AXIAL FLOW VACUUM PUMP WITH CURVED ROTOR AND STATOR BLADES

Abstract

An axial flow vacuum pump for evacuating a chamber in a semiconductor manufacturing process comprises a rotor having a plurality of rotor blades and a stator having a plurality of stator blades, wherein the rotor blades and stator blades have a curved shape.

Claims

1. An axial flow vacuum pump for evacuating a chamber in a semiconductor manufacturing process, the axial flow vacuum pump comprising: a rotor having a plurality of rotor blades; and a stator having a plurality of stator blades, wherein the rotor blades and stator blades have a curved cross-sectional shape.

2. The axial flow vacuum pump of claim 1, wherein the rotor is supported for rotation relative to the stator by magnetic bearings.

3. The axial flow vacuum pump of claim 1, wherein the rotor is formed from stainless steel.

4. The axial flow vacuum pump of claim 1, wherein an inlet stage of the pump comprises blades having a first radial length and an adjacent downstream stage of the pump comprises blades having a second radial length, wherein the ratio of first radial length to second radial length is 2:1 or greater.

5. The axial flow vacuum pump of claim 1, comprising between 4 and 10 pumping stages, each pumping stage comprising a row of rotor blades and a row of stator blades.

6. The axial flow vacuum pump of claim 1, comprising a bypass conduit for directing a portion of the gas from the outlet of the pump towards the inlet of the pump.

7. The axial flow vacuum pump of claim 6, wherein the bypass conduit comprises a pressure relief valve.

8. An apparatus for manufacturing semiconductor equipment comprising: a chamber for manufacturing semiconductor equipment in; a backing pump system positioned remote from the chamber and configured to evacuate gas from the chamber; a foreline for fluidly connecting the backing pump system to the chamber; and an axial flow vacuum pump according to claim 1 configured to evacuate gas from the chamber, wherein the axial flow vacuum pump is connected between the chamber and foreline.

9. The apparatus of claim 8, wherein the axial flow vacuum pump is positioned less than 2 meters from the chamber.

10. The apparatus of claim 8, wherein the backing pump system is positioned more than 8 meters from the chamber.

11. A method of evacuating a semiconductor fabrication chamber comprising: using an axial flow vacuum pump as described in claim 1 to evacuate gas from the chamber; operating the axial flow vacuum pump to pump gas with a pressure of 1 mbar or higher; operating the axial flow vacuum pump to pump gas with a pressure of between 1 mbar and 10-3 mbar; and operating the axial flow vacuum pump to pump gas with a pressure of 10-3 mbar or lower.

12. The method of claim 11, comprising using a backing pump system to evacuate gas from the chamber, the backing pump system being positioned remotely from the chamber and axial flow vacuum pump.

13. The method of claim 11, wherein the axial flow vacuum pump is positioned less than 2 meters from the chamber.

14. The method of claim 11, comprising operating the axial flow vacuum pump to pump gas at a temperature of 130° C. or higher.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0041] FIG. 1 shows a semiconductor fabrication chamber and a pumping arrangement for evacuation the chamber according to an embodiment;

[0042] FIG. 2 shows a schematic sectional view of a vacuum pump according to an embodiment of the invention;

[0043] FIG. 3 shows the vacuum pump of FIG. 2 with a bypass configuration;

[0044] FIG. 4 shows example cross sectional profiles of blades for a compression stage of the pump of FIG. 2;

[0045] FIG. 5 shows further example cross sectional profiles of blades for a compression stage of the pump of FIG. 2; and

[0046] FIG. 6 illustrates a method of evacuating a semiconductor fabrication chamber.

DETAILED DESCRIPTION

[0047] FIG. 1 is a schematic illustration of apparatus 10 for manufacturing semiconductor equipment. The illustrated apparatus 10 is positioned over two floors. An upper floor 12 having a clean room in which a chamber 16 and axial flow vacuum pump 18 is positioned and a lower floor 14 in which a backing pump system 20 is positioned. The chamber 16 and axial flow vacuum pump 18 are connected to the backing pump system 20 via a foreline 22. Although only two floors are illustrated for simplicity, it will be appreciated that the apparatus 10 may be positioned over further floors, particularly where additional equipment such as exhaust management and temperature management systems may be required. Moreover, each floor may comprise multiple rooms in which various parts of the apparatus may be positioned, as is known in the art.

[0048] In use, semiconductor equipment is manufactured within the chamber 16 using one or more tools (not shown). In order to effectively manufacture semiconductor equipment, the gas pressure in the chamber should be very low. For example, in many semiconductor processes, the pressure in the chamber 16 needs to be 10.sup.-2 mbar or lower. As such the axial flow vacuum pump 18 and backing pump system 20 are configured to evacuate gas from the chamber 16 to achieve such pressures.

