Apparatus for preventing or removing deposits of process gases, vacuum pump system and method

Abstract

Apparatus 120 for, and a method of, preventing or removing deposits of process gases from a vacuum pump assembly 110. The vacuum pump assembly comprises at least one first vacuum pump 111-115 having a

Description

24 07 24 APPARATUS FOR PREVENTING OR REMOVING DEPOSITS OF PROCESS GASES, VACUUM PUMP SYSTEM AND METHOD FIELD OF THE INVENTION The field of the invention relates to vacuum pumps, and more specifically to apparatuses and methods for preventing or removing deposits of process gases from vacuum pumps. BACKGROUND Vacuum pumps are typically employed as a component of a vacuum system to evacuate working gases from the system. These pumps can be used to evacuate fabrication equipment used in, for example, the production of semiconductors. Whilst compression from a vacuum to atmosphere may be performed in a single stage using a single pump, it is common in such applications to provide multi-stage vacuum pumps wherein each stage performs a portion of the compression range required to transition from a vacuum to atmospheric pressure. Vacuum pumps may include dry pumps and booster pumps. Deposition of process by-products is one of the critical factors determining the lifetime of a vacuum pump. Deposits on rotors and stators may comprise solid particulate deposits or scale-type deposits. When the thickness of such deposits increases the clearance between the rotor and stator components is reduced, ultimately to a point where rotor and stator meet and the vacuum pump operation is ceased. This tends to be one of the most frequent failure modes of dry vacuum pumps. Such a problem is particularly pertinent in semiconductor manufacturing and fabrication. Unexpected byproducts of the semiconductor manufacturing and fabrication could be deposited in the process gas path which includes in the pump chambers, in any interconnecting pipework and in the exhaust pipework. It follows that a vacuum pump assembly typically requires frequent servicing. Indeed, a typical servicing frequency may see a vacuum pump 24 07 24 assembly serviced ten times across its lifetime. A significant time and cost saving can therefore be achieved if servicing can be reduced and the lifetime of a vacuum pump be increased. Hence, it is desirable to provide apparatuses and methods that mitigate these issues. SUMMARY OF THE INVENTION In a first aspect, there is provided an apparatus for preventing or removing deposits of process gases from a vacuum pump assembly, the vacuum pump assembly comprising at least one first vacuum pump having a first inlet for receiving process gases and a first outlet connected to an exhaust through which the process gases are exhausted, wherein the apparatus comprises: at least one second vacuum pump having a second inlet and a second outlet; connecting means for connecting the second inlet of the at least one second vacuum pump to the exhaust of the vacuum pump assembly or directly to the at least one first vacuum pump; and controller means for controlling the at least one second vacuum pump to evacuate the vacuum pump assembly, such that deposits of the process gases can be prevented in or removed from the vacuum pump assembly. The controller means is configured to: deactivate the at least one second vacuum pump from evacuating the vacuum pump assembly when the at least one first vacuum pump is in an on-duty mode wherein it is receiving process gases; and activate the at least one second vacuum pump to evacuate the vacuum pump assembly when the at least one first vacuum pump is in an off-duty mode wherein it is not receiving process gases. The inventor has realised that whilst prior art systems and methods focus on minimising process gas deposits from establishing in a vacuum pump assembly, less focus has been placed on the actual physical removal of deposits that do form. Deposits from process gases can be induced to evaporate or sublimate if they are subjected to appropriate conditions. In a typical vacuum pump, 24 07 24 particularly multi-stage vacuum pumps, the pressures in later pump stages (i.e., pump stages closer to the outlet) are not sufficiently low to encourage evaporation or sublimation to occur. This is despite the corresponding stator and rotor components being relatively ‘hot’ in respect of their temperatures. An 5 option would be to replace legacy vacuum pumps with pumps that operate at much higher temperatures, to encourage sublimation or evaporation of deposits, or prevent deposits occurring at all. However, such an approach may be cost prohibitive and relatively disruptive for systems already installed at an installation location. 10 By connecting the at least one second vacuum pump to the exhaust and evacuating the vacuum pump assembly, the pressure in the vacuum pump assembly and particularly in the at least one first vacuum pump, can be drastically reduced. The deposits of process gases thereby tend to be provided with conditions allowing greater evaporation and sublimation. Evaporation and 15 sublimation of the deposits can thus be induced leading to their subsequent removal from the assembly through the at least one second vacuum pump. The removal of deposits tends to be achieved without the need to dismantle, service, or replace the vacuum pump assembly itself, which may already be preinstalled at an installation location (such as a customer 20 premises). Instead, the apparatus can be retrofitted to preinstalled or preexisting vacuum pump assemblies achieving less overall disruption. Furthermore, the removal of deposits tends to enable the lifetime of the vacuum pump assembly and its constituent components to be prolonged, with improved servicing intervals. 