Method and device for detecting particles in a gas of a process environment and coating system comprising such a device

Abstract

A method for detecting particles in a gas of a process environment present in a process chamber, the method comprising the steps of: directing the gas having particles into an ionization and charging unit (11) in fluid communication with the process chamber, where the ionization and charging unit has an anode (12) and a cathode (13), and adapted and configured to at least partially ionize the gas and charge at least some of the particles; igniting 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 the anode or flowing to the anode and / or flowing from the cathode and flowing to the cathode; particles are detected based on a transient or AC component of the measured current. The invention is also directed to a device for detecting particles, to a coating system comprising such a device and to the use of an ionization unit.

Description

Technical Field

[0001] The invention relates to a method for detecting particles (such as "macromolecules" having a mass of more than 1000 Daltons) and particles up to micrometer size in a gas (e.g. air) of a process environment. The ambient pressure at which the detection is carried out is in particular less than atmospheric pressure. Furthermore, the invention relates to an apparatus for implementing the method according to the invention and a coating system comprising such an apparatus. Background Art

[0002] For example, in applications in the semiconductor industry, if particles are present in a process step, they can fall on the silicon wafer and adhere. In a later step, these particles are, for example, incorporated into the functional layer being manufactured and cause it to malfunction. Such a functional layer can, for example, include a transistor. Therefore, in order to achieve the expected yield, the number of particles (and their size distribution) should be monitored. This is usually done on the pump side of the system. The sensor is located there and monitors the particles in the gas from the process chamber. If a change towards an unacceptable particle concentration is detected, the process is stopped and the cause can be determined.

[0003] The technology for detecting and measuring particles in gases with the help of light is well established. Descartes originally disclosed the principle of optical detection of particles in gases in 1637. A different way to determine particles is mass spectrometry, which has proven itself as an analytical means for many applications, including measuring relatively small particles (e.g., having a mass less than 1,000,000 Daltons) in many applications. Mobility spectrometers, commonly referred to as ion mobility spectrometers (IMS), originated in the 1950s. Their size is much smaller than mass spectrometers.

[0004] These prior art devices have the following disadvantages:

[0005] Optical instruments always require a window or lens that is exposed on at least one side to the medium to be measured. This makes the design inherently complex and susceptible to contamination, which in turn leads to even more complex designs. For the measurement of smaller particles, strong light sources are preferred, which in turn requires special safety measures for the operation of these light sources. Another disadvantage of applying light sources that emit increased light intensity is that the background signal is also increased, so that no net win is likely to occur.

[0006] Mass spectrometers are very complex and large devices, which are also very expensive and usually require additional vacuum chambers and corresponding pumping equipment. In addition, they are not always easy to dispose of.

[0007] The use of a mobility spectrometer only works under constant environmental conditions, such as constant gas composition and constant surrounding pressure or constant flow conditions in the drift tube. Even small traces of water or acetone, for example, can lead to a complete change of the chemistry in the drift tube. If this is not the case in the application (which is true for many process systems), their use becomes expensive, since pressure stability and gas type stability should first be established in the analytical part.

[0008] Therefore, there is a need for a component for detecting particles in a gas that overcomes the disadvantages of the known devices. Summary of the invention

[0009] The object of the invention is to provide a simple method for detecting particles (such as, for example, "large molecules" having a mass greater than 1000 Daltons) in a gas (eg, air) of a process environment. This object is achieved by the method specified in claim 1.

[0010] Particles can be detected in gas based on the following principle. Particles are ionized by bombarding them with electrons, which have a kinetic energy of some electron volts, resulting in impact ionization of particles. Depending on the type of particle, positively charged particles (i.e., lack of electrons) or negatively charged particles (i.e., electrons have been added) are produced. Metal particles carry more positive charges and insulating particles carry more negative charges. In vacuum coating applications, the composition of particles is a complex issue because they are mostly formed relatively uncontrolled in physicochemical processes with relatively high energy compared to 1 / 40eV. Only in the case of wear of moving parts (for example, in the case of valve movement or robot arm movement) do particles have clear material composition. The charged particles are then accelerated in the electric field. The intensity and direction of the electric field drive the movement of the particles. Preferably, the electric field present in the ionization and charging unit is configured so that the particles reach an energy higher than 50eV before they collide with the electrode. To achieve this, high voltage (>100V) is preferred. The acceleration performed by the electric field provides the particles with the energy and momentum required in the next step. The particles then hit the metal anode or cathode, depending on the charge of the particles. Two things happen in this process. First, the particles try to neutralize their charge, and second, the impact force (the momentum of the particle) produces secondary electrons and, at high energies, secondary ions and neutrals. Due to the three effects mentioned, namely neutralization, secondary electrons and secondary ions, the charge of the electrode onto which the particle impacts changes. The charging current to and from the electrode (i.e. to and from the anode or cathode, respectively) is measured and indicates the impact and a signature based on the current also indicates the class of the particle.

