U.S. patent application number 10/959575 was filed with the patent office on 2005-04-28 for semiconductor device fabricating system and semiconductor device fabricating method.
Invention is credited to Okabe, Tsuneyuki, Takadou, Makoto.
Application Number | 20050087299 10/959575 |
Document ID | / |
Family ID | 34509715 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087299 |
Kind Code |
A1 |
Okabe, Tsuneyuki ; et
al. |
April 28, 2005 |
Semiconductor device fabricating system and semiconductor device
fabricating method
Abstract
Shutoff valves are placed in parts of the process gas supply
lines at positions near the processing vessel. A main purge gas
supply line branches into branch purge gas supply lines, each of
which is provided with an orifice called sonic nozzle. The branch
purge gas supply lines are connected to parts of the process gas
supply lines extending between the shutoff valves and the
processing vessel. The ratio P1/P2, where P1 is primary pressure on
the primary side of the orifice and P2 is secondary pressure on the
secondary side of the orifice, is controlled to be not less than a
predetermined value, for example, two, thereby, the purge gas can
always be supplied at equal flow rates into the process gas supply
lines. The total flow rate of the purge gas is controlled by a mass
flow controller placed in the main purge gas supply line.
Inventors: |
Okabe, Tsuneyuki; (Tokyo-To,
JP) ; Takadou, Makoto; (Tokyo-To, JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
1850 M STREET, N.W., SUITE 800
WASHINGTON
DC
20036
US
|
Family ID: |
34509715 |
Appl. No.: |
10/959575 |
Filed: |
October 7, 2004 |
Current U.S.
Class: |
156/345.26 ;
118/715; 257/E21.293 |
Current CPC
Class: |
H01L 21/3185 20130101;
C23C 16/455 20130101; C23C 16/4401 20130101; C23C 16/345
20130101 |
Class at
Publication: |
156/345.26 ;
118/715 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 2003 |
JP |
2003-349893 |
Claims
What is claimed is:
1. A semiconductor device fabricating system comprising: a
processing vessel; process gas supply lines each connected to the
processing vessel to supply a process gas into the processing
vessel; shutoff valves each placed in each of the process gas
supply lines at a position adjacent to the processing vessel; a
main purge gas supply line for carrying a purge gas; branch purge
gas supply lines branched from the main purge gas supply line, each
of the branch purge gas supply lines being connected to a part of
each of the process gas supply lines extending between the shutoff
valve and the processing vessel; a flow controller placed in the
main purge gas supply line to control a sum of flow rates at which
the purge gas flows through the branch purge gas supply lines; and
orifices each placed in each of the branch purge gas supply lines,
each of the orifices being configured so that a flow rate of the
purge gas flowing through the orifice is determined according to a
primary pressure on a primary side of the orifice when pressure
ratio P1/P2, where P1 is a primary pressure on the primary side of
the orifice, and P2 is a secondary pressure on a secondary side of
the orifice, is not smaller than a predetermined value.
2. The semiconductor device fabricating system according to claim
1, wherein the flow controller comprises a mass flow
controller.
3. The semiconductor device fabricating system according to claim
1, wherein the flow controller includes a flow measuring device,
and a pressure regulating device for regulating the primary
pressure P1 on the primary side of the orifices based on a measured
flow rate measured by the flow measuring device.
4. The semiconductor device fabricating system according to claim
1, wherein the predetermined value is not less than two.
5. A semiconductor device fabricating system comprising: a
processing vessel; process gas supply lines each connected to the
processing vessel to supply a process gas into the processing
vessel; shutoff valves each placed in each of the process gas
supply lines at a position adjacent to the processing vessel; a
main purge gas supply line for carrying a purge gas; branch purge
gas supply lines branched from the main purge gas supply line, each
of the branch purge gas supply lines being connected to a part of
each of the process gas supply lines extending between the shutoff
valve and the processing vessel; and flow controllers each placed
in the each of the branch purge gas supply lines to control a flow
rate at which the purge gas flows through each of the branch purge
gas lines.
6. A semiconductor device fabricating method of processing a
substrate by a predetermined process in a processing vessel to
fabricate semiconductor devices on the substrate by using process
gases supplied through process gas supply lines connected to the
processing vessel, said semiconductor device fabricating method
comprising: supplying a purge gas through a main purge gas supply
line and controlling the flow of the purge gas flowing through the
main purge gas supply line; distributing the purge gas flowing
through the main purge gas supply line to a plurality of branch
purge gas supply lines; passing the purge gas distributed to the
branch purge gas supply lines through orifices capable of
determining, when pressure ratio P1/P2, where P1 is primary
pressure on a primary side of the orifice and P2 is secondary
pressure on a secondary side of the orifice, is not smaller than a
predetermined value, a flow rate according to the primary pressure
P1; supplying the purge gas passed through the orifices to parts of
the process gas supply lines extending between the processing
vessel and shutoff valves placed in the process gas supply lines at
positions adjacent to the processing vessel; regulating pressure so
that the pressure ratio P1/P2 is not smaller than a predetermined
value; and closing at least one of the shutoff valves placed in the
process gas supply lines to purge the process gas remaining in a
part of the process gas supply line provided with the closed
shutoff valve extending below the closed shutoff valve by the purge
gas passed through the orifice.