25 The controller means may comprise a controller comprising at least one memory coupled to at least one processor, the at least one memory comprising instructions which when executed by the at least one processor cause the controller to control the at least one second vacuum pump to evacuate the vacuum pump assembly, such that deposits of the process gases can be 30 removed from the vacuum pump assembly. The at least one second vacuum pump may be considered as Toughing’ or ‘sucking’ the exhaust. 24 07 24 The activation and deactivation ensures that the second vacuum pump / s do not affect normal operation of the vacuum pump assembly when the vacuum pump assembly is operating with process gases. Again, this tends to offer a solution for preventing and / or removing deposits that can be retrofitted to 5 preexisting / deployed vacuum pump assemblies. In some embodiments, the connecting means for connecting the second inlet to the exhaust of the vacuum pump assembly comprises a first valve means, the first valve means being configured to be operable between a first configuration (optionally when the at least one first vacuum pump is in the onio duty mode), and a second configuration (optionally when the at least one first vacuum pump is in the off-duty mode), wherein: the first configuration provides a first flow path that bypasses the at least one second vacuum pump; and the second configuration provides a second flow path through the at least one second vacuum pump. 15 By providing the valve means, the at least one second vacuum pump is not exposed to exhausted process gases when the at least one first vacuum pump is in the on-duty mode. Hence the build-up of process gas deposits in the at least one second vacuum pump can be mitigated. This tends to allow for the at least one second vacuum pump to have a greater lifespan and / or improved 20 service interval. In some alternative embodiments, the at least one second vacuum pump may be connected directly in-line with the exhaust. In these alternative embodiments, less components are required but the at least one second vacuum pump is continuously exposed to exhausted process gases when the at 25 least one first vacuum, pump is in the on-duty and off-duty modes. This can lead to an increased rate of build-up of deposits in the at least one second vacuum pump, however this can be mitigated by providing a second vacuum pump that operates at a higher temperature (for instance through the removal of cooling or addition of heater elements). The additional temperature can further 30 assist with evaporating or sublimating deposits (in this instance, within the at least one second vacuum pump). 24 07 24 The valve means may be a single valve or a plurality of valves. The connecting means may further comprise interconnecting pipework. In some embodiments, the at least one second vacuum pump comprises a plurality of second vacuum pumps. 5 In some embodiments, the at least one second vacuum pump may comprise a high-vacuum pump. For example, in some embodiments, the at least one second vacuum pump comprises a turbomolecular pump. Some embodiments comprise heating means for heating the at least one second vacuum pump. 10 The heating means may comprise one or more heater elements. The heating means may comprise means for disabling cooling components provided with the second vacuum pump. By heating the at least one second vacuum pump, conditions for evaporation or sublimation of process gas deposits, within the second vacuum pump, can be improved. This tends to further assist in 15 mitigating deposition within the at least one second vacuum pump. By way of example, the at least one second vacuum pump may be heated to 100°C, 200 °C, 500 °C, or any temperature therebetween. Some heating will naturally occur owing to the compression of gases during operation of the at least one second vacuum pump. 20 In some embodiments, the at least one second vacuum pump is configured to evacuate the vacuum pump assembly to a pressure in the range 0.1 Pa - 0.001 Pa. A pressure of 0.1 Pa (equivalently 0.001 mbar) can be achieved with a single vacuum pump of a plurality of different types. A pressure of 0.001 Pa 25 (equivalently 10-5mbar) can be achieved with high vacuum pumps (i.e., turbomolecular pumps). Certain turbomolecular pumps or combinations of pumps may be able to achieve pressures lower than 0.001 Pa. According to a second aspect, there is provided a vacuum pump system comprising: a vacuum pump assembly comprising at least one first vacuum 30 pump having a first inlet for receiving process gases and a first outlet connected to an exhaust through which the process gases are exhausted; and the 24 07 24 apparatus of the first aspect, wherein the second inlet of the at least one second vacuum pump is connected to the exhaust of the vacuum pump assembly or directly to the at least one first vacuum pump. In some embodiments, the at least one first vacuum pump comprises a 5 plurality of first vacuum pumps. In some embodiments, the at least one first vacuum pump comprise dry pumps. Deposition can cause failure of dry pumps that comprise multiple pump stages. This is because, in later pump stages (that is, pump stages closer to the 10 outlet), the pressure within the pump stage is not low enough to allow for evaporation or sublimation of process gas deposits. Indeed, in such later pump stages pressures of 100,000Pa can be experienced (equivalently WOOmbar). In some embodiments, the at least one first vacuum pump is configured to operate continuously. 