U.S. patent application number 09/258399 was filed with the patent office on 2001-06-07 for system for manufacturing a semiconductor device.
Invention is credited to NISHIKAWA, KAZUYASU, TOMOHISA, SHINGO.
Application Number | 20010002581 09/258399 |
Document ID | / |
Family ID | 17194377 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002581 |
Kind Code |
A1 |
NISHIKAWA, KAZUYASU ; et
al. |
June 7, 2001 |
SYSTEM FOR MANUFACTURING A SEMICONDUCTOR DEVICE
Abstract
A gas supply system for supplying a gas into a reaction chamber
is provided with a pulse valve, a mass flow controller and a back
pressure controller. The mass flow controller includes a flow meter
and a variable flow control valve, and the back pressure controller
includes a pressure gauge and a pressure control valve. The pulse
valve, the mass flow controller and the back pressure controller
are connected to a controller so that operations thereof are
controlled by this controller.
Inventors: |
NISHIKAWA, KAZUYASU; (HYOGO,
JP) ; TOMOHISA, SHINGO; (HYOGO, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
17194377 |
Appl. No.: |
09/258399 |
Filed: |
February 26, 1999 |
Current U.S.
Class: |
118/715 |
Current CPC
Class: |
H01L 21/67017 20130101;
C23C 16/45561 20130101; C23C 16/45557 20130101; C23C 16/52
20130101; C23C 16/455 20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 016/455 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 1998 |
JP |
10-249531 |
Claims
What is claimed is:
1. A system for manufacturing a semiconductor device comprising: a
reaction chamber; a gas supply system for supplying a gas into said
reaction chamber; a pulse valve provided on said gas supply system
for pulsatively supplying said gas into said reaction chamber; a
gas flow controller provided on said gas supply system for
controlling the flow rate of said gas supplied to said pulse valve;
a back pressure controller provided on said gas supply system for
controlling the back pressure of said pulse valve; and a control
part for controlling the operations of said pulse valve, said gas
flow controller and said back pressure controller.
2. The system in accordance with claim 1, wherein said back
pressure controller is connected to an inlet of said gas flow
controller.
3. The system in accordance with claim 1, wherein said gas flow
controller includes a flow meter and a variable flow control valve,
said back pressure controller includes a pressure gauge and a
pressure control valve, and said control part selects at least
either flow control by said variable flow control valve or back
pressure control by said pressure control valve in response to flow
rate change of said gas detected by said flow meter.
4. The system in accordance with claim 1, wherein said gas flow
controller includes a flow meter and a variable flow control valve,
said back pressure controller includes a pressure gauge and a
pressure control valve, and said control part selects at least
either flow control by said variable flow control valve or back
pressure control by said pressure control valve in response to the
pressure value of said gas detected by said pressure gauge.
5. The system in accordance with claim 1, wherein said gas flow
controller is a mass flow controller, and said pulse valve and said
mass flow controller are integrated or directly connected with each
other.
6. The system in accordance with claim 1, wherein said gas supply
system has a gas cylinder and a regulator for reducing the pressure
of said gas from said gas cylinder for preventing said pulse valve
and said gas flow controller from breakage, and said back pressure
controller has both of a decompressing function and a pressure
intensifying function.
7. The system in accordance with claim 1, wherein said gas supply
system has a gas cylinder charged with a gas having a low vapor
pressure and is connected to only one said reaction chamber.
8. The system in accordance with claim 1, comprising a plurality of
said gas supply systems, wherein said gas flow controller and said
back pressure controller are provided on each said gas supply
system.
9. The system in accordance with claim 8, wherein one said pulse
valve is provided for said plurality of gas supply systems.
10. The system in accordance with claim 8, wherein said pulse valve
is provided for each said gas supply system.
11. The system in accordance with claim 1, wherein said gas supply
system includes a gas cylinder, and said gas supply system shares
said gas cylinder with another gas supply system connected with
another reaction chamber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a system for manufacturing
a semiconductor device, and more specifically, it relates to a
system for forming a thin film on a surface of a sample or etching
the surface of the sample with plasma.
[0003] 2. Description of the Prior Art
[0004] FIG. 12 illustrates the structure of a plasma system
described in Japanese Patent Laying-Open No. 7-263353 (1995). As
shown in FIG. 12, the plasma system includes a reaction chamber 1,
a stage 12 for receiving a sample 11 thereon, a pulse gas valve 20,
a gas introduction tube 141, a pressure detector 142, a pressure
controller 143 and a pressure regulator 144.
[0005] The gas introduction tube 141 supplies a gas from a gas
cylinder (not shown) into the pulse gas valve 20. The pressure
detector 142 and the pressure regulator 144 are connected to
intermediate portions of the gas introduction tube 141. The
pressure controller 143 drives the pressure regulator 144 on the
basis of a signal from the pressure detector 142.
