JP2000039514A - Optical thin film manufacturing method - Google Patents

Abstract

[PROBLEMS] To form an optical thin film having a film thickness distribution on a disk substrate by increasing the total number of rotations of a shielding mask on the assumption that the deposition rate of the thin film is conventionally constant. A method for achieving a desired film thickness distribution has been adopted. However, in this method, it is necessary to stabilize the deposition rate of the thin film, and it takes time to manufacture. Kind Code: A1 A change in the deposition rate of a thin film obtained from a film thickness monitor is detected, and the detection result is fed back to a motor control system to control the number of rotations, thereby reducing the total number of rotations of the shielding mask. Further, by providing a reference mark on the rotary encoder or the disk substrate and thereby defining the absolute position on the disk substrate, the positional accuracy of the multilayer film formation can be improved, and an optical multilayer film filter with good characteristics can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a high-quality wavelength filter used in an optical thin film, for example, an optical communication system.

[0002]

2. Description of the Related Art Conventionally, when a thin film is formed in a vacuum, a plurality of shielding masks are arranged in multiple layers, each of which is rotated at different speeds. There is a method of manufacturing an optical filter by forming an optical thin film whose thickness changes in proportion to the thickness of the optical filter on a disk. The principle and technology of this method are disclosed in US Pat. No. 3,442,572 (patent date: May 6, 1962).

FIG. 7 shows the simplest example, in which two shielding masks 1 and 2 are arranged close to a disk substrate 3 serving as a sample on which an optical thin film is formed. The shielding masks 1 and 2 and the spindle 4 of the disk substrate 3 are held coaxially and can be rotated at different rotational speeds. An optical thin film is deposited on a substrate by vertically irradiating such a shielding mask with a molecular beam or an atomic beam. Various methods such as electron beam evaporation, ECR sputtering, RF sputtering, and ion beam sputtering can be used to form a thin film using such molecular / atomic beams.

[0004] The rotation speeds ω ₁ ,
When the ratio of ω ₂ is an integer, M ₁ and M ₂ are arbitrary integers,

[0005]

(Equation 1)

When the relationship is satisfied, the amount of change in the film thickness with respect to the expected angle is represented by the total number of rotations of the shielding mask until the film formation is completed by m, and the opening angle of the opening of the shielding mask 1 by 2φ _1. The opening angle of the opening of the shielding mask 2 is 2φ ₂ ,
When the deposition rate of the thin film is constant, as described in the above document,

[0007]

(Equation 2)

[0008] That is, when the total number m of rotations of the shielding mask is infinite, the obtained film thickness is the expected angle 見 込 み
Changes in proportion to Therefore, in order to form an optical thin film having a desired thickness with high accuracy while reducing the influence of the deposition rate fluctuation, it is necessary to increase the total number of rotations of the shielding mask. As a result, when the number of rotations m of the shielding mask increases, the film formation time increases, and high-speed rotation of the shielding mask is required. However, since it is difficult to rotate the shielding mask with high precision and high speed in the thin film forming apparatus, the rotation speed of the shielding mask is reduced by lowering the deposition rate, and at the same time, the deposition rate due to the variation of the dose of the molecule / atomic beam is reduced. The influence has to be averaged to form a thin film, and the time required to form an optical thin film has been prolonged, making it difficult to improve production efficiency.

[0009]

As described above, the conventional method has the following problems.

[0010] 1. In order to obtain an optical thin film having a change in film thickness with respect to an expected angle as designed for a shielding mask having a fan-shaped window, it is necessary to minimize the variation in deposition rate over a long period of time. However, in the above-described deposition method, molecules /
At present, it is difficult to keep the dose of the atomic beam strictly constant.

2. Since only the relative speeds of the plurality of shielding masks are controlled, it is difficult to deposit an optical thin film having the above-mentioned film thickness distribution based on the absolute position on the disk substrate. Therefore, in order to deposit a multilayer film with high positional accuracy, it is necessary to maintain a state in which a disk substrate serving as a sample is mounted on the apparatus. For this reason, when an attempt is made to manufacture a composite thin film combining the layer having the film thickness distribution and a uniform layer, an error in the mechanical reproducibility of the mounting position in the disk substrate mounting state causes the relative thinness of each thin film of the composite thin film to increase. A shift occurs in the target position, and the optical characteristics of the thin film deteriorate.

3. With the conventional method, it is impossible in principle to deposit an optical thin film having an arbitrary film thickness distribution with respect to the expected angle の of the fan-shaped window with high accuracy, as shown in the equation (2).

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and highly precisely deposits an optical thin film having a desired film thickness on a disk substrate with respect to an expected angle of a shielding mask. It is intended to provide a way.

[0014]

In order to achieve the above object, the present invention employs the following method.

In the first aspect, a plurality of shielding masks forming fan-shaped windows are arranged along the surface of the disk substrate on which the optical thin film is deposited, and at least one or more of the plurality of shielding masks is provided. A method of depositing an optical thin film on a disk substrate such that the thickness of the optical thin film changes according to the expected angle of a fan-shaped window along the circumferential direction of the disk substrate by rotating the optical thin film at different rotational speeds. According to a method of controlling the rotation speed of the shielding mask that rotates at least one or more different rotation speeds in accordance with the deposition speed.

According to a second aspect of the present invention, in the method for manufacturing an optical thin film according to the first aspect, the rotational speed of the shielding mask is controlled on the basis of a high-precision pattern previously written in the circumferential direction on the disk substrate. And how to do it.

According to a third aspect of the present invention, the object on which the high-precision pattern on the disk substrate is recorded is a magnetic, magneto-optical or phase-change recording medium. In this method, the rotation speed of the disk substrate is controlled in synchronization with a clock.

[0018]

In FIG. 7, it is assumed that one of the two fan-shaped shielding masks is fixed (the fan-shaped mask 2 in the figure) and the other (the fan-shaped mask 1 in the figure) is rotated only once to deposit the optical thin film.

Assuming that the deposition rate of a thin film in proportion to the dose of the molecule / atom beam to be deposited is Λ and the film thickness is D (Θ),

[0020]

(Equation 3)

## EQU1 ## On the other hand, the gradient κ of the film thickness on the disk substrate is

[0022]

(Equation 4)

## EQU1 ## The rotation speed ω ₁ of the fan mask 2 on the rotation side is

[0024]

(Equation 5)

Therefore, when the equations (3) and (4) are combined,

[0026]

(Equation 6)

## EQU1 ## Therefore, by detecting the deposition rate Λ corresponding to the dose and controlling the rotational speed ω ₁ of the disk substrate according to the equation (6), it is possible to obtain a film thickness distribution as designed. Note that κ is determined in advance based on a pattern described on the disc, and is uniquely given to the estimated angle Θ detected according to the criterion. For this reason, the film thickness distribution can always be given based on a fixed reference without depending on the apparatus.

According to the method described above, one fan-shaped mask is
This is a method of rotating only once, which can greatly simplify the conventional method. Also, since the total deposition time is short, molecules /
It is also easy to keep the dose of the atomic beam almost constant.
This greatly reduces the load on the rotation speed control mechanism for achieving a desired film thickness distribution.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention, in which two shielding masks 1 and 2 forming a fan-shaped window are provided.
And the disk substrate 3 are held coaxially. One of the shielding masks 1 and 2 forming the fan-shaped window (for example, the shielding mask 1) is fixed relatively to the disk substrate 3, and the disk substrate 3 and the shielding mask 1 rotate integrally with the rotation of the motor 4. I do. The rotation speed of the motor 4 is detected by a rotary encoder 5, and the output of the rotary encoder 5 is input to a rotation control circuit 6 (for example, a phase locked loop stabilizing circuit) of the motor 4, and at the same time, the disk substrate 3 is output via an integrator 7. Detect the absolute position above. The optimum rotation speed of the shielding masks 1 and 2 is determined by the film thickness control circuit 9 from the output of the integrator 7 as the detected absolute position information and the differential film thickness obtained from the film thickness monitor 8, and the motor rotation control is performed. The data is input to the circuit 6 as rotation speed data corresponding to the optimum rotation speed of the shielding mask. As the film thickness monitor 8, an ordinary crystal oscillator film thickness meter can be used. By such loop control of the film thickness control system, it becomes possible to deposit an optical thin film having the film thickness distribution set by the film thickness control circuit 9.

FIG. 2A shows a rotation detecting disk used in the rotary encoder 5, which has a grid pattern arranged at equal intervals in the circumferential direction and has one reference mark. The head for detecting the number of rotations uses the change in the intensity of the diffracted light of the coherent light emitted from two directions due to the lattice pattern as shown in FIG. Since the phase of the detection signal is shifted by shifting the phase of one of the emitted lights, it is possible to detect not only the rotation speed but also the rotation direction. By mounting such a disk having a lattice pattern as a rotary encoder 5 on the rotating shaft of the motor 4, it is possible to precisely monitor the number and direction of rotation of the motor. Also,
If the reference mark written on the grid pattern of this disk is used as a mark for frame synchronization,
As shown in FIG. 3, by adjusting the trigger level, a frame synchronization signal can be obtained for each rotation. Based on this signal, the absolute position on the disk substrate 3 can be identified on the time axis.

