Apparatus for producing semiconductors

The present invention relates to an apparatus for producing semiconductors utilizing vacuum chemical epitaxy (VCE) method. Said VCE method has a high utilization efficiency of reactant gas and can finish the surface of a semiconductor layer formed on the surface of a substrate smoothly in comparision with a conventional Metalorganic Chemical Vapor Deposition Method(MOCVD). However, in case of forming semiconductor layer on the surface of a substrate with a large area, it is impossible to form homogeneous semiconductor layer. According to the present invention, a reactant gas dispersing chamber is disposed under a reaction chamber disposed within a vacuum chamber, the both chambers are communicated by a plurality of communicating holes, a feeding pipe for supplying reactant gas is extended into the reactant gas dispersing chamber, an end opening thereof is faced downward and a color portion is formed in parallel at the circumference of the end opening. Said reactant gas is blown off downward from the end opening of the feeding pipe and dispersed in parallel along the collar portion and dispersed homogeneously in the reactant gas dispersing chamber, and in the state, is introduced to the reaction chamber via said communicating holes. Therefore, even if on a substrate with a large area, homogeneous semiconductor layer can be formed.

FIELD OF THE INVENTION 
This invention relates to an apparatus for producing semiconductors wherein 
compound semiconductor layers are grown in a vacuum chemical epitaxy (VCE) 
system. 
BACKGROUND OF THE INVENTION 
In recent years, the demand for compound semiconductors especially Group 
III-V compounds (e.g. GaAs) has been growing because of their being 
superior in performance charcteristics to the conventinal silicon 
semiconductors. For the production of such Group III-V compound 
semiconductors, there are known, among others, the so-called molecular 
beam epitaxy (MBE) process which comprises causing atoms required for a 
compound to be epitaxially grown to evaporate from a solid material using 
a heat gun and causing them to collide, in the molecular beam form, 
against a substrate in an ultrahigh vacuum to thereby cause growth of a 
film of said material on said substrate, and the so-called metal organic 
chemical vapor deposition (MOCVD) process which comprises introducing the 
vapor of methyl-metal or ethyl-metal compound into a reaction chamber at 
atmospheric pressure or under reduced pressure by means of a carrier gas 
such as H.sub.2, allowing said vapor to mix with a Group V metal hydride 
and allowing the reaction therebetween to take place on a heated substrate 
for crystal growth. 
However, the MBE process among said two processes is not suited for a 
large-scale production, hence can hardly meet the needs of the market 
because .circle.1 it requires about 10.sup.-11 Torr of ultra-high 
vacuum, .circle.2 downtime generates when refilling material and 
.circle.3 it requires a substrate rotating mechanism in order to conduct 
a homogeneous growth. Therefore, MOCVD process is now paid attention and 
practically used. However, it has disadvantages in that .circle.1 a 
distribution is easily caused in a flow direction and it is difficult to 
analyze the flow at a scale-up since it is a process in a laminar flow 
area and .circle.2 reactant gas is expensive and the utilization 
efficienty of the reactant gas is low because of the growth mechanism. 
Since a large quantity of unreacted gas, which is toxic, is produced 
because of the efficiency of reactant gas utilization being low, as 
mentioned above, since the carrier gas constitutes an additional waste gas 
portion, a large quantity of a toxic waste gas is discharged, and this 
fact leads to waste gas disposal problems. 
Thus, since each of the MBE process and the MOCVD process have 
disadvantages respectively, it is desired to provide an apparatus for 
producing semiconductors removed these disadvantages completely. 
Accordingly, the inventors succeeded in developing an apparatus for 
producing semiconductors in which advantages of both MBE and MOCVD process 
are incorporated and filed a patent application (Japanese patent 
application No. 63-191060). The structure of this apparatus is shown in 
FIGS. 5 and 6. In these figures, the reference numeral 101 indicates the 
vacuum chamber of vacuum chemical epitaxy, the vacuum chamber 101 has a 
reaction chamber 102 therein, which is formed by a base plate 106, 
surrounding walls 107 and a top plate 108 placed, slidably in one 
direction, on the upper edges of the surrounding walls 107. The top plate 
has, in the middle portion thereof, openings 108a. Disc-form GaAs 
substrates 113 are detachably mounted on the openings 108a respectively. 
