JPS60228674A - Method for controlling film thickness - Google Patents

Abstract

PURPOSE:To control film thickness in addition to integer times of lambdao/4 as well by comparing the information obtd. from a detecting part which detects the change rate of the quantity of transmitted light with respect to the designed wavelength of a sample substrate and a setting part and adjusting a shutter which shuts off vapor flow. CONSTITUTION:The change rate of the quantity of the transmitted light with respect to the design wavelength of the sample substrate 2 under formation of the thin film is detected in the detecting part 34. The change rate of the quantity of the transmitted light until the optical film thickness of the thin film formed on the substrate 2 attains a desired value is outputted as information in the setting part 30. Both sets of the above-described detection information are compared and when the information obtd. from the part 34 is made identical with the information on the desired optical film thickness set in the part 30, a control part 8 for vapor deposition is controlled to control the thin film to be formed on the substrate 2. Said control part 8 controls an evaporating source 6 and the shutter 7 which shuts off the vapor flow evaporating therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of controlling film thickness when forming an optical thin film by vacuum deposition.

2.B-7 Structure of conventional example and its problems It is well known that optical thin films such as antireflection films are formed on the surfaces of optical components such as lenses. Also,
In recent years, with the development of light wave technology, opportunities to form and use optical thin films with various characteristics on the surfaces of optical components have increased. As mentioned above, vacuum evaporation is generally used as a means of forming optical thin films on the surfaces of optical components, but in the case of optical thin films, the film thickness of each layer can be determined with relative precision whether it is a single layer film or a multilayer film. It is important to control.

Conventionally, as a means for controlling the thickness of an optical thin film, a method of controlling the film thickness by measuring the amount of light transmitted through a sample substrate during thin film formation is often used.

A conventional film thickness control method will be described below with reference to the drawings. Figure 1 shows a configuration diagram of a vacuum evaporation apparatus showing a conventional film thickness control method, in which 1 indicates a light projector that emits a modulated light flux for film thickness control, and a sample substrate for 2-tri film thickness monitoring. , 3 is a wavelength selection filter, 4 is a light flux detection unit for film thickness control, 5 is a display unit that displays information corresponding to the amount of change in the amount of transmitted light of the sample substrate 2, 6 is an evaporation source, 7 is a shutter for controlling the evaporation flow from the evaporation source 6; 8 is a evaporation control section for controlling the Iri evaporation source 6 and the shutter 7; 9 is a vacuum evaporation tank.

A method of controlling the film thickness of the vacuum evaporation apparatus configured as described above will be described below. The modulated light beam emitted from the light projecting unit 1 passes through a window 10 provided in the vacuum deposition tank 9, and passes through the window 10 provided in the vacuum deposition tank 9.
Guided within. The light flux is normally modulated at about 1000Hz in order to eliminate stray light from evaporation sources and the like. The light flux guided into the vacuum deposition tank passes through a sample substrate 2 for film thickness monitoring, and then passes through a window 1.
1. The light passes through a wavelength selection filter 3, selects a wavelength for film thickness control, and enters a detection unit 4, such as a photoelectric converter.

The energy of the light beam is usually converted and amplified into an electric signal in the detection section 4, and a signal corresponding to the amount of transmitted light is displayed on the display section 5.

The amount of transmitted light theoretically depends on the optical thickness of the thin film.If the refractive index of the thin film is lower than the refractive index of the substrate, the amount of transmitted light will depend on the optical thickness of the thin film, and if the refractive index of the thin film is higher than the refractive index of the substrate, it will be λ of the design wavelength λO changes as shown in the figure. Since it is known that the extreme value is reached when the value is an integer multiple of /4, the extreme value is read from the display section 5, and the evaporation flow from the evaporation source 6 is shut off by the evaporation control section 8 using the shutter 7. The optical thickness of the thin film is controlled by this method. In other words, in the past, the design wavelength was basically λ. λ. The smokeological film thickness was controlled by an integer multiple of /4.

However, in recent years, optical films with higher performance characteristics than before have been designed, and in this case, the optical film thickness of each layer is not necessarily equal to the design wavelength λ. λ. It is not an integral multiple of /4.

For example, an anti-reflection film is sometimes formed using an equivalent film, but this equivalent film is made of alternating films of low refractive index material and high refractive index material, and by changing the film thickness of each layer, it is possible to obtain an arbitrary refractive index. optical film thickness λ. /4 layer, and may be applied to some of the layers of the antireflection film. In an equivalent film, the thickness of each layer is λ. It may be slightly thinner than /4. If the film thickness is different from 4, change the wavelength selection filter to λ. to some extent, the membrane 5-
/゛Although it can be used for refining, there is a limit to the sensitivity of the detector used in the detection part, and it still takes time to replace it.

As described above, when forming a layer whose optical thickness is not an integral multiple of /4, using the conventional film thickness control method described above is time-consuming and difficult to apply.

OBJECTS OF THE INVENTION An object of the present invention is to provide a film thickness control method that makes it possible to easily control the thickness of a thin film even if the optical film thickness is not an integral multiple of 4.

