Vacuum pump, vacuum pump assembly for evacuating a semiconductor processing chamber, and method for evacuating a semiconductor processing chamber

Abstract

A vacuum pump, a vacuum pump assembly, and a method for evacuating a semiconductor processing chamber are disclosed. The vacuum pump is configured to be installed in a semiconductor processing chamber to evacuate the chamber to 1 mbar and 5×10 ‑2 mbar. The vacuum pump comprises: a rotor rotatably mounted within a stator. The rotor comprises a plurality of angled blades arranged along a spiral path from an inlet to an outlet. The stator comprises a plurality of perforated elements arranged to intersect the spiral path, the perforations allowing gas molecules traveling along the spiral path to pass through the perforated elements. The rotor is mounted on a magnetic bearing; and the perforated elements positioned toward the inlet of the vacuum pump comprise a permeability greater than 40%, and the perforated elements positioned toward the outlet of the vacuum pump comprise a permeability greater than 30%.

Description

Technical Field

[0001] The field of the invention relates to vacuum pumps and methods of evacuating semiconductor processing chambers. Background Art

[0002] Vacuum pumps are designed and constructed to operate efficiently within a specific pressure range. No single pump can operate efficiently across all pressure ranges.

[0003] Figure 1 is a graph showing pumping speed versus pressure, and showing flow regimes operating in different pressure ranges and pumps that are effective when pumping in these flow regimes and pressure ranges. Thus, at high vacuum in the molecular flow regime 100, a turbomolecular pump 110 is effective, while at low vacuum in the viscous flow regime 300, a rough pump 150 such as a Roots blower pump is effective. In the transitional flow regime 200, at pressures where both molecular and viscous flows occur, a drag pump 140 may be used. A compound pump 120 formed as a vane and drag combination extends from the molecular flow to the higher vacuum portion of the transitional flow regime.

[0004] The pumping mechanism of a conventional drag pump requires the rotor to rotate close to the stator in order to optimize the compression ratio of the pump, which limits the depth of the stator passages, which in turn limits the pumping capacity of the conventional drag pump.

[0005] There is an increasing need to operate semiconductor processing chambers within a pressure range that may be too high for a turbo pump to maintain without overheating (typically pressures above 0.05 mbar), but too low for a remotely mounted Roots blower to be effective (typically less than 0.2 mbar) due to the conductivity of the connecting pipes.

[0006] It is desirable to provide a pump that has reasonable capacity and is efficient at pumping at the pressures required in certain semiconductor processing chambers. Summary of the invention

[0007] A first aspect provides a vacuum pump for installation in a semiconductor processing chamber to evacuate the chamber to a pressure of 1 mbar and 5×10 -2mbar, the vacuum pump comprising: a rotor rotatably mounted within a stator; the rotor comprising a plurality of angled blades arranged along a spiral path from an inlet to an outlet; the stator comprising a plurality of perforated elements arranged to intersect the spiral path, the perforations allowing gas molecules traveling along the spiral path to pass through the perforated elements; the rotor being mounted on a magnetic bearing; and the perforated elements positioned toward the inlet of the vacuum pump comprising a transparency greater than 40%, and the perforated elements positioned toward the outlet of the vacuum pump having a transparency greater than 30%.

[0008] Permeability is the ratio of the total area of ​​the perforations of the perforated element that intersect the gas flow channel to the total area of ​​the element that intersects a given flow path channel.

[0009] A pump is provided which is capable of pumping within the pressure range of conventional drag pumps but which also has a high permeability such that the pump can pump efficiently at relatively high pumping rates at lower pressures, while at higher pressures the permeability of the pump allows efficient pumping when the pump is backed by another pump such as a Roots blower. The permeability does reduce compression, particularly at higher pressures, but this is acceptable because at these pressures a backing pump can pump efficiently even when connected from a distance, provided the permeability of any pump between the backing pump and the chamber is not so high that it unduly impedes flow. Thus, the pump is Figure 1 The pump effectively pumps in the transitional flow regime 200 of FIG. 1 , and can be viewed as providing the effect of a drag plus pump 130 .

