Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-10-05
2003-06-24
VerSteeg, Steven H. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298080, C427S445000, C427S569000, C118S7230MW, C118S7230ER, C118S715000
Reexamination Certificate
active
06582566
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 51 508.8, filed on Oct. 18, 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 to related devices for reducing the ignition voltage of plasmas operated using pulses of pulsed power with a long pulse-off time. Such plasmas are used for treating substrates in, e.g., atomization processes which utilize vacuum coating devices, in plasma activation as part of various coating processes, and in other processes utilizing vacuum technology. Cathode atomization processes, also known as sputtering, represent a primary area of application for pulsed plasmas within the coating technology. With their aid, many things such as components, tools, partially finished products, as well as finished products which are used in optics and mechanical engineering can be coated. Many parts, such as those used in the packaging, glass, and electronics industries are also coated with individual layers or layer systems being deposited on a respective substrate.
2. Discussion of Background Information
In deposited layer systems of this type, bonding agent layers and functional layers with layer thicknesses of only a few nanometers are usually required. In order to deposit layers with such low layer thicknesses, the feed rate of the substrate during the coating process can usually be selected as being set relatively high, in order to shorten the coating duration, or the lag time of the substrate in the coating zone can be kept low, or the electrical power applied can be set very low, which leads to a low depositing of material on the targets of the atomization cathodes, and to a low growth rate of the layers to be deposited.
The substrate speed or the lag time has often been determined by the depositing rates of other layers present in the layer system or to be deposited subsequently. Because of the required stability of the coating plasma, an arbitrary reduction of the electrical power applied is not possible because if the power density is too low, it causes inhomogeneities in the coating plasma and therefore layer inhomogeneities and instability of the coating process. This is particularly problematic in the case of larger cathode arrangements. In practice, stable coating plasmas with a low power feed are presently possible only by using blinds and/or by covering of the sputtering cathodes. This, however, results in a considerable loss of effectiveness.
The bonding agent and functional layers mentioned above are pivotal in determining the properties of the entire layer system, based on their physical properties. Thus, it is important to deposit very thin layers, with precisely defined properties, having a high degree of evenness and reproducibility of these properties, in order to achieve certain target parameters of the entire layer system.
Research has shown that, with the aid of high power densities on the target, the properties of deposited layers can be influenced and, optionally, improved, i.e., Kouznetsov et al., “A Novel Pulsed Magnetron Technique Using Very High Target Power Densities,” Surface and Coatings Technology, Vol. 122, 1999, pages 290-293, the disclosure of which is expressly incorporated by reference in its entirety.
Thus, it is often physically necessary to deposit very thin and/or slowly growing layers on the target, as well as using high power densities.
Devices are already known that, with the aid of a pulsed power supply, produce pulses with high electric pulse power utilizing, at the same time, a low average introduced electric power, e.g., DE 41 27 317 A1, the disclosure of which is expressly incorporated by reference in its entirety. The result is a high plasma density on the sputtering target during the pulse-on time. This stabilizes the sputtering plasma at low average electric power levels. However, at the time of coating, a high plasma density is constantly available on the target. The deciding disadvantage of this arrangement lies in the fact that, due to pulse-off times during re-ignition of the discharge on the target, a high ignition voltage results. The value of the ignition voltage depends primarily on the ratio of the pulse-on time to the pulse-off time and the length of the pulse-off time. If the pulse-off times are increased and the pulse-on times are decreased, a very high plasma density on the sputtering target will indeed be achieved at the same average electric power; however, as a result of the long pulse-off time the ignition voltage increases to values that lie substantially above the burning voltage of the plasma and may amount to several kilovolts. This can again cause damage in the various switching arrangements and undesired arcs. Such a result is caused by the fact that, during the long pulse-off time, i.e., at pulse-off times of greater than approximately 1 &mgr;s, a sputtering plasma becomes depleted of charge carriers and, as a result, may go out. At the beginning of each pulse, the production of charge carriers must occur again until enough charge carriers are present that ensure that the initially excessive ignition voltage is decreased to the value of the actual burning voltage of the sputtering plasma.
The problem described above generally occurs in plasmas that are pulsed at medium frequency. Wherever the pulse duty factor, i.e., the ratio between pulse-on and pulse off times, is set in such a way that the pulse-off time increases above a critical value or when a longer pulse-off time is necessary for another reason, the critical excesses in ignition voltage may occur.
SUMMARY OF THE INVENTION
The invention provides for a process for operating pulsed plasmas which, independently of the pulse-off time, causes an increase in ignition voltage that is as low as possible relative to the burning voltage of the plasma. The process should be suitable in various devices for various vacuum technology processes.
The invention provides for a process for reducing an ignition voltage of power pulses in plasmas operated in a pulsed manner with long pulse-off times, the process comprising generating a power pulsed plasma at a pulse duty factor, the pulse duty factor being a ratio of pulse-on time to pulse-off time, and at least before the beginning of the pulse-on time of the power pulses, producing charge carriers using an additional plasma discharge at a lower power than that of the power pulses.
The charge carriers may be produced by the additional plasma discharge during the entire pulse-off time of the power pulses. The charge carriers may be produced by the additional plasma discharge during part of the pulse-off time of the power pulses. The charge carriers may be produced by the additional plasma discharge partially during the pulse-on time of the power pulses. The charge carriers may be produced by the additional plasma discharge during the entire pulse-off time and pulse-on time of the power pulses. The charge carriers may be produced in a pulsed manner by the additional plasma discharge. The process may further comprise feeding the additional plasma discharge using a separate energy supply device. The process may further comprise regulating a power density of the additional plasma discharge.
The invention also provides for a device for reducing an ignition voltage of power pulses in plasmas operated in a pulsed manner, the device comprising a vacuum chamber or vessel including at least one pump system. An arrangement for producing plasma is provided and the arrangement includes at least one anode and at least one cathode. An energy source is connected to the cathode and the anode which can be pulsed in the frequency range of between approximately 10 Hz to approximately 1 MHz. A mechanism for one of producing an additional plasma discharge is also provided.
The mechanism for producing the additional plasma discharge may be adapted to regulate the additional plasma discharge. The mech
Krause Uwe
List Matthias
Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung
Greenblum & Bernstein P.L.C.
VerSteeg Steven H.
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