7. A semiconductor device fabricating method of processing a
substrate by a predetermined process in a processing vessel to
fabricate semiconductor devices on the substrate by using process
gases supplied through process gas supply lines connected to the
processing vessel, said semiconductor device fabricating method
comprising: supplying a purge gas through a main purge gas supply
line; distributing the purge gas flowing through the main purge gas
supply line to a plurality of branch purge gas supply lines;
controlling flow rates of the purge gas flowing through the branch
purge gas supply lines by flow control means respectively placed in
the branch purge gas supply lines; supplying the purge gas
distributed to the branch purge gas supply lines to parts of the
process gas supply lines extending between the processing vessel
and shutoff valves placed in the process gas supply lines at
positions adjacent to the processing vessel, respectively; and
closing at least one of the shutoff valves placed in the process
gas supply lines to purge the process gas remaining in a part of
the process gas supply line provided with the closed shutoff valve
extending below the closed shutoff valve by the purge gas passed
through the branch purge gas supply line.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor device
fabricating method of processing a substrate on which semiconductor
devices are to be fabricated in a processing vessel by supplying a
process gas into the processing vessel and a semiconductor
fabricating system for carrying out the semiconductor device
fabricating method.
[0003] 2. Description of the Related Art
[0004] Some semiconductor device fabricating methods carry out
predetermined processes continuously to process a substrate in a
processing vessel and a cleaning process for cleaning the interior
of the processing vessel by selectively supplying process gases and
cleaning gases through a plurality of gas supply lines connected to
the processing vessel. If a process gas supplied through the open
gas supply line into the processing vessel flows into the other
closed gas supply lines not supplying the gases, it is possible
that a product is deposited in the closed gas supply lines causing
contamination with particles or the gas supply lines are corroded.
Therefore, it Is important to supply a purge gas into the closed
gas supply lines to prevent the backflow of a reaction gas from the
processing vessel into the closed gas supply lines. Such a backflow
preventing method is disclosed in JP4-24921A.
[0005] The prior art backflow preventing method supplies a purge
gas through pipes connected to closed process gas supply pipes not
carrying process gases during a process for forming a film on a
surface of a substrate by supplying process gases through process
gas supply pipes into a processing vessel to prevent the diffusion
of the process gases supplied into the processing vessel into the
closed process gas supply lines. When a purge gas, such as an inert
gas, is supplied into the closed process gas supply pipes, the
process gas supplied into the processing vessel is diluted by the
purge gas supplied into the closed process gas supply pipes.
Therefore, it is desirably to supply the purge gas always at a
predetermined flow rate into the closed process gas supply pipes
regardless of the number of the closed process supply pipes to
maintain a predetermined process gas concentration in the
processing vessel. Moreover, the purge gas must be supplied into
the closed process gas supply pipes at a flow rate not lower than a
predetermined flow rate. Nothing about this requirement is
mentioned in JP4-24921A.
[0006] The inventors of the present invention proposed piping
systems shown in FIGS. 6 to 9 to solve the foregoing problems.
[0007] The piping system shown in FIG. 6 includes a processing
vessel 100 included in a vertical thermal processing apparatus, gas
supply lines 101, 102 and 103 respectively for supplying process
gases A, B and C, and a purge gas supply line 104. Branch lines
branching from the purge gas supply line 104 are connected to the
process gas supply lines 101, 102 and 103 to supply a purge gas
into the closed ones of the process gas supply lines 101, 102 and
103. Mass flow controllers 105 are placed in the gas supply lines
101, 102, 103 and 104 to control the flow rates of gases supplied
from gas sources 201 to 204, respectively. In FIG. 6, indicated at
V0 is a valve, at V1 to V4 are shutoff valves and at V are valves.
The valves above the mass flow controllers are designated by the
same reference character V for convenience.
[0008] Suppose that the process gas A and the process gas B are
used for carrying out a predetermined process, such as a film
deposition process in the processing vessel 100. Nitrogen gas,
namely, a purge gas, is supplied at a low flow rate through the
purge gas supply line 104 into the closed process gas supply line
103 for supplying the process gas C and at a low rate through the
purge gas supply line 104. The sum of those flow rates is a
predetermined purge gas flow rate.
