High peak power plasma pulsed supply with arc handling

[0002] 1. Field of the Invention

[0003] This invention is related generally to apparatus and methods for magnetron sputtering of highly ionized, high-density metal plasmas, and more particularly to magnetron sputtering apparatus that delivers peak powers of 0.1 mega Watts to several mega Watts, with peak power density of 1 kW/cm²and higher to a sputtering magnetron plasma load with arc handling capability.

[0004] 2. Brief Description of the Prior Art

[0005] It is desirable to coat some substrates by generating metal ions and attracting the ions to the work piece by means of an electrical bias, which attracts the ions. The utility of this approach includes application of coatings to surfaces with irregularities that would prevent uniform deposition by normal sputtering, which essentially requires line of sight. Indeed coating and even filling high aspect ratio trenches in semiconductor devices is possible by biasing the wafer to attract the ions, as reported by Monteiro in JVST B 17(3), 1999 pg. 1094 and Lu and Kushner in JVST A 19(5), 2001 pg. 2652.

[0006] A technique for generating highly ionized, high density metal plasma by driving conventional sputtering magnetrons with electrical pulses having high peak power and low duty factor has been reported by Kouznetzov, et al. in Surface and Coatings Technology 122 (1999) pg. 290. Additional teachings can be found by Macak, et al, JVST A 18(4), 2000 pg. 1533; Gudmundsson, et al., APL, Vol. 78, No. 22, May 28, 2001, pg. 3427; and Ehiasarian, et al., Vacuum 65 (2002) p. 147, and U.S. Pat. No. 6,296,742 B1, Oct. 2, 2001.

[0007] The appeal of this technique is the ability to generate a large population of ionized species that can in turn be attracted to the work piece by the application of a bias voltage. The above references on the high peak power technique appear to use a simple capacitor discharge through an inductor. However, the technique taught by these references does not disclose any arc handling capability, and in fact suggests that an arc free region actually exists. Unavoidable imperfections in hardware make the physical realization of a completely arc free region of operation essentially impossible, even if its existence is suggested by theory. Use of the technique without arc handling capability makes commercial utilization impractical. Thus, it would be desirable to provide apparatus that enables commercial processes using high peak power pulses to magnetrons to produce high density, highly ionized metal plasmas by minimizing arc energy that in turn keeps product and target damage due to arcing within acceptable limits.

[0008] Typically arc control and arc diverting apparatus have been comprised of circuits that either detect the arc and disconnect the power supply from the load or are comprised of a switching circuit that effectively short circuits the power supply to extinguish the arc. These types of arc handling methods are very costly because they may result in a complete shut down of the process wasting expensive stock material, or require dissipation of energy stored in the power supply circuits. In high power applications short circuits to the power supply may result in extremely high currents that can cause destruction of the power supply itself, and repetitive dissipation of stored energy requires expensive resistive elements capable of high peak power and high average power, as well as the means for cooling them.

[0009] It would also be desirable if there were provided a magnetron sputtering apparatus and method that could deliver peak powers of 1 mega Watt or greater with arc handling capability for high yield commercial applications. It is an object of this invention to provide a magnetron sputtering plasma system that has the capability to detect arcs and take action to limit the energy delivered to the arc.

[0010] There is provided by this invention an apparatus and method for producing a high voltage pulse suited for delivering high peak power to high-density magnetron plasmas with efficient arc handling capability. A pulsing circuit comprised of an energy storage capacitor is repetitively charged and then discharged through an inductor in series with the plasma. The combination of the inductor and capacitor serve to shape the pulse, to provide an impedance match to the plasma, and to limit the current rate of rise and peak magnitude in the event of an arc. An arc is detected by either the fall of the discharge voltage below a preset voltage threshold during a pulse, or an increase in discharge current above a preset current threshold. When an arc is detected the energy storage capacitor is disconnected from the series inductor to stop the current rise. The pulsing circuit is then disconnected from the plasma load and the inductor energy is recycled to the energy storage capacitor.

[0011] FIG. 1 is a schematic representation of a magnetron plasma processing system incorporating the principles of this invention;

[0012] FIG. 2 illustrates the waveforms for normal operation of the magnetron plasma processing system shown in FIG. 1; and

[0013] FIG. 3 illustrates the waveforms for arc handling operation.

