Crystal growth method and apparatus therefor

A crystal growth method is based on a molecular beam epitaxy method. The crystal growth method includes the steps of opening/closing a shutter member provided between a deposition source and a substrate in an ultra-high vacuum so as to form a region having a predetermined pattern on the substrate and forming a crystal growth layer only in the region having the pattern on the substrate during an epitaxial growth step.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of selectively forming 
semiconductor devices such as a semiconductor laser (a laser diode) and a 
field effect transistor on a substrate, and an apparatus therefor and, 
more particularly, to integration of these semiconductor devices. 
2. Description of the Prior Art 
As a conventional method of integrating semiconductor devices having 
different characteristics on the surface of a substrate, the following 
techniques of performing crystal growth once, then patterning in the 
atmosphere, and crystal growth again are known. 
One technique of integrating a two-wavelength laser structure is described 
in Applied Physics Letters, Vol. 58, No. 23, 10 Jun. 1991, pp. 
2,698-2,700. According to this technique, a GaAs laser structure having an 
emission wavelength of 0.85 .mu.m is formed by Molecular Beam Epitaxy (to 
be referred to as MBE hereinafter), this laser structure is removed by 
patterning to form stripes at a pitch of 250 .mu.m, and an InGaAs laser 
structure having an emission wavelength of 1.0 .mu.m is grown again by 
MBE. 
Another technique related to a vertical cavity-type laser is described in 
Japanese Journal of Applied Physics, Vol. 32 (1993), pp. 600-603. In this 
technique, one vertical cavity is grown by MBE, and the cavity is removed 
by patterning to form stripes at a pitch of 125 to 250 .mu.m. Then, a 
vertical cavity is grown again by MBE to integrate a laser structure of 
the single cavity and a detector of the double cavity. 
In any one of the above two conventional techniques, however, a grown 
substrate is unloaded into the outer atmosphere after performing crystal 
growth once in a high vacuum, and patterning is performed on the 
substrate. Thereafter, crystal growth must be performed on the resultant 
substrate again in a high vacuum in the growth chamber. These steps 
complicate the process. In addition, these steps cause degradation in 
quality of the regrown crystal and formation of a depletion layer at an 
interface. For this reason, the device characteristics may be inferior to 
those of a device formed by consistent growth in a vacuum. 
SUMMARY OF THE INVENTION 
The present invention has been made in consideration of the above 
situation, and has as its object to provide a crystal growth method by 
which a shutter means provided between a deposition source and a substrate 
is opened/closed in an ultra-high vacuum so as to form a region having a 
predetermined pattern on the substrate, thereby selectively forming a 
crystal layer in a predetermined region on the substrate only by MBE. 
In order to achieve the above object, according to the first aspect of the 
present invention, there is provided a crystal growth method based on 
molecular beam epitaxy, comprising the steps of: opening/closing shutter 
means provided between a deposition source and a substrate in an 
ultra-high vacuum so as to form a region having a predetermined pattern on 
the substrate; and forming a crystal growth layer only in the region 
having the pattern on substrate during an epitaxial growth step. 
According to the second aspect of the present invention, there is provided 
a crystal growth method further comprising the step of rotating the 
substrate in synchronism with an opening/closing operation portion of the 
shutter means. 
In the crystal growth method described in the first or second aspect, As is 
supplied to a gap between the shutter means and the substrate during 
closing the shutter means, or a temperature of the substrate is decreased 
to about 450.degree. C. during closing the shutter means. 
According to the third aspect of the present invention, there is provided a 
crystal growth apparatus for performing molecular beam epitaxy, comprising 
a shutter mechanism which is provided between a deposition source and a 
substrate, has an opening with a predetermined pattern, and can be 
opened/closed in an ultra-high vacuum. 
According to the fourth aspect of the present invention, there is provided 
a crystal growth apparatus further comprising means capable of rotating 
the shutter mechanism described in the third aspect in synchronism with 
the substrate. 
According to the present invention, a shutter plate is positioned between 
the deposition source and the substrate, is freely opened/closed or moved 
in an ultra-high vacuum, and has an opening having a predetermined 
pattern. By using this shutter plate, selective crystal growth based on 
MBE can be performed. Therefore, an optical device such as a laser diode 
and an electronic device can be integrated on the substrate. According to 
the method of the present invention, since patterning in the atmosphere 
and regrowth are not required, the number of steps can be decreased. In 
addition, crystal growth with high quality can be obtained to improve the 
device characteristics. 
The above and many other advantages, features and additional objects of the 
present invention will become manifest to those versed in the art upon 
making reference to the following detailed description and accompanying 
drawings in which preferred structural embodiments incorporating the 
principles of the present invention are shown by way of illustrative 
example.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention will be described below with reference to preferred 
embodiments shown in the accompanying drawings. 