[0009] The flow rates of the purge gas are controlled by the mass
flow controllers 105 placed in the gas supply lines 101 to 104. The
capacities of the mass flow controllers 105 placed in the gas
supply lines 101 to 104 are excessively large to control the low
flow rate of the purge gas. The capacities of the mass flow
controllers 105 for controlling the flow of the process gases are,
for example, 5 l/min. A mass flow controller for controlling the
flow of an inert gas has a control capacity of 50 l/min. If the
mass flow controller having such a large control capacity of 50
l/min is used for controlling a very low flow rate on the order of
50 cm.sup.3/min, the value of a controlled variable is in the range
of about 1 to about 2% of the control capacity. Consequently, it is
difficult to adjust the flow rate of the inert gas to values in a
desired flow rate range and accurate flow rate control cannot be
achieved. Therefore, the total purge gas flow rate cannot be
accurately controlled, the process gas concentration varies and,
consequently, it is possible that the process becomes unstable.
[0010] The piping system shown in FIG. 7 has branch lines 107
branched from a purge gas supply line 104, connected to process gas
supply lines 101 to 103 and provided with mass flow controllers 106
having a control capacity of, for example 50 cm.sup.3/min,
respectively. A bypass line 108 is connected to the purge gas
supply line 104 and a mass flow controller 106 having a small
control capacity is placed in the bypass line 108. The flow of the
purge gas supplied to the closed process gas supply lines is
controlled by the mass flow controllers 106 to supply the purge gas
for purging at a low flow rate into the closed process gas supply
lines. Since a total flow rate is the sum of dividual flow rates at
which the mass flow controllers 106 control the flow of the purge
gas, errors in flow rates controlled by the mass flow controllers
106 are accumulated and hence the accuracy of control of the total
flow rate of the purge gas decreases. Since all the branch lines
107 are provided with the mass flow controllers 106, this piping
system is costly.
[0011] When the process gas supply lines 101 to 103 of the piping
system shown in FIG. 7 are selectively opened to carry out
processes, such as a first film deposition process and a second
film deposition process, continuously, when monoatomic or
monomolecular films are formed successively in layers by
selectively using process gases, or when a film deposition process
is carried out after a cleaning process for cleaning the interior
of the processing vessel, a long time is necessary for purging the
residual gases remaining in the process gas supply lines. (Note
that processes mentioned in this specification include a cleaning
process.)
[0012] The foregoing problems will be explained with reference to
FIGS. 8 and 9. Referring to FIG. 8, the process gases A and B are
supplied respectively through the process gas supply lines 101 and
102, and a purge gas is supplied at a low flow rate into the
process gas supply line 103 and the purge gas supply line 104 to
carry out a first process. Suppose that the valves V connected to
the process gas supply lines 101 and 102 are operated to stop
supplying the process gases A and B and to start supplying the
purge gas at a low flow rate to the process gas supply lines 101
and 102 and the valves connected to the process gas supply line 103
are operated to stop supplying the purge gas into the process gas
supply line 103 and to start supplying the process gas C into the
process gas supply line 103 to start a second process subsequently
to the first process. Then, the process gases remaining in the
process gas supply lines 101 and 102 need to be replaced with the
purge gas to avoid the adverse effect of the process gases
remaining in the process gas supply lines 101 and 102 and diffused
into the processing vessel 100 on the second process. After the
supply of the process gases A and B through the process gas supply
lines 101 and 102 has been stopped, the shutoff valves V1 and V2
are kept open to pas the purge gas at a low flow rate through the
process gas supply lines 101 and 102. Therefore, the process gases
remaining in the lines extending between the processing vessel 100
and the valves V in a gas box remote from the processing vessel 100
need to be purged, which needs a long time and increases tact
time.
SUMMARY OF THE INVENTION
[0013] The present invention has been made in view of the foregoing
problems and it is therefore an object of the present invention to
provide a semiconductor device fabricating method capable of
accurately controlling the flow of a purge gas in a process gas
supply pipes connected to a processing vessel, and a semiconductor
conductor fabricating system for carrying out the semiconductor
device fabricating method.
[0014] Another object of the present invention is to provide a
semiconductor device fabricating method capable of quickly purging
a process gas remaining in a process gas supply pipe, and a
semiconductor device fabricating system for carrying out the
semiconductor device fabricating method.
