U.S. patent application number 10/203191 was filed with the patent office on 2003-08-07 for gas supply device for precursors with a low vapor pressure.
Invention is credited to Bauch, Hartmut, Bewig, Lars, Klippe, Lutz, Kupper, Thomas.
Application Number | 20030145789 10/203191 |
Document ID | / |
Family ID | 7630411 |
Filed Date | 2003-08-07 |
United States Patent
Application |
20030145789 |
Kind Code |
A1 |
Bauch, Hartmut ; et
al. |
August 7, 2003 |
Gas supply device for precursors with a low vapor pressure
Abstract
The invention relates to a gas supply device for delivering
precursors with a low vapor pressure to CVD coating systems. Said
gas supply device has a supply container for the precursor which is
at a first temperature T1, an intermediate storage device for
intermediately storing the vaporous precursor at a second
temperature T2 and at a constant pressure p2, a first gas line
between the supply container and the intermediate storage device
and a second gas line for removing gas from the intermediate
storage device. According to the invention, the gas supply device
is developed in such a way that the first temperature T1 is higher
than the second temperature T2. The lower temperature T2 of the
intermediate storage device facilitates maintenance work on the
same, while the precursor evaporates at a greater rate at the
higher temperature T1 in the supply container. According to a
particularly advantageous embodiment, a first precursor vapor is
mixed with a gas and/or a second precursor vapor in the
intermediate storage device. The partial pressure of the first
precursor vapor in the intermediate storage device is lower than
that of the undiluted first precursor vapor at a constant overall
pressure in said intermediate storage device, so that the
temperature T2 of the intermediate storage device and the
successive lines can be reduced. Reducing the temperature T2 allows
less expensive components to be used.
Inventors: |
Bauch, Hartmut; (Weilrod,
DE) ; Bewig, Lars; (Bad Gandersheim, DE) ;
Klippe, Lutz; (Wiesbaden, DE) ; Kupper, Thomas;
(Bad Gandersheim, DE) |
Correspondence
Address: |
Baker & Daniels
Suite 800
111 East Wayne Street
Fort Wayne
IN
46802
US
|
Family ID: |
7630411 |
Appl. No.: |
10/203191 |
Filed: |
November 13, 2002 |
PCT Filed: |
January 27, 2001 |
PCT NO: |
PCT/EP01/00888 |
Current U.S.
Class: |
118/715 |
Current CPC
Class: |
C23C 16/448
20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 10, 2000 |
DE |
100 05 820.5 |
Claims
1. Gas supply device for precursors with a low vapor pressure,
especially for CVD coating systems, with a supply container (2) for
a first precursor with a low vapor pressure, where the supply
container (2) with the precursor is maintained at a first
temperature T1, with an intermediate storage device (4) for
intermediate storage of the vaporous first precursor, where the
intermediate storage device (4) is maintained at a second
temperature T2 and at a constant pressure p2 which is lower than a
pressure p1 in the supply container (2), with a first gas line (3)
between the supply container (2) and the intermediate storage
device (4), and with a second gas line (10) on the intermediate
storage device (4) for removing gas from the intermediate storage
device (4), characterized in that the first temperature T1 is
higher than the second temperature T2.
2. Gas supply device as defined in claim 1, characterized in that
the temperature T2 in the intermediate storage device (4) is set
such that the saturation vapor pressure of the first precursor is
higher than its partial pressure in the intermediate storage device
(4).
3. Gas supply device as defined in claim 1 or 2, characterized in
that the pressure p1 of the first precursor in the supply container
(2) is the saturation vapor pressure and the first precursor is in
equilibrium between the liquid or solid phase and the vaporous
phase.
4. Gas supply device as defined in claim 3, characterized in that
the temperature T1 of the supply container (2) is set such that the
pressure p1 of the first precursor in the supply container (2) is
between 1.5 and 10 times higher than the pressure p2.
5. Gas supply device as defined in claim 4, characterized in that
the pressure p1 is approximately twice as high as the pressure
p2.
6. Gas supply device as defined in any of the preceding claims 1 to
5, characterized in that between the supply container (2) and the
intermediate storage device (4) a first metering device (6) is
disposed for adjusting the mass flow from the supply container (2)
to the intermediate storage device (4).