The surrounding walls of the reaction chamber 102 have exhaust ports 110 
at certain given intervals around the same. The total area of these 
exhaust ports 110 is preferably about 4% of the surface area of the top 
plate 108 of the reaction chamber 102. The base plate 106 has nozzle 
openings 109 formed at predetermined intervals therein, which are in 
communication with openings 109 or 134 in the ceiling of a first 
dispersing chamber 104 disposed under the reaction chamber 102. Each 
opening 109 is in communication with the first dispersing chamber 104, 
whereas each opening 134 is in communication with a second dispersing 
chamber 124 via a duct 119 which passes through the first dispersing 
chamber 104. The first dispersing chamber 104 is in communication with a 
starting material inlet tube 121. Said starting material inlet tube 121 
serves for introducing into the first dispersing chamber 104 a Group III 
compound (reactant gas) such as trimethylgallium (TMGa) or triethylgallium 
(TEGa). The second dispersing chamber 124 has an opening in the lower 
part, and an exhaust valve 136, suitably a poppet valve, is disposed 
displaceably in said opening for opening or closing said opening. Said 
second dispersing chamber 124 is in communication, through one side wall 
thereof, with a starting material inlet tube 121. Through said inlet tube 
121, an n-type or p-type dopant or a Group III compound such as 
triethylaluminum (TEA l) enters the second dispersing chamber 124. A 
feeding tube 142 for feeding a Group V compound such as AsH.sub.3 to the 
reaction chamber 102 has a plurality of holes 142a and 142b at certain 
definite intervals and in two rows (right and left). A heater 105 is 
disposed above the top plate 108 of the reaction chamber 102, with a 
leveling plate 105c. In this apparatus for MESFET epitaxy layer growth, 
the reaction chamber 10 is fitted with the substrates 113 (the surfaces 
face below respectively) thereon, then, the vacuum chamber 101 is 
evacuated to a vacuum of less than 10.sup.-7 Torr and the heater 105 is 
electrically loaded so that the heater 105 can generate heat. A Group V 
compound, such as AsH.sub.3 is fed to the feeding tube 142 with the 
substrate temperature 500.degree. C., so that it enters the reaction 
chamber 102 through the holes 142a and 142b. The Group V compound thus fed 
to the reaction chamber 102 flows toward the exhaust ports 110 across the 
surfaces of the substrates 113. During the flow, AsH.sub.3 or TEAs is 
collided against the walls of the reaction chamber, which are hot walls, 
many times and thermally cracked to give As.sub.2. After the temperature 
of the substrates reaches predetermined process temperature 
(600.degree..about.650.degree. C.), a Group III compound such as 
triethylgallium (TEGa) is supplied into the first dispersing chamber 104 
from the starting material inlet tube 121 of the reaction chamber 102, is 
mixed homogeneously and then is blown toward the substrates 113 from 
nozzles 109 in a homogeneous molecular density. At this time, since the 
mean free path of molecules of the Group III compound is set longer than 
the distance from orifice to wafer, the molecules of the Group III 
compound reaches substrates without having dispersion by collision between 
material molecules. The molecule of the Group III compound, together with 
As.sub.2, come into contact with the surface of the substrates 113 and 
grows on said surface in the form of an undoped gallium arsenide (GaAs) 
layer or the like. The unconsumed compound that has not come into contact 
with the substrates 113 leaves the reaction chamber via the exhaust ports 
110 and enters the vacuum chamber 101, which they then leave laterally 
under the action of an exhaustion means. Then, an n-type dopant, either 
alone or in admixture with the above-mentioned Group III or V compound, is 
fed to the reaction chamber 102 from the second dispersing chamber 124 so 
that an n-type active layer can grow on the surface of said undoped GaAs 
layer. Thereafter, all the gas supplies are discontinued and the system is 
maintained as it is for about 15 minutes. Then, the substrates 113 are 
cooled and then taken out of the reaction chamber 102 (hence, from the 
vacuum chamber 101). In this way, Group III-V compound semiconductors 
layer can be obtained. 
