JPS5984205A - Preparation of optical integrated circuit - Google Patents

Abstract

PURPOSE:To form a diffraction grating on a desired region in a desired size by removing a thin film coating a substrate by a desired spot to open a window and etching only the spot of the window in a grating form. CONSTITUTION:A nonetchable thin film 10 is formed on a semiconductor substrate, and a desired window is opened by the photolithographic technique to disclose the substrate at the spot A of this window 11. A photoresist 12 film is formed by spin coating, and interference exposure is carried out with two luminous fluxes to form a diffraction grating by development. A desired diffraction grating 13 is formed on a desired region A by etching this pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Purpose of the Invention The object of the present invention is to provide a method for manufacturing a diffraction grating of any period and size at any location on a semiconductor substrate.

(a) Optical ICs, in which waveguide-type diffraction grating semiconductor lasers, optical waveguides, modulators, splitting elements, etc. are formed seven-dimensionally on a semiconductor substrate, are expected to emerge in the fields of optical communication, optical information processing, etc. It is an optical device.

Functional elements constituting an optical IC include a wavelength demultiplexing/multiplexing element, a distributed feedback laser, a polarizing mirror, etc., which are important components for wavelength division multiplexing communication. In order to manufacture these functional elements, waveguide-shaped diffraction gratings are a particularly important basic element.

The development of a technique for producing a diffraction grating of a desired size and a desired period at a desired location on a semiconductor substrate is essential for realizing optical IC buttons.

Currently, waveguide-shaped diffraction gratings are manufactured using methods such as three-beam interference method or electron beam exposure method.

(1) Electron Beam Exposure Method A thin electron beam is irradiated onto a photoresist or 14-oxide film on a semiconductor substrate on which an integrated circuit is to be fabricated to fabricate diffraction gratings and other elements.

Scanning of the electron beam can be performed according to a preprogrammed pattern by an electronic computer.

A diffraction grating with desired dimensions can be produced at a desired location using an electron beam. However, the diameter of the electron beam is finite and cannot be narrowed down to a certain degree (for example, 0.1 μmφ). For this reason, it is difficult to draw a fine periodic pattern required for the diffraction grating of an optical IC by electron beam exposure.

Currently, the lower limit of the grating period of a diffraction grating that can be manufactured by electron beam exposure is 0.511 m.

It is not possible to obtain the structure required for a diffraction grating for optical IC.

B) Three-beam interference exposure method FIG. 1 is a diagram showing the configuration of an optical system showing an outline of the three-beam interference exposure method.

The semiconductor substrate 1 is coated with a photoresist 2 (or an oxide film) in advance.

The laser 3 is, for example, a He--Cd laser and generates coherent light with a wavelength of 4416λ. The laser beam that passes through the shutter 4 and is reflected by the mirror 5 is split into two beams by the beam splitter 6. Each is expanded in diameter by a beam exunupander 7.7.

The enlarged laser light, which is close to a plane wave, is reflected by a mirror 8.8 and enters the substrate 1 from the opposite side at an equal incident angle θ.

Since the two beams are separated coherent lights, interference fringes are created in a direction perpendicular to the direction of incidence. Interference fringes are recorded on the photoresist 2 by exposure. By developing the photoresist and etching the substrate 1, periodic uneven lines are formed on the substrate.

In the three-beam interference exposure method, the period d of interference fringes is represented by λ. Here, λ is the wavelength of the laser beam, n is the 6 index of refraction of the medium facing the resist, and θ is the incident angle of the laser beam onto the substrate.

The three-beam interference exposure method uses a short-wavelength visible light laser (He-
If a Cd laser or the like) is used, a diffraction grating with a sufficiently small period can be exposed. It is possible to obtain a diffraction grating with a submicron period (about 0.2 pm) necessary for optical communication using visible light and near-infrared light.

However, since the two beams with enlarged diameter interfere with each other, it is difficult to locally limit the area in which the diffraction grating is formed.

It is necessary to create a diffraction grating of any shape and size at any location. For this reason, as shown in FIG. 2, a method has been attempted in which a slit and a mask 9 are placed on top of the photoresist 2 to locally expose the photoresist.

However, slits, galanu masks, etc. are thick. Two beams of light enter the resist 2 through the opening or the transparent part, but the laser beam is diffracted at the edges of the opening or the transparent part. Due to this diffraction, the laser beam is no longer a regular plane wave near the edge, and the pattern of interference fringes is disturbed. For this reason, a good diffraction grating pattern cannot be obtained.

There were some difficulties.

The present invention provides a local diffraction grating fabrication method that solves these drawbacks.

(4) Fabrication of diffraction gratings using thin films The entire substrate is covered in advance with a thin film that will not be etched, only the thin film at desired locations is removed to open windows, and only the window portions are etched in a grid pattern. It is.

The photoresist is applied to the entire surface of the substrate, and the three-beam interference exposure is also performed over a wide area or the entire surface of the substrate, but since there is a thin film, the diffraction grating can be formed only in a desired location.

FIG. 3 is a cross-sectional view of an element showing the steps of the method for producing a diffraction grating of the present invention.

In FIG. 3(1), a thin film 10 is placed on the upper surface of the semiconductor substrate 1.
is formed uniformly. The thin film 10 may be of any material as long as it is not etched, and photoresist, SiO2, or the like may be used.

Next, a window is opened at a location where a diffraction grating is desired to be made using a normal photolithography technique.

For those who have opened the window 11, the surface of the substrate is exposed.

The other parts are covered with a thin film. FIG. 3(2) is a sectional view of the element substrate after the window opening, and the window opening part A and the covering part B are illustrated.