[0015] The present invention provides a semiconductor device
fabricating system, which includes: a processing vessel; process
gas supply lines each connected to the processing vessel to supply
a process gas into the processing vessel; shutoff valves each
placed In each of the process gas supply lines at a position
adjacent to the processing vessel; a main purge gas supply line for
carrying a purge gas; branch purge gas supply lines branched from
the main purge gas supply line, each of the branch purge gas supply
lines being connected to a part of each of the process gas supply
lines extending between the shutoff valve and the processing
vessel; a flow controller placed in the main purge gas supply line
to control a sum of flow rates at which the purge gas flows through
the branch purge gas supply lines; and orifices each placed in each
of the branch purge gas supply lines, each of the orifices being
configured so that a flow rate of the purge gas flowing through the
orifice is determined according to a primary pressure on a primary
side of the orifices when pressure ratio P1/P2, where P1 is a
primary pressure on the primary side of the orifice, and P2 is a
secondary pressure on a secondary side of the orifice, is not
smaller than a predetermined value.
[0016] In the operation of the semiconductor device fabricating
system, the pressure ratio P1/P2 is controlled to be not smaller
than the predetermined value, for example, not smaller than two.
Thus the purge gas flows through the orifice at a sonic speed and
hence the purge gas flowing through the main purge gas supply line
can be equally distributed to the branch purge gas supply
lines.
[0017] The flow controller may be a mass flow controller. In this
case, the total flow rate of the purge gas can be controlled
accurately.
[0018] The flow controller may include a flow measuring device, and
a pressure regulating device for regulating the primary pressure P1
on the primary side of the orifices on the basis of a measured flow
rate measured by the flow measuring device. The flow measuring
device measures the flow rate of the purge gas flowing through the
orifices and the primary pressure P1 is controlled always on the
basis of the measured flow rate to maintain the primary pressure P1
at a level not lower than the predetermined value.
[0019] The prevent invention also provides a semiconductor device
fabricating system, which includes: a processing vessel; process
gas supply lines each connected to the processing vessel to supply
a process gas into the processing vessel; shutoff valves each
placed in each of the process gas supply lines at a position
adjacent to the processing vessel; a main purge gas supply line for
carrying a purge gas; branch purge gas supply lines branched from
the main purge gas supply line, each of the branch purge gas supply
lines being connected to a part of each of the process gas supply
lines extending between the shutoff valve and the processing
vessel; and flow controllers each placed in the each of the branch
purge gas supply lines to control a flow rate at which the purge
gas flows through each of the branch purge gas lines.
[0020] According to another aspect of the present invention, there
is provided a semiconductor device fabricating method for
processing a substrate by a predetermined process in a processing
vessel to fabricate semiconductor devices on the substrate by using
process gases supplied through process gas supply lines connected
to the processing vessel. The method includes: supplying a purge
gas through a main purge gas supply line and controlling the flow
of the purge gas flowing through the main purge gas supply line;
distributing the purge gas flowing through the main purge gas
supply line to a plurality of branch purge gas supply lines;
passing the purge gas distributed to the branch purge gas supply
lines through orifices capable of determining, when pressure ratio
P1/P2, where P1 is primary pressure on a primary side of the
orifice and P2 is secondary pressure on a secondary side of the
orifice, is not smaller than a predetermined value, a flow rate
according to the primary pressure P1; supplying the purge gas
passed through the orifices to parts of the process gas supply
lines extending between the processing vessel and shutoff valves
placed in the process gas supply lines at positions near the
processing vessel; regulating pressure so that the pressure ratio
P1/P2 is not smaller than a predetermined value; and closing at
least one of the shutoff valves placed in the process gas supply
lines to purge the process gas remaining in a part of the process
gas supply line provided with the closed shutoff valve extending
below the closed shutoff valve by the purge gas passed through the
orifice.
[0021] The present invention also provides a semiconductor device
fabricating method for processing a substrate by a predetermined
process in a processing vessel to fabricate semiconductor devices
on the substrate by using process gases supplied through process
gas supply lines connected to the processing vessel, the method
including the steps of: supplying a purge gas through a main purge
gas supply line; distributing the purge gas flowing through the
main purge gas supply line to a plurality of branch purge gas
supply lines; controlling the flow rate of the purge gas in the
branch purge gas supply lines by flow control units respectively
placed In the branch purge gas supply lines; supplying the purge
gas distributed to each of the branch purge gas supply lines to a
part of the process gas supply line at a position between the
processing vessel and a shutoff valve placed in a part of the
process gas supply line near the processing vessel; and closing the
shutoff valve placed in at least one of the process gas supply
lines to purge the process gas remaining in a part of this process
gas supply line below the shutoff valve by the purge gas passed
through the branch purge gas supply line.
[0022] According to the present invention, the shutoff valves are
placed in parts of the process gas supply lines close to the
processing vessel, and the purge gas is supplied to parts of the
process gas supply lines each extending between the shutoff valve
and the processing vessel. Therefore, only the process gas
remaining in the short parts of the process gas supply line
extending below the shutoff valve needs to be purged in changing
the process, and the residual process gas can be quickly purged.