However, in the apparatus for producing semiconductors with said structure, 
when growth of substrates with large area or a plurality of substrates is 
conducted, that is, when the distance between a supplying tube and exhaust 
ports becomes long, there is a disadvantage in that the distribution of 
the molecular density of the Group V compound is caused between a 
supplying tube of Group V compound such as AsH.sub.3 and the exhaust 
ports, and thereby it is difficult to form an homogeneous semiconductor 
layer in some case (when the layer grows at low V/III ratio). As shown in 
FIG. 7, since peripheral part of the substrates 113 are supported by 
substrate holding part comprising a supporting part 108b along the whole 
circumference, molecular beams which go upward as an arrow mark from the 
lower part of the reaction chamber 102 are obstructed by said supporting 
part 108b and do not reach the peripheral part of the substrates 113. 
Therefore, the peripheral parts of substrates 113, as shown in FIG. 8, are 
left as untreated part and are thus uneconomical. 
Accordingly, it is an object to provide an apparatus for producing 
semiconductors which can distribute all the reactant gas into the reaction 
chamber in a homogeneous state. 
SUMMARY OF THE INVENTION 
The present invention provides a modified semiconductor production 
apparatus provided with a vacuum chamber, a reaction chamber disposed 
within said vacuum chamber, substrate holding means disposed at a ceiling 
portion of said reaction chamber so as to hold the substrates in a state 
such that the substrates contact a reacting space, a substrate heating 
means disposed at the upper part of said reaction chamber for heating said 
substrates, a reactant gas dispersing chamber disposed under said reaction 
chamber, a plurality of communicating holes disposed at the border part 
between said reactant gas dispersing chamber and reaction chamber at 
predetermined intervals on the whole surface to communicate the two 
chambers, a first reactant gas feeding pipe of which one end extends into 
said reactant gas dispersing chamber and opens toward the bottom surface 
of reactant gas dispersing chamber, a collar portion disposed in parallel 
at the peripheral portion of said end opening of said first reactant gas 
feeding pipe, a second dispersing chamber disposed under said reactant gas 
dispersing chamber, a plurality of communicating pipes extended from the 
ceiling portion of said second dispersing chamber into said each 
communicating hole of said reactant gas dispersing chamber respectively so 
that a clearance can be made between itself and the hole wall, and a 
second reactant gas feeding pipe for supplying second reactant gas to said 
second dispersing chamber.

DETAILED DESCRIPTION OF THE INVENTION 
In an apparatus for producing semiconductors according to the present 
invention, a reactant gas dispersing chamber is newly provided at the 
lower part of a reaction chamber, a first reactant gas feeding pipe is 
extended into said reactant gas dispersing chamber and an end opening 
thereof is faced toward the bottom surface of said reactant gas dispersing 
chamber and a collar portion is formed in parallel around the periphery of 
the end opening. Therefore, a first reactant gas, such as AsH.sub.3, blows 
off into the reactant gas dispersing chamber having a gas dispersing 
effect downwardly, and then comes in contact with a collar portion, 
extends in parallel and in all direction along the collar portion to 
disperse homogeneously in said reactant gas dispersing chamber, and then 
is supplied to the reaction chamber via communication holes disposed at 
the border between the reactant gas dispersing chamber and the reaction 
chamber. So that reactant gas is supplied to the reaction chamber in a 
uniform molecular beam state. That is, in the apparatus for producing 
semiconductors, by operations of a downward opening of the first reactant 
gas feeding pipe, a collar portion disposed at the circumference of said 
opening, a reactant gas dispersing effect of the reactant gas dispersing 
chamber, and a plurality of communicating holes disposed in the whole 
surface at predetermined intervals at a border portion between the 
reactant gas dispersing chamber and the reaction chamber, a Group V 
reactant gas such as AsH.sub.3 is supplied to the reaction chamber in a 
uniform molecular beam state. 
