WO2006100428A1

WO2006100428A1 - Method and apparatus for evacuating a chamber prior to its filling with a noble gas

Info

Publication number: WO2006100428A1
Application number: PCT/GB2006/000809
Authority: WO
Inventors: Robert Bruce Grant
Original assignee: The Boc Group Plc
Priority date: 2005-03-24
Filing date: 2006-03-07
Publication date: 2006-09-28
Also published as: TW200637644A; GB0506076D0

Abstract

A method is described for suppressing the contamination of a noble gas used in the processing of a device within a process chamber. The method comprises the steps of supplying a purge gas to a process chamber, the purge gas being substantially free from noble gas; suppressing the ingress of air into the chamber as a device is inserted into the purge gas-filled chamber; and, prior to supplying noble gas to the evacuated chamber for device processing, at least partially evacuating the chamber by drawing the purge gas therefrom. By suppressing the contamination of the noble gas with other noble gases in this manner, the subsequent recovery of the noble gas from the gas stream can be facilitated, and the lifetime of the noble gas can be increased before it requires replacement.

Description

METHOD AND APPARATUS FOR EVACUATING A CHAMBER PRIOR TO ITS FILLING WITH A NOBLE GAS

The present invention relates to a method of, and apparatus for, suppressing or inhibiting the contamination of a noble gas supplied to a process chamber, for example, for filling a device located therein.

Many batch processes require samples or devices to be treated with specific process gas combinations at various pressures. Noble gases are commonly supplied to a process chamber for the filling of various devices, such as lamps and plasma displays. Noble gases are present in atmospheric air in only very low concentrations, and so their cost is very high (for example, the current cost of xenon is around $4/sl). As only small amounts of the noble gas are normally consumed in the actual process, it is very desirable to recover and re-use the noble gases contained within the gas stream exhaust from the process chamber.

When the process gas combination is to be recovered and recycled, as, for example in Xe lamp filling, some atmospheric air can enter the recovery loop. The reactive components of the air can be easily removed with purifiers and getters, but the noble gases, most notably argon, contained within the air are hard to remove, and so these unwanted noble gases will build up within the recirculated gas, reaching an un-acceptable level over time. By way of illustration, consider a xenon lamp filling process comprising a 20-litre process chamber that is initially evacuated to 10^"2 mbar and then backfilled to 500 mbar with xenon. The volume of xenon utilised in filling the lamps is 0.1 litres and the remainder of the xenon is recovered and recirculated in a recirculation loop containing 80 litres of gas. Prior to the introduction of the xenon process gas, the chamber contains 20 litres of air, and hence around 1 litre of Ar, at 10^"2 mbar. This will contribute 1 ppm of argon to the process gas in the chamber, and assuming complete mixing in the recovery system will contribute approximately 200 ppb every process cycle. If the allowable argon level in the process gas is 5 ppm then in 20 cycles the xenon will be completely contaminated with argon. Removing unwanted argon from a process gas comprising xenon or a mixture of xenon and neon, or removing unwanted neon from an argon process gas, at flow rates above a few litres per minute can only be done with high efficiency by using expensive cryogenic techniques. Therefore, it is normal for the contaminated process gas to be simply exhausted to the atmosphere and replaced by fresh process gas, thereby also increasing costs.

One solution to inhibit contamination of the process chamber is to evacuate the process chamber to a relatively low pressure, for example around 10^~2 mbar to remove atmospheric air from the process chamber, and transferring process devices into the process chamber from a load lock chamber. When a process device is inserted into the load lock chamber, that chamber is evacuated. When the correct vacuum level is achieved in the load lock chamber, the process device is transferred to the process chamber to be exposed to the process gas. However, this solution increases the complexity and price of the process system and is impractical for applications such as lamp filling. Furthermore, the time required to achieve a pressure of between 10^'2 and 10^"3 mbar within the process and load loclc chambers can unacceptably increase the overall process cycle time, whereas providing larger vacuum pumps to achieve this vacuum level within an acceptable period time can unacceptably increase costs.

It is an aim of at least the preferred embodiments of the present invention to seek to provide a relatively simple and low cost method of suppressing contamination of a noble gas supplied to, and recovered from, a process chamber.