[0006] The gas introduced from the gas introduction tube 141 is
supplied into the pulse gas valve 20 and pulsatively introduced
into the reaction chamber 1. The pressure detector 142 sequentially
detects the pressure in the gas introduction tube 141 and feeds
back the same to the pressure controller 143. The pressure
controller 143 controls the pressure regulator 144 for maintaining
the pressure in the gas introduction tube 141 at a prescribed
value.
[0007] Even if the back pressure of the pulse gas valve 20
fluctuates, therefore, the flow rate of an etching gas introduced
into the reaction chamber 1 can be kept under prescribed conditions
for maintaining the pressure in the reaction chamber 1 at a
prescribed value.
[0008] However, the aforementioned conventional plasma system has
the following problems:
[0009] In the aforementioned gas supply system, the flow rate of
the gas supplied from the pulse gas valve 20 into the reaction
chamber 1 is univocally determined by the pressure at the inlet of
the pulse gas valve 20. In order to stably pulsatively supply the
gas at a prescribed flow rate, therefore, the pressure at the inlet
of the pulse gas valve 20 must be maintained constant through the
pressure controller 143. The pressure controller 143 must be
employed also for changing the gas flow rate. However, the gas flow
rate cannot be correctly controlled or finely regulated through the
pressure controller 143.
[0010] Further, the flow rate of the gas supplied into the reaction
chamber 1, which is controlled by the pressure controller 143, must
be calculated from the pressure in the reaction chamber 1.
Therefore, the correct gas flow rate cannot be immediately
recognized.
[0011] The pressure controller 143 controlling the pressure through
the feedback signal from the pressure detector 142 is effective for
slow pressure change. However, the pressure controller 143 cannot
cope with abrupt pressure change, and hence it is difficult to
maintain the gas flow rate at a constant value when remarkable
pressure change takes place.
[0012] In case of supplying a gaseous mixture into the reaction
chamber 1 through the single pulse gas valve 20, the gas mixing
ratio (flow ratio partial pressure ratio) is determined through the
ratios of the specific heat of the gases and the pressure at the
inlet of the pulse gas valve 20. When the difference between the
ratios of specific heat of the gases or the pressure difference
between the gases is remarkable, therefore, it is difficult to
obtain a desired mixing ratio.
[0013] In case of employing a plurality of pulse gas valves 20 or
exchanging the pulse gas valve 20, gases are supplied at different
flow rates even if the valves 20 are pulsatively driven under the
same conditions, due to the individual difference between the
opening degrees thereof. It is difficult to obtain a desired gas
flow rate also in this case.
[0014] When supplying a gas into a plurality of reaction chambers 1
from a single gas cylinder and starting processing in one of the
reaction chambers 1 during processing in another reaction chamber
1, the pressure in a pipe temporarily fluctuates to change the flow
rate of the gas supplied into the reaction chambers 1. It is
difficult to obtain a desired gas flow rate also in this case.
SUMMARY OF THE INVENTION
[0015] The present invention has been proposed in order to solve
the aforementioned various problems, and an object thereof is to
control the flow rate of a gas supplied into a reaction chamber at
a desired value under all situations.
[0016] Another object of the present invention is to control the
mixing ratio of gases supplied into a reaction chamber 1 at a
desired value under all situations.
[0017] A manufacturing system according to the present invention
includes a reaction chamber, a gas supply system, a pulse valve, a
gas flow controller, a back pressure controller, and a control
part. The gas supply system supplies a gas into the reaction
chamber. The pulse valve is provided on the gas supply system and
pulsatively supplies the gas into the reaction chamber. The gas
flow controller is provided on the gas supply system and controls
the flow rate of the gas supplied to the pulse valve. The back
pressure controller is provided on the gas supply system and
controls the back pressure of the pulse valve. The control part
controls the operations of the pulse valve, the gas flow controller
and the back pressure controller.
[0018] The gas flow rate can be finely regulated by providing the
gas flow controller as described above. The back pressure
controller can suppress fluctuation of the back pressure of the
pulse valve, for suppressing fluctuation of the gas flow rate
resulting from fluctuation of the back pressure. Consequently, the
gas flow rate can be correctly controlled and finely regulated.
Further, the gas flow rate can be immediately detected due to
employment of the gas flow controller. Even if the difference
between ratios of specific heat of gases or pressure difference
between gases is remarkable, a desired mixing ratio can be obtained
by employing the gas flow controller as well as the back pressure
controller, and the gas flow rate can be controlled despite
individual difference between pulse valves or fluctuation of the
pressure in a pipe. The problems of the prior art can be solved in
the aforementioned manner, while the gas flow controller and the
back pressure controller can be controlled to compensate for mutual
disadvantages. This also can contribute to correct control of the
gas flow rate.
[0019] The back pressure controller is preferably connected to an
inlet of the gas flow controller.
[0020] Thus, a gas controlled at a constant pressure can be
supplied to the gas flow controller, for stably supplying a
prescribed volume of gas into the reaction chamber. This is
particularly effective for abrupt pressure change.
[0021] The gas flow controller preferably includes a flow meter and
a variable flow control valve. The back pressure controller
preferably includes a pressure gauge and a pressure control valve.