7. Gas supply device as defined in claim 6, characterized in that
the first metering device (6) is a controllable mass flow
controller.
8. Gas supply device as defined in any of the claims 1 to 7,
characterized in that the intermediate storage device (4) is
coupled to a gas outlet via a second metering device (15).
9. Gas supply device as defined in claim 8, characterized in that
the second metering device (15) is a flow control valve.
10. Gas supply device as defined in claim 8 or 9, characterized in
that the gas outlet is connected to a vacuum pump (8) and/or cold
trap.
11. Gas supply device as defined in any of the claims 8 to 10,
characterized in that the constant pressure p2 in the intermediate
storage device (4) is set by the second metering device (15).
12. Gas supply device as defined in any of the claims 1 to 11,
characterized in that a carrier gas can be delivered into the first
gas line (3) between the supply container (2) and the intermediate
storage device (4).
13. Gas supply device as defined in any of the claims 6 to 11,
characterized in that a carrier gas can be delivered into the first
gas line (3) between the first metering device (6) and the
intermediate storage device (4).
14. Gas supply device as defined in claim 12 or 13, characterized
in that the carrier gas is delivered via a third metering device
(9).
15. Gas supply device as defined in claim 14, characterized in that
the third metering device (9) is a mass flow controller.
16. Gas supply device as defined in any of the claims 14 or 15,
characterized in that the constant pressure p2 is set by the mass
flows of the first and third metering devices (6, 9) with a fixed
cross-section of the opening of the second metering device
(15).
17. Gas supply device as defined in any of the claims 12 to 16,
characterized in that the mass flow of the carrier gas is
proportional to the mass flow of the first precursor from the
supply container (2) to the intermediate storage device (4).
18. Gas supply device as defined in any of the claims 1 to 17,
characterized in that the precursor is an Nb, Ta, Ti or Al
compound.
19. Gas supply device as defined in claim 18, characterized in that
the Nb compound is NbCl.sub.5 or Nb ethoxide.
20. Gas supply device as defined in claim 18, characterized in that
the Ta compound is TaCl.sub.5 or Ta ethoxide.
21. Gas supply device as defined in claim 18, characterized in that
the Al compound is AICl.sub.3.
22. Gas supply device as defined in claim 18, characterized in that
the Ti compound is TIPT (titanium isopropylate).
23. Gas supply device as defined in any of the claims 12 to 22,
characterized in that the carrier gas is an inert gas, a second
precursor or a gas mix with a second precursor, where under normal
conditions each of the carrier gases is gaseous.
24. Gas supply device as defined in claim 23, characterized in that
the carrier gas is or contains oxygen.
Description
[0001] The invention relates to a gas supply device for precursors
with a low vapor pressure, especially for CVD coating systems
according to the characterizing portion of claim 1.
[0002] In modern CVD coating systems (chemical vapor deposition),
more and more specialized coatings are applied to components or
substrates. The coatings, which may also consist of a series of
different thin layers, must satisfy very high requirements with
regard to their properties. In order to achieve such properties the
deposition must also be of very high quality. This includes the
deposition rate as a deposition parameter, for example, which has a
considerable effect on the coating quality. In CVD deposition, the
deposition rate is fundamentally determined by the partial pressure
of a gaseous precursor. Therefore, the partial pressure must be set
very precisely and must not fluctuate.
[0003] Special coating materials are used for coating which are
delivered to the coater via selected precursors. Precursors used
for producing TiO.sub.2/SiO.sub.2 alternating coatings are titanium
tetrachloride (TiCl.sub.4) or hexamethyl disiloxane (HDMSO), for
example, which, under normal conditions, have a low vapor pressure
far below the atmospheric pressure. Such a low vapor pressure is
usually too low for an adequate deposition rate required for
industrial coating. Therefore, the precursors must be heated up to
a first evaporation temperature in a supply container so as to
generate an adequate vapor pressure.
[0004] In order to prevent the precursor from condensing on the way
to the coater, the gas supply device must then be heated between
the supply container and the coater to a second temperature, which
is higher than the first evaporation temperature.
