CN115516208A

CN115516208A - Apparatus and method for monitoring the exhaust of a vacuum pump for deposits of reaction by-products

Info

Publication number: CN115516208A
Application number: CN202180034276.XA
Authority: CN
Inventors: 神原久徳
Original assignee: Pfeiffer Vacuum SAS
Current assignee: Pfeiffer Vacuum SAS
Priority date: 2020-05-11
Filing date: 2021-04-16
Publication date: 2022-12-23
Also published as: DE112021002719T5; WO2021228490A1; FR3109965B1; TW202208748A; FR3109965A1; JP2023525086A

Abstract

An apparatus (200) for monitoring an exhaust port (7) of a vacuum pump (1: -a thermal flow meter (20), the thermal flow meter (20) comprising a first temperature probe placed at an upstream position in the gas flow direction at the exhaust port (7), a second temperature probe placed at a downstream position, a heating element interposed between the temperature probes, a substrate isolating the temperature probes and the heating element from each other, and-a processing unit (22) configured to perform measurements by the thermal flow meter (20) in order to determine the presence of deposits of reaction byproducts at the exhaust port (7) from the difference between the flow rate determined by the thermal flow meter (20) and an estimated value of the gas flow rate pumped by the vacuum pump (1.

Description

Apparatus and method for monitoring the exhaust of a vacuum pump for deposits of reaction by-products

Technical Field

The invention relates to an apparatus and method for monitoring the exhaust of a vacuum pump for deposits of reaction by-products. The invention also relates to a vacuum pump provided with the monitoring device.

Background

In vacuum applications, particularly in the semiconductor industry or thin film deposition processes, vacuum pumps deliver various types of gases and vaporized materials that may deposit on the inner surfaces of the vacuum pump due to changes in pressure or temperature conditions or changes in the nature of chemical reactions.

The deposits of reaction by-products can be solids, polymers or even dust. These deposits tend to accumulate in particular in the high-pressure or cold regions of the vacuum pump. They reduce the gas passage cross section, which reduces the pumping performance. The reduction in gas cross-sectional size also produces a pressure increase that causes greater byproduct deposition through a cascading effect.

Therefore, regular maintenance must be scheduled to clean the vacuum pump from time to time. However, such maintenance is incompatible with productivity requirements. It is therefore sought to monitor the formation of deposits in the vacuum pump in order to separate as much as possible the intervals between maintenance operations. However, one of the difficulties is that it is not possible to observe the interior of the vacuum pump without stopping the vacuum pump to completely or partially disassemble it. Furthermore, in certain applications, exposure of the vacuum pump interior to open air can be hazardous.

Many known sensor technologies allow monitoring of these deposits and their growth in vacuum pumps.

In the case of a turbo-molecular vacuum pump, one known method involves measuring the current of the motor or the position of the magnetically levitated rotor in order to determine the possible presence of by-products. Changes in motor current or in the position of the magnetically levitated rotor may provide information about the presence of deposits. However, such a solution may not be accurate enough, in particular because the increase in current is usually detected too late (only a few seconds or fractions of a second before the collision), and it is not possible to intervene in time.

Disclosure of Invention

It is therefore an object of the present invention to propose a device and a method for monitoring the deposition of by-products which at least partially solve one of the above drawbacks.

To this end, the subject of the invention is a device for monitoring the exhaust of a vacuum pump for deposits of reaction by-products, characterized in that it comprises:

-a thermal flow meter comprising:

-a first temperature probe placed at the discharge opening at an upstream position in the gas flow direction,

-a second temperature probe placed at a downstream location,

a heating element interposed between these temperature probes,

a substrate which insulates the temperature probes and the heating element from each other, and

-a processing unit configured to perform measurements by means of the thermal flow meter in order to determine the presence of deposits of reaction by-products at the exhaust from the difference between the flow rate determined by means of the thermal flow meter and the estimated value of the flow rate of the gas pumped by means of the vacuum pump.

Thus, the monitoring device allows the presence of deposits at the exhaust of the vacuum pump to be detected more accurately and as early as possible.

The monitoring device may also include one or more of the features described below, either alone or in combination.