Second reactant gas such as TEAl and the like and third reactant gas such 
as TEGa and the like are mixed in a second dispersing chamber disposed 
under the reactant gas dispersing chamber, and the mixture is 
homogeneously supplied into said reaction chamber via the communicating 
pipes. In this case, a recess is formed at the bottom of the second 
dispersing chamber and an obstructing plate is disposed about above an 
opening of said recess to form a space made by the recess and the 
obstructing plate as a third dispersing chamber. Said second reactant gas 
feeding pipe and the third reactant gas feeding pipe are disposed at the 
surrounding walls of the third dispersing chamber in a state that openings 
of those pipes face each other. When second and third reactant gas are 
supplied to said second dispersing chamber from the clearance between the 
obstructing plate of said second dispersing chamber and opening of said 
recess after blowing off both second and third gases from said both 
openings of each feeding pipe and the mixing, mixing of both gases are 
well-done. When cuttings of which the diameter is almost the same as that 
of substrates are formed at the ceiling portion of said reaction chamber 
and substrate holding pieces are disposed at peripheral portion of the 
cuttings which face to the reaction chamber at predetermined intervals 
along the circumference of the cuttings, almost all of the substrate 
surface can be utilized to form semiconductor layer because the part of 
the substrate hidden by the substrate holding piece is remarkably reduced 
in comparison with a case that the holding part is disposed at whole part 
of cutting circumference. 
Following examples will illustrate the invention in detail. 
(A), (B) & (C) of FIG. 1 illustrate structure of an embodiment of the 
present invention. In FIG. (A), the reference numeral 1 indicates a 
cylindrical vacuum chamber made of stainless steel of vacuum chemical 
epitaxy system. The inside thereof is evacuated by a vacuum exhaustion 
system (not shown in the figure) disposed at the bottom side of the vacuum 
chamber. In this vacuum chamber 1, a carbon graphite reaction chamber 2, 
of which the wall surfaces are coated with silicon carbide, a reactant gas 
dispersing chamber 3, made of carbon graphite as well as said reaction 
chamber 2, and a second dispersing chamber 4 made of stainless steel are 
integrally disposed. The reaction chamber 2 is constructed of a base plate 
6, a surrounding wall 7 and a ceiling plate 8. The wall surface of the 
reaction chamber 2 is made of carbon graphite so that the wall surface 
becomes a hot wall by heating with a heater 5 to reflect molecular grain 
without adhering thereto even if a molecular beam of the reactant gas 
collides with the wall surface. A plurality of communicating holes 9 are 
formed in said base plate 6 at predetermined intervals. The reaction 
chamber 2 and the reactant gas dispersing chamber 3 thereunder thereby 
communicated with each other. An exhaust port 10 is formed at the upper 
part of said surrounding wall 7 along its circumference in a linear state. 
Four round holes 11 are formed in said ceiling plate 8 as shown in FIG. 
1(B). Substrate supporting pieces 12 are protruded at the lower peripheral 
portion of each hole 11 at 90.degree. intervals in a circumferential 
direction as shown in FIGS. 2 and 3. The substrate holding part comprises 
the four substrate supporting pieces 12. Round substrates 13 are placed 
replaceably over said holes 11 and are supported by said substrate 
supporting pieces 12. 
