JPH0759752B2 - Thin film formation method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thin film, which enables optical non-destructive control of the thickness of a thin film to be formed.

2. Description of the Related Art In recent years, the vacuum vapor deposition method and the sputtering method have been positioned as the main methods for forming thin films, and they have become indispensable technologies for forming thin films such as semiconductors, optical memory disks, and thin film magnetic heads. There is an extremely high demand for forming a device by laminating a number of thin films.

There are various important parameters in forming a thin film, but the formed film thickness is a particularly important parameter. As an example, a dielectric layer, a recording layer, a dielectric layer,
In the case of an optical memory disk in which reflective layers are sequentially stacked, for example, even if the film thickness of the dielectric layer between the recording layer and the reflective layer deviates from the optimum film thickness by 5%, the obtained output may be significantly reduced. Therefore, it is important to strictly control the film thickness.

Usually, the film thickness control in thin film formation is performed by the crystal oscillator method. The crystal oscillator method measures the change in the natural frequency of the oscillator by depositing a thin film on the crystal oscillator to obtain the mass film thickness on the oscillator, and estimates the film thickness of the thin film actually formed on the substrate. To do.

Problems to be Solved by the Invention When a thin film is formed on a crystal unit, the natural frequency decreases, but the limit of use of the crystal unit is that the natural frequency change is 0.1 MHz.
Until. Normally, the natural frequency used for vapor deposition is several MHz, and if the natural frequency is 6 MHz as an example, it can be used up to 5.9 MHz, but if the frequency drops below that, the crystal oscillator Must be replaced.

Recently, there has been a trend toward continuous operation in thin film formation. As shown in FIG. 5, one example is a substrate loading chamber 515 for forming a thin film, a thin film forming chamber 516, and a substrate unloading chamber 517. The valve 518 constitutes a thin film forming apparatus, and the substrate loading / unloading chambers 515 and 517 repeatedly perform exhaust air suction, but the thin film forming chamber 5
16 keeps a vacuum state at all times so that a thin film can be formed. However, when the crystal oscillator method is used to control the film thickness, it is a kind of destructive control method, so the thin film forming chamber 516
It is necessary to frequently break the vacuum and replace the crystal unit, which is a major obstacle to the continuous thin film formation. The present invention is to solve the above problems, non-destructive film thickness control in thin film formation,
It is an object of the present invention to provide a thin film forming method that enables continuous thin film formation.

Means for Solving the Problems In the present invention, when a transparent thin film having a film thickness of d ₁ is formed on a substrate on which at least one thin film is formed, when the transparent thin film has a refractive index of n ₁ , m Is an integer greater than or equal to 1, λ =
Select incident light of wavelength λ with a relationship of 2n ₁ d ₁ / m, irradiate the substrate, measure the total reflected light amount of the substrate and the thin film in-process as a function of time, and form the transparent thin film on the substrate. The formation of the transparent thin film is terminated and the film thickness is controlled at the m-th time when the reflected light amount is the same as the reflected light amount and the sign of the value obtained by differentiating the reflected light amount is the same.

The reflectance of the substrate on which at least one thin film is formed has various values depending on the optical constant of the thin film or its thickness, and the number of laminated thin films. While irradiating the substrate on which at least one thin film is formed with incident light of wavelength λ, formation of a transparent thin film having an extinction coefficient k of 0 is started on the surface of the substrate opposite to the incident light side. In-process measurement of the reflected light amount R as a function of time t yields a reflected light amount curve as shown in FIG. The amount of reflected light R ₁ from the substrate on which the thin film has already been formed is from time t ₀ to time t _1, but when the formation of the target transparent thin film is started on the thin film already formed at time t _1. The reflected light amount R fluctuates due to multiple interference of the thin film, and repeats maximum and minimum, is the same as the reflected light amount R ₁ at time t ₁ at time t ₂ , and is a value obtained by differentiating the reflected light amount with time Is the same as the sign. Further reaches the time t ₃ is repeatedly reflected light amount curve from the time t ₁ again from time t ₂ to time t _2, shows the same quantity of reflected light R ₁ and time t _1. Further, at the time point t ₄ , the same amount of reflected light is shown. Here, when the refractive index of the transparent thin film and n _1, λ / 2n ₁ in the film thickness of the transparent thin film formed from the time t ₁ time t ₂ by multiple interference theory, the time t ₃ at lambda / n _1, the time t ₄ in 3λ /
It becomes 2n ₁ . That is, when m is an integer of 1 or more, mλ /
At a film thickness of 2n _1, the amount of reflected light is the same as at the formation start time t ₁ of the transparent thin film, and the sign of the value obtained by differentiating the amount of reflected light is the same. Therefore, when obtaining a transparent thin film with a film thickness d _{1 on} a thin film already formed on the substrate, The wavelength λ that satisfies the relation By selecting the light having the wavelength λ to be the incident light, the m-th time point at which the reflected light amount has the same sign as the reflected light amount and the sign of the value obtained by differentiating the reflected light amount with time is detected. When the thin film formation is completed by the above, the film thickness d ₁ can be obtained.

In this way, by selecting the wavelength λ of the incident light so as to satisfy the conditions in the present invention, it is possible to make the film thickness d ₁ correspond to the easily recognizable time point indicating the target reflected light amount,
Non-destructive film thickness control is possible without using the crystal oscillator method.

The thin film that has already been formed may have any optical constant (refractive index, extinction coefficient), and even if it is laminated over the opposite layers, a transparent thin film with a thickness of d ₁ Can be formed.