The thermal flow meter may be a MEMS component.

The monitoring device may further comprise a pressure sensor configured to determine a pressure at the exhaust of the vacuum pump, the processing unit being configured to estimate the pumped gas flow based on information related to power parameters of the motor and measurements from the pressure sensor. Thus, an estimate of the pumped gas flow rate can be obtained from information obtained only via the vacuum pump, that is, information relating to the quantity and nature of the gas introduced upstream of the vacuum pump need not be obtained.

The power parameter of the motor of the vacuum pump may be a current.

The processing unit may be configured to communicate with a processing chamber depressurized by means of a vacuum pump to estimate a pumped gas flow. Thus, the information transmitted by the process chamber to the processing unit may allow accurate estimation of the value of the pumped gas flow.

Another subject of the invention is a vacuum pump comprising:

a stator comprising an inlet aperture and an outlet aperture,

at least one rotor arranged in the stator and configured to drive gas to be pumped between the inlet and outlet apertures,

characterized in that it further comprises a monitoring device as described above, the thermal flow meter being arranged inside said vacuum pump.

The monitoring device thus allows the presence of deposits in the vacuum pump exhaust to be detected more accurately and as early as possible, which makes it possible to better manage the schedule of maintenance interventions. The monitoring can be performed in situ, that is to say without dismantling the vacuum pump. The measuring means are non-invasive. It does not create pressure or seal losses. It has no moving parts, which limits the possibility of malfunction.

The thermal flow meter is arranged, for example, in the conduit of the discharge opening.

The vacuum pump is, for example, a turbo-molecular vacuum pump.

According to another example, the vacuum pump is a rough vacuum pump comprising two rotors configured to counter-rotate in synchronism in at least one pumping stage to drive gas pumped between an inlet aperture and an outlet aperture.

A further subject of the invention is a method for monitoring the exhaust port of a vacuum pump for deposits of reaction by-products by means of a monitoring device as described above, in which a measurement is carried out by means of a thermal flow meter in order to determine the presence of deposits of reaction by-products at the exhaust port on the basis of the difference between the flow rate determined by means of the thermal flow meter and the estimated value of the flow rate of the gas pumped by the vacuum pump.

The heating elements of the thermal flow meter may be powered to perform measurements at intervals that are more than 10 hours apart, such as daily measurements. The measurement duration of the thermal flow meter may be less than a few minutes, such as less than two minutes, or even less than one minute. The highest deposition rates observed in turbomolecular vacuum pumps, in particular in semiconductor manufacturing processes such as etching equipment, are typically less than 1mm per week, i.e. about 5 μm per hour, so that a relatively low measurement frequency is sufficient to observe the occurrence of deposits. Limiting the duration of the measurement to a few seconds per day prevents the measurements performed by the thermal flow meter from being able to tamper with the results by preventing deposition of condensable matter at the tip of the flow meter due to input of heat from the heating element. In fact, deposits at high temperatures are reduced or even absent.

The thickness of the deposit can be estimated from a deviation value of the measurement result of the thermal type flow meter.

The method for monitoring deposits may comprise a preliminary calibration step in which at least one measurement value of a thermal flow meter obtained for a predetermined gas flow rate in the vacuum pump is recorded. The various data collected in the preliminary calibration step may allow a better interpretation of the values measured by the thermal flow meter, in particular as a function of the pumped gas flow rate, the type of pumped gas, the nature of the deposit and the thickness of the deposit.

These measurements may be performed on the flow and property values of the gases defined in the recipes/protocols to be performed in the process chambers connected to the vacuum pumps, particularly for the characteristic steps of these recipes.

For example, when the monitoring method provides measurements performed at a particular threshold and knows the gas flow and gas properties of the pumped gas at that time, the preliminary calibration step may record the measurements obtained by the thermal flow meter for the values of the gas flow and properties for that particular operating point.

Drawings

Other objects, features and advantages of the present invention will appear from the following description of particular embodiments, given with reference to the accompanying drawings, in which:

fig. 1 shows a schematic view of a process chamber of a manufacturing apparatus connected to a vacuum line.

