Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
1999-06-08
2001-04-24
Bettendorf, Justin P. (Department: 2817)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C118S7230ER, C204S298090
Reexamination Certificate
active
06222321
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention pertains generally to power supplies and more particularly to pulsed DC power supplies that are used for generating plasmas that are used in thin film processing techniques for etching, deposition, etc.
2. Definitions
Alternating polarities means a current flow at any particular point in a circuit or plasma that changes direction, or a voltage at any particular point in a circuit that changes magnitudes around any desired neutral voltage.
Current connections means locations or points in a circuit that are coupled to electrodes of a plasma chamber.
Current controlled power source means a power source that is capable of maintaining a substantially constant current for a wide range of load impedances and has a low amount of capacitively stored energy.
Current reversing switches means any desired arrangement of switches that are capable of causing current to flow in different directions at a preselected location in a circuit.
Direct current means current that has a substantially constant magnitude.
Direction means the course of the flow of current on a conductor in a circuit.
Generating means initiating and/or maintaining.
Inductor means an electrical component that is designed to store energy in a magnetic field.
Plasma means a state of matter in which electrons and ions in a gas discharge are separated but together form a neutral assembly.
Plasma chamber means a device in which plasmas can be generated.
Power source means a device that is capable of supplying electrical energy.
Predetermined positions means either an opened or closed position of a switch.
Pulsed direct current means a current that flows at a particular point in a circuit that has a first substantially constant magnitude during a first period of time, and then has at least one additional substantially constant magnitude that is different from the first substantially constant magnitude during at least one additional subsequent period of time, and may repeat.
Substantially constant supply means a substantially constant magnitude.
DESCRIPTION OF THE BACKGROUND
Plasma processing techniques have found wide-spread use in industry for commercial processes such as plasma vapor deposition, sputtering, etc. These processes have become particularly useful in thin film applications. To generate a plasma, a power supply creates an electric potential between a cathode and one or more anodes that are placed in a plasma chamber containing the gases that are used to form the plasma. When using these processes for deposition, the plasma acts upon the material of a target placed in the plasma chamber that normally comprises the cathode surface. Plasma ions cause target material to be dislodged from the cathode surface. The target materials are then deposited on a substrate deposition surface to form a thin film. The thin film may constitute material sputtered by the plasma from the target surface, as disclosed above, or may be the result of a reaction between the target material and some other element included in the plasma. The materials and elements involved, as well as the specific applications of the plasma processing techniques vary greatly. Applications may range from coating architectural glass to deposition of thin film layers on microchips, or deposition of aluminum layers on compact disks.
In the past, high frequency voltage sources have been used to generate a high electrical potential that produces a plasma within a plasma chamber. These high-frequency voltage sources are expensive to construct and maintain, as well as dangerous to operate. Additionally, if the deposition material is formed by reaction with an element in the plasma, and further, is electronically insulating, the anode in the chamber can be coated with the insulator; this deposit can then prevent the anode from performing its function of collecting the electrons released from the plasma during the deposition process.
To overcome these disadvantages, pulsed DC voltage sources have been employed such as disclosed in U.S. Pat. No. 5,303,139 issued Apr. 12, 1994 to Mark, which is specifically incorporated herein by reference for all that it discloses and teaches. Mark discloses a constant voltage pulsed power supply that has alternating pulse polarities. The advantages of such a constant voltage pulsed power supply over the AC power supplies are that they are less expensive, easier to connect and set up, and overcome the problem of coating the anode if used with two target units. That is, the process of reversing polarities allows the electrodes to alternately act as anode and cathode; the sputtering process that occurs during the cathode phase cleans off any deposited insulating material and permits uninhabited operation of the electrode as an anode during the anode phase. Additionally, the process of reversing polarities allows both electrodes to alternatively act as a cathode so that both electrode surfaces are capable of providing target material.
Despite the advantages that constant voltage pulsed power sources provide, problems exist with regard to generation of excessive currents and spark discharges in the plasma chamber. As part of this problem, it has been found that as the current through a plasma increases, the resistance of the plasma decreases in an exponential manner to almost zero. Small changes in the voltage level of a voltage power source result in large changes in the current. Consequently, excessive current increases can be generated from only very small changes in the voltage level, and a high degree of accuracy is required for controlling voltage controlled power supplies to prevent excessive current increases.
To exacerbate the problem, it has been found that various benefits accrue including increases in efficiency as the plasma temperature is increased in the plasma chamber. It is therefore desirable to produce high temperature plasmas that have low resistances and that require the use of power supplies that operate in a controlled manner to prevent the generation of excessive currents. The high power required to produce the desired plasma temperatures places extreme demands on the power supply. For example, the power handling capabilities of switches and other electrical components must be increased to meet such high power specifications.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages the limitations of the prior art by providing a current controlled power supply that produces direct current pulses having alternating polarities to generate high temperature plasmas. A single power source, multiple power sources and/or multiple electrodes can be employed in accordance with the present invention.
The present invention therefore may comprise an apparatus for generating a pulsed direct current having alternating polarities to be applied to a plasma chamber to generate plasmas comprising, a power source that generates a substantially constant supply of direct current, current connections for delivering the pulsed-direct current to the plasma chamber, and current reversing switches having at least two pre-determined positions, the current reversing switches coupled to the power source and the current connections that cause the substantially constant supply of the direct current to flow in a first direction through the current connections whenever the current reversing switches are set in a first pre-determined position, and in a second direction through the current connections whenever the current reversing switches are set in a second pre-determined position.
The present invention may also comprise a method of generating a source of pulsed current having alternating polarities for use in generating a plasma comprising the steps of, generating a substantially constant supply of current from a current controlled power source, and switching current flow direction of the substantially constant supply of current to be supplied to said plasma using flow reversing switches that produce the source of pulsed current having alternating polarities f
Christie David J.
Scholl Richard A.
Advanced Energy Industries Inc.
Bettendorf Justin P.
Santangelo Law Offices P.C.
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