WO2013087822A1

WO2013087822A1 - Multi-stage vacuum pump device

Info

Publication number: WO2013087822A1
Application number: PCT/EP2012/075505
Authority: WO
Inventors: Thierry Neel; Laetitia POPIN; Sébastien BARDEL; Pierrick GODINAT
Original assignee: Adixen Vacuum Products
Priority date: 2011-12-15
Filing date: 2012-12-14
Publication date: 2013-06-20
Also published as: FR2984423A1

Abstract

The invention relates to a device for pumping gas intended to be connected to a chamber that is to be pumped, comprising a first pumping stage (7) intended to be connected to the outlet of the chamber that is to be pumped, and at least one second pumping stage (17), the pumping stages (7, 17) being connected in series one after the other in a predetermined order and being configured in such a way that the delivery generated per pumping stage (7, 17) decreases with the position of the pumping stage (7, 17) in the series, characterized in that the pumping device further comprises:- a third pumping stage (27) arranged in series at the outlet of the last second pumping stage (175), and having a generated delivery higher than the delivery of the last second pumping stage (175), and - at least one fourth pumping stage (37) in series with the third pumping stage (27) and having a generated delivery lower than the delivery of the third pumping stage (27). The invention also relates to an item of equipment for the manufacture of flat screens comprising a process chamber comprising means for injecting gas containing dioxygen and/or an oxidizing gas such as a halogen, characterized in that it further comprises such a gas pumping device (1).

Description

MULTI-STAGE VACUUM PUMP DEVICE

The present invention relates to a device for pumping gas from an enclosure such as a process chamber and more particularly for the evacuation of reactive gas residues from manufacturing processes, for example flat screens, such as crystal screens. liquids. These manufacturing processes include various stages, some of which, such as etching require the evacuation of toxic gases, corrosive, or even harmful to the environment. For this purpose, a group of vacuum pumps, for example of the dry type, connected to devices for treating these gases before discharge into the atmosphere is used.

For this purpose, the vacuum pumps generally comprise pumping stages connected in series one after the other with a decreasing generated flow rate with the position of the pumping stage in the series.

In known manner, the operation of dry type vacuum pumps is carried out without any mechanical contact between the rotors and the body of the pump, which allows the total absence of oil in the compression chamber.

Since the operation of these pumps is carried out without mechanical contact between the stators and the lobe rotors, but via very small clearances, these pumps require a particular parameterization, especially of the temperature, when they are used with processes pollutants, such as manufacturing processes, including flat screens.

However, the pump bodies, usually cast iron, can be corroded under the action of these gases manufacturing processes; these include gases with a strong oxidizing power such as halogens, mention may be made of chlorine (CL ₂ ) or difluor (F ₂ ) and oxygen (0 ₂ ).

The manufacture of flat screens can generate a large volume of corrosive gases to be pumped by the group of vacuum pumps.

The successive adsorption of these gases on the surface of the vacuum pump materials in high concentrations and partial high pressures accelerates the corrosion process. A known solution is to dilute the gases to be pumped with injected purge gas along the pumping stages. This solution is described in particular in the patent application EPI 990543.

A complementary solution consists in keeping the gases at a sufficiently high temperature to maintain in gaseous form the species that are likely to condense or risk initiating chemical reactions in a pumping stage of the vacuum pump.

In pumps, high surface temperatures are therefore necessary to avoid condensation deposits resulting from the chemical reactions of these semiconductor processes.

However, these high temperatures also have the disadvantage of activating the corrosion rate.

Indeed, the adsorption phenomena of corrosive gases on metal surfaces are mainly of a chemical nature. The reactivity as well as the diffusion in the metal of the corrosive gas molecules is more active towards the increasing temperatures.

The major disadvantage of this strong corrosion is a rapid deterioration of the performance of the pumping device resulting in particular by a loss of compression ratio of the stages discharging at atmospheric pressure, by an increase in the limit pressure and by an increase in consumption. electric.

In order to overcome this problem, a state-of-the-art solution is to use new materials that are more resistant to corrosions. Such materials are, for example, alloys based on nickel or chromium.

However, these more resistant materials have the disadvantage of significantly increase the manufacturing cost of vacuum pumps.

According to another known solution, electrochemically depositing a thin nickel deposit on the order of a few microns on the cast iron material to be protected.

However, with this solution, the material may be fragile in the event of prolonged contact with a rotating part. Indeed, the coefficient of friction is generally unfavorable with a nickel-plated surface and often causes tearing of this deposition of its substrate.