[0049] The backing pump system 20 comprises a roots blower and primary pump or other similar arrangement for backing the axial flow vacuum pump 18. Such a backing pump system can be very bulky and create considerable noise, as such it is positioned separately from the main manufacturing processes in the chamber 16, in the illustrated example, the backing pump system 20 is positioned on a floor below the chamber 16 in a so called ‛subfab’ area of the manufacturing facility. As the chamber 16 and backing pump system 20 are on separate floors there is a considerable distance between the chamber 16 and backing pump system 20. As such the foreline 22 is eight meters long or greater. A long gas flow path between the backing pump system 20 and chamber 16 reduces pumping effectiveness of the backing pump system 20 particularly at low pressures.

[0050] An axial flow vacuum pump 18 is attached directly to the chamber 16. It will be appreciated that the axial flow vacuum pump 18 may also be positioned close to the chamber 16 such that a short conduit, less than 2 meters, runs between the chamber 16 and axial flow vacuum pump 18.

[0051] The combination of the axial flow vacuum pump 18, with relatively high pumping capacity attached close to the chamber 16, and the backing pump system 20, which can pump effectively at the high pressures of the effective pumping range, provides a set of pumps which pump effectively across the desired pumping range with an increased pumping capacity compared to known systems.

[0052] FIG. 2 shows a cross sectional view of an example axial flow vacuum pump 18 for the pumping apparatus 10 of FIG. 1.

[0053] The axial flow vacuum pump 18 comprises a rotor 30 configured to rotate about the pump axis 32 during use and has a plurality of rotor blades 34 mounted on it. The pump 18 further comprises a stator 38 surrounding the rotor 30 and having a plurality of stator blades 36 mounted on it. The rotor 30 and stator 38 define an annular flow path 40 extending from an inlet 42 to an outlet 44 of the pump into which the rotor blades 34 and stator blades 36 extend. The annular flow path 40 has a cross-sectional area that decreases along axial direction from the inlet 42 to the outlet 44.

[0054] The rotor 30 is supported for rotation relative to the stator 38 by magnetic bearings 46. Although the illustrated embodiment shows a single magnetic bearing 46 positioned near the outlet end of the rotor 30, it will be appreciated that other bearing configurations including one or more bearings may be used.

[0055] The rotor 30 is formed from high strength stainless steel which is capable of effectively operating at temperatures between 150 and 180° C., in use.

[0056] The rotors blades 34 and stator blades 36 are arranged in stages 50, 52, 54, 56 as shown in FIG. 2. Each stage 50, 52, 54, 56 comprises a row of rotor blades 34 configured to rotate about the axis 32 in use and a row of stator blades 36 configured to remain stationary, fixed to the stator 38, in use. The illustrated vacuum pump 18 has four stages 50, 52, 54, 56. An inlet stage 50, comprising an inlet rotor blades 34 and inlet stator blades 36, is positioned at the inlet 42 to the pump 18. Three further compression stages 52, 54, 56, each comprising a row of rotor blades 34 and a row of stator blades 36, are positioned downstream of the inlet stage 42 towards the outlet 44 of the pump 18. Although four stages have been shown in FIG. 2, it will be appreciated that fewer or more stages may be present depending on the desired compression characteristics of the pump 18.

[0057] Each stage of the pump 18 has an associated volume that decreases from the inlet 42 towards the outlet 44 such that an upstream stage will have a greater volume than stage downstream of. This volume decrease facilitates compression of the gas in the viscous flow regime. The volume decrease may be achieved by decreasing the internal diameter of the stator 38 and/or increasing the external diameter of the rotor 30 along the axis 32 of the pump 18 in a direction from the inlet 42 to the outlet 44. In the illustrated example, the internal diameter of the stator 38 decreases in the inlet stage 50 but remains generally fixed in the further compression stages 52, 54, 56 and the external diameter of the rotor 30 increases throughout all stages. It will be appreciated that other configurations of stator 38 and rotor 30 geometries that achieve the desired volume decrease, as set out in more detail below, are also within the scope of the invention.

[0058] Accordingly, each stage 50, 52, 54, 56 has a compression ratio which is defined as a ratio of the volume of that stage to the volume of the adjacent downstream stage. The compression ratio of the further compression stages 52, 54, 56 (i.e. downstream of the inlet stage) is around 1.2:1. The compression ratio of the stage will directly affect the length of the rotor and stator blades 34, 36 of the stage compared to the length of the rotor and stator blades 34, 36 in the adjacent downstream stage. More specifically, the rotor blades 34 in each row have a radial length 60 extending from the rotor 30 towards the stator 38 and the stator blades 36 each have a radial length 62 extending from the stator 38 towards the rotor 30. Where the compression ratio is around 1.2:1 ratio between radial length of rotor blade (or stator blade) between stages is also around 1.2:1.