Said reactant gas dispersing chamber 3, disposed under the reaction chamber 
2, comprises a base plate, a surrounding wall and a ceiling plate, which 
is a base plate 6 of the reaction chamber 2, and the wall surface thereof 
is considered to be a hot wall as well as said reaction chamber. A first 
reactant gas feeding pipe 15 is extended into the reactant gas dispersing 
chamber 3 from outside, the end part thereof is bent downwardly and an 
opening 16 therein opens downwardly. A disc-form collar portion 17 is 
formed at the peripheral portion of the opening 16 in parallel. The first 
reactant gas discharged from said opening 16 is thereby dispersed 
homogeniously in parallel and in all directions along the collar portion 
17. A second dispersing chamber 4 is formed under the reactant gas 
dispersing chamber 3. 
Said second dispersing chamber comprises a base plate 18, a surrounding 
wall 7 and a ceiling plate, which is the base plate 14 of the reactant gas 
dispersing chamber 3, and is made of stainless steel because it is less 
necessary to make the wall surface a hot wall. A plurality of 
communicating tubes 19 made of stainless steel are extended from the 
ceiling plate of the dispersing chamber 4 toward a plurality of 
communicating holes 9 formed on the ceiling plate 6 of the reactant gas 
dispersing chamber 3 respectively. In this case, a clearance is made 
between said communicating tube 19 and and hole wall of the communication 
hole 9 to which the communicating tube 19 is extended. The second 
dispersing chamber 4 and the reaction chamber 2 are communicated by said 
communicating tube 19 and the reactant gas dispersing chamber 3 and 
reaction chamber 2 are communicated by the clearances between the 
communicating tubes 19 and the hole walls of the communicating holes 9. A 
recess 20 is formed at the central portion of the bottom of said second 
dispersing chamber 4. End openings 21a and 22a of first and second feeding 
pipes 21, 22 open at opposite sides of surrounding wall portions in a 
state where both openings face each other. An obstructing plate 23 is 
disposed a little over the recess 20 in a state that the plate 23 faces 
the opening thereof. A third dispersing chamber 24 is formed by the 
obstructing plate 23 and said recess 20. Said second and third reactant 
gases are homogeneously mixed by operations of their blowing off pressure 
and the obstructing plate 23 in the third dispersing chamber 24 and the 
mixture enters into said second dispersing chamber 4 through said 
clearance between the obstructing plate 23 and said opening of the recess. 
Then said mixed gas reaches the reaction chamber 2 through said 
communicating tubes 19 after being further mixed homogeneously in the 
second dispersing chamber 4. 
In FIG. 1(A), a reference numeral 5 indicates a plate type heater and 5a 
indicates a levelling plate. The temperature is set so that semiconductor 
compound can grow on the surface of the substrate 13 by heating mainly 
with radiant heat from the above. Said heater 5 is constructed by forming 
alternate stripe-form cuttings 5' on carbon graphite plate and disposing 
electrodes on both ends. While uniform planar heating is possible with 
such heater 5 alone, the use of the heat leveling plate 5a disposed below 
the heater 5 can make the planar heating more uniform. 
In operation for MESFET epitaxy layer growth, the reaction chamber 2 is 
fitted with the substrates 13 (the surfaces face below respectively.) 