As shown in FIG. 1, a shutter plate 2 having a predetermined opening is 
provided immediately above a substrate 1 in an apparatus for executing 
MBE. Crystal growth is performed in this state. Since the crystal growth 
is performed in an ultra-high vacuum, a beam of a vapor 3 moves straight 
and reaches the substrate 1. The vapor 3 is selectively deposited to grow 
a layer only in a region which is not covered with the shutter plate. If 
this shutter plate having the opening is opened/closed or moved by a drive 
unit in an ultra-high vacuum, patterning can be performed in an arbitrary 
crystal growth region on the surface of the crystal growth substrate by a 
consistent vacuum process in a crystal growth chamber. If the shutter 
portion is rotated together with the substrate, uniformity of the 
thickness of a grown layer on the surface of the substrate can be 
obtained. 
First Embodiment: 
FIGS. 2A to 2C are views of steps of integrating lasers having two 
wavelengths for explaining the first embodiment of the present invention. 
A 100- .mu.m thick tantalum shutter plate 2a is set immediately above an 
n-type GaAs substrate 1 by a distance of 200 .mu.m, and has striped 
openings which are aligned at a pitch of 500 .mu.m and each of which has a 
width of 250 .mu.m. First of all, this shutter plate 2a is closed (FIG. 
2A). In this state, a lower n-type Al.sub.0.5 Ga.sub.0.5 As cladding layer 
(thickness: 1.5 .mu.m) 5a, a GaAs single quantum well layer (thickness: 10 
.mu.m ) 6, an upper p-type Al.sub.0.5 Ga.sub.0.5 As cladding layer 
(thickness: 1.5 .mu.m) 7a, and a p-type GaAs contact layer (thickness: 0.2 
.mu.m) 8a are sequehtially grown. 
At this time, each growth region is determined by the incident direction of 
a deposition beam 9a, and a positional relationship between the shutter 
plate 2a and the substrate 1, as shown in FIG. 2A. Assume that the 
substrate temperature is set at a normal growth temperature of 600.degree. 
C. In this case, if an As beam is not incident on each region which is 
shaded by the shutter plate, As is discharged from the surface of the 
substrate. In order to suppress this discharge of As, an As beam 9b is 
incident from the horizontal direction with respect to the substrate, and 
As is supplied from a gap between the shutter and the substrate. The 
shutter plate 2a is then opened, while another shutter plate 2b is closed 
(FIG. 2B). This shutter plate 2b has striped openings similar to the above 
shutter plate 2a. The shutter plate 2b has the following positional 
relationship with the shutter plate 2a. When the shutters are closed, the 
openings of the shutter plate 2b are shifted from those of the shutter 
plate 2a by 250 .mu.m in a direction perpendicular to a direction along 
which the stripes extend. When the shutter plate 2b is closed to perform 
crystal growth, the region wherein the deposition beam 9a is shielded by 
the shutter plate 2a is subjected to crystal growth at this time. In a 
state of closing the shutter plate 2b, a lower n-type Al.sub.0.5 
Ga.sub.0.5 As cladding layer (thickness: 1.5 .mu.m) 5b, an In.sub.0.2 
Ga.sub.0.8 As single quantum well layer (thickness: 10 .mu.m) 10, an upper 
p-type Al.sub.0.5 Ga.sub.0.5 As cladding layer (thickness: 1.5 .mu.m) 7b, 
and a p-type GaAs contact layer (thickness: 0.2 .mu.m) 8b are sequentially 
grown. With this operation, a structure wherein lasers of GaAs active 
layers each for a wavelength of 0.85 .mu.m and lasers of In.sub.0.2 
Ga.sub.0.8 As active layers each for a wavelength of 1.0 .mu.m are 
integrated at a pitch of 250 .mu.m can be formed. As shown in FIG. 2C, an 
SiO.sub.2 film 11 is selectively formed, and electrodes 12 are formed on 
the resultant structure upon crystal growth. According to this method, the 
crystal growth including a patterning process is performed in a series of 
steps in an ultra-high vacuum. Therefore, this method desirably has a 
smaller number of steps than that of a method wherein a substrate is 
unloaded into the outer atmosphere once and processed, and then regrowth 
is performed on the resultant structure. Also, this method has no 
degradation in crystallinity caused by regrowth. 
