Method and apparatus for detecting particles in a gas of a process environment, and a coating system including such an apparatus

Abstract

A method for detecting particles in a gas of a process environment present in a process chamber, the method comprising: directing a gas having particles therein to an ionization and charging unit (11) in fluid communication with the process chamber and having an anode (12) and a cathode (13), the ionization and charging unit configured and arranged to at least partially ionize the gas and charge at least a portion of the particles; initiating and maintaining a discharge in the gas by applying a voltage between the anode and the cathode of the ionization and charging unit; measuring a current flowing from or to the anode and / or from or to the cathode; and detecting particles based on an AC component or a transient in the measured current. The present invention further relates to an apparatus for detecting particles, a coating system including such an apparatus, and the use of an ionization unit.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a method for detecting particles, such as "large molecules" having a mass of more than 1000 Daltons and particles up to micrometer size, in a gas of a process environment, such as air. The detection is carried out at an ambient pressure, in particular below atmospheric pressure. Furthermore, the present invention relates to an apparatus for carrying out the method of the present invention, as well as a coating system comprising such an apparatus. [Background technology]

[0002] Background of the Invention In applications in the semiconductor industry, for example, if particles are present during a process step, they can fall onto and adhere to silicon wafers. In later steps, these particles can, for example, be incorporated into functional layers during fabrication and cause defects in the functional layers. Such functional layers may include, for example, transistors. Therefore, to achieve a desired yield, the number of particles (and their size distribution) needs to be monitored. This is typically done on the pump side of the system. A sensor is positioned there to monitor particles in the gas coming from the process chamber. If a change to an unacceptable particle concentration is detected, the process can be stopped and the cause determined.

[0003] Techniques for detecting and measuring particles in gases with the aid of light are well established. Descartes first described the principle of optical detection of particles in gases in 1637. Another technique for particle determination is mass spectrometry, which has become accepted as an analytical instrument for many applications, including the measurement of relatively small particles (e.g., having a mass less than 1,000,000 daltons). Mobility spectrometers, often called ion mobility spectrometers (IMS), arose in the 1950s. Their size is significantly smaller than that of mass spectrometers.

[0004] These state-of-the-art devices have the following drawbacks: Optical instruments always require a window or lens that is exposed on at least one side to the medium being measured. This makes the design inherently complex and susceptible to contamination, which in turn leads to even more complex designs. For measuring smaller particles, stronger light sources are preferred, and therefore special safety precautions are required regarding the operation of these light sources. Another drawback of applying light sources that emit high light intensities is that the background signal also increases, resulting in a net loss of success.

[0005] Mass spectrometers are very complex and large instruments, they are also very expensive, they usually require additional vacuum chambers and corresponding pumping equipment, and they are not always easy to handle.

[0006] The use of mobility spectrometers only works under certain environmental conditions, such as a constant gas composition and constant ambient pressure or constant flow conditions in the drift tube. For example, the presence of even traces of water or acetone can completely change the chemistry in the drift tube. If this is not the case in an application (as is the case in many process systems), their use becomes expensive, as pressure stability and gas species stability must first be established in the analytical section.

[0007] Therefore, there is a need for a means for detecting particles in a gas that overcomes the drawbacks of the known devices discussed above. Summary of the Invention [Means for solving the problem]

[0008] Summary of the Invention It is an object of the present invention to provide a simple method for detecting particles, such as "large molecules" having a mass above 1000 Daltons, in a gas of a process environment, such as air. This object is achieved by the method according to claim 1.

[0009] Particles can be detected in gases based on the following principle: Particles are ionized by bombarding them with electrons having a kinetic energy of several electron volts, resulting in particle impact ionization. Depending on the type of particle, positively charged particles, i.e., particles lacking electrons, or negatively charged particles, i.e., particles with added electrons, are generated. Metallic particles are more positively charged, while insulating particles are more negatively charged. In vacuum coating applications, particles are complex substances because their composition is largely uncontrolled in physical and chemical processes at relatively high energies compared to 1 / 40 eV. Only in the case of wear of moving parts (e.g., valve operation or robot arm movement) do particles have a clear material composition. Charged particles are then accelerated in an electric field. The strength and direction of the electric field drive the particle motion. Preferably, the electric field present in the ionization and charging unit is set so that the particles reach energies exceeding 50 eV before colliding with the electrode. To achieve this, high voltages (>100 V) are preferred. Acceleration by the electric field provides the particle with the energy and momentum required for the next step. The particle then impacts a metal anode or cathode, depending on the particle's charge. Two things occur during this process: first, the particle attempts to neutralize its own charge; second, the force of the impact (the particle's momentum) produces secondary electrons, and at high energies, secondary ions and neutrals. The charge on the electrode the particle impacts is altered by the three effects mentioned above: neutralization, secondary electrons, and secondary ions. The charge currents to and from the electrode, i.e., the charge current to and from the anode or cathode, respectively, are measured to represent the impact and, based on the current characteristics, the type of particle.

