TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a vacuum line, to a pumping device intended to be connected to such a vacuum line, and to an installation comprising the vacuum line. The invention also relates to a thermal regulation process for thermal regulation of a rough-vacuum pump.

TECHNICAL BACKGROUND OF THE INVENTION

[0002] In the manufacturing industry for semiconductors, flat screens or photovoltaics, the manufacturing processes require vacuum lines for notably obtaining a vacuum in the load locks and/or in the process chambers that is able to implement the manufacturing steps but also the discharge of the gases used in the process chambers.

[0003] The vacuum line thus has to comprise vacuum pumps intended to create a sufficient vacuum for the manufacturing processes. More precisely, in the case of the connection to at least one process chamber, the vacuum line may comprise a high- vacuum pump which is connected to at least one process chamber and which communicates in series with at least one rough-vacuum pump making it possible to deliver the gases of the process chamber at atmospheric pressure. In accordance with the dangerousness of the gases drawn into the vacuum line at the process chamber, the delivery of the rough-vacuum pump may open out into a treatment device configured to capture and/or destroy any gaseous residue originating from the process chamber. In the case of the connection to at least one load lock upstream of at least one process chamber, the vacuum line may comprise at least one rough-vacuum pump making it possible, for each component transfer towards a process chamber, to deliver the gases of the load lock at atmospheric pressure.

[0004] A rough-vacuum pump generally comprises several pumping stages in series, each pumping stage comprising a pair of rotors rotating in a synchronized manner and in opposite directions in a closed volume delimited by a stator in order to pump a fluid between a suction inlet and a delivery outlet. A clearance, that is to say an interstice, of the order of a few tens to a few hundreds of micrometres is present between the rotors and the stator in order to render pumping possible.

[0005] A differential thermal expansion between the shafts and the stator may take place during operation of the vacuum pumps which may induce seizure between the rotors and the stator, that is to say a reduction in the clearance leading to undesired contact between at least one of the rotors and the internal surface of the stator. This becomes increasingly possible when the materials of the shafts and of the rotors are of different natures. Thus, in accordance with the pumped gases, the architecture of the vacuum line (such as several vacuum pumps mounted in series) and the changes in operation of the pumps, it is often necessary to adapt the rough-vacuum pumps to the installation so as to not risk damaging of said pumps.

[0006] One solution could be to increase the clearances at critical locations, that is to say at the location where seizure between at least one of the rotors and the internal surface of the stator has been observed, such that the differential expansion does not lead to contact between the rotors and the internal surface of the stator of the rough-vacuum pump. However, this solution degrades the efficiency of each pumping stage in which the clearance has been intentionally increased.

[0007] Another solution is to adapt the operation (temperature, rotational speed of the shafts, etc.) of the pumping device at critical moments at which seizure between at least one of the rotors and the internal surface of the stator may be observed, such that the differential expansion does not lead to contact between the rotors and the internal surface of the stator of the rough-vacuum pump. This other solution may consist, in the event of a threshold temperature of the stator being exceeded, in reducing the rotational speed of the rotors until said temperature threshold has been undershot again. However, this other solution also degrades the efficiency of the rough-vacuum pump, but this time of all the pumping stages at the same time.

SUMMARY OF THE INVENTION

[0008] The invention notably has the aim of providing a vacuum line which is able to regulate the localized temperature-increase phenomena in at least one pumping stage of at least one rough-vacuum pump, that is to say without having to increase the clearance between the rotors and the stator and without having to reduce the rotational speed of the shafts of the rotors, in order to maintain the efficiency and the reliability of the vacuum line.

[0009] To this end, a subject of the invention is a vacuum line comprising a pumping device comprising at least one rough-vacuum pump, characterized in that the vacuum line comprises an injection system for injecting suspended elements into the vacuum line in order to form an aerosol in the vacuum line so as to use at least a portion of the suspended elements in the aerosol to absorb, by change of state, at least a portion of the heat generated by compression taking place in the rough-vacuum pump.

[0010] Advantageously according to the invention, the aerosol is used to offer a very large exchange specific surface for the suspended elements. Specifically, the sizes of the particles of suspended elements, such as the droplets or the crystals, and the injection flow rate permit a reactivity of change of state compatible with the residence time (typically less than 100 milliseconds) in each pumping stage of the rough-vacuum pump. Furthermore, suspended elements are easy to mix into the pumped gases notably of the process chamber, this permitting homogeneity of suspended elements in the internal volumes of the stator of the vacuum pump.

[0011] The invention makes it possible to advantageously use the enthalpy of vaporization, also called latent heat of vaporization (passage from the liquid state to the gaseous state), and, possibly, also that of fusion (in the case of crystals, passage from the solid state to the liquid state and then from the liquid state to the gaseous state) or, alternatively, of sublimation (in the case of crystals, passage from the solid state directly to the gaseous state) of the suspended elements in order to absorb, at constant temperature (dependent on the pressure in the pumping stage in question), by change of state, at least a portion of the heat, or even, preferably, all the heat generated by compression taking place in the rough-vacuum pump.

[0012] Specifically, in a known manner, a change of state is effected at constant pressure and at constant temperature. Hence, in accordance with the pressure of the pumping stage of the rough-vacuum pump, the temperature of vaporization (or of fusion or of sublimation) is known as a function of the type of the suspended elements in the aerosol (for example 100 degrees Celsius for water at one atmosphere). Thus, since the temperatures of vaporization (or of fusion or of sublimation) are lower than the temperatures conventionally observed in a rough-vacuum pump, the gas which will be produced from the suspended elements will not be a source of heat prejudicial to the functional parts of the rough-vacuum pump in comparison with the very high heat generated by the compression of the gases in the pumping stages.

[0013] It should also be understood that, as long as suspended elements of the aerosol which have not changed state are present in the pumping stages, the absorption of energy takes place immediately at the location where compression of the gases occurs. The absorption of energy is therefore advantageously automatic and localized, making implementation of the invention very easy. In an empirical manner, it has been observed that compressions of gas could occur in each pumping stage. Compressions of the gases are dependent on the architecture of the vacuum pumps, on the pumped flow of gas and the pressure cycles imposed by the operation of the installation.

[0014] Advantageously according to the invention, each rough-vacuum pump of the vacuum line is therefore more reliable with respect to risks of seizure notably during transition periods (very high flows, very low flows, or even during zero flow), making the vacuum line more robust. It is also obvious that the real-time and localized thermal compensation avoid having to adapt the architecture and parametrization of each roughvacuum pump as a function of the installation to which they belong and/or the type of manufacture taking place in the process chamber. This suggests a possibility of reducing the number of different references of the same type of rough-vacuum pump, that is to say production standardization, permitting lower production costs.

[0015] The invention may also comprise one or more of the following optional features, considered on their own or in combination.

[0016] The injection system may comprise a generation device for generating suspended elements. An aerosol may be formed by the generation device by mixing the produced suspended elements into a carrier gas such as air, a fuel or an inert gas which is then injected into the vacuum line, or the suspended elements produced by the generation device are injected into the vacuum line and mix into the gas or the gas mixture drawn into the vacuum line to form the aerosol. Such a generation device may thus be a nebulizer of the pneumatic type, of the ultrasonic type, of the sieve type or of the spray type.

