JPS6320835A - Chemical etching of semiconductor crystal - Google Patents

Abstract

PURPOSE:To carry out uniformly and easily an etching treatment for a substance as mentioned hereunder: In (Ga1-xAlx)P(0.2<=x<=1) and furthermore, obtain etching selection rations that are enough to GaAs or InGaP and the like by using a hot sulfuric acid liquid as one of the etching liquids. CONSTITUTION:In the case of an etching treatment of a semiconductor crystal where a substance of In (Ga1-xAlx)P(0.2<=x<=1) is etched, sulfuric acid liquid is used. In such a case, its temperature is set within the range of 60-90 deg.C. This approach makes it possible to carry out selective etching treatments for In (Ga1-xAlx)P-(0.2<=x<=1) to GaAs or InGaP and the like. Furthermore, if only the temperature of sulfuric acid liquid is set within the range of 60-90 deg.C, its etching is carried out at a sufficiently fast speed without bringing upon a roughness of the etching surface.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to In(GaAl!)P(0,21-
x x ≦x≦1) The present invention relates to a method of etching a crystal, and in particular to a method of chemically etching a semiconductor crystal for selectively etching the above-mentioned crystal with respect to InGaP, GaAs, etc.

(Prior Art) In recent years, with the improvement of crystal growth technology of vapor phase growth, InGaAiP has been attracting attention as a compound semiconductor material. Although products using this material are still in the early stages of development, their application to short-wavelength semiconductor lasers, for example, is conceivable.

Short-wavelength semiconductor lasers are attracting attention as an alternative to conventional He-Ne lasers as light sources for optical recording of video discs, laser printers, and the like. Use as a light source for optical recording requires a structure that confines optical energy and injected current in a specific area, such as an internal stripe current confinement structure. Furthermore, for optical discs etc., the laser beam is 1 [μm
Since it is necessary to narrow down the light to a co-order minute spot light,
Transverse mode control is required to confine light parallel to the active layer of the semiconductor.

As a transverse mode control structure, for semiconductor lasers made of GaAJAs, for example, a ridge-embedded laser has been proposed (Reference, Proceedings of the 46th Japan Society of Applied Physics Conference, 4P-N-7, P223, 1985) ). This semiconductor laser is constructed as shown in FIG. 5, and is manufactured as follows. That is, the first GaAJAs cladding layer 7 that confines light and carriers is formed on the GaAs substrate 71.
2. GaAs active layer 73. Second GaA
An s cladding layer 74 and a Ga'A s ohmic contact layer 75 are crystal-grown in sequence, and an oxide film such as 5i02 is further formed thereon by sputter deposition or the like. Then,
Using this oxide film as a stripe-shaped mask using photolithography or the like, etching is performed up to part of the contact layer 75 and second cladding layer 74 to form a stripe-shaped ridge. Then, using selective growth techniques,
Both sides of the ridge are filled with a GaAs buried layer 76 of a conductivity type different from that of the second cladding layer 74, and then an electrode process is performed to complete the structure.

Note that the above-mentioned selective growth technique for GaAs is reported, for example, in the literature (Society of Applied Physics, Crystal Engineering Subcommittee, 2nd Crystal Engineering Symposium Lecture U, pH, 1985).

As can be seen from FIG. 7, in the ridge-buried type laser, the GaA, ffAs cladding layer 74 other than the ridge portion is thin, so the electromagnetic waves standing there are transmitted to the GaAs contact layer 74.
It oozes out. Therefore, a so-called loss guide structure is formed in which electromagnetic waves are guided only to the ridge portion, and stable transverse mode oscillation is achieved.

By the way, when forming the ridge, GaAs and G
It is necessary to etch aA and gAs into a predetermined shape. Regarding GaAs and GaAlAs, various etching solutions have been reported so far, including those that etch only GaAs, those that etch only GaA and f7As, and those that can be used for both and have approximately the same etching speed. .

