JP2525776B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for etching an In (Ga _1-x Al _x ) P (0.2 ≦ x ≦ 1) crystal, and particularly to the above-mentioned method. InGaP or G
The present invention relates to a chemical etching method for semiconductor crystals for selective etching with respect to aAs and the like.

(Prior Art) In recent years, InGaAlP has been attracting attention as a compound semiconductor material with the improvement of the crystal growth technique of vapor phase growth. Although products using this material are still in the process of development, they can be applied to, for example, short wavelength semiconductor lasers.

Short-wavelength semiconductor lasers are attracting attention as an alternative to conventional He-Ne lasers as optical recording light sources for video disks, laser printers, and the like. For use as a light source for optical recording, a structure capable of confining light energy and injection current in a specific region, for example, an internal stripe current constriction structure is required. Further, in the case of an optical disc or the like, the laser light is 1 [μm]
Since it is necessary to narrow down to a spot light of the order, lateral mode control is required to confine the light in parallel with the active layer of the semiconductor.

As a semiconductor laser made of GaAlAs as a lateral mode control structure, for example, a ridge-embedded laser has been proposed (Reference, Proceedings of the 46th Annual Meeting of the Japan Society for Applied Physics, 4P-
N-7, P223, 1985). This semiconductor laser is constructed as shown in FIG. 7 and is produced as follows.
That is, the first confines of light and carriers on the GaAs substrate 71
The GaAlAs clad layer 72, the GaA active layer 73, the second GaAlAs clad layer 74 and the GaAs ohmic contact layer 75 are successively crystal-grown, and an oxide film such as SiO ₂ is formed on the crystal layer by sputter deposition or the like. Next, this oxide film is used as a stripe-shaped mask by a photolithography technique or the like, and etching is performed up to a part of the contact layer 75 and the second cladding layer 74 to form a stripe-shaped ridge. Then
A second cladding layer is formed on both sides of the ridge using the selective growth technique.
It is completed by burying with a GaAs burying layer 76 or the like having a conductivity type different from 74, and then performing an electrode process. The selective growth technique of GaAs is described in, for example, the literature (Crystal Engineering Subcommittee of the Japan Society of Applied Physics, 2nd Crystal Engineering Symposium Proceedings, P1).
1, 1985).

In the ridge-embedded laser, as can be seen from FIG. 7, the GaAlAs clad layer 74 other than the ridge portion is thin, so the electromagnetic waves standing there ooze out to the GaAs contact layer 75. Therefore, a so-called loss guide structure 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 GaAl
It is necessary to etch As into a predetermined shape. GaAs and
With respect to GaAlAs, various etching solutions have been reported so far, and there are those that can be used commonly for both GaAs only and GaAlAs only and have approximately the same etching rate. A mixture of ammonia water and hydrogen peroxide (PA etchant) can be used for etching only GaAs, and hot phosphoric acid, hydrofluoric acid, hydrochloric acid, etc. can be used for etching only GaAlAs. Examples include a mixed solution of water + sulfuric acid + hydrogen peroxide (SH etchant), a mixed solution of water + phosphoric acid + hydrogen peroxide (PH etchant), and the like.

To form a ridge type waveguide as shown in FIG. 7,
The method shown in FIG. 8 or 9 can be considered. In the method shown in FIG. 8, first, a SiO ₂ mask 77 is formed as shown in (a), then only GaAs is etched using, for example, a PA etchant, and then hot phosphoric acid is used as shown in (b).
Only GaAlAs is etched. In the method shown in FIG. 9, a mask 77 is first formed as shown in FIG.
Using H and PH etchants, as shown in (b), GaAs, GaAlA
s is etched at the same time.