[0017] The suspended elements may comprise water (H2O) and/or an alcohol and/or carbon dioxide (CO2) and/or any other compound capable of changing state under the thermodynamic conditions of the rough-vacuum pump. In the case of water, demineralized water, also called deionized water, is preferred, or distilled water in order to avoid a situation in which particles present in the water clog the injection conduit to the vacuum line. It is preferred to use pure waters which are already present in the installations for semiconductors and which typically have a resistivity of between 14 and 18 megaohms-centimetre (MQ cm) at 25 degrees Celsius (some ultra-pure waters with a resistivity of 18.2 MQ cm are sold). Water is preferred because its enthalpy of vaporization is very high (around 2500 kilojoules per kilogram (kJ ■ kg ¹ )), allowing a lot of energy to be absorbed upon each change of state. In the case of carbon dioxide (CO2), it is preferred to use the liquid or solid form (dry ice). Dry ice may, for example, be obtained by pressure reduction to atmospheric pressure at a temperature lower than -78.5°C.

[0018] The suspended elements may further comprise a surfactant and/or nanoparticles and/or microparticles in order to calibrate the size of the suspended elements. Specifically, a surfactant will make it possible for the droplets of the aerosol to be divided into smaller sizes (notably for water which has a very high surface tension of 72 millinewtons per metre (rnN m ^-1 ) at 20 degrees Celsius), while the nanoparticles (having a greatest dimension of between at least one nanometre and less than 1000 nanometres) and/or the microparticles (having a greatest dimension of between at least one micrometre and less than 1000 micrometres) will make it possible to form a multiplicity of base substrates for the agglomeration of elements in liquid and/or solid form in the aerosol for avoidance of a situation in which too many elements agglomerate with one another from the same base (snowball effect).

[0019] The injection system may further comprise a thermal regulation device in order to inject the suspended elements into the vacuum line at a predetermined temperature. Thus, the thermal regulation device can make it possible to bring the aerosol to a lower temperature a few degrees Celsius below the boiling temperature (or fusion temperature) at one atmosphere of the suspended elements which are used to absorb, by change of state, at least a portion of the heat generated by compression of the gases in order to inject the suspended elements into the vacuum line under conditions close to their evaporation (or fusion) so as to permit an increased reactivity of absorption by vaporization (or fusion or sublimation) of the suspended elements, that is to say notably to maximize the dynamics of the desired change of state. According to another strategy, it may be envisaged to use the thermal regulation device in order to inject the aerosol into the vacuum line at another chosen temperature.

[0020] The injection system may be configured to form the aerosol upstream of the rough-vacuum pump. Specifically, since the absorption of energy is advantageously automatic and localized according to the invention, the injection can be effected upstream of the critical locations with respect to seizure of the rotors with the stator. Absorption by the suspended elements will take place only when an input of energy allows them to change state in the internal volume of the stator of the rough-vacuum pump. In accordance with the configuration of the pumping device, the injection system may, for example, form the aerosol between a turbomolecular pump and a rotary lobe vacuum pump, or Roots compressor (known as “Roots blower”), or between a rotary lobe vacuum pump, or Roots compressor, and the rough-vacuum pump which delivers at atmospheric pressure. This upstream introduction is also preferred because it permits better homogenization of the aerosol (whether or not the carrier gas is formed solely by the pumped gases) before arrival at the critical locations with respect to seizure of the rotors with the stator.

[0021] As an alternative or in addition, the injection system may be configured to form the aerosol in at least one pumping stage of the rough-vacuum pump. Specifically, for example for considerations of reactivity with respect to the pumped gases or to avoid/limit rising of aerosol into the process chamber (or into the load lock), it may be preferred that the introduction is effected in the rough-vacuum pump. Typically, the introduction may take place in one or more pumping stages directly (fluidic communication with the pumping stage) or preferably indirectly (fluidic communication by way of a conduit between two pumping stages).

[0022] In order to avoid a situation in which the suspended elements and more generally the aerosol rises towards the process chamber or towards the load lock, for example due to backstreaming phenomena, it is preferred to introduce the suspended elements at the suction inlet of the rough-vacuum pump, between the suction inlet of the rough-vacuum pump and the suction inlet of the pumping device or in the rough-vacuum pump.

[0023] The invention also relates to a pumping device intended to be connected to a vacuum line as presented above and comprising at least one rough-vacuum pump, characterized in that the pumping device comprises an injection system configured to form at least one aerosol upstream of the pumping device or in the pumping device in order to use at least a portion of the suspended elements in the aerosol to absorb, by change of state, at least a portion of the heat generated by compression taking place in the rough-vacuum pump.

[0024] It should thus advantageously be understood according to the invention that a supplementary injection system or the injection system of the vacuum line is integrated into the pumping device, this making it possible to easily integrate the invention into an installation during its assembly or in after-sales service. The installer only has to connect the pumping device to the rest of the vacuum line in a customary manner to benefit from the advantages of the invention.

[0025] The invention furthermore relates to an installation comprising at least one process chamber connected to a vacuum line as presented above, wherein the injection system comprises a control unit, characterized in that the control unit of the injection system is connected to a control unit of the process chamber in order to identify the type of gas used in the process chamber so as to adapt the flow of injected suspended elements to the type of gas used in the process chamber.

[0026] Typically, for example, the control unit may thus be configured to turn off the injection system when the control unit runs a cleaning phase of the process chamber.

[0027] Moreover, the invention relates to an installation comprising at least one load lock connected to a vacuum line as presented above, wherein the injection system comprises a control unit, characterized in that the control unit of the injection system is connected to a control unit of the rough-vacuum pump in order to determine the moment at which the load lock is filled so as to adapt the flow of injected elements to the pressure variations in the load lock. In each filling operation, the load lock is filled with air at ambient pressure, resulting in a strong increase in the load of the rough-vacuum pump. The connection between the control unit and the control unit aims to make it possible to detect these variations in load. Specifically, it has been observed that characteristics of the roughvacuum pump may make it possible to interpret variations in operation of the load lock. It should be understood that the pumping device may therefore be autonomous so as to adapt the control of the injection system, that is to say may not necessarily be connected to the control unit of the load lock.

[0028] Typically, for example, the control unit may be configured to introduce a flow rate of suspended elements into the vacuum line that is proportional to the electrical power consumed by the motor of the rough-vacuum pump provided by the control unit and/or a flow rate of suspended elements into the vacuum line that is proportional to the pressure upstream of the rough-vacuum pump provided by a pressure sensor connected to the control unit and/or a predetermined flow rate of suspended elements into the vacuum line for a predetermined duration.