The invention aims to provide an alternative to prevent corrosion vacuum pumps and avoid the formation of condensates, while overcoming the disadvantages of the prior art.

To this end, the subject of the invention is a device for pumping gas intended to be connected to an enclosure to be pumped, comprising a first pumping stage intended to be connected to the outlet of the enclosure to be pumped, and at least one second pumping stage, the pumping stages being connected in series one after the other in a predetermined order and being configured so that the flow rate generated per pumping stage decreases with the position of the pumping stage in the series characterized in that the pumping device further comprises:

a third pumping stage arranged in series at the outlet of the last second pumping stage, and having a flow generated greater than the flow rate of the last second pumping stage, and

at least one fourth pumping stage in series with the third pumping stage having a generated flow rate lower than the flow rate of the third pumping stage.

The first and second pumping stages of the pumping device thus form a low pressure zone and the third and fourth pumping stages form a high pressure zone.

This arrangement makes it possible to significantly reduce the rate of corrosion on the metal parts in contact with the gases by acting on parameters such as the partial pressure of the corrosive gases, the residence time of the reactive species and the operating temperature.

Indeed, the third stage of the high pressure zone makes it possible to obtain a low pressure at the outlet of the last second stage of the low pressure zone by locally increasing the generated flow rate of the third pumping stage.

Thus, the low pressure zone has partial pressures of low condensable gases and thus can be controlled at a reduced temperature.

In addition, the high pressure zone also has low partial pressures of condensable gases because they are highly diluted by the succession of purge gas injection.

As a result, it is not necessary to change the nature of the standard vacuum pump materials subjected to the action of these gases; this avoids the use of more resistant but expensive materials.

The device may further comprise one or more of the following features, taken separately or in combination:

the third pumping stage is capable of maintaining a suction pressure less than or equal to 10 Torr, ie less than or equal to 1333 Pa;

the device comprises: first means for injecting a purge fluid into the second pumping stage, so as to dilute the gas to be pumped a first time, and second means for injecting a purge fluid into the fourth pump stage, so as to dilute the gas to be pumped a second time;

the flow rate of the third pumping stage is of the order of 300 to 2400 m ³ / h;

the third pumping stage has a volume generated greater than the generated volume of the last second pumping stage;

the third pumping stage has a rotational speed greater than the rotation speed of the last second pumping stage;

the second pumping stage has a generated flow rate of the order of 150 m ³ / h; the device comprises: a first vacuum pump comprising the first pumping stage, and comprising a first motor and two rotary shafts driven by the first motor so as to drive in rotation the rotors of the first pumping stage, and a second pump to vacuum comprising the second pumping stage, and comprising a second motor and two rotary shafts driven by the second motor so as to rotate the rotors of the second pumping stage;

the device comprises: a third vacuum pump comprising the third pumping stage, and comprising a third motor and two rotary shafts driven by the third motor so as to rotate the rotors of the third pumping stage, and a fourth pump to empty including the fourth floor of pumping, and comprising a fourth motor and two rotary shafts driven by the fourth motor so as to rotate the rotors of the fourth pump stage;

the first and / or third vacuum pump is a single-stage pump of Roots type;

the second and / or the fourth vacuum pump is a Roots multi-stage vacuum pump;

the first pumping stage has a generated flow rate greater than the flow rate of the third pumping stage;

the device is configured to evacuate the gas from a process chamber for manufacturing flat screens, and the gas to be discharged comprises oxygen and / or an oxidizing gas such as a halogen.

The invention also relates to a flat panel manufacturing equipment comprising gas injection means comprising oxygen and / or an oxidizing gas such as a halogen, characterized in that it further comprises a pumping device of gas as defined above.

Other features and advantages of the invention will emerge from the following description given by way of example, without limitation, with reference to the accompanying drawings, in which:

FIG. 1 schematically represents a pumping device according to the invention intended to be connected to an enclosure to be emptied,

FIG. 2 schematically represents the successive generated flows of the pumping device of FIG. 1.

The invention is particularly applicable to pumping gas from an enclosure (not shown), such as a process chamber for manufacturing flat screens, in particular liquid crystal displays or LCDs for the English "Liquid Crystal Display ». In the embodiment of the invention illustrated in FIG. 1, an evacuation device 1 comprises:

a first low pressure pumping zone 3a, and

a second high pressure pumping zone 3b.

In the present, the term "pressure" means the total pressure, ie the sum of the partial pressures of the gases.

According to the first embodiment shown in FIG. 1, the first low-pressure pumping zone 3 has a first vacuum pump P1 and a second vacuum pump P_2.

