JPH0378279A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve reproducibility by burying a light wave guide path with II-VI compound semiconductor, and etching it through a mask which has an opening of specified stripe width. CONSTITUTION:An n-GaAs buffer layer 2, an n-Al0.5Ga0.5As clad layer 3, an Al0.15Ga0.85As active layer 4, a P-Al0.5Ga0.5As clad layer 5, and a p-GaAs contact layer are stacked in order on an n-GaAs substrate 1 so as to form a substrate in DH structure. This is etched using a mask 7 such as Si O2, etc., so as to form a rib. ZnSe is grown to bury the rib, and at the region excluding the rib, a single crystal ZnSe layer 8, and on the rib, a polycrystalline ZnSe layer 9, are formed. Thereon, a dielectric mask, which has a stripe width equal to or longer than the width of rib upper part, is formed, and the ZnSe layer 9 on the rib is removed by etching. Thence, a P-type electrode 10 and an N-type electrode 11 are formed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a semiconductor laser.

[Prior Art] Group II-VI compound semiconductors such as ZnSe/ZnSe, zinc sulfide (ZeS), and mixed crystals thereof are
It has features that other material systems do not have, such as a wide forbidden band, high resistivity, and low refractive index.
For example, Zn5e thin films are used as current confinement layers and optical confinement layers in AlGaAs semiconductor laser devices.

FIG. 4 is a cross-sectional view of the structure of a Zn5e-embedded WAI GaAs semiconductor laser published by Iwano et al. in the Proceedings of the Society of Applied Physics Society (Spring 1988, 28p-ZH-8).

Zn5e eyebrows (8) are formed to embed the ribs. Note that the Zn5e layer is not formed on the upper surface of the rib to form an electrode, and the contact layer is exposed in a striped manner.

When it is desired to selectively form a Zn5e thin film layer on a semiconductor substrate as in this structure, first an N-VR group compound semiconductor is laminated on the entire surface of the semiconductor substrate, and then a mask such as a photoresist is formed by a photophosphorography process. After that, the portion of the II-VI group compound semiconductor to be removed is removed by wet etching. The etchant mainly used includes a mixture of nitric acid-hydrochloric acid-water, an aqueous sodium hydroxide solution, and hydrochloric acid.

[Problems to be Solved by the Invention] However, the etching of II-VI group compound semiconductors according to the prior art has the following problems.

A problem with wet etching technology in general is that it lacks reproducibility. A constant etching rate cannot be obtained unless the temperature, etchant composition, etc. are controlled very strictly.

For example, when only Zn5e grown on a GaAs substrate is removed using a nitric acid-hydrochloric acid-water etchant, the GaAs will also be etched by the etchant. Therefore, if the etching rate cannot be controlled, the GaAs substrate will also be etched, making it extremely difficult to selectively remove only the ZnSe. Also, NaO
When etching is performed using an H aqueous solution, there is a problem in that the surface morphology is extremely deteriorated.

In addition, as an etching method other than wet etching technology, there is a dry etching technology such as RIBE.
It also has the problem that Z
It is difficult to selectively etch only n-VI group compound semiconductors such as nSe.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and an object of the present invention is to provide a method for manufacturing a buried type II-VI compound semiconductor laser with excellent reproducibility.

[Means for Solving the Problems] A method for manufacturing a semiconductor laser of the present invention includes a step of forming a dielectric mask on a stacked structure of m-v group compound semiconductors, and forming a rib-shaped light guide using the dielectric mask. a step of forming a wave path, a step of burying the side and top surfaces of the optical waveguide with a II-VI group compound semiconductor while leaving the dielectric mask remaining, and removing the II-VI group compound semiconductor layered on the ribs by etching. A method of manufacturing a semiconductor laser including the step of manufacturing a semiconductor laser is characterized in that the stripe width of the dielectric mask is equal to or larger than the width of the upper part of the rib.

[Example] As a first example of the present invention, a double heterojunction (D
H) A part of the manufacturing process of a Zn5e-embedded AlGaAs semiconductor laser device in which the rib formed on the upper part is embedded with Zn5e and used for current confinement and optical confinement will be explained. FIGS. 1(a) to 1(e) illustrate a first embodiment, and are schematic cross-sectional views of a substrate in the middle of an element manufacturing process.