For etching only GaAs, a mixed solution of ammonia water and hydrogen peroxide (PA Niche Yant), GaA1As
For etching only, hot phosphoric acid solution, hydrofluoric acid, hydrochloric acid, etc.
A mixed solution of water + sulfuric acid + hydrogen peroxide (SH etchant), which can be used in both cases and has the same etching speed,
There are mixed solutions of water + phosphoric acid and hydrogen peroxide (PH etchant), etc.

To form a ridge-type waveguide as shown in FIG. 7,
A method shown in FIG. 8 or 9 can be considered. In the method shown in FIG. 8, first a mask 77 of SiO2 is formed as shown in (a), then only GaAs is etched using, for example, a PA etchant, and then hot phosphoric acid is used to etch (b).
), only GaA and gAs are etched. 9th
In the method shown in the figure, a mask 77 is first formed as shown in (a), and then GaAs, GaA, and ff-As are simultaneously etched as shown in (b) using, for example, SH and PH etchants.

Comparing these methods, in the case of the method shown in Figure 9,
Since GaAs and GaA/As are etched simultaneously, the ridge widths of these two layers cannot be controlled independently. On the other hand, in the case of the method shown in FIG. 8, since the widths can be controlled independently, the degree of freedom in designing the device structure is increased. For example, in semiconductor lasers used in video discs, semiconductor lasers that utilize self-sustained pulsation, such as the IS3 laser (Japanese Patent Application Laid-Open No. 59-246258), are used in order to reduce noise caused by returned light. In order to realize such a structure, it is necessary to narrow the current injection width in response to the structure of the waveguide mode, and it is necessary to narrow the current injection width in response to the expansion of the waveguide mode. The width of the layer that determines the spread and the width of the layer that performs current confinement must be controlled independently.

In order to realize such a (14 structure) using InGaA, i'P material, the active layer 73 and cladding layer in FIG.
2,74, InGaP, InGaAiP, and GaAs are used as the ohmic contact layer 75, respectively; in that case, InGaA, i'P and GaAs are used.
An etching solution is required to selectively etch both. However, there have been no reports regarding etching solutions for InGaAJP materials, and the etchant, etching conditions, etc. are currently largely unknown.

(Problems to be Solved by the Invention) As described above, etching solutions for InGaA and &P have not been known so far, and
It was necessary to develop a device that etches I materials and a device that has etching selectivity with respect to GaAs and InGaP.

The present invention has been made in consideration of the above circumstances, and its purpose is to
To provide a method for chemically etching a semiconductor crystal, which can uniformly and easily perform etching of x P (0,2≦x≦1), and which also provides a sufficient etching selectivity for GaAs, InGaP, etc. be.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to use a hot sulfuric acid solution as an etching solution for InGaAIP.

In(GaA))Pl-X
x (0, 2 ≦
It has been found that there is sufficient etching selectivity for nGaP. Further, as a result of further intensive research and experiments by the present inventors, it was found that a sufficient etching rate could be obtained by setting the temperature of the sulfuric acid solution to 60 [°C or higher; ] It has been found that etching control is easy and the etching surface does not become rough when set as follows.

The present invention focuses on such points, and In(Ga A, ff )P(0,2≦x≦1)
21-X It's a method.

(Action) In the above method, In(Ga A))1-x
It becomes possible to selectively etch x P (0,2≦x≦1) with respect to GaAs, InGaP, etc. Further, if the temperature of the sulfuric acid solution is set within the range of 60 to 90 [°C], etching can be performed at a sufficiently high etching rate without causing roughness of the etching surface.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

First, In(GaA)1-x using sulfuric acid solution
In the etching of x P, AI! It was investigated how the etching rate changes depending on the mixed crystal ratio X.

Furthermore, the temperature of the sulfuric acid solution is 40.80.80.90 [℃
] The change in etching rate was similarly investigated for each case. As a result, characteristics as shown in FIG. 1 were obtained. That is, in the case of InGaP having an A mixed crystal ratio of x-0, the etching rate is very slow and almost no etching occurs.