The control part preferably selects at least either flow control by
the variable flow control valve or back pressure control by the
pressure control valve in response to change of the gas flow rate
detected by the flow meter.
[0022] Thus, the preferable control system can be selected in
response to change of the gas flow rate, whereby the flow rate of
the gas can be correctly and readily controlled.
[0023] The control part may select at least either the flow control
by the variable flow control valve or the back pressure control by
the pressure control valve in response to the pressure of the gas
detected by the pressure gauge.
[0024] Also in this case, the flow rate of the gas can be correctly
and readily controlled similarly to the above.
[0025] Preferably, the gas flow controller is a mass flow
controller. In this case, the pulse valve and the mass flow
controller are preferably integrated or directly connected with
each other.
[0026] Thus, it is possible to prevent difference between a value
indicated by the mass flow controller and the actual flow rate due
to conductance between the pulse valve and the mass flow
controller. This can also contribute to correct gas flow
control.
[0027] The gas supply system preferably has a gas cylinder and a
regulator for reducing the pressure of the gas from the gas
cylinder and preventing the pulse valve, the gas flow controller
and the like from breakage. The back pressure controller preferably
has both of a decompressing (reducing) function and a pressure
intensifying (pressurizing) function.
[0028] The pulse valve, the gas flow controller and the like can be
prevented from breakage due to the regulator. Further, the back
pressure of the pulse valve can be controlled due to the
decompressing function and the pressure intensifying function of
the back pressure controller.
[0029] The gas supply system may have a gas cylinder charged with a
gas having a low vapor pressure. In this case, the gas supply
system is connected to only one reaction chamber. Throughout the
specification, the term "gas having a low vapor pressure" indicates
a gas such as liquefied gas having a vapor pressure of less than
several atm.
[0030] Thus, interference from another reaction chamber can be
eliminated and the gas flow rate can be maintained at a prescribed
value.
[0031] The manufacturing system preferably includes a plurality of
gas supply systems. Each gas supply system is preferably provided
with both of the gas flow controller and the back pressure
controller.
[0032] Thus, the aforementioned flow control can be performed in
every gas supply system.
[0033] A single pulse valve may be provided for the plurality of
gas supply systems.
[0034] In this case, fluctuation of the gas flow rate resulting
from individual difference between pulse valves can be avoided.
Also when supplying a plurality of gases into the reaction chamber
through a single pulse valve, the gases can be supplied in a
desired mixing ratio by performing the aforementioned flow control
according to the present invention.
[0035] Alternatively, the pulse valve may be provided for each gas
supply system.
[0036] If the pressure difference between the gases is remarkable,
it is easier to control the flow rate by providing the pulse valve
for each gas supply system as compared with the case of supplying a
plurality of gases into the reaction chamber through a single pulse
valve. In this case, into the reaction chamber through a single
pulse valve. In this case, fluctuation of the gas flow rate
resulting from individual difference between the pulse valves can
be effectively suppressed by employing both of the gas flow
controller and the back pressure controller.
[0037] The gas supply system may share the gas cylinder with
another gas supply system connected with another reaction
chamber.
[0038] If simultaneously performing processing in a plurality of
reaction chambers supplied with a gas from the same gas cylinder,
the pressure in a pipe may fluctuate. However, the gas can be
stably supplied into the reaction chambers by employing both of the
gas flow controller and the back pressure controller.
[0039] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a block diagram showing a plasma system according
to an embodiment 1 of the present invention.
[0041] FIGS. 2A to 2C illustrate relations between maximum flow
rates Q.sub.max of gases and back pressures P.sub.o.
[0042] FIG. 3 is a flow chart showing an exemplary method of
controlling a gas flow rate in the embodiment 1.
[0043] FIG. 4 is a flow chart showing another exemplary method of
controlling a gas flow rate in the embodiment 1.
[0044] FIGS. 5A to 5C illustrate a pulse operation of a pulse
valve, a flow rate Q.sub.in of a gas supplied from the pulse valve
and following pressure change in a reaction chamber
respectively.
[0045] FIG. 6 is a block diagram showing a plasma system according
to an embodiment 2 of the present invention.
[0046] FIGS. 7A to 7C illustrate a pulse operation of a pulse
valve, a flow rate of a gas supplied from the pulse valve and
following pressure change in a reaction chamber respectively.
[0047] FIG. 8 is a block diagram showing a plasma system according
to an embodiment 3 of the present invention.
[0048] FIGS. 9A to 9C illustrate a pulse operation of a pulse
valve, a flow rate of a gas supplied from the pulse valve and
following pressure change in a reaction chamber respectively.
[0049] FIG. 10 is a block diagram showing a plasma system according
to an embodiment 4 of the present invention.
[0050] FIG. 11 is a block diagram showing a plasma system according
to an embodiment 5 of the present invention.
[0051] FIG. 12 is a block diagram showing an exemplary conventional
plasma system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] Embodiments of the present invention are now described with
reference to FIGS. 1 to 11.
