JPH06283813A - Fabrication of diffraction grating - Google Patents

Abstract

PURPOSE:To realize a diffraction grating having two uniform diffraction grating patterns in two regions on the surface of a semiconductor substrate by exposing one photoresist layer to an electron beam while the other photoresist layer to ultraviolet rays. CONSTITUTION:A photosensitive photoresist layer 2 is formed on a semiconductor substrate 1 and a photoresist layer 3 sensitive to electron beam is formed thereon. The photoresist layer 3 is then exposed to an electron beam and removed selectively thus exposing one surface of the photoresist layer 2. The semiconductor substrate 1 then inclined and the surfaces of the photoresist films 2, 3, exposed by two beam interference exposure, are exposed in diffraction grating pattern. The photoresist film 3 is then removed and the pattern is removed selectively by etching thus forming a diffraction grating pattern of photoresist. This method allows formation of a uniform etching pattern of photoresist layer thus allowing formation of a diffraction grating region for imparting a different phase to a transmitted light on the surface of a semiconductor substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction grating, and more particularly to a method of manufacturing a diffraction grating suitable for a semiconductor laser.

[0002]

2. Description of the Related Art Among semiconductor laser elements, there is a light emitting laser element with a diffraction grating having a filter function of selecting light having a predetermined wavelength from an emission beam. Conventionally, a method of manufacturing such a diffraction grating for a light emitting laser element is disclosed in, for example, Japanese Patent Laid-Open No. 61-289688. According to the method of manufacturing a diffraction grating according to this prior art document, after the photoresist film and the dielectric film are formed on the compound semiconductor substrate, the dielectric film is exposed to ultraviolet light through a mask. Then, this dielectric film is selectively removed by etching in order to form two interference pattern regions on the surface of the compound semiconductor substrate. In this case, since the photosensitivity of the photoresist film to ultraviolet rays is one digit lower than that of the dielectric film,
Almost no exposure. Subsequently, the semiconductor substrate is tilted and subjected to interference exposure, and then the photoresist is developed to obtain an interference pattern of the photoresist. By etching the surface of the compound semiconductor substrate using the obtained photoresist pattern as a mask, a diffraction grating having an interference pattern in two regions is formed.

[0003]

However, according to the above-described method of manufacturing a diffraction grating, the dielectric film is thick,
In addition, when the photoresist film has a positive type photosensitivity, the exposure time becomes long, so that the photoresist film may be exposed. Further, when the dielectric film is of a positive type, the photoresist may not be sufficiently exposed because the dielectric film also retains the photosensitivity at the time of interference exposure.

An object of the present invention is to provide a method of manufacturing a diffraction grating having two diffraction grating patterns uniformly in two regions on the surface of a semiconductor substrate.

[0005]

In order to achieve the above object, a method of manufacturing a diffraction grating of the present invention comprises forming a first photoresist layer which is exposed to light on a semiconductor substrate, and forming a first photoresist. Forming a second photoresist layer sensitive to the electron beam on the layer, exposing the second photoresist layer with the electron beam, and selectively removing the second photoresist layer to remove the first photoresist layer; The surface of the first photoresist film and the second resist film exposed by using the two-beam interference exposure method with one surface exposed and the semiconductor substrate tilted is exposed in a diffraction grating pattern to form a second photoresist film. After removing the first photoresist pattern, the first photoresist pattern is selectively removed by etching to form a diffraction grating pattern of the first photoresist, and the surface of the semiconductor substrate using the diffraction grating pattern as a mask It is selectively removed, and characterized by comprising the step of forming a diffraction grating on the surface of the semiconductor substrate.

[0006]

According to the present invention, after forming the two photoresist layers formed on the surface of the semiconductor substrate, one photoresist layer is exposed with an electron beam and the other photoresist layer is exposed with ultraviolet rays. As a result, both photoresist layers are not affected by the exposure process. Therefore, a photoresist layer having two uniform diffraction grating patterns can be formed on the surface of the semiconductor substrate. As a result, it is possible to highly accurately form two diffraction grating pattern regions that give different phases to transmitted light on the semiconductor substrate surface.

