JPH04287918A - Etching method of semiconductor multilayer film - Google Patents

Abstract

PURPOSE:To acquire a processing surface without irregularities in a sidewall by providing both a process for forming a mixed crystal part by inducing mutual diffusion in a part of a semiconductor multilayer film and a process for acquiring a desired mesa structure by etching the mixed crystal part alone. CONSTITUTION:A semiconductor multilayer film structure 2 is formed which consists of a 200A-thick GaAs layer 2a and a 200A-thick AlAs layer 2b laminated alternately on a GaAs substrate 1. Then, an SiO2 film is deposited by CVD method. A 2mum-diameter circular SiO2 mask 3 is formed by selectively etching the SiO2 film by hydrofluoric acid water solution using a photoresist as a mask. Thereafter, Zn is introduced by removing and thermally treating the circular SiO2 mask 3 after ion implantation of Zn and mutual diffusion of GaAs and AlAs is induced to make the region an Al0.5Ga0.5As mixed crystal part 4. Etching is performed vertically to a depth of 2.2mum by RIBE method using Cl<-> to form a cylinder of the semiconductor multilayer film 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to selective etching of semiconductor multilayer films grown on semiconductor substrates.

0002

2. Description of the Related Art Surface-emitting lasers, which emit laser light perpendicular to the substrate surface, are known as devices using a semiconductor multilayer film formed on the surface of a semiconductor substrate, and are being actively researched and developed.

For example, J. L. Jewel et a
7th International Conference on Optical Integration and Optical Communications (7th I
nt. Conf. on IOOC, Di
gest, vol. 5, p. 8 to 9) introduce a surface-emitting laser using a laser reflecting mirror made of a semiconductor multilayer film of GaAs and AlAs with 23 periods.

In surface emitting lasers, in order to lower the emission threshold current, the semiconductor multilayer film has a diameter of 1 to 5 μm and a height of several μm.
It is processed into a cylindrical shape of m.

[0005]

[Problems to be Solved by the Invention] In order to process semiconductor multilayer films, dry etching using a reactive gas such as Cl2, such as reactive ion beam etching (RI), is usually used.
BE), chemical assisted ion beam etching (CAIBE), etc. are used.

In these conventional etching methods, the etching rate tends to depend on the composition of the semiconductor.

Asakawa et al. Applied Physics vol. 54, no
．． 11, 1985, pp. 1136-1153
reported that, particularly in the case of GaAs and AlAs, if the ultimate vacuum in the etching chamber is not better than 10-7 Torr, the etching rate of AlAs becomes extremely low due to the influence of residual moisture.

[0008] Due to these phenomena, when a semiconductor multilayer film is etched, the side wall becomes uneven, and a smooth processed surface cannot be obtained.

Furthermore, even if the residual moisture in the etching chamber is sufficiently low, AlAs may selectively react with the chlorine component adsorbed and remaining on the processed surface after etching when the processed wafer is taken out into the atmosphere. As a result, there is a problem in that unevenness is ultimately formed.

As described above, in the conventional etching method, it is difficult to obtain a smooth processed surface of a semiconductor multilayer film, and it is difficult to control the processed shape, which adversely affects device performance.

An object of the present invention is to provide a method for etching a semiconductor multilayer film that is easy to put into practical use and that provides a smooth processed surface with good controllability and is highly reliable.

0012

[Means for Solving the Problems] A method for etching a semiconductor multilayer film of the present invention includes a method in which a first semiconductor layer and a second semiconductor layer having a different forbidden band width from the first semiconductor layer are alternately stacked. In a method of etching a semiconductor multilayer film,
This method consists of a step of inducing interdiffusion in a part of the semiconductor multilayer film to form a mixed crystal part, and a step of etching only the mixed crystal part to obtain a desired mesa structure.

[0013]

[Operation] The problem with the conventional etching method is that the reaction rate with the etchant differs depending on the composition of the semiconductor layers constituting the semiconductor multilayer film.

In the present invention, the dependence of the reaction rate on the composition is eliminated by inducing interdiffusion in advance in the region to be processed, thereby breaking the multilayer film structure and creating a mixed crystal with an almost single composition. There is.

[0015]

[Example] Regarding an example of the present invention, FIGS. 1(a) to (
This will be explained with reference to e).