Embodiment 1
[0053] An embodiment 1 of the present invention is described with
reference to FIGS. 1 to 5. FIG. 1 is a block diagram showing a
plasma system (apparatus) according to the embodiment 1 of the
present invention.
[0054] As shown in FIG. 1, the plasma system includes a reaction
chamber 1, a pulse valve 2, a mass flow controller (gas flow
controller) 3, a back pressure controller 4, a controller (control
part) 5, a gas pipe 6, a regulator 7, a gas cylinder 8, a computer
10 and a stage 12.
[0055] The pulse valve 2 can pulsatively supply a gas into the
reaction chamber 1. The mass flow controller 3 including a flow
meter 3a and a variable flow control valve 3b controls the flow
rate of the gas. The back pressure controller 4 has a pressure
gauge 4a1 and a pressure control valve 4b. The back pressure
controller 4 has a decompressing (reducing) function and a pressure
intensifying (pressurizing) function, and controls the pressure of
the gas to be constant with respect to a certain set value.
[0056] The controller 5 is connected with the pulse valve 2, the
mass flow controller 3 and the back pressure controller 4 through
signal lines 9 and controls the operations thereof. The controller
5 is also connected with the computer 10. The controller 5 is
further connected with a pressure gauge 4a2.
[0057] The regulator 7 for preventing the pulse valve 2, the mass
flow controller 3 and the like from breakage reduces the pressure
of the gas supplied from the gas cylinder 8.
[0058] A sample 11 is placed on the stage 12. This sample 11 is
processed with plasma in the reaction chamber 1.
[0059] In the aforementioned structure, the gas introduced into the
gas pipe 6 from the gas cylinder 8 is supplied to the pulse valve
2, to be pulsatively supplied into the reaction chamber 1. The
pressure gauge 4a1 sequentially detects the pressure in the gas
pipe 6, and the back pressure controller 4 operates for maintaining
the pressure at an inlet of the mass flow controller 3 at a
prescribed value. The mass flow controller 3 controls the flow rate
of the gas maintained at the constant pressure, and supplies the
gas to the pulse valve 2.
[0060] At this time, the mass flow controller 3 can finely regulate
the gas flow rate. Further, the back pressure controller 4 can
supply the gas to the inlet of the mass flow controller 3 at a
constant pressure as described above. Even if the gas pressure
changes in the gas pipe 6 between the gas cylinder 8 and the back
pressure controller 4, therefore, it is possible to prevent abrupt
fluctuation of the pressure at the inlet of the mass flow
controller 3. Thus, the gas can be prevented from jetting out from
the mass flow controller 3 at a flow rate exceeding the set
value.
[0061] When the pressure in the gas pipe 6 is reduced below the set
value, however, the back pressure controller 4 must operate to
pressurize the gas in gas pipe 6 and hence a certain degree of time
is required for attaining a constant pressure. Further, the back
pressure controller 4 may be incapable of coping with abrupt
fluctuation of the pressure in the gas pipe 6. Also in this case,
the back pressure controller 4 slows down the fluctuation of the
gas pressure and hence it is possible to prevent the pressure at
the inlet of the mass flow controller 3 from abrupt fluctuation.
Therefore, the gas can be prevented from jetting out from the mass
flow controller 3 at a flow rate exceeding the set value.
[0062] It is also possible to cope with abrupt pressure fluctuation
in the following manner. When the mass flow controller 3 is fully
opened under pulse valve operating conditions shown in FIGS. 5A to
5C, the maximum suppliable flow rate is 76 sccm at 0.5 atm. or 227
sccm at 1.5 atm. Referring to FIGS. 5A to 5C, the mass flow
controller 3 is set at a flow rate of 70 scm, and hence the gas can
be supplied into the reaction chamber 1 at a constant flow rate
even if the pressure abruptly changes from 1.5 atm. to 0.5 atm. and
a time is required for coping with this change. Even if remarkable
pressure fluctuation takes place, the gas can be stably supplied
into the reaction chamber 1 at a desired flow rate by setting the
flow rate of the mass flow controller 3 below the maximum flow rate
at the predicted minimum pressure.
[0063] When the pulse valve 2 is exchanged, it is difficult to
obtain a desired gas flow rate since the new pulse valve supplies
the gas at a different flow rate even if the same is pulsatively
driven under the same conditions, due to the opening degree varying
with the pulse valve 2. However, the desired gas flow rate can be
obtained by controlling the flow rate with the mass flow controller
3.
[0064] It is possible to prevent possible difference between a
value indicated by the mass flow controller 3 and the actual flow
rate resulting from the conductance of the pipe 6 connecting the
pulse valve 2 with the mass flow controller 3 by integrating or
directly connecting the mass flow controller 3 with the pulse valve
2. The mass flow controller 3 can be integrated with the pulse
valve 2 by adding a function of changing the internal conductance
within a certain range to the pulse valve 2 and assembling a flow
meter into the same, for example.
[0065] Even if the pressure in the gas pipe 6 fluctuates, the flow
rate of the gas such as an etching gas introduced into the reaction
chamber 1 can be maintained at a prescribed value by controlling
the back pressure and the flow rate through the aforementioned
structure. Thus, the pressure in the reaction chamber 1 can be
maintained under prescribed conditions.
