GB2363129A

GB2363129A - Gas supply method and apparatus

Info

Publication number: GB2363129A
Application number: GB0010831A
Authority: GB
Inventors: Leslie George Stevenson; Nigel Robert John Anderson; Paul Michael Espitalier-Noel
Original assignee: BOC Group Ltd
Current assignee: BOC Group Ltd
Priority date: 2000-05-04
Filing date: 2000-05-04
Publication date: 2001-12-12
Also published as: GB0010831D0

Abstract

Liquid nitrogen is supplied from a storage vessel 2 to a cooling shroud 10 surrounding a chamber 12 housing molecular beam epitaxy equipment for use in the manufacture of semiconductor devices. The liquid nitrogen thus cools the molecular bean epitaxy equipment in its use. Resulting nitrogen vapour flows through a pipeline 14 and is employed to perform a second duty in or associated with the manufacture of the semiconductor devices, for example the cooling of hot exhaust gas in heat exchanger 20.

Description

2363129 M00131 08/MW GAS SUPPLY METHOD AND APPARATUS This invention

relates to a gas supply method and apparatus for use in the manufacture of devices, including integrated circuits, that employ at least one semiconductor ('semiconductor devices').

One example of such a device is a so-called "wafer"which typically has semiconducting and conducting members that can be used as components in various electronic equipment, for example mobile telephones.

Plants for making such wafers are highly capital intensive, typically including a large number of individual processing steps necessary for the deposition of various different layers of semi conducting and conducting material. Typically one or more of the processing steps requires a supply of high purity gaseous nitrogen. At least one other step typically requires supply of a cryogenic liquid, for example liquid nitrogen, for cooling purposes. It is normal to vent to the atmosphere resulting vaporised nitrogen.

It is an aim of the present invention to provide a method and apparatus which improves the utilisation of nitrogen in the manufacture of a semiconductor device.

According to the present invention there is provided a gas supply method for the operation of a plant in which semiconductor devices are made, including the steps of supplying liquid nitrogen to perform a cooling duty in or associated with the plant, recovering vaporised nitrogen from the cooling duty, and employing the vaporised nitrogen to perform a second duty in or associated with the plant.

The invention also provides apparatus for the supply of nitrogen to a plant for the manufacture of semiconductor devices including means for supplying liquid nitrogen to a manufacturing stage requiring cooling so as to cool said stage, means for recovering vaporised nitrogen from said stage, and means for supplying the vaporised nitrogen to perform another duty in the plant.

By using the nitrogen to perform a plurality of duties, the overall cost of supply of nitrogen is kept down.

The cooling duty typically resides in cooling a molecular beam epitaxy chamber. Because molecular beam epitaxy requires an ultra high vacuum, the chamber in which the process is performed is typically fitted with a shroud through which liquid nitrogen is circulated so as to reduce the temperature within the chamber and thereby facilitate the removal of residual gases from the chamber by vacuum pumping.

The secondary duty may, for example, be:

the dilution of waste gas, typically containing one or more toxic components, from another stage of the manufacturing plant, typically at a region upstream of a scrubber for removing the toxic component(s); the cooling of hot waste gas from another stage of the manufacturing plant; the blanketing of a vessel containing water, particularly deionised water;

the purging of gas from another stage of the manufacturing plant; or the provision of an inert or non-reactive atmosphere in at least one other stage of the manufacturing plant.

Particularly if the vaporised nitrogen is to be used for other than the cooling duty, it is typically compressed upstream of being supplied to the second duty. The vaporised nitrogen may be purified if it is to be used in forming a non-reactive atmosphere in another stage of the plant.

The method and apparatus according to the invention will now be described by way of example with reference to the accompanying drawing which is a schematic flow diagram illustrating uses of nitrogen in a plant for making semiconductor devices. The drawing is not to scale.

Referring to the drawing, liquid nitrogen supply apparatus includes a liquid nitrogen storage vessel 2 for storing liquid nitrogen under pressure. A thermally-insulated pipeline 4 leads from the storage vessel 2 to a thermal ly-insu lated phase separator 6. There is a second thermally insulated pipeline 8 leading from the phase separator 6 to a cooling shroud 10 surrounding a chamber 12 forming part of a plant for manufacturing semiconductor devices such as wafers, the chamber 12 being employed to house molecular beam epitaxy equipment (not shown). There is a return thermally insulated pipeline 14 from the shroud 10 for a liquidvapour mixture. The liquid and vapour phases disengage from one another in the phase separator 6, There is a pipeline 16 at the top of the phase separator 6 for conducting vapour therefrom to a second duty within or associated with the wafer manufacturing plant. The pipeline 16 is typically thermally insulated if it is required to use the nitrogen vapour to perform a cooling duty.

As shown in the drawing, at least part of the cold nitrogen is used in a heat exchanger 20 to cool by indirect heat exchange hot exhaust gas from another part of the manufacturing plant. In an alternative, the cold nitrogen is mixed directly with the hot exhaust gas. Any part of the cold nitrogen not required may be vented to the atmosphere.