15 By ensuring the at least one first vacuum pump operates continuously, the natural compression of gases by the pumps causes a heating of the stator and rotor components. This further enables evaporation and / or sublimation when the at least one second vacuum pump evacuates the vacuum pump assembly. Furthermore, any heaters will continue to operate to maintain a set 20 temperature of the at least one vacuum pump. In some embodiments, the first inlet is connected to a semiconductor manufacturing apparatus. Semiconductor manufacturing and fabrication create harsh / corrosive conditions and can feature process gases including chlorine gas and fluoride 25 gas. Substantial deposits can form in vacuum pump assemblies that include but are not limited to bypass products of the manufacturing and fabrication processes. It is considered that the claimed apparatus and vacuum pump system are particularly applicable to semiconductor manufacturing and fabrication. Alternatively, the apparatus and vacuum pump system may be 30 applicable to degassing applications. 24 07 24 According to a third aspect, there is provided a method of preventing or removing deposits of process gases from a vacuum pump assembly, the vacuum pump assembly comprising at least one first vacuum pump having a first inlet for receiving process gases and a first outlet connected to an exhaust 5 through which the process gases are exhausted, wherein the method comprises: providing the apparatus of the first aspect, wherein the second inlet of the at least one second vacuum pump is connected to the exhaust of the vacuum pump assembly or directly to the at least one first vacuum pump using the connecting means; and controlling the at least one second vacuum pump to 10 evacuate the vacuum pump assembly, such that deposits of the process gases can be prevented in or removed from the vacuum pump assembly. In some embodiments, the controlling the at least one second vacuum pump comprises: deactivating the at least one second vacuum pump from evacuating the vacuum pump assembly when the at least one first vacuum 15 pump is in an on-duty mode wherein it is receiving process gases; and activating the at least one second vacuum pump to evacuate the vacuum pump assembly when the at least one first vacuum pump is in an off-duty mode wherein it is not receiving process gases. It will be appreciated that particular features of different aspects of the 20 invention tend to share the technical effects and benefits of corresponding features of other aspects of the invention. More specifically, the methods described herein share the same technical benefits as the apparatus and vacuum pump system described herein. It will also be appreciated that the use of the terms “first” and “second”, 25 and the like, are merely intended to help distinguish between similar features and are not intended to indicate a relative importance of one feature over another, unless otherwise specified. 30 BRIEF DESCRIPTION OF THE DRAWINGS 24 07 24 The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1A shows an example of a vacuum pump system; Figure 1B shows the vacuum pump system of Figure 1A in an on-duty 5 mode; Figure 1C shows the vacuum pump system of Figure 1A in an off-duty mode; Figure 2A shows an example of a method of removing deposits of process gases from a vacuum pump assembly; and 10 Figure 2B shows the method of Figure 2A in greater detail. DETAILED DESCRIPTION Figure 1A shows an example of a vacuum pump system 100 in schematic form. The vacuum pump system 100 comprises a vacuum pump 15 assembly 110 and an apparatus 120 for removing deposits of process gases from the vacuum pump assembly 110. The vacuum pump assembly 110 comprises a plurality of first vacuum pumps 111-115. Each first vacuum pump 111-115 has a respective first inlet 111 a-115a for receiving process gases. Each first vacuum pump 111-115 has a 20 respective first outlet 111 b-115b connected to an exhaust 116 through which the process gases are exhausted. The exhaust 116 is illustrated as comprising a plurality of pipes connected to the plurality of first outlets 111 b-115b that converge to a single pipe connected to abatement 130. The vacuum pump assembly 110 may be considered a preinstalled or deployed assembly at a 25 customer premises. For instance, vacuum pump assembly 110 may be connected to a semiconductor fabrication apparatus (not shown). Each first vacuum pump 111-115 is a dry pump. More specifically each first vacuum pump 111-115 is a multi-stage dry pump comprising a plurality of pump chambers arranged between a respective first inlet 111 a-115a and first 30 outlet 111 b-115b. 24 07 24 The apparatus 120 may be considered to have been retrofitted to the existing vacuum pump assembly 110. The apparatus 120 comprises at least one second vacuum pump 121 having a second inlet 121a and a second outlet 121b. Connecting means 122, 