The first vacuum pump PJ_ is responsible for ensuring the pumping speed necessary to obtain the performance expected by the process, such as an etching process, namely a working pressure limit for a given gas flow.

For this purpose, the first vacuum pump PJ_ is connected to the enclosure to be pumped. The first vacuum pump PJ_ comprises a first motor 5.

This first vacuum pump PJ_ comprises a first pumping stage 7 of higher flow generated compared to the other pumping stages; this is to ensure the pumping performance of the process.

The flow range generated by the first stage 7 is for example between 1000 m ³ / h and 7000 m ³ / h.

According to the illustrated embodiment it is a single-stage vacuum pump dry type. A single-stage vacuum pump comprises only one pumping stage 7 in which circulates a gas to be pumped between a gas intake inlet and a gas discharge outlet.

For example, it may be a rotary lobe pump also known as "Roots" pumps with two or three lobes (bi-lobes, tri-lobes).

In general, a rotary lobe pump "Roots" comprises two rotors of identical profiles, rotating inside a stator 9 in opposite directions.

The first motor 5 rotates two shafts (not shown) which make it possible to rotate the two rotors (not visible in the figures) of the first stage pumping 7.

During rotation, the sucked gas is trapped in the free space between the rotors and the stator 9, and it is discharged. The operation is carried out without any mechanical contact between the rotors and the stator 9 of the pump, which allows the total absence of oil in the pumping stage 7.

The first vacuum pump PJ_ has a gas suction port connected by a suction pipe 11 to the enclosure to be emptied (not shown).

The vacuum pump PJ_ still has a gas outlet port connected to a discharge pipe 13. A check valve can be provided at the discharge pipe.

The vacuum pump PJ sucks the gases from the chamber at its inlet, and compresses them in the pumping stage 7 to discharge them at its outlet into the discharge pipe 13.

Furthermore, the vacuum pump PJ_ works in this embodiment at a speed of the order of 80Hz.

The second vacuum pump P_2 comprises a second motor 15 and at least one second pumping stage 17.

The second vacuum pump P_2 is according to the embodiment illustrated in Figure 1, a multi-stage vacuum pump dry type, for example Roots or Hooke or Claw type or screw.

The second multi-stage vacuum pump P_2 therefore comprises a plurality of second pumping stages 17, pumping five storeys 17 _{l 5} 17 ₂ 173.17 _4, 17 ₅ in this exemplary embodiment. As for the first vacuum pump PI, the pumping stages 17 i, 172, 173, 174, 175 are assembled in a one-piece pump body (or stator), for example made of cast iron. The second vacuum pump P_2 also comprises means for controlling the temperature of the pump body.

The pumping stages of the second vacuum pump P_2 comprise a stator 19 and two rotating shafts (not visible) which can rotate inside the stator 19. The second motor 15 drives in rotation the two shafts (not shown) which make it possible to turn the rotors in the stator 19 of the second pump stages 17. For example, the speed of rotation is of the order of 60 Hz.

The vacuum pump is called "dry" because in operation, the rotors rotate inside the stator 19 of the vacuum pump in the opposite direction without any contact between the rotors and the stator 19, which allows the total absence of 'oil.

The stages 17 are arranged in series between a suction and a discharge of the vacuum pump, in a predetermined order.

The gas to be pumped can circulate in stages 17 in series.

Each stage 17 _{1 5} 17 ₂ , 17 ₃ , 17 ₄ , 17 ₅ comprises for example first injection means 41 of a purge fluid so as to dilute the gas to be pumped. The purge fluid used is for example an inert gas, such as nitrogen (N ₂ ).

The first means 41 for injecting purge fluid into the first pumping zone 3a are shown schematically by arrows in FIG. 1.

The flow of purge fluid is for example of the order of 80-90 slm.

The injection of purge fluid is for example continuous.

The gas leaving the enclosure (not shown) pumped by the first pumping zone 3a is thus diluted a first time in the second vacuum pump P2.

Each stage 17 _{l 5} February _17, 17 _3, 17 _April, 17 ₅ comprises an inlet and an outlet. The successive stages 17 are connected in series one after the other, by respective inter-stage lines connecting the output of a pumping stage 17 which precedes the entry of the stage 17 which follows.

The pumping stage 17i whose inlet communicates with the suction is also called "suction stage".

The last pump stage 17 ₅ whose outlet communicates with the outlet of the second P_2 vacuum pump is also called "discharge stage."

The gas to be pumped can thus be sucked from the suction stage 17i to the discharge stage 17 ₅ , after successively passing through three stages 17 ₂ , 17 ₃ , 17 ₄ .