[0010] Based on this principle, a method for detecting particles in a gas of a process environment, in particular in a process chamber of a coating system, is according to the invention, which comprises: directing the particle-laden gas to an ionization and charging unit in fluid communication with the process chamber and having an anode and a cathode, the ionization and charging unit configured and arranged to at least partially ionize the gas and charge at least a portion of the particles; Initiating and maintaining a discharge in the gas by applying a voltage between the anode and the cathode of an ionization and charging unit; measuring the current flowing from or to the anode and / or from or to the cathode; Detecting particles based on the AC (alternating current) component or transients of the measured current; Includes.

[0011] The gas in the process environment whose particle concentration is being monitored may be, for example, the gas in the process chamber of a coating system. The gas may be any process gas or inert gas, such as nitrogen, oxygen, hydrogen, helium, or argon. The gas may be accompanied by one or more particles, but may also be a clean gas that is completely particle-free. The method may be used to verify that the gas is clean in this sense.

[0012] The ionization and charging unit may be constructed to enable continuous discharge. This can be achieved, for example, by providing a combination of electric and magnetic fields within the ionization and charging device, which act on electrons in a manner that causes them to move along a path longer than a straight line between electrodes of opposite polarity. The provided electric and magnetic fields may have a strength and geometry that maintains the electron's kinetic energy in the range of 0 to 200 eV. For example, the anode, cathode, and means for generating a magnetic field may have cylindrical symmetry, providing a radial electric field and a longitudinal magnetic field in a cylindrical arrangement. In this way, the vector product of the electric and magnetic fields points in the azimuthal direction of the cylindrical arrangement, and the path following the direction of this vector product forms a closed loop. Electric and magnetic field configurations with these characteristics are known from cold cathode gauges, particularly those in the form of magnetrons, inverted magnetrons, or Penning gauges. The inventors of the present invention recognized that the electrode configuration and the means for generating a magnetic field can be easily transferred from a cold cathode gauge to the ionization and charging device of the present invention.

[0013] Fluid communication between the process chamber and the ionization and charging unit can be established by positioning the ionization and charging unit in a delivery pipe for delivering gas to the process chamber or in an exhaust pipe for exhausting gas from the process chamber. The ionization and charging unit can be dimensioned such that a significant portion of the cross section of an exhaust pipe having a diameter in the range of 40 to 100 millimeters is occupied by the cross section of the ionization and charging unit positioned in the exhaust pipe. The ionization and charging unit can be installed upstream of the pumping means, particularly immediately before the pumping means when viewed in the direction of the gas flow path.

[0014] Depending on the geometry of the anode and cathode, initiating and sustaining a discharge may require higher or lower voltages. Typically, a field strength of several hundred kilovolts per meter (kV / m) is applied. Magnetrons can be sized so that the distance between the electrodes is about 15 millimeters, and a voltage of about 5 kV is applied between the electrodes, resulting in a field strength of about 300 kV / m across the magnetron. The small radius of the electrode tips or the small diameter of wire-shaped electrodes are geometric characteristics that locally increase the electric field at a given voltage.

