VACUUM PUMP, VACUUM PUMP SET FOR EVACUATING A SEMICONDUCTOR PROCESSING CHAMBER AND METHOD OF EVACUATING A SEMICONDUCTOR PROCESSING CHAMBER

Abstract

A vacuum pump, vacuum pump set and method for evacuating a semiconductor processing chamber is disclosed. The vacuum pump is configured for mounting to a semiconductor processing chamber to evacuate the chamber to pressures between 1 mbar and 5×10.sup.−2 mbar. The vacuum pump comprises: a rotor rotatably mounted within a stator. The rotor comprises a plurality of angled blades arranged along a helical path from an inlet to an outlet. The stator comprises a plurality of perforated elements arranged to intersect the helical path, the perforations allowing gas molecules travelling along the helical path to pass through the perforated elements. The rotor mounted on a magnetically levitated bearing; and the perforated elements located towards an inlet of the vacuum pump comprise a transparency of more than 40% and the perforated elements located towards an outlet of the vacuum pump comprise a transparency of more than 30%.

Claims

1. A vacuum pump for mounting to a semiconductor processing chamber to evacuate said chamber to pressures between 1 mbar and 5×10.sup.−2 mbar, said vacuum pump comprising: a rotor rotatably mounted within a stator; said rotor comprising a plurality of angled blades arranged along a helical path from an inlet to an outlet; said stator comprising a plurality of perforated elements arranged to intersect said helical path, said perforations allowing gas molecules travelling along said helical path to pass through said perforated elements; said rotor being mounted on a magnetically levitated bearing; and said perforated elements located towards an inlet of said vacuum pump comprise a transparency of more than 40% and said perforated elements located towards an outlet of said vacuum pump comprise a transparency of more than 30%.

2. The vacuum pump according to claim 1, wherein said perforated elements located towards an inlet of said vacuum pump comprise a transparency of more than 50% and said perforated elements located towards an outlet of said vacuum pump comprise a transparency of more than 40%.

3. The vacuum pump according to claim 1, wherein said rotor and stator are formed of at least one of stainless steel and aluminium.

4. The vacuum pump according to claim 3, wherein said rotor is formed of stainless steel and said perforated elements of aluminium.

5. The vacuum pump according to claim 1, wherein at least one of said rotor and stator comprise a coating of a high emissivity.

6. The vacuum pump according to claim 1, said vacuum pump being configured to operate at a pumping speed of between 300 and 1200 litres per second.

7. The vacuum pump according to claim 1, said vacuum pump comprising an inlet conduit extending from an inlet of said vacuum pump and configured to connect to said semiconductor processing chamber, said inlet conduit having a length of less than 2 m, preferably less than 1 m.

8. The vacuum pump according to claim 1, said blades of said rotor at an inlet stage of said pump being wider than said blades of said rotor in other stages of said pump.

9. The vacuum pump according to claim 1, said stator further comprising a cylindrical inner surface formed by a stack of rings each having a cylindrical inner surface, said plurality of perforated elements being mounted on respective rings, such that said plurality of perforated elements form a plurality of perforated discs intersecting said helical path at different axial positions.

10. A set of vacuum pumps for evacuating a semiconductor processing chamber, comprising a vacuum pump according to claim 1 and a roots blower and primary vacuum pump arranged as a backing pump combination for said vacuum pump.

11. The set of vacuum pumps according to claim 10, further comprising a conduit of less than 2 m long, preferably less than 1 m for connecting said vacuum pump to said semiconductor processing chamber and a longer conduit for connecting said vacuum pump to said roots blower and primary pump such that said roots blower and primary pump are located remotely from said semiconductor processing chamber.

12. A method of evacuating a semiconductor processing chamber said method comprising: locating a vacuum pump according to claim 1 within a semiconductor fab and attaching said vacuum pump to a semiconductor processing chamber by a conduit of less than 2 m length; locating a roots blower and primary pump in a position remote from the semiconductor fab and attaching an outlet of said vacuum pump to an inlet of said roots blower pump via a longer conduit; operating said vacuum pumps to evacuate said semiconductor processing chamber to a vacuum of between 1 mbar and 5×10.sup.−2 mbar.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0039] FIG. 1 shows a graph illustrating the different pressure ranges that are effectively pumped by different types of pumps;

[0040] FIG. 2 shows a semiconductor processing chamber and a set of pumps for evacuating the semiconductor processing chamber according to an embodiment;

[0041] FIG. 3 shows a vacuum pump of a pump according to an embodiment;

[0042] FIG. 4 shows a rotor for a vacuum pump according to an embodiment;

[0043] FIG. 5 schematically shows gas flow within a pump according to an embodiment; and

[0044] FIG. 6 shows a perforated element portion of the stator according to an embodiment.