Example An example of the present invention will be described below by taking as an example the formation of a ZnS thin film applicable to the dielectric layer of an optical disc. As an example of the structure of an optical disc, there is a case where a dielectric layer 311, a recording layer 312, a dielectric layer 313, and a reflective layer 314 are laminated on a substrate 303 as shown in FIG. explain. The target here is that the dielectric layer 311 and the recording layer 312 are already formed on the substrate 303, and then the transparent dielectric layer 3 is formed.
13 is formed with a film thickness of d ₁ , and this dielectric layer 303
A ZnS thin film that is a transparent thin film is applied to. As an example of the method for forming this ZnS thin film on the disk substrate, the evaporation source is ZnS.
The electron beam heating vapor deposition method described above is used to describe the present invention. The structure is shown in FIG. In the chamber 101 in the vacuum state, the electron beam is focused on the ZnS evaporation source 102 and heated to evaporate ZnS.
Rotating Polycarbonate Substrate With Thin Layers Formed
A ZnS thin film is formed on 103. A shutter 104 is interposed between the evaporation source 102 and the substrate 103, and its opening and closing regulates the start and end of thin film formation on the substrate 103. A certain amount of incident light is emitted from above the substrate 103 from the light emitting unit 106, and the amount of reflected light is detected by the light receiving unit 107 to obtain a reflected light amount signal. Light emitting part 1
Reference numeral 06 denotes a diffraction grating, which is guided through an optical fiber 109 from an optical emitter 108 capable of emitting light at an arbitrary wavelength.

The ZnS thin film is formed on the substrate with the above configuration, and the film thickness d ₁ formed at that time is 2000 Å as an example. Incident light wavelength λ
Is selected from those satisfying the relation of λ = 2n ₁ d ₁ / m. It has been confirmed by an ellipsometer that the refractive index n ₁ of the ZnS thin film is 2.3, and the wavelength λ calculated by setting m to 1 is 9200Å. Then light generator 10
Set the wavelength of the light generated from 8 to 9200Å, and
The substrate 103 was irradiated with incident light from 06, and the amount of reflected light was measured in the in-process of thin film formation. FIG. 1 (b) is the obtained reflected light amount curve as a function of time. Since m is set to 1, the shutter 104 is opened and ZnS is applied to the substrate 103.
The same as the reflected light amount R ₁ at the start time t ₁ of forming a thin film, but a value obtained by differentiating the reflected light amount R with time t Corresponds to the thickness d ₁ to be obtained when t ₂ 1 th is the same as the numerals (= 2000 Å), close the shutter 104 at that time, was terminated formation of a thin film.

As a result of measuring with an ellipsometer to confirm the thickness of the ZnS thin film formed in this way, 2000 Å was obtained, and it was confirmed that it is possible to control non-destructively to a predetermined thickness without using the crystal oscillator method. .

After the reflected light amount curve in this embodiment first shows a maximum,
Although the minimum is shown, it may be shown first as shown in FIG. 4 depending on the conditions of the thin film already formed on the substrate, that is, the optical constants of the thin film, the film thickness, and the number of laminated layers. There is no such thing.

Also, when a groove track is provided on the substrate and a thin film is formed on the grooved surface, the amount of reflected light is lower than that of a substrate having no groove, but the amount of reflected light is the same as at the start of formation and The film thickness is the same at the time when the signs of the values differentiated in are the same, and the film thickness can be similarly controlled.

As the thin film forming method, the vacuum vapor deposition method has been described in the present embodiment, but the present invention is not limited to the vacuum vapor deposition method.
It can also be applied to many other thin film forming methods such as sputtering, ion plating, and CVD. The thin film to be formed is not limited to ZnS, but SiO ₂ , GeO ₂ , S
The present invention can be applied to all transparent thin films having an extinction coefficient k of 0 such as i ₃ N ₄ .

EFFECTS OF THE INVENTION As described above, according to the present invention, when a transparent thin film having a film thickness of d ₁ is formed on a substrate on which one or more thin films are already formed, when the transparent thin film has a refractive index of n ₁ , When m is an integer of 1 or more, incident light of wavelength λ having a relationship of λ = 2n ₁ d ₁ / m is selected and irradiated onto the substrate, and the total reflected light amount of the substrate and the thin film is processed in-process as a function of time. A non-destructive film thickness control method that does not use the crystal oscillator method is measured by terminating the thin film formation at an easily recognizable time when the reflected light amount corresponds to the film thickness d ₁ based on the necessary requirements of the present invention. It is realized and enables continuous thin film formation, and its industrial value is very large.

[Brief description of drawings]

1 is a characteristic diagram and a characteristic diagram of an apparatus for carrying out the thin film forming method of the present invention, FIG. 2 is a characteristic diagram illustrating the principle of the thin film forming method of the present invention, and FIG. 3 is a thin film forming method of the present invention. FIG. 4 is a sectional view of an optical disk constructed by using the optical disk, FIG. 4 is a characteristic view showing a reflected light amount curve in one embodiment of the present invention, and FIG. 5 is a schematic view of a conventional continuous thin film forming apparatus. 102 ... evaporation source, 103, 303 ... substrate, 104 ... shutter, 1
06 …… Light emitting part, 107 …… Light receiving part, 108 …… Light generator, 313
… Dielectric layer.

Claims (1)

[Claims] 1. When forming a transparent thin film with a film thickness of d ₁ on a substrate on which at least one thin film is formed, when the refractive index of the transparent thin film is n ₁ , m is an integer of 1 or more. , Λ = 2n ₁ d ₁ / m The incident light of wavelength λ with the relation of λ = 2n ₁ d ₁ / m is selected and irradiated onto the substrate, and the total reflected light amount of the substrate and the thin film is measured in-process as a function of time. The method for forming a thin film is characterized in that the formation of the transparent thin film is finished at the m-th time point when the amount of reflected light is the same as the amount of reflected light at the start of formation and the sign of the value obtained by differentiating the amount of reflected light is the same.