[0015] Initiating and sustaining a discharge in a gas can be achieved by applying a high constant voltage (DC) between the anode and cathode of the ionization unit. Alternatively, an oscillating voltage (AC) can accomplish this task, provided that half of the oscillation period is sufficiently long compared to the travel time of the charged particles from electrode to electrode. For ionization and charging units with dimensions on the order of a few centimeters, the frequency of the voltage oscillation can be in the kilohertz range or lower. Suitable voltages to achieve this can range from 100 V to 3 kV, especially for sensors with electrode distances in the 1-2 centimeter range. Such voltages are sufficiently high to provide sufficient impulse to ultimately charge the particles. Initiation voltages of up to 6 kV can be applied to ensure that a discharge will initiate under most circumstances. Once initiated, the voltage applied between the anode and cathode serves to maintain a circulating electron current in the at least partially ionized gas. In low-pressure environments, an RF voltage of a few volts may be sufficient to sustain the discharge. A superposition of a low RF voltage with a high DC voltage can be used to increase the discharge current flowing through the residual gas.

[0016] The inventors of the present invention have recognized that a variation of the present method, in addition to monitoring for particles, also allows for the determination of gas pressure by varying the voltage applied between the anode and cathode and observing the resulting change in discharge current. A DC current proportional to pressure can be obtained, or, if the cold cathode is operated outside the proportionality region, at least a pressure-related signature can be obtained from observing the discharge current. Thus, according to this variation of the method, lower frequency AC components, e.g., in the kHz frequency range, can be observed to derive pressure-related information, while higher frequency AC components, e.g., in the MHz frequency range, can be simultaneously observed to detect particles.

[0017] Variations of the method result from the features of dependent claims 2 to 10. In one variation of the method, the method further comprises classifying particles based on the AC component of the measured current or transient characteristics.

[0018] The characteristics of the AC component or transient of the measured current may be one of the following characteristics or a combination of the following characteristics:

[0019] The signal amplitude must be within the noise band. The signal amplitude exceeds the trigger level, i.e., overshoots / undershoots above / below a given threshold. The integral of the absolute value of the signal over a time interval exceeds a threshold value; The steepness of the signal slope after exceeding the trigger level, ·Signal change, The pattern of signal sign changes (e.g., +-+), Peaks of duration shorter than a given time, The minimum number of oscillations in a given short time interval (for example, a time interval of 500 nanoseconds or 5 microseconds after the first crossing of the trigger level), -Temporally asymmetric patterns, e.g. damped oscillations, · Characteristic frequencies in the Fourier transformed signal.

[0020] In one variation of this method, the particles to be detected have a mass greater than 1000 Daltons.

[0021] The dimensions of the ionization and charging units, the voltages applied, and the selection of trigger levels and features evaluated can be configured so that only particles with a mass greater than 1000 Daltons are detected by the method. Detected particles typically have a size less than 1 μm, but may have larger sizes.

[0022] In one variation of this method, the electric field between the anode and cathode has a strength in the range of 300 to 3000 kilovolts per meter (300 to 3000 kV / m).

[0023] In a sensor with a 1 cm distance between the anode and cathode and a 5 kV voltage applied between the anode and cathode, a field strength of 500 kV / m is reached.

[0024] In one variation of this method, the gas is focused towards the opening of the ionization unit by a hydrodynamic lens. Optionally, the hydrodynamic lens can be heated to a temperature above the temperature of the surroundings of the hydrodynamic lens.

[0025] In one variation of this method, the ionization and charging unit has an inlet located at one end and an outlet located at the other end to allow gas to pass through the ionization and charging unit.

[0026] The ionization and charging unit may have a tubular configuration. This configuration can be realized, for example, by electrodes in the form of a hollow cylinder as a cathode and a pin-shaped anode placed on the central axis of the cylinder. The configuration of the ionization and charging unit may have a conical section and may have a circular, quadratic, or rectangular cross section. This configuration may be configured to occupy most of the cross section of a pipe through which the gas flow is to be monitored for the presence of particles.

[0027] In one variation of the method, the gas is included in the group including air, nitrogen, oxygen, hydrogen, helium, and argon.

[0028] Variations in which the gas is air may apply where the process chamber is evacuated after exposure to the ambient atmosphere. In semiconductor manufacturing, nitrogen, oxygen, hydrogen, helium, and argon gases are required for specific functions in the manufacturing process.

[0029] In one variant of the method, the pressure of the gas at which the detection is carried out is below atmospheric pressure, in particular below 10 -8 It drops to mbar.

[0030] The means for initiating and maintaining a discharge in a gas can be adapted to a range of pressures in the medium or high vacuum range by selection of appropriate electrode shapes, additional magnetic fields and voltages applied to the electrodes so that said gas is at least partially ionized at the pressure at which detection takes place.

