Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
1998-08-05
2001-02-06
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S046000
Reexamination Certificate
active
06184049
ABSTRACT:
This disclosure relates to subject matter contained in Japanese patent application No. 225700/1997 (filed on Aug. 7, 1997) which is expressly incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for fabricating a compound semiconductor epitaxial wafer and a vapor phase growth apparatus using the method. More particularly, the present invention concerns a method for fabricating a compound semiconductor epitaxial wafer which is composed of elements belonging to a periodic table groups III and V and suitably used for fabrication of a light emitting diode, and a vapor phase growth apparatus using the method.
2. Description of the Related Art
In order to manufacture a red-, orange- or yellow-color light emitting diode, there is used a compound semiconductor epitaxial wafer in which an epitaxial layer of gallium arsenide phosphide GaAs
1−a
P
a
(where a is a real number satisfying a relationship of 0≦a≦1) having constant alloy compositions (1−a) and a of gallium arsenide GaAs and gallium phosphide GaP respectively is formed on a single-crystalline substrate of gallium phosphide GaP or gallium arsenide GaAs. The emitted light wavelength of the light emitting diode is determined by the alloy composition a, which is 0.9 for the yellow-color light emitting diode, 0.65 for the orange-color diode and 0.57 for the red-color diode.
A compound semiconductor epitaxial wafer
1
having such an epitaxial layer of the gallium arsenide phosphide GaAs
1−a
P
a
as mentioned above is, as shown in
FIG. 3
, made up of a single-crystalline substrate
2
of, e.g., n type gallium phosphide GaP, an n type gallium phosphide GaP epitaxial layer
3
, an alloy composition gradient layer
4
of n type gallium arsenide phosphide GaAs
1−x
P
x
(0≦x≦1) having an alloy composition (1−x) of gallium arsenide GaAs varies in the growth direction of the epitaxial layer, an alloy composition constant layer
5
of gallium arsenide phosphide GaAs
1−a
P
a
(0≦a≦1) having a constant alloy composition (1−a) of gallium arsenide GaAs, and an alloy composition constant layer
6
of n type gallium arsenide phosphide GaAs
1−a
P
a
having a constant alloy composition (1−a) of gallium arsenide GaAs and is doped with nitrogens N as isoelectronic traps, which are sequentially formed on the single-crystalline substrate
2
.
The term “compound semiconductor epitaxial wafer” as used in the present specification refers to a wafer having an epitaxial layer of compound semiconductor. Further, the term “compound semiconductor wafer” as used herein refers to a single-crystalline substrate of compound semiconductor or a compound semiconductor epitaxial wafer. Furthermore, these gallium arsenide phosphide GaAs
1−x
P
x
alloy composition gradient layer
4
, gallium arsenide phosphide GaAs
1−a
P
a
alloy composition constant layer
5
, and gallium arsenide phosphide GaAs
1−a
P
a
alloy composition constant layer
6
doped with nitrogen N will sometimes be generally referred to as the gallium arsenide phosphide GaAsP layers.
In order to grow any of the epitaxial layers
3
,
4
,
5
and
6
on the compound semiconductor wafer to fabricate the aforementioned compound semiconductor epitaxial wafer
1
, there has conventionally been used such a vapor phase growth apparatus
20
as shown, e.g., in FIG.
4
.
In the vapor phase growth apparatus
20
, compound semiconductor wafers
21
a
,
21
b
and
21
c
are placed on a wafer holder
27
disposed inside a reaction furnace
29
so that the reaction furnace
29
is heated by a heater (not shown) located outside the reaction furnace
29
while a hydrogen H
2
gas as a carrier gas
22
is introduced into the reaction furnace
29
.
Collectively supplied together with the carrier gas
22
from a gas inlet
24
at one end of the reaction furnace
29
to a gas outlet
26
at the other end thereof are a group III source gas
23
containing gallium chloride GaCl, and a group V source gas
25
containing phosphine PH
3
and/or arsine AsH
3
. The group III source gas
23
and group V source gas
25
react with each other on the compound semiconductor wafers
21
a
,
21
b
and
21
c
to grow epitaxial layers.
The above vapor phase epitaxial growth method, however, has a defect that, since the group III source gas
23
and group V source gas
25
are collectively supplied from one end of the reaction furnace
29
, the epitaxial layer formed as grown on the wafer placed closer to the upstream side is thicker and the epitaxial layer on the wafer placed closer to the downstream side is thinner, because the downstream side has less source gases. This is because most of the group III source gas
23
and group V source gas
25
react on the side closer to the gas inlet
24
with the result that a relatively large amount of reaction product deposits on the upstream-side wafer; whereas, the residual source gases react on the side closer to the gas outlet
26
with the result that a relatively small amount of reaction product deposits on the downstream-side wafer. The thickness of the epitaxial layer greatly varies between the upstream and downstream wafers, and the maximum of the variation sometimes reaches 3 or 4 times the minimum of the variation in the reaction furnace.
Since the thickness of the epitaxial layer is associated with characteristics of emitted light wavelength, luminance, forward voltage, etc., variations in the thickness of the epitaxial layer will cause variations in the above quality characteristics.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for fabricating a compound semiconductor epitaxial wafer which can overcome the above problems in the related art and can eliminate variations in the thickness of an epitaxial layer grown in a reaction furnace to obtain a uniform film thickness distribution, and also to provide a vapor phase growth apparatus for implementing the method.
In accordance with an aspect of the present invention, the above object is attained by providing a method for fabricating a compound semiconductor epitaxial wafer wherein a periodic table group III source gas and a periodic table group V source gas are supplied into a reaction furnace of a vapor phase growth apparatus to epitaxially grow a compound semiconductor film on main surfaces of a plurality of compound semiconductor wafers arranged within the reaction furnace. In the method, the group III source gas is flowed from one end of the reaction furnace to the other end thereof in such a manner that a flow path of the group III source gas is established along an array direction of the plurality of compound semiconductor wafers. And the group V source gas is supplied as dispersedly from a plurality of locations at halfway of the flow path of the group III source gas.
In the method, the gas supply step is carried out by directing the group V source gas toward the compound semiconductor wafers from their vicinities.
In particular, when the plurality of compound semiconductor wafers are arranged so that the main surfaces of the wafers are parallel to the flow path of the group III source gas, it is preferable that the group V source gas be supplied from positions opposed to the compound semiconductor wafers.
In this case, the supply positions of the group V source gas are set, from the viewpoint of causing a sufficient amount of group V source gas to reach the wafer surfaces, so that a vertical distance between the supply positions and the main surfaces of the compound semiconductor wafers is preferably not smaller than 1 mm and not larger than 20 mm. In this connection, when the vertical distance is too small, the gas discharge ports become too close to the compound semiconductor film or brought into contact therewith as the epitaxial growth of the compound semiconductor film advances, making it difficult to smoothly feed the group V source gas. When the vertical distance is too large, on the other hand, the
Kaise Tsuneyuki
Shinohara Masayuki
Watanabe Masataka
Hoang Quoc
Nelms David
Shin-Etsu Handotai & Co., Ltd.
Snider Ronald R.
Snider & Associates
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