JPS61253408A - Film thickness control of optical thin film - Google Patents

Abstract

PURPOSE:To enable measurement of an optical film thickness with a wavelength less than 1/4 of the incident monochromic light, by irradiating a monochromic light beam in process of forming a thin film and monitor-controlling the thickness of the thin film by an optical phase angle calculated by the reciprocal of its transmissivity and differential value. CONSTITUTION:When increased vacuum intensity inside a vacuum chamber 1 and a closed shutter 2, preliminary vacuum deposition is made by heating the vacuum deposited substance 3 and the vacuum intensity is increased further and a monochromic light beam is irradiated into the vacuum chamber 1 from a light flasher 6 and a reciprocal of transmissivity only of the substrate 5 is calculated. Next, after heating the vacuum depositing substance, the shutter 2 is opened for starting forming of the thin film. At this moment, when irradiation of the monochromatic light beam is continued, the quantity of the transmitted light is decreased in reversed proportion of the film thickness. The transmitted light is received by a light receiver 7 and an electric signal corresponding to the received quantity of light is supplied to a controlling unit 8. The controlling unit 8 amplifies this signal for conversion into a digital signal and after uniformizing process with the laser time difference, an optical phase angle is calculated. Next, comparison is made with the set value decided by the required film thickness and upon achieving this value, a closing signal is issued to the shutter 12. Thus, control of the film thickness in the range of wavelengths less than 1/4 also can be available.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for controlling the thickness of an optical thin film, and particularly to a method for controlling a film thickness suitable for controlling a film thickness of 1/4 wavelength or less of incident monochromatic light. .

[Background of the invention]

A conventional film thickness control device for an optical thin film is, for example, disclosed in Japanese Patent Application Laid-Open No. 1986-
As described in Japanese Patent No. 46404, it utilizes the fact that when a thin film is irradiated with monochromatic light, the reflectance of reflected light or the transmittance of transmitted light changes periodically due to original interference by the thin film. . However, with this method, the film thickness that can be measured is a film thickness equivalent to 1/4 wavelength of the incident monochromatic light, and in order to obtain a desired film thickness, it is necessary to change the wavelength of the incident monochromatic light. Therefore, the measurable film thickness naturally depends on the wavelength of the incident monochromatic light, and especially on the short wavelength side of 400 nm or less, the effects of absorption by the substrate and refractive index dispersion of the film cannot be avoided, making it difficult to measure thin films of 100 nm or less. is not suitable. On the other hand, as described in Japanese Patent Application Laid-Open No. 58-140605, there is a method that can measure any film thickness without changing the wavelength of the incident monochromatic light;
It is necessary to know the value of the transmittance corresponding to /4 wavelength, and as mentioned above, it is not suitable for measuring film thickness of 1/4 wavelength or less.

[Purpose of the invention]

An object of the present invention is to enable measurement and control of any film thickness without changing the wavelength of incident monochromatic light, and to
It is an object of the present invention to provide a film thickness control method that enables measurement and control of film thickness of 74 wavelengths or less.

[Summary of the invention]

For example, monochromatic light with a wavelength λ is incident on a thin film formed on a substrate by vapor deposition. If the transmittance of transmitted light at this time is T, its reciprocal 1/+III can be found by the following equation (1).

'/T = A + Csinδ 0000
1300910. (1) A = (1-)-n) /
4n 1B = ”, 7% δ = (2yt / λ) −
Nd%C=(CB+n)-A)/4n where n is the refractive index of the substrate, N is the refractive index of the deposited film, d is the film thickness, and δ is the optical phase angle. 1/T obtained in this way is the optical phase angle δ
When differentiated by Δ(1/'[' )=2Csinδ−0δ
・-Song--...(2). Therefore, from equations (1) and (2), (1Δ-A)/Δ('/T)=1/
2.−δ (3) is obtained.

Here, A is a measured value of 1/T of the initial value, ie, δ=0 (when no thin film is formed on the substrate).

Therefore, the reciprocal 1/T of the transmittance measurement value is measured in real time,
If the arithmetic processing for calculating the ratio of (1/T - A ) and Δl/T) is performed in real time, it is possible to always measure the optical phase angle δ.

