JPH03225302A - Production of optical waveguide of semiconductor - Google Patents

Abstract

PURPOSE:To improve the controllability of etching depth by continuously carrying out etching with a gas having relatively low reactivity and etching with a gas having relatively high reactivity in an etching stage at the time of forming a rib part. CONSTITUTION:First clad layer 2 of Al0.5Ga0.5As is grown on a GaAs substrate 1 and waveguide layer 3 of AlGaAs and a second clad layer 4 of Al0.5Ga0.5As are formed on the layer 2. A photoresist mask having the shape of a waveguide to be formed on the layer 3 is then formed on the layer 4 and the part of the layer 4 not covered with the mask is etched with a gas having low reactivity in a first etching stage. The etched part is further etched with a gas having high reactivity in a second etching stage. Since clean etched surfaces having the same state are always obtd. after the first etching stage and then second etching is carried out, the controllability of etching depth is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor waveguide used in semiconductor optical integrated circuits and the like.

(Prior Art) Along with advances in optoelectronics, research and development into the integration of semiconductor optical devices has been actively progressing in recent years. In particular, semiconductor optical waveguides can be realized on semiconductor substrates by applying microfabrication technology cultivated in semiconductor electronic devices, and can be used for connections between each switch of a semiconductor optical matrix switch, and between semiconductor optical functional elements on the same substrate. (for example, connecting a light source to a switch or amplifier, etc.)
It is considered one of the important components of semiconductor optical integrated circuits. As a method for forming such a semiconductor optical waveguide, a waveguide-shaped mask is formed on a semiconductor substrate using a normal photolithography method, and then a rib-shaped optical guide is formed using a reactive ion beam etching method (RIBE method) using BCΩ3 gas. Electronics Letters Vol. 22, p. 1243 (E
LCTRONIC3LETTER8Vol, 22p,
1243).

(Problems to be Solved by the Invention) Incidentally, when forming a semiconductor optical waveguide, controllability of the height of the rib portion, that is, the etching depth is important.

This is because the depth of etching directly affects the strength of light confinement in the semiconductor optical waveguide. For example, when manufacturing a directional coupler type semiconductor optical switch, the etching depth when forming the rib portion is Unless it is controlled with some degree of precision, the designed operation cannot be obtained. However, in dry etching using the conventional RIBE method, the controllability of the etching depth is affected by the surface condition of the wafer, and the controllability of the etching depth is about ±5% at most. As described above, the conventional semiconductor waveguide manufacturing method has a problem to be solved regarding the controllability of the depth of the rib-type waveguide.

(Means for Solving the Problems) In order to solve the above-mentioned problems, a method for manufacturing a semiconductor optical waveguide according to the present invention includes at least a semiconductor first cladding layer, a semiconductor waveguide layer, and a semiconductor second cladding layer on a semiconductor substrate. a step of stacking to form a stacked structure semiconductor wafer;
A step of providing an etching mask in the shape of an optical waveguide to be formed on the laminated structure semiconductor wafer, and removing the second semiconductor cladding layer other than the portion covered by the mask by etching to form a rib-type optical waveguide. The step of removing the semiconductor second cladding layer other than the portion covered by the mask by etching to form a rib-type optical waveguide is a first etching step using a relatively low-reactivity gas. It is characterized in that the second etching step using a relatively highly reactive gas is performed continuously.

(Function) Generally, when forming a rib portion of a semiconductor optical waveguide, controllability of etching depth is important. This is because the depth of etching directly affects the strength of light confinement in the semiconductor optical waveguide. For example, when manufacturing a directional coupler type semiconductor optical switch, the etching depth when forming the rib portion is Unless it is controlled with some degree of precision, the designed operation cannot be obtained. However, in dry etching using the conventional RIBE method, the controllability of the etching depth depends on the surface condition of the wafer, making it impossible to obtain an etching depth with good controllability.

On the other hand, in the present invention, in the dry etching process when forming the rib portion, the first etching process is performed using a gas with relatively low reactivity. controllability is improved. Furthermore, since a second etching process using a relatively highly reactive gas is performed after this, a selectivity with the mask is ensured, and there is no concern that the perpendicularity will decrease due to mask recession, and damage to the etched surface is avoided. few. For this reason,
The etching depth is more controllable than etching using only a highly reactive gas from beginning to end, and the etching surface is more perpendicular and less damaged than etching using only a less reactive gas from beginning to end.

(Example) The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 shows Ga produced by an embodiment of the method of the present invention.
FIG. 2 is a cross-sectional view showing the structure of an As/A, l/GaAs semiconductor optical waveguide. AΩ on the GaAs substrate 1. 5 Ga
O,5A S first cladding layer 2 is grown, AΩo 5
Gao, 5A GaA on the first cladding layer 2
An s-waveguide layer 3 is grown. On the GaAs waveguide layer 3, there is a rib portion AΩo, Ga 0.5 A
An S second cladding layer 4 is formed.