thereon. Then the vacuum chamber 2 is evacuated to a high vacuum state and 
the heater 5 is electrically loaded so that the heater 5 can generate 
heat. A Group V compound, such as AsH.sub.3 is fed to the gas dispersing 
chamber 3 through the first reactant gas feeding pipe 15 with the 
substrate temperature at about 500.degree. C. to provide a homogeneous 
dispersing state therein. Then it is fed into the reaction chamber 2 
through communicating holes 9 formed in the surface of the reactant gas 
dispersing chamber at uniform intervals. In the reaction chamber 2, gas 
such as AsH.sub.3 flows toward exhaust ports which are disposed in a 
linear state in the surface of the surrounding wall of the reaction 
chamber 2 along the circumference dispersedly contacting the surfaces of 
the substrates 13. During the flow, AsH.sub.3 and the like is thermally 
cracked to give As.sub.2. Thereafter, a Group III compound such as TEGa is 
fed into the third dispersing chamber 24 from the second reactant gas 
supplying tube 21 after the temperature of the substrates reaches a 
predetermined temperature (600.degree..about.650.degree. C.) and at the 
same time the Group III compound, triethylaluminium (TEAl) is fed into the 
third dispersing chamber 24 and mixed with the former reactant gas. The 
mixture is fed into the second dispersing chamber 4 and it, together with 
As.sub.2, comes into contact with the surface of the substrates and grows 
on said surface in the form of an undoped gallium arsenide (GaAs) layer or 
the like. The unconsumed compound that has not come into contact with the 
substrates 13 leaves the reaction chamber via the exhaust ports 10 under 
the action of an exhaustion means. In this case, since the exhaust port 10 
is formed in a linear state in the surrounding wall of the reaction 
chamber 2 along the circumference, the exhaustion of the unconsumed gas is 
conducted through all circumference of the surrounding wall to thereby 
contribute to a homogeneous dispersion of the reactant gas in the reaction 
chamber. Then, an n-type dopant, either alone or in admixture with the 
above-mentioned Group III or V compound, is fed to the reaction chamber 2 
from the second dispersing chamber 4 so that an n-type active layer can 
grow on the surface of said undoped GaAs layer. Thereafter, all the gas 
supplies are discontinued and the system is maintained for a predetermined 
time as it is and the substrates 13 are cooled and then taken out of the 
reaction chamber 2. Thus, semiconductors having a uniform MESFET 
semiconductor layer can be obtained. 
In this way, according to the embodiment, since the rection chamber 2, 
whose capacity is smaller than the vacuum chamber 1, is disposed in the 
vacuum chamber 1 and the substrates are placed in the reaction chamber and 
in that state the reactant gas is supplied in a molecular beam state to 
let it grow, there is little wasted gas and utilization efficiency of the 
reactant gas is largely improved. In this apparatus, the vacuum chamber 1 
can be evacuated to a high degree, the Group III compound, of which the 
evaporation pressure is low, can be used by gasifying it as is. Therefore, 
a carrier gas for carrying the compound is not necesary, so that 
exhaustion treatment of gas after use becomes small. Particularly in said 
apparatus, since the reactant gas dispersing chamber 3 is newly disposed, 
the first reactant gas supplying tube 15 is disposed downwardly, and the 
end opening 16 thereof has a collar portion 17, the reactant gas therein 
is in a homogeneously dispersted state. Therefore, the reactant gas is 
supplied into the reaction chamber 2 in a homogeneous state, so that 
formation of a homogeneous semiconductor layer can be carried out on a 
large area substrate and a plurality of substrates without rotating the 
substrate or suceptor. In said embodiment, four substrates 13 are used, 
but the number of substrates is not limited to this, either single or 
plural is all right. 
FIG. 4 shows another embodiment. In this embodiment, foil 13' made of 
metal, such as stainless steel and the like, is disposed cylindrically at 
the circumference of a second dispersing chamber 4 made of cheap stainless 
steel and fixed removably with a bis and the like. The lower portion of 
said cylindrically disposed foil 13' is formed skirt-like. The reference 
numeral 1 indicates a lid portion disposed at the part of the vacuum 
chamber 1 for disposing said foil 13'. 
The numeral 4a indicates a cooling pipe made of stainless steel for cooling 
said dispersing chamber 4. Otherwise the apparatus is the same as FIG. 
1(A). 
As a result of this construction, since unconsumed reaction product which 
leaves from the reaction chamber 2 when forming semiconductor layer is 
adhered to the surface of the cylindrical foil 13', other parts in the 
vacuum chamber 1 is prevented pollution in a wide range. That is, since 
the temperature of the second dispersing chamber is rather lower than that 
of the reaction chamber 2, the unconsumed reactive material is adhered 
preferentially to said part of which the temperature is low. Therefore, 
the circumference of the dispersing chamber 4 is prevented from the 
pollution by said cylindrical foil 13'.