In a first aspect, the present invention provides a method of suppressing contamination of a noble gas supplied to, and recovered from, a process chamber, the method comprising the steps of, prior to the insertion of a device for processing into the chamber, supplying a purge gas to a process chamber, the purge gas being substantially free from noble gas; and, prior to the supply of the noble gas to the chamber, at least partially evacuating the chamber.

By using a gas that is substantially free from noble gas as a purge gas that is supplied to the chamber before a device is inserted into the chamber, the initial contamination of the process chamber with unwanted noble gas can be inhibited. Examples of suitable purge gases include gases comprising at least one of nitrogen and oxygen, such as synthetic air. Once the device has been inserted into the purge gas-filled chamber for processing, the chamber is then evacuated to reduce the level of chamber contamination resulting from the insertion of the device into the process chamber, and to enable the chamber to be backfilled with noble gas for device processing. However, due to the relatively low level of chamber contamination (due to the noble-gas free atmosphere existing in the chamber prior to insertion of the device), the pressure to which the chamber needs to be evacuated to reduce the chamber contamination to an acceptable level is relatively low. For example, for the aforementioned illustration, the chamber would only need to be evacuated to around 10^"1 mbar. The time required to achieve the acceptable purity level within the chamber can therefore be significantly reduced, shortening the overall process time cycle.

Thus, the combination of a gas purge and vacuum pumping can enable fast process times to be achieved in combination with an acceptable gas purity without the cost of expensive vacuum pumping or cryogenic gas purification systems.

The method preferably also comprises the step of suppressing the ingress of air into the chamber as a device is inserted into the chamber. For example, in the preferred embodiment the ingress of air into the chamber is suppressed by conveying the device through a laminar gas flow as it is inserted into the chamber. This laminar gas flow may be generated external of the chamber, for example, by a fan that generates a localised, controlled noble gas-free and moisture-free gas flow across an opening to the process chamber such that only gas from this controlled stream enters the chamber as the device is inserted into the chamber through the opening, or it may be generated within the chamber. Such an internal laminar gas flow may be directed against the direction in which the device is inserted into the chamber, or it may be substantially orthogonal thereto. This gas flow may be formed from a gas containing at least one of nitrogen and oxygen, and so may conveniently be formed from the purge gas supplied to the chamber. Alternatively, this airflow may be generated from a separate gas source.

By suppressing the ingress of air into the chamber as a device is inserted thereinto, the level of contamination of the chamber can be reduced. As a result, the level of contamination, by unwanted noble gases, of the noble gas subsequently recovered from the process chamber following device processing can be reduced, typically by a factor of 10 to 100. Consequently, the number of process cycles that can be performed before the recovered noble gas requires replacement can be significantly increased.

In a second aspect, the present invention provides a method of filling a device with noble gas, the method comprising the steps of supplying a purge gas to a process chamber, the purge gas being substantially free from noble gas; suppressing the ingress of air into the chamber as a device is inserted into the chamber; at least partially evacuating the chamber by drawing the purge gas therefrom; supplying noble gas to the evacuated chamber for filling the device; and subsequently extracting a gas stream containing the noble gas from the chamber and recovering the noble gas contained within the gas stream for subsequent re-supply to the chamber.

The noble gas is preferably recovered by removing one or more components from a gas stream extracted from the process chamber to produce a noble gas-rich gas, and collecting the noble gas-rich gas for re-supply to the process chamber. The collected noble gas-rich gas may be purified prior to re-supply to the process chamber in order to ensure that the collected noble gas is supplied to the chamber with an acceptable purity level.

In a third aspect, the present invention provides a processing system comprising a process chamber having an opening through which devices are inserted into and withdrawn from the chamber, means for supplying a purge gas to a process chamber, the purge gas being substantially free from noble gas, means for suppressing the ingress of air into the purge gas-filled chamber as a device is inserted into the chamber, means for at least partially evacuating the chamber by drawing the purge gas therefrom, means for supplying noble gas to the evacuated chamber for device processing, and means for recovering the noble gas contained within a gas stream subsequently drawn from the chamber for re-supply to the chamber.

Features described above relating to the method aspects of the invention are equally applicable to the system aspect, and vice versa.

Preferred features of the present invention will now be described, by way of example only with reference to the accompanying drawings, in which:

Figure 1 illustrates schematically a system for supplying a noble gas to, and subsequently recovering the noble gas from, a process chamber;

Figure 2 illustrates an apparatus for suppressing ingress of air into the process chamber of Figure 1 as a device is inserted into the chamber; and

Figure 3 illustrates in more detail a system for recovering the noble gas supplied to the process chamber of Figure 1.