Structure of the Invention The film thickness control method of the present invention includes: a detection unit that detects a change in amount of transmitted light with respect to a design wavelength of a sample substrate during thin film formation and outputs information corresponding to the design wavelength; The image information obtained from the setting section outputs the amount of change in the amount of transmitted light until the optical thickness of the thin film reaches a desired value as information corresponding to the design wavelength, and The device is characterized in that the optical thickness of the thin film formed on the sample substrate is controlled by controlling a evaporation control section that controls a shutter that blocks the evaporation flow from the sample substrate.
This method allows the optical thickness of the thin film to be adjusted to the design wavelength λ. It is possible to easily control values other than integral multiples of NON/4.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a configuration diagram of an embodiment of a vacuum evaporation apparatus showing the film thickness control method of the present invention.

In FIG. 3, 34 is a detection unit that monitors the amount of change in the amount of transmitted light with respect to the design wavelength of the sample substrate 2 during thin film formation and outputs information corresponding to the design wavelength. This is a setting unit that outputs the amount of change in the amount of transmitted light until the target film thickness reaches a desired value as information corresponding to the design wavelength.

The film thickness control method of the present invention will be explained below regarding the vacuum evaporation apparatus configured as above. The modulated light beam emitted from the light projector 1 passes through a window 10 provided in the vacuum deposition tank 9 and is guided into the vacuum deposition tank 9.

The light flux guided into the vacuum deposition tank passes through a sample substrate 2 for film thickness monitoring, passes through a window 11, a wavelength selection filter 3, selects a wavelength for film thickness control, and then passes through a detection unit 4 such as a photoelectric converter. to go into. The detection unit 4 detects the amount of change in the amount of incident light and outputs information corresponding to the selected wavelength. The above information is preset information output from the setting section 30, that is, information corresponding to the amount of change in the amount of transmitted light until the optical thickness of the thin film formed on the sample substrate 2 reaches a desired value. It is successively compared. Therefore, when the information from the detection section 4 matches the information at the desired value set in the setting section 30, the vapor deposition control section 8 is controlled to close the shutter 7 and stop the vapor deposition. The set information is, for example, as shown in FIG. The conditions in FIG. 4 are that a thin film of magnesium fluoride with a refractive index of 1.38 is formed on a glass substrate with a refractive index of 1.54, the design wavelength λ0 is 560 nm, and the optical film thickness is λ. An example of information when vapor deposition is performed up to /4 is shown. In this case, the information obtained from the detection section is compared with the sequentially set information, and for example, if the optical film thickness is to be set to /8, the information obtained from the detection section corresponds to point A in Fig. 4. It is sufficient to stop the vapor deposition when the value is reached, and as soon as the optical film thickness is set to λO/20, the vapor deposition may be stopped at the value corresponding to point B.

As described above, according to this embodiment, the optical film thickness is λ. /4
Easy film thickness control is achieved even when the thickness is not an integer multiple of . In the above embodiment, the formed thin film is a single layer film, but the present invention can be similarly utilized for controlling the thickness of a multilayer film.

Effects of the Invention As is clear from the above explanation, the film thickness control method of the present invention includes a detection unit that detects the amount of change in the amount of transmitted light with respect to the design wavelength of the sample substrate and outputs information corresponding to the design wavelength; The image information obtained from the detection section is compared with the image information obtained from the setting section, which outputs the amount of change in the amount of transmitted light at the time when the optical thickness of the thin film to be formed reaches the desired value as information corresponding to the design wavelength. When the information obtained corresponds to the desired optical film thickness set in the setting section, the evaporation source and evaporation 9f\
-7゛The optical thickness of the thin film is designed to control the optical thickness of the thin film formed on the sample substrate by controlling the evaporation control device that controls the shutter that blocks the evaporation flow from the source. wavelength λ
. It can be controlled with values other than integral multiples of λO/4, and its practical value is considerable.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a vacuum evaporation apparatus showing a conventional film thickness control method; FIG. 3 is a diagram showing the configuration of an embodiment of a vacuum evaporation apparatus showing the film thickness control method of the present invention, and FIG. 4 is a diagram showing an example of information set in the setting section. 1...Light emitter, 2...Sample substrate, 3...
...Wavelength selection filter, 4...Detection section, 5.
... Display section, 6 ... Evaporation source, 7 ...
...Shutter, 8... Vapor deposition control section, 9...
・Vacuum deposition tank, 10.11...window, 34...
...Detection section, 3o...Setting section. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2 - 尤tg - 会勺71 (also) L Gol Ao/s '/2 ''/4 z. 4) J/O・- Figure 4

Claims (1)

[Scope of Claims] A detecting unit configured to detect a change in amount of transmitted light with respect to a design wavelength of a sample substrate during thin film formation and output information corresponding to the design wavelength; and a detection unit formed on the sample substrate. The image information obtained from the detection section is compared with the image information obtained from the setting section that outputs the amount of change in the amount of transmitted light until the optical thickness of the thin film reaches a desired value as information corresponding to the design wavelength. When the information becomes the desired optical film thickness set in the setting section, the evaporation control section that controls the evaporation source and the shutter that blocks the evaporation flow from the evaporation source is controlled to form the film on the sample substrate. A film thickness control method characterized by controlling the optical thickness of a thin film.