[0010] As the gas flows through the pump, it is compressed, and this compression means that the open or permeable area may decrease towards the outlet.

[0011] In some embodiments, the perforated element positioned towards the inlet of the vacuum pump comprises a permeability greater than 50%, and the perforated element positioned towards the outlet of the vacuum pump comprises a permeability greater than 40%.

[0012] In some embodiments, the rotor and stator are formed from at least one of stainless steel and aluminum.

[0013] An advantage of forming at least one of the rotor and stator from stainless steel is that stainless steel can operate at relatively high temperatures and this enables the pump to operate at elevated temperatures. This is advantageous where the pump is pumping from a semiconductor processing chamber as the higher temperatures reduce the amount of deposition of particles within the pump.

[0014] Aluminum cannot operate at such high temperatures, however it does have the advantage of high thermal conductivity and helps conduct heat away from the interior of the pump.

[0015] In some embodiments, the rotor is formed from stainless steel and the perforated element is formed from aluminum.

[0016] The rotor within the pump will heat to a higher temperature than the stator because it is easier to cool the stator than the rotating rotor. Therefore, it is advantageous to form a stainless steel rotor that can operate at relatively high temperatures, while forming an aluminum stator that has a higher thermal conductivity and can be used to conduct heat away from the interior of the pump.

[0017] In embodiments where the stator includes perforated elements that extend into the pump and through which the gas travels, it is important that these perforated elements do not overheat as this may cause them to buckle. Any deformation of these elements may be problematic as the clearance between the rotor and these stator elements is typically quite tight to provide efficient pumping, and any buckling may result in collisions between the rotor and stator elements. Forming the perforated elements from aluminum allows heat to be conducted from the center portion of the stator towards the cooler edges and helps to reduce the temperature rise of the stator and mitigate such buckling or deformation.

[0018] In some embodiments, at least one of the rotor and the stator includes a high emissivity coating.

[0019] As previously mentioned, it is desirable to remove at least some heat from the pump to avoid overheating it, and providing a high emissivity coating on the rotor and / or stator can help reduce temperature increases.

[0020] In some embodiments, the vacuum pump is configured to operate at a pumping speed between 300 and 1200 liters / second.

[0021] One advantage of the vacuum pump according to an embodiment is its relatively high pumping speed at relatively low pressures, which makes it particularly effective for evacuating semiconductor processing chambers. This is in contrast to many conventional drag pumps. In this regard, there is no channel with a limited depth between the rotor and the stator (which exists in conventional drag pumps), which allows the pumping speed to be increased, although it does reduce the compression ratio, especially at the higher pressures of its operating range. However, since a backing pump such as a Roots blower pump can provide effective compression at these "higher" pressures, this reduction in compression is acceptable.

[0022] In some embodiments, the vacuum pump comprises an inlet conduit extending from an inlet of the vacuum pump and configured to be connected to the semiconductor processing chamber, the inlet conduit having a length of less than 2 m, preferably less than 1 m.

[0023] Another advantage of the vacuum pump according to an embodiment is that it is mounted on a magnetic bearing. This allows the vacuum pump to be placed in a semiconductor production plant and close to the semiconductor processing chamber when the semiconductor processing chamber is evacuated. This allows the vacuum pump to be connected to the semiconductor processing chamber by a relatively short conduit, in some embodiments, the connecting conduit is less than 2 m, preferably less than 1 m. When pumping at low pressure, having a long conduit between the pump and the chamber to be evacuated significantly reduces the pumping efficiency and is one reason why many conventional vacuum pumps (such as Roots blowers) that do not have magnetic bearings and therefore need to be far away from the semiconductor processing chamber are not suitable for pumping these chambers to low pressure.

[0024] In some embodiments, the blades of the rotor at the inlet stage of the pump are wider than the blades of the rotor in other stages of the pump.

[0025] In some cases, it may be advantageous to extend the width of the blades at the inlet stage of the pump to capture more gas molecules at the inlet of the pump and send them into the pumping channel to proceed through the pump. The inlet of the pump is subject to the lowest pressure, and capture of molecules is most challenging at this location.

