Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
  • F04C29/0092—Removing solid or liquid contaminants from the gas under pumping, e.g. by filtering or deposition; Purging; Scrubbing; Cleaning
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
  • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C25/00—Adaptations of pumps for special use of pumps for elastic fluids
  • F04C25/02—Adaptations of pumps for special use of pumps for elastic fluids for producing high vacuum
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
  • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
  • F04C18/123—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with radially or approximately radially from the rotor body extending tooth-like elements, co-operating with recesses in the other rotor, e.g. one tooth
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
  • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
  • F04C18/126—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with radially from the rotor body extending elements, not necessarily co-operating with corresponding recesses in the other rotor, e.g. lobes, Roots type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2220/00—Application
  • F04C2220/30—Use in a chemical vapor deposition [CVD] process or in a similar process
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2280/00—Arrangements for preventing or removing deposits or corrosion
  • F04C2280/02—Preventing solid deposits in pumps, e.g. in vacuum pumps with chemical vapour deposition [CVD] processes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C23/00—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids
  • F04C23/001—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids of similar working principle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C23/00—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids
  • F04C23/005—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids of dissimilar working principle

Definitions

• the present invention relates to a method of pumping gas, and in particular to a method of pumping a gas stream comprising a light gas, such as hydrogen, and a condensable species.
• a light gas such as hydrogen
• a primary step in the fabrication of semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of vapour precursors.
• One known technique for depositing a thin film on a substrate is chemical vapour deposition (CVD).
• CVD chemical vapour deposition
• process gases are supplied to a process chamber housing the substrate and react to form a thin film over the surface of the substrate.
• Group Ul-V compound semiconductors are generally formed using a form of CVD usually known as MOCVD (metal organic chemical vapour deposition).
• MOCVD metal organic chemical vapour deposition
• this process involves reacting together volatile organometallic sources of the required group III with group V elements supplied from hydride gases such as AsH 3 and PH 3 .
• group V elements supplied from hydride gases such as AsH 3 and PH 3 .
• a thin film of GaInP may be formed on a suitable substrate material by supplying to a process chamber trimethyl gallium ((CH 3 ) 3 Ga) as the source of gallium, trimethyl indium ((CH 3 ) 3 ln) as the source of indium, and phosphine (PH 3 ) as the source of phosphorus.
• Hydrogen gas is generally also present, providing a carrier gas for the organometallic sources and any other process gases and to complete the reaction chemistry by mopping up dangling bonds.
• the residence time of the deposition gases in the processing chamber is relatively short, and only a small proportion of the gas supplied to the chamber is consumed during the deposition process. Consequently, much of the deposition gases supplied to the chamber is exhausted from the chamber together with by-products from the deposition process. If the unconsumed process gas or by-product is condensable, condensation on lower temperature surfaces can result in the accumulation of powder or dust within a vacuum pump used to draw the exhaust gases from the process chamber.
• the gas exhaust from the chamber will typically include relatively large amounts of hydrogen, phosphine and phosphorus vapour, and so there is a risk that the phosphorus vapour may condense as solid phosphorus within the pump and, over time, effectively fill the vacant running clearance between the rotor and stator elements of the pump, leading to a loss of pumping performance and ultimately pump failure.
• Epitaxial deposition processes are increasingly used for high-speed semiconductor devices, both for silicon and compound semiconductor applications.
• An epitaxial layer is a carefully grown, single crystal silicon film.
• Epitaxial deposition utilizes a silicon source gas, typically silane or one of the chlorosilane compounds, such as trichlorosilane or dichlorosilane, in a hydrogen atmosphere at high temperature, typically around 800 - 1100 0 C, and under a vacuum condition.
• Epitaxial deposition processes are often doped with small amounts of boron, phosphorus, germanium, arsenic, or carbon, as required, for the device being fabricated.
• Hydrogen chloride may also be used to clean the chamber between deposition runs.
• By-products of the epitaxial process tend to be compounds of silicon and chlorine, or compounds of silicon and hydrogen. These by-products may include chlorosilane polymers of the form Si x CIyH 2 . These polymers can be converted to self-ignitable or explosive materials, for example polysiloxanes, if exposed to moisture contained in the atmosphere.
• a light gas such as hydrogen
• condensable species such as phosphorus vapour or polymeric vapours.
• the present invention provides a method of pumping a gas stream containing a condensable species and a light gas, the method comprising the steps of conveying the gas stream to a multistage vacuum pump comprising an inlet stage and an exhaust stage downstream from the inlet stage, and adding to the gas stream upstream of or at the inlet stage a purge gas heavier than the light gas to both inhibit migration of the light gas from the exhaust stage towards the inlet stage and to inhibit condensation of the condensable species within the pump.
