Method of producing semiconductor laser diode

Details Method of producing semiconductor laser diode Method of producing semiconductor laser diode

1999-09-14

2001-08-21

Nguyen, Tuan H. (Department: 2813)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

C438S039000, C438S029000, C438S040000, C438S047000

Reexamination Certificate

active

06277663

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a semiconductor laser diode used mainly in optical communications and particularly an embedded double junction semiconductor laser diode based on InP and that has a current blocking layer.
2. Description of the Related Art
Semiconductor laser diodes that have embedded layers based on InP on both sides of a mesa have been used as the light source for optical communications.
FIGS. 26A-26D
are schematic diagrams for explaining the respective steps in the production of the semiconductor laser diode of a conventional example (hereinafter referred to as a first conventional example). The semiconductor laser diode of the conventional example has been produced by forming an n cladding layer
2
made of n-InP, an active layer
3
and a p cladding layer
4
made of p-InP successively on a substrate
1
made of n-InP as shown in FIG.
26
A. Thereafter, as shown in
FIG. 26B
, an oxide film
205
is formed on a portion where a mesa is to be formed, and the other portion is etched away thereby forming the mesa. During this etching step, so-called undercut occurs below both edges of the oxide film
205
, causing the edges of the oxide film
205
to project in a manner of overhang on both sides.
Then a p-InP layer
206
and an n-InP layer
207
are grown on both sides of the mesa as shown in
FIG. 26C
, and the oxide film
205
is removed while forming a p contact layer
8
and a contact layer
9
as shown in FIG.
26
D. The semiconductor laser diode of the first conventional example thus produced has a problem of a current leakage path
210
being formed as shown in
FIG. 26D
that allows current leakage. A method of producing a semiconductor laser diode (hereinafter referred to as a second conventional example) that minimizes the current leakage is disclosed, for example, in the Japanese Patent No. 2828628. The production method disclosed in the Japanese Patent No. 2828628 comprises forming the n cladding layer
2
made of n-InP, the active layer
3
and the p cladding layer
4
made of p-InP successively on the substrate
1
made of n-InP as shown in
FIG. 27A
, followed by the formation of a nitride film
211
and an oxide film
212
on the p cladding layer
4
that is made of p-InP.
Then as shown in
FIG. 27B
, a photosensitive film
213
is formed on a portion where a mesa is to be formed, and the nitride film
211
and the oxide film
212
are etched away by using the photosensitive film
213
as a mask in a wet etching step using hydrofluoric acid, thereby forming a nitride film
211
a
and an oxide film
212
a
. In this wet etching step, since the etching rate is higher for the oxide film than for the nitride film, the oxide film
211
a
becomes smaller than the nitride film
212
a
as shown in FIG.
27
B. Then as shown in
FIG. 27C
, the photosensitive film
213
is removed and the mesa is formed by etching with the nitride film
211
a
and the oxide film
212
a
as the mask. During this etching step, undercut occurs below both edges of the nitride film
211
a
, making the nitride film
211
a
wider than the width of the mesa as shown in
FIG. 27A
, and therefore protruding edges are formed similarly to the first conventional example.
Then as shown in
FIG. 28A
, the protruding edges of the nitride film
211
a
are removed through dry etching by making use of the fact that the etching rate is higher for the nitride
211
a
film than for the oxide film
212
a
in dry etching. Thereafter, as shown in
FIG. 28B
, a p-InP layer
214
and an n-InP layer
215
are grown on both sides of the mesa, followed by removal of the oxide film
212
a
and the nitride film
211
a
thereby to form a p contact layer
216
and a contact layer
217
as shown in FIG.
28
C. In the semiconductor laser diode of the second conventional example thus produced, leakage current is less than that in the semiconductor laser diode of the first conventional example.
However, the semiconductor laser diode of the first conventional example had such a problem that the leakage current cannot be reduced as described above.
There was also a problem that an active layer is exposed on side faces of the mesa during dry etching of the protruding edges of the nitride film, resulting in a possibility of lowering the reliability of the active layer
3
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing the semiconductor laser diode that has high reliability with minimized leakage current.
In order to achieve the object described above, the present invention provides a method of producing the first semiconductor laser diode having a mesa of a predetermined width formed on the semiconductor substrate with the longitudinal direction thereof being aligned with the direction of resonance and the current block layer formed by selective growth on both sides of the mesa, which comprises:
forming a two-stage mask comprising a first mask of SiO
2
in contacting with the top semiconductor layer of semiconductor layers formed on a semiconductor substrate and a second mask of SiN with width different from that of the first mask,
forming said mesa by etching said semiconductor layers positioned at both sides of said two-stage mask,
forming a selective growth mask by etching said two-stage mask to make the width equal to the smaller width of said first mask and said second mask, and
selectively growing said current block layer on both sides of said selective growth mask.
With this method, optimum mask can be used in the etching step to form the mesa and in the selective growth step, and therefore it is made possible to form the current block layer having sufficient width in the vicinity of the mesa. As a consequence, according to the method of producing the first semiconductor laser diode of the present invention, the semiconductor laser diode with less leakage current can be produced.
In the method of producing the first semiconductor laser diode according to the present invention, width of the first mask may be made larger than that of the second mask.
In the method of producing the first semiconductor laser diode according to the present invention, width of the first mask may also be made smaller than that of the second mask.
The present invention provides a method of producing the fourth semiconductor laser diode having a mesa of a predetermined width formed on a semiconductor substrate with a longitudinal direction thereof being aligned with the direction of resonance and a current block layer formed by selective growth on both sides of the mesa,
wherein a selective growth mask comprising a first mask and a portion made of a different material is made by forming the portion of different material, having thermal expansion coefficient different from that of the first mask, on at least part of the first mask that is formed in contact with the mesa.
This makes it possible to prevent the shape of the selective growth mask from deforming thus accelerating the selective growth in the vicinity of the mesa during selective growth, and prevent the selective growth mask from deforming thus impeding the selective growth in the vicinity of the mesa.
The different material mentioned in this specification refers not only to those of different composition but also to those having the same composition but different crystalline structure or internal deformation.
Therefore it is made possible to prevent such a deformation of the selective growth mask that accelerates the selective growth in the vicinity of the mesa during selective growth, or prevent such a deformation of the selective growth mask that impedes the selective growth in the vicinity of the mesa, and it is made possible to form the current block layer having sufficient thickness in the vicinity of the mesa. As a consequence, the semiconductor laser diode with less leakage current can be produced.
In the method of producing the fourth semiconductor laser diode according to the present invention, it is preferable to select the different ma

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