[0029] Lastly, the invention relates to a thermal regulation process for thermal regulation of a rough-vacuum pump, characterized in that the process comprises at least one step of injecting suspended elements into a flow of a vacuum line pumped by the roughvacuum pump in order to form an aerosol in the vacuum line so as to use at least a portion of the suspended elements in the aerosol to absorb, by change of state, at least a portion of the heat generated by compression taking place in the rough-vacuum pump.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further particular features and advantages of the invention will become clearly apparent from the following description thereof, which is given by way of entirely nonlimiting indication, with reference to the appended drawings, in which:

Figure 1 is a schematic view of an example of an installation according to the invention;

Figure 2 is a schematic view of an example of a rough-vacuum pump according to the invention;

Figure 3 is a graph of a first example of control of the injection system according to the invention as a function of the electrical power consumed by the motor of the rough-vacuum pump;

Figure 4 is a pumping device which makes it possible to implement the first example of control of the injection system according to the invention;

Figure 5 is a graph of a second example of control of the injection system according to the invention as a function of the electrical power consumed by the motor of the rough-vacuum pump;

Figure 6 is a pumping device which makes it possible to implement the second example of control of the injection system according to the invention; Figure 7 is a graph of a third example of control of the injection system according to the invention as a function of the electrical power consumed by the motor of the rough-vacuum pump;

Figure 8 is a pumping device which makes it possible to implement the third example of control of the injection system according to the invention;

Figure 9 is a graph of a fourth example of control of the injection system according to the invention as a function of the pressure upstream of the rough-vacuum pump;

Figure 10 is a pumping device which makes it possible to implement the fourth example of control of the injection system according to the invention;

Figure 11 is a graph of a fifth example of control of the injection system according to the invention as a function of several parameters of the rough-vacuum pump; Figure 12 is a pumping device which makes it possible to implement the fifth example of control of the injection system according to the invention.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

[0031] In the various figures, identical or similar elements bear the same references, possibly with an added index. The description of their structure and of their function is therefore not systematically repeated.

[0032] Throughout the following, the orientations are the orientations of the figures. In particular, the terms “top”, “bottom”, “left”, “right”, “above”, “below”, “towards the front” and “towards the rear” are understood generally with respect to the direction of representation of the figures. Furthermore, the terms “upstream” and “downstream” are understood generally with respect to the direction of the pumping flow.

[0033] “Aerosol” is understood to mean any dispersion of elements as very fine particles of a liquid (droplets), of a solution (solid in a liquid) or of a solid (crystals) in a carrier gas, the carrier gas being able to be injected at the same time as the suspended elements, or the carrier gas being the gas or the gas mixture drawn into the vacuum line 1 .

[0034] “High-vacuum pump 2” is understood to mean any device, such as a turbomolecular vacuum pump, that is capable, after connection to a closed volume, of creating a vacuum in this closed volume, that is to say notably of being able to obtain a high vacuum lower than or equal to 10' ¹ Pa and typically of between 10' ¹ Pa and 10' ⁶ Pa (equivalent respectively to 10' ³ mbar and 10' ⁸ mbar).

[0035] “Rough-vacuum pump 4” is understood to mean any device that is capable, after connection to a closed volume, of creating a vacuum in this closed volume, that is to say notably of being able to obtain a rough vacuum of between 100 and 0.1 Pa. A backing pump is a pump which is configured to be able to start at atmospheric pressure and which is able to deliver at atmospheric pressure. In the case of the invention, the rough-vacuum pump 4 is preferably a pump having at least one pumping stage comprising two parallel rotor drive shafts which are driven in rotation by a dedicated motor 22, such as a rotary lobe (Roots), screw or claw pump. More generally, all the rotors that are compatible with a two-shaft drive can be envisaged for implementation of the invention. It should therefore be understood that the invention can be applied to any type of dry vacuum pump irrespective of its architecture such as the number of pumping stages or the shape of the rotors.

[0036] “Supplementary vacuum pump 4'” is understood to mean any device, such as a rotary lobe vacuum pump (also called “Roots compressor” or “Roots blower”), configured to draw in, transfer and then deliver a gas to be pumped notably for the application of the invention to a vacuum line 1 connected to at least one process chamber 17 or a load lock 25. The supplementary vacuum pump 4' is intended to supplement the suction of the rough-vacuum pump 4 of a pumping device and is, preferably, mounted upstream of and in series with the rough-vacuum pump 4 for the application to a process chamber 17 or a load lock 25. The supplementary vacuum pump 4' may comprise between one and three pumping stages mounted in series, each pumping stage comprising a pair of rotors which are driven in rotation by a dedicated motor. The supplementary vacuum pump 4' primarily differs from the rough-vacuum pump 4 in the larger dimensions of the pumping stages due to the higher pumping capacities required for the application to a process chamber 17 or a load lock 25, the larger clearance tolerances, and the fact that the supplementary vacuum pump 4' cannot deliver at atmospheric pressure, thus explaining the mounting in series upstream of a rough-vacuum pump 4.

[0037] An example of a manufacturing installation 21 is visible in Figure 1 , in which a vacuum line 1 according to the invention is used. In the example of Figure 1 , at least one process chamber 17, the control unit 18 of which manages the inflow of process gases, is used to manufacture parts for example on the basis of semiconductors. The process chamber 17 may, for example, implement physical vapour deposition (PVD) or chemical vapour deposition (CVD) processes, diffusion of chemical elements, doping or etching. The process chamber 17 is connected to the vacuum line 1 which is configured to draw in the gases present in the process chamber 17 and to deliver the pumped gases, preferably at atmospheric pressure, to the treatment device 19 for treating delivered gases.

[0038] In the example illustrated in Figure 1 , the vacuum line 1 also comprises a high- vacuum pump 2, a pumping device 3 and an injection system 5. The high-vacuum pump 2 may be a turbomolecular vacuum pump. The pumping device 3, mounted downstream with respect to the direction of the pumping flow and in series with the high-vacuum pump 2, comprises at least one rough-vacuum pump 4 intended to generate a vacuum that is able to permit the manufacture of parts in the process chamber 17. In the specific example of Figure 1 for the application of the invention to a vacuum line 1 connected to at least one process chamber 17, the pumping device 3 comprises a supplementary rotary lobe vacuum pump 4' which has one pumping stage and which is mounted upstream of and in series with a rough-vacuum pump 4 which has several pumping stages 11a, 11 b, 11c, 11d, 11e, 11f (the delivery outlet 7' of the supplementary vacuum pump 4' opens out at the suction inlet 6 of the rough-vacuum pump 4).

[0039] A suction inlet 6' of the pumping device 3 is therefore connected indirectly to the process chamber 17 via the high-vacuum pump 2. The pumping device 3 is intended to drive the gaseous residues of the process chamber 17 in a direction of circulation proceeding from the suction inlet 6' to a delivery outlet 7 which is connected, in the example of Figure 1 , to the treatment device 19 for treating delivered gases.

[0040] Of course, if only a rough-vacuum pump 4 is used, the suction inlet and the delivery outlet of the pumping device 3 will respectively be the suction inlet 6 and the delivery outlet 7 of the rough-vacuum pump 4. As will be explained below, the pumping device 3 may comprise only a rough-vacuum pump 4 notably for the application of the invention to a vacuum line 1 connected to at least one load lock 25.

[0041] The rough-vacuum pump 4 comprises, in a known manner, a stator 10 formed of at least one end support 8, 9 (two are shown in Figure 2) intended to support shaft bearings 24 and various items of equipment (cooling device, synchronization elements, motor 22, etc.). Each end support 8, 9 is coupled axially with elements of the stator 10 (for example, in a known manner, half-shells) to form at least one pumping stage 11a, 11b, 11c, 11 d, 11 e, 11f (six pumping stages 11a, 11b, 11c, 11 d, 11 e, 11 f mounted in series are shown in Figure 2) mounted between the suction inlet 6 and the delivery outlet 7. Provision is made of two shafts 24 provided with rotors which are configured to rotate in a synchronized manner in opposite directions in each pumping stage 11a, 11 b, 11c, 11 d, 11 e, 11f so as to drive a gas to be pumped in a direction of circulation proceeding from the suction inlet 6 to the delivery outlet 7.