Fig. 2 shows a schematic view of a thermal flow meter arranged in the discharge conduit of the vacuum line of fig. 1 and in which the heat distribution is schematically shown without gas flow and without deposits.

Fig. 3 shows a view of a thermal flow meter similar to fig. 2 in the presence of an air flow.

Fig. 4 shows a view of a thermal flow meter similar to fig. 3 in the presence of gas flows and deposits.

Fig. 5 shows a schematic cross-sectional view of a turbo-molecular vacuum pump.

Figure 6 shows a partial schematic view of the elements of another exemplary embodiment of a vacuum pump.

In the figures, like elements have like reference numerals. The drawings are simplified to facilitate understanding.

Detailed Description

The following embodiments are examples. While the specification refers to one or more embodiments, this does not necessarily mean that each reference refers to the same embodiment, or that the feature only applies to a single embodiment. Simple features of different embodiments may also be combined or interchanged to provide further embodiments.

"upstream" is understood to mean that one element is placed before another element with respect to the direction of gas flow. On the other hand, "downstream" is understood to mean that one element is placed after the other with respect to the circulation direction of the gas to be pumped.

Fig. 1 shows an example of an apparatus 101 for manufacturing, for example, a flat display screen or a photovoltaic or semiconductor substrate (wafer).

The apparatus 101 comprises a process chamber 102 connected to a vacuum line comprising a turbo molecular vacuum pump 1, the turbo molecular vacuum pump 1 itself being arranged upstream of a roughing vacuum pump 100 by means of an exhaust duct 103.

As can also be seen in fig. 1, the vacuum line comprises a device 200 for monitoring deposits of reaction by-products at the exhaust 7 of the vacuum pump 1.

Monitoring device 200 includes thermal flow meter 20 and processing unit 22.

The thermal flow meter 20 may be arranged at the exhaust 7 of the turbomolecular vacuum pump 1, in the turbomolecular vacuum pump 1 itself as will be seen later, or in an exhaust duct 103 connected to the outlet of the turbomolecular vacuum pump 1 as shown in fig. 1; alternatively, it may be disposed in the rough vacuum pump 100 at the exhaust port of the rough vacuum pump 100, or in a pipe connected to the outlet of the rough vacuum pump 100.

In the first example of fig. 1, the thermal flow meter 20 is arranged in an exhaust conduit 103, the exhaust conduit 103 being connected to the outlet aperture 8 of the turbomolecular vacuum pump 1.

The thermal type flow meter 20 is used to measure the flow rate of gas flowing in a pipe or a duct. The principle of the thermal flow meter 20 is based on heat transfer by fluid convection. As known per se, thermal flow meter 20 comprises two temperature probes: a first temperature probe 23 placed at the discharge port 7 at an upstream position in the gas flow direction and a second temperature probe 24 placed at a downstream position (fig. 2).

Thermal flow meter 20 further includes a heating element 25 interposed between temperature probes 23 and 24, and a substrate 26 that insulates temperature probes 23 and 24 and heating element 25 from each other. The heating element 25 is, for example, a heating resistor. The temperature probes 23, 24 are, for example, thermistors. The substrate 26 encapsulates, for example, the temperature probes 23, 24, thereby electrically and thermally insulating them from each other and protecting them from possible gas attack.

For example, the temperature probes 23, 24 are arranged equidistantly from the heating element 25. The temperature probes 23, 24 and the heating element 25 may be aligned along a line parallel to the axis of the discharge conduit 103, the thermal flow meter 20 being arranged in the discharge conduit 103.

To perform a measurement by means of the thermal flow meter 20, the heating element 25 is supplied with power, the heating element 25 is heated to, for example, 100 ℃, and the temperature difference between the temperature probes 23, 24 is measured.

When there is no gas flow in the exhaust duct 103, the heat dissipated by the heating element 25 is evenly distributed around the heating element 25 (fig. 2). The temperature probes 23, 24 allow measuring a first temperature difference, which is zero when the

probes

23, 24 are equidistant from the heating element 25.

As the air flow flows in the discharge duct 103, the thermal convection reduces the temperature measured by the first temperature probe 23 placed upstream and increases the temperature measured by the second temperature probe 24 placed downstream (fig. 3). The temperature difference observed between the temperature probes 23, 24 is now greater than would be observed without the circulation of the gas flow. This difference allows a measure of the gas flow to be derived therefrom.