First, as shown in FIG. 1(a), GaA
A semiconductor multilayer film structure 2 consisting of a GaAs layer 2a with a thickness of 200A as a first semiconductor layer and an AlAs layer 2b with a thickness of 200A as a second semiconductor layer is grown on an s-substrate 1. There is.

Next, as shown in FIG. 1(b), a SiO2 film is deposited by CVD. Using a photoresist (not shown) as a mask, the SiO2 film is selectively etched with an aqueous hydrofluoric acid solution to form a circular SiO2 mask 3 with a diameter of 2 .mu.m.

Next, as shown in FIG. 1(c), after Zn is ion-implanted, the circular SiO2 mask 3 is removed and heat treatment is performed to introduce Zn and form GaAs and AlA.
s and induces mutual diffusion with Al0.5 Ga.
0.5 As mixed crystal part 4. Zn is also diffused in the lateral direction, and the Al0.5 Ga0.5 As mixed crystal portion 4 slightly enters under the circular mask 3.

Next, as shown in FIG. 1(d), Cl+
A cylinder of the semiconductor multilayer film 2 was formed by vertical etching to a depth of 2.2 μm using the RIBE method. At this time, the Al0.5 Ga0.5 As mixed crystal part 4 is exposed on the processed surface, and conventionally, after etching, Al
The problem of As selectively reacting and forming unevenness has been solved.

Next, as shown in FIG. 1(e), by removing the SiO2 mask 3 by cleaning with an aqueous hydrofluoric acid solution, a cylinder of the GaAs/AlAs semiconductor multilayer film 2 having smooth side surfaces with no unevenness is obtained. It will be done.

In this embodiment, thermal oxidation of Zn was used as the mixed crystallization step, but other impurities capable of causing interdiffusion, such as Si, may also be used. Also effective is a method of introducing impurities by ion implantation and then performing heat treatment.

Furthermore, if intentional introduction of impurities is not desirable, interdiffusion can be achieved only by heat treatment. This is done by forming a SiO2 or Si3N4 film on the region where mixed crystal formation is desired, and then heat-treating it at about 800°C. The accelerated diffusion phenomenon accompanying the diffusion of Si and Ga that occurs at this time is utilized (cap annealing mixed crystallization method).

On the other hand, as an etching method, other dry etching methods such as RIE method and CAIBE method can be used instead of the RIBE method of this embodiment. Also Cl2
It is also possible to apply a direct writing etching method using a focused ion beam or a combination of a focused ion beam and other reactive gases. Further, depending on the case, a chemical gas etching method or a wet etching method may be used alone or in combination with other dry etching methods.

Furthermore, instead of the circular SiO2 mask used in this embodiment, the planar shape may be polygonal or striped. Instead of SiO2 as the mask material,
Similar effects can be obtained using other dielectrics, insulators, or metals such as Si3N4.

[0025]

Effects of the Invention In a semiconductor multilayer film structure formed on a semiconductor substrate, by selectively etching only the mixed crystal region, it was possible to obtain a smooth processed surface with no unevenness on the sidewalls.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention in the order of steps.

[Explanation of symbols]

1 Semiconductor substrate 2 Semiconductor multilayer film 2a GaAs layer 2b AlAs layer 3 SiO2 mask 4 Mixed crystal part

Claims (4)

[Claims] 1. A method for etching a semiconductor multilayer film in which a first semiconductor layer and a second semiconductor layer having a different forbidden band width from the first semiconductor layer are alternately stacked. A method for etching a semiconductor multilayer film, comprising a step of inducing interdiffusion in a part to form a mixed crystal part, and a step of etching only the mixed crystal part to obtain a desired mesa structure. 2. The step of forming the mixed crystal portion includes one of selective thermal diffusion of impurity elements, implantation of impurity ions, and heat treatment.
2. The method of etching a semiconductor multilayer film according to claim 1, comprising at least three steps. 3. The method of etching a semiconductor multilayer film according to claim 1, wherein the mixed crystal portion is etched by dry etching using charged particles. 4. The step of doping impurities using a thin film formed on the semiconductor multilayer film as a mask, and selectively etching the semiconductor multilayer film using the thin film as a mask.
The method of etching a semiconductor multilayer film described above.