[0005] It is also known to intermediately store the precursors or
the TiCl.sub.4 and hexamethyl disiloxane coating materials in an
intermediate storage device at a vapor pressure of approx. 50 mbar
or greater so as to achieve an adequate mass flow rate through the
following valves, mass flow controllers and tube systems. In order
to obtain such a partial pressure, the intermediate storage device
is heated up to at least 50.degree. C. for TiCl.sub.4 and
30.degree. C. for hexamethyl disiloxane.
[0006] Furthermore, Nb.sub.2O.sub.2/SiO.sub.2 alternating coatings
can also be produced offering the advantage that they tend less
toward crystallization. Moreover, NbO.sub.2 can be deposited at
higher deposition rates. Additionally, the coefficient of expansion
of Nb.sub.2O.sub.5 is more suitable to that of SiO.sub.2 than the
coefficient of expansion of TiO.sub.2, so that thicker alternating
coatings can be produced with Nb.sub.2O.sub.5. However, for the
production of Nb.sub.2O.sub.5 coatings only precursors with
comparatively low vapor pressure are available whose vapor pressure
under normal conditions is even far below the vapor pressure of the
HMDSO and TiCl.sub.4 precursors. A commercially available Nb
compound with the highest vapor pressure, NbCl.sub.5, will not have
a pressure of 50 mbar until a temperature of approx. 170.degree. C.
is reached. The temperature dependence of the vapor pressure of
NbCl.sub.5 is illustrated in the bottom curve in FIG. 1. Therefore,
a gas supply device for uniformly supplying a PICVD coating system
with NbCl.sub.5 vapor would have to be maintained at said
temperature.
[0007] A gas supply device for providing precursors with a low
vapor pressure with a supply container for a precursor and an
intermediate storage device for buffering and mixing the vaporous
precursor with other gases is known (JP 2-25 09 77 A2). The supply
container is thermostatted to a first temperature T1 and the
intermediate storage device is thermostatted to a second
temperature T2 where the first temperature T1 is lower than the
second temperature T2 so as to prevent condensation of the
precursor in the intermediate storage device. A carrier gas is
delivered to the supply container which transports the precursor to
the intermediate storage device and from there to a reaction
chamber. The gas supply device can be provided with a second supply
container from which a second precursor is delivered to the
intermediate storage device by means of a carrier gas so as to mix
the two precursors and the carrier gas. In this device, the
intermediate storage device and the equipment connected to the
intermediate storage device must be maintained at the high
temperature T2, which makes maintenance work time-consuming because
of the required cooling down period, and the materials and
equipment must be able to withstand the high temperature T2.
[0008] A type of gas supply device for precursors with a low vapor
pressure, especially for a PICVD coating system, is known where a
supply container for the precursor is held at a first temperature
(DE 42 36 324 C 1). Also, said gas supply device has an
intermediate storage device for intermediate storage of the
vaporous precursor, where the intermediate storage device is
connected to the supply container via a gas line. The gas with the
precursor can be removed from the intermediate storage device for
the PICVD coating system. In this gas supply device, the
intermediate storage device is maintained at a second temperature
which is higher than the first temperature of the supply container.
Pressure fluctuations in the gas with the precursor caused by
removals of varying mass flow rate into the PICVD coating system
are largely compensated by the intermediate storage device.
[0009] For repairs or routine maintenance work on the intermediate
storage device, however, the intermediate storage device and the
equipment connected to said device for supplying and removing the
gas have to be cooled, which is very time-consuming. This also
requires the use of expensive high-temperature mass flow
controllers in the area of the intermediate storage device.
Moreover, in continuous removal, the maximum removable precursor
mass flow is limited by the evaporation rate of the supply
container which is maintained at a lower temperature.
[0010] The aim of the invention is to develop a gas supply device
for a precursor with a low vapor pressure such that maintenance and
repair work on an intermediate storage device can be completed
easily and quickly and using cost-effective components for the
intermediate storage device and its elements without having to
limit the maximum achievable mass flow rate of the precursor.
[0011] The problem is solved by means of the features of claim
1.
[0012] According to claim 1, a gas supply device of the invention
for precursors with a low vapor pressure has a supply container for
storing a first precursor with a low vapor pressure, an
intermediate storage device for intermediate storage of the first
precursor evaporated in the supply container, a first gas line
connecting the supply container to the intermediate storage device,
and a second gas line for removing the gas from the intermediate
storage device. In this embodiment, the gas supply device is also
called a gas generator.