Comparing these methods, in the case of the method of FIG. 9, since GaAs and GaAlAs are simultaneously etched, the ridge widths of these two layers cannot be controlled independently. On the other hand, in the case of the method of FIG. 8, the width can be controlled independently of each other, so that the degree of freedom in designing the device structure is increased. For example, in a semiconductor laser used for a video disk, a semiconductor laser utilizing self-sustained pulsation such as IS ³ laser (Japanese Patent Laid-Open No. 59-246258) is used in order to reduce noise due to returning light. In order to realize such a structure, it is necessary to narrow the current injection width with respect to the lateral spread of the guided mode, and it is necessary to narrow the current injection width with respect to the spread of the guided 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 structure with InGaAlP material, InGaP, InGaAlP, and GaAs are used as the active layer 73, the cladding layers 72 and 74, and the ohmic contact layer 75 in FIG. 7, respectively. An etching solution that selectively etches Si and GaAs is required. However, there are no reports on etching solutions for InGaAlP materials, and the etchant, etching conditions, etc. have so far been unknown.

(Problems to be solved by the invention) As described above, the etching solution for InGaAlP has not been known so far, and the one that etches InGaAlP itself, the one that has etching selectivity with GaAs and InGaP, etc. has been developed. Was needed.

The present invention has been made in consideration of the above circumstances, and an object thereof is In (Ga _1-x Al _x ) P (0.2 ≦ x ≦ 1)
Etching can be performed uniformly and easily.
It is an object of the present invention to provide a chemical etching method for a semiconductor crystal which can obtain a sufficient etching selection ratio with respect to GaAs, InGaP and the like.

[Structure of the Invention] (Means for Solving Problems) The essence of the present invention is to use a sulfuric acid solution or a phosphoric acid solution as an InGaAlP etching solution.

The inventors of the present invention conducted experiments using various solutions as a material for etching an In (Ga _1-x Al _x ) P (0.2 ≦ x ≦ 1) crystal, and the above-mentioned crystal was etched by a sulfuric acid solution or a phosphoric acid solution. We also found that there is sufficient etching selectivity for GaAs and InGaP. Further, as a result of further intensive studies and experiments by the present inventors, it was found that a sufficient etching rate can be obtained by setting the temperature of the sulfuric acid solution or the phosphoric acid solution to 60 [° C.] or higher. It was found that if the temperature is set to 90 [° C] or less, the etching control is easy and the etching surface is not roughened.

Focusing on such a point, the present invention provides a method for manufacturing a semiconductor device, which comprises a step of etching In (Ga _1-x Al _x ) P (0.2 ≦ x ≦ 1).
This is a manufacturing method in which (Ga _1-x Al _x ) P is etched using a sulfuric acid solution or a phosphoric acid solution.

Another method of manufacturing a semiconductor device of the present invention is a step of forming In (Ga _1-x Al _x ) P (0.2 ≦ x ≦ 1) on a semiconductor substrate, and a step of forming In (Ga _1-x Al _x ) P is etched with a sulfuric acid solution or a phosphoric acid solution to obtain the above In (Ga _1-x Al _x ).
And a step of forming a semiconductor layer of P having a predetermined shape.

Here, the temperature of the sulfuric acid solution or the phosphoric acid solution is 60 to
It is desirable to set in the range of 90 [° C].

(Operation) In the above method, In (Ga _1-x Al _x ) P (0.2 ≦ x ≦
1) can be selectively etched with respect to GaAs, InGaP, or the like. Furthermore, by setting the temperature of the sulfuric acid solution or the phosphoric acid solution in the range of 60 to 90 [° C.], it is possible to perform etching at a sufficiently high etching rate without causing roughness of the etching surface.

(Examples) The details of the present invention will be described below with reference to illustrated examples.

First, in the etching of In (Ga _1-x Al _x ) P using a sulfuric acid solution, it was examined how the etching rate changes depending on the mixed crystal ratio x of Al. In addition, the temperature of the sulfuric acid solution is 40,6
The changes in the etching rate were similarly examined for the cases of 0, 80, and 90 [° C]. As a result, the characteristics shown in FIG. 1 were obtained. That is, InGaP with Al mixed crystal ratio x = 0
In this case, the etching rate is very slow and almost no etching is performed. This tendency continues until x = 0.2. Al mixed crystal ratio x
When the value exceeds 0.2, the etching rate gradually increases, and when the Al mixed crystal ratio x = 0.6, the etching rate is about 2.5 [μm /
min], approx. 1.0 [μm / min] at temperature 80 [℃], temperature 60
At [° C], an etching rate of about 0.3 [μm / min] was obtained. It has been confirmed by experiments by the present inventors that hot sulfuric acid does not completely etch GaAs. From these, In (Ga _1-x Al _x ) P (0.2 ≦ x ≦ 1) and InGaP
It can be seen that the etching selectivity with respect to GaAs and GaAs is sufficiently high.