This embodiment employs the opening/closing shutter mechanism. A shutter 
mechanism which is moved in the horizontal direction with respect to a 
substrate may be used. That is, after the shutter plate 2a is closed, and 
the lasers of the GaAs active layers are grown, the shutter plate 2a is 
parallelly moved by 250 .mu.m in a direction perpendicular to the 
direction along which the stripes extend, and then the lasers of the 
In.sub.0.2 Ga.sub.0.8 As active layers are grown. 
In the process of manufacturing the above-described integrated structure, 
although all the crystal growth layers are selectively grown, only the 
active layers may be selectively grown. That is, in a state of opening the 
shutter plate, a lower cladding layer 5 is grown entirely on the 
substrate. After closing the shutter plate 2a, GaAs active layers 6 are 
grown. Then, after the shutter plate 2a is opened, and the shutter plate 
2b is closed, In.sub.0.2 Ga.sub.0.8 As active layers 10 are grown. 
Finally, after opening the shutter plate 2b, an upper cladding layer 7 and 
a contact layer 8 are grown entirely on the substrate. With this 
operation, the same structure as that described above can be obtained. 
As a method of suppressing the discharge of As caused when the shutter 
plate is closed, a method of decreasing the temperature of the substrate 
to about 450.degree. C. after closing the shutter plate to prevent As from 
being discharged, and a method of depositing As on the surface of the 
shutter plate at the substrate side to set an As atmosphere around the 
surface of the substrate using this deposited As even when the shutter is 
closed are considered in addition to the above method. 
Generally, in order to uniform the thickness of the crystal growth layer in 
growth based on MBE, the substrate is rotated during growth. In the 
selective growth of the present invention, in order to obtain the 
uniformity in thickness of the growth layer on the surface of the 
substrate, the substrate is rotated in synchronism with the shutter 
portion to perform growth. This method can be easily executed by 
integrally mounting the shutter portion on a substrate rotating mechanism. 
FIG. 3 shows an arrangement of this shutter portion. As shown in FIG. 3, 
the shutter plate 2 is integrally mounted on a substrate holder 13. When 
the shutter is moved above the substrate to change the growth region, 
growth is stopped temporarily, a manipulator 14 on which the substrate 
holder 13 is mounted is inclined, and then the shutter plate 2 is rotated 
by a predetermined angle or horizontally moved by a predetermined distance 
by another manipulator 15. These steps are performed in an ultra-high 
vacuum. 
In an apparatus which does not have an inclining mechanism of the 
manipulator 14 such as a modification shown in FIG. 3, since the shutter 
plate 2 is operated from an upper portion from which a deposition beam is 
supplied, supply of the deposition beam must be temporarily stopped during 
operation of the shutter plate 2. If the manipulator 14 for setting the 
holder 13 has an opening/closing introduction mechanism of the shutter 
plate 2, the introduction mechanism does not shield the deposition beam 
9a. Therefore, the shutter plate 2 can be moved instantaneously, and the 
selective growth can be realized without interrupting growth. When growth 
is performed during rotating the substrate, the incident direction of the 
deposition beam is changed with this rotation. For this reason, with the 
change in incident direction of the beam, a selective growth region 16 is 
set as shown in FIG. 4 in a positional relationship between a deposition 
source 3, the shutter plate 2, and the substrate 1. 
Second Embodiment: 
FIGS. 5A to 5D are sectional views of steps of integrating a single 
vertical cavity-type laser and a double vertical cavity-type detector for 
explaining the second embodiment of the present invention. A 100- .mu.m 
thick tantalum shutter plate 2 is set immediately above an n-type GaAs 
substrate 1 by a distance of 200 .mu.m, and has striped openings which are 
aligned at a pitch of 500 .mu.m and each of which has a width of 250 
.mu.m. First of all, this shutter plate 2 is opened, and a reflecting 
multilayered film 17 consisting of 7.5 pairs of n-type Ga. As layers 
(thickness: 69.5 .mu.nm) and n-type AlAs layers (thickness: 82.9 .mu.nm) 
is grown by MBE (see FIG. 5A). 
Thereafter, the growth is temporarily stopped, the shutter plate 2 is 
closed, and GaAs 18 having a film thickness of 278.1 .mu.nm equivalent to 
a wavelength .lambda. of 980 .mu.nm is grown only in regions of the 
striped pattern of the openings on the substrate (see FIG. 5B). At this 
time, the substrate 1 is rotated in synchronism with the shutter plate 2 
during growth. An As beam 9b is incident from the horizontal direction 
with respect to the substrate so as to illuminate the substrate even when 
the shutter is closed. As is supplied from a gap between the shutter plate 
2 and the substrate 1. 