[0042] Of course, the pumping device 3 may comprise one (or more) rough-vacuum pump(s) 4 and one (or more) supplementary vacuum pump(s) 4' connecting at least one process chamber 17 and one (or more) treatment device(s) 19 for treating delivered gases without departing from the scope of the invention. Furthermore, the pumping device 3 may comprise one (or more) rough-vacuum pump(s) 4 connecting at least one load lock 25 without departing from the scope of the invention. [0043] Each gas treatment device 19 is configured to treat, at atmospheric pressure, the gases delivered by the pumping device 3, that is to say notably to capture and/or destroy any gaseous residue originating from the process chamber 17. In a manner known per se, the gas treatment device 19 comprises a control unit 20 intended to control, for example, a burner (not shown) configured to produce thermal reactions at high temperatures by combustion of hydrocarbons and/or an electric system configured to produce thermal reactions at high temperatures by means of heating resistors and/or a plasma and/or a scrubber and/or a chemisorption and/or physisorption cartridge.

[0044] According to the invention, the vacuum line 1 further comprises an injection system 5 for injecting suspended elements into the vacuum line 1 in order to form an aerosol in the vacuum line 1 so as to use at least a portion of the suspended elements in the aerosol to absorb, by change of state, at least a portion of the heat, or even, preferably, all the heat generated by compression taking place in the rough-vacuum pump.

[0045] Specifically, it has been determined that the differential expansions between the rotors and stator 10 are primarily due to pseudo-adiabatic, that is to say not entirely adiabatic, compressions of the gases. More precisely, the outside of the stator 10 is generally in contact with the ambient air of the installation 21 (or in a thermoregulated enclosure), while the rotors are enclosed in each pumping stage 11a, 11b, 11c, 11 d, 11 e, 11f in a volume delimited by the stator 10. This results in a limited transfer of heat from the rotors to the outside of the rough-vacuum pump 4, leading to a more rapid heating of the rotors with respect to the stator 10 during the compressions of the gases in the pumping stages 11a, 11b, 11c, 11 d, 11e, 11f. It should therefore be understood that a portion of the heat leaves in the stator 10 (first loss), which is thermally regulated. A second portion is absorbed (second loss) in the thermally insulated shafts 24 (rotors). The remainder is discharged in the form of heated gases downstream of the suction flow (third loss), and so on stage by stage until the hot gases are discarded at the delivery outlet 7. Overall, a significant fraction of the thermodynamic balance lies in the structure (stator 10, rotors) of the vacuum pump which is heated, which ultimately poses problems of differential thermal expansion between the rotors and the stator 10 depending on the pumping flow and pressure conditions.

[0046] In the example illustrated in Figures 1 and 2, the injection system 5 primarily comprises a control unit 13, a generation device 15 for generating suspended elements, and closure (and therefore opening) elements 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i in order to inject the suspended elements upstream of the pumping device 3 (typically at the suction inlet 6' of the supplementary vacuum pump 4' or at the suction inlet 6 of the rough-vacuum pump 4) and/or in at least one pumping stage 11a, 11b, 11c, 11 d, 11 e, 11 f of the rough-vacuum pump 4. The control unit 13 notably makes it possible to control the actuation of the closure elements 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i, such as controlled valves, and/or the type of suspended elements in the aerosol formed. Of course, in the particular application in which the pumping device 3 comprises several vacuum pumps 4, 4', the injection system 5 may thus introduce the suspended elements into each vacuum pump 4, 4' without departing from the scope of the invention. Lastly, the optional injection into the end supports 8, 9 is primarily used in the case explained below in which only a gas is injected (the suspended elements are no longer injected), and has the primary aim of pressurizing the end supports 8, 9 in order to avoid a situation in which the pumped gases pass therethrough (by way of the bearings for example) and more generally in order to make it possible to prevent the pumped gases from exiting the rough-vacuum pump 4.

[0047] Advantageously according to the invention, the aerosol is used to offer a very large exchange specific surface for the suspended elements. Specifically, the sizes of the particles of suspended elements, such as the droplets or the crystals, and the flow rate of the suspended elements permit a reactivity of change of state compatible with the residence time (typically less than 100 milliseconds) in each pumping stage 11a, 11 b, 11c, 11 d, 11 e, 11 f of the rough-vacuum pump 4. Furthermore, an aerosol is easy to mix into the pumped gases notably of a process chamber 17 (or of a load lock 25), this permitting homogeneity of suspended elements in the internal volumes of the stator 10 of the rough-vacuum pump 4.

[0048] The invention makes it possible to advantageously use the enthalpy of vaporization, also called latent heat of vaporization, and, possibly, also that of fusion or, alternatively, of sublimation of the suspended elements in order to absorb, at constant temperature (dependent on the pressure in the pumping stage 11a, 11b, 11c, 11 d, 11e, 11f in question), by change of state, all or some of the heat generated by compression taking place in the rough-vacuum pump 4 (and, possibly, in the supplementary vacuum pump 4'). Specifically, in a known manner, a change of state is effected at constant pressure and at constant temperature. Hence, in accordance with the pressure of the pumping stage 11a, 11b, 11c, 11d, 11e, 11f of the rough-vacuum pump 4 (and, possibly, of the supplementary vacuum pump 4'), the temperature of vaporization (or of fusion or of sublimation) is known as a function of the type of the suspended elements in the aerosol (for example 100 degrees Celsius (°C) for water at one atmosphere). Thus, since the vaporization temperatures are lower than the temperatures conventionally observed in a rough-vacuum pump 4, 4', the gas which will be produced from the suspended elements will not be a source of heat prejudicial to the functional parts of the roughvacuum pump 4, 4' in comparison with the very high heat generated by the compression of the gases.

[0049] It should also be understood that, as long as suspended elements of the aerosol which have not changed state are present in the pumping stages 11a, 11 b, 11c, 11d, 11e, 11 f, the absorption of energy takes place immediately at the location where compression of the gases occurs. The absorption of energy is therefore advantageously automatic and localized, making implementation of the invention very easy. In an empirical manner, it has been observed that compressions of the gases could occur in each pumping stage 11a, 11 b, 11c, 11d, 11e, 11f. Compressions of the gases are dependent on the architecture of the vacuum pumps 4', 4, on the pumped flow of gas and the pressure cycles imposed by the operation of the installation 1.

[0050] The increase in temperature due to the compression is directly proportional to the increase in pressure according to the ideal gas law PV = nRT (the volume V of the stator 10 being constant). Thus, since the pressure difference, in absolute value, is very low in the first stages (a few tenths of a millibar), the heating may be considerably lower (except if a rotary lobe pump, or Roots compressor, 4' is upstream of the rough-vacuum pump 4) than in the last stages in which the pressure is increased by a few tens to a few hundreds of millibar.

[0051] Advantageously according to the invention, each rough-vacuum pump 4 (and, possibly, each supplementary vacuum pump 4') of the vacuum line is therefore more reliable with respect to risks of seizure notably during transition periods (passage between full capacity and idle capacity and vice versa, or passage between nonconnected full capacity and full capacity connected to a chamber 17, 25 and vice versa), making the vacuum line 1 more robust. It is also obvious that the architecture and parametrization of each rough-vacuum pump 4 (and, possibly, each supplementary vacuum pump 4') require less adaptation as a function of the installation 21 to which they belong and/or the type of manufacture taking place in the process chamber 17. This suggests a possibility of reducing the number of different references of the same type of rough-vacuum pump 4 (and, possibly, of supplementary vacuum pump 4'), that is to say production standardization, permitting lower production costs.