DETAILED DESCRIPTION

[0045] Before discussing the embodiments in any more detail, first an overview will be provided.

[0046] Drag pumps typically have a relatively low volumetric speed say <100 l/s on a large turbo pump due to the narrow passages that must be used. The ‘Schofield Drag Pump’ described in patent application US2015/0037137 mitigates this speed limitation by passing gas through one of the drag surfaces and thereby enables a much higher capacity machine to be designed. It may provide pumping capacity in the region of 600 l/s.

[0047] The inventor of this drag pump recognised that the properties of the drag pump make it particularly effective for evacuating a semiconductor processing chamber to pressures between 1 mbar and 5×10.sup.31 2 mbar. In particular, were it to be designed with sufficient transparency then it could provide effective pumping at the lower pressures while at higher pressures where it might not be so effective, the transparency would ensure that the flow to a backing pump such as a roots blower was not be unduly impeded or restricted, allowing a combination of pumps to provide effective pumping across a wide pressure range.

[0048] Use of this type of drag pump enables a semiconductor processing chamber to be effectively pumped between 1 mbar and 5×10.sup.−2 mbar. In embodiments, the pump is backed by a conventional dry pump and roots blower combination mounted remotely, typically in the basement of the semiconductor fab.

[0049] A further feature of this drag pump design is that it may be formed from high strength stainless steel, thus enabling the rotor to be used at much higher temperatures than were it made from aluminium. This is important to prevent the condensation of semiconductor by-products within the pump. It is very difficult to make a turbo pump from stainless steel due to the small blade geometry, particularly in the exhaust sections.

[0050] A further feature to improving pumping speeds and transparency is that in some embodiments the exhaust is not unduly restricted, such that the exhaust of the Schofield pump has a size that is similar to that of the inlet to the roots blower pump. That is within 20% of the inlet size, the conduit linking the two also being of a similar size.

[0051] FIG. 2 shows semiconductor processing chamber 5 located within a clean room or semiconductor fab and with a vacuum pump 10 according to an embodiment attached to the semiconductor processing chamber via a relatively short conduit 12. The vacuum pump 10 is a Schofield pump and has a rotor mounted on magnetically levitated bearings such that it may be located within the clean room and be connected to the semiconductor processing chamber 5 by the relatively short and wide conduit 12.

[0052] Remote from the vacuum pump 10 and semiconductor processing chamber 5 is a backing pump combination 90 which comprises a roots blower and a primary pump. These are located in the basement 80 remote from the clean room 70 as their operation generates vibrations, the bearings of the pumps 90 not being magnetically levitated. For this reason the conduit 92 between the backing pump combination 90 and the Schofield pump 10 is relatively long and this affects the effectiveness of the backing pump 90 particularly at low pressures.

[0053] The combination of the Schofield pump 10 with relatively high pumping capacity attached close to the semiconductor processing chamber 5 and with the backing pumps 90 which can pump effectively at the higher pressures of the effective pumping range provide a set of pumps which pump effectively in the transitional flow range and particularly in the higher pressure sides of this flow range providing the effective pumping indicated by the dotted line shown as “drag plus” in FIG. 1.

[0054] The Schofield vacuum pump 10 is shown schematically in FIG. 3. Vacuum pump 10 comprises a plurality of perforated stator elements 14 which comprise perforated discs through which the gas flows from an inlet 16 to an exhaust 18. The perforated discs are mounted at different axial positions on cylindrical rings 40 and extend between rows of blades 30 of rotor 35 which blades 30 form a helical path from the inlet 16 to the outlet 18. The helical rotor 35 is mounted on shaft 42 and rotates during operation. Shaft 42 is mounted on magnetically levitated bearings 45.