[0011] Based on this principle, the method for detecting particles in the gas of a process environment in a process chamber (especially a coating system) according to the present invention comprises the following steps:

[0012] - directing the gas with the particles into an ionization and charging unit in fluid communication with the process chamber, wherein the ionization and charging unit has an anode and a cathode and is adapted and configured to at least partially ionize the gas and charge at least some of the particles;

[0013] - igniting and maintaining a discharge in the gas by applying a voltage between the anode and the cathode of an ionization and charging unit;

[0014] - measuring the current flowing from or to the anode and / or from or to the cathode;

[0015] - Detection of particles based on the transient or AC (alternating current) component of the measured current.

[0016] The gas of the process environment (in which the particle concentration is to be monitored) can be, for example, the gas in the process chamber of the coating system. The gas can be any process gas or an inert gas, such as nitrogen, oxygen, hydrogen, helium or argon. The gas potentially carries one or more particles with it, but can also be a clean gas that contains no particles at all. In this sense, the method can be used to verify that the gas is clean.

[0017] The ionization and charging unit can be constructed, for example, so that continuous discharge is possible. This can be achieved, for example, by providing a combination of electric and magnetic fields in the interior of the ionization and charging device, which field combination acts on the electrons in such a way that they move on a path having a longer length than a straight line between electrodes of opposite polarity. The provided electric and magnetic fields can have a strength and are geometrically arranged so that the kinetic energy of the electrons can be maintained in the range of 0-200 eV. For example, the anode, cathode and components for generating a magnetic field can have a cylindrical symmetry, and an electric field is provided in the radial direction of the cylindrical arrangement and a magnetic field is provided in the longitudinal direction of the cylindrical arrangement. In this way, the vector product of the electric and magnetic fields points to the azimuthal direction of the cylindrical arrangement, and a closed loop is formed along the path in the direction of this vector product. The configuration of electric and magnetic fields with these properties is known from a cold cathode vacuum gauge, in particular from a cold cathode vacuum gauge in the form of a magnetron, an inverted magnetron or a Penning vacuum gauge. The inventors have realised that the components and electrode configurations for generating the magnetic field can be readily transferred from a cold cathode vacuum gauge to the ionisation and charging apparatus of the present invention.

[0018] Fluid communication between the process chamber and the ionization and charging unit can be established in that the ionization and charging unit is located in a delivery pipe for delivering gas to the process chamber or in a discharge pipe for discharging gas from the process chamber. The ionization and charging unit can be dimensioned so that a large part of the cross section of the discharge pipe with a diameter in the range of 40-100 mm is covered by the cross section of the ionization and charging unit located in the discharge pipe. The ionization and charging unit can be placed upstream of the pumping component, in particular, it can be placed directly in front of the pumping component when seen in the direction of the gas flow path.

[0019] Depending on the geometry of the anode and cathode, ignition and maintenance of the discharge may require higher or lower voltages. Typically, an electric field strength of about several hundred kilovolts per meter (kV / m) is applied. The magnetron may have dimensions resulting in a distance between the electrodes of about 15 millimeters, and a voltage of about 5 kV is applied between the electrodes, so that an electric field strength of about 300 kV / m exists in the magnetron. The small radius of the electrode tip or the small diameter of the electrode in the form of a wire is a geometric attribute that locally increases the electric field at a given voltage.