[0013] The supply container is maintained at a first temperature
T1. Via the first gas line, the gas enters the intermediate storage
device where it is maintained at a second temperature T2. Also, the
pressure in the intermediate storage device is held at a constant
pressure p2 which is lower than the pressure p1 in the supply
container so that the vaporous first precursor flows into the
intermediate storage device because of the higher pressure in the
supply container. According to the invention, the first temperature
T1 in the supply container is higher than the second temperature T2
in the intermediate storage device.
[0014] The gas removed via the second gas line on the intermediate
storage device serves to supply the coaters with the gaseous first
precursor. Coaters are especially CVD coating systems or the like.
Precursors are also frequently called educt species, starting
materials or coating material. Precursors with a low vapor pressure
should be understood to mean solid or liquid coating compounds with
a vapor pressure of less than 10 mbar at temperatures of 50.degree.
C., for example.
[0015] A supply container is usually a quartz flask or a high-grade
steel container or the like, where the material of the container is
resistant to reactions with the precursor. The intermediate storage
device can also consist of quartz, high-grade steel or the like.
Advantageously, the intermediate storage device is voluminous so as
to buffer pressure fluctuations caused by irregular gas removal
from the intermediate storage device. The optimal volume of an
intermediate storage device is known from DE 42 36 324 C1 whose
disclosure content is hereby incorporated.
[0016] The maximum removable mass flow from the supply container
depends on the pressure p1. In normal operation, the gas volume of
the supply container is filled with pure precursor vapor so that
the pressure p1 is equal to the equilibrium vapor pressure of the
precursor, which increases with the temperature T1. The maximum
removable precursor mass flow from the intermediate storage device
for a coater is limited by the mass flow between the supply
container and the intermediate storage device.
[0017] Consequently, as the temperature T1 and thus the pressure p1
increase the maximum usable mass flow for coating can be
increased.
[0018] The evaporation rate of the first precursor in the supply
container depends on the temperature T1 and on the partial pressure
of the first precursor in the supply container. The evaporation
rate increases as the temperature rises. If the vaporous precursor
is now removed for the intermediate storage device the precursor is
very quickly replaced because of the evaporation. In the supply
container, the saturation vapor pressure of the precursor is
virtually maintained. Because the saturation vapor pressure depends
very highly on the temperature (see FIG. 2) a minor change in the
temperature T1 can achieve a significant change in the pressure
p1.
[0019] Because the precursor is preferably present only in gaseous
form in the intermediate storage device because of the lower
pressure p2 in the intermediate storage device, the maximum
removable mass flow in a suitable temperature interval is not
limited by the lower temperature T2 in a suitable temperature
interval of the intermediate storage device. Therefore, the setting
of the temperature T2 is not dependent on the temperature T1, and
the intermediate storage device and the equipment connected to the
intermediate storage device have to be heat-resistant only with
regard to the lower temperature T2, which allows the use of less
expensive components, for example flow rate controllers and valves.
For maintenance or repair work in the area of the intermediate
storage device, the waiting period until the intermediate storage
device and the equipment connected to said device have cooled down
is reduced thereby.
[0020] Also, the lower temperature T2 at which the high volume
intermediate storage device must be held contributes to saving
energy. In contrast, the supply container can be small compared to
the intermediate storage device and it can be integrated so as to
be heat insulated in the heated area of the intermediate storage
device.
[0021] Advantageously, the temperature T2 of the intermediate
storage device is set such that the maximum partial pressure of the
first precursor in the intermediate storage device is below the
saturation vapor pressure of the precursor in the intermediate
storage device at the temperature T2. This is to prevent that the
first precursor condenses and remains in the intermediate storage
device.
[0022] When the pressure p1 is more than 1.5 [times] higher than
the pressure p2 in the intermediate storage device, a pressure
difference is obtained between the supply container and the
intermediate storage device where a locking of a connection between
the supply container and the intermediate storage device is
achieved. Then, the rate of transportation explicitly depends upon
the pressure difference (p1-p2) and the conductance of the tube
connection between the supply container and the intermediate
storage device. In the limiting case of an ideally locked flow, the
maximum mass flow is solely determined by p1 and the cross-section
of the line at the locking point (tube end or valve opening, for
example).