123 connects the second inlet 121a of the at 5 least one second vacuum pump 121 to the exhaust 116 of the vacuum pump assembly 110. The connecting means 122, 123 comprises pipework 122 and a first valve means 123. The second vacuum pump 121 is a “hotter” pump relative to the first vacuum pump / s 111-115. Put differently, the second vacuum pump 121 operates at a higher temperature than the first vacuum pump / s 111-115 to 10 mitigate deposition. The first valve means 123 defines a junction of the pipework 122 and exhaust 116. More specifically the first valve means 123 comprises a valve configured to be operable between a first configuration when the at least one first vacuum pump 111-115 is in an on-duty mode, and a second configuration 15 when the at least one first vacuum pump 111-115 is in an off-duty mode. In the first configuration a first flow path is provided that bypasses the at least one second vacuum pump 121. In the second configuration a second flow path is provided through the at least one second vacuum pump 121. The first and second configurations and the on and off duty modes will be described in 20 greater detail with respect to Figures 1B-1C. Further shown in the example 100 as part of apparatus 120 are further pipework 124 and second valve means 125. These provide connecting means for connecting the second outlet 124 of second vacuum pump 121 to the abatement 130 further downstream along the exhaust 116. The operation of the 25 second valve means 125 is similar to the first valve means 123 and hence will not be discussed in further detail. The apparatus 120 also comprises a controller means (not shown) for controlling the at least one second vacuum pump 121 to evacuate the vacuum pump assembly 110, such that deposits of the process gases can be removed 30 from the vacuum pump assembly 100. The controller means may comprise a controller having at least one memory and at least one processor coupled to the at least one memory. The at least one memory may comprise instructions which 24 07 24 when executed by the at least one processor cause the controller to control the at least one second vacuum pump 121. The operation of the vacuum pump system 100 will now be further described with respect to Figures 1B and 1C. 5 Figure 1B shows the example 100 of Figure 1A when the first vacuum pumps 111-115 are in the on-duty mode. In the on-duty mode the first vacuum pumps 111-115 are receiving process gases at their respective first inlets 11 la-115a and pumping said gases through their first outlets 111 b-115b to exhaust 116. The first valve means 123 and second valve means 125 are in the first 10 configuration whereby a first flow path 140 for the process gases is shown as bypassing the at least one second vacuum pump 121. The first flow path 140 takes the exhaust process gases directly to abatement 130. No gases flow through second vacuum pump 121. As shown in Figure 1B, the apparatus 120 is not interfering with the 15 normal operation of the vacuum pump assembly 110 when operating ‘on-duty’ and evacuating process gases from semiconductor fabrication apparatus connected at the first inlets 111a-115a. During the ‘on-duty’ operation, deposition of the process gases occurs in the first vacuum pumps 111-115. More specifically, deposits are formed on the stator components and rotor 20 components in the first vacuum pumps 111-115 that if left would build-up over time and stop the first vacuum pumps 111-115 from operating resulting in operational efficiency issues. Furthermore, when the first vacuum pumps 111-115 are in the ‘on-duty’ mode of Figure 1B, the controller means (not shown) deactivates the at least 25 one second vacuum pump 121 from evacuating the vacuum pump assembly 110. Figure 1C shows the example 100 of Figure 1A when the first vacuum pumps 111-115 are in the off-duty mode. In the off-duty mode the first vacuum pumps 111-115 are running but not receiving process gases at their respective 30 first inlets 111 a-115a. The first valve means 123 and second valve means 125 are in the second configuration whereby a second flow path 150 is shown as passing through the at least one second vacuum pump 121 from the exhaust 24 07 24 116 via first valve means 123 and back to exhaust 116 via second valve means 125 and to abatement 130. No flow path is provided directly from exhaust to abatement 130. Furthermore, when the first vacuum pumps 111-115 are in the ‘off-duty’ 5 mode of Figure 1C, the controller means (not shown) activates the at least one second vacuum pump 121 to evacuate the vacuum pump assembly 110. The operation of the second vacuum pump 121 reduces the pressure in the first vacuum pumps 111-115, inducing evaporation and / or sublimation of deposits from process gases. Hence the deposits are effectively removed and 10 transported via the second vacuum pump 121 to abatement 130. The pressure at first vacuum pumps 111-115 may be 0.001 Pa or less. By provided a relatively ‘hot’ second vacuum pump 121, redeposition in second vacuum pump 121 can be mitigated. However, even in embodiments where redeposition occurs in second vacuum pump 121 and the second vacuum pump 121 requires 15 subsequent replacement or servicing, this still tends to be less disruptive and more economical than replacing or servicing vacuum pump assembly 110. Figure 2A shows an example of a method 200 of removing deposits of process gases from