[0031] In one variation of this method, the detecting includes amplifying the charging and / or discharging current with an AC amplifier circuit having a bandwidth of at least 500 megahertz (MHz).

[0032] The amplifier circuit used in this variant of the method can be considered an extremely fast amplifier circuit capable of processing signals with short timescales in the nanosecond range. The amplifier circuit may be based on active components such as an operational amplifier (op-amp) with a gain-bandwidth product greater than 500 MHz. The amplifier circuit may be configured to operate as a voltage follower or a buffer amplifier. Thus, the amplifier circuit may have a voltage gain of 1 or slightly less than 1. Such a buffer amplifier prevents the signal source from being affected by the current required at the output of the amplifier circuit.

[0033] In a further variation, the method includes indicating that a particle is detected if the AC component or transient exceeds a predetermined threshold, and / or indicating that a particular type of particle is detected if an associated feature is detected.

[0034] In particular, the method may include indicating that one or more predetermined features of the AC component or transient have been detected. Possible features may be selected from the list above.

[0035] A further object of the present invention is to provide an alternative device for detecting particles, such as "large molecules" having a mass above 1000 Daltons, in a gas of a process environment, such as air. More specifically, a simpler, smaller and cheaper device for particle detection purposes is desired. This object is achieved by an apparatus according to claim 11.

[0036] The apparatus according to the present invention is an apparatus for detecting particles in a gas of a process environment in a process chamber. an ionization and charging unit comprising an anode and a cathode, the ionization and charging unit being constructed and arranged to at least partially ionize the gas and charge at least a portion of the particles; a voltage source connected between the anode and the cathode of the ionization and charging unit; a current measurement unit configured to measure the current from / to the anode and / or the current from / to the cathode; a particle classification unit configured to detect particles based on an AC component or transient of the measured current; Equipped with.

[0037] The ionization and charging unit may be constructed so as to allow for continuous discharge, as mentioned in the context of the method, which can be achieved in particular by an arrangement of electrodes and magnets similar to a magnetron, an inverted magnetron, or a cold cathode gauge in the form of a Penning gauge.

[0038] The voltage source may be configured to provide a DC voltage, for example, in the range of 100 V to 10 kV. The voltage source may be configured to provide a superposition of AC and DC voltages, for example, and may be specifically configured to be controlled to perform the steps of the above-described method. In combination, the voltage source and electrode geometry may be configured to generate an electric field of several hundred kilovolts per meter (kV / m) within the ionization and charging unit.

[0039] The components of the device, particularly the anode, cathode, and hydrodynamic lens in embodiments comprising the hydrodynamic lens, may be constructed of alloys from a group including Hastelloy, Inconel, or stainless steel, and more generally, iron-based alloys having a nickel content greater than 10% and a chromium content greater than 10%. These materials are compatible with semiconductor processes. To achieve long electrode life, it is particularly useful to select materials with extremely low sputter yields. The inventors of the present invention have recognized that molybdenum, titanium, and high-grade stainless steel are suitable materials for the device components.

[0040] The apparatus may include a heating means configured to heat the apparatus or a component of the apparatus to a temperature above ambient temperature to avoid deposition of material on the surface of the hydrodynamic lens. Temperatures that may be useful to achieve this goal may range from 80°C to 300°C, particularly about 200°C. The heating means may be configured to keep the temperature below a predetermined temperature limit, e.g., below 150°C, to protect adjacent components that cannot withstand higher temperatures. Some ALD or CVD processes may require heating to a temperature of 300°C to prevent material deposition on the apparatus. The apparatus may be constructed to heat itself by the discharge current flowing during normal operation, i.e., maintaining a discharge in the gas, as well as by minimizing heat rejection to other components, e.g., by having small cross-sections of mechanical connections to the environment.

[0041] Specific embodiments of the device according to the invention are given in the dependent claims 12 to 18. In one embodiment of the apparatus, the particle sorting unit is further configured to sort particles based on characteristics of AC components or transients in the measured charging and / or discharging currents, possible characteristics being described above in the context of one variant of the method.

[0042] In one embodiment, the device is designed and configured to detect particles having a mass greater than 1000 Daltons. The particles detected typically have a size less than 1 μm, but may have a larger size.

