GAS SUPPLY APPARATUS

Abstract

An improved purge gas supply that is less susceptible to the shortcomings of known systems. The disclosure aims to reduce backflow or recirculation of pumped gases into the purge supply apparatus by providing an arrangement where the purge ports on a multistage vacuum pump contains purge gas at sufficient pressure to resist the backflow, particularly when the vacuum pump is operating outside of its ultimate pressure regime. Embodiments of the purge supply apparatus described herein do not necessarily need a non-return valve to resist the unwanted pump gas back-flow.

Claims

1. A multistage vacuum pump purge gas supply apparatus, comprising: a gas inlet in fluid communication with a plurality of gas outlets for supplying gas to respective purge ports of a multistage vacuum pump; and a flow controller disposed immediately upstream of the plurality of gas outlets, the flow controller comprising an input for receiving gas, a volume for containing gas at a given pressure, and a variable flow restrictor disposed between the volume and each of the plurality of gas outlets, wherein the variable flow restrictor is moveable with respect to the volume to facilitate continuous variance of the flow of gas in proportion to each gas outlet of the plurality of gas outlets, between a first and second flow rate, and wherein the variable flow restrictor comprises a first section arranged to connect the volume with each gas outlet of the plurality of gas outlets, wherein the first section is moveable with respect to the volume, the first section comprising a drum rotatable about a longitudinal axis, the drum comprising a series of through-holes each arranged to connect a corresponding gas outlet of the plurality of gas outlets with the volume.

2. The apparatus according to claim 1, wherein the variable flow restrictor is arranged to provide a continuous range of rates of flow between a first and second flow rate.

3. The apparatus according to claim 2, wherein the first flow rate is a predetermined maximum flow rate through the outlet.

4. The apparatus according to claim 2, wherein the second flow rate is a predetermined minimum flow rate, or wherein the second flow rate is zero.

5. The apparatus according to claim 1, wherein the first section is either rotatable or linearly moveable with respect to the volume.

6. The apparatus according to claim 1, wherein each through-hole cooperates with an aperture in the volume to allow gas to exit the volume such that movement of the first section relative to the volume enables provision of the continuous range of rates of flow between the first flow rate and the second flow rate.

7. The apparatus according to claim 1, further comprising control orifices arranged so that gas can be supplied to the respective purge ports at proportionally fixed gas flow rates.

8. A multistage vacuum pump purge gas supply apparatus, comprising: a gas inlet in fluid communication with a plurality of gas outlets for supplying gas to respective ports of the multistage vacuum pump; and a flow controller disposed immediately upstream of the plurality of gas outlets, the flow controller comprising an input for receiving gas, a manifold defining a volume for containing gas at a given pressure, and a variable flow restrictor disposed between the manifold and the plurality of gas outlets, wherein during operation, the pressure of the gas in the volume is higher than the pressure of the gas within any pump chambers of the multistage vacuum pump at any one of the ports of the multistage pump, and wherein the variable flow restrictor comprises a first section arranged to connect the volume with each gas outlet of the plurality of gas outlets, wherein the first section is moveable with respect to the volume, the first section comprising a drum rotatable about a longitudinal axis, the drum comprising a series of through-holes each arranged to connect a corresponding gas outlet of the plurality of gas outlets with the volume.

9. The apparatus according to claim 8, wherein the variable flow restrictor is arranged to provide a continuous range of rates of flow between a first and second flow rate.

10. The apparatus according to claim 9, wherein the first flow rate is a predetermined maximum flow rate through the outlet.

11. The apparatus according to claim 9, wherein the second flow rate is a predetermined minimum flow rate, or wherein the second flow rate is zero.

12. The apparatus according to claim 8, wherein the first section is either rotatable or linearly moveable with respect to the volume.

13. The apparatus according to claim 8, wherein each through-hole cooperates with an aperture in the volume to allow gas to exit the volume such that movement of the first section relative to the volume enables provision of the continuous range of rates of flow between the first flow rate and the second flow rate.

14. The apparatus according to claim 8, further comprising control orifices arranged so that gas can be supplied to the respective purge ports at proportionally fixed gas flow rates.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A preferred embodiment of the present disclosure will now be described, by way of example only, with reference to the accompanying Figures.

[0020] FIG. 1 is a schematic diagram of a known pump system comprising a purge gas supply.

[0021] FIG. 2 is a schematic diagram of an embodiment of a purge gas supply apparatus embodying the present disclosure.

[0022] FIG. 3 is another schematic diagram of an embodiment of the present disclosure.

[0023] FIG. 4 is a schematic diagram of an alternative embodiment of the present disclosure.

[0024] FIG. 5 is a schematic flow diagram of another alternative embodiment of the present disclosure.

DETAILED DESCRIPTION

[0025] A schematic overview of a pump system 1 in fluid communication with a processing tool 3 is shown schematically in FIG. 1. The pump system 1 is coupled to a variable purge system 5 operable in accordance with the present disclosure.