• the introduction of the purge gas into the gas stream also serves to reduce the partial pressure of condensable species, such as phosphorus vapour, ammonium chloride or polymeric vapours.
• condensable species such as phosphorus vapour, ammonium chloride or polymeric vapours.
• the purge gas is compressed with the gas stream as it passes through the pump from the inlet stage to the exhaust stage, generating heat.
• the additional heat generated by the compression of the purge gas serves to increase the temperature of the gas stream as it passes through the pump which, coupled with the reduction in partial pressure of the condensable species due to the presence of the purge gas, serves to inhibit condensation of the condensable species within the pump without the need to provide any external heating systems.
• the pump preferably has a relatively high volume ratio, that is, the ratio between the volume of the inlet stage of the pump and the volume of the exhaust stage of the pump is relatively high.
• the exhaust stage may have a volume at least three times smaller than that of the inlet stage, more preferably a volume at least five times smaller than that of the inlet stage.
• the present invention provides a method of pumping a gas stream containing a condensable species and a light gas having a flow rate of at least 20 slm, the method comprising the steps of conveying the gas stream to a multistage vacuum pump comprising an inlet stage and an exhaust stage having a volume at least three times smaller than the inlet stage, and adding to the gas stream upstream of or at the inlet stage a purge gas heavier than said light gas at a rate of at least 10 slm.
• the purge gas is preferably added to the gas stream at a rate of at least 20 slm.
• purge gas may also supplied to the pump between stages of the pump.
• purge gas may be supplied between the third stage and the fourth stage of the pump, and/or between the fourth stage and the fifth (exhaust) stage of the pump without condensation of condensable species within the pump.
• the further purge gas is preferably supplied at a flow rate of at least 20 slm.
• This invention is particularly suitable for use with a multistage vacuum pump comprising at least one, preferably a plurality of pumping stages which compress the gas stream, such as Northey (or "claw") pumping stages.
• Northey pumping stages are essentially self-valving, in that the back-migration of gaseous species such as nitrogen towards the pump inlet is inhibited by the Northey pumping mechanism, and so the introduction of purge gas at locations between stages of the pump does not affect the pressure at the inlet of the pump.
• the present invention provides a vacuum pumping arrangement for pumping a gas stream containing a condensable species and a light gas
• the pumping arrangement comprising a multistage vacuum pump comprising an inlet stage and an exhaust stage downstream from the inlet stage, and a purge gas supply for adding to the gas stream upstream of or at the inlet stage a purge gas heavier than the light gas to both inhibit migration of the light gas from the exhaust stage towards the inlet stage and to inhibit condensation of the condensable species within the pump.
• the present invention provides a vacuum pumping arrangement for pumping a gas stream containing a condensable species and a light gas having a flow rate of at least 20 slm, the pumping arrangement comprising a multistage vacuum pump comprising an inlet stage and an exhaust stage downstream from the inlet stage and having a volume at least three times smaller than the inlet stage, and a purge gas supply for adding to the gas stream upstream of or at the inlet stage a purge gas heavier than the light gas at a rate of at least 1O sIm.
• Figure 1 illustrates a multistage vacuum pump
• Figure 2 illustrates the variation of the partial pressure of phosphor with temperature (i) when purge gas is supplied only to the exhaust of a multistage vacuum pump and (ii) when some of the purge gas is supplied to the inlet stage of the pump of Figure 1.
• a multistage vacuum pump 10 comprises a stator 12 housing a multistage rotor assembly 14.
• the stator 12 comprises a plurality of transverse walls 16 which divide the stator 12 into a plurality of pumping chambers.
• the stator 12 is divided into five pumping stages, although the stator 12 may be divided into any number of pumping stages required to provide the pump 10 with the desired pumping capacity.
• the rotor assembly 14 comprises two intermeshing sets of rotor components 18, 20, 22, 24, 26, each set being mounted on a respective shaft 28, 30.
• the rotor components may have a Roots or a Northey (or "claw" profile).
• the rotor components 18 may have a Roots profile, with the other rotor components 20, 22, 24, 26 having a Northey profile.
• the sets of rotor components are preferably profiled in order to maintain a small running clearance between the faces of the rotor components and the facing surfaces of the stator 12.
• Each shaft 28, 30 is supported by bearings 32, 34 for rotation relative to the stator 12.
• the shafts 28, 30 are mounted within the stator 12 so that each pumping chamber houses a pair of intermeshing rotor components, which together provide a stage of the pump 10.
• a motor 36 is connected to one end of shaft 28.
• the other shaft 30 is connected to shaft 28 by means of meshed timing gears 38 so that the shafts 28, 30 are rotated synchronously but in opposite directions within the stator 12.
• the gears 38 are formed from magnetic material.
• a pump inlet 40 communicates directly with the inlet pumping stage, which comprises rotor components 18 and pump exhaust 42 communicates directly with the exhaust pumping stage, which comprises rotor components 26.