[0020] Ignition and maintenance of the discharge in the gas can be achieved by applying a high constant voltage (DC) between the anode and cathode of the ionization unit. Alternatively, if half an oscillation period is long enough compared to the travel time of the charged particles from electrode to electrode, an oscillating voltage (AC) can do the job. In an ionization and charging unit with a size of about centimeters, the oscillation frequency of the voltage can be in the kilohertz range or below. For sensors with an electrode distance in the range of 1-2 centimeters, a voltage suitable for achieving this can be in the range of 100V to 3kV in particular. Such a voltage is high enough to cause enough impact, which eventually charges the particles. An ignition voltage of up to 6kV can be applied to ensure that the discharge is ignited in most cases. Once the discharge has been ignited, the voltage applied between the anode and cathode is used to maintain a circulating electron flow in the at least partially ionized gas. In a low-pressure environment, a RF voltage of several volts may be sufficient to maintain the discharge. The superposition of a low RF voltage and a high voltage DC can be used to increase the discharge current flowing in the residual gas.

[0021] The inventors have recognized that by varying the voltage applied between the anode and cathode and observing the change in the discharge current caused by the varying voltage, a variation of the method allows the pressure of the gas to be determined in addition to monitoring the particles. A DC current proportional to the pressure can be generated, or in the case where the cold cathode is operated outside the proportional regime, at least a signature for the pressure can be generated from observing the discharge current. Thus, according to a variation of the method, a lower frequency AC component (e.g., in the kHz frequency range) can be observed to obtain pressure-related information, and a higher frequency AC component (e.g., in the MHz frequency range) can be simultaneously observed to detect particles.

[0022] Variants of the method result from the features of dependent claims 2 to 10 .

[0023] In a variation of the method, it further comprises the step of classifying the particles based on the signature of the transient or AC component of the measurement current.

[0024] The signature of the transient or AC component of the measured current can be a single one of the following characteristics or a combination of the following characteristics:

[0025] - the signal amplitude leaves the noise band,

[0026] - the signal amplitude exceeds the trigger level, i.e. overshoot / undershoot above / below a given threshold,

[0027] - the integral of the absolute value of the signal over the time interval exceeds the threshold,

[0028] - the steepness of the signal slope after exceeding the trigger level,

[0029] - the sign change of the signal,

[0030] - the pattern of sign changes of the signal (e.g. +-+),

[0031] - a peak that lasts shorter than a predetermined time,

[0032] - Minimum number of oscillations within a predetermined short time interval (e.g., within 500 nanoseconds or 5 microseconds after the trigger level is first exceeded)

[0033] -temporally asymmetric patterns, such as decaying oscillations,

[0034] -Characteristic frequencies in the Fourier transformed signal.

[0035] In a variant of the method, the particles to be detected have a mass greater than 1000 Daltons.

[0036] The size of the ionization and charging unit, the applied voltage and the choice of trigger level and the signature evaluated can be adapted so that only particles with a mass above 1000 Dalton are detected by the method. The particles to be detected typically have a size of less than 1 μm, but may also have larger sizes.

[0037] In a variation of the method, the electric field between the anode and the cathode has a strength in the range from 300 to 3000 kilovolts per meter (300 to 3000 kV / m).

[0038] In a sensor with a distance between anode and cathode of 1 cm and in which a voltage of 5 kV is applied between anode and cathode, an electric field strength of 500 kV / m is achieved.

[0039] In a variation of the method, the gas is focused into the opening of the ionization cell by a hydrodynamic lens. Optionally, the hydrodynamic lens may be heated to a temperature higher than the temperature of its surroundings.

[0040] In a variation of the method, the ionization and charging unit has an inlet at one end and an outlet at the other end, so that the gas can pass through the ionization and charging unit.

[0041] The ionization and charging unit may have a tubular form. This form may be achieved, for example, by an electrode in the form of a hollow cylinder as cathode and a needle-shaped anode placed on the central axis of the cylinder. The form of the ionization and charging unit may have a conical cross section and have a circular, square or rectangular cross section. This form may be suitable for covering a large part of the cross section of the tube in which the gas flow is to be monitored for the presence of particles.

[0042] In a variation of the method, the gas is in the group consisting of air, nitrogen, oxygen, hydrogen, helium and argon.

[0043] When the process chamber is evacuated after exposure to the surrounding atmosphere, a variation in which the gas is air may be applied.For semiconductor manufacturing, the gases nitrogen, oxygen, hydrogen, helium, and argon are required for specific functions in the manufacturing process.

[0044] In a variant of the method, the pressure of the gas is below atmospheric pressure, in particular down to 10 -8 mbar, with the pressure stated, for testing.

[0045] By means of suitable electrode geometry, an additional magnetic field and a choice of voltage applied to the electrodes, the components for igniting and maintaining a discharge in a gas can be adapted to a pressure range in the medium vacuum range or in the high vacuum range, so that the gas is at least partially ionized at said pressure and detection can be performed at said pressure.