Since the orifice controls the flow of the purge gas flowing
through each branch purge gas supply line accurately, the flow
controller needs to be placed only in the main purge gas supply
line, the total flow rate of the purge gas equal to the sum of the
flow rates of the purge gas flowing through the branch purge gas
supply lines can be accurately controlled and the process can be
stably carried out.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a piping diagram showing a piping system included
in a semiconductor device fabricating system in a first embodiment
according to the present invention;
[0024] FIG. 2 is a schematic view of a shutoff valve included in
the piping system shown in FIG. 1;
[0025] FIG. 3 is a piping diagram showing the piping system
included in the semiconductor device fabricating system shown in
FIG. 1;
[0026] FIG. 4 is a piping diagram showing a piping system included
In a semiconductor device fabricating system in a second embodiment
according to the present invention;
[0027] FIG. 5 is a piping diagram showing a piping system included
in a semiconductor device fabricating system in a third embodiment
according to the present invention;
[0028] FIG. 6 is a piping diagram showing a piping system included
in a first prior art semiconductor device fabricating system;
[0029] FIG. 7 is a piping diagram showing a piping system included
in second prior art semiconductor device fabricating system;
[0030] FIG. 8 is a piping diagram showing a piping system included
in a third prior art semiconductor device fabricating system;
and
[0031] FIG. 9 is a piping diagram showing a piping system included
in a fourth prior art semiconductor device fabricating system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] FIG. 1 shows a piping system included, in a vertical thermal
processing system, namely, semiconductor device fabricating system,
in a first embodiment according to the present invention. The
vertical thermal processing system includes, as principal
components; a processing vessel 1 for processing a semiconductor
wafer, i.e., a substrate on which semiconductor devices are to be
fabricated, by a thermal process, such as a film deposition process
for depositing a film on the semiconductor wafer (hereinafter,
referred to simply as "wafer"); three process gas sources 10, 11
and 12, i.e., a dichlorosilane source 10, an ammonia source 11 and
a cleaning gas source 12; process gas supply lines 13, 14 and 15,
i.e., a dichlorosilane supply line 13, an ammonia supply line 14
and a cleaning gas supply line 15, respectively connecting the
process gas sources 10, 11 and 12 to the processing vessel 1; a
discharge line 34 connected to the processing vessel 1; and a purge
gas supply unit 5 for supplying a purge gas into the process gas
supply lines 13, 14 and 15. A purge gas source 18 is connected to
the processing vessel 1 by a purge gas supply line 16 to supply a
purge gas into the processing vessel 1 so that pressure in the
processing vessel is returned to the atmospheric pressure.
[0033] First mass flow controllers 19 are placed in parts of the
process gas supply lines 13, 14 and 15 and the purge gas supply
line 16 distant from the processing vessel 1, respectively. Shutoff
valves V1 to V4 for cutting off gas supply into the processing
vessel 1 are placed in parts of the process gas supply lines 13, 14
and 15 and the purge gas supply line 16 near the processing vessel
1.
[0034] As shown in FIG. 2, each of the shutoff valves V1 to V4 has
a valve body 21 provided with a process gas inlet port 22, a purge
gas inlet port 23 and an outlet port 24. The process gas and the
purge gas flow respectively through the process gas inlet port 22
and the purge gas inlet port 23 into the valve body 21 and flow out
of the valve body 21 through the outlet port 24. When a valve
element (not shown) arranged in the valve body 21 is closed, the
flow of the process gas is intercepted while the flow of the purge
gas is not intercepted. Thus the purge gas flows always through the
shutoff valves V1 to V4 placed In the process gas supply lines 13,
14 and 15 and the purge gas supply line 16 into the processing
vessel 1.
[0035] The construction of the processing vessel 1 will be briefly
explained. The processing vessel 1 includes an inner tube 31 having
opened opposite ends, and an outer tube 32 having a top wall. A
wafer boat 33 supporting a plurality of wafers W in a stack is
loaded into a space surrounded by the inner tube 31 from below the
inner tube 31. A discharge pipe 34 has one end connected to the
outer tube 32 and the other end connected to a vacuum pump 35,
namely, an evacuating means. A gas supplied into a lower region in
the space surrounded by the inner tube 21 flows upward inside the
inner tube 31, flows downward through an annular space between the
inner tube 31 and the outer tube 32, and is discharged through the
discharge pipe 34.
[0036] Although not shown in the drawings, each of the process gas
supply lines 13, 14 and 15 and the purge gas supply line 16 is
provided with, for example, a particle filter, a pressure sensor, a
regulator and such.
