Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Fluid growth step with preceding and subsequent diverse...
Reexamination Certificate
2001-06-20
2003-04-08
Dang, Trung (Department: 2823)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Fluid growth step with preceding and subsequent diverse...
C438S478000, C438S483000
Reexamination Certificate
active
06544869
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for depositing a semiconductor film on a wafer by making source gases supplied flow almost horizontally to the surface of the wafer. The present invention also relates to a method for fabricating a semiconductor device by using the film deposition method or apparatus.
Group II-VI or III-V compound semiconductors are direct transition type semiconductors with wide bandgap energy, and are hopefully applicable to emitting light at various wave-lengths that range from visible through ultraviolet regions of the spectrum.
Among other things, Group III-V nitride semiconductors, including gallium (Ga) or aluminum (Al) as a Group III constituent and nitrogen (N) as a Group V constituent, have attracted much attention, because those semiconductors exhibit crystallographically excellent properties. Thus, a method for depositing a film of a nitride semiconductor just as intended is in high demand.
A metalorganic chemical vapor deposition (MOCVD) process has been researched and developed widely and vigorously as one of industrially implementable methods of promise.
Hereinafter, a so-called “horizontal MOCVD reactor”, which is so constructed as to make source gases flow horizontally to the wafer surface, will be described as a known semiconductor film deposition apparatus with reference to
FIGS. 7A and 7B
.
As shown in
FIGS. 7A and 7B
, the horizontal reactor
200
includes: reactor body
201
; gas inlet tube
202
with a gas inlet port
221
; and susceptor
211
attached to the bottom of the reactor body
201
. In this case, the reactor body
201
and gas inlet tube
202
are made of quartz glass, for example. Also, a gas outlet port
212
is provided at the other end of the reactor body
201
on the opposite side to the gas inlet tube
202
.
The susceptor
211
holds a wafer
100
thereon to heat the wafer
100
up to a predetermined temperature.
A source gas
101
, supplied through the gas inlet port
221
, should be a laminar flow with no vortices after the gas
101
enters the tube
202
through the inlet port
221
and until the gas
101
reaches the space over the susceptor
211
. The gas
101
also needs to flow in such a manner as to show spatially uniform velocity distribution over the wafer
100
to grow compound semiconductor crystals of quality.
However, the opening width of the gas inlet port
221
is relatively small as defined by its manufacturing standard, and the gas, supplied through the inlet port
221
, should expand to cover an area equal to or greater in width than that of the susceptor
211
. For that purpose, the gas inlet tube
202
has an expanded portion
222
, the width of which gradually increases from the gas inlet port
221
toward the susceptor
211
. In this case, if the angle &agr; of expansion of the expanded portion
222
is large, then a streamline, which has flowed along the inner wall surface of the tube
202
, separates from the surface in a velocity boundary layer near the wall of the expanded portion
222
as shown in FIG.
7
A. Then, the streamline flows backward, i.e., toward the gas inlet port
221
, to turn into a separated streamline (or vortex stream-line)
102
. Also, a wake, or a vortex
103
, is created inside a curvature formed by the separated streamline
102
. In other words, a backward flow, moving upstream along the wall surface of the expanded portion
222
, is created and then separated from the wall surface at a separation point to form the separated streamline
102
. In
FIG. 7A
, only the streamlines flowing along the wall on the left-hand side of the gas flow are illustrated. Actually, though, similar streamlines also flow along the right-hand-side wall surface almost symmetrically to the illustrated ones about the centerline.
If the vortex
103
is created in the expanded portion
222
, then the channel width of the gas flow is substantially decreased or deformed. As a result, the velocity distribution of the gas flow over the susceptor
211
cannot be spatially uniform anymore. In addition, the source gas
101
gets partially stuck inside the vortex
103
, thus adversely delaying the exchange of one source gas for another. In that case, even if the semiconductor film being deposited should have its composition changed, the interfacial profile cannot be steep enough.
To solve these problems, G. B. Stringfellow proposed expanding the sidewalls of the expanded portion
222
gently by setting the expansion angle &agr; to 7 degrees or less (see “Organometallic Vapor-Phase Epitaxy”, Second Edition, p. 364, Academic Press).
Another solution is disposing a netlike or porous diffuser
223
in the expanded portion
222
of the gas inlet tube
202
as shown in
FIGS. 8A and 8B
or
9
A and
9
B to prevent the vortex from being created in the expanded portion
222
.
However, the known horizontal reactor
200
has the following drawbacks. Specifically, if the expansion angle &agr; of the expanded portion
222
is set to about 7 degrees or less, then the distance from the gas inlet port
221
to the gas outlet port
212
of that reactor
200
becomes very long. Accordingly, it may take an excessively large area to dispose such a bulky reactor. Or that long reactor may break very easily, so too much care should be taken in handling such a reactor.
On the other hand, if the diffuser
223
is disposed inside the gas inlet tube
202
, then the spatial uniformity in the velocity distribution of the gas flow improves. Nevertheless, the gas flow is reflected by the diffuser
223
to create another type of vortex, thus also delaying the exchange of one source gas for another.
In addition, if the horizontal reactor
200
should be re-designed every time some process condition, e.g., the flow velocity or pressure of a source gas, is changed and optimized, then the productivity should decline or the costs would increase disadvantageously.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to save the need for re-designing a horizontal reactor even if some condition, like the flow velocity or pressure of a source gas, for a film deposition process to be carried in the reactor has been changed and optimized.
To achieve this object, in depositing a semiconductor film, a gas flow rate is fixed at a predetermined value according to the present invention by keeping the product of the flow velocity and pressure of source gases inside the reactor constant.
The present inventors carried out various types of research on a process for depositing a compound semiconductor film using a horizontal reactor. As a result, we found that the spatial distributions of velocity and temperature of source gases and that of the thickness of a film to be deposited on a wafer are substantially controllable in the reactor by the flow rates of the source gases. The velocity and temperature distributions of reactant gases, resulting from chemical reaction between the source gases, were also controllable by the flow rates. As is well known in the art, the flow rate of a gas is proportional to the product of the flow velocity and pressure of the gas. Accordingly, each of those spatial distributions can be kept substantially uniform during the film deposition process only if the flow velocity or pressure of the source gases is changed in such a manner as to maintain a predetermined gas flow rate.
Specifically, a first inventive film deposition method is for use to deposit a semiconductor film on a wafer by making a source gas supplied flow almost horizontally to the surface of the wafer. In this method, the source gas has its flow velocity and/or pressure changed so that the source gas is supplied at a substantially constant flow rate.
According to the first inventive method, a source gas supplied has its flow velocity near its inlet port and pressure inside a reactor changed so that the source gas is supplied onto a wafer at a substantially constant flow rate. Thus, it is clear from our findings that even if the flow velocity of the source gas is changed to deposit a film a
Ban Yuzaburo
Harafuji Kenji
Ishibashi Akihiko
Ohnaka Kiyoshi
Dang Trung
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Studebaker Donald R.
LandOfFree
Method and apparatus for depositing semiconductor film and... 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 and apparatus for depositing semiconductor film and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for depositing semiconductor film and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3070294