Thermal flow meter 20 may be a MEMS (micro-electro-mechanical system) component fabricated from semiconductor materials. The thermal flow meter 20 is less than one centimeter in size.

The processing unit 22 comprises a controller or microcontroller or computer or programmable logic controller and a computer program configured to implement a method for monitoring deposits of reaction by-products at the exhaust of the vacuum pump 1. The processing unit 22 is, for example, a controller of the vacuum pump 1, which allows, inter alia, controlling the rotational frequency of the rotor of the vacuum pump 1.

The processing unit 22 is configured to perform measurement by the thermal flow meter 20 so as to judge whether there is a deposit of a reaction by-product at the discharge port 7, based on a difference between the flow rate measured by the thermal flow meter 20 and the estimated value of the flow rate of the gas pumped by the vacuum pump 1.

The estimate of the pumped gas flow rate can be derived only from the information available to the vacuum pump 1, that is, it is not necessary to obtain information relating to the quantity and nature of the gas introduced upstream of the vacuum pump 1.

To this end, according to an exemplary embodiment, the monitoring device 200 comprises a pressure sensor 21, which pressure sensor 21 is configured to determine the pressure at the exhaust 7 of the vacuum pump 1 (fig. 1).

The processing unit 22 is thus configured to estimate the pumped gas flow rate from the information related to the power parameters of the motor 16 of the vacuum pump 1 and the measured values of the pressure sensor 21.

The power parameter of the motor 16 of the vacuum pump 1 is, for example, an electric current. The current consumed by the motor 16 and the pressure at the exhaust 7 of the vacuum pump 1 depend on the gas flow rate and the nature of the gas being pumped. By measuring the pressure at the discharge opening 7 and knowing the current consumed by the motor 16, it is possible to estimate a pumped gas flow value, which can be compared with the value measured by the thermal flow meter 20.

According to another exemplary embodiment, the processing unit 22 is configured to communicate with the process chamber 102 depressurized by means of the vacuum pump 1 to estimate the pumped gas flow. The process chamber 102 uses the following recipe/recipe: which defines the duration, nature, flow rate and pressure of the gas introduced into the chamber. These recipes, or elements of these recipes, are information that can be transmitted by the process chamber 102 to the processing unit 22, and the processing unit 22 can then accurately estimate the pumped gas flow value. The information transmitted by the chamber 102 may be a digital signal or a dry junction, etc.

The variation of the difference between the value measured by thermal flow meter 20 and the estimated value of the pumped gas flow makes it possible to determine the presence of deposits 27 of reaction by-products in conduit 103 (fig. 4).

In fact, in the absence of deposits, the difference between the temperatures determined by the temperature probes 23, 24 is the same for the same flow rate and the same nature of the gas, identified for example by the pressure measurement and the motor current consumed.

However, when deposits 27 appear on the inner wall of discharge pipe 103, particularly on thermal flow meter 20, a change in the difference in measured temperature is observed. A layer of deposits 27 deposited on the temperature probes 23, 24 reduces the heat transfer to the second temperature probe 24 placed downstream (fig. 4). The temperature measured by the second temperature probe 24 is reduced with respect to the case without deposits (figure 3) for the same flow rate of the same gas. Therefore, the flow rates measured by the thermal flowmeter 20 in the presence of deposits are different for the same flow rate of the same gas.

The difference observed between the flow rate measured by thermal flow meter 20 and the value of the pumped gas flow rate estimated by means of, for example, a pressure measurement and a consumption current value, makes it possible to deduce the presence of deposits 27 of reaction by-products.

The measurement duration of thermal flow meter 20 may be less than two minutes, for example less than one minute. The measurements are performed, for example, daily measurements, separated by intervals of more than 10 hours, for example, by thermal flow meter 20.