[0014] Referring to FIG. 1 there is shown a magnetron plasma processing system 10. A dc power supply 12 is connected to a magnetron plasma-processing chamber 14 via a pulsing circuit 16. The magnetron plasma-processing chamber may be a conventional magnetron chamber well known to those skilled in the art having a magnetron cathode 18 and an anode 20. The pulsed supply 16 may be of the type such as a MegaPulser™ model manufactured by Advanced Energy Industries, Inc. which supplies a high voltage pulse across the cathode 18 and anode 20 to ignite a plasma 22 between the electrodes in a manner well known to those skilled in the art. As with all conventional plasma processing chambers the plasma acts upon the material of the cathode 18 so as to result in a coating on a substrate 26 located within the chamber. It is generally known and well understood that at high voltages and with variances in the processing environment within the chamber, arc discharges can occur from the plasma 22 or cathode 18 to the anode 20. Also, connected to the magnetron plasma-processing chamber is a smaller dc power supply 28 that maintains a minimum voltage to the magnetron to keep the plasma ignited between the high voltage pulses from the pulse circuit 16. This power supply may also be used to initially ignite the plasma before the high pulse operation begins.

[0015] For application of high voltage pulses to the magnetron processing chamber the pulsing circuit 16 is comprised of energy storage capacitor C₁serially connected to an inductor L₁via switch S₁. The inductor L₁is connected to the cathode of the magnetron via switch S₂.

[0016] FIG. 2 illustrates the waveforms for normal operation of the circuit. S₂is closed and S₃are open for the whole sequence. The capacitor C₁is charged to its initial voltage by the dc power supply 12. The discharge is initiated by S₁, and capacitor C₁is discharged through inductor L₁into the plasma load. A control circuit initiates the timing of the switches to control the charge time of the capacitor C₁and its pulse discharge to the load. The shapes of the V_C, i_inductor, V_LOAD, and I_loadwaveforms are determined solely by the initial value of V_C, the values of C₁and L₁and the characteristics of the plasma load and the output cable.

[0017] FIG. 3 shows waveforms representative of an arc occurring during a pulse from the pulsing circuit 16. The sequence begins as shown in FIG. 2 and described above, but when an arc occurs the current rises and the voltage falls until the arc is detected. Arcs are detected by one of two means. Specific circuit techniques required to implement the arc detection means are well known to those skilled in the art. First, an arc may be detected as the load current exceeding a preset threshold. This threshold can actually be updated on a pulse by pulse basis by predicting the output current, based on plasma load characteristics and the initial value of V_Cand the values of C₁and L₁and adding a margin to prevent false detections. Prediction of the output current based on these parameters is well known to those skilled in the art. Alternately, the current threshold may be based on the average peak current, with some margin added to prevent false arc detections. In this case, it may be desirable to leave pulses with high arc currents out of the average calculation. Second, an arc may be detected as the load voltage being below a preset threshold when the load current is above a second current threshold, used only for this second method. When the arc is detected, S₁is opened immediately and S₃is closed after a short delay, and then S₂is opened after another short delay. This disconnects the load from the pulse circuit 16 and initiates the resonant transfer of energy from inductor L₁to capacitor C₁. The result is that the energy present in inductor L₁when the arc occurred is recycled to capacitor C₁. This arc handling sequence minimizes the energy delivered to the load in the event of an arc. Without the arc handling provisions, the energy stored in C₁and the energy stored in L₁would be delivered to the arc, almost certainly causing damage to the target and the work piece. Arc handling provisions enable commercial use of this process.

[0018] It can be readily seen that there is provided a novel high peak power plasma pulsed supply for pulsed magnetrons with arc handling that minimizes damage due to arcs by disconnecting the pulsing circuit from the plasma load and recycling the inductor energy stored for the high peak power pulse back to the energy storage capacitor at the detection of an arc condition.

[0019] Although there is illustrated and described specific structure and details of operation, it is clearly understood that the same were merely for purposes of illustration and that changes and modifications may be readily made therein by those skilled in the art without departing from the spirit and the scope of this invention.