The second vacuum pump P_2 has a gas suction port connected to the discharge conduit 13 of the first vacuum pump PJ_. The second vacuum pump P_2 also has a gas outlet port connected to a discharge pipe 21.

The second vacuum pump P_2 draws the gases from the chamber at its inlet, and compresses them in the pumping stages 17 to discharge them at its outlet into the discharge pipe 21.

This discharge pipe 21 of the second vacuum pump P_2 communicates with a suction pipe 23 connected to a suction port of the third vacuum pump P3_ arranged between the second vacuum pump P_2 and the fourth vacuum pump P_4. The third vacuum pump P3_ and the fourth vacuum pump P4 belong to the second high pressure pumping zone 3b.

In this exemplary embodiment, with a second multi-stage vacuum pump P 2, the second pumping stages 17 are such that the flow rate generated per stage decreases with the position of the pumping stage in the series.

Flow rate generated means the cubic capacity corresponding to the volume swept by the pistons of the pump multiplied by the number of minute revolutions, according to formula (1) below:

(1) Generated flow = 60 * N * Qo (where N is the number of revolutions minutes: rpm, and Q ₀ is the cubic capacity in m ³ / revolution).

This generated flow rate is expressed in cubic meters per hour (m ³ / h).

More precisely, the suction stage 17i has, for example, a flow rate of the order of 150 m ³ / h and this flow rate decreases in the pumping stages 17 until reaching a flow rate, for example of the order of 70.degree. 80m ³ / h in the last discharge stage 17 ₅ .

The second stages 17 have a lower flow rate with respect to the first pumping stage 7. It may, for example, be a ratio of about 7 to 20 vis-à-vis the first pumping stage 7.

The output of the last second pumping stage 17 ₅ , or discharge stage, of the first pumping zone 3a is connected in series with the second high-pressure pumping zone 3b. Thus, the second high-pressure pumping zone 3b is dimensioned so as to reach a maximum pressure of 10 Torr at the stage of delivery of the second vacuum pump P_2. For example, the discharge pressure of the second vacuum pump P_2 in the discharge pipe 21 is in a pressure range from 0.24 Torr to 10 Torr, namely a range of 32 Pa to 1333 Pa.

Thus, the first pumping zone 3 operates with a pressure difference between the suction (conduit 11) and the discharge (conduit 21), less than or equal to 10 Torr.

It is therefore a low pressure zone of the pumping device 1.

This low pressure which must be at most 10 Torr at the discharge of the vacuum pump P2 is necessary in order to maintain the partial pressures of weak corrosive gases. This makes it possible to reduce the corrosive attack by these gases and to avoid the formation of condensates, remaining above the pressure / temperature condensate formation torque without having to increase the temperature.

The temperature of the second vacuum pump P_2 can thus be maintained at a lower temperature than in the known solutions of the prior art.

Indeed, in comparison with solutions of the prior art, the pump body of each stage 17 of the second vacuum pump P_2 is controlled at 60 ° C and no longer at 120 ° C.

In addition, in the first pumping zone 3a known as the low-pressure zone, the injection of the purge fluid into the various stages 17 makes it possible to reduce the partial pressure of the active gases a little more, to reduce the residence times of the species by to the progressive increase of mass gas flow.

The low pressure operation combined with a dilution also makes it possible to reduce the partial pressures of saturating vapors of the condensable gases from the etching process.

Furthermore, as regards the second high-pressure pumping zone 3b, it is arranged in series at the outlet of the last second pumping stage 17 ₅ , or discharge stage, of the first pumping zone 3a. The second pumping zone 3b is, by way of example, dimensioned so as to reach a maximum pressure of 10 Torr for a total maximum gas flow of 105slm including the process gas stream and the inert gas dilution gas stream injected into the first pumping zone 3a at low pressure.

According to the embodiment illustrated in FIG. 1, this second pumping zone 3b presents:

a third vacuum pump P3_ arranged in series with the second vacuum pump P_2, and more particularly at the outlet of the last second pumping stage 17 ₅ , and

a fourth vacuum pump P_4 arranged in series with the third vacuum pump P3_.

The third vacuum pump P3_ comprises a third motor 25 and a third pumping stage 27. It is therefore an intermediate pumping stage 27 arranged downstream of the last second pumping stage 17 ₅ of the first pumping zone 3a. and upstream of the fourth vacuum pump P_4. The terms "upstream" and "downstream" are used here according to the direction of flow of the gas to be pumped.