FIG. 2 shows the etching rate when InGa _0.6 Al _0.4 P is etched by changing the temperature of the sulfuric acid solution to 20 to 100 [° C.]. From this figure, temperature 60 [℃]
It is understood that a sufficient etching rate can be obtained by the above. Further, when the temperature is 90 [° C.] or higher, the etching rate changes abruptly with a temperature change of several [° C.], which makes it difficult to control the etching rate. This tendency is alleviated when the Al mixed crystal ratio x is small, but when hot sulfuric acid of 90 [° C.] or higher is used where the Al mixed crystal ratio x is small, the etching surface tends to be rough. From these, the temperature of the hot sulfuric acid solution is 60 to 90 [° C]
By setting the range to the range of InGa _1-x Al _x P at a sufficient etching rate without causing the etching surface to become rough.
It can be seen that (0.2 ≦ x ≦ 1) can be selectively etched.

Thus, according to the method of the present embodiment, In (Ga _1-x Al _x )
When etching a P (0.2 ≦ x ≦ 1) crystal, the temperature should be 6
By using a sulfuric acid solution in the range of 0 to 90 [° C.], the above crystal can be selectively etched with respect to InGaP, GaAs and the like. Further, it is possible to perform the etching at a sufficiently high etching rate without causing the etching surface to be rough. Therefore, InGaAl with a ridge waveguide
When applied to the production of semiconductor lasers using P material, etc., a great effect can be obtained.

The structure and manufacturing process of a semiconductor laser using InGaAlP having the ridge waveguide or a material will be briefly described with reference to FIGS. 3 and 4. First, as shown in FIG. 4 (a), N-InGaAlP is formed on the N-GaAs substrate 31.
Clad layer 32, InGaP active layer 33, P-InGaAlP clad layer 34
Then, a P-GaAs ohmic contact layer 35 is sequentially grown. Here, the Al mixed crystal ratio x of the cladding layers 32 and 34 is, eg, 0.4. Next, as shown in FIG. 4B, a striped mask 37 of SiO ₂ or the like is formed on the contact layer 35, and the GaAs contact layer 35 is etched using a PA etchant.

Next, as shown in FIG. 4 (c), the InGaAlP cladding layer 34 is partially etched using the etching solution according to the present invention (sulfuric acid solution at a temperature of 80 ° C.) using the GaAs contact layer 35 as a mask. By this etching, the ridge width of the cladding layer 34 is made shorter than the ridge width of the contact layer 35. After that, as shown in FIG. 4D, the N-GaAs burying layers 36 are buried on both sides of the ridge by the selective growth method. After that, by depositing the electrode layers 38 and 39 on both main surfaces of the substrate, the semiconductor laser having the structure shown in FIG. 3 is completed.

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

The present inventors have found that the InGaAlP can be etched in the same manner as in the previous embodiment even when a hot phosphoric acid solution is used instead of the hot sulfuric acid solution described above. FIG. 5 shows In for Al mixed crystal ratio x.
It is a characteristic diagram showing an etching rate change of _{(Ga 1-x Al x)} P. From this figure, it can be seen that the etching rate of InGaP having an Al mixed crystal ratio x = 0 is very slow and hardly etched. This tendency continues until about x = 0.2. Al mixed crystal ratio x
When the ratio exceeds 0.2, the etching rate gradually increases, and when the Al mixed crystal ratio x = 0.6, the temperature is about 1.2 [μm /
min], approx. 0.9 [μm / min] at temperature 80 [℃], temperature 60
At [° C], an etching rate of about 0.2 [μm / min] was obtained. It has been confirmed by experiments by the present inventors that hot phosphoric acid does not etch GaAs at all. From these, it is understood that the selectivity between In (Ga _1-x Al _x ) P (0.2 ≦ x ≦ 1) and InGaP and GaAs is sufficiently high.