[0046] In a variation of the method, the detecting step comprises amplifying the charging current and / or the discharging current by means of an AC amplifier circuit having a bandwidth of at least 500 MHz (megahertz).

[0047] The amplifier circuit for this variant of the method can be considered as a very fast amplifier circuit capable of handling signals of short time scales in the nanosecond range. The amplifier circuit can be based on active elements, such as operational amplifiers (opamps), having a gain bandwidth product higher than 500MHz. The amplifier circuit can be configured to operate as a voltage follower or a buffer amplifier. Therefore, the amplifier circuit can have a voltage gain of 1 or even slightly less. Such a buffer amplifier prevents the signal source from being affected by the current required on the output side of the amplifier circuit.

[0048] In further variations, the method includes the steps of indicating that a particle has been detected when an AC component or transient exceeds a predetermined threshold, and / or indicating that a certain class of particles has been detected when an associated signature has been detected.

[0049] In particular, the method may comprise the step of indicating when an associated signature of one or more predetermined signatures from an AC component or a transient has been detected.The possible signatures may be selected from the list discussed above.

[0050] A further object of the invention is to provide an alternative device for detecting particles (such as, for example, "large molecules" having a mass greater than 1000 Daltons) in a gas (e.g., air) of a process environment. More specifically, a simpler, smaller and cheaper device for the purpose of detecting particles is desired. This object is achieved by the device specified in claim 11.

[0051] The device according to the present invention is a device for detecting particles in a gas of a process environment in a process chamber. The device comprises:

[0052] - an ionization and charging unit having an anode and a cathode, adapted and configured to at least partially ionize said gas and to charge at least some of said particles;

[0053] - a voltage source connected between said anode and said cathode of the ionization and charging unit;

[0054] - a current measuring unit adapted to measure the current from or to the anode and / or the current from and to the cathode;

[0055] - A particle classification unit adapted to detect particles based on the transient or AC component of the measured electric current.

[0056] The ionization and charging unit can be constructed, as discussed in the context of the method, so that a continuous discharge is possible. This can be achieved, for example, by an arrangement of magnets and electrodes similar to a cold cathode vacuum gauge, in particular in the form of a magnetron, an inverted magnetron or a Penning vacuum gauge.

[0057] The voltage source may for example be adapted to deliver a DC voltage in the range from 100 V to 10 kV. The voltage source may for example be adapted to deliver a superposition of AC and DC voltages, and in particular may be adapted to be controlled to perform the steps of the method as discussed above. In combination, the voltage source and the geometry of the electrodes may be adapted to generate an electric field with several hundred kilovolts per meter (kV / m) in the interior of the ionization and charging unit.

[0058] The components of the device (in particular the anode, cathode) and (if an embodiment comprising a hydrodynamic lens is concerned) the hydrodynamic lens may be composed of an alloy from the group consisting of Hastelloy, Inconel or stainless steel, more generally an iron-based alloy with a nickel content higher than 10% and a chromium content higher than 10%. These materials are compatible with semiconductor processes. In order to achieve a long lifetime of the electrodes, it is particularly useful to select a material with a very low sputtering rate. The inventors have recognized that molybdenum, titanium and high-grade stainless steel are suitable materials for the components of the device.

[0059] The device may comprise a heating component which may be adapted to heat the device or a component of the device to a temperature which is always higher than the temperature of the surroundings in order to avoid deposition of material on the surface of the hydrodynamic lens. Temperatures which may be useful for achieving this goal may be in the range from 80°C to 300°C, in particular around 200°C. The heating component may be adapted to keep the temperature below a predetermined temperature limit (e.g. below 150°C) in order to protect adjacent components which are not tolerant to higher temperatures. Some ALD or CVD processes may require heating to a temperature of 300°C in order to prevent deposition of material onto the device. The device may be constructed to heat itself by means of the discharge current flowing in normal operation (i.e. in the discharge in the sustaining gas) and by minimizing heat emissions to other components (e.g. because the mechanical connections to the surroundings have a small cross-section).

[0060] Specific embodiments of the device according to the invention are given in the dependent claims 12 to 18 .

[0061] In an embodiment of the device, the particle classification unit is further adapted to classify the particles based on a signature of the measured transient or AC component of the charging current and / or discharging current.Possible signatures are discussed above in the context of variations of the method.