The highest deposition rates observed in turbomolecular vacuum pumps 1, in particular during semiconductor manufacturing processes such as etching equipment, are typically less than 1mm per week, i.e. about 5 μm per hour, so that a relatively low measurement frequency is sufficient to observe the occurrence of deposits. Limiting the duration of the measurements to a few seconds per day prevents the measurements performed by the thermal flow meter 20 from being able to falsify the results by preventing deposition of condensable matter at the tip of the flow meter 20 due to input of heat from the heating element 25. In fact, deposits at high temperatures are reduced or even absent.

The thickness of the deposit 27 can also be estimated from the deviation values of the measured values given by the thermal flow meter 20. The greater the deviation of the temperature difference measured by the thermal flowmeter 20 from the expected value, the greater the thickness of the deposit 27.

The monitoring method may further comprise a preliminary calibration step, wherein at least one measurement value from the thermal flow meter 20 obtained for a predetermined flow rate of gas pumped by the vacuum pump 1 is recorded in the processing unit 22.

For example, several measurements from the thermal flow meter 20 are recorded for different gas flows and/or different gas species pumped by the vacuum pump 1.

These measurements may be performed on values of flow and properties of gases defined in a recipe to be executed in the process chamber 102 connected to the vacuum pump 1.

These measurements may be performed for the characteristic steps of these recipes.

For example, when the monitoring method provides measurements performed at a particular threshold and knows the gas flow and properties of the gas being pumped at that time, the preliminary calibration step may record the measurements obtained by thermal flow meter 20 for the gas flow values and gas properties at that particular operating point.

These measurements may be performed in the presence of deposits 27 on the inner wall of discharge conduit 103, for example for several thicknesses of deposits 27, to allow the thickness of deposits 27 to be evaluated from an offset estimate of the measurements from thermal flow meter 20.

These measurements can also be made without deposits, for example after each maintenance operation, at start-up, when the discharge line 103 is free of deposits. The measurements performed during the monitoring method may then be compared with these reference values.

The various data that can be collected during the preliminary calibration step may allow a better interpretation of the values measured by thermal flow meter 20, in particular as a function of the flow rate of the pumped gas, the type of gas pumped, the nature of the deposit and the thickness of the deposit.

As can be understood from what has just been described, the monitoring method and device allow the presence of deposits at the exhaust 7 of the vacuum pump 1 to be detected more accurately at the earliest possible moment.

Fig. 5 shows a second exemplary embodiment, in which a thermal flow meter 20 is arranged inside a turbo molecular vacuum pump 1.

As seen more particularly in this figure, the turbomolecular vacuum pump 1 comprises a stator 2 and a rotor 3, the rotor 3 being arranged in the stator 2 and configured to drive gas to be pumped between an inlet aperture 6 and an outlet aperture 8 of the stator 2 in a gas flow direction indicated by arrows in fig. 5.

Vacuum pump 1 comprises a turbomolecular stage 4 and a molecular stage 5 located downstream of turbomolecular stage 4 in the direction of gas flow. The pumped gas enters through inlet port 6, passes first through turbomolecular stage 4, then through molecular stage 5, and then through exhaust port 7, to be subsequently exhausted through outlet port 8 of vacuum pump 1. The outlet opening 8 is connected to a rough vacuum pump.

In the turbomolecular stage 4, the rotor 3 comprises at least two stages of blades 9 and the stator 2 comprises at least one stage of fins 10. The blades 9 and the fins 10 of the stages follow each other axially along the axis of rotation I-I of the rotor 3 in the turbomolecular stage 4. The rotor 3 includes, for example, four or more stages of blades 9, for example, between four and eight stages of blades 9 (six stages in the example shown in fig. 1).

Each stage of blades 9 of the rotor 3 comprises inclined blades extending substantially radially from a hub 11 of the rotor 3, which hub 11 is fixed to a shaft 12 of the turbomolecular vacuum pump 1. The blades 9 are evenly distributed over the outer circumference of the hub 11.

Each stage of the fins 10 of the stator 2 includes a crown ring (crown ring) from which inclined fins extend in a substantially radial direction, the inclined fins being evenly distributed on the inner periphery of the crown ring. Each of the first-stage fins 10 of the stator 2 is engaged between each of the successive two-stage blades 9 of the rotor 3. The vanes of the rotor 3 and the fins of the stator 2 are inclined to direct the pumped gas molecules to the molecular stage 5.