This tendency continues up to about x-0.2. When the A mixed crystal ratio X exceeds 0.2, the etching rate gradually increases, and when the A mixed crystal ratio ], at a temperature of 80 [℃], approximately 1
．． 0 [μm/a+in], approximately 0 at a temperature of 60 [℃]
．． An etching rate of 3 μm/ml was obtained.

Furthermore, it has been confirmed through experiments by the present inventors that hot sulfuric acid does not etch GaAs at all. From these facts, In(GaAl2)1-x
It can be seen that the etching selectivity between x P (0,2≦x≦1) and InGaP and GaAs is sufficiently high.

FIG. 2 shows the elatin 0.0.
8 shows the etching rate when etching was carried out by changing the temperature of the sulfuric acid solution from 20 to 100 [°C].

From this figure, it can be seen that a sufficient etching rate can be obtained at a temperature of 80[° C.] or higher. Furthermore, at temperatures above 90 ["01], the etching rate changes suddenly with a temperature change of several ["C], making it difficult to control the etching rate. This tendency is alleviated as the A mixed crystal ratio X becomes smaller, but when hot sulfuric acid at a temperature of 90 [° C.] or higher is used where the A mixed crystal ratio X is small, there is a tendency for the etched surface to become rough. For these reasons, by setting the temperature of the hot sulfuric acid solution in the range of 60 to 90 [°C], InGa A, i can be etched at a sufficient etching rate without causing roughness of the etching surface.
'Pl-x x (0, 2≦x≦1) can be selectively etched.

In this way, according to the method of this embodiment, In(Ga
A) ) P (0,2≦x≦1) crystal 1-x
x When etching, by using a sulfuric acid solution at a temperature in the range of 60 to 90[l], the above crystal can be selectively etched with respect to InGaP, Ga-As, etc. Furthermore, the etching surface It is possible to perform etching at a sufficiently high etching speed without causing roughness etc. Therefore, InGaA with a ridge waveguide
Great effects can be obtained when applied to the manufacture of semiconductor lasers using iP materials.

The structure and manufacturing process of a semiconductor laser using InGaA]P material having the above-mentioned ridge waveguide will be briefly explained with reference to FIGS. 3 and 4. First, the fourth
As shown in Figure <a), N-
InGaAiP cladding layer 32. InGaP active layer 33
．． P-1n Ga A No P cladding layer 34 and P
- A GaAs ohmic contact layer 35 is sequentially grown. Here, the cladding layer 32.34(7)A,I! The mixed crystal ratio x let is, for example, 0.4.

Next, as shown in FIG. 4(b), a striped mask 37 such as 5i02 is formed on the contact layer 35, and a PA
The GaAs contact layer 35 is etched using an etchant.

Next, as shown in FIG. 4(C), the InGaAiP cladding layer 34 is etched using an etching solution according to the present invention (a sulfuric acid solution at a temperature of 80° C.) and using the GaAs contact layer 35 as a mask. By this etching, the ridge width of the cladding layer 34 is adjusted to the contact layer 3.
Make it shorter than the ridge width of 5. Thereafter, as shown in FIG. 4(d), N-G is formed on both sides of the ridge by selective growth.
Embed an aAs embedding layer 36. After this, electrode layers 38 and 39 are deposited on both main surfaces of the substrate, thereby completing a semiconductor laser having the structure shown in FIG. 3.

Next, another embodiment of the present invention will be described.

The inventors mentioned above? It has been found that even if a hot phosphoric acid solution is used instead of the sulfuric acid solution A, InGaA and f7P can be etched in the same manner as in the previous example. Figure 5 shows In(Ga A,f')l-X with respect to the A mixed crystal ratio X.
FIG. 3 is a characteristic diagram showing changes in etching speed of xP. From this figure, it can be seen that the etching rate of InGaP with an A mixed crystal ratio of x-0 is very slow and is hardly etched. This trend continues until about x-0.2. A mixed crystal ratio X
When the etching rate exceeds 0.2, the etching rate gradually increases, and for A, fl' mixed crystal ratio 0.9 [μm/min], about 0 at a temperature of 60 [℃]
．． An etching rate of 2 [μ77Z/ll1ln] was obtained. Furthermore, it has been confirmed through experiments by the present inventors that hot phosphoric acid does not etch GaAs at all. From these facts, In(Ga A,ff)1-X
It can be seen that the selectivity between X P (0,2≦x≦1) and InGaP and GaAs is sufficiently high.