[0043] In one embodiment, the apparatus is configured so that the electric field between the anode and cathode can have a strength in the range of 300 to 3000 kV / m.

[0044] In one embodiment, the apparatus further comprises a hydrodynamic lens configured to collect the gas towards the opening of the ionization and charging unit. Optionally, the hydrodynamic lens is in thermal contact with heating means for increasing the temperature of the hydrodynamic lens relative to its surroundings. In particular, the heating means may be configured to heat the hydrodynamic lens to a temperature in the range of 80°C to 300°C in order to avoid deposition of substances on the surface of the hydrodynamic lens. The issues mentioned above in the context of heating the apparatus also apply to heating the hydrodynamic lens.

[0045] In one embodiment of the apparatus, the ionization and charging unit has an inlet located at one end and an outlet located at the other end to allow gas to pass through the ionization and charging unit. The ionization and charging unit may have a tubular form.

[0046] In one embodiment, the device further comprises an amplifier circuit for amplifying the charging and / or discharging current, the amplifier circuit having a bandwidth of at least 500 MHz. The amplifier circuit may have the features as described above in the context of the method.

[0047] In one embodiment, the device further comprises a signal output to indicate that a particle has been detected if the AC component or transient exceeds a predetermined threshold and / or that a particular type of particle has been detected if a relevant feature of the AC component or transient, particularly one or more predetermined features, is detected.

[0048] Further included within the scope of the present invention is a coating system, an etching system or a lithography system according to claim 19.

[0049] The system of the present invention comprises the device of the present invention and a process chamber, and can carry out a coating, etching, or lithography process, depending on the type of system. The system can comprise a delivery pipe for delivering gas to the process chamber or an exhaust pipe for exhausting gas from the process chamber. The process chamber is the space in which the coating, etching, or lithography process takes place. The device of the present invention can be located in the delivery pipe or the exhaust pipe, especially upstream of the pumping device.

[0050] In one embodiment, the coating system, etching system, or lithography system is configured to perform a chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD), or atomic layer deposition (ALD) process, or the coating system is an epitaxy system.

[0051] The inventors of the present invention have recognized that by incorporating the apparatus of the present invention into systems of the types mentioned above, particularly coating systems that apply CVD, PVD, PECVD, ALD, or epitactic coatings, particle detection or monitoring can be performed in an efficient and reliable manner.

[0052] Furthermore, the scope of the present invention includes the use of an ionization unit as defined in claim 21. The ionization unit may, for example, be a cold cathode pressure gauge of the magnetron or inverted magnetron type or of the Penning type. According to the present invention, the ionization unit is used to detect particles in a gas of the process environment in a process chamber, the particles to be detected having in particular a mass above 1000 Daltons. The inventors of the present invention have realized that ionization units known for other purposes can be used to carry out the method according to the present invention and can also serve as the ionization and charging unit according to the method, i.e., to ionize the particle-carrying gas and charge the particles.

[0053] In one variant, the use of an ionization unit is such that the ambient pressure at which detection takes place is less than atmospheric pressure, in particular less than 10 -8 This relates to situations where the temperature drops to mbar.

[0054] In a further variant of the use of the ionization unit, the gas is included in the group comprising air, nitrogen, oxygen, hydrogen and argon.

[0055] Returning to the overall configuration of the system in which the present invention is implemented, multiple ionization and charging units can be operated simultaneously to monitor the presence of particles. Two or more ionization and charging units may be arranged in series along the direction of gas flow. Two or more ionization and charging units may also be arranged in parallel. A bundle of several ionization and charging units, for example, realized in the form of cold cathodes, may be arranged in a tube with a diameter of more than 100 mm.