[0007]

1 is an embodiment showing a method for manufacturing a diffraction grating according to the present invention.

In the step shown in FIG. 1A, a compound semiconductor substrate, for example, an InP semiconductor substrate 1 is prepared. next,
A photoresist layer 2 having a thickness of 500Å is formed on the surface of the semiconductor substrate 1 on the two types of diffraction grating formation regions by spin coating. The material of the photoresist layer 2 is for light exposure (for example, ultraviolet exposure), and is, for example, microposit (trade name). Subsequently, a photoresist layer 3 for electron beam exposure having a thickness of 1 mm is formed on the surface of the photoresist layer 2. An example of this electron beam photoresist material is polymethylmethacrylate (PMMA)
Is preferred. In order to expose a predetermined surface of the photoresist layer 2, the photoresist layer 3 is exposed to a dose of about 6 for example.
After selectively exposing with an electron beam of 00 μC, the exposed portion is removed by etching.

In the step of FIG. 1B, the InP semiconductor substrate 1 obtained in the previous step is subjected to a two-beam interference exposure method using an Ar laser. In this process, InP
The semiconductor substrate 1 is provided with an inclination of about 15 degrees,
The surface of the photoresist layer 2 on the semiconductor substrate 1 is subjected to interference exposure for about 30 seconds with 8 Å Ar laser light. By this interference exposure, the photoresist layer 2 is exposed in a regular pattern. Therefore, the refracted light reaches the photoresist layer 2 existing under the photoresist layer 3, so that the photoresist layer 2 with the photoresist layer 3 and the photoresist layer 2 without the photoresist layer 3 have a phase-shifted lattice pattern. Exposed.

In the step of FIG. 1-c), after removing the photoresist layer 3 with an etching solution, the photoresist layer 2 is developed to form a lattice pattern 4 of the photoresist layer 2.

In the step of FIG. 1D, the lattice pattern 4 of the InP substrate 1 obtained in the previous step is used as an etching mask, and the substrate 1 is immersed in, for example, a bromine-based etching solution, the InP substrate 1 A diffraction grating 5 having a period of the diffraction grating pattern 4 of 2400Å is formed on the surface of the. Thereby, two diffraction grating regions having different shift amounts can be formed simultaneously and uniformly on the InP semiconductor substrate 1.

[0012]

As described above, in the method of manufacturing a diffraction grating according to the present invention, after forming two photoresist layers on the surface of a semiconductor substrate, one photoresist layer is exposed with an electron beam and the other photoresist layer is exposed. Since the photoresist layer is exposed to ultraviolet rays, both photoresist layers are not affected by the exposure process. Therefore, a uniform etching pattern of the photoresist layer can be formed. As a result, a diffraction grating region that gives different phases to transmitted light can be formed on the surface of the semiconductor substrate.

[Brief description of drawings]

FIG. 1 is a sectional view showing a manufacturing process of a diffraction grating according to the present invention.

[Explanation of symbols]

 1 InP compound semiconductor substrate 2 photoresist film 3 photoresist film 4 diffraction grating pattern 5 diffraction grating

Claims (1)

[Claims] 1. A step of forming a first photoresist layer sensitive to light on a semiconductor substrate; a step of forming a second photoresist layer sensitive to electron beams on the first photoresist layer; Exposing the second photoresist layer with an electron beam; selectively removing the second photoresist layer and exposing one surface of the first photoresist layer; tilting the semiconductor substrate; The first
The surface of the photoresist film and the second resist film is
Exposing to a diffraction grating pattern using a light flux interference exposure method; after removing the second resist film, selectively etching away the first photoresist pattern,
Forming a diffraction grating pattern of the first photoresist; using the diffraction grating pattern of the first photoresist as a mask, selectively removing the surface of the semiconductor substrate to form a diffraction grating on the surface of the semiconductor substrate Diffraction grating manufacturing method characterized by including the steps of: