Nova Patents
WO0113402A1

Electric supply unit for plasma installations

Abstract

The invention relates to an electric supply unit for plasma installations, such as plasma processing or plasma coating devices, in which arcs or disruptive discharges can occur between the electrodes. The inventive power supply unit comprises a direct voltage or direct current source (1) whose output terminals are connected to the electrodes of the plasma installation (2) via at least one inductor and one power circuit breaker (V3). The inventive unit also comprises a circuit (3) for identifying arcs or disruptive discharges which, in the instance of an arc or disruptive discharge, actuates the power circuit breaker in such a way that electric power is no longer applied to the electrodes. The invention is characterized in that the inductor(s) (L1, L2) is/are interconnected to a recovery diode (V1, V2), and in that the power circuit breaker is a series switch (V3).

WO0113402A1, drawing sheet 1
Sheet 1 of 4

Term

No projected expiry on record.

  1. Priority
  2. Filed
  3. Published
  4. Today

29 claims: 1 independent, 28 dependent

  1. 1
    TECHNICAL FIELD The invention relates to an electrical supply unit for plasma systems, such as plasma processing or coating devices, in which arcs can occur, in particular between the electrodes, according to the preamble of the independent claims. Plasma systems for which the generic electrical supply units are intended have a variety of applications and are used, for example, for sputtering of targets. As a rule, they have an electrical power of the order of approx. a few kW up to more than 100 kW. The operating voltage applied to the electrodes is typically of the order of 400 V. Of course, deviations are up or down - also depending on the application - possible. In particular, in the so-called "reactive" sputtering, which is used for example for the production of oxide or nitride films, or in the use of reactive gases, problems arise due to the occurrence of breakdowns and / or the formation of insulating layers on the conductive target which can form parasitic capacitors. Background Art A variety of passive and active circuits are known which serve to extinguish arcs that have formed due to breakdowns. All these circuits have in common that for a certain period of time, the voltage applied to the electrodes is switched off. For this purpose, reference is made by way of example only to US Pat. Nos. 4,692,230, 5,009,764, 5,015,493 and 5,682,067, to which reference is otherwise expressly made to the explanation of all details and possible applications not described in more detail here. Moreover, US Pat. No. 5,682,067 describes the state of the art from which the wording of the preamble of the independent patent claims was based. A disadvantage of the circuits known from these documents is that after the reconnection of the operating voltage, the system requires a comparatively long time to sputter again with "full power" or edit the target in other ways. The same applies if the system is operated in a so-called asymmetric pulse mode in order to prevent the formation of insulating layers on the target. Furthermore, it is known that the voltage applied to the electrodes periodically - regardless of whether a breakdown or an arc occurs - turn off for a short period of time. In this approach, the duty cycle must be selected so that during the time during which the voltage is applied, no breakdown or no arc occurs. Thus, although the occurrence of breakdowns or Arcs are prevented by the periodic shutdown and the subsequent re-application of the voltage, however, the efficiency of the system is significantly reduced. The invention has for its object to provide an electrical supply unit for plasma systems, in which after re-applying the operating voltage to the electrodes, the system reaches its full capacity as quickly as possible, and / or in the efficiency reduction by the occurrence of arcs or Breakthrough, for example, by the "prophylactic" switching off the operating voltage is minimized. Inventive solutions to this problem are specified in the patent claims 1 and 18, respectively. Further developments of the invention are the subject of the dependent claims. According to the invention is based on an electrical supply unit, which is a DC voltage or DC source whose output terminals are connected via at least one inductance and a power switch with the electrodes of the plasma system, and optionally a circuit for detecting arcs or Having blow through, the occurrence of an arc or a punch operates the switch so that no electrical energy is applied to the electrodes. Based on such a known supply unit, the invention consists in that the inductance (s) is (are) each connected to a freewheeling diode, and that the switch is a series switch. Due to this design, the