[0023] The locking also prevents that the precursor vapor can
diffuse from the intermediate storage device back into the supply
container. Using a gas mix of the precursor vapor with another gas
in the intermediate storage device prevents the precursor from
mixing with other gases in the supply container.
[0024] If a valve is used, for example, for adjusting the mass flow
between the intermediate storage device and the supply container,
its conductance can be set such that the mass flow through the
valve is affected only by the pressure p1 on the inlet side and
that it is independent of the pressure p2 on the outlet side
(locking conditions). The pressure p1 is preferably twice as high
as the pressure p2.
[0025] According to an advantageous embodiment of the gas supply
device, a metering device is provided between the supply container
and the intermediate storage device. The metering device is used
for setting the mass flow from the supply container to the
intermediate storage device. A metering device is usually a nozzle
restricting the cross-section of the line, a valve for opening and
closing, a metering valve with variable cross-section and the like.
The metering device is used to restrict the mass flow from the
supply container to the intermediate storage device. The metering
device is preferably controlled, for example by means of a
controller, in such a way that the mass flow increases when the
pressure in the intermediate storage device falls below the
constant pressure p2, and that the mass flow decreases when the
pressure in the intermediate storage device exceeds p2.
[0026] The first metering device is advantageously a controllable
mass flow controller so that on the one hand, control is possible
via a control unit or a regulator, and on the other hand, the mass
flow flowing between the supply container and the intermediate
storage device can be measured.
[0027] According to another embodiment of the gas supply device,
gas is discharged via a second metering device from the
intermediate storage device to a gas outlet. With this arrangement,
gas can be discharged continuously from the intermediate storage
device. Alternatively, the second metering device can be adjusted
such that when the pressure p2 is exceeded gas can be discharged
from the intermediate storage device so as to maintain a constant
pressure in the intermediate storage device. The outlet can also be
used for evacuating and purging the intermediate storage
device.
[0028] Advantageously, the second metering device can be a flow
control valve, where the cross-section can be adjusted for
discharging the gas.
[0029] According to another embodiment, the gas outlet is connected
to a vacuum pump and/or cold trap. The vacuum pump evacuates the
outlet side of the gas outlet to a pressure below the pressure p2
of the intermediate storage device so as to generate a pressure
difference and allowing a gas discharge. Alternatively, the vacuum
pump and the cold trap can be used together so that the condensable
gas freezes out on the cold trap, while the non-condensable gas can
be suctioned off by the vacuum pump. Using a cold trap allows that
the usually expensive precursors with a low vapor pressure can be
retained so as to reuse them.
[0030] According to an especially advantageous embodiment of the
gas supply device, a carrier gas is delivered into the first gas
line between the supply container and the intermediate storage
device. The carrier gas can be an inert gas, a second precursor or
a gas mix with a second precursor. Carrier gases are used in CVD
processes for transporting the precursors more rapidly to the
object to be coated and for removing reaction products or
impurities from there. Therefore, the carrier gas transports the
first precursor faster through the gas supply device, and mixing
the first precursor with the carrier gas has the additional
advantageous effect that as a result of diluting the first
precursor its partial pressure in the intermediate storage device
is lower than the total pressure p2 in the intermediate storage
device. This allows another decrease in the temperature T2 in the
intermediate storage device because the condensation of the
precursor depends solely on the partial pressure of the first
precursor and not on the total pressure in the intermediate storage
device. By decreasing the partial pressure in the intermediate
storage device the temperature T2 can be reduced even further. The
temperature T2 is restricted by the lower limit at which the
temperature-dependent saturation vapor pressure is higher than the
partial pressure of the first precursor in the intermediate storage
device, which prevents condensation.
[0031] In the above embodiment, a mix is stored in the intermediate
storage device whose precursor concentration (or molar fraction) is
set to be constant. This is ensured by setting a constant ratio
between the two gas inflows (precursor and transport/reaction gas).
By producing the above described locking between the supply
container and the intermediate storage device and at a constant
pressure p1 a defined mass flow from the supply container to the
intermediate storage device is ensured. Additionally, the locking
prevents the gas mix from diffusing from the intermediate storage
device back into the supply container.
