AUXILIARY VACUUM PUMPS COMBINATION SYSTEM

Description

The present invention relates generally to vacuum pumping systems and, more particularly, to auxiliary pumping systems evacuating an equipment chamber thanks to the combination of multiple pumps connected to said equipment chamber through vacuum-tight openings such as, for example, vacuum flanges. In the following, reference is made to vacuum flanges but the invention is not limited to this type of vacuum-tight openings.

The vacuum pumping system of the present invention is defined as auxiliary as it is not self-standing and it is designed to be coupled with at least one other high-vacuum pump and at least an equipment chamber.

In many scientific and technological applications equipment, there is the need of providing vacuum chambers inside which High Vacuum (IV) or Ultra High Vacuum (UHV) conditions are provided. In a manner known per se such conditions are obtained with the combined use of at least two different types of pumps.

The first pump is usually of the mechanical type and is needed for lowering pressure inside the equipment chamber from atmospheric pressure down to a first vacuum level with pressure values usually comprised between 10 Pa and 0.1 Pa. Reaching such first vacuum level is necessary for allowing operations of a second type of pump, which could not work at pressures above the aforementioned first vacuum level.

The second type of pump is intended to further reduce the pressure inside the chamber from the first vacuum level of pressure; such second pumps can be for example cryopumps, and most commonly turbomolecular pumps (TMP).

As mentioned, turbomolecular pumps are generally used as second pumps for UHV chambers/systems, but they have some drawbacks typically related to their mechanical vibrations, which is an aspect of particular relevance in applications such as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).

Therefore, they have to be installed far from the vacuum chamber that must be evacuated by means of a long conduit, resulting in decreased evacuation performances, such as pumping speed. This drawback is of particular relevance in portable systems such as the ones shown in the article “Optimized DLP linear ion trap for a portable non-scanning mass spectrometer”, International Journal of Mass Spectrometry 369, (2014) pages 30-35.

The well-known use of the combination of multiple pumps to evacuate a vacuum equipment chamber is described in WO 2020240152 and in UTS 5161955.

More specifically, the system described in WO 2020240152, which represents one of the most recent developments, shows a vacuum pumping assembly comprising ahigh-pressure getter pump and a non-mechanical high-vacuum pump (ion getter pump, evaporable/non-evaporable getter pump, sublimation pump) mounted on the same flange, which is connected to the equipment chamber to be evacuated.

The system described in U.S. Pat. No. 5,161,955 is used to evacuate a vessel by a rough pump and a high-pressure getter pump separately and alternately connected to an equipment vacuum chamber. The switch between operation of these two pumps is handled by a pressure sensor and two valves. In the preferred embodiments shown in this patent, the activation of the high-pressure getter pump requires an external heater device made of a series of annular coil-segments powered through a power cord: this increases the total volume of the system and the complexity of the connections. Moreover, the getter pump housing is almost entirely surrounded by an insulating material, which limits pumping performances of the getter material.

WO 2020079396 and EP 3945210 also disclose vacuum pumping systems comprising the combination of a primary pump and a non-mechanical NEG high-vacuum pump.

The object of the present invention is to provide a new vacuum pumping system, which proves to be better for ease of installation, reduction of size and energy consumption, as well as being adaptable to a greater number of possible devices and applications. This is a great advantage especially when the space in which to install the system is limited, for example in complex vacuum equipment like SEM, TEM, surface science tools.

In a first aspect, the invention consists in an auxiliary pumping system comprising a primary pump, an intermediate vacuum chamber connected to said primary pump through a first flange, and a high-pressure Non-Evaporable Getter (NEG) pump contained in the intermediate vacuum chamber, wherein the primary pump operates from atmospheric pressure to a first level of vacuum and the NEG pump operates from said first level of vacuum to a second level of vacuum, characterized in that:

• • the primary pump is flanged over a vacuum conduit distancing the intermediate vacuum chamber from the primary pump, wherein the length of said conduit is comprised between 5 and 200 cm, and
  • the ratio between the volume of the getter pump and the volume of the intermediate vacuum chamber is comprised between 0.022 and 0.540.

The definition of “volume of the getter pump” is to be considered here as the total volume of its elements and components physically located within the intermediate vacuum chamber; therefore elements or components whose placement is outside the intermediate vacuum chamber, such as flanges, connectors, etc., should not be included in this definition.

The term “vacuum conduit” encompasses also the equivalent concept and realization of more vacuum conduits connected in series, with one or more vacuum components interposed therebetween (such as, for example, a valve block as better described further on), and the vacuum conduit overall length is considered the sum of the length contributions of each vacuum conduit interposed between the primary pump and the intermediate vacuum chamber.