As shown in FIG. 5C, the shutter plate 2 is opened again. Then, an n-type 
reflecting multilayered film 19 consisting of 15.5 pairs of layers, an 
Al.sub.0.3 Ga.sub.0.7 As layer 20 with a .lambda. thickness (294.1 .mu.nm) 
including an In.sub.0.18 Ga.sub.0.82 As active layer (thickness: 10 
.mu.nm) 21, and a p-type reflecting multilayered film 22 consisting of 
14.5 pairs of layers are sequentially grown entirely on the substrate. 
With this operation, a structure wherein a single vertical cavity-type 
layer 23 and a double vertical cavity-type detector 24 are integrated is 
formed on the substrate 1. The double cavity is suitable for a detector 
because it has a wider wavelength band than that of the single cavity. 
As shown in FIG. 5D, upon crystal growth, an SiO.sub.2 film 25, and 
electrodes 26 and 27 are formed. In this embodiment, the crystal growth 
including a patterning process is performed in a series of steps in an 
ultra-high vacuum. Therefore, this method desirably has a smaller number 
of steps than that of a method wherein a substrate is unloaded into the 
outer atmosphere once and processed, and then regrowth is performed on the 
resultant structure. Also, this method has no degradation in crystallinity 
caused by regrowth. When the selective growth is to be performed, the 
thickness of the growth layer can be controlled on the order of 
subnanometers using the MBE growth. By rotating the substrate, the surface 
of the substrate is highly uniformed. 
Third Embodiment: 
FIGS. 8A to 8C are views of steps of integrating vertical cavity-type 
lasers having eight wavelengths for explaining the third embodiment of the 
present invention. As shown in FIG. 6, a 100- .mu.m thick shutter plate 28 
has regions 29A, 29B, and 30, and an opening 31 having each side of 2 cm 
around the rotation center of the shutter. In each of the regions 29A and 
29B, striped openings each having a width of 250 .mu.m are aligned at a 
pitch of 500 .mu.m, and in the region 30, striped openings each having a 
width of 500 .mu.m are aligned at a pitch of 1,000 .mu.m. As shown in FIG. 
7, the shutter plate 28 is positioned to be vertically spaced apart from a 
substrate 1 by 200 .mu.m. First of all, the shutter plate 28 is 
positioned-to set the opening 31 having each side of 2 cm above the GaAs 
substrate 1. A reflecting multilayered film consisting of 15 pairs of 
n-type GaAs layers (thickness: 71.2 .mu.m) and n-type AlAs layers 
(thickness: 84.7 .mu.nm), and an Al.sub.0.25 Ga.sub.0.75 As interlayer 
including an 10- .mu.nm thick In.sub.0.18 Ga.sub.0.75 As active layer are 
grown to have a thickness of 291.4 .mu.nm by MBE. The reflecting 
multilayered film has a high reflectance of 99.9% or more, and its 
reflection band has a wavelength of 950 .mu.nm to 1,050 .mu.nm. The 
thickness of the interlayer is equivalent to a wavelength .lambda. of 980 
.mu.nm. 
The shutter plate 28 is rotated through 90.degree. to set the region 29A 
with the 250- .mu.m wide striped openings above the substrate 1. As shown 
in FIG. 8A, Al.sub.0.25 Ga.sub.0.75 As is grown to have a thickness of 2 
.mu.m. The shutter plate 28 is further rotated through 90.degree. to set 
the region 29B with the 250- .mu.m wide striped openings above the 
substrate 1. As shown in FIG. 8B, Al.sub.0.25 Ga.sub.0.75 As is grown to 
have a thickness of 4 .mu.nm. The shutter plate 28 is still further 
rotated through 90.degree. to set the region 30 with the 500- .mu.m wide 
striped openings above the substrate 1. As shown in FIG. 8C, Al.sub.0.25 
Ga.sub.0.75 As is grown to have a thickness of 8 .mu.nm. Reference 
numerals in FIGS. 8A to 8C denote thicknesses by which the interlayer is 
increased from the initial thickness of 291.4 .mu.nm. With this operation, 
the interlayers finally have eight thicknesses from 291.4 .mu.nm to 305.4 
.mu.nm for every step of 2 .mu.nm in a region having a size of 500 
.mu.m.times.1,000 .mu.m. These thicknesses are converted into eight 
wavelengths .lambda. from 980 .mu.nm to 1,020 .mu.nm. The shutter plate 28 
is still further rotated through 90.degree. to set the opening 31 having 
each side of 2 cm above the substrate 1. A p-type reflecting multilayered 
film consisting of 20 pairs of layers is grown. After the MBE growth, 
electrodes are formed (not shown). With this operation, the vertical 
cavity-type lasers having eight wavelengths from 980 .mu.nm to 1,020 
.mu.nm for every step of about 5 .mu.nm can be integrated.