through a photodetecting part 8 and is intensified with an amplifier 9. The ratio between the amplitude which is the inverse number of the transmittance of the monochromatic incident light and the constant amplitude determined by the refractive index of the evaporating source material is determined with constant power sources 10, 10' and calculators 11, 11', then the outputs which are equal to the square of the sine of optical phase angles and change periodically with an increase in optical film thickness are drawn by a recorder 12. The vapor deposition is suspended by the device 2 upon attaining of the required optical film thickness, whereby the thin films are formed to the prescribed film thickness with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the optical thickness of a deposited thin film, which is characterized in that a predetermined film thickness is obtained by measuring the inverse proportional value of monochromatic incident transmitted light. 0 Light-receiving equipment such as lenses and prisms [1111 attached] Vacuum deposition, which has been carried out to improve light-receiving effects such as transparency and spectral properties, is difficult because the thin film formation is delicate and tends to lack stability.
Until now, this work has been left to a very limited number of skilled engineers, and as a result, it has become impossible to meet the demand for thin films that has accompanied the recent advances in light-receiving equipment.

The film thickness measurement method that has been used to date to ensure proper thin film formation utilizes the interference of monochromatic light that hits the thin film to generate a signal that shows an intensity proportional to the transmitted or reflected light. It was done using

In this method, when the optical film thickness is near the outer quadrant of the wavelength of monochromatic light, the change in monochromatic transmitted light or reflected light due to the change in optical film thickness becomes significantly small, resulting in a lack of accuracy in measurement; It is not possible to measure the thickness, and there is a regret that it is not possible to keep up with the increasing complexity and variety of light receiving equipment that is strongly required at present.
Although it is possible to measure the mass film thickness using a crystal resonator plate, which is clearly emphasized by P. Rastis and G. Sarapuri et al., it is not possible to immediately measure the optical film thickness, which is optically defined, and the JOOC Vapor deposition carried out at high temperatures from J zocS to This method avoids the drawbacks seen in the film thickness control method of 2005 and enables mass production of high-precision light receiving equipment without increasing the cost. First, the principle behind the invention will be described. the refractive index of n, respectively.

N, the thickness of the thin film formed by the evaporation source material is d, and the optical film thickness is N.
d, and its optical phase angle is θ=(2/λ)N
a, the wavelength in vacuum of monochromatic light passing through a thin film is T, the transmittance is T, the reciprocal of T is A, a=(1+n)'', b-n/N
If s c=(b+n)"-a, then according to the principle of interference, m (a+c81n'θ)/4n・-・・・・・・・・・・
It is expressed as +11. If A when no vapor deposition source substance is attached is written as Ao, then θ
= r (1) F) Ao=a/4n λ 1(x o, 1.2.3.・-・・・・・・・・・・・・;
If Nd = 7 (+1 to 2)), = A1, then θ = 90° x (+1 to 2), and from (1), A
=(a0c)/4nyotteAo-mu=-c sin'
θ/4n・・・・・・・・・・・・・・・・・・−
・・・・・・+I+Ao−＾= c/4n・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...(i) 8 (Muo A)/(Muo-A)=si
n”＃・・・・・・・・・・・・・・・・・・
・・・・・・・・・ The formula (rin) + 1) shows the reciprocal of the transmittance at any film thickness when the origin is the reciprocal of the transmittance when no evaporation source substance is attached, Equation (1) shows the constant amplitude value of the reciprocal of transmitted light when the optical film thickness is λ 2 (2+1). Equation (1) shows that the ratio of the amplitude of the reciprocal of the transmittance of monochromatic incident light to the constant amplitude determined by the refractive index of the material to be evaporated and the evaporation source material is a function only of the optical phase angle θ, and the ratio is expressed by the square of the sine. This shows that the optical film thickness N(l) changes periodically as the optical film thickness N(l) increases. Therefore, by observing the output expressed by the formula (1),... The optical film thickness can be easily controlled.

121 (Since the m1 formula is unrelated to the refractive index of the evaporation target material and the evaporation source material, any optical film thickness can be easily and accurately controlled even when the refractive index is unknown.

