JPS62155580A - Manufacture of grating - Google Patents

Abstract

PURPOSE:To manufacture easily and with excellent reproducibility, a grating having a phase shift region corresponding with lambda/4, by forming a photo resist in the manner in which the top part of a grating formed on the upper layer surface of a semiconductor layer having a step difference is exposed, and performing an etching applying the resist as a mask. CONSTITUTION:A step difference 3b is formed by constituting a groove 3a having a period 2L, width L and depth of (h) on the surface of a p-InGaAsP layer 3. After a first grating 5 is formed on the surface of the step difference by a holographic exposure, the first grating 5 having a lambda/4-phase shift region 5b is formed by performing an etching which applies a photo resist 6 formed on the first grating as a mask. A p-InP layer 7, clad layer, is formed thereon, and an objective DFB laser is completed by means of, for example, cleaving along a dot and dash chain line. Consequently, the DFB laser capable of single longitudinal mode oscillation can be manufactured with excellent reproducibility, while a complicated and different technology such as electron beam lithography and the like is not necessary for forming the region 5b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a grating, and the present invention relates to a method for manufacturing a grating, which uses a distributed feedback
It is most suitable for forming gratings for ack) type lasers (hereinafter referred to as DFB lasers).

[Summary of the invention]

The present invention provides a method for manufacturing a grating, including a step of forming a grating on a surface of a semiconductor layer having a step, and exposing a top portion of a convex portion forming the grating formed on the surface of the semiconductor layer above the step. A step of forming a photoresist on the surface of the grating so as to etching the grating, and a step of etching the grating using the photoresist as a mask are respectively provided. By forming a phase shift region corresponding to λ (wavelength of light), a grating having a phase shift jD region corresponding to λ/4 can be manufactured easily and with good reproducibility. It is.

[Conventional technology]

DFB lasers are highly anticipated as lasers that can realize single-longitudinal mode oscillation. In this DFB laser, a grating (diffraction grating) with a uniform pitch of concavo-convex portions has conventionally been used for distributing light by Bragg reflection. However, in a DFB laser with a uniform grating, two longitudinal mode oscillations with the same gain may occur simultaneously or by mode hopping, so a single-mode oscillation is possible.
Achieving longitudinal mode oscillation was not easy.

In order to correct these drawbacks and realize single-longitudinal mode oscillation, we created a grating as shown in Figure 3, in which the phase is shifted by locally changing the pitch of the periodic asperities in the center of the grating. In recent years, a DFB laser has been proposed in which a phase difference of π, that is, a phase shift corresponding to λ/4 (λ: wavelength of light) is generated in the light.

Gratings having a λ/4 phase shift region as shown in FIG. 3 described above have conventionally been formed using electron beam lithography or other problematic processes in the following manner. That is, for example, when forming a grating using electron beam lithography technology, first the DF
After forming a semiconductor layer to serve as a guide layer for the B laser, an electron beam resist is applied on this half-layer. Next, when this resist is exposed to light using electronic cotton, the drawing pitch is locally changed in a portion that will become a λ/4 phase shift region, and then development is performed to form a resist in a predetermined pattern. Next, using this resist pattern as a mask, the semiconductor layer was etched to form a grating as shown in FIG.

However, when using the above-mentioned electron beam lithography technology, it is difficult to produce a grating with a λ/4 phase shift region as shown in Figure 3 with good reproducibility, and it is also difficult in terms of process. There are drawbacks.

As a prior art related to the method for manufacturing gratings, there is a method proposed by the present inventor in Japanese Patent Application No. 60-53810. A method of manufacturing a grating is described.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for manufacturing a grating that corrects the above-mentioned drawbacks of the prior art.

[Means for solving problems]

A method for manufacturing a grating according to the present invention includes a step of forming a grating on a surface of a semiconductor layer having steps;
Forming a photoresist 1 on the surface of the grating so that the top portion of the convex portion forming the grating formed on the surface of the semiconductor layer above the step is exposed; and masking the photoresist. and a step of etching the grating to form a phase shift region corresponding to λ/4 (λ: wavelength of light) in a portion of the grating corresponding to the step.

〔Example〕

Hereinafter, the present invention will be described as a long wavelength band D of wavelength λ = 1.3 to 1.5 μm.
An embodiment applied to the manufacture of an FB laser will be described with reference to the drawings. Note that the pitch A of the primary grating used in this DFB laser is usually about 0.2 to 0.
It is 25 μm.