a vacuum pump assembly. The vacuum pump assembly may be the vacuum pump assembly 110 shown in Figures 1A-1C, comprising at 20 least one first vacuum pump 111-115 having a first inlet 111 a-115a for receiving process gases and a first outlet 111 b-115b connected to an exhaust 116 through which the process gases are exhausted. The method 200 comprises a first step 210 of providing the apparatus of the first aspect. The apparatus may be the apparatus 120 shown in Figures 1A-25 1C comprising at least one second vacuum pump 121 having a second inlet 121a and a second outlet 121b; connecting means 122, 123 for connecting the second inlet 121a of the at least one second vacuum pump 121 to the exhaust 116 of the vacuum pump assembly 110; and controller means for controlling the at least one second vacuum pump 121 to evacuate the vacuum pump assembly 30 110, such that deposits of the process gases can be removed from the vacuum pump assembly 110. 24 07 24 The method 200 comprises the further step 220 of controlling the at least one second vacuum pump 121 to evacuate the vacuum pump assembly 110, such that deposits of the process gases can be removed from the vacuum pump assembly 110. 5 Figure 2B shows the method 200 of Figure 2A in greater detail. More specifically, the step 220 of controlling the at least one second vacuum pump 121 comprises sub-steps 222 and 224. The sub-step 222 comprises deactivating the at least one second vacuum pump 121 from evacuating the vacuum pump assembly 110 when the 10 at least one first vacuum pump 111-115 is in an on-duty mode wherein it is receiving process gases. The sub-step 224 comprises activating the at least one second vacuum pump 121 to evacuate the vacuum pump assembly 110 when the at least one first vacuum pump 111-115 is in an off-duty mode wherein it is not receiving 15 process gases. Whilst specific embodiments described herein may show single vacuum pumps, this is not intended to be limiting. The first vacuum pump or second vacuum pump may comprise respective pluralities of vacuum pumps. The first vacuum pumps may be referred to herein as multi-stage or 20 multi-chamber dry pumps owing to the problem of deposition being pertinent with such pump designs. However, the apparatus described herein may equally operate to remove deposits from other pump types. It will be appreciated that the embodiments and drawings are shown by way of example only. Dimensions or sizing are not intended to be limiting. 25 Appropriate pump sizes, pipe sizes, materials and compositions will be determined according to the application with which a vacuum pump assembly is associated or deployed. Whilst the embodiments described herein refer to an apparatus for removing deposits of process gases, the apparatus may also be suitable for 30 preventing deposition of or build-up of deposits from process gases. This tends to be because the apparatus provides the appropriate conditions for sublimation 24 07 24 and / or evaporation. In this regard, the disclosure herein further provides: apparatus for preventing deposits of process gases in a vacuum pump assembly, the vacuum pump assembly comprising at least one first vacuum pump having a first inlet for receiving process gases, and a first outlet 5 connected to an exhaust through which the process gases are exhausted, wherein the apparatus comprises: at least one second vacuum pump having a second inlet and a second outlet; connecting means for connecting the second inlet of the at least one second vacuum pump to the exhaust of the vacuum pump assembly or directly to the at least one first vacuum pump; and controller 10 means for controlling the at least one second vacuum pump to evacuate the vacuum pump assembly, such that deposits from process gases are prevented in the vacuum pump assembly. The at least one second vacuum pump may be operable to evacuate the first vacuum pump whilst the first vacuum pump is on-duty. 15 Whilst the embodiments described herein refer to connecting means for connecting the second inlet of the at least one second vacuum pump to the exhaust of the vacuum pump assembly, alternative embodiments are envisaged wherein the connecting means is for connecting the second inlet of the at least one second vacuum pump directly to a pump chamber or pump mechanism of 20 the vacuum pump assembly. By way of example, a vacuum pump assembly may comprise a vacuum pump having an inlet and an outlet and one or more pump stages / chambers arranged between the inlet and the outlet. An access port or conduit may be provided to the one or more pump stages / chambers to which the connecting means may connect. The connecting means may 25 alternatively connect directly to the first outlet of the at least one first vacuum pump. This would allow the one or more pump stages / chambers to be connected directly to the second vacuum pump without a requirement to connect through the exhaust. 30 Reference numeral list 100 Vacuum pump system 24 07 24 110 Vacuum pump assembly 111-115 First vacuum pumps 111 a-115a First inlets 111b-115b First outlets 5 116 Exhaust 120 Apparatus 121 Second vacuum pump 121a Second inlet 121b Second outlet 10 122 Pipework 123 First valve means 124 Further pipework 125 Second valve means 130 Abatement 15 140 First flow path 150 Second flow path 200 Method 210 First method step 220 Further method step 20 222 Sub-step of method 224 Sub-step of method