supply unit according to the invention operates as follows:The switch, which switches the electric power applied to the electrodes (hereinafter also referred to as power switch), opens the current flow between the DC voltage source and the electrodes when an arc is detected. The diodes, which are reverse-connected with respect to the normal operating voltage, prevent opening of the circuit breaker, that the voltages on the inductors increase and at the same time cause the current in the inductors decreases only very slowly. If the circuit breaker is switched on again after a short time, typically about a few milliseconds, the current stored in the inductors is immediately available so that the system achieves its full power faster than in the prior art. The supply unit according to the invention thus has a current source characteristic when the circuit breaker is switched on again. Thus, in the electrical supply unit according to the invention, the losses in the power due to the switching off of the operating voltage to extinguish arcs substantially lower than in the prior art. This invention - specified in claim 1 - basic circuit can be extended under various aspects, which can also be combined with each other: In particular, it is possible to provide an inductance with an associated freewheeling diode in each line which connects one terminal of the DC voltage or DC power source to the respective associated electrode. This gives a particularly symmetrical circuit structure. However, it is possible to use only one inductor;In this case, only one free-wheeling diode is required. As a switch, of course, the most diverse circuit breakers can be used. However, in view of the high performance, it is preferable that the switch is an IGBT. As a power supply, a variety of power supplies can be used, also in view of the high performance, it is preferred if the DC voltage source is a switching regulator power supply. In this case, it is advantageous if between the terminals of DC voltage or DC power source is connected a capacitor. This capacitor serves to avoid voltage spikes which may occur due to the supply lead inductances in the supply unit. Furthermore, this capacitor is charged in the time in which the circuit breaker is turned off to the full open circuit voltage, so that when the circuit breaker through the full voltages for igniting the plasma is available. The supply unit according to the invention can be used for a variety of plasma systems, such as plasma systems, in which one electrode has at least one arranged in a plasma chamber cathode, and the other electrode is the housing of the plasma chamber. The supply unit according to the invention also has the particular advantage that it can also be used for plasma systems in which at least two separate cathodes are provided, each of which is connected via a series switch with the connected to a freewheeling diode inductance at the one terminal of the DC voltage source. In such systems, for example, can be switched alternately between the cathodes. This has the advantage that arcs "onset" at one cathode are reliably erased in the comparatively long period of time during which it is switched to the other cathode. Of course, it is also possible to sputter from several cathodes simultaneously. In a development of the invention, a diode is connected between the electrode connections or the electrode pairs. The function of this diode is explained below: When the circuit-breaker is opened, the voltage at the supply inductances reverses to the plasma chamber, so that voltage peaks would result without further circuit measures. The diode connected between the electrode terminals short-circuits this voltage so that the energy stored in the lead inductances is dissipated. Furthermore, it is possible to connect an LC element in parallel to the diode, which supports the erasure of the arc as a passive element. However, it is particularly preferred if the extinguishment of the arc is supported by active circuit elements: For this purpose, a capacitor may be connected in series with the diode. Between cathode terminal and the connection point diode / capacitor then another series switch is connected. By this circuit construction, the energy resulting from the line inductance and the flowing current is reloaded as voltage into the capacitor when opening the circuit breaker. After a short delay, this voltage is applied to the electrodes via the further series switch, so that the arc is extinguished much faster than with a passive circuit. In order to obtain a correspondingly large inverted voltage for erasing, even in the case of small line inductances or small currents, it is furthermore possible to provide an inversion voltage source. This Inversspannungsquelle can be in particular an (auxiliary) DC voltage source whose negative pole is connected to the anode and its positive pole via a diode connected in the forward direction to one terminal of another series switch. In any case, it is preferred that the circuit for detecting arcs except the circuit breaker also controls the other switch. The arc detection circuit can evaluate at least one of the following criteria: Voltage dip, exceeding the maximum voltage limit, below the minimum voltage limit Fast current increase, exceeding the maximum current limit. Furthermore, in a manner known per se, a control unit, which may in particular be part of the circuit for detecting arcs, may be provided, which "off prophylactically" with a fixed period removes and preferably switches over the voltage applied to the electrodes. If the voltage applied to the electrodes is regularly reversed for a short moment, the formation of arcs can be substantially reduced or Arcs can be erased in their formation. Due to the inventive design, which leads to a rapid achievement of the power after the restarting, the regular reversal of the voltage leads only to a very small reduction of the sputtering, provided that the period of time during which the voltage applied to the electrodes is switched substantially shorter than the time during which a plasma operation is being performed. Furthermore, the time period during which the voltage is switched, of course, must be so short that the current in the circuit "inductance / recovery diode" is stored. The frequency with which the control unit switches off or switches the voltage applied to the electrodes can be up to 100 kHz. Instead of a periodic prophylactic switching with a fixed period, regardless of the process parameters and the dependent frequency of arcs or However, it is preferable if the control unit in the manner of an adaptive control adjusts the duty cycle of the voltage so that "straight" no arc or Puncture occurs. In this further solution of the invention according to the object, which can also be used in addition to the solution according to claim 1, it is advantageous if a tax or Control unit is provided, the occurrence of an arc or Breakdown by switching off the voltage applied to the electrodes 10 or switching to an inverse voltage for a certain period of time (switch-off duration), and that the control or Control unit after the occurrence of at least one arc or Penetration reduces the duty cycle of a plasma operation causing voltage. It is particularly advantageous if the Steuerbzw. Control unit reduces the duty cycle to a period of time that is smaller than the current time interval between two successive arcs or breakdowns. Since the operating parameters of a plant can change during a processing operation, it is furthermore preferred if the control unit also increases the duty cycle: For this purpose, it is possible, for example, that the control unit increases the duty cycle when no arc or breakdown or only a certain number of arcs or breakdowns has occurred over a certain period or over a certain number of switch-on. The control unit can extend the duty cycle to CW operation. In order not to weight the random occurrence of arcs in the adaptive control so strong, it is also preferable if the control or Control unit reduces the duty cycle only if, during a certain time, a certain number of arcs or Punches has occurred. Furthermore, it is preferred if the tax or Control unit at the beginning of the plasma operation, the voltage applied to the electrodes either permanently or for a certain (predeterminable before the start of the process) duty cycle, then off for a certain off period or preferably switching, and then the voltage turns on again and the occurrence of arcs or. Breakdown reduces the duty cycle of the voltage. In order to be able to adapt the supply unit according to the invention to the most varied of machining or application processes, it is also advantageous if the initial values ​​of the switch-on duration and the switch-off duration and / or the number of arcs and the time unit in which this number occurs , are adjustable. In any case, it is also advantageous if the duty cycle is associated with the frequency of occurrence of arcs or breakdowns via a variable characteristic curve, which may be dependent on further process parameters. In order to keep the reduction of the power of the plasma system as low as possible, it is also advantageous if the control unit optimizes the switch-off duration or the switchover duration. The off or switching time is set "straight" so long that the arc or breakdown (Are) "sustainable" is deleted. Brief Description of the Drawings The invention will be described in more detail below with reference to the drawing, in which: 1 shows the circuit of a first embodiment of the invention, Fig.
  2. 2
    2 a voltage / time diagram for explaining the operation of the circuit shown in Fig. 1, Fig.