(3) Since the arbitrary film thickness can be easily controlled, θ can be set to an arbitrary value, thereby making p the conventional λ, (2 + 1) x? The accuracy is dramatically increased compared to the method of controlling using θ. The maximum accuracy can be obtained by
Tol) when θ = 45° + 906 The evaporation source material (3) placed inside the switch (2) is heated, and the material to be evaporated (5) located inside/in the dome (4) is exposed to monochromatic light from the K projector (6). The light that has passed through the material to be deposited (5) is sent to the measuring mechanism (7).In the measuring mechanism (7), the incident light is passed through the light receiving part (8) and the amplified part (
9), and +11 from the constant voltage gradient ai and the calculator uajK.
The composition value shown on the left side, and therefore the value proportional to the squared sine value on the right side, is drawn as a signal on the recorder (2), and when the required optical film thickness is reached, the vapor deposition is stopped by a switch.

Next, examples of the present invention that have been actually measured using one specific numerical value will be listed.

(b) The optical film thickness is 1.2574 of the wavelength of monochromatic incident light (
Example of control using a focused electron beam with a phase angle of 112.5°) Using the apparatus shown schematically in FIG.
/10' high vacuum, the source material to be evaporated [j The mechanism schematically shown in FIG. 2 allows light with a wavelength of 1000 angstroms to pass through the set, resulting in an output of 0.05 nm as shown in FIG. 3. Ij41 (sin Lee sin' (1
115°) 1α854), the vapor deposition was stopped by a switch. After the deposition was completed, the material to be deposited (5) was taken out and measured with a spectrometer, and it was confirmed that the optical film thickness could be controlled to /2jλ/4. Control example of forming a multilayer film A cavity-type band-pass filter consisting of 23 thin films of zinc sulfide, Zn8, and cryolite, each of which has a film thickness equal to a quarter of the wavelength, is made of a resistor in a high vacuum. Wavelength i of incident light formed by heating; 1j
44 CoO angstroms, optical film thickness (phase angle): 2230 for a single cavity layer, //2 for alternate layers. Jo, and the center wavelength of the filter was set to 1,770 on guest worm. As a result, a filter with the spectral characteristics shown in Fig. μ can be fabricated with a film thickness error of 0. j It was possible to manufacture it under the conditions of 4 or less.

(c) Control example of supercoating of KH2-j K heated at /jOcK in a high vacuum of 1/10'' of 1 torr
H2-sK, zinc ilide Zn8, barium fluoride BaF
The optical film thickness (phase angle) of 1m is Oo, +120, respectively.
A J-layer symmetrical anti-reflection film made of ZnS s BaFs was coated on the substrate to form an anti-reflection film having a transmittance shown in FIG.

The present invention secures high-performance characteristics as well as reproducibility that shows typical A1 (B), (C), and K types in terms of film thickness. When manufacturing is not only in the field of widely used light receiving equipment, but also in fields such as medical equipment and optical communication, which have recently become popular, it is necessary to check whether the calculated value and m1ll match, or if the As the film thickness can be set accurately to any value, it is suitable for a wide range of thin film applications and exhibits remarkable effectiveness.

[Brief explanation of drawings]

The drawings show embodiments (a), (b), and (c) of the present invention, and FIGS. 1, 2, and 3 show the processing device, measuring mechanism, and signal characteristics of (a), respectively. Figure 5 shows the spectral characteristics of 10) and (/→, respectively. In the figure, (1) is the vacuum chamber, (2) is the switch, and +31 F.
ii source substance, (4) rotating fornix, (5) Fi fumigation 7IIN41! J quality (6) is the emitter, (7) is the measurement mechanism, (8) is the light receiving part, (9) is the intensifier part, the constant power supply for AI,
a]) Qltl is a calculator, (2) is a recorder, LFi light,
P is the recorder output, S is the starting point, T is the transmittance, λ is the wavelength, θ
is the optical phase angle, and μ is micro, which means -10th of 7 millimeters. Patent applicant: M Koshin Kogaku (and others)

Claims (1)

[Claims] A method of controlling a predetermined optical film thickness by passing monochromatic light through the thin film and measuring the inversely proportional value of its transmittance during thin film deposition.・