[0037] The purge gas supply unit 5 is branched off from the purge
gas supply line 16. The purge gas supply unit 5 has a main purge
gas supply line 50 connected to the purge gas supply line 16, and
four branch purge gas supply lines 51 branching off from the main
branch gas supply line 50. A second mass flow controller 52 is
placed in the main purge gas supply line 50 to control the total
flow rate of the purge gas to be distributed to the branch purge
gas supply lines 51. A valve 5, a filter F and a pressure sensor
PD1 are placed in the main purge gas supply line 50 downstream of
the second mass flow controller 52. The respective primary sides of
orifices 53 are connected to the branch purge gas supply lines 51,
respectively, and the respective secondary sides of the same are
connected to parts of the process gas supply lines 13, 14 and 15
and the purge gas supply line 16 extending from the shutoff valves
V1 to V4 to the processing vessel 1, respectively. The orifices 53
permit the purge gas to flow at a low flow rate into the supply
lines 13 to 16. It appears from FIG. 2 that the branch purge gas
supply lines 51 are connected to the shutoff valves V1 to V4.
However, actually, a first gas passage formed in the valve body 21
connecting the process gas Inlet port 22 and the outlet port 24 is
provided with the not-shown valve element, and a gas second passage
formed in the valve body 21 connected to the purge gas inlet port
23 is connected to the first gas passage at a position downstream
of the not-shown valve element. Thus, the branch purge gas supply
lines 51 are actually connected to parts of the gas supply lines 13
to 16 extending between the shutoff valves V1 to V4 and the
processing vessel 1 as shown in the piping diagram of FIG. 1. In
the illustrated embodiment, each of the orifices 53 is a metal
plate provided with an aperture flaring out downstream and having a
maximum diameter of about 70 .mu.m, which is generally called a
sonic nozzle. When pressure ratio P1/P2, where P1 is pressure on
the primary side of the orifice 53 and P2 is pressure on the
secondary side of the orifice 53, is not lower than a predetermined
value, such as when the pressure ratio P1/P2 is two or above, the
gas flows at a sonic speed through the orifice 53, and the flow
rate of the gas flowing through the orifice 53 is dependent on the
primary pressure P1. Thus the purge gas flows through the orifices
53 at equal flow rates and the purge gas flowing through the main
purge gas supply line 50 is divided into four equal purge gas
flows.
[0038] The operation of the semiconductor device fabricating device
in the first embodiment will be described with reference to FIGS. 1
and 3 on an assumption that a film deposition process for forming a
silicon nitride film on a surface of a wafer W using dichlorosilane
(SiH.sub.2Cl.sub.2) and ammonia (NH.sub.3) as process gases, a
cleaning process for cleaning the interior of the processing vessel
1 using a cleaning gas, such as a mixed gas prepared by mixing
fluorine and hydrogen fluoride, and a film deposition process for
forming a silicon nitride film are conducted successively in that
order.
[0039] In FIGS. 1 and 3, dotted arrows indicate flows and flowing
directions of gases flowing into the processing vessel 1 and the
gas supply lines 13 to 16.
[0040] Referring to FIG. 1, a wafer boat 33 holding a plurality of
wafers W is loaded into the processing vessel 1, and then a
predetermined hot and evacuated atmosphere are created in the
processing vessel 1 to start a film forming process. The valves V
on the process gas supply lines 13 and 14 are opened to supply
dichlorosilane from the dichlorosilane source 10 and to supply
ammonia from the ammonia source 11. The mass flow controller 19 on
the process gas supply line 13 controls the flow of the
dichlorosilane gas such that the dichlorosilane gas flows through
the process gas supply line 13 into the processing vessel at, for
example, 50 sccm. The mass flow controller 19 on the process gas
supply line 14 controls the flow of ammonia gas such that ammonia
gas flows through the process gas supply line 14 into the
processing vessel 1 at, for example, 500 sccm. At this stage, the
valves V on the process gas supply line 15 and the purge gas supply
line 16 are kept closed and hence any gases flow through the
process gas supply line 15 and the purge gas supply line 16.
[0041] The dichlorosilane gas and the ammonia gas interact in the
processing vessel 1 to deposit a silicon nitride film on the
surface of the wafer W. After the duration of the film forming
process for a predetermined time, the valves V on the process gas
supply lines 13 and 14 are closed.
[0042] The valve V5 on the main purge gas supply line 50 is opened
during the film forming process. The primary pressure P1 on the
primary side of the orifices 53 is, for example, in the range of
about 0.3 to about 0.4 MPa. Pressure in the processing vessel 1 is
133 Pa or below. The pressure in the processing vessel 1
corresponds to the secondary pressure P2 on the secondary sides of
the orifices 53. Thus the pressure ratio P1/P2 is in the range of
about 2250 and about 3000. The purge gas flows through the orifice
53 at a flow rate corresponding to the primary pressure P1.