  3. 3
    3 the circuit of a second embodiment of the invention, Fig. 4 a voltage / time diagram for explaining the operation of the in Fig. 3 shown circuit, Fig. 5 a voltage / time diagram for explaining the operation of a modification of FIG. 3 shown circuit, Fig. 6 the circuit of a third embodiment of the invention, Fig. 7 a voltage / time diagram for explaining the operation of the third embodiment, and 8th a block diagram of a fourth embodiment, and Fig. 9 a representation for explaining the operation of the fourth embodiment. Representation of embodiments Fig. 1 shows a first embodiment of the invention. The power supply unit has a switching regulator power supply 1 which, for example (ie without limitation of generality) a DC voltage of approx. 400 V supplies. The negative output terminal A- of the power supply 1 is connected via an inductance Ll and a circuit breaker designed as a series switch V3 with a cathode K in a plasma chamber 2, whose housing is grounded. The series switch 1 is an IGBT in the embodiment shown. The positive output terminal A + of the power supply 1 is connected via an inductance L2 to the housing of the plasma chamber 2. This is symbolically denoted by GND. Parallel to the inductors Ll and L2, diodes VI and V2 are switched according to the invention, which are polarized such that they lock during plasma operation. Further, a capacitor C1 is connected between the output terminals A- and A +. Between the cathode terminal and GND, a diode V4 is connected, which is polarized in the reverse direction during plasma operation. Further, there is provided a circuit 3 for detecting arcs which controls the series switch V3 via the output terminal "Gate." In order to detect an arc, also referred to as Are, the circuit 3 measures the flowing current I and 14 - the Voltage U and evaluates the measured quantities according to the following criteria:Voltage dip, exceeding the maximum voltage limit, below the minimum voltage limit Fast current increase, exceeding the maximum current limit. Upon detection of an arc, the power switch V3 is opened by the circuit 3, so that the flow of current between the power supply 1 and the electrodes of the plasma chamber 2 is interrupted. When the circuit breaker is opened, the voltage at the supply inductances to the plasma chamber 2 poles;In order to avoid that this leads to voltage peaks, the electrodes are short-circuited via the diode V4 and the energy stored in the lead inductances is dissipated. On the one hand, the diodes VI and V2 prevent the voltages at the inductors L1 and L2 from increasing when the circuit breaker is opened and at the same time cause the current in the inductors to decrease only very slowly. The inductors L1 and L2 can also be magnetically coupled. The capacitor Cl serves to avoid voltage spikes that may occur due to the lead inductances. In the following, the operation of the in Fig. 1 shown electrical supply unit with reference to FIG. 2, in which a voltage / time diagram is shown, are described in more detail: At time T 1, the voltage U breaks due to an arc to that for an arc or Breakdown typical voltage UARC. After the adjustable delay time T1-T2, the switch V3 is opened and the power supply is interrupted. After the adjustable arc break T2-T3, the switch V3 is closed again, the voltage rises to the ignition voltage UZÜND and breaks back to the burning voltage UPLASMA. By inventively provided freewheeling diodes VI and V2 of the generator output current is stored at the time of shutdown, so that when restarting the original operating state is reached very quickly again. Fig. 3 shows a modification of the embodiment shown in Fig. 1. The same parts as in Fig. 1 are provided with the same reference numerals, so that dispenses with a new idea. In this embodiment, a capacitor C2 is connected in series with the diode V4. Between the terminal of the cathode K and the connection point diode V4 / capacitor C2, a further series switch V5 is connected, which is also driven by the circuit 3 via the output terminal gate2. Furthermore, optionally, an Inversspannungsquelle be provided, which has a (auxiliary) DC voltage source Ul, which typically provides a voltage of about 30V. The negative pole of the DC voltage source U1-16 is connected to the anode, while the positive pole of the DC voltage source U1 is connected to the one terminal of the further series switch V5 via a diode V6 connected in the forward direction. In the following the operation of the second embodiment shown in Fig. 3 will be explained in more detail with reference to Fig. 4, which shows a voltage / time diagram. When an arc occurs (time Tl), the voltage from the plasma voltage UPlasma breaks down to the arc voltage UArc together. The circuit 3 then opens the circuit breaker V3. By connected in series with the diode V4 capacitor C2 which resulting from the line inductance and the current energy is transferred as a voltage in the capacitor C2. At time T2, these voltages are applied as an inverse voltage to the electrodes of the plasma chamber 2, so that the arc is extinguished much faster than without active erasure. By the optional voltage source Ul, the applied Inversspannung can be increased. Providing the circuit 3 with an additional pulse generator, so the voltage applied to the plasma chamber voltage can be reversed not only when an arc occurs, but regularly for a short moment. As a result, the probability of the formation of arcs can be significantly reduced or Arcs can be erased already in the beginning. In addition, it is prevented that oxide layers form on the target during reactive sputtering;Furthermore, oxidized targets can be freedputtertert. 