[0056] BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further illustrated by way of the drawings. [Brief explanation of the drawings]

[0057] [Figure 1] 1 shows a cross-sectional view across the central component of one embodiment of the device. [Figure 2] 10 shows a cross-sectional view across the central component of another embodiment of the device. [Figure 3] 3 shows a cross-sectional view of one embodiment of the device taken perpendicular to the view shown in FIGS. 1 and 2. FIG. [Figure 4] 1 shows a circuit diagram illustrating an amplifier circuit of one embodiment of the device. [Figure 5] 1 shows the approximate time dependence of a voltage signal representing the current measured by this method. [Figure 6] 1 shows a simplified schematic example of a voltage signal representing a current measured with the present method. [Figure 7] 1 shows a simplified schematic example of a voltage signal representing a current measured with the present method. [Figure 8] 1 shows a simplified schematic example of a voltage signal representing a current measured with the present method. DETAILED DESCRIPTION OF THE INVENTION

[0058] Detailed Description of the Invention An advantageous effect of the present invention is that the proposed method and device for particle detection are simple and robust. They can be used in most coating systems, such as CVD, PVD, and ALD, as well as epitaxy. Furthermore, they can also be used in etching systems. The ion source proposed above works very reliably down to a few mbar. It can be used at low pressures (<10 -8 mbar), it can be difficult to maintain a discharge.

[0059] Compared to all-optical processes, no optical elements such as observation windows or beam-extending mirrors that may change during processing are required. Cold cathode gauges operating under the E×B principle, such as magnetrons, inverted magnetrons, or Penning gauges, sputter cleanly themselves in most applications. In extremely demanding applications, the device according to the present invention can easily be designed to be heated up to 150°C or even 300°C to avoid deposits or other undesirable changes to the electrode surface. Compared to mass spectrometers or similar equipment, magnetrons, inverted magnetrons, or Penning gauges are much easier to set up and operate.

[0060] Commercially, the robustness and simplicity of the design will allow particle monitors to enter application areas where they have not previously been used online / in the field.

[0061] FIG. 1 shows a cross-sectional view of the central component of an apparatus combining features of several of the above-described embodiments. At the top, arrows indicate the inflow of gas 20. This gas flow originates from or is directed to a process chamber by establishing a fluid communication (not shown). The illustrated embodiment includes a hydrodynamic lens 14 that focuses the gas flow toward the inlet side of a tubular cathode 13. An anode pin 12 is located on the central axis of the cylindrical cathode 13. The anode 12, the cathode 13, and a magnet, represented by a south pole and a north pole, located on the outside of the cathode cooperate to form an ionization and charging unit 11 configured and arranged to at least partially ionize the gas. In this process, particles carried with the gas become electrically charged. The ionization and charging unit in the illustrated embodiment has the form of a magnetron. Unlike magnetron-type manometers, this ionization and charging unit has inlet and outlet openings and opposite ends to allow gas flow across the ionization and charging unit. The cross section cuts the anode's electrical contact, which is led via an insulating feedthrough to the outside of the pipe where the ionization and charging unit is located. The anode pin 12, cathode 13, hydrodynamic lens 14, and pipe 17 may have rotational symmetry about a central axis shown by the dashed-dotted line. A web 16 holds the ionization and charging unit in the center of pipe 17. Web 16 does not extend all the way around to allow gas flow radially outside the cathode but still inside pipe 17.

[0062] FIG. 2 shows a cross-sectional view across the central component of another embodiment of a device having similar components to the device shown in FIG. 1, but without the hydrodynamic lens.

[0063] Figure 3 shows a cross-sectional view of a variant similar to that shown in Figures 1 and 2, in which only three webs 16 of small cross section hold the cathode 13 inside the pipe 17. A permanent magnet arrangement M is positioned radially outside the cathode and generates a magnetic field inside the cathode. The anode pin 12 is centrally located so that the electric field is directed radially and essentially perpendicular to the magnetic field in the ionization and charging unit. The arrangement shown here is particularly suitable for self-heating of the ionization and charging unit, since the flow of thermal energy through the webs is minimal.

[0064] FIG. 4 shows a schematic diagram of the amplifier circuit for one embodiment of the device. A high-voltage UHV source is connected to the anode and cathode of the gauge, i.e., the anode and cathode of the ionization and charging unit, at the connection points shown in the left part of the diagram. The current supplied to the cathode is measured as a voltage drop across a shunt resistor, which in this case is selected to be 47 kΩ. An amplifier 15, in this case an operational amplifier, forms the active component of the amplifier circuit. An operational amplifier that meets the high requirements for measurements on short time scales of a few nanoseconds is commercially available from Texas Instruments under the name "OPA859." The amplifier circuit shown here is suitable for the OPA859. The ±2.5 volt voltage supply and amplifier circuit are located in a shielded area connected to ground, the device flange, and the cathode of the ionization and charging unit. An oscilloscope or any other analytical device can be connected to the output side to detect particles based on the AC component or transients of the measured current. The voltage signal on the output side represents the time course of the current flowing from or to the anode and / or from or to the cathode. The amplifier circuit shown here functions as a buffer amplifier, so that the current extracted on the output side, for example to operate an oscilloscope, does not affect the ionization and charging unit side, and therefore very small and fast oscillating currents can be observed.