[0026] In some embodiments, the stator further comprises a cylindrical surface formed by a stack of rings, each ring having a cylindrical inner surface, the plurality of perforated elements being mounted on respective rings such that the plurality of perforated elements form a plurality of perforated disks intersecting the spiral path at different axial positions.

[0027] The spiral channel may be within a cylindrical surface within which the rotor rotates. The cylindrical surface may be formed by a stack of rings, and the perforated disks of the stator may be mounted at different axial positions between the stack of rings. Thus, as the gas flows through the pump, the spiral path is intercepted by the perforated disks at different axial positions. The axis involved here is the axis of rotation of the rotor.

[0028] A second aspect provides a vacuum pump package for evacuating a semiconductor processing chamber, comprising a vacuum pump according to any preceding claim and a Roots blower and a primary vacuum pump arranged as a backing pump for the vacuum pump.

[0029] A vacuum pump assembly comprising a vacuum pump according to the first aspect supported by a Roots blower and a primary pump provides an efficient pumping arrangement for a vacuum chamber such as a semiconductor processing chamber, which is evacuated to 1 mbar and 5×10 -2mbar. Such pressures are suitable for semiconductor processes, including semiconductor device manufacturing processes, such as ALD (atomic layer deposition) processes. The vacuum pump according to the first aspect provides a relatively high pumping speed at a relatively low pressure, but has only a modest compression ratio, particularly at the higher pressures of its operating range. However, when used in combination with a Roots blower pump, due to the characteristics of the Roots blower and the high permeability of the vacuum pump of the first aspect, the combination can provide the required compression over the entire pressure range. In this regard, in the evacuation of semiconductor vacuum chambers, the effective operation of the Roots blower is limited by the length of the duct required due to the fact that the Roots blower cannot be installed in a clean room. However, by using it in combination with the vacuum pump of the first aspect, the vacuum pump can be installed in a clean room / production plant and effectively evacuate at the lower pressures of the operating range, providing a vacuum pump that can be used in the range of 1 mbar to 5×10 -2 A combination of pumps for efficiently evacuating semiconductor processing chambers over the entire pressure range of mbar.

[0030] In some embodiments, the vacuum pump group also includes a conduit having a length of less than 2 m, preferably less than 1 m, for connecting the vacuum pump to the semiconductor processing chamber and a longer conduit for connecting the vacuum pump to the Roots blower and the primary pump, so that the Roots blower and the primary pump are located away from the semiconductor processing chamber. The longer conduit allows the Roots blower pump to be placed away from the vacuum chamber and the clean room, and in some embodiments, the longer conduit is at least 8 m long.

[0031] A third aspect provides a method for evacuating a semiconductor processing chamber, the method comprising: positioning a vacuum pump according to any preceding claim in a semiconductor production plant and attaching the vacuum pump to the semiconductor processing chamber via a conduit having a length of less than 2 m; positioning a Roots blower and a primary pump at a location away from the semiconductor production plant and attaching the outlet of the vacuum pump to the inlet of the Roots blower pump via a longer conduit; operating the vacuum pump to evacuate the semiconductor processing chamber to 1 mbar and 5×10 -2 Vacuum between mbar.

[0032] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

[0033] Where an equipment feature is described as being operable to provide a function, it will be understood that this includes equipment features that provide that function or that are adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention will now be further described with reference to the accompanying drawings, in which:

[0035] Figure 1 A graph is shown which illustrates the different pressure ranges that can be effectively pumped by different types of pumps;

[0036] Figure 2 A semiconductor processing chamber and a pump assembly for evacuating the semiconductor processing chamber according to an embodiment are shown;

[0037] Figure 3 A vacuum pump of a pump according to an embodiment is shown;

[0038] Figure 4 shows a rotor for a vacuum pump according to an embodiment;

[0039] Figure 5 schematically illustrates airflow within a pump according to an embodiment; and

[0040] Figure 6 A perforated element portion of a stator according to an embodiment is shown. DETAILED DESCRIPTION

[0041] Before discussing the embodiments in more detail, an overview will first be provided.