An embodiment of the present invention will now be described with reference to the supply of xenon to a process chamber for, for example, the filling of lamps. However, the invention is not restricted to the supply of xenon, or to the filling of devices with noble gas. The invention is also suitable for the supply of other gases, such as argon, neon and krypton, and a mixture of such gases. For example, a mixture of xenon and neon may be supplied to a process chamber for the filling of a plasma display device. The term "noble gas" used herein is therefore not limited to a single gas, but also includes a mixture of two or more noble gases.

Referring to Figure 1 , a process chamber 10 is provided with a first inlet 12 for receiving xenon from a xenon supply 14. The xenon supply 14 typically comprises one or more gas cylinders that provide xenon to a pressurised storage tank 16 from which xenon is supplied to the first inlet 12. A system controller 18 may control a valve 20, or mass flow controller, to control the supply of xenon to the process chamber 10.

The process chamber 10 is also provided with a second inlet 22 for receiving a purge gas from a purge gas supply 24. The purge gas consists of a gas that is substantially free from noble gases. In this example, the purge gas consists of synthetic air, although any other gas, such as nitrogen or oxygen, may be used. The supply of purge gas to the.second inlet 22 is controlled by the system controller 18 through signals issued to valve 26 located between the second inlet 22 and the purge gas supply 24. A gas stream is drawn from the outlet 28 of the process chamber 10 by a pumping system indicated at 30 in Figure 1 , which can be selectively isolated from the process chamber using valve 32 under the control of the controller 18.

In use, to flush atmospheric air from the process chamber 10, the process chamber 10 is initially purged with purge gas by closing valves 20, 32 and opening valve 26. This creates a substantially noble gas-free, and moisture- free, atmosphere within the process chamber 10. One or more devices for filling with xenon are then inserted into the process chamber 10 through an opening 34 provided in a wall of the process chamber 10. In order to suppress the ingress of air into the process chamber 10 as the devices are inserted into the process chamber 10, a laminar airflow 36 is generated, through which the devices are inserted into the chamber 10. In the example illustrated in Figure 2, the laminar airflow 36 is generated from the purge gas used to flush air from the chamber 10. As illustrated, the purge gas is supplied to a head 38 located within the chamber 10, the head 38 having a plurality of spaced outlets 40 for emitting the purge gas in a laminar form and directed against the direction in which the devices are inserted into chamber 10.

Returning to Figure 1 , following the insertion of the devices into the process chamber 10, the valve 26 is closed and valve 32 opened to enable the pumping system 30 to partially evacuate the chamber 10 prior to the subsequently backfilling of the chamber 10 with xenon for filling the devices. This evacuation of the chamber 10 also serves to reduce the contamination of the chamber 10 resulting from the insertion of the devices thereinto, and the degree to which the chamber 10 is evacuated will depend on the extent to which the ingress of air during device insertion is suppressed by the laminar airflow. For example, a vacuum of around 10^~1 to 10^"2 mbar may be sufficient; the lower the required vacuum level, the shorter the time required to evacuate the chamber 10. During the evacuation of the process chamber 10, a three-way valve 42 connected to the exhaust from the pumping system 30 vents the exhaust gas to the atmosphere.

Once the pressure within the process chamber 10 has been reduced to a first predetermined level, as determined by the controller 18 using signals received from a vacuum sensor 44 provided in fluid communication with the chamber 10, the valve 32 is closed and the valve 20 is opened to backfill the process chamber 10 with xenon for filling the devices located therein. The valve 20 is closed either after a predetermined period of time, or when the pressure in the process chamber 10 reaches a second predetermined value. Where this second predetermined value is below atmospheric pressure, for example, around 500 mbar, the controller 18 detects that this predetermined pressure has been reached from signals output from sensor 44. Where this second predetermined value is above atmospheric pressure, for example, around 2 to 3 bar, the controller 18 detects that this predetermined pressure has been reached from signals output from pressure sensor 46 provided in fluid communication with the process chamber 10.