[0065] Since any oscillations in the voltage supply can corrupt the signal measured at the output of the amplifier circuit, it is preferable that the voltage supply provide a very stable voltage over time. Smoothing the voltage over time can be achieved by connecting an inductor in series and / or a capacitor in parallel with the voltage source.

[0066] FIG. 5 shows a schematic time-voltage diagram of signal elements representing the measured current, which can be used as a feature to determine whether a particle has been detected and, in some cases, to classify the particles according to their size or composition. The horizontal axis t represents the time axis. The vertical axis represents the voltage signal U, here in arbitrary units. The voltage signal represents the current measured with respect to the anode or cathode of the device and may, for example, be generated by an amplifier circuit such as that shown in FIG. 4. During times when no particle is detected, a noise signal within a typical noise band 50 is observed. The noise band is indicated by a dashed-dotted line. A first indicator of a particle impact on one of the electrodes is the signal exiting the noise band (51). A second indicator of a particle impact is the signal reaching a trigger level 52, which may be a trigger level reflecting the size of the particle to be detected. The trigger level is indicated by a dashed line. Positive and negative amplitude trigger levels are defined here. A third indicator of a particle impact is the signal integral. Here, the integral is shown as the shaded area under the signal curve in the regions showing the first and second indices as described above, taking into account the time the signal remains positive. Alternatively, the integral can be calculated for a predetermined time interval or a time interval whose end is determined by another criterion. If positive and negative signal values ​​occur during the integration time interval, the absolute value or square of the signal value can be integrated to obtain an indication of the size of the particle impact. The combination of all three indices can determine whether particle counts contribute to the observed signal.

[0067] Figure 6 shows the signal observed after a particle impact on one of the electrodes, showing typical features. The signal has the form of a damped oscillation, with the positive half-wave being significantly larger than the negative half-wave. Two complete oscillations are observed on a time scale shorter than 500 ns.

[0068] Figure 7 shows another example of the signal observed after a particle impacts one of the electrodes. Here, the time scale is nonlinear to show the longer time range, up to 10 microseconds, along with the short-time scale behavior in the first 500 nanoseconds. Initially, the signal rises rapidly and saturates above 100 mV. Then, several oscillations occur, initially on short time scales, followed by relatively slower oscillations.

[0069] Figure 8 shows a disturbance that can be actively excluded from counting as a particle hit by appropriate signal processing. The signal's large amplitude can leave the noise band and reach the trigger level. However, this signal does not have the temporal asymmetry typical of signals resulting from particle hits at time 0, defined by the particle's first impact on one of the electrodes.

[0070] Reference symbol enumeration 10. Devices for detecting particles 11 Ionization and charging unit 12 anodes 13 Cathode 14 Hydrodynamic Lens 15 Amplifier (High Gain AC Amplifier) 16 Web 17 Pipe (delivery pipe or discharge pipe) 20 Gas Flow 50 noise band 51 Signal emerges from noise band (first indicator) 52 Signal reaches trigger level (second indicator) 53 Integral (third index) M magnet N North pole of permanent magnet S South pole of permanent magnet UHV High voltage source U (measurement signal) voltage t time

Claims

1. 1. A method for detecting particles in a gas of a process environment present in a process chamber, comprising: - directing the gas, possibly carrying one or more particles, to an ionization and charging unit (11) in fluid communication with the process chamber, the ionization and charging unit having an anode (12) and a cathode (13), configured and arranged to at least partially ionize the gas and charge at least a portion of the particles; - initiating and maintaining a discharge in the gas by applying a voltage between the anode and the cathode of the ionization and charging unit; measuring the current flowing from or to the anode and / or from or to the cathode; detecting the particle based on an AC component or transient of the measured current; A method comprising:

2. The method of claim 1 , further comprising classifying the particles based on the AC component of the measured current or a characteristic of the transient.