[0062] In an embodiment, the device is designed and configured to detect particles having a mass greater than 1000 Daltons.The particles to be detected typically have a size below 1 μm, but may also have larger sizes.

[0063] In an embodiment, the apparatus is adapted such that the electric field between the anode and the cathode may have a strength in the range from 300 to 3000 kV / m.

[0064] In an embodiment, the device further comprises a hydrodynamic lens adapted to focus the gas into the opening of the ionization and charging unit. Optionally, the hydrodynamic lens is in thermal contact with a heating component for increasing the temperature of the hydrodynamic lens relative to its surroundings. In particular, the heating component may be adapted to heat the hydrodynamic lens up to a temperature in the range from 80°C to 300°C to avoid deposition of substances on the surface of the hydrodynamic lens. The issues discussed above in the context of the heating device also apply to heating the hydrodynamic lens.

[0065] In an embodiment of the device, the ionization and charging unit has an inlet at one end and an outlet at the other end so that the gas can pass through the ionization and charging unit.The ionization and charging unit may have a tubular form.

[0066] In an embodiment, the device further comprises an amplifier circuit for amplifying the charging current and / or the discharging current, wherein the amplifier circuit has a bandwidth of at least 500 MHz.The amplifier circuit may have features as discussed above in the context of the method.

[0067] In an embodiment, the device also includes an output for a signal indicating that a particle has been detected when an AC component or transient exceeds a predetermined threshold, and / or indicating that a certain class of particle has been detected when an AC component or transient, in particular an associated signature from one or more predetermined signatures, has been detected.

[0068] Furthermore, a coating system, an etching system or a photolithography system according to claim 19 is within the scope of the present invention.

[0069] The system of the invention comprises the device of the invention and a process chamber in which, depending on the type of system, a coating, etching or lithography process can be performed. The system can comprise a delivery pipe for delivering gases to the process chamber or a discharge pipe for discharging gases from the process chamber. The process chamber is a space in which a coating process, an etching process or a lithography process is carried out. The device according to the invention can in particular be located in a delivery pipe or in a discharge pipe, in particular upstream of a pumping arrangement.

[0070] In an embodiment, the coating system, etching system or lithography system as discussed above is suitable for performing a CVD (chemical vapor deposition), PVD (physical vapor deposition), PECVD (plasma enhanced chemical vapor deposition) or ALD (atomic layer deposition) process, or the coating system is an epitaxial system.

[0071] The inventors have realized that by building the apparatus of the present invention into a system of the type mentioned, in particular into a coating system applying CVD, PVD, PECVD, ALD or epitaxial coating, the detection or monitoring of particles can be accomplished in an efficient and reliable manner.

[0072] Furthermore, the use of an ionization unit as defined in claim 21 is within the scope of the invention. The ionization unit can be, for example, a cold cathode pressure vacuum gauge, for example of the magnetron type or of the inverted image magnetron type or of the Penning type. According to the invention, the ionization unit is used for detecting particles in a gas of a process environment in a process chamber, wherein the particles to be detected have in particular a mass greater than 1000 Daltons. The inventors have recognized that ionization units known for other purposes can be used to carry out the method according to the invention and have the role of an ionization and charging unit according to the method, i.e. for ionizing the gas carrying the particles with it and also for charging the particles.

[0073] In a variant, the use of an ionization cell refers to an ionization cell in which the surrounding pressure is less than atmospheric pressure (in particular, as low as 10 - 8 mbar), the detection is carried out with the ambient pressure.

[0074] In a further variant of the use of the ionization unit, the gas is in the group consisting of air, nitrogen, oxygen, hydrogen and argon.

[0075] Returning to the configuration of the overall system in which the 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 can be arranged in series along the direction of the gas flow. Two or more ionization and charging units can be arranged in parallel. A bundle of several ionization and charging units, for example implemented in the form of a cold cathode, can be arranged in a tube with a diameter of more than 100 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The present invention will now be further illustrated with the aid of the accompanying drawings. The drawings show:

[0077] Figure 1 is a cross-sectional view across a central assembly of an embodiment of the apparatus;

[0078] Figure 2 is a cross-sectional view across a central assembly of another embodiment of the device;

[0079] Figure 3 is perpendicular to Figure 1 and Figure 2 A cross-sectional view of an embodiment of the device shown in FIG.