Concerning said primary pump, it can preferably be chosen between so-called “dry pumps” such as Roots, Scroll, membrane or diaphragm pumps, and oil lubricated pumps, such as rotary vane pumps, and it operates from atmospheric pressure to a first level of vacuum between 10 Pa and 0.1 Pa.

Getter pumps are known since a long time and are getting more diffused use and appreciation thanks also to continuous improvements, such as for example with regards to the characteristics of getter alloys used in the getter pump, as described in WO 2013175340, WO 2015075648, WO 2017203015.

The high-pressure Non-Evaporable Getter (NEG) pump operates from said first level of vacuum to a second level of vacuum between 0.01 Pa and 0.001 Pa, and such operating vacuum ranges identify this element in the context of the present invention. Some examples of such pumps are given in the already mentioned WO 2020240152. It is also to be underlined that, thanks to the specific design of the auxiliary pumping system of the present invention, also “standard” high-vacuum getter pumps such as the ones described in WO 2013175340, WO 2015075648, and WO 2017203015 can be operated at higher starting pressures and therefore fall in the definition of high-pressure getter pump according to the present invention.

The invention will be further illustrated with the help of the annexed non-limiting figures where:

FIG. 1 is a schematic perspective view of an equipment vacuum chamber on which an auxiliary pumping system according to a first embodiment of the present invention is mounted.

FIG. 2 is a schematic perspective view of an auxiliary pumping system according to a second embodiment of the present invention, coupled with a HV pump.

FIG. 3 is a schematic perspective view of an intermediate vacuum chamber according to a third embodiment of the present invention, coupled with a HV pump.

FIG. 4 is a schematic perspective view of an auxiliary pumping system according to a fourth embodiment of the present invention, coupled with a first HV pump and a second HV pump.

FIG. 5 is a top view of the intermediate vacuum chamber according to the fourth embodiment of the present invention.

FIG. 6 is a sectional view according to line A-A of FIG. 5.

With regards to the above figures it is to be underlined that, in order to improve their understanding, dimensions and dimensional ratios of certain elements in some cases may have been altered, with particular and non-exclusive reference to the distance between each getter disk composing the NEG pumps in FIG. 6 or the volume of the equipment vacuum chamber of FIG. 1.

The most simple auxiliary pumping system configuration according to the present invention is shown in the schematic representation of FIG. 1, where an auxiliary pumping system 1000 is mounted on an equipment vacuum chamber 1 having a High-Vacuum (HV) pump 2 mounted thereon. The intermediate vacuum chamber 10 has a first flange 11 for the connection to a primary pump 12, optionally through a valve block 13 and an elbow 131, via a vacuum conduit 14, which is preferably flexible to favor dampening of the vibrations coming from the primary pump 12.

The configuration of the optional valve block 13 is commonly known to a person skilled in the art and usually envisions, in addition to a shut-off valve, suitable coupling flanges.

The intermediate vacuum chamber 10 has also a second flange 15 for a high-pressure NEG pump inserted in the intermediate vacuum chamber 10, and a third flange 16 to connect with the equipment vacuum chamber 1. As already outlined, the auxiliary pumping system of the present invention cannot achieve pressures below the second vacuum level, therefore properly evacuating the equipment chamber of a high-vacuum device requires the presence of at least an additional HV pump either mounted on the equipment vacuum chamber 1 itself as shown in FIG. 1 or, as shown in the preferred embodiment of FIG. 2, on an additional fourth flange present on the intermediate vacuum chamber.

FIG. 2 shows an auxiliary pumping system 2000 whose configuration according to the present invention includes an intermediate vacuum chamber 20 with a first flange 21 for the connection to a primary pump 22, optionally through a valve block 23 and elbow 231, via a flexible conduit 24, a second flange 25 for a high-pressure NEG pump inserted in the intermediate vacuum chamber 20, a third flange 26 to connect to an equipment vacuum chamber (not shown), positioned opposite the second flange 25, and a fourth flange 27 to mount a HV pump 28 (this latter not being part of the auxiliary pumping system of the present invention).

FIG. 3 shows another possible alternative configuration 300 with an intermediate vacuum chamber 30 coupled with a HV pump 38, having a first flange 31 for the connection to a primary pump (not shown), a second flange 35 for a high-pressure NEG pump inserted in the intermediate vacuum chamber 30, a third flange 36 to connect to an equipment vacuum chamber (not shown), and a fourth flange 37 to mount a HV pump 38 (this latter not being part of the auxiliary pumping system of the present invention). The third embodiment has the same number and type of flanges as the second embodiment but differently arranged, since the HV pump flange 37 is positioned at the opposite end of the intermediate vacuum chamber 30 with respect to the high-pressure NEG pump flange 35.

