Method for growing a liquid phase epitaxial layer on a semiconductor substrate

A method for selectively growing a liquid phase epitaxial layer on a semiconductor substrate comprises a first step of supplying a liquid phase epitaxial solution in a chamber of an upper body and supplying a semiconductor substrate on which is selectively coated an insulating layer in a recess in an under body, the upper surface of which constituting the bottom of said chamber; a second step of heating said semiconductor substrate and said solution to a predetermined temperature and sliding said upper body and said under body relative to each other so as to position said chamber above said recess, thereby effecting contact between said solution and said semiconductor substrate; a third step of effecting said sliding again so as to separate said recess and said chamber so that said solution remains on the regions of said semiconductor substrate surface on which said insulating layer is not coated; and a fourth step of cooling said solution and said semiconductor substrate at a constant cooling rate so as to grow a liquid phase epitaxial layer.

The present invention relates to a method for manufacturing semiconductor 
devices, in particular, light-emitting diodes based on the selective 
liquid phase epitaxial growth process. In selectively growing a liquid 
phase epitaxial layer on a semiconductor substrate based on an LPE (liquid 
phase epitaxy) system, a device is used which comprises an upper body with 
a chamber for containing a liquid solution and an under body with a recess 
for accommodating a semiconductor substrate on which is selectively coated 
an insulating layer, this under body constituting the bottom of said 
chamber. This device is so designed that the upper body and the under body 
are slidable relative to each other. In a conventional method, the 
epitaxial solution and the semiconductor substrate contact each other by 
the relative sliding movement of the upper body and the under body. The 
bodies are maintained at a high temperature for a certain period of time 
and cooled for growing an epitaxial layer. During this growing procedure, 
since the exposed surface of the semiconductor substrate and the 
insulating layer are in contact with a large amount of the epitaxial 
solution located thereabove, it is hard to control the thickness and width 
of the growing epitaxial layer. 
The present invention has for its object to eliminate these problems with 
the conventional methods and is characterized in that the cooling process 
for growing the epitaxial layer is performed while only a required amount 
of the epitaxial solution remains on the exposed surface of the 
semiconductor substrate.