As shown in FIG. 1A, first, an n-
InGaAsP layer 2 constituting an active layer on 1nP substrate 1
, the p −1nGaAs P layer 3 constituting the guide layer is M
Epitaxial growth is performed sequentially by ILE method or MOCVD method.

Next, as shown in FIG. 1B, a /41ζ 3a having a width and a depth h is formed with a period of 2L on the surface of this p-InGaAs P layer 3 by a conventionally known photolithography technique. Here, the width is selected to be approximately equal to the length of the resonator of the DFB laser in the completed state (see FIG. 2), and the depth h is selected to be approximately equal to the depth and height of the unevenness of the grating to be formed. Note that the level difference produced on the surface of the p-InGaAs P layer 3 by forming the groove 3a is indicated by 3b.

Next, as shown in FIG. 1C, the p −1nGaAs
After applying a predetermined photoresist 4 to the surface of the P layer 3,
For example, the photoresist 4 is linearly exposed with a pinch equivalent to a primary grating by a conventionally known holographic exposure method using ultraviolet laser light.

Next, after developing the photoresist 4, the p-1nGaAs P layer 3 is etched using a predetermined pattern of photoresist (not shown) left by the development as a mask, so that the surface is etched as shown in FIG. 1D. A primary grating 5 having steps is formed. After this, the remaining photoresist 4 is removed.

Next, as shown in FIG. 1E, a photoresist 6 is applied so that the surface of the primary grating 5 is completely covered, and then this photoresist 6 is selectively removed through, for example, an exposure and development process. As a result, the top portion of the convex portion 5a of the primary grating 5 is exposed.

Next, the primary grating 5 is etched from the top portion exposed in this manner, and as shown in FIG. At the same time,
A phase shift region 5b corresponding to λ/4 is formed at a position corresponding to the first formed step 3b.

After that, as shown in FIG. 1G, a p-1nP layer 7 constituting a cladding layer is formed on the primary grating 5, and then a second
As shown in the figure, the desired DFB laser is completed.

According to the embodiment described above, as shown in FIG. 1B, p −
The surface of the 1nGaAs P layer 3 has a period of 2L and a width L1 and a depth h.
A step 3b is formed by forming grooves 3a, and then a primary grating 5 is formed on the surface of the step 3b by holographic exposure as shown in FIG. By performing etching using the etched photoresist 6 as a mask, the primary grating 5 having the λ/4 phase shift region 5b as shown in FIG. 1F is formed, which has the following advantages. That is, the λ/4 phase shift region 5
Since there is no need to use complicated and difficult techniques such as electron beam lithography to form the λ/4 phase shift region 5b, the primary grating 5 having the λ/4 phase shift region 5b can be easily formed with good reproducibility. Therefore, the λ/4 phase shift region 5b of the primary grating 5 enables single-longitudinal mode oscillation, making it possible to easily manufacture an FB laser with good reproducibility.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made based on the technical idea of the present invention. For example, the primary grating 5 shown in FIG. 1D can be formed by a method other than holographic ink exposure. Furthermore, in the above-mentioned embodiments, the present invention is applied to InGaAs P/
Although the case where it is applied to a DFB laser with an InP heterostructure has been explained, it is applicable to a DFB laser with other types of heterostructures.
It goes without saying that the present invention can be applied to lasers, but also to gratings for various uses that generally have a phase shift region of λ/4.

Existing necessity [of the invention]

According to the present invention, a grating having a +[] shift region corresponding to λ/4 can be easily manufactured with good reproducibility.

[Brief explanation of drawings]

1A to 1F are cross-sectional views showing a method for manufacturing a DFB laser according to an embodiment of the present invention in order of steps, and FIG.
DFB manufactured by the manufacturing method shown in Figures A to 1G
A perspective view of the laser, and FIG. 3 is a cross-sectional view of a conventional grating. In the symbols used in the drawings, 1----------111--n -InP substrate 2----------1nGaAsP layer 3-
--------p -1nGaAs P layer 3b---
−−・−・−・−・One step difference 5−−−−−−・4th order grating 5 a, −−−−−, −,, −−−−−, -1 convex portion 5b----------1-- Phase shift region 7------------p -1nP layer.

Claims (1)

[Scope of Claims] A step of forming a grating on a surface of a semiconductor layer having a step, and a step of forming a grating on a surface of the semiconductor layer above the step so that the top portion of a convex portion constituting the grating is exposed. The method includes a step of forming a photoresist on the surface of the grating, and a step of etching the grating using the photoresist as a mask. 1. A method for manufacturing a grating, characterized in that a phase shift region corresponding to a wavelength is formed.