[0052] The generation device 15 for generating suspended elements is intended to form the suspended elements either in a carrier gas such as air, a fuel (CH4, H2) or an inert gas (N2, Ar2), or in the gas or the gas mixture drawn into the vacuum line 1. An aerosol may thus be formed by the generation device 15 by mixing the produced suspended elements into a carrier gas such as air, a fuel or an inert gas which is then injected into the vacuum line 1 , or the aerosol may be formed by injecting/mixing the suspended elements produced by the generation device 15 into the gas or the gas mixture drawn into the vacuum line 1. Such a generation device 15 may thus be a nebulizer of the pneumatic type (for example a Venturi nebulizer), of the ultrasonic type, of the sieve type (using vibrations to compel the formation of droplets calibrated by the passage through the opening cross sections of the sieve) or of the spray type (for example a nebulizer having an atomization nozzle), which are or are not coupled to a thermal regulation device 14.

[0053] According to the invention, the size of the particles of suspended elements formed by the generation device 15 preferably has a greatest dimension of between 10 and 300 micrometres (pm), that is to say droplets or crystals the greatest dimension of which from among the length, the width and the thickness is between 10 and 300 micrometres, such as 10 pm, 20 pm, 30 pm, 40 pm, 50 pm, 100 pm, 150 pm, 200 pm, 250 pm or 300 pm. Of course, the size could be greater or smaller than the preferred range of values without departing from the scope of the invention.

[0054] For the application of the invention to a vacuum line 1 connected to at least one process chamber 17, the flow rate of the aerosol may preferably range between zero and 200 grams per minute of suspended elements, that is to say for example 0 g-min ^-1 , 5 g min ^-1 , 10 g min ^-1 , 15 g min ^-1 , 20 g min ^-1 , 25 g mim ¹ , 30 g min ^-1 , 40 g min ^-1 , 50 g min ^-1 , 60 g min ^-1 , 70 g min ^-1 , 80 g min ^-1 , 90 g min ^-1 , 100 g min ^-1 , 110 g min ^-1 , 120 g min ^-1 , 130 g min ^-1 , 140 g min ^-1 , 150 g min ^-1 , 160 g min ^-1 , 170 g min ^-1 , 180 g min ^-1 , 190 g min ^-1 , 200 g min ^-1 . Of course, in accordance with the type of suspended elements, the flow rate could be greater or smaller than the preferred range of values without departing from the scope of the invention. Typically, as explained below, depending on the desired settings, it may be envisaged that no suspended element is introduced into the vacuum line 1 by the injection device 5 but that the carrier gas produced by the generation device 15 is still introduced or that nothing is introduced into the vacuum line 1 by the injection device 5.

[0055] The suspended elements formed by the generation device 15 may comprise water (H2O) and/or an alcohol and/or carbon dioxide (CO2) and/or any other compound capable of changing state under the thermodynamic conditions of the rough-vacuum pump 4. In the case of water, demineralized water, also called deionized water, is preferred, or distilled water in order to avoid a situation in which particles present in the water clog the injection conduit to the vacuum line 1 . It is preferred to use pure waters which are already present in the installations for semiconductors and which typically have a resistivity of between 14 and 18 megaohms-centimetre (MQ cm) at 25 degrees Celsius, that is to say notably 14 MQ cm, 14.5 MQ cm, 15 MQ cm, 15.5 MQ cm, 16 MQ cm, 16.5 MQ cm, 17 MQ cm, 17.5 MQ cm, 18 MQ cm. Some ultra-pure waters with a resistivity of 18.2 MQ cm are sold. Water is preferred because its enthalpy of vaporization is very high (around 2500 kilojoules per kilogram (kJ-kg ^-1 )), allowing a lot of energy to be absorbed upon each change of state. The alcohol may comprise, for example, a methanol or an ethanol. In the case of carbon dioxide (CO2), it is preferred to use the liquid or solid form (dry ice). Dry ice may, for example, be obtained by pressure reduction to atmospheric pressure at a temperature lower than -78.5°C.

[0056] For the application of the invention to a vacuum line 1 connected to at least one process chamber 17, it has been calculated theoretically that, for a flow rate of the aerosol at 100 g min' ¹ of water, that is to say 6 l h’ ¹ of sprayed water, it is possible to extract approximately 4.2 kilowatts of compression energy.

[0057] The suspended elements may further comprise a surfactant and/or nanoparticles and/or microparticles in order to limit or even calibrate the size of the suspended elements. Specifically, a surfactant will make it possible for the droplets of the aerosol to be divided into smaller sizes (notably for water which has a very high surface tension of 72 millinewtons per metre (rnN m ^-1 ) at 20 degrees Celsius). A surfactant comprising a quaternary ammonium salt (for example NH4+) or an alcohol (for example methanol, CH3OH, or ethanol, C2H5OH, etc.) may be envisaged.

[0058] Nanoparticles (having a greatest dimension of between at least one nanometre and less than 1000 nanometres) and/or microparticles (having a greatest dimension of between at least one micrometre and less than 1000 micrometres) will make it possible to maximize the specific surface area to give rise to fine nucleation of suspended elements in liquid and/or solid form in the aerosol for avoidance of a situation in which too many elements agglomerate with one another from the same base (snowball effect). Thus, the highest possible specific surface areas (in m ² kg) are sought in order to maximize the kinetics of evaporation (or of sublimation). Dimensions below 10 pm bring about very large specific surface areas. By way of example, a specific surface area greater than 1000 m ² kg' ¹ for droplet diameters of 10 pm, and 6000 m ² kg' ¹ for droplet diameters of 1 pm.

[0059] Nanoparticles and/or microparticles comprising an inert material such as a silica (SiO2) or a silicate (SiO4) may be envisaged.

[0060] The thermal regulation device 14 for the aerosol makes it possible to inject the suspended elements at a predetermined temperature, for example lower than the boiling temperature (or fusion temperature) at one atmosphere of the suspended elements which are used to absorb, by change of state, all or some of the heat generated by compression taking place in the rough-vacuum pump 4. More generally, the temperature adjustment makes it possible to bring the suspended elements (liquid or solid) to a chosen predetermined temperature for obtaining, by change of state, the most rapid and most complete thermal absorption possible, considering the very short residence time. It should be understood that a decrease or an increase in the temperature, for example of the pressure reduction or compression type, can be obtained by way of the thermal regulation device 14. Using a Mollier diagram, for example in the case of water, it is found that the boiling temperature at 1 bar is 100°C and, at 123 mbar, 50°C. In order to optimize the phase change in the last pumping stage which delivers at atmospheric pressure, the thermal regulation device 14 makes it possible to bring the liquid water in suspension to a temperature of between 85 and 95 degrees Celsius, that is say for example 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91 °C, 92°C, 93°C, 94°C or 95°C, in order to form the aerosol in the vacuum line 1 under conditions close to its evaporation so as to permit an increased reactivity of absorption, by vaporization of the suspended elements, of all or some of the heat generated by compression taking place in the rough-vacuum pump. Of course, according to another strategy, it may be envisaged to use the thermal regulation device 14 in order to inject the suspended elements into the vacuum line 1 at another chosen temperature, such as between zero and 20 degrees Celsius, that is to say for example 0°C, 5°C, 10°C, 15°C or 20°C.