[0042] Drag pumps typically have relatively low volumetric velocities, e.g. less than 100 l / s on large turbine pumps, due to the narrow passages that must be used. The "Schofield Drag Pump" described in patent application US2015 / 0037137 alleviates this velocity limitation by passing the gas through one of the drag surfaces, and thereby enables the design of a much higher capacity machine. It can provide a pumping capacity of around 600 l / s.

[0043] The inventors of the present drag pump have recognized that the properties of the drag pump make it useful for evacuating semiconductor processing chambers to pressures of 1 mbar and 5×10 -2 In particular, if it is designed to have sufficient permeability, it can provide effective pumping at lower pressures, while at higher pressures it may not be so effective, the permeability ensuring that the flow to the backing pump such as a Roots blower is not unduly obstructed or restricted, thereby allowing the combination of pumps to provide effective pumping over a wide pressure range.

[0044] The use of this type of drag pump allows semiconductor processing chambers to be efficiently cooled at 1 mbar and 5 × 10 -2 In an embodiment, the pump is supported by a conventional dry pump and Roots blower combination mounted remotely, typically in the basement of a semiconductor manufacturing plant.

[0045] Another feature of this drag pump design is that it can be formed from high strength stainless steel, thus enabling the rotor to be used at much higher temperatures than rotors made from aluminum. This is important to prevent condensation of semiconductor byproducts within the pump. It is very difficult to manufacture a turbo pump from stainless steel due to the small blade geometry, especially in the discharge section.

[0046] Another feature that improves pumping speed and permeability is that in some embodiments, the discharge port is not overly restricted, so that the discharge port of the Schofield pump has a size similar to the size of the inlet port of the Roots blower pump, that is, within 20% of the inlet size, and the conduit connecting the two is also of similar size.

[0047] Figure 2 A semiconductor processing chamber 5 is shown located within a clean room or semiconductor production plant and has 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 magnetic bearings so that it can be located within the clean room and connected to the semiconductor processing chamber 5 by a relatively short and wide conduit 12.

[0048] Remote from the vacuum pump 10 and the semiconductor processing chamber 5 is a backing pump assembly 90, which includes a Roots blower and a primary pump. These are located in a basement 80 remote from the clean room 70, and because their operation generates vibrations, the bearings of the pump 90 are not magnetically suspended. For this reason, the conduit 92 between the backing pump assembly 90 and the Schofield pump 10 is relatively long, and this affects the efficiency of the backing pump 90, especially at low pressures.

[0049] The combination of a Schofield pump 10 having a relatively high pumping capacity (which is attached close to the semiconductor processing chamber 5) and a backing pump 90 (which can effectively pump at the higher pressures of the effective pumping range) provides a pumping unit that effectively pumps in the transition flow range, especially on the higher pressure side of the flow range, thereby providing a pumping system that is effectively pumped in the transition flow range. Figure 1 The effective pumping is represented by the dashed line shown as "drag enhancement".

[0050] Figure 3 A Schofield vacuum pump 10 is schematically shown. The vacuum pump 10 comprises a plurality of perforated stator elements 14, which include perforated discs through which gas flows from an inlet 16 to a discharge 18. The perforated discs are mounted at different axial positions on a cylindrical ring 40 and extend between rows of blades 30 of a rotor 35, which form a helical path from the inlet 16 to the outlet 18, and the helical rotor 35 is mounted on a shaft 42 and rotates during operation. The shaft 42 is mounted on a magnetic bearing 45.

[0051] Figure 4 Another view of the rotor 35 is shown, showing the helical blades 30. As can be seen, the helical rotor blades 30 form a helical path. The rotation of the rotor 35 imparts momentum to the gas molecules that the blades contact and passes them through the perforated element 14 (see FIG. Figure 3 ) are sent towards the outlet 18. Impact with the non-perforated portion of the stator disk slows down the gas molecules and provides a drag that drags the pump, pulling the molecular trajectories towards the output. Figure 5 Some exemplary molecular trajectories are shown.