5 shows schematically the voltage curve for this modification of the exemplary embodiment shown in FIG. 3. The pulse frequencies can be up to 100 kHz depending on the circuit breaker used. Fig. 6 shows the circuit of a third embodiment of the invention, in which two cathodes Kl and K2 are arranged in the plasma chamber 2, which each own power switches V3 and V5 and diodes V4 and V6 are assigned. By simultaneously switching on the circuit breakers V3 and V5, the two cathodes operate in parallel operation. If the two switches are switched on alternately, the effective power of the cathodes can be regulated by varying the switch-on times. Switching frequencies up to several kHz are possible. Fig. 7 shows a voltage / time diagram in which the alternating switching of the two switches is shown schematically. Of course, more than two cathodes can be used. Fig. 8 shows a fourth embodiment of the invention, in which the power reduction, which results in the procedure of FIG. 5 by the prophylactic switching of the voltage with a fixed, predetermined frequency is significantly reduced: In this embodiment, the Circuit 3 supplemented by an adaptive control unit 4 with a start value setting unit 5. Due to the use of an adaptive control unit 4, the duty cycle of the voltage applied to the electrodes is not fixed. During operation, the highest possible duty cycle is set by the adaptive control unit 4 in order not to unnecessarily blank the plasma process in a plasma system 6 - as shown in FIG. 5 and 7 to interrupt. However, if arcs occur, the duty cycle will be shortened after erasing the arc. This reduces the probability of the occurrence of a repeated arc. If an ace still occurs despite the shortened switch-on duration, the switch-on duration is further reduced until stable, Are-free operation is possible. Accordingly, the duty cycle is extended if no arcs have occurred over a certain period of time. The duty cycle is then extended until again arcs occur in the process. The extension of the switch-on time can go so far that the system is operated in "continuous mode" (CW mode). The switch-on time and the Are frequency can be determined via a variable characteristic of the adaptive control unit, that of other process parameters - process gases, target and sputter materials, etc. - can be dependent, linked together or be correlated. FIG. 9 shows qualitatively a characteristic curve which correlates the Are frequency (1 / s) plotted on the abscissa with the on-ordinate applied on-time (s). It should be pointed out that corresponding characteristics are not only determined by several parameters, but also by the geometry of the plasma system, the process materials, etc. depend. The characteristic curves are preferably determined empirically and / or set adaptively by the control unit 4, which may have a microprocessor, for example. Certain values ​​for the switch-on duration, as well as the switch-off or switch-off duration at the beginning of the plasma operation, which are recognized as advantageous, can be predefined via the start value specification unit 5, or certain already determined characteristic curve can be selected. By using an adaptive control algorithm, the parameters of the are management are optimally adapted to the process parameters. In this case, it is also possible in particular to set the switch-off or switchover period optimally-if appropriate also adaptively. The invention has been described above by means of embodiments without loss of generality. In particular, the supply unit according to the invention can be used for all applications known from the introductory literature. Furthermore, the various properties of the exemplary embodiments can be combined with one another: It is thus possible to combine the pulsed operation or the adaptive control, the active arc extinction and the switching between two or more cathodes partially or completely, or between the individual operating modes described switch. - 20 - PATENT REQUIREMENTS Electrical supply unit for plasma systems, such as plasma processing or Coating devices in which there are arcs or Can come through, in particular from an electrode, with a DC voltage or DC source whose output terminals are connected via at least one inductor and a power switch with the electrodes of the plasma system, and optionally a circuit for detecting arcs or Punctures that occur when an arc occurs or Punch the switch operated so that no more plasma-generating electrical energy is applied to the electrodes, characterized in that the inductance (s) (Ll, L2) each having a freewheeling diode (VI, V2) is connected (are), and that the switch is a series switch (V3). Supply unit according to Claim 1, characterized in that an inductance (L 1, L 2) with an associated free-wheeling diode (VI , V2) is provided. 21 3. Supply unit according to claim 1 or 2, characterized in that the switch (V3) is an IGBT.
  4. 4
    4th Supply unit according to one of Claims 1 to 3, characterized in that the DC voltage source is a switching regulator power supply unit (1).
  5. 5
    5th Supply unit according to one of Claims 1 to 4, characterized in that a capacitor (C1) is connected between the terminals (A-, A +) of the DC or DC source (1).
  6. 6
    6th Supply unit according to one of Claims 1 to 5, characterized in that the one electrode has at least one cathode arranged in a plasma chamber, and the other electrode is the housing of the plasma chamber (GND).
  7. 7
    7th Supply unit according to Claim 6, characterized in that at least two separate cathodes (cathode 1, cathode 2) are provided, each of which is connected via a series switch (V3, V5) to the inductance (L1) connected to a freewheeling diode.
  8. 9
    9th Supply unit according to one of Claims 1 to 8, characterized in that a diode (V4) is connected between the electrode terminals.
  9. 10
    10th Supply unit according to Claim 9, characterized in that a capacitor (C2) is connected in series with the diode (V4), and in that a further series switch (V5) is connected between the cathode connection and the connection point diode (V4) / capacitor (C2) is.
  10. 11
    11th Supply unit according to one of claims 1 to 10, characterized in that a Inversspannungs- source is provided.
  11. 12
    12th Supply unit according to Claim 11, characterized in that the inverse voltage source is an (auxiliary) DC voltage source (U1) whose negative pole connects to the anode and its positive pole via a diode (V6) connected in the forward direction to the one terminal of the further series switch (V5). connected is.
  12. 13
    13th Supply unit according to one of claims 1 to 12, characterized in that the circuit (3) for detecting arcs in addition to the power switch (V3) also controls the further switch (V5). - 23 -
  13. 15
    15th Supply in the unit according to one of claims 1 to 14, characterized in that a control unit is provided which periodically decreases the voltage applied to the electrodes and preferably switches.
  14. 16
    16th Supply unit according to Claim 15, characterized in that the frequency with which the control unit switches off or switches off the voltage applied to the electrodes is up to 100 kHz.
  15. 18
    18th Supply unit according to one of claims 1 to 14 or according to the preamble of patent claim 1, characterized in that a control or Control unit (4) is provided, which occurs when an arc or Arcs (Arcs) this clears by switching off the voltage applied to the electrodes or switching to an Inversspannung for a certain period of time (off duration), and that the control or Control unit after the occurrence of at least one arc or Penetration reduces the duty cycle of a plasma operation causing voltage.
  16. 21
    21st Supply unit according to one of Claims 18 to 20, characterized in that the control and regulating unit increases the switch-on duration when there is no arc or breakdown or only a certain number of arcs over a certain period of time or over a certain number of switch-on periods or punctures has occurred.
  17. 22
    22nd Supply unit according to one of Claims 18 to 21, characterized in that the control and regulation unit can extend the on-time to CW operation.
  18. 23
    23rd Supply unit according to one of Claims 18 to 22, characterized in that the control or Control unit (4) at the beginning of the plasma operation, the voltage applied to the electrodes (cathode K, GND) either permanently or for a certain duty cycle, then off or preferably switches for a certain off period, and then the voltage turns back on, and that the Tax or Control unit when arcing occurs or Breakdown reduces the on-time of the voltage.
  19. 24
    24th Supply unit according to Claim 23, characterized in that the initial values ​​of the switch-on duration and the switch-off duration and / or the number of arcs and the time unit in which this number occurs can be set. - 26 -
  20. 25
    25th Supply unit according to one of Claims 18 to 24, characterized in that the switch-on duration is linked to the frequency of the occurrence of arcs or breakdowns via a variable characteristic which may depend on further process parameters.
  21. 26
    26th Supply unit according to one of Claims 15 to 25, characterized in that the control unit optimizes the switch-off duration.
  22. 27
    27th Supply unit according to one of Claims 15 to 26, characterized in that the control unit (4) is part of the circuit (3) for detecting arcs.
  23. 28
    28th Supply unit according to one of Claims 15 to 27, characterized in that a presetting unit (5) is provided, with which starting values ​​and / or characteristic curves can be set.
  24. 29
    29th Supply unit according to one of Claims 1 to 28, characterized in that it can be switched over between at least two of the operating modes described above - rapid switching off only when arcs occur, periodic switching off or switching over, adaptive control, etc.
Independent claims24