Process and switching arrangement for pulsing energy...

Details Process and switching arrangement for pulsing energy... Process and switching arrangement for pulsing energy...

2001-03-27

2003-02-18

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Discharge device load with fluent material supply to the...

Plasma generating

C204S192120

Reexamination Certificate

active

06522076

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 15 244.9, filed on Mar. 28, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and a control arrangement for pulsing introduction of electric energy into a glow discharge of the magnetron type. These so-called magnetron discharges are widely used for performing plasma technological processes, in particular, for plasma treatment of surfaces and for vacuum coating of work pieces with thin layers using magnetron sputtering. Typical areas of application are the refining of glass, plastic, and metal surfaces in electronics, optics, engineering, and memory technology.
2. Discussion of Background Information
Plasmas for surface treatment and coating can be fed with direct current when the work pieces to be treated and/or the material to be deposited is electrically conductive. Thus, for instance, direct current spraying of metallic layered work pieces is widely used, [e.g., G. Kienel (Pub.) Vakuumbeschichtung Vol. 1, ch. 5, p. 127 ff, VDI-Verlag Düsseldorf, 1995; and R. A. Haefer:Oberflächen- und Dünnschicht-Technologie, Part I, Chap. 4, p. 56 ff. and chap. 6, p. 95 ff., Springer-Verlag 1987].
When non-metal materials are to be sputtered, a high-frequency plasma is suitable, which is preferably operated at a frequency of 13.56 MHZ (see above lit. and DE39 42 560 A1).
By introducing pulsed plasma of medium frequency for spraying (DE 252 205 A1, DE 38 02 852 C2), sweeping technical advancements were achieved in the reactive depositing of electrically insulating layers; in particular, considerably higher coating rates can be achieved and high energy loss in matching networks, unavoidable in high-frequency spraying, can be prevented.
For this purpose, it is known for a sine-shaped alternating current in the frequency range of about 10 to 100 kHz to be introduced into a plasma via an oscillating converter (DE 40 42 287 A1; DE 41 06 770 C2). This procedure has the disadvantage that the plasma discharge of the negative and the positive polarity cannot be controlled independently of each other. Additionally, the form of pulsing can be influenced only with difficulty, particularly with respect to a certain relation between pulse length and pulse pause. Thus, considerable disadvantages result for a number of applications which can lead to the plasma processes being impossible to perform.
It is known to perform magnetron discharges by introducing rectangularly shaped unipolar power impulses (DE 37 00 633 C1). However, no instructions for designing such power introduction are provided and no suitable control arrangements are given by which almost rectangular power impulses can be created for high-powered magnetron discharge.
It is known to use so-called voltage source converters for energy introduction (EP 0 534 068 A2, EP 0 692 550 A1). In the pulsed introduction of energy into magnetron discharge with frequencies in the range from about 10 to 100 kHz, the discharge stops after each pulse and has to be ignited anew during the subsequent pulse. When creating a rectangular voltage impulse using a voltage source converter, first the generating of charge carriers begins before the plasma ignites. After the plasma has been ignited, some of the voltage created by the voltage source converter, the so-called ignition voltage, is falling over the plasma. The inductive behavior of the voltage source converter and the entire arrangement as well as the difference between the applied voltage and the ignition voltage determine the increase in current after the ignition of the plasma so that a serrated current impulse with relatively slow speeds of current increase results in practical use. It is disadvantageous that this current progression with its slowly increasing discharge current presents a drastic limit for the average time of the discharge power that can be introduced into the discharge. Therefore, very high values of peak current are necessary in order to achieve a certain desired value of the discharge power. This corresponds to high requirements of the electronic control elements for the capability of carrying current and, thus, causes high expenses. High peak currents also connected to a high plasma concentration, which can sometimes cause instabilities in the plasma process, e.g., the occurrence of undesired arc discharge.
In these cases, the recognition and purposeful avoidance and/or cancellation of such arc discharges is difficult since high peak currents can hardly be differentiated from spikes in current as an arc discharge is beginning.
It is also known that pulsed plasma can be operated with such a current pulser (DE 44 38 463 C1; U.S. Pat. No. 5,718,813). Here, a constant discharge current is introduced during the pulse phase in order to overcome the above-mentioned disadvantages. However, one disadvantage of this process using a current pulser is that, during the introduction of the predetermined current, at the beginning of the discharge a very high voltage peak is created in each pulse during the initial generation of the voltage carriers until the primary ignition is achieved, since the current is carried by too few voltage carriers at first. The voltage reaches values that are a multiple of the ignition voltage of the discharge after the primary ignition. Voltages of such high values can cause destruction of electronic components.
Control arrangements are known which limit high voltage occurring due to the introduction of a constant current by buffering in a discharge network (DE 35 38 494 A1). Along with the control expense corresponding therewith a loss of power in the discharge network is caused, which is particularly unacceptable, for high discharge power, i.e., high discharge currents, as well, and presents a considerable disadvantage of such control arrangements.
It is further known to introduce energy into a magnetron discharge in form of pulse packets having different current directions (DE 197 02 187 A). Depending on the type of the pulser used, such processes also have the above-mentioned disadvantages that result from the manner of creating single pulses.
SUMMARY OF THE INVENTION
The present invention provides a process and a control arrangement for performing the process by which, in each pulse phase, i.e., immediately after a pulse pause as well, a maximal pulse power can be introduced at a predetermined current without causing considerable excess voltage. Therefore, a largely rectangular time progression of the current as well as the voltage of the introduced pulse is to be provided for the introduction of magnetron discharges even in frequency ranges in which the magnetron discharge stops after each pulse and must be reignited in the subsequent pulse.
Accordingly, the present invention relates to a process for pulsing energy introduction into magnetron discharges with a charge being fed to the electrodes of a magnetron arrangement by a ignition source at a time t
0
. Further, after the feeding of the electric charge, an ignition of the magnetron discharge is determined, in that the introduction of the current, having a predetermined value, from a boost source begins at a time t
1
, determined by the ignition of the magnetron discharge, in that, at a time t
2
, also determined by the ignition of the magnetron discharge, the separation of the ignition source from the electrodes of the magnetron arrangement is performed. The introduction of the current by the boost source is continued for a certain duration t
EIN
, in that the introduction of the electric energy is subsequently interrupted for a predetermined time t
AUS
, and in the separate process elements are then repeated, beginning with the feeding of the charge by means of the ignition source.
For t
1
, and t
2
, the condition t
2
≧t
1
, is observed. Further, The electric charge of the ignition source and/or the predetermined value of the

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