Downstream of the heat exchanger 20 at least a part of the resulting warmed nitrogen may flow to a compressor 22 in which its pressure is raised to above the operating pressure of another stage of the wafer manufacturing process. Typically, compressed nitrogen flows from the compressor 22 into a buffer vessel 24. Typically, there is a pressure control valve 26 located in a pipeline downstream of the buffer vessel 24. The pressure in the buffer vessel 24 is set by the pressure control valve 26. At least part of the nitrogen flows from the buffer vessel 24 through a filter 28 upstream of its supply to another stage (not shown) of the manufacturing plant.

In an alternative or additional supply scheme, there is a further tank or vessel 30 for the supply of nitrogen in gaseous state to the wafer manufacturing plant. The tank 30 has a pressure control valve 32 associated with it. In order to ensure that the nitrogen supply is of a particularly high purity, there is a pipeline 34 leading from the pressure control valve 32 to a purifier 36, of conventional type, for removing trace impurities such as carbon monoxide and hydrogen from the nitrogen. Solid particles may be removed from the purified nitrogen in a filter 40. As shown in the drawing, some of the nitrogen may be fed from the nitrogen compressor 22 to a region upstream of the purifier 36 so as to become mixed with the nitrogen supplied from the tank 30.

Although the various illustrated means of supplying the vaporised nitrogen in the wafer manufacturing plant for secondary use. It is not essential that all be used together. If desired, only one need be used.

In operation, nitrogen vapour is formed in the liquid nitrogen flowing around the shroud 10 as a result of the heat absorbed from the molecular beam epitaxy chamber 12. In addition, if the nitrogen is stored as a higher pressure than the shroud 10 is operated, additional nitrogen vapour is formed as flash gas typically by passage through an expansion valve (not shown) intermediate the storage vessel 2 and the phase separator 6. As a result, a considerable amount of nitrogen is available for further use. This nitrogen is still at a cryogenic temperature and therefore has considerable cooling potential and may therefore be used in a wide range of different cooling processes as described above. Even if there is no other cooling process available for it to be used in, the nitrogen still has value as a blanketing or purge gas.

The recycle of cold nitrogen vapour from the phase separator 6 is preferably subject to pressure control so as to maintain the pressure within the phase separator 6 in a chosen range. Also for a fab installation there may be more than one molecular beam epitaxy chamber requiring nitrogen cooling and therefore more than one phase separator 6 may be required, each being used to feed cold gas to the pipeline 16.

The availability of recycle gas may be at variable flowrate and therefore the secondary use may require either temperature or pressure control to supplement the recycle gas flow with alternative cold or inert nitrogen sources.

For example, if the nitrogen from the cold application is being recycled for inert blanketing the flowrate should be such that in normal operation there is excess recycled nitrogen with the excess typically being vented. However, if the recycle nitrogen flowrate drops as a result of, for example, partial system maintenance, any arising shortfall of nitrogen may be made up in response to a pressure controller (not shown) from a conventional gas supply tank (e.g. 30). Similarly, if the recycle nitrogen is being used for cooling it may be necessary in response to a temperature controller (not shown) to supplement the recycle cooling with a conventional chiller.

Claims

A gas supply method for the operation of a plant in which semiconductors are made, including the steps of supplying liquid nitrogen to perform a cooling duty in or associated with the plant, recovering vaporised nitrogen from the cooling duty, and employing the vaporised nitrogen to perform a second duty in or associated with the plant.
2. A gas supply method as claimed in claim 1, wherein the cooling duty resides in cooling molecular beam epitaxy chamber.
3. A gas supply method as claimed in claim 1 or claim 2, wherein the secondary duty is the cooling of hot waste gas from another stage of the plant.
4. A gas supply method as claimed in claim 1 or claim 2, wherein the secondary duty is the dilution of waste gas from another stage of the plant.
5. A gas supply method as claimed in claim 1 or claim 2, wherein the secondary duty is the blanketing of vessel containing water.
6. A gas supply method as claimed in claim 1 or claim 2, wherein the secondary duty is the purging of gas from another stage of the plant.
7. A gas supply method as claimed in claim 1 or claim 2, wherein the secondary duty resides in the position of a non-reactive atmosphere in at least one other stage of the manufacturing plant.
8. A gas supply method as claimed in any one of the preceding claims, additionally including the step of compressing the vaporised ntirogen upstream. of the secondary duty.
9. A gas supply method as claimed in claim 9, wherein the compressed nitrogen is purified upstream of the secondary duty.
10. Apparatus for the supply of nitrogen to a plant for the manufacture of semiconductor devices including means for supplying liquid nitrogen to a manufacturing stage requiring cooling so as to cool said stage, means for recovering vaporised from said stage, and means for supplying the vaporised nitrogen to perform another duty in the plant.
11. Apparatus as claimed in claim 10, wherein the said manufacturing stage is a molecular team epitaxy stage.