Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
2001-09-06
2003-01-28
Chaudhuri, Olik (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S590000
Reexamination Certificate
active
06511858
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for fabricating semiconductor device, more specifically a method for fabricating a semiconductor device including an optical integrated circuit, etc. for use in optical communication, photocoupling, etc.
In an optical semiconductor device of an InP-based material, horizontal light confinement depends on refractive index differences between the InGaAsP core and the InP buried layer, which guide light. As a structure for realizing such light confinement, the buried hetero (BH) structure used in semiconductor lasers is known.
A method for fabricating a semiconductor laser of the BH structure will be explained with reference to
FIGS. 10A-10E
.
FIGS. 10A-10E
are sectional views of the semiconductor laser in the steps of the method for fabricating the semiconductor laser.
As shown in
FIG. 10A
, an InGaAsP/InGaAsP multi-quantum well layer
102
, a p type InP clad layer
104
are formed sequentially on an n type InP substrate
100
.
Then, as shown in
FIG. 10B
, an SiO
2
film
106
as an etching protection film is formed on the p type InP clad layer
104
, and an active layer mesa stripe
108
are formed by dry etching. The active layer mesa stripe
108
has <011> direction.
Subsequently, as shown in
FIG. 10C
, with the SiO
2
film
106
as a selective growth mask, a p type InP buried layer
110
and an n type InP buried layer
112
are sequentially crystal-grown on the InP substrate
100
around the active layer mesa stripe
108
by metal organic vapor phase epitaxy (MOVPE). In the crystal growth by the MOVPE, a chlorine-based gas, such as CH
3
Cl or others, is added so that, as shown in
FIG. 10C
, the crystal growth of the n type InP buried layer
112
stops at a (
111
) B plane as the growth stop face. Thus, the n type InP buried layer
112
can be formed, not growing over the SiO
2
film
106
.
Following the formation of the n type InP buried layer
112
, the SiO
2
film
106
is removed by etching using HF, and a p type InP clad layer
114
and a p type InGaAs contact layer
116
are sequentially formed on the entire surface.
Finally, an n type electrode
118
is formed on the underside of the n type InP substrate
100
, and a p type electrode
120
is formed on a p type InGaAs contact layer
116
. Thus, the fabrication of the semiconductor laser of the BH structure is completed.
Recently in the optical communication technique, for multi-wavelength communication and high-speed light modulation, optical integrated circuits having photodividers, photocouplers, photomodulators, photoswitches, etc. integrated have become key devices. Such optical integrated circuits are fabricated by the same method as the semiconductor laser of the BH structure described above.
However, in fabricating the optical integrated circuit of the BH structure, the step of forming the buried layer after forming the active layer mesa stripe has problems although the step has no problem in fabricating the semiconductor laser.
The resonator of the above-described semiconductor laser has <011> direction. As shown in
FIG. 10C
, the crystal growth of the n type InP buried layer
112
stops at the (
111
) B plane as the growth stop plane, so that the n type InP buried layer
112
can be formed, not growing over the selective growth mask.
On the other hand, the wave guide of the optical integrated circuit has the function of coupling various devices and, for the function, has parts of different directions, a branch part and a terminal part.
FIG. 11
is a view of a structure of the active layer mesa stripe of the optical integrated circuit with SiO
2
film as the selective growth mask. As shown in
FIG. 11
, a branch part
122
and a terminal part
124
are formed in the active layer mesa stripe
121
of the optical integrated circuit, and a part
126
of a direction other than <011> direction is formed in the active layer mesa stripe. In order to form the buried layer in such active layer mesa stripe
121
the SiO
2
film
128
is formed as a selective growth mask.
In a case that the selective growth mask is formed at the branch part
122
or the terminal part
124
, or a part
126
of a direction other than <011> direction, no specific growth stop plane is present in forming the buried layer. Accordingly, the buried layer grows over the selective growth mask.
FIGS. 12
A,
12
B and
12
C respectively show growth of the buried layer at the branch part
122
, the terminal part
124
and the part
126
of a direction other than <011> direction. As shown in
FIGS. 12A-12C
, at the branch part
122
and the others the buried layer
120
is formed, growing over the SiO
2
film
128
, which is the selective growth mask formed on the active layer mesa stripe
121
. Such over growth of the buried layer
130
cannot be prevented even by addition of chlorine gas at the time of the crystal growth.
In the optical integrated circuit, stacking dislocations unpreferably occur in a part where the above-described over growth has taken place. Furthermore, the overhang of the buried layer formed by the over growth form voids therebelow in the step of removing the selective growth mask to form a clad layer and a contact layer.
FIG. 13
shows one example of the sectional configuration of the optical integrated circuit having a void formed by the over growth of the buried layer.
As shown in
FIG. 13
, a p type InP buried layer
134
and an n type InP buried layer
136
are formed in layers on both sides of the active layer mesa stripe
121
formed on an n type InP substrate
132
. Furthermore, on the upper surface of these layers a p type InP clad layer
138
, a p type InGaAs contact layer
140
are sequentially formed. The n type InP buried layer
136
has overhanging parts
142
growing over the active layer mesa stripe
121
. Below the overhanging parts
142
the p type InP clad layer
138
is not formed, forming voids
144
.
The stacking dislocation and void due to the above-described over growth of the buried layer cause deflection of a refractive index which hinders waveguide of light, and furthermore cause electric characteristic deterioration in the operation of the device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for fabricating semiconductor device which can grow a buried layer on a projected structure, such as a mesa stripe, without over growth.
The above-described object is achieved by a method for fabricating semiconductor device comprising: the step of forming a buried layer of III-V group semiconductor with Se or S added in an above 5×10
18
cm
−3
concentration against a projected structure including a surface with a mask formed on, at a peripheral part of the mesa structure without the mask formed on.
In the above-described method for fabricating semiconductor device it is possible that the III-V group semiconductor is InP.
In the above-described method for fabricating semiconductor device it is possible that the projected structure is a mesa stripe having a branching part.
In the above-described method for fabricating semiconductor device it is possible that the projected structure is a mesa stripe having a terminal part.
In the above-described method for fabricating semiconductor device it is possible that the projected structure is a mesa stripe having a <011> direction part and a part of a direction other than <011> direction.
In the above-described method for fabricating semiconductor device it is possible that a gas containing chlorine is introduced when the buried layer is formed.
In the above-described method for fabricating semiconductor device it is possible that the mask is a film of silicon oxide and/or silicon nitride.
REFERENCES:
patent: 5822349 (1998-10-01), Takaoka et al.
patent: 1014430 (2000-06-01), None
patent: 61032585 (1986-02-01), None
patent: 363152180 (1988-06-01), None
patent: 401315184 (1989-12-01), None
patent: 06283816 (1994-10-01), None
patent: 8-250808 (1996-08-01), None
patent: 410178236 (1998-06-01), None
Blum David S
Chaudhuri Olik
Fujitsu Quantum Devices Limited
LandOfFree
Method for fabricating semiconductor device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for fabricating semiconductor device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for fabricating semiconductor device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3071527