FIG. 6 shows the eratin 0.
6 shows the etching rate when etching was carried out by changing the temperature of the phosphoric acid solution from 20 to 100 [''C].

From this figure, a sufficient etching rate is obtained at a temperature of 60 [°C] or higher, and a tendency towards saturation is seen at a temperature of 90 [°C] or higher. From the point where this saturation tendency was observed, the etched surface also tended to gradually become non-uniform. This tendency was the same even when the A, ff mixed crystal ratio X was in the range of 0.2 to 1. For these reasons, the temperature of the hot phosphoric acid solution should be set at 60 to 9
By setting the temperature within the range of 0°C, the etching speed can be maintained at a sufficient rate without causing roughness on the etching surface.
n (G a -8A, l?x) P (0,2≦x
≦1) can be selectively etched.

In this way, according to the method of this embodiment, In(Ga
A) ') P (0,2≦x≦1) crystals
x When etching, by using a phosphoric acid solution with a temperature in the range of 60 to 90 [''C], the above crystal can be selectively etched with respect to InGaP, GaAs, etc., as in the previous embodiment.Furthermore, Etching can be performed at a sufficiently high etching speed without causing roughness of the etching surface.

Therefore, the same effects as in the previous embodiment can be obtained.

Note that the present invention is not limited to the method of the embodiment described above. For example, the operating temperature of the sulfuric acid solution is not necessarily 6
The temperature is not limited to the range of 0 to 90[° C.], and may be in a range exceeding this depending on the conditions required for the InGaA or i7P crystal to be etched. However, in order to eliminate roughness of the etched surface and obtain a sufficient etching rate, the above range of 60 to 90 ["C] is desirable. In addition, the degree of 1 degree of sulfuric acid solution can be adjusted as appropriate depending on the specifications. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, by using a hot sulfuric acid solution, etching of In(GaA) )1-x x P (0,2≦x≦1) can be uniformly etched. Moreover, it can be easily carried out, and a sufficient etching selectivity for GaAs, InGaP, etc. can be obtained.

[Brief explanation of the drawing]

Figures 1 to 4 are for explaining one embodiment of the method of the present invention. Figure 1 is a characteristic diagram showing changes in etching rate with respect to the 177 mixed crystal ratio, and Figure 2 is a characteristic diagram showing changes in etching rate with respect to the temperature of the etching solution. Figure 3 is a cross-sectional view showing the schematic structure of a semiconductor laser with a bridge-type waveguide.
FIG. 4 is a sectional view showing the manufacturing process of the above laser, and FIGS. 5 and 6 are for explaining other embodiments of the method of the present invention. FIG. 5 shows the change in etching rate with respect to the A mixed crystal ratio. FIG. 6 is a characteristic diagram showing the change in etching rate with respect to the temperature of the etching solution. FIG. 7 is a cross-sectional view showing the schematic structure of a conventional semiconductor laser having a ridge-type waveguide. FIGS. FIG. 9 is a cross-sectional view showing a method of forming a ridge portion. 31・=N-GaAs substrate, 32-N-Pn G
a-A122911 layer, 33... InGaP active layer,
34...P-InGaA, 17P cladding layer, 35...
・P-GaAs ohmic contact layer, 36...N
-GaAs buried layer, 37...S i 02 mask. Applicant's agent: Patent attorney Takehiko Suzue - Figure 3 (b) (d) !
“η Fig. 5

Claims (2)

[Claims] (1) In(Ga_1_-_xAl_x)P(0.2≦
A method for chemically etching a semiconductor crystal, characterized in that a sulfuric acid solution is used in the method for etching x≦1). (2) The method for chemically etching a semiconductor crystal according to claim 1, wherein the temperature of the sulfuric acid solution is set in a range of 60 to 90 [°C].