According to an exemplary embodiment, the rotor 3 comprises a Holweck skirt 13 in the molecular stage 5, which is formed by a smooth cylinder forming a revolution shape against the helical groove of the stator 2. The helical groove allows the pumped gas to be compressed and directed to the discharge opening 7.

The rotor 3 is fixed on a shaft 12, the shaft 12 being driven by means of an electric motor 16 of the turbomolecular vacuum pump 1 to rotate in the stator 2 at a high axial rotational speed, for example at a speed exceeding 20000 revolutions per minute. The motor 16 is arranged, for example, below the cover of the stator 2, which cover is itself arranged below the Holweck skirt 13 of the rotor 3. The rotor 3 is guided laterally and axially by magnetic or mechanical bearings 18. The vacuum pump 1 may also comprise a supporting rolling bearing 19.

The thermal flow meter 20 is placed inside the vacuum pump 1 at the discharge opening 7, the discharge opening 7 corresponding to the volume comprised between the outlet of the rotor 3, that is to say here the end of the Holweck skirt 13, and the outlet orifice 8, and the thermal flow meter 20 being in: at this point, the gas is no longer compressed in the vacuum pump 1 but the pressure is highest and the risk of deposition is greatest.

For example, the thermal flow meter 20 is arranged in the conduit 14 of the outlet opening 7, that is to say a pipe which usually has the standard diameter of a vacuum coupling and passes through the outlet opening 8.

As in the previous examples, the processing unit 22 is configured to perform measurements by the thermal flow meter 20 in order to determine the presence of deposits of reaction by-products at the exhaust 7 of the vacuum pump 1 from the difference between the flow rate determined by the thermal flow meter 20 and the estimated value of the gas flow rate pumped by the vacuum pump 1.

As previously mentioned, the estimate of the pumped gas flow rate can be derived from only the information available from the vacuum pump 1, that is, without having to obtain information about the quantity and nature of the gas introduced upstream of the vacuum pump 1.

To this end, according to an exemplary embodiment, the monitoring device 200 comprises a pressure sensor 21, which pressure sensor 21 is configured to determine the pressure at the exhaust 7 of the vacuum pump 1. The pressure sensor 21 is also arranged, for example, in the duct 14 of the stator 2.

The observed difference between the flow rate measured by thermal flow meter 20 and the estimated value of the pumped gas flow rate obtained by means of, for example, the pressure measurement and the consumed current value, makes it possible to deduce the presence of deposits 27 of reaction by-products.

The monitoring device 200 thus allows the presence of deposits in the exhaust 7 of the vacuum pump 1 to be detected more accurately at a moment as early as possible, which allows a better management of the schedule of maintenance interventions.

The monitoring can be performed on site, that is to say without dismantling the vacuum pump 1. The measuring device is non-invasive. It does not create pressure or seal losses. It has no moving parts, which limits the possibility of malfunction.

Fig. 6 shows a third exemplary embodiment, in which a thermal flow meter 20 is arranged inside a rough vacuum pump 100.

As shown in this figure, the rough vacuum pump 100 comprises a stator 2 forming at least one pumping stage, for example two to ten pumping stages, here five pumping stages, mounted in series between an inlet aperture 6 and an outlet aperture 8 of the stator 2, in which the gas to be pumped can circulate.

The pumping stage communicating with the inlet aperture 6 of the vacuum pump 100 is the first pumping stage or lowest pressure stage and the pumping stage communicating with the outlet aperture 8 is the last pumping stage or highest pressure stage.

The vacuum pump 1 further comprises two rotors 300, which rotors 300 are arranged in the stator 2 and are configured to rotate in opposite synchronizations in the pumping stages to drive gas to be pumped between the inlet 6 and outlet 8 apertures. The rotor 300 has, for example, vanes of the same profile, for example of the "roots" type with two vanes, three vanes or more, or of the "claw" type, or on the basis of another similar positive-displacement vacuum pump principle.

In operation, the rotor 300 is driven in rotation by a motor, which is arranged, for example, at one end of the vacuum pump 1, for example, on the side of the outlet aperture 8.

