Coating apparatus – Gas or vapor deposition
Reexamination Certificate
2001-04-26
2003-11-11
Crane, Sara (Department: 2811)
Coating apparatus
Gas or vapor deposition
C427S255340
Reexamination Certificate
active
06645302
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vapor deposition apparatus for forming a semiconductor stacked layer structure, and more particularly to a vapor deposition apparatus that is suitable for forming a semiconductor heterojunction interface where there is a sharp change in composition. Also, the present invention relates to a vapor deposition process using the vapor deposition apparatus; a stacked layer structure produced by the process; a field effect transistor comprising the stacked layer structure; a semiconductor Hall device comprising the stacked layer structure; and a semiconductor light-emitting device comprising the stacked layer structure.
BACKGROUND OF THE INVENTION
Conventionally, an epitaxial stacked layer structure employed in light-emitting devices of singlehetero (SH)- or doublehetero (DH)-structure or in two-dimensional electron gas field effect transistors (TEGFETs); or a structure similar to the stacked layer structure is formed by a vapor deposition technique such as metal-organic chemical vapor deposition (MOCVD) (see Solid State Electron., vol. 43 (1999), pp. 1577-1589). Particularly, when a stacked layer structure employed in a TEGFET is formed, composition must change sharply at the heterojunction interface in order to efficiently exert the effect of two-dimensional electron gas (TEG) (see Nippon Butsuri Gakkai ed., “HANDOTAICHOKOSHI NO BUTSURI TO OYO,” 4th printing of 1st edition, published on Sep. 30, 1986 by Baifukan, pp. 139-145).
A conventional vapor deposition apparatus in which semiconductor crystal layers, for example, group III-V compound semicoriductor crystal layers, are vapor-grown by MOCVD does not include a piping system through which a group III or group V element source passes constantly, regardless of whether or not the source is necessary for the growth of the crystal layers (see J. Crystal Growth, vol. 55 (1981), pp. 64-73, 92-106, 164-172, and 213-222). The conventional vapor deposition apparatus has a piping system so that an element source or a dopant source is supplied to a vapor deposition region through the piping only when the supply of the source is necessary. Therefore, in the apparatus, the supply of the source gas, which is temporarily unnecessary for the vapor-growth of the crystal layers, is temporarily stopped by means of valve operation.
In the piping system of such a conventional vapor deposition apparatus, when the source gas becomes necessary again, the valve must be opened to resume supply of the gas to the vapor deposition region. However, when the supply of the source gas is resumed after the supply is stopped, the flow rate of the gas varies temporarily in accordance with variance in pressure in the piping by the opening of valve. In addition, the purity of the source gas lowers, since the gas is confined or retained in the piping. Temporal variance in the flow rate of the source gas and lowering of the purity of the gas cause variance in compositional proportions of elements constituting the crystal layers. As a result, forming a junction interface where there is a sharp change in composition is difficult. Therefore, such a conventional vapor deposition apparatus having the aforementioned piping system is inappropriate for vapor-growth of a stacked layer structure, which must have a heterojunction interface where the composition changes sharply employed in a TEGFET.
In order to solve the problems involved in the piping system of such a vapor deposition apparatus and to form a semiconductor junction interface where the composition changes sharply, there has been proposed a piping system to the supply a source gas called a vent/run system, which has a mechanism that enables constant flow of a source gas and instantaneous switching of the gas supplied to a vapor deposition region (see J. Crystal Growth, vol. 68 (1984), pp. 412-421 and 466-473; and “III-V ZOKU KAGOBUTSU HANDOTAI,” edited by Isamu Akasaki, published on May 20, 1994 by Baifukan, 1st edition, pp. 68-70). A vent line (exhaust line) is provided to constantly supply a source gas to the outside of a vapor deposition region in advance to maintain a constant flow rate of the gas, regardless of whether or not the gas is necessary for vapor-growth of the intended crystal layers. A run line (source supply line) is connected directly to the vapor deposition region, and is provided for supplying the source gas necessary to the region for vapor-growth of the intended crystal layers, the flow of the source gas being switched from the vent line to the run line. That is, unlike the conventional piping system containing only a source supply line, the vent/run system includes the vent line through which the source gas passes constantly.
FIG. 1
illustrates a vent/run-type source gas supply piping system. Source gas passages
13
,
14
, and
15
are provided for passing source gasses
10
,
11
, and
12
, respectively. Each source gas consists of a gas source or gas accompanied by vapor of the source. The flow rates of the source gasses
10
through
12
passing through the passage
13
through
15
are regulated by flowmeters
16
,
17
, and
18
. Conventionally, the passages
13
through
15
corresponding to the respective source gasses are connected to a run line
25
and a vent line
26
via two-way valves
19
through
24
. Whether or not a fluid is passed through a single line is determined through an opening and closing operation of the corresponding two-way valve. The run line
25
is connected directly to a vapor deposition region in which crystal layers are formed. The vent line
26
is detoured away from the vapor deposition region and connected directly to an exhaust system in which exhaust of gas is carried out.
Switching of the flow of the source gasses
10
through
12
from the run line
25
to the vent line
26
and vice versa is carried out by an opening and closing operation of the flow path switching valves
19
through
24
provided on the source gas passages
13
through
15
. For example, in order to switch the path through which the source gas
10
flows via the source gas passage
13
from the vent line
26
to the run line
25
, the two-way valve
22
is closed and, simultaneously, the two-way valve
19
is opened. Usually, the two-way valves
19
and
22
are not opened simultaneously; nor are the two-way valves
20
and
23
and the two-way valves
21
and
24
.
The conventional vent/run-type piping system consists of a combination of a single run line (i.e., the line
25
) and a single vent line (i.e., the line
26
). In the vent/run-type piping system consisting of such a combination; i.e., a single vent/run-type piping system, the flow rate of the source gas varies periodically immediately after the path of a source gas is switched from the vent line
26
to the run line
25
. Variance in the flow rate of the source gas gradually decreases while the gas is supplied through the line
25
to a vapor deposition region, but the amount of the gas supplied to the vapor deposition region still varies. Variance in the amount of the gas supplied causes variance in the compositional proportions of elements constituting crystal layers in a vertical direction with respect to the layers, and also impedes sharp change in composition at a heterojunction interface of the crystal layers.
Problems involved in the conventional single vent/run-type source supply piping system will be described in more detail with reference to FIG.
1
. For example, suppose when two source gasses
10
and
11
are passed through the run line
25
at a constant flow rate via the source gas passages
13
and
14
to thereby vapor-grow a crystal layer, and subsequently a mixed-crystal layer is vapor-grown from the three source gasses
10
through
12
. In such a case, in order to grow the mixed-crystal layer, the path of the source gas
12
must be switched from the vent line
26
to the run line
25
by an opening and closing operation of the two-way valves
21
and
24
. Immediately after the path is switched, the flow rate of the source gas
12
varies p
Crane Sara
Showa Denko Kabushiki Kaisha
Sughrue & Mion, PLLC
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