JPH05299761A - Diffraction grating and its manufacture - Google Patents

Abstract

PURPOSE:To provide a diffraction grating wherein, even when the depth of grooves is the same, its coupling coefficient is distributed and its photolithographic process and its etching process are required only once and to provide its manufacturing method. CONSTITUTION:An InP substrate 11 is coated with a resist 12 for electron-beam exposure; It is exposed by using an electron beam whose spot diameter is, e.g. 0.05mum in such a way that the line width of an exposure part 13 at the right part on the InP substrate 11 is set at 0.05mum and that the line width of an exposure part 14 at the left part on the InP substrate 11 is set at 0.12mum. At this time, an unexposed part in the former part is 0.19mum, and that in the latter part is 0.12mum. Thereby, a diffraction-grating resist pattern 15 at a pitch of 0.24mum can be formed on the whole face of the InP substrate 11. After that, a diffraction grating 16 is transferred to the InP substrate 11 by, e.g. a dry etching operation, and the resist 12 for electron-beam exposure is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction grating used for selecting a wavelength of light in a semiconductor laser device or the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a technique in this field, "3rd
8th Joint Lecture Meeting on Applied Physics, Proceedings, No.
3, page 966, "Formation of non-uniform depth diffraction grating by RIE" Osamu Matsuda et al. According to this, as a method of controlling the axial light distribution in the distributed feedback (DFB) semiconductor laser and improving the threshold gain difference between the oscillation longitudinal modes, a structure in which the coupling coefficient is distributed can be considered.
As a method for realizing this, a structure is shown in which the depth of the groove of the diffraction grating is deep near the central portion and shallow in other portions.

The manufacturing process of a conventional diffraction grating will be described below with reference to FIG. First, as shown in FIG. 2A, a negative resist 2 is coated on the entire surface of the substrate 1, and then a diffraction grating resist pattern is formed by a two-beam interference exposure method. As shown in FIG. A diffraction grating is formed on the entire surface by dry etching. After that, Figure 2
As shown in (c), the positive resist 3 is coated, only the resist near the central portion is removed by the photolithography method, and dry etching is performed again as shown in FIG. 2 (d). Next, the positive resist 3 and the negative resist 2 are removed to form a diffraction grating in which the diffraction grating near the central portion is deep and the other portions are shallow as shown in FIG. 2 (e).

[0004]

However, in the above-mentioned diffraction grating, when the crystal is grown on the diffraction grating, the thickness of the grown crystal layer varies due to the difference in the groove depth of the diffraction grating. There is a problem in that it occurs, and a photolithography process and an etching process are required twice in the manufacturing method, which takes time, and the yield is deteriorated.

According to the present invention, variations in the thickness of the crystal growth layer on the diffraction grating caused by the difference in groove depth of the diffraction grating described above and the photolithography process and the etching process are required twice in the manufacturing process. In order to eliminate the problem,
It is an object of the present invention to provide a diffraction grating and a method for manufacturing the same in which the coupling coefficient is distributed while the grooves have the same depth, and the photolithography process and the etching process are performed only once.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a diffraction grating used for wavelength selection of light, in which the sum of the line widths of lines and spaces is set to be constant and the depth is Is constant and has a structure in which the ratio of lines and spaces is partially changed. In addition, in the method of manufacturing a diffraction grating used to select the wavelength of light, the line width is set to a constant line width and the line width is changed by changing the exposed or unexposed line width during the photolithography process. And the ratio of space is changed.

[0007]

According to the present invention, as described above, the sum of the line widths of lines and spaces is set to be constant by the electron beam exposure method, the depth is constant, and the ratio of lines to spaces is set. Try to partially change. This is because the coupling coefficient of the diffraction grating changes depending on the ratio of the unevenness of the diffraction grating. At this time,
Even if the ratio of the irregularities changes, the value of the selected wavelength does not change because the pitch is constant.

Therefore, the photolithography / etching process is performed only once, and the process time can be shortened. Furthermore,
The depth of the grooves of the diffraction grating can also be formed uniformly over the entire surface.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view of a diffraction grating manufacturing process showing an embodiment of the present invention. First, as shown in FIG. 1A, for example, an InP substrate 11 is coated with an electron beam exposure resist [for example, PMMA (trade name)] 12. On the other hand, the spot diameter is, for example, 0.0
Using an electron beam of 5 μm, the line width of the exposed portion 13 on the right side of the InP substrate 11 is 0.05 μm,
Exposure is performed with the line width of the exposed portion 14 on the left side of 0.12 μm. At this time, the unexposed area is 0.19μ in the former case.
m, and the latter is 0.12 μm.

As a result, the diffraction grating resist pattern 15 having a pitch of 0.24 μm can be formed on the entire surface of the InP substrate 11. Thereafter, as shown in FIG. 1B, the diffraction grating 16 is transferred to the InP substrate 11 by, for example, dry etching, and a resist for electron beam exposure (for example, PMM) is used.
A) Remove 12

With this configuration, the sum of the line widths of the line and the space is constant, and the depth is constant,
The proportion of lines and spaces can be partially changed. In the above embodiment, the substrate is In
Although the P substrate is used, GaAs may be used instead of this.

Further, as a resist for electron beam exposure,
An EB resist may be used. It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0013]

As described above in detail, according to the present invention, by changing the line width of the exposed portion of the resist by one exposure method, the ratio of the line and the space is partially different. Since the resist pattern is formed and then the diffraction grating is transferred to the substrate by etching, only one photolithography etching step is required, the process time is short, and the yield does not change.

Further, the depth of the grooves of the diffraction grating can be made uniform over the entire surface.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of manufacturing steps of a conventional diffraction grating.

[Explanation of symbols]

11 InP substrate 12 resist for electron beam exposure (for example, PMM
A) The exposed portion of the right portion of the 13 InP substrate (line width 0.05
μm) 14 InP substrate left exposed part (line width 0.12
μm) 15 Diffraction grating resist pattern 16 Diffraction grating

Claims (3)

[Claims] 1. In a diffraction grating used for wavelength selection of light, the sum of the line widths of lines and spaces is set to be constant, the depth is constant, and the ratio of lines to spaces is partially changed. A diffraction grating having a different structure. 2. A method of manufacturing a diffraction grating used for wavelength selection of light, wherein: (a) the sum of the line widths of lines and spaces is set to be constant, and (b) the exposed line width or unexposed during the photolithography process. A method of manufacturing a diffraction grating, characterized in that the ratio of lines to spaces is changed by changing the line width. 3. A method for manufacturing a diffraction grating used for wavelength selection of light, wherein (a) a substrate is coated with a resist for electron beam exposure, and (b) the sum of the line widths of lines and spaces is constant. (C) by using the electron beam to reduce the line width of the exposed portion on one part of the substrate and expose it on the other part of the substrate by increasing the line width of the exposed part. A method of manufacturing a diffraction grating, in which a resist pattern having a varied space ratio is formed, (d) a diffraction grating is transferred to the substrate by dry etching, and the resist pattern is removed.