Similarly to the first vacuum pump P1, this third vacuum pump P3 can be a dry type single stage vacuum pump.

This third vacuum pump P3_ thus comprises a third motor 25 and a single pumping stage 27 in which a gas to be pumped at the outlet of the second vacuum pump P_2 flows between a gas intake inlet and a gas discharge outlet. .

For example, it may be a rotary lobe pump also known as a "Roots" pump with two or three lobes (bi-lobes, tri-lobes) comprising two rotors of identical profiles, rotating at the same time. inside a stator 29 in opposite directions without any mechanical contact between the rotors and the stator 29 of the pump.

The third motor 25 rotates two shafts (not shown) which make it possible to turn the two rotors (not visible in the figures) of the third pumping stage 7.

The third vacuum pump P_3_ has a gas suction port connected by the suction duct 23 to the discharge duct 21 of the second vacuum pump P_2. The third vacuum pump P3_ still has a gas outlet port connected to a discharge pipe 31.

This discharge pipe 31 is in communication with the fourth vacuum pump P_4.

The third vacuum pump P3_ has a flow rate greater than the flow rate of the last pump stage of the second vacuum pump P_2. For example, the third vacuum pump P3_ has a flow rate of the order of 300 to 2400m ³ / h.

It is a vacuum pump of high flow generated but of lower flow than the first vacuum pump PL

As said above, the flow range generated by the first stage 7 of the first vacuum pump PI is for example between 1000 m ³ / h and 7000 m ³ / h.

By way of illustrative example, it can be provided in particular that when the first stage 7 of the first vacuum pump PI has a generated flow rate of the order of 1000 m ³ / h, the third pump stage 27, that is, that is, the pumping stage of the third vacuum pump P3 has a generated flow rate of about 300 m ³ / h; and when the first stage 7 of the first vacuum pump PI has a generated flow rate of the order of 7000 m ³ / h, the third pumping stage 27, that is to say the pumping stage 27 of the third vacuum pump P3, has a generated flow rate of about 2400 m ³ / h.

The third vacuum pump P_3_ is therefore oversized for a higher generated flow compared to the second vacuum pump P_2.

For example, in operation, the third vacuum pump P_3_ which has a suction pressure of the order of 10 Torr is capable of absorbing a total gas flow to be pumped on the order of 105 slm (for standard Liter per minute in English).

More specifically, the third vacuum pump P_3_ is able to maintain a suction pressure of less than or equal to 10 Torr and is able to absorb the flow of purge fluid injected into the second pump stages 17. By way of example, a generated flow rate of the order of 800 m ³ / h can maintain a pressure of about 10 Torr without heating the third vacuum pump P_3_.

This configuration of the third vacuum pump P_3_ makes it possible to maintain a low pressure at the discharge of the first pumping zone 3a which must be at maximum of 10 Torr.

In fact, by increasing the flow rate generated at the discharge of the first pumping zone 3 a, the pressure at this discharge is reduced.

In order to increase the suction flow rate of the second high-pressure zone 3b, it is possible, according to a first variant, to increase the volume generated, that is to say the mass flow rate of pumped gas. To do this, we increase the swept volume of the third stage 27 relative to the volume of the last second stage 17 _5, which precedes it.

This variant is illustrated schematically in FIG.

In a second variant, the generated flow can be increased by increasing the rotational speed of the third stage 27 with respect to the rotational speed of the last second stage 17 _5, which precedes it. According to this second variant, the third stage 27 is an independent stage, that is to say that it is not part of a series of stages, that it is a single stage P_3_ pump (figure 1). Regarding the fourth vacuum pump P_4 disposed in series with the third vacuum pump P_3_, it has a gas suction port connected to the discharge conduit 31 of the third vacuum pump P_3_.

Of course, this fourth vacuum pump P_4 also comprises a gas outlet port connected by a discharge conduit 33 to the general discharge of gases, for example to a gas treatment system at atmospheric pressure.

The fourth vacuum pump P_4 makes it possible to compress the gases against the atmospheric pressure.

This fourth vacuum pump P_4 comprises a fourth motor 35 and at least a fourth pump stage 37.

Similar to the second vacuum pump P_2, the fourth vacuum pump

P4 is according to the embodiment illustrated in Figure 1, a dry multi-stage vacuum pump for example Roots type or Hooke or Claw or screw.