A method for manufacturing the semiconductor optical waveguide shown in FIG. 1 will be described below. A molecular beam epitaxial growth method (MBE method) or a metal organic vapor phase epitaxy method (M
O-CVD method), A41' o, G a o,
5 As first cladding layer 2, GaAs waveguide layer 3, Aj
? 0.5 Gao, s A S second cladding layer 4
grow. The thickness of each layer is AgO,5G ao,5
As the first cladding layer 2 has a thickness of about 1 to 2 μm and is made of GaAs.
Waveguide layer 3 is about 0.2 μn+, AΩo5G a o, 5
The second cladding layer 4 has a thickness of about 1.2 μm.

After growing the crystal as described above, the waveguide rib portion is RI
Formed by BE method. An outline of this process is shown in Figure 2. First, as shown in FIG.
Waveguide-shaped photoresist mask 11 to be formed on
form. Next, as shown in FIG. 2(b), the portion not covered with the photoresist 11 is etched by about 0.1 μm by a first etching process using Ar gas with low reactivity. At this time, photoresist mask 1
1 is etched by about 0.1 μm at most.

After this, the etching chamber is evacuated once, and then a second etching step using highly reactive C (12 gas) is performed to further etch the portion not covered by the photoresist 11 by about 0.9 μm. .

Thereafter, when the photoresist 11 is removed using an organic solvent or the like, a semiconductor optical waveguide as shown in FIG. 2(c) is obtained.

The above is an embodiment of the method for manufacturing a semiconductor optical waveguide according to the present invention, and the principle by which the controllability of the etching depth is improved by the above-mentioned manufacturing method will be explained below.

Conventionally, the controllability of the etching depth by dry etching depends on the surface condition of the wafer 1 to be etched, and if dry etching is performed using a highly reactive gas from the beginning, the etching depth will vary depending on the surface condition of the wafer. Things were falling apart. On the other hand, in this embodiment, the surface of the wafer 1 is soothed by about 0.1 μm in the first etching process using Ar gas with low reactivity, so the etching depth is as low as 0.1 μm. It does not depend on the surface condition of the etched surface, and a clean etched surface can be newly exposed in a vacuum. Furthermore, since it is a gas with low reactivity, molecules are less likely to participate in bonding at this etching interface. For this reason,
After the first etching step is completed, a clean etched surface in the same state is always obtained. After this, the second etching step using the highly reactive CΩ2 gas is performed, so that the controllability of the etching depth is improved compared to etching performed only with the CΩ2 gas from the beginning. Furthermore, since the second etching process using highly reactive CD2 gas is performed after the first etching process, a selectivity with respect to the comparison mask is ensured when etching is performed with Ar gas from beginning to end, and vertical etching due to mask recession is ensured. There is no need to worry about deterioration in quality, and there is less damage to the etched surface.

Although the RIBE method was used in this embodiment, the present invention is not limited to this, and the present invention can also be applied to other dry etching methods such as reactive ion etching (RIE). In addition, CΩ2 was used in the second etching step, or it is not limited to this as long as it has high reactivity; for example, BC, Q3 may be used, or B
It may be r2.

(Effects of the Invention) As described above, according to the present invention, the controllability of the etching depth is improved in the dry etching step when forming the rib portion, regardless of the surface condition of the wafer. moreover,
The etching selectivity with respect to the mask is ensured, there is no concern that the perpendicularity will deteriorate due to mask recession, and there is little plasma damage to the etched surface.

[Brief explanation of drawings]

FIG. 1 shows G a A produced by the method of one embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the structure of the s/AΩGaAs semiconductor optical waveguide, and a conceptual diagram showing the etching process in the embodiment. 1-GaAs substrate, 2-AΩo, Gao, 5
As first cladding layer, 3...GaAs waveguide layer, 4
-AΩ. , 5 Gao, 5 A S second cladding layer, 10... Ga As/AΩGaAs wafer, 11... Photoresist mask. Figure 1 Figure (a) Figure (b) Figure (c)

Claims (1)

[Claims] A step of laminating at least a semiconductor first cladding layer, a semiconductor waveguide layer, and a semiconductor second cladding layer on a semiconductor substrate to form a laminated semiconductor wafer, and applying an etching mask in the form of an optical waveguide to be formed to the laminated structure. In the method for manufacturing a semiconductor optical waveguide, the method includes a step of providing the second cladding layer on a semiconductor wafer, and a step of removing the semiconductor second cladding layer other than the portion covered by the mask by etching to form a rib-type optical waveguide. The process of removing the semiconductor second cladding layer other than the covered portion by etching to form a rib-shaped optical waveguide consists of a first etching process using a gas with relatively low reactivity and a second etching process using a gas with relatively high reactivity. 1. A method for manufacturing a semiconductor optical waveguide, characterized in that the second etching step and the second etching step are successively performed.