&K, spin coat photoresist 12.

The photoresist covers the entire substrate and thin film. The photoresist is in close contact with the substrate 1 at the window opening A. FIG. 3(3) is a cross-sectional view after photoresist coating.

In this state, three-beam interference exposure is performed.

FIG. 3(4) shows the exposure process.

Upon further development, a diffraction grating pattern is formed over the entire surface of the substrate, as shown in FIG. 3(5).

However, the diffraction grating pattern of the photoresist is in close contact with the substrate only at the window opening A. In the covering section B, the substrate 1 remains covered with the thin film 10.

When this is etched, as shown in Figure 3 (6),
Only the window opening A is etched. A desired diffraction grating 13 is formed only in a limited area of the window opening A. In the covering part B, the thin film 10 prevents etching, so that the substrate 1 is not affected in any way.

Finally, as shown in FIG. 3 (7), the resist and thin film are peeled off and removed. Diffraction grating 13 remains.

As described above, according to the present invention, a diffraction grating of any size and any period can be produced at any location.

The thinner the resist 12 applied in FIG. 3(3) is, the more advantageous it is in forming the pattern of the diffraction grating in the substrate exposed portion (window opening portion) A. In fact, because of the resistance of the resist in the part that comes into close contact with the substrate (the opening part A), the thin film 10 initially formed on the substrate must also be made as thin as possible.

If there are 10 thin films of SiO2, CV D (Chemi
It can be formed on the substrate 1 by vapor deposition (vapor deposition) or sputter deposition. If the thin film is a photoresist, a spin code method can be used.

According to these methods, a thin film having a thickness of 0.111 m or less can be easily produced.

When using a photoresist as a thin film, the resist is applied and then heated and cured to provide sufficient strength.

The peeling of the thin film after etching the substrate is Sin.

In this case, the same solution (hydrofluoric acid HF) as the etching solution used in the process can be used for the window opening in FIG. 3(2).

If a photoresist is used as the thin film 10, the windowing process can be performed using a developer. After etching, acetone or a stripping solution is used to strip the photoresist thin film 10. This is because photoresist is thermoset.

Further, if there is no particular influence on the substrate, the film such as 5i02 may be left.

The above description is based on examples of SiO2 and photoresist as the thin film of the covering part B.

However, other materials may be used as the thin film to coat the substrate, depending on the substrate's sufficient resistance to the solution that etches the thin film. For example, A7,
A metal thin film such as 'ri, Au, etc. can also be used.

Diffraction gratings having the same period and direction in multiple regions on the same substrate can be produced by performing the above steps only once.

To provide gratings with different periods and directions in a plurality of regions, the same process is repeated many times.

(B) Effects of the present invention (1) A diffraction grating used in an optical IC can be formed in a desired area and in a desired size on a substrate.

This is because a photoresist pattern is formed only in a limited area by shielding with a thin film and then etched.

(11) Diffraction gratings with different periods and directions can be fabricated at several locations on the same substrate.

In the present invention, a diffraction grating with any period and any direction can be locally produced by limiting the area, so by repeating this process, a large number of diffraction gratings with any period and any direction can be produced.

(a) Application of the invention This invention can be applied to optical filter circuits, optical circuits, distributed feedback semiconductor lasers, optical demultiplexers, optical multiplexers, etc.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the optical system configuration of the two-beam interference exposure method. Figure 2 is a cross-sectional view showing an example in which the exposure area is limited using a slit and a glass mask. FIG. 8 is a process diagram of the method for manufacturing a diffraction grating of the present invention using a thin film. (1) is the process of forming a thin film on the substrate, (2) is the window opening process, (3) is the photoresin coating process, (4) is the three-beam interference exposure process, (5) is the development process, (6) (7) shows the etching process, and (7) shows the resist and thin film peeling process. 1 ・・・・・・・・・ Board 2
・・・・・・・・・ Photoresinuto 3 ・・・
・・・ ・・・ し - THE 4
・・・・・・・・・ Shirt
Ta 5...Mirror 6... Beam Nuprita 7 ・
・・・・・・・・・ Beam expander 8・・・・・・
...Mirror 9 ...... Slit, glass mask 1
0... Thin film 11
・・・・・・・・・Window 12 ・・・・・・・・・ Photo resin 13...
・・・・・・Diffraction grating A ・・・・・・・・・ Window opening B
・・・・・・・・・ Covering part
Author Ken Okamoto Yu Nishiwaki
Haru Wamatsu Oka Haruji Nishiura Yozo (11) Figure 1 (12) Figure 3 March 9, 1981 1. Indication of the incident Patent Application No. 1988-1948 2. Name of the invention Method for manufacturing optical integrated circuits 3. Relationship with the case of the person making the amendment Patent Applicant Residence 5-15 Kitahama, Higashi-ku, Osaka Name (213) Sumitomo Electric Industries Co., Ltd. Representative President Tetsu Kawakami Department 4 Agent Kumo 537

Claims (1)

[Claims] (1) Three-beam interference exposure consisting of a coherent light source, a beam splitter that splits the light emitted from the light source into three beams, a collimating thread that expands the diameter of the beam, and a mirror that causes the three beams to interfere on the substrate. A method for producing a diffraction grating by exposing, developing, and etching a substrate coated with photoresinut using an apparatus.
Second, a thin film is coated, a window is opened in the thin film at a desired location, a photoresist layer is formed on the thin film, three-beam interference exposure is performed, development is performed, and etching is performed. 1. A method for manufacturing an optical integrated circuit, which comprises manufacturing a diffraction grating only at a desired location on a substrate.