[0066] The basic idea of the method of controlling the gas flow
rate specific to the present invention is now described with
reference to FIGS. 2A to 2C.
[0067] According to the present invention, the gas flow rate can be
controlled through both of back pressure control for controlling
the back pressure of the pulse valve 2 and flow control by the mass
flow controller 3 with compensation for mutual disadvantages. Thus,
a desired gas flow rate can be accurately obtained. The reason for
this is now described in detail.
[0068] A problem in case of controlling the flow rate only by back
pressure control is now described.
[0069] When the gas flow rate Q remarkably increases with respect
to the back pressure Po as shown in FIG. 2A, the gas flow rate
changes susceptively to slight change of the back pressure.
Therefore, a fluctuation of the back pressure with respect to the
set value must be extremely reduced. In practice, it is difficult
to supply the gas at a constant flow rate due to a certain
fluctuation of the back pressure.
[0070] A problem in case of controlling the flow rate only with the
mass flow controller 3 is now described. Referring to FIG. 2B, a
dotted line shows the maximum flow rate of the mass flow controller
(MFC) 3. If the maximum flow rate of the mass flow controller 3 is
excessive, an error increases when feeding the gas at a small flow
rate. When feeding a gas having a low vapor pressure, the pressure
applied to the mass flow controller 3 is so small that the gas is
hard to feed. Thus, it is difficult to supply the gas at a constant
flow rate.
[0071] In order to obtain a desired gas flow rate by solving the
aforementioned problems, the pulse valve 2, the mass flow
controller 3 and the back pressure controller 4 are properly
controlled in the present invention. As shown in FIG. 2C, flow rate
setting by the mass flow controller 3 prevents instability of the
flow rate due to a fluctuation of the back pressure. In a region
with a low pressure, the accuracy is improved by controlling the
flow rate not with the mass flow controller 3 but with the back
pressure of the pulse valve 2, and hence the respective elements
are controlled for performing the back pressure control. Thus, a
desired gas flow rate can be obtained under any conditions.
[0072] Exemplary methods of controlling the pulse valve 2, the mass
flow controller 3 and the back pressure controller 4 with the
controller 5 are now described with reference to FIGS. 3 and 4.
FIGS. 3 and 4 are flow charts showing the control methods.
[0073] Referring to FIG. 3, various conditions are set at a step
S1. The term "pulse valve operating condition" indicates an ON/OFF
time of the pulse valve 2 (time change of the opening degree of the
pulse valve 2). A conductance valve is set under prescribed
conditions for regulating a pumping speed.
[0074] After setting the conditions, the controller 5 calculates
the pressure P in the reactor (reaction chamber) 1 and the flow
rate of the gas. The pressure P in the reaction chamber 1 and the
mass flow rate m can be obtained through the following expressions
(1) and (2): 1 P ( t ) t = P 0 v s A ( t ) V ( 2 + 1 ) ( + 1 ) / 2
( - 1 ) - S V P ( 1 ) m t = SP v s 2 ( 2 )
[0075] where Po represents the pressure (back pressure) applied to
the pulse valve 2, Vs represents the sound velocity, A(t)
represents time change of the opening degree of the pulse valve 2,
V represents the volume of the reaction chamber 1, S represents the
pumping speed, m represents the mass of the gas, and .gamma.
represents the ratio of specific heat of the gas. While the above
mathematical expressions are on the premise that the gas is an
ideal gas, the inventors have confirmed that the pressure obtained
from these mathematical expressions well matches with an
experimental value.
[0076] At a step S3, the controller 5 determines either the back
pressure control or the flow rate control on the basis of flow rate
change with respect to pressure change. Referring to FIG. 3, P
represents the pressure and .DELTA.P represents dispersion of the
pressure. The pressure P is within a controllable region. Further,
Q.sup.PV.sub.max represents the maximum flow rate of the gas
flowable from the pulse valve 2 under the pressure P, and
.DELTA.Q.sup.PV.sub.max represents dispersion (width of deflection)
of the flow rate with respect to the .DELTA.P. The maximum flow
rate may be replaced with a mean flow rate.
[0077] .alpha. defines the width of deflection of the flow rate of
the gas from the pulse valve 2. In general, the limit of the flow
control of the mass flow controller 3 is about 1% of the maximum
flow rate thereof. For example, a mass flow controller 3 having the
maximum flow rate of 10 sccm can control the flow rate with
accuracy of 0.1 sccm. When .alpha. is within 1%, therefore, the
flow rate can be more correctly controlled with back pressure
control as compared with that with the mass flow controller 3.
[0078] In consideration of the above, the controller 5 selects the
back pressure control when the value of
.DELTA.Q.sup.PV.sub.max/Q.sup.PV.sub.m- ax is smaller than .alpha.,
while selecting the flow rate control when the value of
.DELTA.Q.sup.PV.sub.max/Q.sup.PV.sub.max is not less than
.alpha..