This fourth vacuum pump P_4 therefore comprises a plurality of fourth pumping stages 37, pumping five storeys 37 _{l 5} 37 _2, 37 _3, 37 _4, 37 ₅ ^ _{αη8 QQT exem} pi _e d _e embodiment. Pumping stages 37 _{l 5} 37 ₂ 373.37 _4, 37 ₅ are assembled in one body monobloc pump (or stator), for example made of cast iron. The fourth vacuum pump P4 also comprises means for controlling the temperature of the pump body.

The fourth vacuum pump P4 comprises a stator 39 and two rotating shafts (not visible) rotatable inside the stator 39 in the opposite direction and without any contact between the rotors and the stator 39.

The fourth motor 35 rotates the two shafts (not shown) which make it possible to rotate the rotors (not visible in the figures) of all the fourth stages 37.

The stages 37 are arranged in series between a suction and a discharge of the vacuum pump. The gas to be pumped can circulate in stages 37 in series.

Each stage 37 _{l 5} 37 _2, 37 _3, 37 _4, 37 ₅ comprises an inlet and an outlet. The successive stages 37 are connected in series one after the other, by respective inter-stage lines connecting the output of the pumping stage 37 which precedes the entry of the stage 37 which follows.

The pumping stage 37i the input of which communicates with the suction is also called "suction stage", and the pumping stage 37 ₅ whose outlet communicates with the outlet of the fourth vacuum pump P4 is also named "Discharge stage".

The gas to be pumped can thus be sucked from the suction stage 37i to the discharge stage 37 _5, after having successively crossed three floors 37 _2, 37 _3, 37 _4.

The fourth vacuum pump P4 draws its gas at the outlet of the third vacuum pump P3_, and compresses them in the pumping stages 37 to discharge them at its outlet into the discharge pipe 33.

In this exemplary embodiment, the first stage of the fourth vacuum pump P4 has a generated flow rate of the order of 150 m ³ / h. Similarly to the second vacuum pump P2, this flow decreases in the successive stages 37 to reach for example 70-80 m ³ / h in the last stage 37 ₅ discharge.

This flow rate is lower than that of the third vacuum pump P3_. The ratio is for example of the order of 7 to 20 vis-à-vis the third pumping stage 27. Moreover, the fourth vacuum pump P4 works in this embodiment at a speed of the order of 60 Hz.

Each stage 37 _{l 5} 37 ₂ 373.37 ₄ 37 ₅ may include second injection means 43 of a purge fluid so as to dilute the gas to be pumped. The purge fluid used is for example an inert gas, such as nitrogen (N ₂ ).

The second purge fluid injection means 43 in the second pumping zone 3b are schematically represented by arrows in FIG.

The gas to be pumped by the second pumping zone 3b is again diluted in the fourth pump P4 with the aid of a purge fluid.

The set of stages 27, 37 of the second high-pressure pumping zone 3b is therefore dimensioned so as to be able to continuously absorb the gaseous flow coming from the first pumping zone 3 at low pressure. The fourth stages 37 are further dimensioned so as to also absorb the dilution gas stream injected into the high pressure stages 37.

At the second pumping zone 3b, the gas is highly diluted.

Thus, although the partial pressure values of the corrosive gases increase as one approaches the last discharge stage compressing against atmospheric pressure, the mole fraction of the corrosive gases continuously decreases. The residence times and accommodation coefficient of the corrosive gases are a little reduced because of the high mass gas flows induced by the gradual addition of purge fluid, such as an inert gas such as nitrogen (N ₂ ).

In addition, the high dilution rate in the second pumping zone 3b allows operation of the second pumping zone 3b at low temperature without risking the formation of condensates. On the other hand, this high dilution rate limits the diffusion of corrosive species to metal surfaces.

The second pumping zone 3b forms, as opposed to the first pumping zone 3a, a high pressure zone of the pumping device 1.

The set of stages of the high pressure zone 3b is dimensioned so as to be able to evacuate large gaseous flows at high pressure. This new staging configuration consisting of a low pressure zone and a high pressure zone in series has the effect that the transition zone is constituted by a stage 27 of high flow inserted between two stages 17,37 of smaller flow rate. generated. This intermediate stage 27 is dedicated to the maintenance at low pressure of the first pumping zone 3 a.

By re-increasing the flow rate at the third vacuum pump P3_, before decreasing again at the fourth vacuum pump P_4, the second vacuum pump P_2 can operate at low pressure and at low temperature.

Indeed, as said before the second vacuum pump P_2 can work at a pressure less than 10 Torr until discharge.

The first pumping zone 3a has a pressure difference between the suction (duct 11) and the discharge (duct 21) less than or equal to 10 Torr.