Claims

1. Apparatus for preventing or removing deposits of process gases from a vacuum pump assembly, the vacuum pump assembly comprising at least one first vacuum pump having a first inlet for receiving process gases, and a first outlet connected to an exhaust through which the process gases are exhausted, wherein the apparatus comprises:at least one second vacuum pump having a second inlet and a second outlet;connecting means for connecting the second inlet of the at least one second vacuum pump to the exhaust of the vacuum pump assembly or directly to the at least one first vacuum pump; andcontroller means for controlling the at least one second vacuum pump to evacuate the vacuum pump assembly, such that deposits of the process gases can be prevented in or removed from the vacuum pump assembly;wherein the controller means is configured to:deactivate the at least one second vacuum pump from evacuating the vacuum pump assembly when the at least one first vacuum pump is in an on-duty mode wherein it is receiving process gases; andactivate the at least one second vacuum pump to evacuate the vacuum pump assembly when the at least one first vacuum pump is in an off-duty mode wherein it is not receiving process gases.

2. The apparatus of claim 1, wherein the connecting means for connecting the second inlet to the exhaust of the vacuum pump assembly comprises a first valve means, the first valve means being configured to be operable between a first configuration and a second configuration, wherein:the first configuration provides a first flow path that bypasses the at least one second vacuum pump; andthe second configuration provides a second flow path through the at least one second vacuum pump.

3. The apparatus of any preceding claim, wherein the at least one second vacuum pump comprises a plurality of second vacuum pumps.

4. The apparatus of any preceding claim, wherein the at least one second vacuum pump comprises a turbomolecular pump.

5. The apparatus of any preceding claim, further comprising heating means for heating the at least one second vacuum pump.

6. The apparatus of any preceding claim, wherein the at least one second vacuum pump is configured to evacuate the vacuum pump assembly to a pressure in the range 0.1 Pa - 0.001 Pa.

7. A vacuum pump system comprising:a vacuum pump assembly comprising at least one first vacuum pump having a first inlet for receiving process gases, and a first outlet connected to an exhaust through which the process gases are exhausted; andthe apparatus of any preceding claim, wherein the second inlet of the at least one second vacuum pump is connected to the exhaust or directly to the at least one first vacuum pump.

8. The vacuum pump system of claim 7, wherein the at least one first vacuum pump comprises a plurality of first vacuum pumps.

9. The vacuum pump system of any one of claims 7-8, wherein the at least one first vacuum pump comprises dry pumps.

10. The vacuum pump system of any one of claims 7-9, wherein the at least one first vacuum pump is configured to operate continuously.

11. The vacuum pump system of any one of claims 7-10, wherein the first inlet is connected to semiconductor manufacturing apparatus.

12. A method of preventing or removing deposits of process gases from a vacuum pump assembly, the vacuum pump assembly comprising at least one first vacuum pump having a first inlet for receiving process gases, and a first outlet connected to an exhaust through which the process gases are exhausted, wherein the method comprises:providing the apparatus of any one of claims 1-6, wherein the second inlet of the at least one second vacuum pump is connected to the exhaust of the vacuum pump assembly or directly to the at least one first vacuum pump using the connecting means; andcontrolling the at least one second vacuum pump to evacuate the vacuum pump assembly, such that deposits of the process gases can be prevented in or removed from the vacuum pump assembly.

13. The method of claim 12, wherein the controlling the at least one second vacuum pump comprises:deactivating the at least one second vacuum pump from evacuating the vacuum pump assembly when the at least one first vacuum pump is in an on-duty mode wherein it is receiving process gases; andactivating the at least one second vacuum pump to evacuate the vacuum pump assembly when the at least one first vacuum pump is in an off-duty mode wherein it is not receiving process gases.

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