[0052] Figure 5 A circumferential cross section of a portion of the mechanism of the pump is schematically shown and illustrates the operating principle. When in operation, a rotor with angled blades 30 rotates at a relatively high speed. The operating principle illustrates the components of the pump in a linear manner, with the rotary motion of the rotor being illustrated as a linear motion indicated by the arrows.

[0053] In this embodiment, there are four stator perforated discs 14 which divide the pump into five stages A to E. Stage A is upstream of the first stator element 50, successive downstream stages being separated by successive stator elements 51-53.

[0054] The angled rotor blades 30 form a spiral flow path passage from the inlet 16 to the outlet 18 , with the perforated disk element 14 intersecting the flow path passage. Figure 5 Some different possible gas molecule paths are shown. The first path is shown by arrow 60. The molecule enters the inlet of the pump operating at high vacuum pressure. It strikes the rotor blade 30 and momentum is imparted to the molecule by the relative motion of the rotor and the molecule is deflected towards the stator element where it strikes the solid portion and is decelerated. Next, the molecule strikes the underside surface of the rotor blade 30 and is again directed towards the stator element where the molecule's path interacts with the disk perforations 38 allowing the molecule to pass through the intersecting disks into the next section of the pump, i.e., section B as shown.

[0055] The second path of another molecule is shown by arrow 62. Here, the molecule's path passes through a perforation in the rotor, allowing the molecule to proceed from section B to section C, where the molecule interacts with the rotor blade 30 and is launched from the surface toward the stator element 51 that it has just passed through. Here, it interacts with the downstream surface of the stator element and is therefore retained within section C. Its path then continues onto the third stator element 52, from here to the opposite side wall of the channel, i.e. the underside of the rotor blade 30, and then through the perforations of the third stator into section D. Thus, momentum can be transferred to the gas molecule through either side wall of the channel formed by the upper and lower surfaces of the rotor blades, or through both surfaces.

[0056] The third path of the different molecules is shown by arrow 64. Here, the molecules enter segment C from segment B via the perforations in the second stator 51 where they are deflected by the rotor blades 30 and return to segment B through the perforations 38 of the stator and contact the underside of the rotor blades 30.

[0057] Thus, gas molecules migrating into the inlet of the pump encounter the surface of the rotor blades 30 or perforated stator disk 14. Some molecules pass through the perforations 38 and strike the surface of the rotor. The momentum of the gas molecules leaving the rotor surface is affected by the rotational motion of the rotor, and it is likely that the molecules have momentum transferred to them that has a major component in the direction of the rotor motion. As a result, most of the molecules that strike and leave the rotor surface are pushed toward the discharge port.

[0058] exist Figure 5 In the example of , the compression of the gas increases from stage A to stage E, while the rotor spacing decreases and / or the inclination angle of the sidewall relative to the rotor axis increases toward stage E. This can help maintain pump efficiency as the gas molecules are compressed toward the outlet. In other embodiments, the stator disk spacing and rotor blade angle are constant in different stages, however, the inlet stage may have rotor blades of increasing width to capture more gas molecules at the high vacuum inlet.

[0059] Figure 6 A perforated stator element 14 is shown. In this embodiment, the perforated stator disc is formed from two elements which are joined together to form the disc. The perforated stator disc has a permeability greater than 30% and, in a preferred embodiment, includes radially extending walls extending between the perforations so as to conduct heat from the central portion to the outer portion, thereby limiting heat gain in the central ring of the disc. In addition, an indent is provided in the central ring of the disc and in some cases a gap is provided between the two elements forming the disc, and these provide space for the inner ring to expand into, thereby reducing the likelihood that the expansion will result in buckling of the ring and associated axial movement which can result in collisions between the rotor and stator.