For the same application, according to a solution of the prior art providing for a single pumping unit or pump similar to the first pumping zone 3a, this pressure difference was of the order of 760 Torr.

It is the arrangement of the third largest vacuum pump P_3_, between the second vacuum pump P_2 and the fourth vacuum pump P_4, which allows the second vacuum pump P_2 to work at low pressure less than or equal to at 10 Torr.

In particular, the intermediate stage 27 with the highest flow rate relative to the second 17 and third 37 pumping stages is configured to maintain a maximum pressure of 100 R T for a gas flow rate of the order of 105 μM in the case of a semiconductor etching process where the amount of active gas can be up to 12slm.

With such an arrangement, the inventor has found in particular a pressure reduction factor of nearly 10 for example in the second stage of the second vacuum pump P_2, compared to a solution of the prior art using a single unit pumping.

The comparison is made here with respect to the second stage of the second vacuum pump P_2 because the inventor has found that the corrosion by the gases starts effective in this second floor.

In particular, the first pumping zone 3 operating at low pressure has the advantage of substantially reducing the partial pressure of the corrosive gases.

By way of example, with regard to oxygen (O ₂ ), for a given flow rate, its partial pressure is, for example, less than 1 Torr in the five pumping stages 17 of the second vacuum pump P_2 according to the arrangement previously defined.

On the contrary, for a solution of the prior art with the same flow rate, the oxygen has a partial pressure of up to 100 Torr in the stages of a pumping unit similar to the first pumping zone 3a but used alone.

In particular, the inventor has found, for example, in the second stage of the second vacuum pump P_2, a dioxygen partial pressure decrease factor of nearly 10 compared to a solution of the prior art using two pumps. vacuum in parallel, and a factor of nearly 17 compared to a solution using a single pumping unit.

Furthermore, as said before, in comparison with solutions of the prior art, the pump body of the second vacuum pump P_2 is controlled at 60 ° C and no longer at 120 ° C.

Indeed, the small pressure difference maintained between the suction (duct 11) and the discharge (duct 21) of the first pumping zone 3 has induced a low electrical power consumption and therefore a lower operating temperature compared with known solutions of the prior art.

By lowering the partial pressures of the gases in the pumping stages 17 of the second vacuum pump P_2, and by lowering the temperature, the corrosion rate of the gases is decreased. This avoids premature wear of the second vacuum pump P_2.

In fact, the low average pressure in the stages of the first pumping zone 3a makes it possible to significantly reduce the corrosion by, in particular, reducing the residence times of the corrosive species, the capacity of accommodation and adsorption of these gases.

The low partial pressure of gas as well as a low coefficient of accommodation of the gases can greatly limit the formation of a monolayer of gas which is the starting point of corrosion on the metal surface.

A pump device 1 comprising four vacuum pumps P1 to P4 in series has been described above.

The pumping device 1 can, depending on the constraints provided by the corrosive gas concentrations, be reduced to three vacuum pumps, or two vacuum pumps, or even a single multi-stage vacuum pump, but having two distinct "low pressure" zones. and "high pressure", performing the functions described above.

In all cases, the first low pressure pumping zone 3a and the second high pressure pumping zone 3b are such that:

the first pumping zone 3a comprises a first pumping stage 7 intended to be connected to the outlet of the enclosure to be pumped, and at least one second pumping stage 17, the pumping stages 7, 17 being connected in series. one after the other in a predetermined order and such that the flow rate generated per pump stage decreases with the position of the pump stage in the series, and that

the second pumping zone 3b is arranged in series at the outlet of the last second pumping stage 17 of the first pumping zone 3a and comprises a third pumping stage 27 having a flow generated greater than the flow rate of the last second pumping stage 17, and at least a fourth pumping stage 37 in series with the third stage 27, the pumping stages 27, 37 being connected in series one after the other in a predetermined order and such that the flow rate generated per stage of pumping decreases with the position of the pumping stage in the series.

According to this variant, an intermediate stage 27 is arranged in series between a pumping stage 17 of the "low pressure" zone and a pumping stage 37 of the "high pressure" zone. This intermediate stage 27 is dimensioned with a higher generated flow rate than the upstream pumping stage 17 belonging to the so-called "low pressure" zone and the downstream pumping stage 37 belonging to the so-called "high" zone. "Printing", so as to reduce the partial pressures of the gases in the pumping stages of the first pumping zone 3a, and thus reduce the rate of corrosion.

It is therefore an intermediate stage of high flow generated in series with a lower flow generated stage belonging to the "low pressure" zone and with a lower flow generated stage belonging to the so-called "high pressure zone" ".