Therefore, when a desired total flow rate equal to the sum of the
flow rates at which the purge gas flows through the branch purge
gas supply lines 51 is, for example, 200 sccm, the second mass flow
controller 52 controls the flow of the purge gas such that the
primary pressure P1 causes the purge gas to flow through the
orifices 53 at 50 sccm, Consequently, the purge gas flows through
the main purge gas supply line 50 at 200 sccm, the orifices 53
divide the flow of the purge gas accurately into four equal flows
of purge gas so that the purge gas flows through the branch purge
gas supply line 51 at 50 sccm. Then, the purge gas flows through
parts of the gas supply lines 13 to 15 on the secondary side of the
shutoff valves V1 to V4 into the processing vessel 1. Even though
the process gasses are flowing through the process gas supply lines
13 and 14 and the secondary pressure P2 on the secondary side of
the orifices 53 is different from pressures in the process gas
supply line 15 and the purge gas supply line 16, the purge gas can
be accurately distributed without being affected by the secondary
pressure because the pressure ratio P1/P2.gtoreq.2 meeting a
condition for sonic flow. Consequently, the dichlorosilane gas and
the ammonia gas supplied into the processing vessel 1 are unable to
flow through the outlets of the cleaning gas supply line 15 and the
purge gas supply line 16 into the cleaning gas supply line 15 and
the purge gas supply line 16, and hence the deposition of reaction
products, such as silicon nitride and ammonium chloride, in the gas
supply lines can be prevented. The pressure sensors PD1 and PD2
respectively placed in the main purge gas supply line 50 and the
discharge line 34 measure pressures in the main purge gas supply
line 50 and the discharge line 34, respectively. A controller, not
shown, monitors the pressure ratio P1/P2, provides an alarm when
the pressure ratio P1/P2 drops below two, and closes the valve V5
when P1 is less than P2.
[0043] After the film forming process has been completed, the
shutoff valves V1 and V2 on the gas supply lines 13 and 14 are
closed, the processing vessel 1 is evacuated, the purge gas is
supplied through the purge gas supply line 16 into the processing
vessel 1 to set the space in the processing vessel 1 at the
atmospheric pressure, and then, the wafer boat 33 holding the
wafers W is unloaded from the processing vessel 1. Since the purge
gas flows continuously through the branch purge gas supply lines 51
into the processing vessel 1 before the wafer boat 33 holding the
wafers W is unloaded from the processing vessel 1, the process
gases, namely, the dichlorosilane gas and the ammonia gas,
remaining in parts of the process gas supply lines 13 and 14
extending between the shutoff valves V1 and V2 and the processing
vessel 1 can be quickly replaced with the purge gas.
[0044] A cleaning process is conducted after the wafer boat 33
holding the processed wafers W has been unloaded from the
processing vessel. The wafers W are removed from the wafer boat 33,
the empty wafer boat 33 is placed in the processing vessel 1, and
then a cleaning gas is supplied from the cleaning gas source 12
through the cleaning gas supply line 15 into the processing vessel
1 to remove a film forming material and reaction products deposited
on the inner surface of the processing vessel 1 and the wafer boat
33.
[0045] The valve V5 on the main purge gas supply line 50 is kept
open during the cleaning process. The pressure in the processing
vessel 1 corresponding to the secondary pressure P2 on the
secondary side of the orifices 53 is, for example 5.3.times.104 Pa
during the cleaning process. Therefore, the pressure ratio P1/P2 is
two or above during the cleaning process, and the purge gas is
supplied from the branch purge gas supply lines 51 to the gas
supply lines 13 to 16 at equal low flow rates.
[0046] After the completion of the cleaning process, the next film
forming process is started. In the piping system shown in FIG. 6,
the purging gas is supplied at a low flow rate into parts of the
gas supply lines 101 to 104 upstream of the shutoff valves V1 to V4
and hence the shutoff valves V3 and V4 on the gas supply lines 102
and 103 not participating in the film forming process are kept open
during the film forming process. Therefore, the cleaning gas
remaining in a long parts of the cleaning gas supply line 102
extending between a position above the first mass flow controller
105 in the gas box and the inlet port of the processing vessel 1
needs to be replaced with the purging gas before starting the film
forming process. With the piping system in this embodiment
according to the present invention, the purge gas is supplied at a
low flow rate into the parts of the gas supply lines extending
between the shutoff valves V1 to V4 and the processing vessel 1.
Therefore, only the cleaning gas remaining in parts of the cleaning
gas supply line 15 on the secondary side of the valve V3 needs to
be replaced with the purging gas. An operation for replacing the
cleaning gas remaining in the short part of the cleaning gas supply
line 15 with the purging gas can be accomplished in a very short
time.
