Abstract:
A method of generating a highly ionized plasma in a plasma chamber. A neutral gas is provided to be ionized in the plasma chamber at pressure below 50 Pa. At least one high energy high power electrical pulse is supplied with power equal or larger than 100 kW and energy equal or larger than 10 J, to at least one magnetron cathode in connection with a target in the plasma chamber. A highly ionized plasma is produced directly from the neutral gas in a plasma volume such that the plasma volume cross section increases during a current rise period. Atoms are sputtered from the target with the highly ionized plasma. At least part of the sputtered atoms are ionized.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to generating a highly ionized plasma in a plasma chamber. 
       BACKGROUND 
       [0002]    In a typical sputter coating process, an electric discharge produces electrons that collide with a sputtering gas, thereby ionizing the gas. This sputter process is typically in a pressure range between 10 Pa and 0.1 Pa. In this pressure range the number of atoms or molecules is between 5*10 15 cm −3  and 2*10  13 cm −3 . As ions bombard a target, atoms are detached from the target, the atoms deposit at a substrate to be coated. The process of detaching atoms from the target is called sputter process. This sputter process can also be used for etching. In some systems, improved target utilization and coating uniformity may be achieved by producing a highly ionized plasma in the vicinity of the target. In such systems, a partially ionized plasma is first generated at a low voltage, and then a highly ionized plasma is generated through the application of high power discharge pulses. A highly ionized plasma in this context is reached, when the number of ions is above 10 12  cm −3 . 
         [0003]    However, a high power discharge pulse in combination with an upstream low ionization step has been found to reduce the adhesion of the film produced during the sputtering and may result in target poisoning during reactive sputtering processes. Furthermore, the need to apply a low voltage during the first period of time limits the simultaneous use of the power supply for other purposes, for example, etching. 
         [0004]    In EP 1 560 943 B1 a two-step approach for creating a highly ionized plasma is described. For a first period of time a low voltage is applied to a discharge gap and then for a short period of time a higher voltage is applied. This leads at first to a low ionization of the gas and then to a high ionization of the gas. 
       SUMMARY 
       [0005]    It is the object of the present invention, to provide a method and an apparatus for producing a highly ionized plasma in a plasma chamber being suitable for etching and building high adhesion during sputter deposition, and avoiding poisoning of the electrodes, target, plasma chamber, or substrate during reactive sputtering. 
         [0006]    In a first aspect generating a highly ionized plasma in a plasma chamber, is achieved by:
       a. providing a neutral gas to be ionized in the plasma chamber at pressure below 50 Pa;   b. supplying at least one high energy, high power electrical pulse with power equal or larger than 100 kW and energy equal or larger than 10 J to at least one magnetron cathode in connection with a target in the plasma chamber   c. producing a highly ionized plasma directly from the neutral gas in a plasma volume such that the plasma volume cross section increases during a current rise period   d. sputtering atoms from the target with the highly ionized plasma,   e. ionizing at least part of the sputtered atoms.       
 
         [0012]    A plasma is a state of matter similar to a gas in which a certain portion of the particles are ionized. Despite the fact that the plasma contains free charge particles, in the macroscopic scale the plasma is electrically neutral. This means that it contains the same number of positive and negative charges in an equilibrium state. According to the invention a highly ionized plasma is generated directly from the neutral gas by influencing the conditions in the plasma chamber and thus the plasma generation process during a current rise time period. 
         [0013]    The duration of the high energy, high power pulse may be shorter than 500 μs, preferably not longer than 300 μs, more preferably not longer than 200 μs. This means the whole energy is applied in a very short pulse. The voltage rise time and the current rise time must therefore be very short. This leads to a very high ionization of the plasma. 
         [0014]    In an aspect the plasma volume cross section increases during a current rise period while maintaining a substantially constant current density and/or a substantially constant ionization degree. So a higher adhesion during sputter deposition can be achieved. Or in other words: a substantially constant current density and/or a substantially constant ionization degree is maintained while the plasma volume cross section increases during a current rise period. 
         [0015]    According to this approach a highly ionized plasma is created directly from a neutral gas. During the current rise period a spatial growth of highly ionized regions in the plasma chamber may be initiated. This leads to a homogeneous, highly ionized plasma and thus improves target utilization. 
         [0016]    A spatial growth of the plasma cross section means growth of current with substantially constant current density, i.e. I=SJ, where I=current, S=plasma volume cross section (rising value), and J=current density (constant). Hereby the current reflects a highly ionized plasma volume growth and not an ionization degree. 
         [0017]    According to aspects of this method, the gas provided in the chamber can adopt a highly ionized plasma state without going through a weakly or low ionized plasma stage or other preparatory plasma stages such as glow discharge or arc discharge, i.e., a highly ionized plasma is produced directly from the neutral gas. The gas may go through one or several breakdown stages which do not form a plasma stage before going directly to a highly ionized plasma state. This is possible by providing a high enough energy which exceeds the ionization electric breakdown threshold instantaneously in an electric pulse. At the same time the current rise time may be controlled or the current pulse may shaped to achieve the highly ionized plasma without going through a low ionized plasma or an arc discharge state. The process development may be dependent on a large number of parameters, where the following are a list of the most important:
   gas pressure,   gas mixture, especially when reactive gas is used,   target material,   temperature of the gas, target and plasma chamber,   strength and shape of the magnetic field,   strength and shape of the electric field,   direction of the electrical field in respect to the direction of the magnetic field,   velocity of the voltage rise and the current rise,   energy provided during the pulse,   power rise time,   duration of the pulse,   repetition rate of pulses   etc.   
 
         [0031]    Due to the large number of parameters which influence the development into the highly ionized plasma and due to the mutual interactions of these parameters, it is advantageous to monitor the plasma development at least during start of operation and/or during maintenance intervals. With optical instruments such as electro-optical photography, spectroscopy, very fast CCD cameras, selected for the monitoring of the dedicated plasma process and with variation of the electrical, magnetic and physical as well as chemical settings it is possible to reach a set of parameters for the highly ionization plasma without going through an arc discharge or low ionized plasma. This is explained in more detail in the following. The monitoring of a plasma process is known in the art and described in Helmersson et al. “Ionized physical vapor deposition (IPVD): A review of technology and applications”, Thin Solid Films, Elsevier-Sequoia S. A. Lausanne, C H, vol. 513, no. 1-2, (Aug. 14, 2006), pages 1-24 and in particular pages 9-11; this publication is cited as the ‘IPVD Review’ in the following. 
         [0032]    At the beginning of the voltage rise of the high energy, high power pulse a number of free electrons may be provided to be accelerated by an electrical field caused by the pulse. This number of electrons may be provided by an electron source or by cosmic x-ray radiation or other methods. The accelerated free electrons in the gas may create an avalanche-type ionization process, which initiates an electric breakdown in the gas. 
         [0033]    The high energy, high power pulse may produce or may be selected to produce at least as many ionized atoms of the provided gas as it produces ionized atoms of sputtered material. This helps achieving a highly ionized plasma in a short time and also improves the sputtering process. This improves the adhesion of deposited coatings with the sputtered atoms. In reactive processes also the reactive gas may be ionized. This leads to better yield in the sputter process and improved compound of the sputtered atoms or ions with the reactive gas and therefore also to better adhesion. 
         [0034]    Electron avalanches may be initiated in the neutral gas prior to a steady plasma state. An electron avalanche is a process, in which a number of free electrons in a gas are subjected to strong acceleration by an electric field, ionizing the atoms of the gas by collision called impact ionization, thereby forming secondary electrons to undergo the same process in successive cycles. Electron avalanches are essential to the dielectric breakdown process within gases. 
         [0035]    Ionization waves may be initiated prior to a steady plasma state. In particular, the voltage pulse may be applied between a cathode and an anode of the plasma chamber causing electron avalanches followed by ionization waves. The formation of the ionization waves is described in more detail in the following. 
         [0036]    The avalanche type ionization process, the electron avalanches and the ionization waves are stages of breakdown. These stages of breakdown do not constitute a plasma state because, in contrast to a plasma, they are highly non-equilibrium, non-uniform in given space, have more negative than positive charges, and occur prior to the establishment of a sheath. 
         [0037]    A high energy, high power pulse may be applied to at least one electrode, where the resulting voltage across the at least one electrode and a second electrode is higher than a static breakdown voltage of the neutral gas or a dynamic breakdown voltage and the pulses supply enough current and/or power rise capacity that a highly ionized plasma is generated without going through a low ionized plasma or through an arc discharge. This leads to very fast creation of a highly ionized plasma. The disadvantages associated with arc discharge or a low ionized plasma can be avoided. The static breakdown voltage is the minimum voltage that causes a portion of an insulator to become electrically conductive. A dynamic or pulse breakdown voltage refers to the fact that during specified time intervals a gap can sustain voltages which are higher than the static breakdown voltage without breakdown. But when the dynamic or pulse breakdown voltage will be reached, the gap becomes conductive much faster as if only the static breakdown voltage would be reached. 
         [0038]    The high energy, high power pulse may be selected such that the voltage between the electrode and the plasma chamber or between an anode and a cathode in the plasma chamber reaches more than 80% of its maximum value, before the current density or the ionization degree in the plasma chamber reaches more than 80% of its maximum value. This ensures that the voltage, current and/or power pulse is large enough to create a highly ionized plasma in the plasma chamber directly from a neutral gas, without going through a low ionized plasma or an arc discharge. 
         [0039]    The high energy, high power pulse may be selected such that the current density or the ionization degree in the plasma chamber reaches more than 30%, preferably more than 50%, more preferably more than 80%, even more preferably more than 90% of its maximum value, before the current into the electrode reaches more than 80% of its maximum value. 
         [0040]    The high energy, high power pulse may be selected such that the number of avalanches my rise during the current rise period. This ensures the transformation of the neutral gas to a highly ionized plasma. 
         [0041]    In another aspect generating a highly ionized plasma in a plasma chamber is achieved by:
       a. providing a neutral gas to be ionized in the plasma chamber at pressure below 50 Pa;   b. supplying at least one high energy, high power electrical pulse with power equal or larger than 100 kW, in particular 500 kW, and energy equal or larger than 10 J, in particular 50 J, to at least one magnetron cathode in connection with a target in the plasma chamber   c. producing a highly ionized plasma directly from the neutral gas such that during a current rise period   d. the current density in the plasma chamber reaches more than 80% of its maximum value, before the current into the electrode reaches more than 80% of its maximum value.       
 
         [0046]    According to aspects of this method, the gas provided in the chamber can adopt a highly ionized plasma state without going through a weakly or low ionized plasma stage or other preparatory plasma stages such as glow discharge or arc discharge, i.e., a highly ionized plasma is produced directly from the neutral gas. The gas may go through one or several breakdown stages which do not form plasma stages before going directly to a highly ionized plasma state. This leads to improved adhesion during sputter deposition, makes the plasma process suitable for etching, and avoids poisoning of the electrodes, target, plasma chamber, or substrate during reactive sputtering. According to the invention a highly ionized plasma is generated directly from the neutral gas by influencing the conditions in the plasma chamber and thus the plasma generation process during a current rise time period 
         [0047]    The monitoring of current density is known in the art. Disclosure of such a measurement may be found in ‘IPVD Review’ on page 9,  FIG. 11  and description to  FIG. 11 . 
         [0048]    This method can be combined with all above mentioned method steps individually or as a combination. 
         [0049]    In another aspect generating a highly ionized plasma in a plasma chamber is achieved by:
       a. providing a neutral gas to be ionized together with few free electrons in the plasma chamber;   b. supplying at least one high energy, high power electrical pulse with power equal or larger than 100 kW, in particular 500 kW, and energy equal or larger than 10 J, in particular 50 J, between an anode and a magnetron cathode in the plasma chamber in order to produce an electrical field between the anode and the cathode,   c. accelerating the free electrons in order to ionize atoms of the neutral gas and to generate secondary electrons,   d. deviate the direction of flow of accelerated electrons by a magnetic field   e. creating non-equilibrium or macroscopically not neutral ionization avalanches,   f. absorbing electrons at the anode,   g. building positive ion charges near the anode,   h. accelerating ionized gas atoms towards the cathode thereby building a first ionization wave,   i. sputtering target material from a target in electrical connection with the cathode,   j. ionizing the target atoms sputtered from the target.       
 
         [0060]    Hence, according to this aspect of the invention also a highly ionized plasma is generated directly from the neutral gas by influencing the conditions in the plasma chamber. 
         [0061]    According to aspects of this method, the gas provided in the chamber can adopt a highly ionized plasma state without going through a weakly or low ionized plasma stage or other preparatory plasma stages such as glow discharge or arc discharge. The gas may go through one or several breakdown stages which do not form plasma stages before going directly to a highly ionized plasma state. This leads to improved adhesion during sputter deposition, makes the plasma process suitable for etching, and avoids poisoning of the electrodes, target, plasma chamber, or substrate during reactive sputtering. 
         [0062]    Also this method can be combined with all above mentioned method steps individually or as a combination. 
         [0063]    In a further aspect a magnetically enhanced sputtering apparatus includes:
       a. at least one magnet configured to provide a magnetic field in a magnetron configuration at the surface of a sputtering target, from which material is to be sputtered,   b. a plasma chamber configured to receive the sputtering target, the chamber having an inlet for introduction into the chamber of a neutral gas to be ionized,   c. an anode and a cathode in the chamber, the cathode in electrical connection with the target,   d. a high energy pulse power source configured to apply a high energy, high power electrical pulse with power equal or larger than 100 kW and energy equal or larger than 10 J between the anode and the cathode in the chamber,   e. wherein responsive to said high energy pulse power source a highly ionized plasma is generated directly from the neutral gas such that the plasma volume cross section increases during a current rise period.       
 
         [0069]    Such an apparatus may be suitable for creating a highly ionized plasma without going through the stages of arc discharge or low ionization, i.e. for producing a plasma directly from a neutral gas. 
         [0070]    The apparatus may be configured such that during at least part of the current rise period a substantially constant current density and/or a substantially constant ionization degree is maintained. 
         [0071]    The voltage source may produce a voltage pulse such that a degree of ionization of at least 10 12  cm −3  is reached. Thus, a highly ionized plasma is produced, which is suitable for a sputtering or etching process. 
         [0072]    In another aspect the invention relates to a high energy pulse power source for delivering electrical pulses for magnetically enhanced sputtering which is configured to produce a high energy, high power electrical pulse with power equal or larger than 100 kW, in particular 500 kW, and energy equal or larger than 10 J, in particular 50 J, to be supplied to at least one magnetron cathode of a plasma chamber for producing a highly ionized plasma from a neutral gas in the plasma chamber such that during a current rise period the plasma volume cross section increases. 
         [0073]    The same advantages as for the corresponding method steps apply. 
         [0074]    The source may be configured for maintaining a substantially constant current density and/or a substantially constant ionization degree during the current rise period. 
         [0075]    In another aspect the invention also relates to a source for delivering electrical pulses for magnetically enhanced sputtering, the high energy pulse power source being configured to produce a high energy, high power electrical pulse with power equal or larger than 100 kW, in particular 500 kW, and energy equal or larger than 10 J, in particular 50 J, to be supplied to at least one magnetron cathode of a plasma chamber in less than 200 μs for producing a highly ionized plasma from a neutral gas in the plasma chamber, the source being configured such that the voltage between an anode and a cathode in a plasma chamber reaches more than 80% of its maximum value, before the current density reaches more than 80% of its maximum value. 
         [0076]    Moreover, the high energy, high power pulse may be configured such that the current density in the plasma chamber reaches more than 30%, preferably more than 50%, more preferably more than 80%, even more preferably more than 90% of its maximum value, before the current into the electrode reaches more than 80% of its maximum value. 
         [0077]    The high energy pulse power source may comprise a switch configured to be closed when the high energy, high power electrical pulses are produced and configured to be opened, when the current increases above a threshold value. 
         [0078]    The high energy pulse power source may comprise a switch configured to be closed when the high energy, high power electrical pulses are produced, and may be configured to close again, when the current decreases under a second threshold value or after a predetermined time duration which is shorter than 50 μs. 
         [0079]    The high energy pulse power sources described above may be used in an apparatus described earlier. 
         [0080]    The high energy pulse power source or an apparatus for magnetically enhanced sputtering may comprise a matching circuit with configurable inductors and/or capacitors and/or resistors. The matching circuit may be part of the high energy pulse power source or may be provided external to the high energy pulse power source. In the latter case it may be part of an apparatus for magnetically enhanced sputtering mentioned above. 
         [0081]    The high energy pulse power source or the apparatus for magnetically enhanced sputtering may comprise a pulse control which switches a plurality of transistors connected in series and/or in parallel simultaneously. 
         [0082]    Additional objects and advantages of the invention will be set forth in the description which follows, and will be obvious from the description. The objects and advantages of the invention may be realized and obtained by means of a method, processes, instrumentalities and combinations, particularly pointed out in the claims. 
         [0083]    A detailed description of non-limiting embodiments is presented hereinbelow with reference to the accompanying drawings, in which: 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0084]      FIG. 1  is a schematic representation of an apparatus for magnetically enhanced sputtering; 
           [0085]      FIG. 2  is a diagram showing current, current density and ionization degree over time. 
           [0086]      FIG. 3   a  is a schematic representation of an apparatus for magnetically enhanced sputtering; 
           [0087]      FIG. 3   b  is another schematic representation of an apparatus for magnetically enhanced sputtering; 
           [0088]      FIG. 4   a  is a schematic representation of an apparatus for magnetically enhanced sputtering with neutral gas and free electrons; 
           [0089]      FIG. 4   b  is a schematic representation of an apparatus for magnetically enhanced sputtering with formation of an ionization wave; 
           [0090]      FIG. 4   c  is a schematic representation of an apparatus for magnetically enhanced sputtering with formation of two ionization waves; 
           [0091]      FIG. 4   d  is a schematic representation of an apparatus for magnetically enhanced sputtering with formation of an ionization wave and a growing plasma volume; 
           [0092]      FIG. 5  is a schematic representation of an apparatus for magnetically enhanced sputtering with a more detailed view of the high energy pulse power source; 
           [0093]      FIG. 6  is a schematic representation of a matching circuit; 
           [0094]      FIG. 7  is a schematic representation of a pulse unit; 
           [0095]      FIG. 8  is a diagram showing a pulse power; 
           [0096]      FIG. 9  is a diagram showing a voltage and current waveform of the high energy, high power pulse; 
           [0097]      FIG. 10  is a diagram showing a current waveform of the high energy, high power pulse; 
           [0098]      FIG. 11  shows three views of building up of highly ionized plasma volumes; 
           [0099]      FIG. 12  shows a schematic representation of an apparatus for magnetically enhanced sputtering as in  FIG. 5  with an additional energy absorber circuit; 
           [0100]      FIG. 13  shows energy absorber circuit of  FIG. 12  in more detail; 
           [0101]      FIG. 14  shows a bank of switches connected in series and parallel. 
       
    
    
     DETAILED DESCRIPTION 
       [0102]      FIG. 1  shows an apparatus  1 , which is suitable for sputtering. The apparatus  1  comprises a plasma chamber  2 , having a gas inlet  3  for providing a neutral gas. The plasma chamber  2  is vacuumed with a vacuum pump  18 . Neutral gas to be ionized is let in via a valve  17  from a gas container  19 . 
         [0103]    In the plasma chamber  2  a magnet  4  is provided for providing a magnetic field at the surface of a sputtering target  5 . The target  5  is provided on top of an electrode  6 , configured as a cathode. In particular, the target  5  is in electrical connection with the cathode  6 . Opposite the target  5  is provided a substrate  7  to be coated with target material. The substrate  7  is provided on an anode  8 . The anode  8  and cathode  6  are connected with a high energy pulse power source  9  for applying voltage pulses between the anode  8  and the cathode  6  in the plasma chamber  2 . The high energy pulse power source  9  can be controlled to produce pulses in order to produce a highly ionized plasma from the neutral gas as such that during a current rise period the plasma volume cross section increases while maintaining a substantially constant current density and/or a substantially constant ionization degree of the plasma, which is formed in the plasma chamber  2 . 
         [0104]    The diagram of  FIG. 2  illustrates the formation of a highly ionized plasma. At time t 0  a voltage pulse is applied between anode  8  and cathode  6  in order to provide a transition from a neutral gas to a highly ionized plasma. This means that upon application of a voltage pulse instantaneously a highly ionized plasma with a high ionization degree is formed. This is represented by line  10 . As the current, which is represented by line  11  rises from t 0  to t 3 , wherein the time interval between t 0  and t 3  represents a current rise period, the ionization degree represented by line  10  remains constant. At time t 0  the volume  12  of the highly ionized plasma is relatively small. It increases with time, as the current rises. This is illustrated by the volumes  13 ,  14 , and  15 . As the volume of the ionized plasma grows, also the cross section of the ionized plasma increases. In  FIG. 2  it can also be seen that the current density, which is represented by line  16  quickly rises to a high and constant value at time t 0 . The rise time of current density is normally less than 10 μs. Depending on circumstances like pressure, target material, magnetic field etc. the rise time may be less than 1 μs. From then on the current density remains constant during the current rise period. This means that the increase in ionized plasma volume is only due to an increase in current, whereas the current density and ionization degree remain constant. 
         [0105]      FIG. 3   a  shows a schematic representation of an apparatus for magnetically enhanced sputtering with a high energy pulse power source  23  which is connected via a power line  23   a  to a cathode  24  and via a power line  23   b  to an anode  25 . The anode  25  and cathode  24  are placed in a plasma chamber  20 . The cathode  24  is in direct electrical connection with a target  27 . When the high energy pulse power source  23  applies a pulse, an electrical field establishes between the anode  25  and the cathode  24 . A strong magnet  21  is positioned behind the target which builds out a magnetic field. The field lines of the magnetic field  28  (dashed lines) are at least partially perpendicular to the field lines of the electrical field  26 . 
         [0106]      FIG. 3   b  shows another schematic representation of an apparatus for magnetically enhanced sputtering, in which the same parts are not referenced again.  FIG. 3   b  differs from  FIG. 3   a  in the position and form of the anodes  25   a ,  25   b , which is in  FIG. 3   b  on both sides of the cathode. the field lines of the electrical field  26   a ,  26   b  are also at least partially perpendicular to the field lines of the magnetic field  28 . In  FIG. 3   b  is also shown a substrate  29 , where sputtered atoms and/or ions may be deposited. 
         [0107]      FIG. 4   a  is a schematic representation of an apparatus for magnetically enhanced sputtering with neutral gas and free electrons. The neutrons  31  are indicated as a ‘o’; The electrons are indicated as ‘−’. With the electrical field the free electrons are accelerated towards the anode. The at least partially perpendicular magnetic field deviates the flow direction of the electrons. This leads to a completely different behavior of the now starting avalanche process as in breakdowns without such a magnetic field. The electrons are trapped to a volume near the cathode. As mentioned above, a neutral gas can be transformed to a plasma state by an electrical field breakdown in a gap between a cathode and an anode. The breakdown is a transformation process, where electrical charge multiplies and becomes homogeneous. Upon application of a voltage, a statistical time lag exists before the discharge starts to develop. This is followed by the acceleration of a free electron in the chamber which collides with gas atoms, ionizes them, creates more electrons, thereby initiating an electron ionization avalanche. 
         [0108]      FIG. 4   b  shows the apparatus of  FIG. 4   a  with an ionization wave  33 . As electrons from the avalanche reach the anode, they are absorbed and a positive ion charge  34  builds. The positive charged ions are indicated as a ‘+’ and are accelerated by the electrical field towards the cathode. This gives rise to ionization waves that traverse the gap several times, which is indicated with arrows  35 , the charge distribution becomes more homogeneous and a cathode and anode sheath form. In  FIG. 4   b  is still indicated a free electron  32 . More and more avalanches form (avalanche multiplication), increasing the cross sectional area and the number of ionized channels to the full face of the cathode. At this point a plasma is created and the discharge enters a state of spatial uniform glow. If the breakdown occurs with very high energy (caused by a dynamic voltage rise) the produced plasma is highly ionized. Typically an ionization degree of above 10 12 cm−3 describes a highly ionized plasma. 
         [0109]      FIG. 4   c  shows the apparatus of  FIG. 4   a  with formation of two ionization waves  33  and  36 . In the ionization wave  33  the positive charges have moved in direction of the cathode in respect to  FIG. 4   b . Also the spatial dimension and the cross section of the ionization wave  33  have increased compared to  FIG. 4   b.    
         [0110]      FIG. 4   d  shows the apparatus of  FIG. 4   a , b and c with formation of an ionization wave  36  and a growing highly ionized plasma volume  37 . 
         [0111]      FIG. 5  shows a schematic representation of an apparatus for magnetically enhanced sputtering with a more detailed view of the high energy pulse power source  40 . It has a connection to mains network via a power line and connector  41 , which may be a plug. The power from the mains is connected to a DC power supply  42  which is known in the art. This may be a switch mode power supply with a transformer to disconnect the output potential from the mains potential. At the output of the DC power supply  42  a DC power is supplied via two or more power lines to a pulse unit  43 . DC power supply  42  has also a communication and control line input and output, so it can be connected to the pulse unit or to an external control  39  which may be a panel or computer or to other parts. In  FIG. 5  is shown a data communication line  48   a  between DC power supply  42  and pulse unit  43 . A further data line  48   c  to an external control  39  is in  FIG. 5  connected to the pulse unit  43 . It may also be connected to the DC power supply  42 . DC power supply  42  and pulse unit  43  may be placed in two separate housings or in one housing. A third data communication line  48   b  goes from the pulse unit  43  to the matching circuit  45 . The matching circuit  45  is placed in the power line which goes from the pulse unit to the cathode  47  of the plasma chamber  46 . The matching circuit is not absolutely necessary, but it gives the user the possibility to dampen oscillations, to shape the current waveform in order to achieve the highly ionized plasma without going through a low ionized plasma or through an arc discharge. 
         [0112]    To ensure the plasma process starts at every high power pulse with the formation of a highly ionized plasma it is possible to monitor the plasma formation for example with a fast camera  49  which is connected to the external control  39  via a communication line  38 . As mentioned above, the plasma development is dependent on a quite large number of parameters, some of which cannot be influenced by the pulse shape as it comes from the power supply. But it is possible to vary some parameters as for example the magnetic field strength and position by varying the position of the magnets. If the position of the field lines varies because of target erosion, it is possible to vary the electrical behavior of the high power pulse via external control or via modification of the matching circuit  45 . 
         [0113]      FIG. 6  shows a schematic representation of a matching circuit  45 . It includes one or several inductors  53 , some of them may be variable like indicated with inductor  53   a.  It includes further one or more capacitors  54 , some of them may be variable like indicated with capacitor  54   a.  It includes further one or more resistors  55 , some of them may be variable like indicated with resistor  55   a.  Resistors, inductors and capacitors are replaceable, it is possible to shortcut them. This is all possible due to connection means  56 . Not all connection means in  FIG. 6  are referenced with a number. So there is a big variety to shape the pulse form. The variable element can also be controlled electrically by external control. 
         [0114]      FIG. 7  shows a schematic representation of a pulse unit  43 . It includes a charge current shaping unit  60  which is connected via power lines  61   a ,  61   b  to the DC power supply  42 . The charge current shaping unit  60  delivers current via a charging diode  63  to charge a capacitor  62 . The capacitor  62  may be a capacitor bank of several parallel and serial connected capacitors to store enough energy for the high energy pulses. The pulse unit  43  includes also a pulse control  65  which controls a switch  64 . The switch  64  closes for short controllable pulse durations of 1 μs to 300 μs. It may be a bank of MOSFET switches connected in series and parallel, all switched on and off at the same time in order to lead the high current and to switch the high voltage of the high energy, high power pulse. When the switch  64  turns off, the current in the power lines  69   a ,  69   b , which lead to the plasma chamber via the optional matching circuit  45 , will continue to flow due to inherent inductances in the matching circuit and in the power lines. In order to avoid destruction of the pulse unit  43 , especially the switch  64 , a freewheeling diode  67  is provided between the lines  69   a  and  69   b . A current sensor  66  is included which gives a signal corresponding to the current into the plasma chamber to the pulse control  65 . 
         [0115]      FIG. 8  shows a diagram of a typical pulse duration and repetition time. On the vertical axis the power is indicated in kilowatts. This means the shown pulses have a peak power of about 1 MW. On the horizontal axis is the time scale. Three pulses  83   a ,  83   b ,  83   c  are shown. They may have a repetition time  85  of about 1 ms to 1 s. The pulse duration  84  may be between 1 μs and 300 μs. Even longer pulse duration times are possible if a current control or regulation is implemented which will be explained later on. In the diagram is also shown the average delivered power  86  which is in this case about 1.5 kW which is a typical value for sputtering purposes with large areas to coat. 
         [0116]      FIG. 9  shows a diagram with a typical voltage waveform  87  and a current waveform  89  of the high power pulse; 
         [0117]      FIG. 10  shows a diagram with a typical current waveform of the high power pulse, if the pulse should be longer than 300 μs. If the duration of the pulse should be longer than about 300 μs the risk to come into an arc discharge rises. Arc discharges should be avoided, because they lead to target and substrate damages. Arc discharges can be detected by a huge current rise or a huge current rise velocity. This can be monitored with the current sensor  66 , and when an arc discharge is detected, the switch  64  may be opened immediately by pulse control  65 . The arc then quenches in about 100 μs. Only the remaining energy in the power lines and matching circuit is delivered to the plasma, which is often too much. To avoid even the delivery of this energy a further arc diverter is necessary which will be explained later on. To avoid the arcing it is advantageous to control or to limit the current after a time of about 1 μs to 200 μs. This can also be done with the current sensor  66  and with the pulse control  65 . If the current rises over a given threshold, which may be variable, the switch  64  is turned off. As can be seen from  FIG. 9 , the current does not break down immediately but falls with an e-function. If the current is further monitored, the switch  64  can be closed again, when the monitored current falls below a given second threshold. It is also possible to wait a given time before reclosing the switch. In this way the current can be regulated as shown in  FIG. 10 . The signal  94  shows the switching on and off of the switch  64 . The waveform  93  is the waveform of the current measured with the current sensor  66 . 
         [0118]      FIG. 11  shows some typical views which may be obtained by a camera  49  shown in  FIG. 5 . In the picture  101  the formation of five highly ionized plasma volumes is seen. In picture  102  which is a picture taken some nanoseconds later, these five plasma volumes have already grown. Also a new sixth plasma volume has formed. At picture  103  which is again some nanoseconds later all, six plasma volumes have increased again. It is easy to imagine how a uniform plasma builds in this way. Whether the plasma is really highly ionized and whether ionized atoms of the sputtered material are as well present, is detectable via spectroscopic filters or pictures of this view. If this monitoring shows that the high ionization starts up from the beginning, than all parameters are well set. If this monitoring shows that the highly ionization starts after a low ionization stage, then parameters such as values listed above should be changed. 
         [0119]      FIG. 12  shows a schematic representation of an apparatus for magnetically enhanced sputtering as in  FIG. 5  with an additional energy absorber circuit  106 . Also this circuit has a data communication line  48   d  and is in connection with the external control  39 , the pulse unit  43  and the DC power supply  42 . There may also be an optional data connection  48   e  to the matching unit  45 . The additional energy absorber circuit  106  is configured to absorb the energy, at least partly, which is stored in the power lines from the high energy pulse power source  40  to the plasma chamber  46 . It may also at least partly absorb the energy which is stored in the plasma chamber  46 . This energy absorber circuit  106  is configured to be activated when a sensor such as the current sensor  77  of the pulse unit  43  ( FIG. 7 ) detects an abnormal current rise. This may be caused by an arc discharge in the plasma chamber. As mentioned earlier, when an arc discharge is detected, the switch  64  may be opened immediately by pulse control  65 . The arc then quenches in about 100 μs. Only the remaining energy in the power lines and matching circuit  45  is delivered to the plasma, which is often too much. To avoid even the delivery of this energy at least partly, the energy absorber circuit  106  is activated. 
         [0120]      FIG. 13  shows such an energy absorber circuit  106  in more detail. A control section  113  controls a switch  114  which is normally closed. In case of abnormal current rise or arc detection this switch opens as quickly as possible. The current which flows at this moment in the power lines between the high energy pulse power source  40  and the plasma chamber  46  keeps on flowing due to the inherent inductance in the power lines. 
         [0121]    The current flows now via the diode  112  into the capacitor  111 . A precharging and discharging circuit  110  is connected to the capacitor  111 . It precharges the capacitor  111  to a defined voltage, which helps to absorb the energy as quickly as possible. The current decreases while the capacitor  111  will be charged by the current. To avoid an overvoltage at the capacitor  111  after several activations of the energy absorber circuit  106 , the capacitor  111  must be discharged. This can be done by a discharging circuit, which may be also implemented in the precharging and discharging circuit  110 . The capacitor  111  may also be placed in the DC power supply and the energy which comes from the power lines into the capacitor may be used to charge the capacitors  62  of the pulse unit  43 . 
         [0122]      FIG. 14  shows a bank of switches  123  which comprises four switches  120   a,    120   b ,  120   c,    120   d  connected in series and parallel. This is a configuration as it may be used for the switch  64  of the pulse unit  43  or for the switch  114  of the energy absorber circuit  106 . All four switches  120   a,    120   b,    120   c,    120   d,  which may be MOSFETs, are switched on and off at the same time. They are controlled via a control line  121 . A connection  122  between both series connected switch pairs  120   a ,  120   c  and  120   b,    120   d  is optional. 
         [0123]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.