During rotation, the gas drawn in from the inlet orifice 6 is trapped in the volume formed by the rotor 300 and the stator 2 of the pumping stage, and is then compressed and driven to the outlet and the next stage. The vacuum pump 100 is called "dry" because in operation the rotors 300 rotate inside the stator 2, there is no mechanical contact between the rotors or between the rotors and the stator 2, but the clearance is very small, which allows the absence of oil in the compression chamber.

In this embodiment, the discharge opening 7 is defined by the volume contained between the outlet of the rotor 300 of the last pumping stage and the outlet opening 8, and is located at: at this point there is no further compression of the gas, but the pressure is highest and the risk of deposition is greatest.

The thermal flow meter 20 is arranged, for example, in the duct of the discharge opening 7, that is to say in a pipe of standard diameter, usually with a vacuum coupling, which connects the outlet of the rotor 300 of the last pumping stage to the outlet opening 8.

Claims

1. An apparatus (200) for monitoring an exhaust port (7) of a vacuum pump (1:

-a thermal flow meter (20) comprising:

-a first temperature probe (23) placed at the discharge opening (7) at an upstream position in the gas flow direction,

-a second temperature probe (24) placed at a downstream position,

-a heating element (25) interposed between the temperature probes (23, 24),

-a substrate (26) insulating the temperature probe (23, 24) and the heating element (25) from each other, and

-a processing unit (22) configured to perform measurements by means of the thermal flow meter (20) in order to determine the presence of deposits of reaction by-products at the exhaust port (7) as a function of the difference between the flow rate determined by the thermal flow meter (20) and the estimated value of the flow rate of the gas pumped by the vacuum pump (1.

2. The monitoring device (200) according to the preceding claim, wherein the thermal flow meter (20) is a MEMS component.

3. The monitoring device (200) according to any one of the preceding claims, wherein the monitoring device (200) further comprises a pressure sensor (21) configured to determine a pressure at an exhaust (7) of the vacuum pump (1.

4. A monitoring device (200) according to claim 3, characterized in that the power parameter of the motor (16) of the vacuum pump (1.

5. The monitoring device (200) according to any one of the preceding claims, wherein the processing unit (22) is configured to communicate with a process chamber (102) depressurized by means of the vacuum pump (1) to estimate a pumped gas flow rate.

6. A vacuum pump (1:

a stator (2), the stator (2) comprising an inlet aperture (6) and an outlet aperture (8),

-at least one rotor (3,

characterized in that the vacuum pump (1.

7. Vacuum pump (1.

8. Vacuum pump (1) according to any of claims 6 and 7, characterized in that the vacuum pump (1) is a turbo molecular vacuum pump.

9. Vacuum pump (100) according to any of claims 6 and 7, wherein the vacuum pump (100) is a rough vacuum pump comprising two rotors (300) configured to counter-rotate synchronously in at least one pumping stage to drive gas to be pumped between the inlet aperture (6) and the outlet aperture (8).

10. A method of monitoring an exhaust port (7) of a vacuum pump (1, 100) for deposits of reaction by-products by means of a monitoring device (200) according to any one of claims 1 to 5, wherein a measurement is performed by a thermal flow meter (20) to determine the presence of deposits of reaction by-products at the exhaust port (7) from the difference between the flow rate determined by the thermal flow meter (20) and an estimated value of the flow rate of gas pumped by the vacuum pump (1.

11. Method of monitoring deposits according to claim 10, characterized in that the heating elements (25) of the thermal flow meter (20) are powered to perform measurements at intervals separated by more than 10 hours, such as daily measurements.

12. Method of monitoring deposits according to any of claims 10 and 11, wherein the measurement duration of the thermal flow meter (20) is less than two minutes, such as less than one minute.

13. The method of monitoring deposits according to any one of claims 10 to 12, wherein the thickness of deposits is evaluated from a deviation value of the measured values of the thermal flow meter (20).

14. A method of monitoring deposits according to any one of claims 10 to 13, comprising a preliminary calibration step in which at least one measurement value from the thermal flow meter (20) obtained for a predetermined gas flow rate in a vacuum pump (1.