It is thus understood that the series arrangement of the vacuum pumps with a third vacuum pump P3_ sized for a higher generated flow compared to the P_2 vacuum pumps upstream and P4 downstream, reduces the corrosion rate of the gases. to pump in the pumping stages, and thus avoids premature wear of the vacuum pumps.

In particular, the low pressure maintained in the stages of the first pumping zone 3a, the high dilution ratio and the relative low operating temperature of the second pumping zone 3b make it possible to reduce the dwell times of the gases without impact. on the nature of the materials of the vacuum pumps PI to P4 of the pumping device.

Vacuum pumps can therefore include standard materials; it is not necessary to provide corrosion resistant materials efficiently. This particular arrangement thus makes it possible to protect high corrosive gas concentrations against all the compression stages of the pumping device using standard materials.

In addition, such a solution makes it possible to increase the service life of the vacuum pumps that must operate for semiconductor etching processes.

Claims

A gas pumping device intended to be connected to an enclosure to be pumped, comprising a first pumping stage (7) intended to be connected to the outlet of the enclosure to be pumped, and at least one second pumping stage (17). ), the first and second pump stages (7, 17) being connected in series one after the other in a predetermined order and being configured so that the flow rate generated per pump stage (7, 17) decreases with the position of the pumping stage (7, 17) in the series,

characterized in that the pumping device further comprises:

a third pumping stage (27) arranged in series at the outlet of the last second pumping stage (17 ₅ ), and having a flow rate that is greater than the flow rate of the last second pumping stage (17 ₅ ), and

- At least a fourth pump stage (37) in series with the third pump stage (27) having a generated flow rate lower than the flow rate of the third pump stage (27).

2. Device according to claim 1, characterized in that the third pumping stage (27) is able to maintain a suction pressure less than or equal to 10 Torr.

3. Device according to one of claims 1 or 2, characterized in that it comprises:

first injection means (41) of a purge fluid in the second pumping stage (17), so as to dilute the gas to be pumped a first time, and

- Second injection means (43) of a purge fluid in the fourth pump stage (37), so as to dilute a second time the gas to be pumped.

4. Device according to any one of claims 1 to 3, characterized in that the flow rate of the third pumping stage (27) is of the order of 300 to 2400m ³ / h.

5. Device according to any one of claims 1 to 4, characterized in that the third pumping stage (27) has a generated volume greater than the volume generated from the last second pump stage (17 ₅ ).

6. Device according to any one of claims 1 to 4, characterized in that the third pumping stage (27) has a rotational speed greater than the rotational speed of the last second pumping stage (17 ₅ ).

7. Device according to any one of the preceding claims, characterized in that the second pumping stage (17) has a generated flow rate of the order of 150m ³ / h.

8. Device according to any one of the preceding claims, characterized in that it comprises:

a first vacuum pump (PI) comprising the first pump stage (7), and comprising a first motor (5) and two rotary shafts driven by the first motor (5) so as to rotate the rotors of the first stage; pumping (7), and

a second vacuum pump (P2) comprising the second pump stage (17), and comprising a second motor (15) and two rotary shafts driven by the second motor (15) so as to rotate the rotors of the second stage; pumping (17).

9. Device according to any one of the preceding claims, characterized in that it comprises:

a third vacuum pump (P_3_) comprising the third pumping stage (27), and comprising a third motor (25) and two rotary shafts driven by the third motor (25) so as to rotate the rotors of the third stage; pumping (27), and

a fourth vacuum pump (P_4) comprising the fourth pump stage (37), and comprising a fourth motor (35) and two rotary shafts driven by the fourth motor (35) so as to rotate the fourth stage rotors; pumping (37).

10. Device according to one of claims 8 or 9, characterized in that the first (Pl) and / or the third (P3_) vacuum pump is a single-stage Roots type pump.

11. Device according to any one of claims 8 to 10, characterized in that the second (P2) and / or the fourth (P4) vacuum pump is a multi-stage vacuum pump Roots type.

12. Device according to any one of the preceding claims, characterized in that the first pumping stage (7) has a generated flow rate greater than the flow rate of the third pumping stage (27).

13. Device according to any one of the preceding claims, configured to evacuate the gas from a process chamber for manufacturing flat screens, characterized in that the gas to be discharged comprises oxygen and / or an oxidizing gas such as a halogen.

14. Equipment for manufacturing flat screens comprising a process chamber comprising gas injection means comprising oxygen and / or an oxidizing gas such as a halogen, characterized in that it further comprises a pumping device. (1) gas according to any one of the preceding claims.