• Gas passageways 44, 46, 48, 50, 52 are provided within the pump 10 to permit the passage therethrough of pumped gas from the inlet 40 to the exhaust 42.
• the volume of the pumping chambers defined within the stator 12 decreases from the inlet pumping stage, which includes rotor components 18, to the exhaust pumping stage, which includes rotor components 26.
• the exhaust stage may have a volume at least three times smaller than that of the inlet stage, more preferably a volume at least five times smaller than that of the inlet stage.
• the pump 10 is particularly suitable for pumping a gas stream containing a light gas, such as hydrogen, and one or more condensable species, such as phosphorus vapour, ammonium chloride or polymeric vapours, typically output from a semiconductor or flat panel process chamber.
• a purge gas supply system 60 is provided for supplying purge gas, for example, nitrogen, to the pump 10.
• the purge gas supply system 60 comprises a manifold 62 having an inlet 64 and a plurality of outlets 66.
• the inlet 64 is connected to a source of purge gas, typically via a conduit including a check valve and optionally a pressure regulator for controlling the pressure of a stream of purge gas conveyed to the inlet 64.
• the received stream of purge gas typically passes through a mass flow transducer before being split into a plurality of streams for conveyance to the outlets 66.
• the manifold 62 may contain an arrangement of solenoid valves, fixed flow restrictors and/or variable flow restrictors for adjusting the flow rate of each stream of purge gas supplied to an outlet 66.
• the purge gas supply system 60 comprises a number of pipes each for conveying purge gas from a respective outlet 66 of the manifold 62.
• One of the pipes 68a conveys purge gas to a conduit 70 for conveying a gas stream to the inlet 40 of the pump 10 so that the purge gas mixes with the gas stream upstream of the inlet pumping stage.
• the pipe 68a may be configured to supply purge gas to a purge port of the pump 10 so that the purge gas is supplied directly to the inlet pumping stage, or to another location upstream from the inlet pumping stage.
• a second pipe 68b and a third pipe 68c convey purge gas to respective purge ports 72, 74 provided about the pump 10.
• the purge port 72 is located between the third and fourth pumping stages of the pump 10
• the purge port 74 is located between the fourth and fifth (exhaust) pumping stages of the pump 10.
• the pump 10 includes two purge ports, the pump 10 may be provided with any number of purge ports located at various locations about the pump 10.
• the purge gas can perform the dual roles of (i) inhibiting migration of the light gas from the exhaust pumping stage towards the inlet pumping stage and (ii) inhibiting condensation of the condensable species within the pump 10.
• the results of experiments to illustrate this will now be explained with reference to Figure 2.
• a gas stream containing 70 slm of hydrogen and 1 slm of phosphor was conveyed to a five stage Roots pump.
• a purge gas stream containing 55slm of nitrogen was conveyed to the exhaust of this pump.
• purge gas is typically conveyed to the exhaust so that the purge gas enters the pumping mechanism through back- migration of the purge gas without causing pressure fluctuations at the pump inlet.
• the phosphor partial pressure and the temperature of the gas stream were recorded at various different locations along the pump, and at the pump inlet and pump outlet. The recorded values were plotted on a graph having the phosphor partial pressure as the vertical axis and the temperature as the horizontal axis, as illustrated at line 78 in Figure 2.
• Line 80 in Figure 2 is the vapour phase equilibrium curve for phosphor, which defines the temperature and partial pressure at which phosphor will condense or sublime. Above the curve, phosphor vapour starts to condense to form as a solid.
• the additional heat generated by this compression serves to increase the temperature of the gas stream by around 10 0 C as it passes through the pump 10, maintaining the phosphor in the vapour phase as it passes through and is exhaust from the pump 10.
• the additional of nitrogen raises the average molecular size of the gas stream within the pump 10, which tends to inhibit the hydrogen migration towards the inlet stage of the pump 10 and enhance the hydrogen pumping efficiency.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Applications Or Details Of Rotary Compressors (AREA)
• Compressors, Vaccum Pumps And Other Relevant Systems (AREA)
• Chemical Vapour Deposition (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2005
  • 2005-09-28 GB GBGB0519742.1A patent/GB0519742D0/en active Pending
• 2006
  • 2006-09-06 US US11/992,454 patent/US20090269231A1/en not_active Abandoned
  • 2006-09-06 EP EP06779305A patent/EP1931880A1/en not_active Withdrawn
  • 2006-09-06 KR KR1020087007439A patent/KR20080049788A/ko not_active Ceased
  • 2006-09-06 JP JP2008532854A patent/JP2009510321A/ja active Pending
  • 2006-09-06 WO PCT/GB2006/003286 patent/WO2007036689A1/en not_active Ceased

Non-Patent Citations (1)

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