JPH04127157A - Production of semiconductor element - Google Patents

Abstract

PURPOSE:To obtain a mask for dry etching having excellent perpendicularity by subjecting upper resist patterns of a three-layered structure to a high temp. heating treatment after the formation thereof, thereby erasing striation and the laminated cross stripes by the influence of standing waves. CONSTITUTION:A 1st layer photoresist layer 2 is formed on an InP semiconduc tor substrate 1 and is then spin coated with a soln. mixed with orthotitanic acid and is heat treated, by which an intermediate layer 3 is formed. The upper layer photoresist film is therafter formed and is exposed by a reduction stepper to form patterns 4. The striation 5 and the laminated cross stripes 6 generated by the influence of the standing waves are erased by executing the heating treatment for 20 minutes at 170 deg.C. The intermediate layer 3 and the lower layer resist 2 are dry etched in this way, by which the mask for sharp dry etching which is free from the striation at the pattern edges is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of dry etching a light emitting region including an active layer of a semiconductor laser or array through a dry etching mask.

[Conventional technology]

Conventional semiconductor laser cavity end faces are fabricated using dry etching to create a three-layer structure (upper layer resist.

This was done through a mask consisting of an intermediate layer, a Ti vapor deposited film, and a lower resist layer. However, during the fabrication of the upper resist mask, layered horizontal stripes occur due to the effects of striations and standing waves, which are transferred to the laser resonator end face and become a major cause of a decrease in reflectance.

[Problem to be solved by the invention]

The above conventional technology does not take into account the striations and standing waves of the upper resist layer, and when dry etching the end and side surfaces of the light emitting region consisting of convex parts including the active layer in the fabrication of semiconductor lasers and laser arrays, There was a problem in that the laminated horizontal stripes were transferred due to the influence of vibration and standing waves, reducing the reflectance.

[Means to solve the problem]

In order to achieve the above object, the present invention subjects the top layer photoresist mask to a high temperature heat treatment to obtain a top layer mask in which laminated horizontal striped irregularities caused by striations and standing waves are eliminated.

[Effect]

Using the above resist mask, the intermediate layer and lower layer resist are dry etched to produce a sharp dry etching mask with no striations at pattern edges. After that, use the lower resist as a mask,
Tri-etch the light-emitting region including the active layer to remove vertical side surfaces and
It becomes possible to form a smooth striped mesa having an end face, and the processing accuracy of the waveguide and end face is improved, making it possible to manufacture semiconductor lasers and arrays with excellent characteristics.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

A first photoresist layer 2 with a thickness of 2 μm is deposited on an InP semiconductor substrate 1.
The film was formed with a thickness of m to 10 μm (FIG. 1(a)). Here, 0FPR800 (Tokyo Ohka Co., Ltd.: trade name) was used for the first photoresist layer 2.

Heat treatment was performed at 230°C for 20 minutes. Next, a solution containing orthotitanic acid was spin-coated onto the silicon compound ○CD (Tokyo Ohka Co., Ltd.: trade name), and heat treated at 230°C for 20 minutes to form the intermediate layer 3 as shown in Figure 1(b). was formed with a film thickness of 0.08 μm. After that, the upper layer photoresist film was coated with a thickness of 1 μm.
1(c) and exposed with a reduction projection device.
A pattern 4 as shown in FIG.

However, in the upper photoresist layer, striations 5 as shown in FIG. 2(a) and horizontal stripes 6 in a laminated manner are generated due to the influence of standing waves. The laminated horizontal stripes caused by striations and standing waves could be eliminated by heat treatment at 170° C. for 20 minutes, as shown in FIG. 2(b) 7.

For the silicon compound of the intermediate layer, the upper photoresist pattern 4 was transferred to the intermediate layer 3 by dry etching using a mixed gas of CHF and C2F to form a pattern 3' as shown in FIG. 3(a). Next, the pattern 3' was transferred to the lower photoresist layer 3 by dry etching using 02 gas to obtain a dry etching mask 2' with excellent verticality as shown in FIG. 3(b). This dry etching mask yielded a highly accurate photoresist pattern with a width of 1 μm, a length of 100 μm, a height of 3 μm, and a striation of ±0.01 μm or less.

Thereafter, as shown in FIG. 3(c), the substrate 1 is dry-etched using CQ2 gas using the vertical pattern 2' as a mask to a depth of 5 to 10 μm without the influence of striations and horizontal stripes of standing waves. .

A striped mesa having a vertical end surface and a side surface 1' having a width of 1 μm and a length of 100 μm was obtained. A semiconductor layer was formed by buried growth until the convex portion became flat, and ohmic electrodes were formed on the top and bottom of the existing multilayer structure.

Thereafter, the elements on the sides were separated by cleavage, and a semiconductor laser array with a reflectance 5% higher than that of a conventional semiconductor laser array was obtained.

In this example, an InP substrate was used as the workpiece, but S
The material may be an i-substrate or a GaAs substrate. It is applicable not only to semiconductor substrates but also to dielectric materials and metal materials.

〔Effect of the invention〕

According to the present invention, after forming the upper resist pattern of the three-layer structure, high-temperature heat treatment is performed to eliminate striations and horizontal stripes in the stack due to the influence of standing waves, thereby dry processing the middle layer and lower layer photoresist. Therefore, it is possible to create a dry etching mask with excellent verticality. I with a double heterostructure using the above mask
By tri-etching nP crystal, it is possible to form a striped waveguide with vertical and smooth side and end faces, and it is possible to obtain semiconductor lasers and laser arrays with excellent characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the formation process of a three-layer mask for dry etching according to an embodiment of the present invention, FIG. 2 is a perspective view showing the state of the upper photoresist layer of the conventional example and the present invention, and FIG. 3 is a perspective view showing the state of the upper photoresist layer. is a cross-sectional view showing the process of dry etching a semiconductor laser array.

Claims (1)

[Claims] 1. In a method for manufacturing a semiconductor device, a first
After forming a pattern on the organic material layer, the second compound layer or metal layer, and the third photoresist layer, heat treatment is performed until the striations that occur at the edge of the pattern and the unevenness of the laminated horizontal stripes that occur on the side surface of the pattern disappear. After that, a desired pattern is transferred to the second layer and the first layer in sequence,
1. A method of manufacturing a semiconductor device, comprising forming a mask having vertical side surfaces on a substrate to be processed, and then processing vertical semiconductor end faces using a dry etching method. 2. In the step of forming a buffer layer, first cladding layer, laser active layer, and second cladding layer on a semiconductor substrate, and the step of forming a light emitting region having stripes consisting of convex portions in an already double heterostructure, A step of applying a mask material for semiconductor dry etching processing described in item 1 above, and a step of performing crystal dry etching processing on the semiconductor surface excluding the existing mask to form striped convex portions on the semiconductor crystal. a step of filling the periphery of the striped convex portion and forming a semiconductor layer until the buried surface becomes flat;
A method for manufacturing a semiconductor laser, comprising the step of forming ohmic electrodes on top and bottom of an existing multilayer structure.