3. 3. The method of claim 1, wherein the particles to be detected have a mass greater than 1000 Daltons.

4. 2. The method of claim 1, wherein the electric field between the anode and the cathode has a strength in the range of 300 to 3000 kV / m.

5. 2. The method of claim 1, wherein the gas is focused to an opening of the ionization unit by a hydrodynamic lens (14), and the hydrodynamic lens can optionally be heated to a temperature above the temperature of the surroundings of the hydrodynamic lens.

6. 2. The method of claim 1, wherein the ionization and charging unit (11) has an inlet located at one end and an outlet located at the other end to allow the gas to pass through the ionization and charging unit.

7. 2. The method of claim 1, wherein the gas is included in the group including air, nitrogen, oxygen, hydrogen, helium, and argon.

8. The pressure of the gas at which the detection is carried out is below atmospheric pressure, in particular below 10 －８ 2. The method of claim 1, wherein the temperature is reduced to 1000 psi.

9. The method of claim 1 , wherein the detecting includes amplifying the charging and / or discharging current with an AC amplifier circuit having a bandwidth of at least 500 MHz.

10. 10. The method of claim 1, further comprising indicating that a particle is detected if the AC component or the transient exceeds a predetermined threshold, and / or indicating that a particular type of particle is detected if a corresponding one of one or more predetermined features of the AC component or the transient is detected.

11. 1. An apparatus for detecting particles in a gas of a process environment in a process chamber, comprising: an ionization and charging unit (11) comprising an anode (12) and a cathode (13) constructed and arranged to at least partially ionize said gas and to charge at least a portion of said particles; a voltage source connected between the anode and the cathode of the ionization and charging unit; a current measurement unit configured to measure the current from or to the anode and / or the current from or to the cathode; a particle classification unit configured to detect the particles based on an alternating current (AC) component or transients of the measured current; An apparatus comprising:

12. The apparatus of claim 11 , wherein the particle sorting unit is further configured to sort the particles based on characteristics of the AC component or the transient of the measured charging and / or discharging current.

13. 13. The apparatus of claim 11 or 12, wherein the particles to be detected have a mass greater than 1000 Daltons.

14. 12. The apparatus of claim 11, configured so that the electric field between the anode and the cathode can have a strength in the range of 300 to 3000 kV / m.

15. a hydrodynamic lens (14) configured to focus the gas toward an opening of the ionization and charging unit; 12. The apparatus of claim 11, wherein the hydrodynamic lens is optionally in thermal contact with heating means for increasing the temperature of the hydrodynamic lens relative to the surroundings of the hydrodynamic lens.

16. 12. The apparatus of claim 11, wherein the ionization and charging unit has an inlet located at one end and an outlet located at the other end to allow the gas to pass through the ionization and charging unit.

17. The device of claim 11, further comprising a high-speed, high-gain AC amplifier for amplifying the charging current and / or discharging current, the amplifier circuit having a bandwidth of at least 500 MHz.

18. 12. The apparatus of claim 11, further comprising an output for a signal indicating that a particle has been detected if the AC component or the transient exceeds a predetermined threshold and / or that a particular type of particle has been detected if a corresponding one of one or more predetermined features of the AC component or the transient is detected.

19. A coating system, etching system, or lithography system comprising the apparatus of claim 11, the apparatus being positioned within a delivery pipe for delivering the gas to a process chamber and / or within an exhaust pipe for exhausting the gas from the process chamber.

20. 20. The coating, etching, or lithography system of claim 19, wherein the coating, etching, or lithography system is a system for performing a CVD, PVD, PECVD, or ALD process, or is an epitaxy system.

21. 1. Use of an ionization unit for detecting particles in a gas of a process environment in a process chamber, comprising: Use of an ionization unit, wherein the particles to be detected have in particular a mass above 1000 Daltons.

22. The ambient pressure at which the detection is performed is below atmospheric pressure, in particular below 10 －８ 22. Use of an ionization unit according to claim 21, down to mbar.

23. 22. Use of an ionization unit according to claim 21, wherein the gas is included in the group comprising air, nitrogen, oxygen, hydrogen, helium and argon.

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