[0026] The vacuum pump system 1 comprises a multistage vacuum pump 7 having a pump inlet 9, a pump (exhaust) outlet 11 and a plurality of purge ports 13. An electric pump motor 15 drives the vacuum pump 7 in response to control signals from a system controller 17. The system controller 17 comprises a digital processor (not shown) configured to measure the operating current of the pump motor 15 to monitor the status of the vacuum pump 7.

[0027] In the present embodiment, the processing tool 3 is a chemical vapour deposition apparatus comprising a vacuum chamber (not shown), but of course the disclosure is not limited to CVD apparatuses and can be applied to other processes or applications. The vacuum chamber is in fluid communication with the pump inlet 9 via a foreline 19. A gas sensor 21 can be provided in the foreline 19 to detect the type of gas present in the pump inlet 9 and to output a corresponding gas detection signal to the system controller 17.

[0028] The variable purge system 5 comprises a manifold 23 having a purge gas inlet 25 and a plurality of purge gas outlets, each connected to a port 13. Operation of the manifold 23 is controlled by the system controller 17. In this example purge ports 13 are provided for the ¾ interstage purge, ⅘ interstage purge, low vacuum (LV), shaft seal (SS) and exhaust (Exh) stage of the vacuum pump 7. The purge gas is typically nitrogen (N2).

[0029] Typically, in a known system, the rate of flow into the multi-stage vacuum pump is set to customer requirements during the manufacture and commissioning phases. It is usual to set the purge gas supply rate according to the requirements of the pump whilst it is running on a process cycle at its ultimate attainable pressure (the condition known as “running at ultimate”). Running in this condition reactive process gases from the process chamber evacuated by the pump pass through the pump, hence the need for a purge gas to improve the service lifetime of the pump.

[0030] However, the purge module might not be suitable for supplying purge gas to the pump during running conditions outside of the ultimate condition, for instance during a pump down phase (so-called “roughing”) when the pressures of gases inside the pump chambers can be greatly increased. As a result, the pressure of purge gas can be overcome at the purge port and pumped gases might escape the pump volume and enter the purge gas module with undesirable consequences. Embodiments of the present inventive concept aim to reduce the risk of unwanted purge gas module contamination without the need to use additional non-return valves (which are considered to be an expensive solution to this problem).

[0031] Once set, a variable flow restrictor on a known system is left in position and not adjusted further. Thus, the predetermined flow of gas is determined by the size of these orifices and the pressure drop across them. If the gas pressure upstream of the orifices is insufficient then process gas passing through the pump can enter the purge gas supply system and recirculate within the purge apparatus. This is highly undesirable for many reasons, not least because particles in the process gas might block or restrict flow orifices, or corrosive gas can enter the purge system causing damage or malfunctioning of the purge supply.

[0032] FIG. 2 shows an embodiment of purge gas supply module 35 that embodies the present inventive concept. The module comprises an inlet 36 for receiving a supply of purge gas, typically nitrogen from a suitable source. A non-return valve 38 ensures gas cannot leak from the module inlet. A regulator 40 is used to measure and control flow of gas into the module and regulate the pressure within the system. The flow line then splits into two lines 41 and 42, whereby a first purge line 41 is used to supply gas to the inter-stage purge ports of the multi-stage vacuum pump and a second purge line 42 supplies gas to the shaft seal (SS) and exhaust port (Exh). In this example, there are three inter-stage purge ports, located between the fourth and fifth stage, fifth and sixth stage, and the six and seventh stages respectively. A plurality of fixed flow restrictor orifices 43 are used on each of the module to enable proportional flow of gas at different rates to the purge ports according to the requirements stipulated for efficient purge supply. Valves 45 and 47 are disposed on each line of the gas supply to enable the line to isolated from the supply if needs be.

[0033] The gas supply line 41 splits into three branches 41A, 41B and 41C upstream of a variable flow restrictor 50. The variable flow restrictor 50 is used to vary the flow of gas to all of the fixed restrictors 43 that supply purge gas to the inter-stage purge ports and the variable flow restrictor is located immediately upstream of fixed restrictor orifices and the inter-stage purge ports. The variable restrictor 50 comprises adjustment device 51 that is linked to all of the flow valves within the variable restrictor 50 such that a single adjustment is used to adjust the flow of gas to all the inter-stage purge ports supplied by the variable restrictor. This adjustment device can be manually or computer operated according to the desired needs of the purge system.

[0034] This arrangement provides a pressure drop across the flow restrictor arrangement such that the pressure of gas upstream of the fixed restrictors 43 (that is, immediately downstream of the variable restrictor 50) is sufficient to limit recirculation of gases being pumped by the vacuum pump. Furthermore, the pressure of gas upstream of the variable restrictor 50 is determined at least in part by the regulator and can be arranged to limit or prevent backflow of process gas from the pump into the purge system to a location within the purge system that could facilitate recirculation of process gases. In other words, the provision of a system according to the arrangement shown in FIG. 2 uses the purge supply pressure to reduce the risk process gas entering the purge system and passing through the orifices 43, variable controller 50 and three supply lines 41A-C to a location (single supply line 41) where the process gas could mix and recirculate with gas along a different line to the one that had allowed the process gas ingression to occur. The flow can be deduced from pressure gauge readings taken from gauges 52 and 54 disposed either side of the variable flow restrictor, although these gauges are not essential to the operation of the system but do provide useful readings for evaluation of the system's performance.