[0061] As is visible in Figures 1 and 2, the injection system 5 may be configured to form the aerosol upstream of the rough-vacuum pump 4, that is to say typically at the suction inlet 6' of the supplementary vacuum pump 4' for the application for example to a process chamber 17 or at the suction inlet 6 of the rough-vacuum pump 4 for the applications for example to a process chamber 17 or to a load lock 25. Specifically, since the absorption of energy is advantageously automatic and localized according to the invention, the injection can be effected upstream of the critical locations with respect to seizure of the rotors with the stator 10. Absorption by the suspended elements will take place only when an input of energy allows them to change state in the internal volume of the stator 10 of the rough-vacuum pump 4. In accordance with the configuration of the pumping device 3, the injection system 5 may, for example, introduce the suspended elements between a turbomolecular vacuum pump 2 and a rotary lobe vacuum pump 4' (or Roots compressor), or between a rotary lobe vacuum pump 4' (or Roots compressor) and the rough-vacuum pump 4 which delivers at atmospheric pressure. This upstream introduction is also preferred because it permits better homogenization of the aerosol (whether or not the carrier gas is formed by the pumped gases) before arrival at the critical locations with respect to seizure of the rotors with the stator 10. [0062] As an alternative or in addition, the injection system 5 may be configured to introduce the suspended elements into at least one pumping stage 11a, 11b, 11c, 11d, 11e, 11f of the rough-vacuum pump 4 and/or, possibly, of the supplementary vacuum pump 4'. Specifically, for example for considerations of reactivity with respect to the pumped gases or to avoid/limit rising of aerosol into the process chamber 17 (or the load lock 25), it may be preferred that the introduction is effected in the rough-vacuum pump

4 and/or, possibly, the supplementary vacuum pump 4'. Typically, the introduction may take place in one or more pumping stages 11a, 11 b, 11c, 11d, 11 e, 11f directly (fluidic communication with the pumping stage) or preferably indirectly (fluidic communication by way of a conduit between two pumping stages).

[0063] It is immediately clear from what has been set out above that the injection system

5 can be mounted at several locations in the installation 21 without departing from the scope of the invention. According to a particular embodiment, the pumping device 3 may thus comprise an injection system 5 configured to form at least one aerosol upstream of the pumping device 3 or in the pumping device 3 in order to use at least a portion of the suspended elements in the aerosol to absorb, by change of state, at least a portion of the heat, or even, preferably, all the heat generated by compression taking place in the roughvacuum pump.

[0064] It should thus advantageously be understood according to the invention that a supplementary injection system 5 or the injection system 5 of the vacuum line 1 is integrated into the pumping device 3, this making it possible to easily integrate the invention into an installation 21 during its assembly or in after-sales service. The installer only has to connect the pumping device 3 to the rest of the vacuum line 1 in a customary manner to benefit from the advantages of the invention.

[0065] The flow rate of the injection system 5 may also be controlled in an optimized manner on the basis of data measured in the installation 21 . It is thus possible to imagine that the closure elements 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i are controlled with simple action (open or closed) and/or continuously (controllable opening) in such a way as to vary the flow rate of at least one type of suspended elements, that is to say one (or more) type(s) of suspended elements which is (are) different or not, at at least one injection location, that is to say one (or more) location(s) which is (are) different or not, in order to finely thermally regulate at least one rough-vacuum pump 4 of the pumping device 3.

[0066] According to a first example in which the installation 21 comprises at least one process chamber 17 connected to a vacuum line 1 as presented in Figure 1 , the control unit 13 of the injection system 5 may thus be connected to a control unit 18 of the process chamber 17 in order to identify the type of gas used in the process chamber 17 so as to adapt the flow of aerosol to the type of gas used in the process chamber 17.

[0067] Typically, for example, the control unit 13 may thus be configured to turn off the injection system 5 when the control unit 18 runs a cleaning phase of the process chamber 17. Specifically, it is often the case that a cleaning phase uses a cleaning gas (HCI, HF, NF3, etc.) which is reactive with oxygen-based suspended elements, or more particularly with water (H2O). It is therefore advantageous to stop the injection of reactive suspended elements when it is determined that a cleaning gas is being sent into the process chamber 17, in order to be able to use the cleaning gas to also clean the pumping device 3 and, possibly, the high-vacuum pump 2 without degrading the cleaning gas by reaction with the aerosol. For example, in the case of water-based suspended elements, it is sought to minimize the risks of corrosion which are linked to the contact between the aerosol and the cleaning gas. It may thus be envisaged to stop the injection of water-based suspended elements so as to leave only the carrier gas and/or so as to leave only dry ice and/or so as to replace the water with dry ice and/or to inject a neutral gas for a predetermined duration with the inflow of the cleaning gas.

[0068] Conversely, the control unit 13 may thus be configured so that the flow rate of suspended elements is increased when it is determined that a process gas, identified as having the effect of worsening the heat generated by compression of the gases, is injected, this notably being the case for dihydrogen.

[0069] Of course, the control unit 13 may also be connected to another control unit 20, 23 such as that of the treatment device 19 and/or that of the pumping device 3 (this latter case is explained in the second example below) in order to optimize the control of the injection system 5 as a function of changes in the steps of the process upstream of the pumping device 3 and/or as a function of the needs of the treatment device 19 downstream of the pumping device.

[0070] According to a second example in which the installation 21 comprises at least one load lock 25 connected to a vacuum line 1 as presented in Figure 2, the pumped gases will primarily be air and it is possible to use only one rough-vacuum pump 4 to form a rough vacuum in the load lock 25 between each closure and re-opening of the load lock 25. In such a case, provision may be made to connect the control unit 13 of the injection system 5 to a control unit 26 of the load lock 25 in order to determine the moment at which the load lock 25 is filled, that is to say when the pressure in the load lock 25 will return to ambient pressure, so as to adapt the flow of injected suspended elements to the variations in pressure in the load lock 25. Typically, the higher the pressure in the load lock 25, the greater the flow of injected suspended elements preferably is. [0071] Thus, the connection to the control unit 26 of the load lock 25 makes it possible to know the parametrization for opening of the load lock 25, making it possible to inject the maximum amount of suspended elements at the moment of opening so as to thermally compensate any compression in the vacuum pump 4 for a predetermined duration such as half the time between two filling operations of the load lock 25. According to another example, the control unit 13 could be configured to introduce a flow rate of suspended elements that is proportional to the pressure in the load lock 25 provided by a pressure sensor 27 connected to the control unit 26 of the load lock 25.

[0072] It is therefore apparent that the flow rate of suspended elements may be determined on the basis of the parametrization for opening of the load lock 25 and/or the pressure in the load lock 25. Of course, in accordance with the applications, other characteristics of the load lock 25 which are representative of the pressure in the load lock 25 may be used without departing from the scope of the invention.