[0080] Figure 4 is a circuit diagram showing an amplifier circuit of an embodiment of the device;

[0081] Figure 5 is a schematic time dependency of a voltage signal indicative of the current measured in the method;

[0082] Figures 6 to 8 is a simplified and schematic example of a voltage signal indicative of the current measured in this method. DETAILED DESCRIPTION

[0083] An advantageous effect of the invention is that the proposed method and device for particle detection is simple and robust. It can be used in most coating systems, such as CVD, PVD and ALD, as well as epitaxy. It can also be used in etching systems. The above proposed ion source also works very reliably at pressures up to a few mbar. At low pressures (<10 -8 mbar), maintaining discharge may become difficult.

[0084] Compared to all optical processes, no optical elements like viewing windows or mirrors for beam expansion are needed, which can be changed under the process. Cold cathode vacuum gauges such as magnetrons, inverted magnetrons or Penning gauges operating under the ExB principle sputter themselves clean in most applications. In very demanding applications, the devices according to the invention can easily be designed so that they can be heated all the way to 150°C, or even up to 300°C, to avoid any deposition or other unwanted changes to the electrode surface. The setup and operation of a magnetron, inverted magnetron or Penning gauge is much simpler than a mass spectrometer or similar equipment.

[0085] Commercially, due to the robustness and simplicity of the design, it becomes possible to enter application areas where particle monitors have not previously been used on-line / in situ.

[0086] Figure 1A cross-sectional view of the central assembly of the device is shown, in which features of several of the embodiments discussed above are combined. On the top side, the inflow of gas 20 is indicated by arrows. This gas flow comes from the process chamber or is directed to the process chamber by means of a component (not shown in the figure) that establishes fluid communication. The embodiment shown here includes a fluid dynamic lens 14, which focuses the gas flow on the inlet side of the tubular cathode 13. The anode pin 12 is placed on the central axis of the cylindrical cathode 13. The anode 12, the cathode 13 and the magnet placed outside the cathode (indicated by the south pole S and the north pole N) together form an ionization and charging unit 11, which is suitable and configured to at least partially ionize the gas. During this process, the particles carried by the gas are charged. The ionization and charging unit in the shown embodiment has the form of a magnetron. Unlike a pressure vacuum gauge of the magnetron type, this ionization and charging unit has inlet and outlet openings and opposite ends, so that a gas flow across the ionization and charging unit is possible. The section passes through the electrical contacts of the anode, which lead through isolated feedthroughs to the outside of the tube, in which the ionization and charging unit is arranged. The anode pin 12, the cathode 13, the hydrodynamic lens 14 and the tube 17 may have a rotational symmetry with respect to a central axis as indicated by the dotted line. A web 16 holds the ionization and charging unit in the center of the tube 17. The web 16 does not extend around the entire circumference, so that a gas flow radially outside the cathode but still inside the tube 17 is possible.

[0087] Figure 2 A cross-sectional view of a central assembly of another embodiment of the device having a Figure 1 An assembly similar to that shown in , but without the hydrodynamic lens.

[0088] Figure 3 Shown with Figure 1 and Figure 2 The cross section of a variant similar to the variant shown in FIG. 1 is a variant in which only three webs 16 of small cross section hold the cathode 13 inside the tube 17. The permanent magnet arrangement M is radially positioned outside the cathode and generates a magnetic field inside the cathode. The anode pin 12 is centrally placed so that the electric field is radially oriented and substantially orthogonal to the magnetic field inside the ionization and charging unit. The arrangement shown here is particularly suitable for self-heating of the ionization and charging unit, because the heat energy flow through the webs is minimal.

[0089] Figure 4A schematic diagram of an amplifier circuit of an embodiment of the device is shown. A high voltage source UHV is connected to the anode and cathode of the vacuum gauge, i.e., the anode and cathode of the ionization and charging device, at the connection points indicated on the left of the schematic diagram. The current delivered to the cathode is measured as a voltage drop over a shunt resistor, in which case a shunt resistor of 47 kΩ is selected. Amplifier 15 (an operational amplifier in this case) forms an active element of the amplifier circuit. An operational amplifier that meets the high requirements for measurement on a short time scale of nanoseconds is commercially available from Texas Instruments under the name of "OPA 859". The amplifier circuit shown here is suitable for OPA 859. The voltage supply of + / -2.5 volts and the amplifier circuit are in a shielded area connected to the ground, the flange of the device, and the cathode of the ionization and charging unit. At the output side, an oscilloscope or any analysis device can be connected to detect particles based on the transient or AC component of the measured current. The voltage signal on the output side is a signal indicating the time course of the current flowing out of or to the anode and / or flowing out of the cathode and to the cathode. The amplifier circuit shown here acts as a buffer amplifier so that the current drawn on the output side (e.g. for operating an oscilloscope) does not affect the ionization and charging cell side and thus allows very small and fast oscillating currents to be observed.

