Wave transmission lines and networks – Automatically controlled systems – Impedance matching
Reexamination Certificate
1999-11-30
2002-07-23
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Automatically controlled systems
Impedance matching
C333S032000
Reexamination Certificate
active
06424232
ABSTRACT:
COPYRIGHT NOTICE
Contained herein is material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of the patent disclosure by any person as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all rights to the copyright whatsoever.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of impedance matching networks. More specifically, the present invention relates to a method and apparatus for matching the impedance of a load with the internal impedance of a radio frequency (RF) power generator to provide maximum power transfer, where the frequency of the applied voltage generated by the RF power generator and the impedance of the load may independently vary.
2. Description of the Related Art
The Federal Communications Commission (FCC) has designated Industrial, Scientific and Medical (ISM) frequencies at 13.56 MHz, 27.12 MHz and 40.68 MHz, respectively, and other higher frequencies. ISM frequencies may be radiated by equipment into the atmosphere without concern for causing radio frequency disturbances to other equipment. A power density as governed by FCC and CE mark must still be met. Plasma etch and deposition equipment manufacturers have traditionally used the 13.56 MHz frequency to operate a plasma chamber for manufacturing integrated circuits and plasma displays. However, ISM frequencies do not always provide an optimum frequency at which to operate a plasma chamber to achieve critical process steps, especially in view of decreasing integrated circuit dimensions. As a result, equipment manufacturers have developed plasma chambers that are capable of operating over a range of frequencies.
ISM-based RF power generators, however, are commonly designed to assure minimum deviation from a set ISM frequency, e.g., 13.56 MHz. In contrast, a variable frequency RF power generator (“generator”) may be coupled to a load, e.g., a plasma chamber, to manipulate the frequency of the voltage applied to the load so that the load may be operated over a range of voltages and frequencies. However, in an alternating current (AC) circuit, impedance is affected by the frequency of the applied voltage, which impedance, in turn, affects the transfer of power between the generator and the load. Moreover, the impedance of a plasma chamber may vary independent of the frequency of the applied voltage depending on such variables as chamber pressure, gas composition, and plasma ignition. What is needed, therefore, is an impedance matching network that allows the frequency of the applied voltage to vary while maintaining the impedance of the load with respect to the generator, i.e., the impedance that the generator will see.
As is well known to those of ordinary skill in the related art, impedance for a given circuit may be comprised of both a resistive component and a reactive component, the latter of which may be either inductive or capacitive. Maximum power transfer between a generator and an attached load is achieved when the resistance of the load is equal to the internal resistance of the generator and the net reactance between the load and generator is zero. Thus, it is advantageous to counterbalance the reactance between the generator and the load to achieve a net reactance of zero. A net reactance of zero between the generator and load occurs when the impedance of the load is the complex conjugate of the internal impedance of the generator. Thus, if the generator has an inductive reactance, then a load that has a capacitive reactance of equal magnitude and opposite phase will result in a net reactance of zero to the circuit comprising the generator and the load, and vise versa. An impedance matching network may be utilized to maintain an input impedance that is the complex conjugate of the internal impedance of the generator as the frequency of the voltage applied by the generator to the load varies, and/or as the impedance of the load varies, so that maximum power transfer occurs between the generator and the load.
With reference to
FIG. 1
, a prior art impedance matching network
100
is illustrated. A RF power generator can be coupled to RF input
120
. A load such as a plasma chamber can be coupled to RF output
130
. The impedance matching network
100
(“network”) comprises a phase detector
101
that samples the transmission line
108
at a fixed impedance, e.g., 50 ohms, and generates a signal over line
112
to control board
110
. Control board
110
then causes servo motor
107
to turn variable capacitor
106
, depending on the polarity of the phase shift between the input RF voltage and current caused by a non-linear impedance in the load, e.g., as occurs under ignited plasma conditions in a plasma chamber.
Magnitude detector
109
also samples the deviation from an impedance of, e.g., 50 ohms, on transmission line
108
, and generates a signal over line
111
to control board
110
based thereon. Control board
110
then causes servo motor
103
to turn variable capacitor
102
. The capacitance provided by capacitor
102
is also dependent, to a lesser extent, on the polarity of the phase shift between the RF voltage and current. The magnitude detector
109
detects the deviation from a characteristic impedance of, for example, 50 ohms. If the impedance in line
108
is greater than 50 ohms, the signal transmitted over line
111
is positive, and if the impedance in line
108
is less than 50 ohms, the signal transmitted over line
111
is negative. As can be seen, the prior art impedance matching network
100
is relatively slow because of the time needed for servo motors
103
and
107
to turn capacitors
102
and
106
, respectively, to match the impedance of the generator with the impedance of the load. Moreover, the network
100
does not change the frequency of the applied voltage as may be desired depending on the load. It should be noted that
FIG. 1
illustrates the so called L-match version of the prior art impedance matching network
100
. However, the network applies equally to the II-version of the matching network architecture.
Today, semiconductor and flat panel plasma display equipment manufacturing process times are decreasing, such that the amount of time required to establish matching impedance between an RF power generator and a plasma chamber (whose impedance varies) is a limiting factor affecting throughput on the manufacturing line. What is needed is an impedance matching network coupling a generator to a load, e.g., a plasma chamber, that allows the generator to vary the frequency of the voltage applied to the load and utilizes fixed solid state components to rapidly and accurately adjust the input impedance of the attached load to maintain maximum power transfer to the load.
BRIEF SUMMARY OF THE INVENTION
The present invention is related to the field of impedance matching networks. More specifically, the present invention relates to a method and apparatus for matching the variable impedance of a load with the fixed internal impedance of a radio frequency (RF) power generator (“generator”) to provide maximum power transfer to the load, where the frequency of the applied voltage generated by the RF power generator and the impedance of the load may independently vary. The impedance matching network allows a generator to vary the frequency of the voltage applied to a load, for example, a plasma chamber, as may be utilized in semiconductor or flat panel plasma display manufacturing processes, antenna tuning in transmitters, etc. The impedance matching network further utilizes fixed solid state components to adjust, within milliseconds, the input impedance of the attached load to accomplish maximum power transfer to the load. A means for varying the frequency of the applied voltage and a parallel switched capacitor network for very quickly matching the input impedance of the load with the impedance of the generator is used.
REFERENCES:
patent: 2981902 (1961-04-01), Familier
patent: 5195045 (1993-03-01), Keane et al.
p
Lozic Tomislav
Mavretic Anton
Advanced Energy's Voorhees Operations
Jones Stephen E.
Lee Benny
LandOfFree
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