[0060] Although an illustrative embodiment of the present invention has been disclosed in detail herein with reference to the accompanying drawings, it should be understood that the invention is not limited to the precise embodiment and that various changes and modifications may be effected therein by those skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0061] Reference Mark

[0062] 5 Vacuum chamber

[0063] 10 Vacuum pump

[0064] 12, 92 catheter

[0065] 14 Perforated stator elements

[0066] 16 Entrance

[0067] 18 Exit

[0068] 30 Rotor blades

[0069] 35 Rotor

[0070] 38 Piercing

[0071] 40 rings

[0072] 42 Axis

[0073] 45 Bearing

[0074] 50, 51, 52, 53 perforated disc

[0075] 60, 62, 64 Molecular Path

[0076] 70 Clean Room

[0077] 80 Basement

[0078] 90 Foreline Pump Set

[0079] 100 Molecular Flow

[0080] 110 Turbomolecular pump

[0081] 120 Compound Pump

[0082] 130 Towed Intensified Pump

[0083] 140 Trailing Pump

[0084] 150 Rough pump

[0085] 200 Transition Flow

[0086] 300 Viscous Flow

Claims

1. A pump system for evacuating a semiconductor processing chamber, comprising: A vacuum pump for installation into a semiconductor processing chamber to evacuate the chamber to 1 mbar and 5×10 -2 mbar, the vacuum pump comprises: a rotor rotatably mounted within the stator; The rotor includes a plurality of angled blades arranged along a helical path from an inlet to an outlet; The stator includes a plurality of perforated elements arranged to intersect the spiral path, the perforations allowing gas molecules traveling along the spiral path to pass through the perforated elements; The rotor is mounted on a magnetic bearing; and The permeation area of ​​the perforated element decreases towards the outlet, so that the perforated element positioned towards the inlet of the vacuum pump comprises a permeability greater than 40% and the perforated element positioned towards the outlet of the vacuum pump comprises a permeability greater than 30%; a roots blower and a primary vacuum pump arranged as a backing pump combination for the vacuum pump; A conduit having a length of less than 2 m for connecting the vacuum pump to the semiconductor processing chamber; and A longer conduit for connecting the vacuum pump to the Roots blower and the primary pump enables the Roots blower and the primary pump to be positioned away from the semiconductor processing chamber.

2. The pump system according to claim 1, wherein: The perforated element positioned towards the inlet of the vacuum pump comprises a permeability greater than 50%, and the perforated element positioned towards the outlet of the vacuum pump comprises a permeability greater than 40%.

3. The pump system according to claim 1, wherein: The rotor and the stator are formed of at least one of stainless steel and aluminum.

4. The pump system according to claim 3, wherein: The rotor is formed from stainless steel and the perforated element is formed from aluminum.

5. The pump system according to any one of claims 1 to 4, wherein: At least one of the rotor and the stator includes a high emissivity coating.

6. The pump system according to any one of claims 1 to 4, wherein: The vacuum pump is configured to operate at a pumping speed between 300 and 1200 liters / second.

7. The pump system according to any one of claims 1 to 4, wherein: The vacuum pump includes an inlet conduit extending from an inlet of the vacuum pump and configured to be connected to the semiconductor processing chamber, the inlet conduit having a diameter of less than 2 m.

8. The pump system according to any one of claims 1 to 4, wherein: The blades of the rotor at the inlet stage of the pump are wider than the blades of the rotor in other stages of the pump.

9. The pump system according to any one of claims 1 to 4, wherein: The stator also includes a cylindrical inner surface formed by a stack of rings, each ring having a cylindrical inner surface, and the plurality of perforated elements are mounted on respective rings such that the plurality of perforated elements form a plurality of perforated disks that intersect the spiral path at different axial positions.

10. A method of evacuating a semiconductor processing chamber using a pump system according to any preceding claim, the method comprising: Positioning a vacuum pump within a semiconductor manufacturing plant and attaching the vacuum pump to a semiconductor processing chamber via a conduit having a length of less than 2 m; Positioning a Roots blower and a primary pump remote from the semiconductor manufacturing plant, and attaching the outlet of the vacuum pump to the inlet of the Roots blower pump via a longer conduit; The vacuum pump was operated to evacuate the semiconductor processing chamber to 1 mbar and 5×10 -2 Vacuum between mbar.

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