[0079] When controlling the back pressure, the controller 5
compares the maximum flow rate Q.sup.PV.sub.max(Po) of the gas
flowable from the pulse valve 2 at the back pressure Po with the
maximum flow rate Q.sup.MFC.sub.max of the mass flow controller 3.
If Q.sup.PV.sub.max(Po) is below Q.sup.MFC.sub.max, the controller
5 changes the back pressure from Po to P' and sets the gas flow
rate (Q.sub.set) at Q.sup.PV.sub.max(P') at a step S5.
[0080] If Q.sup.PV.sub.max(Po) is larger than Q.sup.MFC.sub.max at
the step S4, the process returns to {circle over (1)}in FIG. 3.
[0081] When controlling the flow rate, on the other hand, the
controller 5 compares Q.sup.MFC.sub.max with Q.sub.set at a step
S6. In other words, the controller 5 determines whether or not the
set flow rate Q.sub.set is below the maximum flow rate
Q.sup.MFC.sub.max of the mass flow controller 3 within a pressure
region (Po.+-..DELTA.P). If Q.sup.MFC.sub.max is in excess of
Q.sub.set, the controller 5 sets the value Q.sup.MFC.sub.max as the
gas flow rate at a step S7. If Q.sup.MFC.sub.max is smaller than
Q.sub.set, on the other hand, the process returns to {circle over
(1)}in FIG. 3.
[0082] After setting the gas flow rate by controlling the back
pressure or the flow rate in the aforementioned manner, the
controller 5 introduces the gas into the reaction chamber 1 and
measures the pressure and the gas flow rate at a step S8.
[0083] Thereafter the controller 5 corrects deviation from the
calculated values and regulates the conductance, the back pressure
and the like at a step S9, and starts the processing at a step
S10.
[0084] The other control method is now described with reference to
FIG. 4. As shown in FIG. 4, only the content of a step S3 is
different from that in FIG. 3, and the remaining contents of this
method are similar to those in FIG. 3.
[0085] At the step S3 in the flow chart shown in FIG. 4, the
controller 5 compares values .DELTA.Q.sup.PV.sub.max,
.alpha.Q.sup.PV.sub.max and Q.sup.MFC.sub.max/100 for pressure
change with each other. The controller 5 selects the back pressure
control when these values satisfy the conditions at the step S3 in
FIG. 4. Otherwise the controller 5 selects the flow rate
control.
[0086] In case of performing control in practice in accordance with
either flow chart, it is preferable to obtain data (calculated
values and actual values) of the gas flow rate, the conductance
valve, the back pressure and the like in advance. Thus, deviation
between the calculated values and the actual values can be
corrected or regulated before starting the processing, for reducing
the time required before starting the processing.
[0087] Also in case of employing a plurality of gas species, the
controller 5 may perform control similar to that shown in FIG. 3 or
4 while setting a flow ratio in initialization. While the
controller 5 controls the gas flow rate at a certain value in the
flow chart shown in each of FIGS. 3 and 4, a control method under a
constant pressure or that rendering the difference between the
maximum and minimum values of the pressure constant is also
conceivable.
[0088] In case of employing a gas having a low vapor pressure, the
controller 5 may control the gas flow rate only by controlling the
back pressure with no flow control with the mass flow controller
3.
[0089] With reference to FIGS. 5A to 5C, pressure change in the
reaction chamber 1 shown in FIG. 1 pulsatively supplied with the
gas is now described. Referring to FIGS. 5A to 5C, the pulse valve
2 having an orifice of 0.5 mm in diameter is driven under an
opening time of 60 msec. and a cycle period of 300 msec. for
supplying chlorine gas into the reaction chamber 1. The pressure of
the chlorine gas is set at 1 atm. at the inlet of the mass flow
controller 3, while the flow rate of the mass flow controller 3 is
set at 70 sccm. The gas pressure set value (1 atm.) is lower than
the pressure of the gas cylinder 8 decompressed by the regulator
7.
[0090] It is understood from FIGS. 5A to 5C that the gas is
supplied into the reaction chamber 1 at a flow rate (Qin)
substantially equal to the set flow rate of the mass flow
controller 3 in response to the pulse operation of pulse valve 2,
to result in change of the pressure in the reaction chamber 1. The
gas can be stably supplied into the reaction chamber 1 at a
constant flow rate, as shown in FIGS. 5A to 5C.
Embodiment 2
[0091] An embodiment 2 of the present invention is now described
with reference to FIGS. 6 and 7A to 7C. According to the embodiment
2 of the present invention, a single pulse valve 2 supplies a
plurality of types of gases. For example, the pulse valve 2
supplies a gaseous mixture of chlorine and oxygen into a reaction
chamber 1. With reference to the embodiment 2 and embodiments 3 to
5 of the present invention, equipment structures are illustrated in
a simplified manner.