During the filling process, only a portion of the xenon gas will be used in the filling of the devices, and therefore it is desirable to recover and re-use the xenon remaining in the process chamber. In view of this, at the end of the filling process the valve 20 is closed and the valve 32 is opened so that a gas stream containing xenon, components of the atmospheric air that may have entered the process chamber 10 during insertion of the devices into the chamber, and other impurities is drawn from the process chamber by the pumping system 30. The three-way valve 42 is controlled so that the gas stream is diverted to a xenon recovery system 50 for recovering the xenon from the gas stream and returning the recovered xenon to the storage tank 16 for subsequent re-supply to the chamber 10 for device filling.

An example of a recovery system 50 is illustrated in Figure 3. The recovery system 50 comprises an oil filter 52 for removing oil from the gas stream received from the three-way valve 42, and a moisture trap 54 for subsequently removing moisture from the gas stream. As shown in Figure 3, two or more removable moisture traps 54, 54' may be provided, each having an inlet valve 56, 56' and outlet valve 58, 58' respectively. The controller 18 can operate these valves to direct the gas stream through a selected one of the moisture traps 54, 54' so that, as one moisture trap 54 becomes full, the gas stream can be directed through the other moisture trap 54' while the full moisture trap 54 is replaced, thereby avoiding system downtime.

The gas stream output from the moisture trap 54, 54' passes through an optional non-return valve 60 to the inlet of a gas compressor 62 for compressing the gas stream, typically to a pressure of around 10 bar, for storage in the storage tank 16. Prior to storage in the storage tank, the compressed gas stream is conveyed through a hot metal getter 64, containing misch metal or barium, for removing species such as hydrocarbons, oxygen, nitrogen and carbon dioxide from the gas stream. The gas stream exhaust from the hot metal getter 64 thus comprises xenon with traces of argon and other noble gases remaining from the atmospheric air that entered the process chamber 10 during device insertion. This xenon-rich gas stream is then conveyed through open valve 66 to the storage tank 16 for storage prior to re-supply to the process chamber 10. When the valve 20 is subsequently opened to enable the xenon-rich gas to flow to the process chamber, the xenon-rich gas passes through a final hot metal getter 68 to ensure that the xenon-rich gas stream entering the process chamber 10 has the required purity.

As further process cycles are performed, the amount of argon and other unwanted noble gases within the xenon-rich gas stream recovered from the process chamber 10 will slowly build up. The quantity of these noble gases within the xenon-rich gas stream can be determined using a detector 70, for example a mass spectrometer^; analysis system, for detecting the purity of this gas stream output from the storage tank 16. Once the purity falls below a threshold value, the storage tank 16 can be isolated from the recovery system 50, by closing valves 20, 66, and fresh xenon from a back-up storage tank 16' can be used instead, thereby avoiding system downtime. The storage tank 16 containing the contaminated xenon can then be removed for purification using, for example, an external cryogenic purification system, and returned for re-use.

For rapid removal of the gas stream from the process chamber, as illustrated in Figure 3 the pumping system 30 may be provided downstream from an evacuation tank 80 which, when valve 32 is closed during the backfilling of the process chamber 10 with xenon, is evacuated by the pumping system 30. Once the valve 32 is opened to draw the gas stream from the outlet 28 of the process chamber 10, the gas stream rushes into the evacuation tank 80 due to the pressure difference between the process chamber 10 and the evacuation tank 80. Furthermore, as also illustrated in Figure 3, a second equalisation tank 82 may be provided between a second outlet 84 from the process chamber 10 and the compressor 62 for use when the pressure in the process chamber during device filling is greater than atmospheric pressure. In order to avoid overloading the pumping system 30 when the gas stream is to be drawn from the process chamber 10 following device filling, valve 32 initially remains closed, and a valve 86 located between the second outlet 84 and the second evacuation tank 82 is opened so that the gas stream initially rushes into the second evacuation tank 82. Once the pressure in the tank has fallen to a predetermined value, for example 1-1.5 bar, as determined from an output from pressure sensor 46, the valve 86 is closed and the valve 32 opened so that the remainder of the gas stream is drawn through the first outlet 28 by the pumping arrangement 30 and the first evacuation tank 80. The compressor 62 serves to draw the gas from the second evacuation tank 82, the non-return valve 60 serving to prevent backflow of this gas to the exhaust of the pumping system 30.

Claims

1. A method of suppressing contamination of a noble gas supplied to, and recovered from, a process chamber, the method comprising the steps of, prior to the insertion of a device for processing into the chamber, supplying a purge gas to a process chamber, the purge gas being substantially free from noble gas; and, prior to the supply of the noble gas to the chamber, at least partially evacuating the chamber.