[0090] The voltage supply preferably delivers a very stable voltage over time, since any oscillations in the voltage supply may corrupt the signal measured at the output side of the amplifier circuit. Smoothing of the voltage time course can be achieved by connecting an inductor in series and / or a capacitor in parallel to the voltage source.

[0091] Figure 5 In the time-voltage diagram, a signal element indicative of the measured current is schematically indicated, which signal element can be used as a signature for deciding whether a particle has been detected, or possibly for classifying the particle with respect to its size or composition. Horizontally, the time axis t is shown. Vertically, a voltage signal U, here in arbitrary units, is shown. This voltage signal indicates the measured current associated with the anode or cathode of the device and can be represented by, for example, Figure 4The amplifier circuit shown in is produced. During the time when no particles are detected, a noise signal within a typical noise band 50 is observed. The noise band is indicated by a dotted line. The first indicator of the impact of a particle on one of the electrodes is that the signal leaves the noise band 51. The second indicator of the impact of a particle is that the signal reaches a trigger level 52, which can be a trigger level that reflects the size of the particle to be detected. Here, the trigger level is indicated by a dotted line. Trigger levels of positive amplitude and negative amplitude are defined here. The third indicator of the impact of a particle is the integral of the signal. Here, the integral is indicated as a cross-hatched area under the signal curve in the area, and the cross-hatched area presents the first and second indicators as discussed above and takes into account the time in which the signal remains positive. Alternatively, the integral can be calculated within a predetermined time interval or time interval, and the end point of the time interval is defined by another standard. If positive and negative values ​​of the signal appear within the time interval of the integration, the absolute value or square of the signal value can be integrated to have an indicator of the size of the impact of the particle. From the combination of all three indicators, a decision can be made as to whether a particle count or no particle count will contribute to the observed signal.

[0092] Figure 6 The signal as can be observed after a particle impacts one of the electrodes is shown, and a typical signature is displayed. The signal has the form of a decaying oscillation, where the positive half-wave is significantly larger than the negative half-wave. Two complete oscillations are observed on a time scale shorter than 500ns.

[0093] Figure 7 Another example of a signal as can be observed after a particle impacts one of the electrodes is shown. Here, the time scale is non-linear in order to show a longer time range up to 10 microseconds as well as short time scale behavior in the first 500 nanoseconds. At the beginning, the signal rises quickly and saturates above 100 mV. Then, several oscillations occur first on a short time scale, and then a rather slow oscillation follows.

[0094] Figure 8 It shows that disturbances can be actively excluded from counting as particle impacts by appropriate signal processing. The high amplitude of the signal may leave the noise band and reach the trigger level. However, this signal does not have the asymmetry in time that is typical for signals generated by particle impacts at time 0, which is defined by the first impact of a particle on one of the electrodes.

[0095] Reference Symbols List

[0096] 10 Equipment for detecting particles

[0097] 11 Ionization and charging unit

[0098] 12 Anode

[0099] 13 Cathode

[0100] 14. Hydrodynamic Lens

[0101] 15 Amplifier (High Gain AC Amplifier)

[0102] 16 Belly

[0103] 17 pipe (transport pipe or discharge pipe)

[0104] 20 Airflow

[0105] 50 Noise Strip

[0106] 51 The signal leaves the noise band (first indicator)

[0107] 52 The signal reaches the trigger level (the second indicator)

[0108] 53 points (third indicator)

[0109] M Magnet

[0110] N North pole of permanent magnet

[0111] S South pole of the permanent magnet

[0112] U HV High voltage source

[0113] U Voltage (of the measuring signal)

[0114] t time

Claims

1. A method for detecting particles in a gas of a process environment present in a process chamber, the method comprising the following steps: - directing the gas, potentially carrying one or more particles therewith, into an ionization and charging unit (11) in fluid communication with the process chamber, wherein the ionization and charging unit has an anode (12) and a cathode (13) and is adapted and configured to at least partially ionize the gas and to charge at least some of the particles; - igniting 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 and to the cathode; - Detecting said particles based on the transient or AC component of the measured current.

