Heating – Work chamber having heating means – Work chamber having gaseous material supply or removal...
Reexamination Certificate
2003-09-29
2004-11-09
Wilson, Gregory (Department: 3749)
Heating
Work chamber having heating means
Work chamber having gaseous material supply or removal...
C438S758000, C118S715000
Reexamination Certificate
active
06814572
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal processing unit and a thermal processing method for carrying out a thermal process while supplying a process gas to an object to be processed.
2. Description of the Related Art
There is a process to form a film on an object to be processed by a so-called reduced-pressure CVD (Chemical vapor deposition) method as one of manufacturing processes of a semiconductor device. A vertical thermal processing unit, as shown in
FIG. 9
, for example, is used as a unit for carrying out such a film-forming process. This vertical thermal processing unit conducts a thermal process to objects to be processed in a batch manner. Specifically, the vertical thermal processing unit is provided with a cylindrical reaction tube
10
consisting of quartz double tubes, an inner tube
11
and an outer tube
12
. A wafer-boat
13
holding many semiconductor wafers (to be referred to as a wafer hereinafter) W, which are the objects to be processed, is conveyed from a lower side of the reaction tube
10
into the reaction tube
10
. Inside of the reaction tube
10
is evacuated by a not-shown vacuum pump via a discharging tube
14
so as to be a reduced-pressure atmosphere. On the other hand, a process gas is introduced into the reaction tube
10
. A not-shown heater surrounds a side circumference of the reaction tube
10
. The film-forming process of the wafers W is carried out by heat generated by the heater.
When the film-forming process is a film-forming process of, for example, a silicon nitride film, ammonium (NH
3
) gas and dichlorosilane (SiH
2
Cl
2
) gas, for example, are used as process gases. A gas-supplying system in this case will be briefly described. The ammonium gas is supplied from a gas supplying source
15
a
through a gas tube
16
a
and the dichlorosilane gas is supplied from a gas supplying source
15
b
through a gas tube
16
b
, into the reaction tube
10
respectively. Incidentally, in order to make a maintenance cycle of the outer tube
12
longer, nitrogen gas as a purge gas is adapted to be supplied from a gas supplying source
15
c
through a gas tube
16
c
into a room between the inner tube
11
and the outer tube
12
. Vc
1
and Vc
2
indicate valves and Mc indicates a flow-rate adjusting part. In the gas tube
16
a
, a valve Va
1
, a flow-rate adjusting part Ma, and a valve Va
2
are provided in this order from an upstream side thereof. In the gas tube
16
b
, a valve Vb
1
, a flow-rate adjusting part Mb and a valve Vb
2
are provided as well.
By the way, the aforementioned process gases are poisonous. Therefore, when the processed wafers W are taken out from the reaction tube
10
immediately after the completion of the film-forming process, the poisonous process gases, which remain in the reaction tube
10
and the gas tubes
16
a
,
16
b
communicated thereto for supplying the process gases, may be flown to the outside. Therefore, the nitrogen gas is flown from the gas supplying source
15
c
to the gas tubes
16
a
,
16
b
as a replacement gas (purge gas) after the completion of the film-forming process, so that the remaining process gases can be replaced with the nitrogen gas.
Specifically, the gas tube
16
c
branches into four tubes, i.e. bypass ways
17
a
,
17
b
,
18
a
,
18
b
at an upstream portion with respect to the flow-rate adjusting part Mc. The bypass ways
17
a
and
18
a
are connected to an upstream side and a downstream side with respect to the flow-rate adjusting part Ma of the gas tube
16
a
, and the bypass ways
17
b
and
18
b
are connected to an upstream side and a downstream side with respect to the flow-rate adjusting part Mb of the gas tube
16
b
. A valve Va
3
is provided with the bypass way
17
a
, a valve Vb
3
is provided with the bypass way
17
b
, a flow-rate adjusting part Md and a valve Vd
4
are provided with the bypass way
18
a
in this order from an upstream side thereof, and a flow-rate adjusting part Me and a valve Vb
4
are provided with the bypass way
18
b
in this order from an upstream side thereof, respectively.
As described above, the nitrogen gas supply is conducted by two lines to each of the gas tubes
16
a
,
16
b
that are for supplying the process gases. This is because a flow-rate adjusting range of each of the process gases is narrow and a maximum flow rate of each of the flow-rate adjusting parts Ma, Mb is small. In other words, the bypass ways
18
a
,
18
b
are provided in order to ensure a flow rate of the nitrogen gas.
SUMMARY OF THE INVENTION
The inventor has been studying a method, for example, illustrated in
FIG. 10
as a method for removing a process gas. First of all, at a time t
1
when a film-forming process is completed, all the gas supplies into the gas tubes
16
a
and
16
b
are stopped. Then, the process gas is discharged toward the discharging tube
14
so that the previous process pressure of 13.3 Pa (0.1 Torr) is reduced to 0.133 Pa. However, the rate for the process gas to be discharged gradually becomes slower. Therefore, in order to enhance a probability of collision of nitrogen gas molecules and process gas molecules by raising the pressure in the reaction tube
10
up to the previous process pressure once, the nitrogen gas supply to the gas tubes
16
a
and
16
b
are started (a time t
2
). This leads a dilution ratio of the process gases remaining in the reaction tube
10
to be lowered to 1.0×10
−2
. Thereafter, the process gases are discharged toward the discharging tube
14
so as to reduce the pressure at a blast (a time t
3
). Then, when the nitrogen gas supply to the gas tubes
16
a
and
16
b
is started again (a time t
4
), the concentration of the remaining process gases becomes about 1.0×10
−4
. By repeating such pressure-raising/lowering steps, the dilution ratio of the process gases in the reaction tube
10
is lowered to be not more than a safety standard value of, for example, 1.0×10
−14
.
However, such a dilution process takes a long time, for example, about 30 minutes. This is because a power usage system is arranged at a position away from the thermal processing unit and a gas supplying unit is provided therein. In other words, since a crossover from the gas supplying unit to the thermal processing unit is long, it takes a long time to put out the process gases remaining in this part. Thereby, a period from the completion of the film-forming process of the wafers W to conveyance of the wafers W is long, which is one of causes of the low throughput.
This invention is based on the above issues and the object thereof is to provide a technique capable of shortening a required time from conveying-in of an object to be processed to conveying-out thereof in a thermal processing unit and a thermal processing method, in which a process gas is supplied to the object to be processed so as to conduct a thermal process.
The present invention is a thermal processing unit comprising: a reaction container which an object to be processed is conveyed into and from; a process-gas introducing part for introducing a process gas into the reaction container; a replacement-gas introducing part for introducing a replacement gas into the reaction container, the replacement-gas introducing part being independent of the process-gas introducing part; a discharging part for discharging a gas in the reaction container; and a controlling part connected to the process-gas introducing part, the replacement-gas introducing part and the discharging part, the controlling part being adapted to: control the discharging part so as to lower a pressure in the reaction container lower than a pressure at a thermal process, then control the process-gas introducing part and the replacement-gas introducing part so as to stop introducing the process gas and introduce the replacement gas into the reaction container as well as control the discharging part so as to raise the pressure in the reaction container higher than the pressure at the thermal process, and then control the dischargin
Smith , Gambrell & Russell, LLP
Tokyo Electron Limited
Wilson Gregory
LandOfFree
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