[0092] As shown in FIG. 6, two gas supply systems are provided in
the embodiment 2. In one of the gas supply systems, a gas pipe 61
supplies chlorine gas decompressed by a regulator 71 provided for a
gas cylinder 81 to the pulse valve 2 through a back pressure
controller 41 and a mass flow controller 31. In the other gas
supply system, a gas pipe 62 supplies oxygen gas decompressed by a
regulator 72 provided for a gas cylinder 82 to the pulse valve 2
through a back pressure controller 42 and a mass flow controller
32. A controller (not shown) controls the mass flow controllers 31
and 32 and the back pressure controllers 41 and 42. The controller
can employ a control method similar to that in the embodiment
1.
[0093] The gases introduced from the gas pipes 61 and 62 are
supplied into the pulse valve 2, to be pulsatively supplied into
the reaction chamber 1. In this case, pressure detectors provided
in the back pressure controllers 41 and 42 sequentially detect the
pressures in the gas pipes 61 and 62, and the back pressure
controllers 41 and 42 operate to maintain the pressures at inlets
of the mass flow controllers 31 and 32 in the gas pipes 61 and 62
at prescribed values. The mass flow controllers 31 and 32 control
the flow rates of the gases maintained at the constant pressures,
for introducing the same into the pulse valve 2.
[0094] FIGS. 7A to 7C show pressure change etc. in case of
supplying a mixing gas prepared by adding oxygen gas to chlorine
gas in a flow ratio of 5%. An operating condition of the pulse
valve 2 is similar to that of the embodiment 1. The flow rates of
the chlorine gas and the oxygen gas are set at 57 sccm and 3 sccm
respectively. The gases are set at pressures of 1 atm. at the
inlets of the mass flow controllers 31 and 32 respectively.
[0095] According to the aforementioned structure, it is also
possible to pulsatively supply a plurality of types of gases into
the reaction chamber 1 through the single pulse valve 2 in a
desired mixing ratio by providing the mass flow controllers 31 and
32 and the back pressure controllers 41 and 42 for the respective
gas supply systems, similarly to the embodiment 1.
Embodiment 3
[0096] The embodiment 3 of the present invention is described with
reference to FIGS. 8 and 9A to 9C. According to this embodiment 3,
a plurality of pulse valves supply a plurality of gases. Also in
the embodiment 3, two gas supply systems are provided similarly to
the embodiment 2.
[0097] As shown in FIG. 8, a gas pipe 61 provided on one of the gas
supply systems supplies c-C.sub.4F.sub.8 gas decompressed by a
regulator 71 provided for a gas cylinder 81 into a pulse valve 21
through a back pressure controller 41 and a mass flow controller
31. A gas pipe 62 provided on the other gas supply system supplies
oxygen gas decompressed by a regulator 72 provided for a gas
cylinder 82 into a pulse valve 22 through a back pressure
controller 42 and a mass flow controller 32. A controller (not
shown) controls the mass flow controllers 31 and 32, the back
pressure controllers 41 and 42 and the pulse valves 21 and 22 by a
method similar to that in each of the embodiments 1 and 2.
[0098] The gases introduced from the gas pipes 61 and 62 are
supplied into the pulse valves 21 and 22, to be pulsatively
supplied into a reaction chamber 1. In this case, pressures in the
gas pipes 61 and 62 are controlled by a method similar to that in
the embodiment 2, so that the mass flow controllers 31 and 32
control the flow rates of the gases maintained at constant
pressures.
[0099] In the gaseous mixture of the chlorine gas and the oxygen
gas employed in the embodiment 2, the pressures of the chlorine gas
and the oxygen gas charged in the gas cylinders 81 and 82 are
substantially identical to each other. In the gaseous mixture of
the c-C.sub.4F.sub.8 gas and the oxygen gas, however, the pressure
of the c-C.sub.4F.sub.8 gas charged in the gas cylinder 81 is lower
than that of the oxygen gas charged in the gas cylinder 82. When
the pressure difference between the gases is thus remarkable, it is
easier to control the flow rates thereof through separate gas
supply systems as compared with the embodiment 2 controlling the
flow rates with the single pulse valve 2.
[0100] FIGS. 9A to 9C show fluctuation of pressures in case of
supplying a gaseous mixture prepared by adding 40% of oxygen gas to
c-C.sub.4F.sub.8 gas into the reaction chamber 1 from the gas
supply systems. The flow rates of the c-C.sub.4F.sub.8 gas and the
oxygen gas (O.sub.2) are set at 15 sccm and 10 sccm respectively.
It is understood from FIGS. 9A to 9C that the gas flow rates (Qin)
and the pressure in the reaction chamber 1 are stably
controlled.
[0101] While the flow rates of the gases supplied through the
plurality of pulse valves 21 and 22 are different from each other
due to different opening degrees of the pulse valves 21 and 22,
desired gas flow rates can be obtained by employing the mass flow
controllers 31 and 32 and the back pressure controllers 41 and 42
as described above.
Embodiment 4
[0102] The embodiment 4 of the present invention is now described
with reference to FIG. 10. According to the embodiment 4, a single
gas cylinder 8 supplies a gas into a plurality of reaction chambers
101 and 102.