[0073] As an alternative, the control unit 13 of the injection system 5 may be connected to (or comprise) a control unit 23 of the rough-vacuum pump 4 and, more generally, to the control unit of the pumping device 3 in order to determine the moment at which the load lock 25 is filled so as to adapt the flow of injected suspended elements to the variations in pressure in the load lock 25. Typically, the higher the pressure, the greater the flow of injected suspended elements preferably is. Thus, characteristics of the roughvacuum pump 4 may make it possible to interpret variations in operation of the load lock 25. It should be understood that the pumping device 3 may therefore be autonomous so as to adapt the control of the injection system 5, that is to say may not necessarily be connected to the control unit 26 of the load lock 25.

[0074] By way of example, the electrical power consumed by the motor 22 of the roughvacuum pump 4 makes it possible to estimate the pressure present in the load lock 25. More precisely, the electrical power consumed by the motor 22 is directly proportional to the flow of pumped gas. The power information is available in real time via an output of the frequency variator of the control unit 23 of the rough-vacuum pump 4. Thus, for example, the control unit 13 may be configured to introduce a flow rate of suspended elements that is proportional to the electrical power consumed by the motor 22 of the rough-vacuum pump 4 provided by the control unit 23.

[0075] In an additional or substitutional manner, the control unit 13 may also be configured to introduce a flow rate of suspended elements that is proportional to the pressure upstream of the rough-vacuum pump 4 provided by a pressure sensor 28 connected to the control unit 23. This solution makes it possible to directly adapt the injection of the suspended elements to the flow of pumped gas measured preferably at the suction inlet 6, as illustrated in Figure 2.

[0076] In an additional or substitutional manner, the control unit 13 may also be configured to introduce a predetermined flow rate of suspended elements for a predetermined duration. This solution is based on the assumption that the operation of a load lock 25 is highly reproducible, that is to say that the time between two filling operations of the load lock 25 is always the same. It then becomes simple to manually input the time between each filling operation into the control unit 13 so that the latter manages the control of the injection system 5, or the connection to the control unit 26 of the load lock 25 makes it possible to know the parametrization for opening of the load lock 25.

[0077] A simple timer comprised in the control unit 13 could then decide the predetermined injection duration, such as between a third and two thirds of the time between two opening operations of the load lock 25, that is notably a 1/3, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 2/3 of the time between two opening operations of the load lock 25. The predetermined flow rate of injected suspended elements may or may not be constant for the predetermined duration. By way of non-limiting example, the flow rate could be constant and as high as possible for 50% of the time between two opening operations of the load lock 25 or decrease according to a pre-established gradient (for example from the highest possible flow rate) for 2/3 of the time between two opening operations of the load lock 25.

[0078] It is therefore apparent that the flow rate of suspended elements may be determined on the basis of the electrical power consumed by the motor 22 of the roughvacuum pump 4 and/or the pressure upstream of the rough-vacuum pump 4 and/or a predetermined duration that the control unit 13 is or is not connected to another member (for example the control units 18, 20, 26). By way of non-limiting example, the flow rate of injected suspended elements may be proportional to the electrical power consumed by the motor 22 of the rough-vacuum pump 4 for 2/3 of the time between two opening operations of the load lock 25. Of course, in accordance with the applications, other characteristics of the vacuum pump 4 which are representative of the pressure in the load lock 25 may be used without departing from the scope of the invention.

[0079] Specifically, in the application to the pumping operation of a load lock 25, it has been observed that, upon each communication between the load lock 25 under ambient atmosphere and the pumping device 3, being able to be effected for example every two to 40 minutes in accordance with the volume of the load lock 25, the electrical power consumed by the motor 22 increases sharply and rapid heating generated by compression of the gases is generated. The torque to be provided may even be so high that the rotational speed of the motor 22 is limited temporarily due to the cap on the possible consumed electrical power.

[0080] The invention then provides its full benefit by limiting the heating generated by compressions of the gases in the pumping stages 11a, 11 b, 11c, 11d, 11 e, 11f. It is clear that by absorbing the heat generated by compressions of the gases at the moment at which the flow to be pumped is greatest, it is possible to maintain the most effective pumping operation of the rough-vacuum pump 4 as possible, that is to say notably the limitation of the heating will make it possible for a pumping cycle to be restarted more rapidly or for the pumping operation to be effected in a shorter time that is optimal for the reliability of the pump. In the case of a load lock 25 with a large capacity (for example 2.2 m ³ ), for an aerosol based on water in suspension in the air, it has been calculated that a theoretical flow rate of between 140 slm of aerosol (at the moment of communication between the load lock 25 under ambient atmosphere and the pumping device 3 when the electrical power consumed by the motor 22 is at a maximum, for example above 5 kW) and 30 slm of aerosol (when the electrical power consumed by the motor 22 is at a minimum, for example below 1 kW) was ideal.

[0081] Thus, advantageously according to the invention, by monitoring the electrical power consumed by the motor 22, no surplus injection of suspended elements is effected, this making it possible to limit the consumption of suspended elements and avoiding a situation in which surplus suspended elements are deposited in the rough-vacuum pump 4, this deposition of surplus suspended elements possibly generating problems of reliability, such as problems of corrosion for water-based suspended elements.

[0082] A first example of control of an injection system 5 according to the invention as a function of the electrical power C consumed by the motor 22 of the rough-vacuum pump 4 is shown in Figures 3 and 4. Each closure (and therefore opening) element 16 is formed by a proportional valve. In the example visible in Figure 4, the generation device 15 for generating liquid water is connected to the proportional valve 16 which communicates via an introduction element 29 of the atomization nozzle type with a pumping stage 11b. As is visible in Figure 3, the control comprises an injection curve I proportional to the curve C of the electrical power consumed by the motor 22 of the rough-vacuum pump 4.

[0083] If the closure (and therefore opening) elements 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i are not proportional valves, the proportionality of the control P of the injection of aerosol with respect to the electrical power C consumed by the motor 22 of the roughvacuum pump 4 is more difficult to obtain. Figures 5 to 8 therefore show two variants of control P of the injection system 5 as a function of the electrical power C consumed by the motor 22 of the rough-vacuum pump 4 in order to achieve a less fine proportionality, that is to say according to a reactivity that is lower than with proportional valves.

[0084] In a second example of control in Figures 5 and 6, each closure element 16 permits only one possible opening flow rate. It should therefore be understood that, in order to adapt to the variations in electrical power C consumed by the motor 22, the duration of injection of the aerosol by the injection system 5 as a function of time T makes it possible to vary the quantity of aerosol injected as a function of the electrical power C consumed by the motor 22. In the example visible in Figure 6, the generation device 15 for generating liquid water is connected to the all-or-nothing valve 16 (open according to a fixed flow rate or closed) which communicates via an introduction element 29 of the atomization nozzle type with a pumping stage 11b. As is visible in Figure 5, the graph comprises a curve C drawn with a solid line showing an example of electrical power consumed by the motor 22 as a function of time T. The same graph shows an example of control P of the injection system 5, as a curve drawn with a dashed line, as a function of time T. Two possible variables should be noted, the duration of injection 11 , I2, I3, I4,

15, I6, I7 and the duration between each injection. At maximum electrical power C1 consumed by the motor 22, the control unit 13 preferably injects the maximum flow rate of aerosol, as in the injection 11 , which stops when the electrical power C consumed by the motor 22 starts to decrease. With the variation of electrical power C consumed by the motor 22, the control unit 13 adapts the durations of injections 11 , I2, I3, I4, I5, I6, I7 and the durations between injections 11 , I2, I3, I4, I5, I6, I7 in order to maintain a quantity of suspended elements in the aerosol that is able to absorb, by change of state, all or some of the heat generated by compression taking place in the rough-vacuum pump 4.

[0085] Preferably, a minimum duration of injection of, for example, between 1 second and 10 seconds is provided when the electrical power C consumed by the motor 22 is below the maximum value C1 that can be consumed by the motor 22. Below this maximum value C1 , the control unit 13 imposes identical durations of injections I3, I4, 15,

16, I7 and adapts the durations between injections I3, I4, I5, I6, I7 in order to maintain a quantity of suspended elements in the aerosol that is able to absorb, by change of state, all or some of the heat generated by compression taking place in the rough-vacuum pump 4, evaluated on the basis of the electrical power C consumed by the motor 22. It should therefore be understood that the duration of injection I2 is thus, in fact, two minimum injections, of which the duration between injections is zero. Of course, a different control P may be implemented in order to obtain the injections illustrated in Figure 5 or in order to obtain injections different from those illustrated in Figure 5 without departing from the scope of the invention. [0086] In a third example of control in Figures 7 and 8, the closure elements 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i each comprise a pair of valves 16, 16', each pair having a first valve with a single first opening flow rate different from the single second opening flow rate of the second valve. It should therefore be understood that, in order to adapt to the variations in electrical power C consumed by the motor 22, the duration of injection of the aerosol and the choice of active valves by the injection system 5 as a function of time T makes it possible to vary the quantity of aerosol injected as a function of the electrical power C consumed by the motor 22. In the example visible in Figure 8, the generation device 15 for generating liquid water is connected in parallel to two all-or- nothing valves 16 (open according to a fixed flow rate or closed) which communicate in parallel via an introduction element 29 of the atomization nozzle type with a pumping stage 11 b. As is visible in Figure 5, the graph comprises a curve C drawn with a solid line showing an example of electrical power consumed by the motor 22 as a function of time T. The same graph shows an example of control P of the injection system 5, as a curve drawn with a dashed line, as a function of time T. Between the maximum electrical power C1 consumed by the motor 22 and a predetermined first value C2 of electrical power C consumed by the motor 22, the control unit 13 preferably injects the maximum flow rate of suspended elements, such as the injection I8+I9 corresponding to the opening of the two valves 16, 16' of a pair of at least one closure element 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i. The first value C2 may be between 80% and 90% of the maximum value C1 of electrical power C consumed by the motor 22, such as 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89% and 90%.

[0087] Below the first value C2 and a predetermined second value C3 of electrical power C consumed by the motor 22, the control unit 13 preferably injects a high flow rate of suspended elements, such as the injection I8 corresponding to the opening of the valve 16 with the highest flow rate of a pair of at least one closure element 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i. The second value C3 may be between 45% and 55% of the maximum value C1 of electrical power C consumed by the motor 22, such as 45%, 46%, 47%, 48%, 49%, 50%, 51 %, 52%, 53%, 54% and 55%. Below the second value C3 and a predetermined third value C4 of electrical power C consumed by the motor 22, the control unit 13 preferably injects a low flow rate of suspended elements, such as the injection I9 corresponding to the opening of the valve 16' with the lowest flow rate of a pair of at least one closure element 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i. The third value C4 may be between 5% and 10% of the maximum value C1 of electrical power C consumed by the motor 22, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% and 15%. Below the third value C4, the control unit 13 preferably no longer injects suspended elements, such as corresponding to the closing of the valves 16, 16' of a pair of at least one closure element 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 16i. Of course, a different control P may be implemented in order to obtain injections different from those illustrated in Figure 7 without departing from the scope of the invention.

[0088] A fourth example of control of an injection system 5 according to the invention as a function of the pressure F upstream of the rough-vacuum pump 4 is shown in Figures 9 and 10. Each closure (and therefore opening) element 16 is formed by a proportional valve. In the example visible in Figure 10, the generation device 15 for generating liquid water is connected to the proportional valve 16 which communicates via an introduction element 29 of the atomization nozzle type with a conduit between the pumping stages 11a, 11b. Furthermore, a pressure sensor 28 is provided to measure the pressure F at the suction inlet 6. As is visible in Figure 9, the control comprises an injection curve I proportional to the curve F of the pressure upstream of the rough-vacuum pump 4.

[0089] A fifth example of control of an injection system 5 according to the invention as a function of several parameters of the rough-vacuum pump 4 is shown in Figures 11 and 12. Each closure (and therefore opening) element 16 is formed by a proportional valve. In the example visible in Figure 12, the generation device 15 for generating liquid water is connected to the proportional valve 16 which communicates via an introduction element 29 of the atomization nozzle type with a transfer duct between the pumping stages 11 b, 11c. Furthermore, a pressure sensor 28 is provided to measure the pressure F at the suction inlet 6. Lastly, the control unit 13 comprises an element 30 for measuring the time and is connected to the control unit 23 of the motor 22 of the rough-vacuum pump 4.

[0090] As is visible in Figure 11 , the control comprises an injection curve I proportional to the curve F of the pressure upstream of the rough-vacuum pump 4 (or proportional to the curve C of the electrical power consumed by the motor 22 of the rough-vacuum pump 4) for a predetermined duration (up to T1), counted by the element 30 for measuring the time, and then subsequently no injection of suspended elements.

[0091] It may also be envisaged to stop the injection of water-based suspended elements so as to leave only the carrier gas produced by the generation device 15 or, alternatively, to inject a neutral dilution gas such as nitrogen for a predetermined duration (between T 1 and T2 counted by the element 30 for measuring the time) with the aid of the gas supply element 31 which communicates via an all-or-nothing valve 32 (open according to a fixed flow rate or closed) with a transfer duct between the pumping stages 11a, 11b. This control with the injection of a gas without suspended elements between T 1 and T2 could make it possible to prepare the rough-vacuum pump 4 for the inflow of a cleaning gas through the suction inlet 6, as explained above.

[0092] It should be understood that the invention also relates to a thermal regulation process for thermal regulation of a rough-vacuum pump 4. The process comprises, advantageously according to the invention, at least one step of injecting suspended elements into a flow of a vacuum line 1 pumped by the rough-vacuum pump 4 in order to form an aerosol in the vacuum line 1 so as to use at least a portion of the suspended elements in the aerosol to absorb, by change of state, at least a portion of the heat, or even, preferably, all the heat generated by compression taking place in the rough-vacuum pump 4, as explained above.

[0093] The invention is not limited to the embodiments and variants presented and other embodiments and variants will be clearly apparent to a person skilled in the art. Thus, the embodiments and variants can be combined with one another without departing from the scope of the invention. By way of non-limiting example, the control unit 13 of the injection system 5, on the basis of the control units 18 and 23 of the process chamber 17 and of the pumping device 3, could thus introduce a first flow rate of a first aerosol upstream of the pumping device 3 and a second flow rate of a second aerosol into the pumping device 3, the first flow rate and the first aerosol being different from the second flow rate and the second aerosol. Of course, in accordance with the applications, at least one type of aerosol other than the examples explained above could be injected without departing from the scope of the invention.

[0094] Furthermore, insofar as the nature of the injected suspended elements could lead to problems of reliability such as a problem of corrosion of parts made of cast iron, one solution could consist in forming a protective coating on the cast iron parts which is insensitive to the nature of the suspended elements, such as a metal deposit of the nickelphosphorus type.