0.5 on an n-type GaAs substrate (1) with (100) plane orientation.
μm thick n-type GaAs buffer layer (2) 1.5 μm thick n-type A 1 @, sGa s, sAs cladding layer (3), 0.1 pm thick non-doped A 1 s, 1
sGa s, ssA $ active layer (4), 1.5μm
A substrate with a DH tank structure laminated consisting of a p-type A 1 s, sGa s, and sAs cladding layer (5) with a thickness of 0.5 μm and a p-type GaAs contact layer (6) with a thickness of 0.5 μm is prepared (see Fig. 1 (a). )). The above DH substrate is etched to the middle of the p-type raft layer using an etching mask made of dielectric material such as 5i02 to form ribs (Fig. 1(b)).
). A typical rib shape is 4 μm wide at the top, 1.7 μm at the bottom, and 1.5 μm high. Then,
In order to embed the ribs, Zn5e is epitaxially grown by metal organic chemical vapor deposition (MOCVD) or the like (FIG. 1(C)).

Furthermore, to form an electrode, polycrystalline Zn5e (
9) is removed by etching. Here, etching is dry etching technology, wet etching technology,
Depends on which one.

In the following, a case will be described in which Zn5e layered on the ribs is removed by dry etching technology. Dry etching techniques include reactive ion beam etching (RIBE) or reactive ion etching (R).
IE) method, etc., and here, the RIBE method using pure chlorine gas as a reactive gas will be explained.

Let the width of the upper part of the rib be R, and the width of 5I02 be S. S≧
FIGS. 3(a) and 3(b) show cross-sectional views of the laser element before and after etching when R, and FIGS. 3(c) and 3(d) show cross-sectional views of the laser element when S<H.

Table 1 also shows the etching rate ratio of polycrystalline Zn5e, 5I02, and GaAS when the etching rate of single crystal ZnSe is set to 1.

Table 1 When S≧R (Fig. 3 (a) (b)), polycrystalline Zn5e
Even if etching is continued after etching is completed, the ribs are completely masked at 5102 where the etching speed is low. Therefore, the upper part of the rib is not etched.

On the other hand, in the case of SIH (Fig. 3(c)(d)), Zn5e
After etching is completed, if you continue etching, S! Etching is stopped in the part where the 02 mask is present, whereas in the part where the 5102 mask is not present, the GaAs of the contact layer above the rib is etched. Since the etching rate of GaAs is about twice as high as that of Zn5e, the part of the rib where S'i 02 does not exist is etched as if it were greatly hollowed out (see Figure 3). d)).

By the way, epitaxial growth of Zn5e or R
In IBE and the like, in-plane distribution may occur in the growth rate or etching rate.

In order to completely remove the polycrystalline Zn5e grown on the ribs, etching may be performed a little more. At this time, if there is a portion not masked by 8102 on the rib, the contact layer in the portion not masked will be etched as described above.

In addition, after Zn5e growth, the surface of polycrystalline Zn5e does not become flat, and as shown in Figure 1, the film thickness is thicker in the center (and thinner at both ends. Therefore, wet etching of polycrystalline Zn5e is performed. In this case, etching ends earlier on both ends of the rib.

If an attempt is made to completely remove the polycrystalline Zn5e layered at the center of the rib, both ends of the rib will be over-etched, so it is necessary to completely cover the top of the rib with 5102, which has a low etching rate. is necessary.

Wet etching technology can also be used to remove the Zn5e layered on the ribs. Here, a case will be described in which polycrystalline Zn5e on the ribs is etched using a mixed solution of nitric acid-hydrochloric acid-water (hereinafter referred to as aqua regia).

On the substrate in which the Zn5e ribs have been embedded, a resist mask having openings only directly above the ribs is formed by a photolithography process. Using the above resist as a mask, polycrystalline Zn5e on the ribs was coated with aqua regia.
Remove in one stroke.

At this time, as in the case of etching by the RIBE method, if etching is continued after polycrystalline Zn5e has been etched, the portion where 5102 does not exist in the case of SKU will become as shown in FIG. 3(d). Part of the contact layer ends up being etched.

However, when S≧R, the ribs are completely covered with the etching rate 5102, so that the GaAs forming the contact layer is not etched.

The same can be said of the etchant used in wet etching, not only the aqua regia mentioned above, but also hydrochloric acid or sodium hydroxide etchants.

Note that when comparing wet etching technology and dry etching technology, dry etching technology is superior in terms of controllability and reproducibility of etching depth, but it is also superior in that it is easy to add etching, and In terms of simplicity, wet etching is also an effective etching method.

FIG. 1(e) shows a semiconductor laser device obtained by removing the etching mask after finishing Zn5e etching on the ribs, forming a P-type electrode (10) and an N-type electrode (11), and then folding the ribs. FIG.

Since the Zn5e layer has high resistance (10MΩ・cm), P
The current injected from the mold electrode (lO) flows concentrated in the rib, and the Zn5e layer (8) plays a role as a current confinement layer.

As a second embodiment of the present invention, a buried (BH) type semiconductor laser device will be described.