[0047] Although the cleaning process and the film forming process
are conducted continuously in the foregoing description, any
different processes may be continuously conducted. For example, a
first film forming process and a second film forming process
different from the first film forming process may be continuously
conducted or a monoatomic film forming process may be conducted by
changing the process gases. For example, a continuous film forming
process includes a first film forming process that forms a silicon
nitride film in the manner mentioned above, and a second film
forming process that forms a silicon oxide film on the silicon
nitride film by supplying TEOS gas and oxygen gas as process gases
through process gas supply lines for carrying those process gases
into the processing vessel 1. In a monoatomic film forming process,
dichlorosilane gas is supplied through the process gas supply line
13 into the processing vessel 1 to deposit a monoatomic silicon
film on wafers W. Then, the valve V3 on the process gas supply line
13 is closed, the valve V on the process gas supply line 14 is
opened and ammonia gas is supplied into the processing vessel 1 to
deposit nitrogen on the monoatomic silicon film. Such steps are
repeated several times to form a very thin silicon nitride
film.
[0048] The above embodiment has the following advantages. Since the
branch purge gas supply lines 51 are provided with the orifices 53
to supply the purge gas at a low rate for purging into the gas
supply lines 13 to 16, the purge gas can be accurately equally
distributed to the gas supply lines 13 to 16. Therefore, only the
single mass flow controller 52 for controlling the total flow rate
of the purge gas needs to be placed in the main purge gas supply
line 50. Consequently, the equipment cost can be reduced, any error
will not be produced in the total flow rate due to the accumulation
of errors produced by a plurality of mass flow controllers and
hence the processes are stable.
[0049] Since the purge gas is supplied at a lower flow rate into
parts of the gas supply lines extending between the shutoff valves
V1 to V4 and the processing vessel 1, the shutoff valves on the gas
supply lines not participating in the process may be kept closed.
Consequently, the process gases used by the preceding process and
remaining in the gas supply lines can be replaced with the purging
gas in a short time before starting the succeeding process, and
hence the succeeding process can be started in a short time after
the completion of the preceding process.
[0050] A piping system included in a semiconductor device
fabricating system in a second embodiment according to the present
invention will be described with reference to FIG. 4. The piping
system shown in FIG. 4 is provided with a flow control unit
including a mass flow meter 54 and an automatic pressure regulator
55 instead of a mass flow controller for controlling the total flow
rate of a purge gas flowing through branch purge gas supply lines
51. A controller, not shown, controls the automatic pressure
regulator 55 arranged downstream of the mass flow meter 54 on the
basis of a measured flow rate measured by the mass flow meter 54 to
control the total flow rate of the purge gas for pressure control.
The primary pressure on the primary side of orifices 53 is
controlled to control the flow rates of the purge gas flowing
through the branch purge gas supply lines 51.
[0051] In a piping system shown in FIG. 5 included in a
semiconductor device fabricating system in a third embodiment
according to the present Invention, mass flow controllers 58 are
placed in branch purge gas supply lines 51, respectively, instead
of the orifices 53. Since the purge gas is supplied at a low flow
rate through the mass flow controllers 58 to parts of gas supply
lines extending between a processing vessel 1 and shutoff valves V1
to V4 placed in the gas supply lines, the shutoff valves V placed
on the gas supply lines not participating in a process may be kept
closed. Therefore, the process gases used for the process and
remaining in the gas supply lines can be replaced with the purge
gas in a very short time before starting the next process and hence
the next process can be started in a short time after the
completion of the preceding process.
[0052] If the purge gas heated at temperatures in the range of, for
example 100 to 200.degree. C. by a heating device, not shown, is
supplied continuously Into the gas supply lines 12 to 16, the parts
of the gas supply lines 13 to 16 extending between the processing
vessel 1 and the shutoff valves V1 to V4 are heated, which prevents
more effectively the deposition of reaction products in the shutoff
valves V1 to V4 and in the gas supply lines.
[0053] In some cases, a cycle purging operation, which alternately
repeats a step of supplying the purge gas through the purge gas
supply line 16 into the processing vessel 1 and a step of
evacuating the processing vessel 1, is executed to purge the
process gases from the processing vessel 1 and to fill up the
processing vessel 1 with the purging gas. When executing the cycle
purging operation, the process gases remaining in parts of the
process gas supply lines 13, 14 and 15 extending between the
processing vessel 1 and the shutoff valves V1 to V3 must be
completely replaced with the purge gas. According to the present
invention, when executing the cycle purging operation, the purging
gas can be supplied into the parts of the gas supply lines
extending between the processing vessel 1 and the shutoff valves V1
to V3, and the process gases remaining in said parts of the process
gas supply lines thus can be pushed out quickly into the processing
vessel 1. Thus, the purging operation can be carried out
effectively and quickly.
[0054] Although the invention has been described as applied to the
batch type vertical semiconductor device fabricating systems, the
present invention is applicable to other systems including
single-wafer thermal processing systems and dry etching
systems.
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