The same effect can be obtained by writing this lattice pattern on the back surface of the disk substrate 3 to be deposited in advance.

FIG. 4 shows a second embodiment of the present invention, in which a monitor signal of a deposition rate corresponding to a dose of a molecular beam or an atomic beam and a rotation speed of the disk substrate 3 is digitally converted by an AD converter 10. The signal is converted into a signal, and the computer 11 controls the rotation speed so that a desired film thickness distribution is obtained. In the figure, computer 1
1 Store the thickness distribution to be controlled in a built-in non-volatile memory (such as a hard disk), and always perform digital arithmetic processing based on the deposition rate corresponding to the dose of molecular beam or atomic beam.
An optical thin film having a desired film thickness distribution can be deposited on the disk by controlling the number of revolutions using a signal obtained by returning the processing result to an analog amount by the D / A converter 12.

FIG. 5 shows a third embodiment of the present invention, in which a disk substrate provided with a magnetic, magneto-optical or phase change recording medium on the outer peripheral portion is used. The area where the optical thin film is deposited is provided on the inner peripheral side. With this configuration, a grid pattern used for the rotary encoder 5 is written in a part of the recording medium area. The functions of the grid pattern written on the medium are the same as those of the first embodiment and the second embodiment.
This embodiment is the same as the above embodiment, except that the optical thin film can be deposited in synchronization with the system clock using the pattern written on the outer peripheral portion. As a result, it is possible to deposit a high-precision optical thin film with high flexibility that can respond to an arbitrary system clock.

[0035]

As described above, according to the present invention, it is possible to deposit an optical thin film having a thickness distribution as designed on a disk substrate with high accuracy. Therefore, for example, as shown in FIG. 6, it is possible to perform deposition of a uniform multilayer film and deposition having a film thickness distribution with different manufacturing apparatuses on the same disk substrate with good reproducibility. Therefore, it becomes easy to manufacture a high-performance optical thin-film element such as a multi-stage filter.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical thin film manufacturing apparatus showing a first embodiment of the present invention.

FIG. 2A is a grid pattern diagram of a rotary encoder that monitors a rotation angle in the first embodiment. (B)
FIG. 2 is a configuration diagram of a grid pattern reading system of the rotary encoder.

FIG. 3 is a waveform diagram of a rotary encoder as a rotation angle monitor according to the first embodiment.

FIG. 4 is a configuration diagram of an optical thin film manufacturing apparatus according to a second embodiment of the present invention.

FIG. 5 is an external view of a disk substrate having a recording area used as a third embodiment of the present invention.

FIG. 6 is a cross-sectional view of a multilayer structure having a film thickness distribution.

FIG. 7 is a configuration diagram of a shielding mask portion for explaining a conventional optical thin film manufacturing method for providing a thickness distribution.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shielding mask 2 Shielding mask 3 Disk substrate 4 Motor 5 Rotary encoder 6 Motor rotation control circuit 7 Integrator 8 Film thickness monitor 9 Film thickness control circuit 10 A / D converter 11 Computer 12 D / A converter

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuo Aida 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Shin Shin Higashi 3-1-23 Nishinaminami, Toda City, Saitama Prefecture No. F-term (Reference) 2H048 GA12 GA60 GA62 2K009 DD03 DD04 DD09 4K029 BC07 BD00 BD11 BD12 DA13 EA00 JA02

Claims (3)

[Claims] A plurality of shielding masks forming fan-shaped windows are arranged along a surface of a disk substrate on which an optical thin film is deposited, and at least one or more of the plurality of shielding masks is rotated at different rotational speeds. A method of depositing an optical thin film on a disk substrate such that the film thickness changes in accordance with an expected angle of a fan-shaped window along a circumferential direction of the disk substrate by rotating the optical thin film. Controlling the rotation speed of the shielding mask that rotates at least one or more different rotation speeds. 2. The optical system according to claim 1, wherein the rotational speed of the shielding mask is controlled based on a high-precision pattern written in advance on at least one of a rotary encoder and the disk substrate. Manufacturing method of thin film. 3. A target for recording a high-precision pattern on the disk substrate is a magnetic, magneto-optical or phase-change recording medium, and a signal of the high-precision pattern read by an optical head is synchronized with a system clock. The method according to claim 2, wherein the rotation speed of the disk substrate is controlled.