[0059] By comparison, the inlet stage 50 comprises blades 34 having a much longer radial length 60 compared to those of adjacent stages, such that the ratio is much higher than would be optimal for achieving desired pressure ratios during viscous flow. More specifically, the inlet stage 50 has a compression ratio of around 3:1 and a rotor and stator blade length 60, 62 such that the ratio of blade length 60, 62 of the inlet stage 50 to the blade length 60 of the adjacent stage 52 of the pump 18 is around 3:1.

[0060] It will be appreciated that more than one inlet stage 50 having longer blades may be provided although the number of inlet stages configured in this way will be fewer than the number of regular compression stages.

[0061] The axial flow vacuum pump of FIG. 2 has a bypass configuration 70 to optimise pumping performance. FIG. 3 is a schematic representation of the pump 18 showing the inlet 72, outlet 74 and bypass conduits 76. An inlet conduit 72 is attached to the inlet 40 of the pump 18 such that gas from the chamber (not shown) is directed into the pump 18 via the inlet conduit 72, in some examples the inlet conduit 72 may be part of the chamber itself such that the pump 18 is mounted directly to the chamber. An outlet conduit 74 is attached to the outlet 44 of the pump 18. The outlet conduit 74 feeds directly into the pumping system foreline (not shown) or may be part of the foreline itself such that the outlet conduit 74 directs gas from the pump 18 towards the backing pump system, eight or more metres away. A bypass conduit 76 is attached to the outlet conduit 74 at or adjacent to the outlet 44 of the pump 18 and is configured to direct a portion of the gas in the outlet conduit 74 back towards the inlet 40 of the pump 18.

[0062] The bypass conduit 76 includes a pressure relief valve 78 positioned between the outlet conduit 74 and inlet conduit 72. The pressure relief valve 78 is configured to open at 100 mbar. It will be appreciated that the pressures relief valve may be configured to open at a pressure of 50 mbar or higher, for example at a pressure of between 50 mbar and 200 mbar or between 80 mbar and 120 mbar, depending on the pressure conditions of system.

[0063] The vacuum pump 18 of FIG. 2 differs from a standard turbomolecular pump in that each of the rotor and stator blades 34, 36 has a substantially curved cross-sectional shape as is shown in greater detail in FIGS. 4 and 5 below.

[0064] FIG. 4 shows an example cross sectional profile of blades 34, 36 for a stage of the pump 18 of FIG. 2. The stage comprises a row of rotor blades 34a and a row of stator blades 36a. For simplicity, only three rotor blades 34a and three stator blades 36a are shown here, however it will be appreciated that many more than three blades will be mounted around the circumference of the rotor 30 at each stage.

[0065] In the configuration of FIG. 4, the blades have a generally uniform thickness 80a along its chord length 82a such that they may be made from sheet metal that is bent to form a curved profile. More specifically the curved shape will include a leading edge 84a at the front of the blade, i.e. towards the inlet of the pump, which is generally flat, and a trailing edge 86a at the rear of the blade, i.e. towards the outlet of the pump or exhaust, which is also generally flat. A curved pressure surface 88a and a curved suction surface 90a extend from the leading edge 84a to the trailing edge 86a of the blade on opposing sides.

[0066] In the alternative configuration of FIG. 5, the blades are aerodynamically optimised to form aerofoil cross-sectional shapes. More specifically the aerofoil shape includes a leading edge 84b at the front of the blade, which is generally curved and a trailing edge 86b at the rear of the blade which is generally pointed. A curved pressure surface 88b and curved suction surface 90b extend from the leading edge 84b to the trailing edge 86b of the blade on opposing sides. The thickness 80b of the cross-sectional profile varies across the chord length 82b such that it has a greater thickness 80b towards the leading edge 84b and a lesser thickness 80b towards the trailing edge 86b.

[0067] FIG. 6 illustrates a method 100 of evacuating a semiconductor fabrication chamber using the apparatus as described above. In particular, the use of the axial flow vacuum pump 18 mounted directly on or very close to the semiconductor chamber 16 as shown in FIG. 1, with the backing pump system 20 backing the axial flow vacuum pump 18 from a position remote from it.

[0068] Step 1 S1 of the method 100 comprises operating the axial flow vacuum pump to pump gas with a pressure of 1 mbar or higher, step 2 S2 comprises operating the axial flow vacuum pump to pump gas with a pressure of between 1 mbar and 10-3 mbar and step 3 S3 comprises operating the axial flow vacuum pump to pump gas with a pressure of 10-3 mbar or lower. As such the axial flow vacuum pump is used to pump gas over the viscous flow regime and molecular flow regime as well as in the transition between the two regimes.

[0069] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0070] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.