[0035] FIG. 3 shows a first embodiment 100 of the present inventive concept, comprising a gas supply assembly 102. The assembly comprises a single inlet 104 to receive purge gas from the mass flow controller 40, and three outlets 106, 108 and 110, respectively. Each of the outlets is coupled to the appropriate respective purge port of the multi-stage vacuum pump. The fixed orifices 43 are located upstream of the outlets. The inlet opens into a manifold volume 112 where the purge gas can be maintained at a given purge supply pressure. The flow of gas to the ports is controlled by a flow adjustor barrel 114 that comprises three through holes 116. Each through hole is supplied by lines 41A, 41B and 41C respectively, which are in gas communication with the manifold 112. The through holes pass through the barrel in a radial direction and each is arranged to cooperate with one of three apertures provided by the opening of the respective supply line 41A-C.

[0036] The flow is controlled by rotating the adjustor barrel relative to the volume. Full flow is achieved when each of the through holes co-axially aligned with a respective aperture or supply line. The flow can be reduced by twisting the barrel so that the through holes and supply lines are now misaligned slightly thereby restricting gas flow through the through hole. The flow can be stopped completely if the barrel is twisted to an angle where the through holes no longer align with the supply lines and the passage for the gas is completely obstructed as a result. Thus, a continually variable flow of gas can be achieved through the restrictor, across a range of flows having a maximum flow rate and zero.

[0037] This embodiment has certain advantages over the known systems because the manifold provides a volume of pressurised gas close to the purge port on the pump. As a result, the purge gas supply module can be set up to provide optimal flow rates of purge gas when the pump is running at ultimate (that is, during low pressure operation) and to reduce or prevent ingression of pumped gas into the purge module when the pump is operating during roughing or pump down (that is during high pressure operation). The volume 112 can be arranged to hold gas at sufficient pressure such that purge gas can flow into the pump ports at the required rates during ultimate operation, but gas from the pump cannot flow into the purge module unless it overcomes the pressure of gas within the volume during other operating conditions.

[0038] FIG. 4 shows an alternative embodiment 145 of the present disclosure. In this embodiment, the volume 112 is provided as before, upstream of a series of flow restrictors 146. In this embodiment the restrictors comprise a needle valve arrangement consisting of an aperture 148 arranged to cooperate with a pin or stop 150 having a tapered point section. The effective size of the aperture (and hence the flow rate of gas through it) is controlled by varying how far the tapered section is inserted into the aperture. When the tapered section is outside of the aperture, then the flow of purge gas through the aperture is effectively determined by the size of the aperture. However, as the tapered section is moved into the aperture, so the effective size of the aperture is reduced in a continuous manner until the aperture physically engages with the tapered section and is closed thereby restricting flow through the aperture to zero.

[0039] In the embodiment shown there are four needle valve arrangements, each being connected to a purge port respectively (B, C, D and E). The valves can be pre-adjusted independently to determine the respective flow rates with respect to the two valve arrangements. A frame or mechanism 155 is provided to allow relative movement of the apertures and needles so that the overall flow of gas through to the outlets and purge ports can also be controlled. Hence, once set, the flow of gas through the system can be controlled by moving the needles relative to the apertures as indicated by arrows A or Z. This can be achieved by providing a manual control means, such as a twistable (156) threaded jack, or an electromechanical arrangement comprising a servo with appropriate drive and control means.

[0040] FIG. 5 is a schematic diagram of a purge system 200 incorporating the second embodiment described above, or any alternative system that embodies the present inventive concept. In this arrangement, the features common to other systems described above have been provided with the same reference numerals. The system in FIG. 5 is similar to one shown in FIG. 2, however the fixed orifices 43 disposed between the purge port and variable regulator 50 in FIG. 2 are not required in the FIG. 5 embodiment. The function of the fixed orifices has been incorporated into the orifices 51A, 51B and 51C used in the variable flow regulator arrangement. The second embodiment described above and shown in FIG. 4 can easily incorporate this arrangement whereby the apertures 148 are designed to provide the same function as the fixed aperture orifices 43 used in other embodiments.

[0041] Alternative embodiments of the present disclosure will be envisaged by the person skilled in the technical field without departing from the general inventive concept. For example, the first embodiment can comprise a sliding barrel as an alternative to the rotating barrel. As the barrel is slid in direction along its major axis the through-holes are no longer coaxially aligned with the apertures and so flow is restricted or reduced from a maximum amount. The amount of misalignment can be adjusted continuously and smoothly through a range of flow rates from zero to a maximum flow when coaxial alignment is achieved.