[0032] It is practical to supply the carrier gas after the first
metering device so that the mass flow flowing through the metering
device solely contains the precursor, and the carrier gas is unable
to flow into the supply container via the metering device because
of the pressure difference.
[0033] According to another embodiment, the carrier gas is
delivered via a third metering device which is preferably a mass
flow controller so that the mass inflow of the carrier gas can be
controlled.
[0034] According to an especially advantageous embodiment, the mass
flow of the carrier gas is set proportionally dependent on the mass
flow of the first precursor from the supply container to the
intermediate storage device. As a result, a mixing ratio between
the first precursor and the carrier gas is defined in the
intermediate storage device by means of the proportionality factor.
The constant mixing ratio in the intermediate storage device allows
a defined supply of the first precursor to the coater and thus
finally, a uniform deposition rate.
[0035] In order to produce optical functional coatings with a
niobium oxide coating, the first precursor is advantageously an Nb
compound, preferably NbCl.sub.5 or an Nb alcoholate, and the
carrier gas is preferably O.sub.2. When SiO.sub.2/Nb.sub.2O.sub.5
alternating coatings are produced, for example, with a gas mix of
O.sub.2 and NbCl.sub.5, the reaction gases are directly available
in the intermediate storage device for depositing the
Nb.sub.2O.sub.5 coating without having to use another gas as a
carrier gas.
[0036] For coatings containing tantalum, TaCl.sub.5 or a Ta
alcoholate can preferably be used. For coatings containing titanium
or aluminum, TIPT (titanium isopropylate) or AICl.sub.3 can
preferably be used.
[0037] An exemplary embodiment of the invention is explained in
more detail by means of the drawings, as follows:
[0038] FIG. 1 is a diagram of the temperature dependence of the
saturation vapor pressure of an NbCl.sub.5 precursor.
[0039] FIG. 2 is an exemplary embodiment of the gas supply device
and a gas exchange station as well as a CVD deposition system,
and
[0040] FIG. 3 is a combination of two gas supply systems with two
coaters that are connected via a gas exchange station.
[0041] The bottom curve in the diagram of FIG. 1 illustrates the
course of the saturation vapor pressure of NbCl.sub.5 in dependence
of the temperature. Niobium pentachloride (NbCl.sub.5) is present
as a solid over the temperature range shown and sublimating
directly into the gas phase. The bottom curve in the diagram shows
the maximum saturation vapor pressure achievable by the partial
pressure of NbCl.sub.5 in the gas phase in equilibrium with the
solid phase. At 50.degree. C., the saturation vapor pressure is at
approx. 0.04 mbar. Said pressure is too low to achieve an adequate
mass flow for NbCl.sub.5 in gaseous state through the tubes and
valves of a gas supply system. In order to provide an adequate
quantity of gas and transporting said gas through a line system the
temperature, and thus the saturation vapor pressure must be
increased.
[0042] The top curve in FIG. 1 shows the maximum setting for the
total pressure or absolute pressure in the case where NbCl.sub.5 is
present in dilution with another gas to a 5% NbCl.sub.5 ratio. The
total pressure can then be approx. 20 times higher than the
saturation vapor pressure of NbCl.sub.5 before NbCl.sub.5 condenses
from said gas mix.
[0043] FIG. 2 shows a diagram of a gas supply device 1 where the
precursor NbCl.sub.5 is stored in a supply container 2. The
evaporation of the precursor generates a first pressure p1 in the
supply container 2. The supply container 2 is connected via a first
gas line 3 to an intermediate storage device 4. In the first gas
line 3, coming from the supply container 2 a first cut-off valve 5
and a mass flow controller 6 (MFC) are disposed. With the first
cut-off valve 5, the first gas line 3 can be locked relative to the
supply container 2 so that the supply container 2 can be removed
from the gas supply device 1 for maintenance work or for refilling
the NbCl.sub.5 precursor.
[0044] During the gas supply operation, the first mass flow
controller 6 is used for measuring the mass flow from the supply
container 2 to the intermediate storage device 4 and for adjusting
the mass flow rate to a specified value.