[0103] As shown in FIG. 10, a regulator 7 decompresses the gas from
the gas cylinder 8, and supplies the same into gas pipes 61 and 62.
The gas supplied into the gas pipe 61 is supplied into the reaction
chamber 101 through a back pressure controller 41, a mass flow
controller 31 and a pulse valve 21. The gas introduced into the gas
pipe 62 is supplied into the reaction chamber 102 through a back
pressure controller 42, a mass flow controller 32 and a pulse valve
22. A controller (not shown) controls the mass flow controllers 31
and 32, the back pressure controllers 41 and 42 and the pulse
valves 21 and 22 by a method similar to that in each of the
embodiments 1 to 3.
[0104] The gas introduced into the gas pipes 61 and 62 is
maintained at a constant pressure in a method similar to that in
the embodiment 2, and supplied into the mass flow controllers 31
and 32. Thereafter the mass flow controllers 31 and 32 control the
flow rate of the gas, which is introduced into the reaction
chambers 101 and 102 through the pulse valves 21 and 22.
[0105] When supplying a gas from a single gas cylinder into a
plurality of reaction chambers and starting processing in a certain
reaction chamber during processing in another reaction chamber, the
pressure in a pipe temporarily fluctuates to change the flow rate
of the gas supplied into the reaction chambers. According to the
embodiment 4, however, the mass flow controllers 31 and 32 and the
back pressure controllers 41 and 42 are provided on respective gas
supply systems for controlling the flow rate and the back pressures
in the respective gas supply systems independently of each other,
whereby the gas can be stably supplied into the reaction chambers
101 and 102. Even if the pressures in the gas pipes 61 and 62
fluctuate, therefore, the flow rate of an etching gas or the like
introduced into the reaction chambers 101 and 102 can be maintained
at a desired value for maintaining the pressures in the reaction
chambers 101 and 102 under prescribed conditions.
Embodiment 5
[0106] The embodiment 5 of the present invention is now described
with reference to FIG. 11.
[0107] While each of the embodiments 1 to 4 is on the premise that
the gas must be decompressed through the regulator when taken out
from the gas cylinder, a certain gas may not be decompressed
through a regulator when taken out from a gas cylinder. In this
case, no regulator may be provided, to result in a different
equipment structure.
[0108] In general, a high-pressure gas must be decompressed through
a regulator. A liquefied gas must also be decompressed through a
regulator if charged at a high pressure. However, a gas having a
low vapor pressure cannot smoothly flow when passed through a
regulator. Therefore, no regulator is employed when using such a
gas.
[0109] When employing the aforementioned gas having a low vapor
pressure, it is unpreferable to employ a structure such as that
according to the embodiment 4 in consideration of possible
interference from another reaction chamber. While no problem arises
by employing the structure of supplying a gas into a plurality of
reaction chambers if the gas is charged at a pressure of at least
several 10 atm., a gas such as SiCl.sub.4 charged at a pressure of
about several atm. is preferably supplied through an independent
gas supply system in order to avoid interference from another
reaction chamber. A gas passed through a regulator may also be
supplied from an independent gas supply system, since the gas is
readily influenced from another reaction chamber if the pressure of
the gas from a gas cylinder is lower than a set value of the
regulator.
[0110] In the embodiment 5 of the present invention, a gas having a
low vapor pressure is employed.
[0111] As shown in FIG. 11, a regulator 7 decompresses a gas from a
gas cylinder 81, for supplying the same into a reaction chamber 1
through a gas pipe 61, a back pressure controller 41, a mass flow
controller 31 and a pulse valve 21. A gas having a low vapor
pressure is supplied from a gas cylinder 82 into the reaction
chamber 1 through a gas pipe 62, a back pressure controller 42, a
mass flow controller 32 and a pulse valve 22. A controller (not
shown) controls the mass flow controllers 31 and 32, the back
pressure controllers 41 and 42 and the pulse valves 21 and 22
similarly to each of the embodiments 1 to 4.
[0112] The controller controls the pressures of the gases
introduced into the gas pipes 61 and 62 in a method similar to that
in the embodiment 2, and introduces the same into the mass flow
controllers 31 and 32.
[0113] The gas cylinder 82 is independently connected with each
reaction chamber 1 for a gas such as liquefied gas whose pressure
is too low to use the regulator 7, in order to avoid interference
from another reaction chamber. Thus, the gas can be maintained at a
prescribed flow rate, for maintaining the pressure in the reaction
chamber 1 under prescribed conditions.
[0114] The types of the gases employed in the embodiments 1 to 5,
the operating conditions of the pulse valves 2, 21 and 22, the gas
flow rates and the pressures are mere illustrative and the present
invention is not restricted to these.
[0115] According to the present invention, as hereinabove
described, a gas can be stably supplied into a reaction chamber at
a desired flow rate by providing a gas flow controller and a back
pressure controller. In case of supplying a plurality of gases into
a reaction chamber, the mixing ratio in the reaction chamber can be
controlled by performing the above flow rate control or the like
for each gas.
[0116] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *