Patent Description:
In vacuum applications, pumps have to convey various types of gases and evaporated substances. As different substances have to be transported through the vacuum pump, materials might deposit on the inner surfaces of the pump, due to changes in pressure or temperature conditions. These by-products could be solid, polymer or dust-like. These deposits might reduce the vacuum pumps performances, in particular because they reduce the gas passage's cross-section.

Moreover, in most applications in semiconductor or thin film deposition industry, the process gases comprise aggressive substances which may react with the metallic parts of the vacuum pump, especially at the exhaust. The reactive halogens (like SF<NUM>, Cl<NUM> or HBr) or acid gases used in said applications might cause corrosion inside the vacuum pump and might have a very negative influence on the performance of the vacuum system.

This is even worse in turbomolecular pumps, wherein such deposit or corrosion, might involve a rapid seizure of the pump, because the high speed rotating parts can have contact with the static parts due to the by-product deposition inside the pump.

This deposition may occur in all parts in contact with process gas. The high pressure section of the turbomolecular pump has more favorable condition to accumulate undesired deposition. This could also be found in other parts of the vacuum system like in the roughing vacuum pump or in the vacuum piping line. The deposition involves a reduction of the size of the pathway and thus, an increase in pressure which can cause, in a cascade effect, even more by-product deposition.

Therefore, it is a requirement for multiple vacuum applications, especially in semiconductor industry or in thin film deposition processes, to monitor the by-product deposits inside the vacuum apparatus.

Many different sensor technologies are known to monitor such deposits and its layer thickness inside of a vacuum pipe or other hollow bodies or vacuum pumps.

For example, a first known method consists in monitoring the motor current of the vacuum pump in order to determine a possible presence of by-product affecting the pumping performance. The evolution of the motor current or magnetically levitated rotor positions may provide information on the amount of deposits in the vacuum pumps. However, this strategy might be not accurate enough to determine the amount or the nature of the deposited materials.

Beside this, other by-product detection technologies use temperature or pressure measurements. However, these strategies generally need to implement dedicated sensors that may be invasive. Moreover, sensors have to be suitably sealed. Tightness is important because the by-product layers within some applications may release hazardous and toxic substances. In addition, the sealing has to be operational so that the conveyed substances do not leak out with time. Furthermore, sensors imbedded in area of deposition risks may accumulate by-product depositions during its function which may cause dysfunctionality and therefore inaccurate measurement results. As example, <CIT> describes a system for monitoring the presence of deposits or build-up on the inner wall of a pipe containing fluid.

One of the objectives of the present invention is therefore to propose a device or a method for monitoring the deposition of by-products that solve at least partially one of the previous above mentioned disadvantages.

To this end, the invention is defined by a vacuum pump or a vacuum line according to claim <NUM> and a method according to claim <NUM>.

An example vacuum apparatus comprises a vacuum enclosure having a circumferential surface and an inner volume to be placed under vacuum wherein it further comprises:.

The conductance of the vacuum enclosure is not affected by the guided surface acoustic waves device as it is arranged outside of the vacuum enclosure. It is a non-invasive measurement technology which therefore has no impact in terms of functionality and performance. Moreover, it can thus be possible to determine information of the by-products deposition without necessarily knowing in advance the composition of the deposit. In addition, as the vacuum apparatus is under vacuum, the signal received by the piezo electric transducer receiver only contains surface acoustic wave that propagate through the circumferential surface of the vacuum enclosure. Any wave transmission through the inner volume of the vacuum apparatus can be completely neglected throughout the whole measurement procedure, because no signal transmission might occur due to the low pressure inside the vacuum enclosure. Moreover, the vacuum apparatus is miniaturized so that it may be implemented everywhere in the vacuum line and separated from its electronics which might be connected via appropriate cables. The vacuum apparatus is thus highly flexible in its application and place of operation.

The vacuum apparatus can also have one or more of the features described below, taken individually or in combination.

The at least one piezo-electric transducer might be made of piezoceramic material. It is therefore made of high temperature resistant material. Thereby the guided surface acoustic waves device, mounted for example directly on the exhaust pipe of a vacuum pump can be operated at high temperatures.

The vacuum enclosure might be of tubular shape.

The piezo-electric transducers might be positioned on opposite locations on the outer diameter of the tube.

The piezo-electric transducer emitter might be configured to excite circumferential surface acoustic waves in opposite directions around the tube that arrive at piezo-electric transducer receiver.

A parameter of a surface acoustic wave propagating between said piezo-electric transducers might be the transmission time.

At least one additional parameter of the surface acoustic wave might be chosen among the wave transmission velocity and/or the amplitude and/or the pattern of a surface acoustic wave.

Said piezo-electric transducers might be configured to excite circumferential surface acoustic waves with a wavelength corresponding to a Lamb wave type. The Lamb-type wave is mainly the antisymmetric type which might be the most suitable mode to be used here for the vacuum apparatus.

The control unit might be configured to also receive information of the temperature of the vacuum enclosure.

Another object of the invention is a vacuum pump, such as a turbomolecular pump or a rough vacuum pump characterized in that it comprises at least one vacuum apparatus as previously described.

The at least one vacuum apparatus might be arranged at the exhaust of the vacuum pump.

Another example is a vacuum line comprising at least one vacuum apparatus as previously described.

Another example is a method for monitoring a deposition of by-products using a vacuum apparatus as previously described, wherein a variation of at least one parameter of a surface acoustic wave of a guided surface acoustic waves device propagating along the circumferential surface of the vacuum enclosure is monitored to detect a by-products deposition on the inner surface of the circumferential surface and/or to determine the properties of the by-product deposition.

The variation of at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure might be monitored for only one passage of the surface acoustic waves in front of the piezo-electric transducer receiver.

The variation of at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure might be monitored for at least two successive passages of the surface acoustic waves in front of the piezo-electric transducer receiver. For example, the different signal transmission times for various layer thicknesses can be summed up after each passage in order to help detecting layer thicknesses down to smaller values. The presence and thickness of the by-product deposition can be better determined based on the varying transmission times of the circumferential surface acoustic waves in more than one passage. By also taking the attenuation of the signals amplitude into account, by-product material characteristics like Young's modulus can also be determined. Due to this, it will not be mandatory to know the precise material properties before the actual measurement and the guided surface acoustic waves device is capable to determine the material with a sufficient accuracy. The range of by-products can vary from polymer like materials to salt like materials and therefore the transmission time and attenuation of the signal - received by the piezo-electric transducer - may also vary in a wide range. The layer thickness and the material properties can thus be known with help of this non-invasive sensor technology.

The method might comprise a preliminary step of calibration in which the propagation of two surface acoustic waves is first analyzed on a clean vacuum enclosure.

Other objects, characteristics, and advantages of the present invention appear from the following description of particular embodiments, made with reference to the accompanying drawings, in which:.

In the figures, identical elements have the same reference numbers. The drawings in the figures are simplified for ease of understanding.

The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features only apply to a single embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments.

<FIG> shows an embodiment of an equipment <NUM> for semiconductor or coating processes.

The equipment <NUM> comprises a process chamber <NUM> configured to receive and process at least one substrate <NUM>, such as a wafer in a semiconductor process or such as a flat panel display in a coating process. The process chamber <NUM> is connected to a vacuum line <NUM> comprising at least one vacuum apparatus <NUM>.

Pumps and associated evacuation canalization used in environment with corrosive gases need to be kept at high temperature, in some cases above <NUM>, in order to minimize by-product deposition risks within. The by-product deposition reaction rate is related to the phase transition characteristic curve of the gas, where solidification rate is higher at higher pressure and lower temperature. This risk is higher at exhaust of the pump where the gas pressure is highest after the pump compression stage.

The vacuum apparatus <NUM> is preferably suitable for an use in high temperature application (more than <NUM>) and therefore, as it will be described later, the piezo-electric transducers themselves <NUM>, <NUM> might be made up of high temperature resistant components.

For example, the vacuum line <NUM> comprises a turbomolecular pump <NUM> whose inlet <NUM> is connected to the process chamber <NUM>, and a rough-vacuum pump <NUM>, whose inlet <NUM> is connected via a pipe <NUM> to the outlet <NUM> of the turbomolecular pump <NUM>. The turbomolecular pump <NUM> is mounted upstream and in series connection with the rough-vacuum pump <NUM>. "Upstream" has to be understood according to the direction of the pumped gases (see arrows in <FIG>).

Different locations are possible for the vacuum apparatus <NUM>.

The vacuum apparatus <NUM> may be arranged inside the turbomolecular pump <NUM>, for example at the exhaust <NUM> of the turbomolecular pump <NUM>, or on a pipe <NUM>, arranged downstream of the outlet <NUM>, between the turbomolecular pump <NUM> and the rough-vacuum pump <NUM>.

As an alternative or in complement, the vacuum apparatus <NUM> can be connected to a dead-end pipe <NUM> arranged in front of a sensor <NUM> of the vacuum line <NUM>, such as a pressure sensor.

As an alternative or in complement, the vacuum apparatus <NUM> can be connected at the inlet <NUM> or at the exhaust <NUM> of the rough-vacuum pump <NUM>, inside the rough-vacuum pump <NUM> or outside, for example on a pipe of the vacuum line <NUM> downstream of an outlet <NUM> of the rough-vacuum pump <NUM>.

More visible in <FIG>, the vacuum apparatus <NUM> comprises a vacuum enclosure <NUM> having a circumferential surface, such as for example a metallic wall, such as stainless steel, and an inner volume to be placed under vacuum, that is to say under a pressure below the atmospheric pressure.

The vacuum apparatus <NUM> further comprises at least one guided surface acoustic waves device <NUM> and a control unit <NUM>.

The guided surface acoustic waves device <NUM> comprises at least a piezo-electric transducer <NUM>, <NUM> for coupling surface acoustic waves on the circumferential surface and for detecting surface acoustic waves propagating along the circumferential surface.

The guided surface waves device <NUM> might comprises at least a piezo-electric transducer emitter <NUM> for coupling surface acoustic waves on the circumferential surface and at least a piezo-electric transducer receiver <NUM> for detecting surface acoustic waves propagating along the circumferential surface. The surface acoustic waves emitted by the piezo-electric transducer emitter <NUM> can thus be detected by the piezo-electric transducer receiver <NUM>.

As an alternative, the piezo-electric transducer emitter <NUM> and the piezo-electric receiver <NUM> are formed by only one piezo-electric transducer <NUM>, <NUM> which is configured to be operated alternately as emitter or receiver.

The at least one piezo-electric transducer <NUM>, <NUM> might be made of high temperature resistant material, such as a piezoceramic material as PIC <NUM>. Thereby the guided surface acoustic waves device <NUM>, mounted for example directly on the exhaust pipe of a vacuum pump <NUM>, <NUM>, can be operated at high temperatures (> <NUM>).

The piezo-electric transducers <NUM>, <NUM> are arranged outside of the vacuum enclosure <NUM>, on the circumferential of the vacuum enclosure <NUM>. Therefore, the method is non-invasive and do not create pressure or tightness losses. The pumping capacity is not affected by the guided surface acoustic waves device <NUM>.

The vacuum enclosure <NUM> may be of tubular shape. The circumferential surface of the vacuum enclosure <NUM> might thus be cylindrical.

It can be realized as a vacuum flange standard used to connect vacuum chambers, tubing and vacuum pumps to each other in the vacuum line <NUM>, such as the ISO standard quick release known by the name DN, as illustrated in <FIG>. It has for example an inner diameter of <NUM>. The vacuum enclosure <NUM> has for example a flange <NUM> that can be joined to another flange by a centering ring and an elastomeric O-ring gasket.

This vacuum flange standard can be the one used for forming the exhaust <NUM> of the turbomolecular pump <NUM>, the opposite part <NUM> of the flange <NUM> being connected to a housing <NUM> of the turbomolecular pump <NUM>. Thus, the vacuum enclosure <NUM> is formed by the tube of the exhaust of the turbomolecular pump <NUM>, without changing existing housings <NUM>.

The control unit <NUM> is configured to control the at least one piezo-electric transducer <NUM>, <NUM> to monitor a variation of at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure <NUM>, between said piezo-electric transducers emitter <NUM> and receiver <NUM> to detect a by-products deposition <NUM> on the inner surface of the circumferential surface and/or to determine the properties of the by-product deposition <NUM> (<FIG>). The control unit <NUM> comprises one or more controllers or processors and a memory. It can be common to several pairs of piezo-electric transducer receiver <NUM> and emitter <NUM>.

The at least one parameter of a surface acoustic wave propagating between said piezo-electric transducers <NUM>, <NUM> can be chosen among the wave transmission velocity and/or the transmission time and/or the amplitude and/or the pattern of a surface acoustic wave. The parameter used a main indicator is for example the time transmission.

Time shifts and possible amplitude changes can be observed due to the presence of a deposition of by-products <NUM> on the inner surface of the vacuum enclosure <NUM> with respect to a clean tube. The thickness of the by-product deposition can be determined based on the varying transmission times of the circumferential surface acoustic wave. The decreasing of the transmission time can be due to the increasing thickness of a deposition of by-products <NUM> for example.

When the vacuum enclosure <NUM> is of tubular shape and when there is two piezo-electric transducers <NUM>, <NUM>, the piezo-electric transducers <NUM>, <NUM> might be positioned on opposite locations on the outer diameter of the tube (diametrically arranged) as it is shown in <FIG>. The piezo-electric transducer emitter <NUM> and the piezo-electric transducer receiver <NUM> are then positioned in circumferential direction around the vacuum enclosure <NUM>, <NUM>° opposite to each other.

The piezo-electric transducer emitter <NUM> might be configured to excite circumferential surface acoustic waves in opposite directions around the tube that arrive at piezo-electric transducer receiver <NUM> (<FIG>). The wavelength corresponds for example to a Lamb-type wave. Both surface acoustic waves should arrive at the piezo-electric transducer receiver <NUM> at the same time when the vacuum enclosure <NUM> is clean.

The Lamb-type wave is mainly the antisymmetric type which might be the most suitable mode to be used here for the vacuum apparatus <NUM>. The piezo-electric transducer <NUM> excites the surface acoustic waves for example with a frequency between <NUM> and <NUM>. This value depends on the geometric configuration of the vacuum enclosure <NUM> and the characteristics of the by-products deposition <NUM>. In addition, this excitation frequency and a tubular shape of the vacuum enclosure <NUM>, favor the formation of Lamb-waves in circumferential directions. With help of these adjustments, the measurement accuracy down to several tenth of a Millimeter by-product layer thickness can be achieved.

The variation of at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure <NUM>, between the piezo-electric transducer emitter <NUM> and the piezo-electric transducer receiver <NUM> can be monitored for just one passage C1 of the surface acoustic waves in front of the piezo-electric transducer receiver <NUM>.

The variation of at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure <NUM>, between the piezo-electric transducer emitter <NUM> and the piezo-electric transducer receiver <NUM> can be monitored for at least two passages C1, C2, C3 of the surface acoustic waves in front of the piezo-electric transducer receiver <NUM>. Multiple passages C1, C2, C3 of the guided surface acoustic waves can thus be taken into account, such as more than two passages.

The different signal transmission times for various layer thicknesses can be summed up after each passage in order to help detecting layer thicknesses down to smaller values.

This method is particularly effective with the configuration of two piezo-electric transducers <NUM>, <NUM> positioned on opposite locations on the outer diameter of the tube.

<FIG> shows an example of signals of the piezo-electric transducer receiver for three passages C1, C2, C3 of the guided surface acoustic waves without deposition (curve A) and with deposition (curve B).

For the first passage C1, we can see that the amplitude of the signal of the piezo-electric transducer receiver of a vacuum enclosure <NUM> having deposition (curve B) is lower than the amplitude of the signal of the piezo-electric transducer receiver of a clean vacuum enclosure <NUM> (curve A). However, the distinction between the transmission times of both signals, with (curve B) and without by-product deposition (curve A), is very small and therefore is more difficult to see. In this case, it can be appropriate to monitor at least the variation of the transmission time for at least two passages C1, C2, C3 of the surface acoustic waves in front of the piezo-electric transducer receiver <NUM>. This "multiple detection" may help to achieve a higher measurement accuracy in case of small by-product deposition (thickness < <NUM>,<NUM>). But when it comes to larger by-product deposition (thickness > <NUM>,<NUM>), only one signal circulation might be enough to measure a sufficient time shift of the received signal.

Thus, for the first three passages C1, C2, C3 of the signal, we can see that the amplitude of the signal decreases as the number of passages C1, C2, C3 of the signal increases. This is the case for both vacuum enclosures <NUM>. However, the amplitude decreases more for the signal of the piezo-electric transducer receiver of a vacuum enclosure <NUM> with deposition (curve B) than for the clean vacuum enclosure <NUM> (curve A).

Moreover, the transmission time is quite constant or slightly decreasing as the number of the passages C1-C3 increases for the clean vacuum enclosure <NUM> (curve A) while it increases with the number of passages C1-C3 for the vacuum enclosure <NUM> with by-product deposition <NUM> (curve B).