[0055] FIG. 4 shows a further view of rotor 35 showing the helical blades 30. As can be seen the helical rotor blades 30 form a helical path. Rotation of rotor 35 imparts momentum to gas molecules that the blades contact, and sends them towards the outlet 18 through the perforated elements 14 (see FIG. 3). Impact with the non-perforated portions of the stator disks slows the gas molecules and provides the drag of the drag pump, pulling the molecule trajectory towards the output. FIG. 5 shows some example molecule trajectories.

[0056] FIG. 5 schematically shows a circumferential cross section of a portion of the mechanism of the pump and illustrates the operational principles. When in operation, the rotor having the angled blades 30 is rotated at a relatively high speed. The principles of operation show the components of the pump in a linear manner with the rotational movement of the rotor shown as a linear movement indicated by the arrow.

[0057] In this embodiment, there are four stator perforated discs 14 dividing the pump into five stages A to E. Stage A is upstream of a first stator element 50, with successive downstream stages being separated by successive stator elements 51-53.

[0058] The angled rotor blades 30 form a helical flow path channel from an inlet 16 to an outlet 18 with the perforated disk elements 14 intersecting the flow path channel.

[0059] FIG. 5 shows some different possible gas molecule paths. A first path is illustrated by arrow 60. The molecule enters the inlet of the pump which operates at high vacuum pressure. It strikes the rotor blade 30 and momentum is imparted to the molecule by the relative movement of the rotor and the molecule is deflected towards the stator element where it strikes a solid part and is slowed. Next, the molecule strikes the underside surface of the rotor blade 30 and is again directed towards the stator element where in this case the molecule's path interacts with a disk perforation 38 allowing the molecule to pass through the intersecting disk into the next section of the pump, namely section B as illustrated.

[0060] A second path of another molecule is illustrated by arrow 62. Here, the molecule's path passes through a perforation on the rotor allowing the molecule to progress from section B to Section C where it then interacts with rotor blade 30 and is emitted from the surface towards the stator element 51 through which it has just passed. Here, it interacts with the downstream surface of the stator element and is retained within section C, as a result. Its path then continues onto the third stator element 52, from here to the opposite sidewall of the channel, namely underside of rotor blade 30 and then through a perforation of the third stator into section D. Thus, momentum can be transferred to gas molecules by either sidewalls of the channel formed by the upper and lower surfaces of the rotor blades, or by both surfaces.

[0061] A third path of a different molecule is illustrated by arrow 64. Here, the molecule passes from Section B into Section C via a perforation in the second stator 51 where it is deflected by the rotor blade 30 and returns to section B through a perforation 38 of the stator and contacts the underside of the rotor blade 30.

[0062] Thus, gas molecules migrating into the inlet of the pump encounter a surface of the rotor blade 30 or perforated stator disk 14. Some molecules pass through a perforation 38 and strike a surface of the rotor. Momentum of the gas molecule leaving the surface of the rotor is influenced by the rotary motion of the rotor and it is likely that the molecule has momentum transferred to it having a major component in the direction of the rotor's movement. As a result, the majority of molecules striking and leaving the rotor's surfaces are urged towards the exhaust.

[0063] In the example of FIG. 5 the compression of gas increases from stage A to stage E with an increasing reduction of rotor spacing towards stage E and/or increased angle of inclination of the sidewalls with respect to the rotor axis. This can assist with maintaining pump efficiency as the gas molecules become compressed towards the outlet. In other embodiments, the stator disc separation and rotor blade angles are constant in the different stages, however, the inlet stage may have rotor blades of an increased width to capture more gas molecules at the high vacuum inlet.

[0064] FIG. 6 shows a perforated stator element 14. In this embodiment the perforated stator disc, is formed of two elements which are joined together to form the disc. The perforated stator disc has a transparency of more than 30% and in preferred embodiments, comprises radially extending walls running between the perforations in order to conduct heat from a central portion to an outer portion, thereby limiting the heat increase of the central ring of the disc. Furthermore, there are indents provided in the central ring of the disc and in some cases gaps between the two elements forming the disc and these provide space for the inner ring to expand into thereby reducing the chances that expansion will cause buckling of the ring with the associated axial movement which can cause clashing between the rotor and stator.

[0065] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0066] 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.

[0067] 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.