2. A method according to Claim 1 , wherein the purge gas comprises at least one of nitrogen and oxygen.

3. A method according to Claim 2, wherein the purge gas comprises synthetic air.

4. A method according to any preceding claim, wherein the chamber is evacuated to a pressure between 10^'1 and 10^"2 mbar.

5. A method according to any preceding claim, comprising the step of suppressing the ingress of air into the chamber as a device is inserted into the chamber.

6. A method according to Claim 5, wherein the ingress of air into the chamber is suppressed by conveying the device through a laminar gas flow as it is inserted into the chamber.

7. A method according to Claim 6, wherein the laminar gas flow is generated within the chamber.

8. A method according to Claim 6 or Claim 7, wherein the laminar gas flow is directed against the direction in which the device is inserted into the chamber.

9. A method according to any of Claims 6 to 8, wherein the laminar gas flow is formed from a gas containing at least one of nitrogen and oxygen.

10. A method according to any of Claims 6 to 9, wherein the laminar gas flow is formed from the purge gas supplied to the chamber.

11. A method of filling a device with noble gas, the method comprising the steps of supplying a purge gas to a process chamber, the purge gas being substantially free from noble gas; suppressing the ingress of air into the chamber as a device is inserted into the chamber; at least partially evacuating the chamber by drawing the purge gas therefrom; supplying noble gas to the evacuated chamber for filling the device; and subsequently extracting a gas stream containing the noble gas from the chamber and recovering the noble gas contained within the gas stream for subsequent re-supply to the chamber.

12. A method according to Claim 11 , wherein the device comprises one of a lamp and a display device.

13. A method according to Claim 11 or Claim 12, the noble gas is recovered by removing one or more components from a gas stream extracted from the process chamber to produce a noble gas-rich gas, and collecting the noble gas-rich gas for re-supply to the process chamber.

14. A method according to Claim 13, wherein the collected noble gas-rich gas is purified prior to re-supply to the process chamber.

15. A method according to any preceding claim, wherein the noble gas comprises at least one of argon, xenon, krypton and neon.

16. A processing system comprising a process chamber having an opening through which devices are inserted into and withdrawn from the chamber, means for supplying a purge gas to a process chamber, the purge gas being substantially free from noble gas, means for suppressing the ingress of air into the purge gas-filled chamber as a device is inserted into the chamber, means for at least partially evacuating the chamber by drawing the purge gas therefrom, means for supplying noble gas to the evacuated chamber for device processing, and means for recovering the noble gas contained within a gas stream subsequently drawn from the chamber for re-supply to the chamber.

17. A processing system according to Claim 16, wherein the purge gas comprises at least one of nitrogen and oxygen.

18. A processing system according to Claim 17, wherein the purge gas comprises synthetic air.

19. A processing system according to any of Claims 16 to 18, wherein said means for at least partially evacuating the chamber is configured to evacuate the chamber to a pressure between 10^"1 and 10^"2 mbar.

20. A processing system according to any of Claims 16 to 19, wherein said means for suppressing the ingress of air into the purge gas-filled chamber as a device is inserted into the chamber comprises means for generating a laminar gas flow through which the device passes as it is inserted into the chamber.

21. A processing system according to Claim 20, wherein the laminar gas flow generating means is at least partially located within the chamber.

22. A processing system according to Claim 20 or Claim 21 , wherein the laminar gas flow generating means is configured to direct the laminar gas flow against the direction in which the device is inserted into the chamber.

23. A processing system according to any of Claims 20 to 22, wherein the laminar gas flow generating means is configured to form the laminar gas flow from a gas containing at least one of nitrogen and oxygen.

24. A processing system according to any of Claims 20 to 23, wherein the laminar gas flow generating means is configured to form the laminar gas flow from the purge gas supplied to the chamber.

25. A processing system according to any of Claims 16 to 24, wherein the noble gas recovery means comprises means for removing one or more components from a gas stream extracted from the process chamber to produce a noble gas-rich gas, and means for collecting the noble gas- rich gas for re-supply to the process chamber.

26. A processing system according to Claim 25, wherein the noble gas recovery means comprises means for purifying the collected noble gas- rich gas prior to re-supply to the process chamber.

27. A processing system according to any of Claims 16 to 26, wherein the noble gas comprises at least one of argon, xenon, krypton and neon.