The presence and thickness of the by-product deposition <NUM> can be better determined based on the varying transmission times of the circumferential surface acoustic waves in more than one passage. By also taking the attenuation of the signals amplitude into account, by-product material characteristics like Young's modulus can also be determined. Due to this, it will not be mandatory to know the precise material properties before the actual measurement and the guided surface acoustic waves device <NUM> is capable to determine the material with a sufficient accuracy. The range of by-products can vary from polymer like materials to salt like materials and therefore the transmission time and attenuation of the signal - received by the piezo-electric transducer <NUM> - may also vary in a wide range. The layer thickness and the material properties can thus be known with help of this non-invasive sensor technology.

As an example of realization, said piezo-electric transducers <NUM>, <NUM> are configured to excite plane surface acoustic waves. For example, the piezo-electric transducers <NUM>, <NUM> have a two-finger electrode structure to excite plane surface acoustic waves perpendicular to the electrode fingers. The orientation of the piezo-electric transducers <NUM>, <NUM> may be chosen such that they excite plane surface acoustic waves predominantly travelling circumferentially in both directions around the tube.

According to an embodiment, the control unit <NUM> is configured to also receive information of the temperature of the vacuum enclosure <NUM>. It is therefore possible to compensate the influence of temperature on the measurements to determine features of the deposition of by-products <NUM> deposited on the inner surface of the vacuum enclosure <NUM>, independently of the temperature of the vacuum enclosure <NUM>.

We will now describe an example of the functioning of the vacuum apparatus <NUM> with respect to <FIG>.

The method can comprise a preliminary step of calibration wherein the propagation of the two surface acoustic waves is first analyzed on a clean vacuum enclosure <NUM> (<FIG>).

The piezo-electric transducers <NUM>, <NUM> excite plane surface acoustic waves predominantly travelling circumferentially in both directions around the tube. Both surface acoustic waves should arrive at the piezo-electric transducer receiver <NUM> at the same time. At least one parameter of a surface acoustic wave propagating between said piezo-electric transducers <NUM>, <NUM> chosen among the wave transmission velocity and/or the transmission time and/or the amplitude and/or the pattern of a surface acoustic wave, is recorded.

In a consecutive step of monitoring, the piezo-electric transducers <NUM>, <NUM> are controlled to monitor a variation of said at least one parameter of a surface acoustic wave propagating between said piezo-electric transducers <NUM>, <NUM>, to detect a by-products deposition on the inner surface of the vacuum enclosure <NUM> or to determine the properties of the by-product deposition. The variation of the at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure <NUM> may be monitored for at least two successive passages of the surface acoustic waves in front of the piezo-electric transducer receiver <NUM>.

Claim 1:
Vacuum pump (<NUM>, <NUM>), such as a turbomolecular pump (<NUM>) or a rough vacuum pump (<NUM>), or vacuum line (<NUM>) comprising at least one vacuum apparatus (<NUM>) comprising a vacuum enclosure (<NUM>) having a circumferential surface and an inner volume under vacuum further comprising:
- at least one guided surface acoustic waves device (<NUM>) comprising a piezo-electric transducer receiver (<NUM>) and a piezo-electric transducer emitter (<NUM>) been positioned on opposite locations on the outer diameter of the vacuum enclosure (<NUM>) of tubular shape or the piezo-electric transducer emitter (<NUM>) and the piezo-electric receiver (<NUM>) being formed by only one piezo-electric transducer (<NUM>, <NUM>) which is configured to be operated alternately as emitter or receiver, for coupling surface acoustic waves on the circumferential surface and for detecting surface acoustic waves propagating along the circumferential surface, the piezo-electric transducers (<NUM>, <NUM>) being arranged outside of the vacuum enclosure (<NUM>),
- a control unit (<NUM>) configured to control the piezo-electric transducers (<NUM>, <NUM>) to monitor a variation of at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure (<NUM>) to detect a by-products deposition (<NUM>) on the inner surface of the circumferential surface and/or to determine the properties of the by-product deposition (<NUM>), the piezo-electric transducers (<NUM>, <NUM>) being made of piezoceramic material, wherein the variation of at least one parameter of a surface acoustic wave propagating along the circumferential surface of the vacuum enclosure (<NUM>) is monitored for at least two successive passages (C1, C2, C3) of the surface acoustic waves in front of the piezo-electric transducer receiver (<NUM>).