In accordance with the present invention, an insulating layer may be a 
single layer made of material such as SiO.sub.2, Si.sub.3 N.sub.4, 
Al.sub.2 O.sub.3 or B.sub.2 O.sub.3.SiO.sub.2.Al.sub.2 O.sub.3 based 
glass; or a laminated body of such layers. Formation of the insulating 
layer on a semiconductor substrate may be performed by the following 
methods: (1) depositing SiO.sub.2 on a semiconductor substrate heated to 
450.degree. C. by the reaction of SiH.sub.4 +O.sub.2 .fwdarw.SiO.sub.2 in 
an Ar atmosphere; (2) painting a liquid compound including Si on a 
substrate, baking it at 200.degree. C., and intensifying its density at 
600.degree. to 800.degree. C.; (3) depositing Si.sub.3 N.sub.4 on a 
substrate by the reaction of SiH.sub.4 +NH.sub.3 .fwdarw.Si.sub.3 N.sub.4 
; (4) depositing Al.sub.2 O.sub.3 by the sputtering method; and (5) 
electrodepositing B.sub.2 O.sub.3.SiO.sub.2.Al.sub.2 O.sub.3 based fine 
glass powder on a substrate in a suspension of this fine glass powder. 
For etching part of this insulating layer so as to selectively expose the 
surface of the substrate, a mixed acid of HF and HNO.sub.3 is used when 
the insulating layer is made of silicon oxide; heated H.sub.3 PO.sub.3 is 
used when the insulating layer is made of silicon nitride or aluminum 
oxide; and NH.sub.4 F is used when the insulating layer is made of B.sub.2 
O.sub.3.SiO.sub.2.Al.sub.2 O.sub.3 based glass. 
The semiconductor substrate may be made of GaP, GaAsP, GaAs, InP, GaAlAs, 
InGaP, GaAlAsP, Si or the like: it may be polycrystalline or of single 
crystal structure. The liquid phase epitaxial solution is a Ga solution 
with saturated As and P when the substrate is made of GaAsP; a Ga solution 
which includes a small amount, and less than the saturated amount, of Al 
and the saturated amount of As when the substrate is made of GaAlAs; a Ga 
solution with saturated P when the substrate is made of GaP; or a Sn 
solution or an Al solution when the substrate is made of Si. 
Devices for performing the liquid phase epitaxy need only satisfy two 
requirements: that both the upper body and the under body be made of 
highly purified carbon to facilitate the relative sliding movement which 
initiates and interrupts contact between the substrate and the solution; 
and that the device be able to heat or cool the substrate according to a 
predetermined temperature program when heated in a furnace. The liquid 
phase epitaxial layer may be an epitaxial layer which comprises a 
semiconductor region grown on a single crystal semiconductor substrate, 
and it may be polycrystalline. 
Embodiments of the present invention will be described hereinafter. As may 
be seen from FIG. 1(A), in the device used, both an upper body 1 and an 
under body 2 are made of carbon. This device comprises the upper body 1 
which has a chamber 4 for containing a liquid phase epitaxial solution 3, 
and the under body 2 which is disposed below this upper body as a bottom 
for the upper body and which is slidable with respect to the upper body. 
The under body 2 has a recess 5 in which is disposed a semiconductor 
substrate 6. In FIG. 1(A), the upper body 1 and the under body 2 are so 
located that the epitaxial solution 3 and the semiconductor substrate 6 do 
not contact each other. In FIG. 1(B), the under body 2 has been slid to a 
point immediately below the chamber 4 of the upper body. In FIG. 1(C), the 
under body 2 has been further slid so that the recess 5 has passed beyond 
the chamber 4. 
Embodiment 1 
In this embodiment, a GaP substrate is used as the semiconductor substrate 
6, on the surface of which is formed an SiO.sub.2 layer by the CVD method. 
This SiO.sub.2 layer has openings which are formed by forming a 
photoresist over the SiO.sub.2 layer and subsequently dissolving the 
exposed regions in a mixed acid of HF and HNO.sub.3. This layer serves as 
an insulating layer 7. 
The openings of this insulating layer are circles each 1 mm in diameter. A 
number of them are distributed in a grid form. The epitaxial solution is a 
Ga solution which includes Zn and O supplied from Zn metal and Ga.sub.2 
O.sub.3, and which includes a saturated amount of P. 
The arrangement as shown in FIG. 1(A) is maintained for 10 minutes at 
1,000.degree. C. Then the under body 2 is slid at this temperature to a 
position as shown in FIG. 1(B). After an interval of 10-20 minutes, the 
under body 2 is further slid to a position as shown in FIG. 1(C), and 
cooling is performed to 800.degree. C. at a cooling rate of 2.degree. C. 
per minute. As a result, a GaP epitaxial layer 8 of about 2.mu. in 
thickness with added Zn and O is formed in the openings of the insulating 
layer 7 on the substrate as shown in FIG. 2. Extra solution 9 is swept 
away. 
Embodiment 2 
In this embodiment, the epitaxial solution is a highly purified Ga 
solution. The device is heated from 30.degree. C. to 1,000.degree. C. 
under the condition shown in FIG. 1(C). After an interval of 20 minutes at 
this temperature, it is cooled to 800.degree. C. at a cooling rate of 
2.degree. C. per minute to obtain a semiconductor element as shown in FIG. 
3. 
A regrowth region 10 is formed inside the GaP substrate below the openings 
of the insulating layer 7. The extra Ga solution 9 is swept away. 
Embodiment 3 
A p-type liquid phase epitaxial region is recrystallized on an n-type GaP 
single crystal substrate manufactured by the pulling method in a 
construction as shown in FIG. 3 by the method of Embodiment 2. The 
epitaxial solution used is a Ga solution with added Zn and O. The p-n 
junction formed in the substrate is used as a red color light-emitting 
diode. 
This diode has a light-emitting efficiency of about 4% and an electric 
current density of 5 mA/mm.sup.2. This is almost double the value for 
conventional products since they only present about 2% light-emitting 
efficiency. Further, in the conventional methods, 8 g of Ga is ordinarily 
consumed per 20 cm.sup.2 of wafer. In this embodiment, only about 3 g of 
Ga is consumed, resulting in economical manufacture. 
Embodiment 4 
In this embodiment, a numerical display device is manufactured in a manner 
similar to that in Embodiment 3, and is shown in the plan view of FIG. 4. 
In FIG. 4, a numerical display region 11 comprises a recrystallized p-type 
layer, the surrounding region comprises an insulating layer, e.g., an 
oxide layer 7, and an n-type region of a substrate (not shown) is disposed 
thereunder. 
Embodiment 5 
The epitaxial solution and the semiconductor substrate as in Embodiment 1 
are used. The device is heated to 1,000.degree. C. for 10 minutes. After 
an interval of 10 minutes under the condition as shown in FIG. 1(B), it is 
heated to 1,050.degree. C. at a rate of 2.degree. C. per minute under the 
condition shown in FIG. 1(C). It is then cooled to 800.degree. C. at a 
cooling rate of 2.degree. C./min. A p-n junction is formed in the 
substrate as a result.