FIGS. 4 and 5 show another possible alternative configuration of an auxiliary pumping system 4000 according to the present invention coupled with a first HV pump 48, where the intermediate vacuum chamber 40 has: a first flange 41 for the connection to a primary pump 42, optionally through a valve block 43 and elbow 431, via a flexible conduit 44, a second flange 45 for a high-pressure NEG pump inserted in the intermediate vacuum chamber 40, a third flange 46 to connect to an equipment vacuum system chamber (not shown), a fourth flange 47 to mount a first HV pump 48, and a fifth flange 49 to mount a second IV pump (not shown in this view) positioned at the opposite end of the intermediate vacuum chamber 40 with respect to the high-pressure NEG pump flange 45 (the HV pumps not being part of the auxiliary pumping system of the present invention).

FIG. 5 shows in a top view the intermediate vacuum chamber 40 without the first IV pump 48, and FIG. 6 is a sectional view along line A-A of FIG. 5 which shows the configuration 400 to illustrate the internal arrangement of the intermediate vacuum chamber 40. More specifically, the second flange 45 is used to mount the high-pressure NEG pump 451 inserted in the intermediate vacuum chamber 40, and the fifth flange 49 is used to mount the second HV pump 491 also inserted in the intermediate vacuum chamber 40 at the opposite end with respect to the high-pressure NEG pump 451.

It is to be underlined that all the flanges mentioned in the description above, either for the connection to the vacuum pumps or the vacuum conduit or the equipment vacuum chamber, may be a separate element or a constituting element already integrated in the intermediate vacuum chamber or in the element connected thereto. In other words, the intermediate vacuum chamber is provided with at least three vacuum-tight mounting openings that in operation are used to sealingly connect it to the required element through a flange or the like.

All of the above embodiments are characterized by having the primary pump that is connected through a vacuum conduit to the intermediate vacuum chamber, wherein the length of said conduit is comprised between 5 and 200 cm, and the ratio between the volume of the Non-Evaporable Getter (NEG) getter pump and the volume of the intimidate vacuum chamber is comprised between 0.022 and 0.540. It is to be underlined that the optional valve block is advantageously present for lengths above 19 cm.

Differently from what is described in WO 2020240152, the present invention addresses the sizing problem of the high-pressure NEG pump with respect to the intermediate vacuum chamber, which is not taken into consideration in the aforementioned international patent application.

In the present invention the primary pump and the high-pressure getter pump are kept apart by a minimal distance of 5 cm, since the inventors have found that this reduces the impact of vibrations during the primary pump starting phase. At the same time, for distances higher than 200 cm the conductance of the system becomes a limiting factor in terms of performance of the auxiliary pumping system according to the present invention.

The other key parameter defining the auxiliary pumping system of the present invention is the ratio between the volume of the getter pump and the volume of the intermediate vacuum chamber, which is comprised between 0.022 and 0.540; such ratio range ensures and achieves a careful performance balance for the high-pressure getter pump in terms of speed and pump lifetime. In particular, for values higher than 0.540 there is a limiting factor associated with vacuum conductance, whereas for values below 0,022 the gaseous load onto the getter material is excessive and would accelerate the pumping performance degradation of the high-pressure getter pump.

In some embodiments the auxiliary pumping system of the present invention also comprises one or more pressure sensors such as, for example, hot-cathode gauges, capacitance manometers, Pirani gauges etc.

It is evident to a person of ordinary skill in the art that the detailed solutions shown in the previously described figures could be suitably combined, giving rise to other configurations still encompassed by the present invention.

It is also important to underline that the use of a NEG pump instead of a turbomolecular pump (TMP) equivalent to it in terms of pumping speed, drastically reduces the weight and overall dimensions of the system. For example, if we consider a pumping speed for N₂ of about 70 l/s, replacing a common TMP on the market with the NEG pump of the present invention results in a reduction in weight of up to 70% and in volume up to 90%.

Moreover the use of the NEG pump allows energy savings, as it is powered only in the activation phase (about 60 minutes) without requiring further power supply, while the TMP must always be powered during its operation.

The present invention is not limited to a specific type on Non-Evaporable Getter (NEG) material, and those are known to a person skilled in the art, as for example described in U.S. Pat. Nos. 8,961,816, 9,416,435 and 6,521,014 or more in general Zr-based alloys or Ti-based alloys, i.e. alloys where this element is the most abundant in the composition. The shape of the NEG material is not limited to disks, but it includes pills, cartridges or laminated powder onto a metallic surface. Also, the getter material in the high-pressure getter pump may be used in sintered or compressed form.

Preferred HV pumps to be used with the auxiliary pumping system of the present invention are chosen from Sputter Ion Pumps (SIP), HV NEG pumps and their combinations.