FIGS. 2(a) to 2(d) explain a second embodiment, and are schematic cross-sectional views of a substrate during the manufacturing process of a BH type semiconductor laser device. The flow of the manufacturing process is the same as that described in the first embodiment shown in FIG. A substrate having a DH structure is prepared, and as shown in FIG. 2(a), etching is performed by photoetching until the n-type GaAs substrate is reached to form ribs.

The height of the ribs is approximately 3.2 μm. Figure 2 (C) is
znsxSea, a mixed crystal of II-VI group compound semiconductor
- is a cross-sectional view after embedding is performed by the MOCVD method.

Figure 2(d) shows Zn5Se on the rib by etching.
(13) is a cross-sectional view after removal. After this, P
A semiconductor laser device is obtained by forming a type electrode and an N-type electrode. Similar to the semiconductor laser device shown in FIG. 1, the device characteristics were improved and the variation in characteristics was significantly reduced.

Although a specific n-vi group compound semiconductor was taken up in the above embodiments, the application of the present invention is not limited to this range. That is, the present invention uses ZnxCa.

It can also be applied to thin films made of combinations of Group II elements such as Hg and Group II elements such as S, Se, Te, and O. Especially A
Z n SxS e I- lattice matched to I GaAs
x significantly reduces the influence of stress on the active region, and is effective in improving the performance and reliability of the laser device.

In addition to 5102, insulators such as silicon nitride and alumina, and metals such as tungsten and molybdenum can also be used as materials for the mask.

In addition, the semiconductor laser of the present invention can be similarly applied to laser materials other than AlGaAs-based materials, such as InGaAsP-based and InGaP-based materials.

Furthermore, the structure of the semiconductor laser is not limited to the one based on the three-layer waveguide shown in the example, but also the LOG structure in which an optical waveguide layer is provided adjacent to one side of the active layer, and the structure in which an optical waveguide layer is provided adjacent to one side of the active layer, and the It can be similarly applied to an SCH structure in which a light guide layer is provided adjacently, and a GRIN-3CH structure in which the refractive index and forbidden band width of these light guide layers are distributed in the film thickness direction. . Furthermore, it is also effective for semiconductor lasers whose active layer has a quantum well structure. In addition, in the example, a structure in which the conductivity type of each layer is all reversed (p
A similar effect can be expected for a structure in which n is replaced with n'e p.

[Effects of the Invention] The method for manufacturing a semiconductor laser of the present invention has the following effects, and makes it possible to manufacture a semiconductor laser that fully takes advantage of the characteristics of a II-VI group compound semiconductor.

(1) Even if the growth surface of the II-VI group compound semiconductor stacked on the rib is not flat or the film thickness is not uniform within the plane, the growth of the n-vi group compound semiconductor on the rib can be performed without etching the contact layer. Compound semiconductor can be completely removed from the entire surface of the wafer.

(2) Even if the etching rate has an in-plane distribution, the II-VI group compound semiconductor on the rib can be completely removed over the entire surface of the wafer and without accidentally etching the contact layer.

The above two points are effects that can be obtained when the II-VI group compound semiconductor on the rib is etched by either dry etching technique or wet etching technique. On the other hand, by using a dry etching technique such as the RIBE method as an etching method, the following effects are added.

(3) RIBE removal process of II-VI group compound semiconductor
By performing this process, steps such as forming a resist mask become unnecessary. As a result, a semiconductor laser can be manufactured with a simplified process, high yield, and good reproducibility.

(4) Since the II-VI group compound semiconductor is etched by a dry process, the controllability and reproducibility are much better than the conventional wet process.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1(a) to 1(e) are process cross-sectional views of a semiconductor laser illustrating a first embodiment of the present invention. FIGS. 2<a> to 2(d) are process cross-sectional views of a semiconductor laser illustrating a second embodiment of the present invention. FIGS. 3(a) to 3(d) are structural sectional views of a semiconductor laser before and after etching for explaining the present invention in detail. FIG. 4 is a structural cross-sectional view of a conventional Zn5e buried semiconductor laser. 9...Polycrystalline Zn O...P ohmide"N ohmide...Single crystal Zn 2...Polycrystalline Zn Se Tsuku electrode Tsuku electrode Se Se Above

Claims (1)

[Claims] A step of forming a dielectric mask on a layered structure of III-V compound semiconductors, a step of forming a rib-shaped optical waveguide using the dielectric mask, and a step of forming the optical waveguide while leaving the dielectric mask remaining. In a semiconductor laser manufacturing method that includes a step of burying the side and top surfaces with II-VI group compound semiconductor and a step of removing by etching the II-VI group compound semiconductor layered on the rib, the stripe width of the dielectric mask is A method for manufacturing a semiconductor laser, characterized in that the width of the semiconductor laser is equal to or greater than the width of the upper part.