[0045] Between the first cut-off valve 5 and the first mass flow
controller 6, another gas line branches off from the first gas line
3, which can be locked by means of a second cut-off valve 7. When
the cut-off valve 7 and the cut-off valve 5 are open, the supply
container 2 can be evacuated by means of a forepump 8. Also, any
purging gas that may have been supplied (supply not shown) can be
pumped out by means of said forepump 8.
[0046] Between the first mass flow controller 6 and the
intermediate storage device 4 another line enters the first gas
line 3. In said line a second mass flow controller 9 is disposed.
Through the second mass flow controller 9, a carrier gas or another
reaction gas, in the present case oxygen (O.sub.2), can be
delivered into the first gas line 3. The NbCl.sub.5 precursor is
then mixed with the carrier gas and delivered to the intermediate
storage device 4.
[0047] Via a second gas line 10 the gas or gas mix can be removed
from the intermediate storage device 4 and delivered to a gas
exchange station 11. Starting at the intermediate storage device 4,
a first metering valve 12 and a third curt-off valve 13 are
disposed in the second gas line 10 before the second gas line 10
enters a deposition system 14. When the third cut-off valve 13 is
open the first metering valve 12 causes a pressure drop between the
intermediate storage device 4 and the outlet side of the first
metering valve 12.
[0048] Another gas line leaves the intermediate storage device 4
via a flow control valve 15 which is also connected to the forepump
8. The pressure in the intermediate storage device 4 is measured
with a pressure sensor 16. The measured pressure value is delivered
to a pressure controller 17 controlling the flow control valve 15.
The pressure controller 17 maintains the pressure in the
intermediate storage device 4 at a specified second pressure value
p2. If the pressure in the intermediate storage device 4 exceeds
the specified second pressure value p2, the pressure controller 17
causes the flow control valve 15 to open and discharge excess gas
to the forepump 8.
[0049] In the gas exchange station 11, behind the third cut-off
valve 13, another deposition gas can alternately be delivered to
the second gas line 10 from another gas line via a fourth cut-off
valve 18. In the present case, the other deposition gas is a
hexamethyl disiloxane-oxygen mix (HMDSO/O.sub.2) for depositing
SiO.sub.2 coatings. Therefore, by switching the cut-off valves 13
and 18, the deposition operation can be switched from
Nb.sub.2O.sub.5 deposition (from the NbCl.sub.5 precursor) to
SiO.sub.2 deposition.
[0050] The gas supply device 1 is divided into two temperature
zones. The first temperature zone is the supply area 19 comprising
the supply container 2, the first cut-off valve 5, a portion of the
first gas line 3, the first mass flow controller 6, the second
cut-off valve 7 and a portion of the incoming and outgoing gas
lines. The supply area 19 is maintained at a first constant
temperature T1. It is heated by means of common heating methods.
The temperature is preferably maintained constant by means of an
automatic control system. As a result of the first temperature T1,
the saturation vapor pressure p1 of the first precursor, in the
present case NbCl.sub.5, is obtained in the supply container.
Heating the elements connected to the supply container 2 prevents
condensation in the supply area 19.
[0051] Furthermore, an intermediate storage area 20 comprising a
portion of the first gas line 3, the intermediate storage device 4,
a portion of the second gas line 10, the first metering valve 12,
the pressure sensor 16, the flow control valve 15 and any gas lines
for purging or delivering other gases is maintained at a second
temperature T2.
[0052] According to the exemplary embodiment, oxygen is supplied
through the second mass flow controller 9 into the first gas line
3. Appropriate control of the mass flow controllers 6 and 9
achieves that the second mass flow controller 9 delivers a mass
flow of oxygen proportional to the first mass flow controller 6. In
the present case, the mass flow of the oxygen is 19 times higher
than the mass flow of NbCl.sub.5, resulting in a mixing ratio of 5%
NbCl.sub.5 gas and 95% oxygen in the intermediate storage device 4.
The intermediate storage device is maintained at a total pressure
of 40 mbar. The partial pressure of the NbCl.sub.5 in the
intermediate storage device is approx. 2 mbar, which is clearly
below the saturation vapor pressure of 4 mbar at 120.degree. C.
(see FIG. 1) and which prevents condensation of NbCl.sub.5.