FIG. 6 shows the etching rate when InGa _0.6 Al _0.4 P is etched by changing the temperature of the phosphoric acid solution to 20 to 100 [° C.]. From this figure, a sufficient etching rate is obtained at a temperature of 60 [° C] or higher, and a saturation tendency is seen at a temperature of 90 [° C] or higher. From around the point where this saturation tendency was observed, the etching surface also tended to become uneven. This tendency was the same even when the Al mixed crystal ratio x was in the range of 0.2 to 1. From these, by setting the temperature of the hot phosphoric acid solution in the range of 60 to 90 [° C.], the In (Ga _1-x Al _x ) P can be sufficiently etched at a sufficient etching rate without causing roughness of the etching surface. It can be seen that (0.2 ≦ x ≦ 1) can be selectively etched.

Thus, according to the method of the present embodiment, In (Ga _1-x Al _x )
When etching a P (0.2 ≦ x ≦ 1) crystal, the temperature should be 6
By using a phosphoric acid solution in the range of 0 to 90 [° C.], the above crystals can be selectively etched with respect to InGaP, GaAs and the like as in the previous embodiment. Further, it is possible to perform the etching at a sufficiently high etching rate without causing the etching surface to be rough. Therefore, the same effect as in the previous embodiment can be obtained.

The present invention is not limited to the method of the embodiment described above. For example, the use temperature of the sulfuric acid solution is not always
The range is not limited to 60 to 90 [° C.], and may be a range exceeding this depending on the conditions required for the InGaAlP crystal to be etched. However, in order to eliminate the roughness of the etching surface and obtain a sufficient etching rate,
The above range of 60 to 90 [° C] is desirable. Further, the concentration of the sulfuric acid solution may be appropriately determined according to the specifications. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, by using a sulfuric acid solution or a phosphoric acid solution, In (Ga _1-x Al _x ) P (0.2 ≦ x
≦ 1) etching can be performed uniformly and easily,
Further, it is possible to obtain a sufficient etching selection ratio for GaAs, InGaP and the like.

[Brief description of drawings]

1 to 4 are for explaining a method of one embodiment of the present invention. FIG. 1 is a characteristic diagram showing a change in etching rate with respect to an Al mixed crystal ratio, and FIG. 2 is an etching rate with respect to the temperature of an etching solution. FIG. 3 is a cross-sectional view showing a schematic structure of a semiconductor laser having a ridge type waveguide, FIG.
FIG. 5 is a sectional view showing a manufacturing process of the above laser, FIGS. 5 and 6 are for explaining a method of another embodiment of the present invention, and FIG. 5 is a characteristic showing a change in etching rate with respect to an Al mixed crystal ratio. 6 and 6 are characteristic diagrams showing changes in etching rate with respect to the temperature of the etching solution, FIG. 7 is a sectional view showing a schematic structure of a conventional semiconductor laser having a ridge type waveguide, and FIGS. 8 and 9 are respectively It is sectional drawing which shows the formation method of a ridge part. 31 ... N-GaAs substrate, 32 ... N-PnGaAlP cladding layer, 3
3 …… InGaP active layer, 34 …… P-InGaAlP clad layer, 35
... P-GaAs ohmic contact layer, 36 ... N-GaAs
Buried layer, 37 …… SiO ₂ mask.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 60-91690 (JP, A) JP 59-129473 (JP, A) JP 56-40496 (JP, B2)

Claims (1)

(57) [Claims] 1. In (Ga _1-x Al _x ) P (0.2 ≦
x ≦ 1) layer and selectively forming a GaAs or InGaP-based compound semiconductor layer on this layer, and using the compound semiconductor layer as a mask, the In (Ga _1-x Al _x ) P layer The 60
To 90 [° C.] by selectively removing it with an etching solution composed of a hot sulfuric acid solution or a hot phosphoric acid solution to obtain a predetermined shape.