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

3. The method according to claim 1 or 2, wherein: The particles to be detected have a mass greater than 1000 Daltons.

4. The method according to any one of claims 1 to 3, wherein: The electric field between the anode and the cathode has a strength in the range from 300 to 3000 kV / m.

5. The method according to any one of claims 1 to 4, wherein: The gas is focused into the opening of the ionization cell by a hydrodynamic lens (14), which may optionally be heated to a temperature higher than that of its surroundings.

6. The method according to any one of claims 1 to 5, wherein: The ionization and charging unit (11) has an inlet at one end and an outlet at the other end, so that the gas can pass through the ionization and charging unit.

7. The method according to any one of claims 1 to 6, wherein: The gas is in the group consisting of air, nitrogen, oxygen, hydrogen, helium and argon.

8. The method according to any one of claims 1 to 7, wherein: The pressure of the gas is less than the atmospheric pressure, in particular as low as 10 -8 mbar, and the detection is performed at the pressure.

9. The method according to any one of claims 1 to 8, wherein: The detecting step includes amplifying the charging current and / or the discharging current by an AC amplifier circuit having a bandwidth of at least 500 MHz.

10. The method according to any one of claims 1 to 9, further comprising the following steps: Indicates that a particle has been detected when the AC component or the transient exceeds a predetermined threshold, and / or indicates that a certain type of particle has been detected when a signature associated with the AC component or the transient, in particular from one or more predetermined signatures, has been detected.

11. A device for detecting particles in a gas of a process environment in a process chamber, the device comprising: - an ionization and charging unit (11) having an anode (12) and a cathode (13), which is suitable and configured to at least partially ionize the gas and to charge at least some of the particles; - a voltage source connected between the anode and the cathode of the ionization and charging unit; - a current measuring unit adapted to measure the current from or to the anode and / or from and to the cathode; - A particle classification unit adapted to detect said particles based on the transient or AC (alternating current) component of the measured electric current.

12. The device according to claim 11, wherein The particle classification unit is further adapted to classify the particles based on a measured signature of the transient state or the AC component of the charging current and / or discharging current.

13. The apparatus according to claim 10 or 11, wherein: The particles to be detected have a mass greater than 1000 Daltons.

14. Apparatus according to any one of claims 10 to 13, adapted so that the electric field between the anode and the cathode can have a strength in the range from 300 to 3000 kV / m.

15. The device according to any one of claims 10 to 14, further comprising a fluid dynamic lens (14) suitable for focusing the gas into the opening of the ionization and charging unit, wherein the fluid dynamic lens is optionally in thermal contact with a heating component for increasing the temperature of the fluid dynamic lens relative to its surroundings.

16. The apparatus according to any one of claims 10 to 15, wherein: The ionization and charging unit has an inlet at one end and an outlet at the other end, so that the gas can pass through the ionization and charging unit.

17. The apparatus of any one of claims 10 to 16, further comprising a fast, high gain AC amplifier for amplifying the charging current and / or the discharging current, wherein the amplifier circuit has a bandwidth of at least 500 MHz.

18. The device according to any one of claims 10 to 17 further includes an output for a signal indicating that a particle has been detected when the AC component or the transient exceeds a predetermined threshold, and / or indicating that a certain type of particle has been detected when a signature associated with the AC component or the transient, in particular from one or more predetermined signatures, has been detected.

19. A coating system, an etching system or a photolithography system, comprising the apparatus according to any one of claims 10 to 18, wherein: The device is located in particular in a supply line for supplying the gas to a process chamber or in a discharge line for discharging the gas from the process chamber.

20. The coating, etching or lithography system according to claim 19, which is used in a system or an epitaxial system that performs a CVD, PVD, PECVD or ALD process.

21. Use of an ionization cell for detecting particles in a gas of a process environment in a process chamber, wherein the particles to be detected have in particular a mass of more than 1000 Daltons.

22. Use of the ionization unit according to claim 21, wherein: The surrounding pressure is less than atmospheric pressure, especially as low as 10 -8 mbar, the detection is performed at the ambient pressure.

23. Use of the ionization unit according to claim 21, wherein: The gas is in the group consisting of air, nitrogen, oxygen, hydrogen, helium and argon.

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