Therefore, in the present invention, (1/T-A) and ΔC1/T) are determined, and the optical phase angle δ is calculated from both. As mentioned above, this optical phase angle δ is δ=(”/2)・N
d, and since λ and N are constants that can be determined in advance, δ and the film thickness d are uniquely determined. Therefore, by setting a predetermined value δ in advance, Nd=
The film thickness can be arbitrarily controlled even in the region of λ/4 or less.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is an overall configuration diagram of a film thickness control device to which the method of the present invention is applied. In FIG. 1, a dome 4 is disposed within a vacuum chamber 1, and a light-transmitting substrate 5 is disposed at a predetermined position of the dome 4. Further, a vapor deposition material 3 is placed at the bottom of the vacuum chamber 1, and a shutter 2 is installed between the vapor deposition material 3 and the substrate 5.

Further, a light projector 6 is provided at the bottom of the outside of the vacuum chamber 1, and a light receiver 7 is provided at the top of the vacuum chamber 1. and,
Converting the amount of monochromatic light emitted from the light receiver 7&i and the projector 6 and transmitted through the substrate 5 into an electrical signal and supplying it to the control unit 8;
The control section 8 controls the opening and closing of the shutter 2 described above.

FIG. 2 is a detailed configuration diagram of the control section 8 shown in FIG. 1.

The control section B includes an amplifier 81. Analog digital converter 8
2. Averaging processing section 85. Arithmetic unit 84° and determination unit 85
It becomes more.

With this configuration, the degree of vacuum in the vacuum chamber 1 is increased and the vapor deposition substance 3 is heated to perform pre-evaporation while the shutter 2 is closed. After that, increase the EX airflow and use the floodlight 6.
Monochromatic light is input into the vacuum chamber 1 from , and the reciprocal of the transmittance T of only the substrate number '/T is calculated. In other words, the above-mentioned (5)
) Next, the vapor deposition substance 5 is heated and the shutter 2 is opened,
Vapor deposition, ie, thin film formation, begins. At this time, monochromatic light is constantly incident from the projector 6.

The amount of transmitted light decreases as the film thickness increases.

This transmitted light is received by the light receiver 7, and an electric signal corresponding to the amount of received light is supplied to the control section B.

In the control section 8 , an electric signal from the light receiving section 7 proportional to the amount of transmitted light is amplified by an amplifier 81 and converted into a digital signal by an analog-digital converter 82 . This signal is averaged over a minute time interval Δt by an averaging processing section 85, and an arithmetic processing section 84 calculates an optical phase angle a from the above-mentioned equation (2). This value δ is then compared with a set value in the determination unit 85, and when the value δ reaches the set value, a closing signal is sent to the shutter 2. δ= <d'f for d
This is a value uniquely determined by Nd.

Note that this embodiment describes the case where a single layer film is formed on a substrate, but if a multilayer film is formed, the person in equation (2) of the substrate and thin film layer may be used. Once measured, a new thin film with a predetermined thickness can be formed thereon in the same manner as in the above embodiment.

〔Effect of the invention〕

According to the present invention, it is possible to measure optical film thickness at a wavelength of 1/4 wavelength or less of the wavelength of incident monochromatic light. Therefore, even when the wavelength of the incident monochromatic light is, for example, 80 Q nfn, a film thickness of about 1001 m can be measured. In addition, it is possible to set an arbitrary film thickness while keeping the wavelength of the incident monochromatic light constant, and it is possible to use a film deposited on a substrate that has refractive index dispersion or absorption on the short wavelength side, or a film that has refractive index dispersion or absorption on the short wavelength side. This has the effect of making it easier to control the measurement of the film thickness of the film.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a film thickness control device to which an embodiment of the present invention is applied, and FIG. 2 is an evaluation configuration diagram of the control section shown in FIG. 1. 1... Vacuum chamber, 2... Shutter, 5... Vapor deposition substance, 4... Dome, 5... Substrate, 6... ...Light emitter, 7...Light receiving section, 8...Control section, 81...Amplifier, 82...Analog-to-digital converter, 8 series・・・
. . . Averaging processing section, 84 . . . Arithmetic section, 85 . . . Judgment section.

Claims (1)

[Claims] 1. In a film thickness control method of forming an optical thin film to a predetermined thickness while measuring the film thickness of an optical thin film ranging from a single layer to a multilayer with monochromatic light, irradiating monochromatic light during the formation of the thin film, The optical phase angle of the thin film being formed is calculated from the reciprocal value of the transmittance and the differential value of the reciprocal value, and the film thickness is controlled by monitoring the film thickness of the thin film using the optical phase angle. A method for controlling the thickness of optical thin films.