[0053] The first temperature T2 is equal to 200.degree. C. so that
the saturation vapor pressure of NbCl.sub.5 according to FIG. 1 is
approx. 105 mbar and therefore p1 is approx. 100 mbar. Accordingly,
a pressure difference with a factor greater than 2 exists between
the supply container 2 and the intermediate storage device 4 so
that the mass flow from the supply container 2 into the
intermediate storage device 4 is ensured.
[0054] The pressure p2 in the intermediate storage device 4 is
controlled by means of the flow control valve 15. The mass flow
controllers are set for constant flow rates. Alternatively, with a
fixed cross-section of the opening of the flow control valve 15 to
the forepump 8, the pressure p2 is controlled via a variable
control of the mass flow rates of the mass flow controllers 6, 9 at
a constant ratio.
[0055] Another pressure drop is caused by the first metering valve
12 between the intermediate storage device and the gas exchange
station, which further decreases the partial pressure of
NbCl.sub.5, and the temperature in the area of the gas exchange
station can be reduced further. In the present case, it is
75.degree. C. so that according to FIG. 1, the maximum partial
pressure of NbCl.sub.5 can be 0.25 mbar, and therefore the total
pressure of the gas mix can be max. 5 mbar. Therefore, between the
intermediate storage area 20 and the gas exchange station 11, the
pressure decreases by at least a factor 8. With such a pressure
drop, a locking takes place in the first metering valve 12, which
means with such a pressure drop the mass flow through the first
metering valve depends solely on its conductance and the pressure
p2 in the intermediate storage device 4 and it is independent of
the pressure in the gas exchange station 11. Therefore, in order to
obtain a constant mass flow from the intermediate storage device 4
to the gas exchange station 11 and continuing to the deposition
system 14, it is not necessary to provide another mass flow
controller because the mass flow rate is determined via the
constant pressure p2 and the conductance setting of the first
metering valve.
[0056] According to another embodiment of the gas supply device,
the first mass flow controller 6 can also be substituted by a
metering valve corresponding to the first metering valve 12,
because again, the pressure drop between the supply container 2 and
the intermediate storage device 4 is greater than a factor 2. This
allows that the high-temperature mass flow controller 6 can be
replaced by a less expensive metering valve.
[0057] The above gas supply device 1 was described merely as an
example for using the NbCl.sub.5 precursor and oxygen as carrier
gas. Other precursors with a low vapor pressure and other carrier
gases can also be used. Examples of precursors are niobium
ethoxide, aluminum trichloride, titanium isopropoxide, tantalum
ethoxide. The temperatures to be set, T1 for the supply area 19, T2
for the intermediate storage area 20 and T3 for the gas exchange
station can then be determined based on the curves of the
saturation vapor pressure for the respective precursor allowing for
the individual concentrations (molar fractions).
[0058] FIG. 3 shows a multi-chamber coating system 14, 14' which
can be supplied by multiple gas supply devices 19, 20; 19', 20' via
a gas exchange station 11 with two different precursors for
producing alternating coatings. The reference numbers used in FIG.
2 and described above are used for identical elements in FIG.
3.
[0059] The functional method of the two gas supply devices 19, 20;
19', 20' substantially corresponds to the gas supply device 1 of
FIG. 2 with the difference that the temperature T1 of the supply
area 19 and the temperature T2 of the intermediate storage area 20
are optimized for the temperature dependence of the precursor in
the supply container 2, and the temperature T4 in the supply area
19' and the temperature T5 in the intermediate storage area 20' are
optimized for the temperature-dependent course of the vapor
pressure of the second precursor in the supply container 2'.
[0060] Reference List
[0061] 1 gas supply device
[0062] 2 supply container
[0063] 3 first gas line
[0064] 4 intermediate storage device
[0065] 5 first cut-off valve
[0066] 6 first mass flow controller
[0067] 7 second cut-off valve
[0068] 8 forepump
[0069] 9 second mass flow controller
[0070] 10 second gas line
[0071] 11 gas exchange station
[0072] 12 first metering valve
[0073] 13 third cut-off valve
[0074] 14 deposition system
[0075] 15 flow control valve
[0076] 16 pressure sensor
[0077] 17 pressure controller
[0078] 18 fourth cut-off valve
[0079] 19 supply area
[0080] 20 intermediate storage area
* * * * *