Lam Research : Patent Issued for Systems and Methods for Tuning an Impedance Matching Network in a Step-Wise Fashion for Multiple States of an RF Generator (USPTO...
Patent Issued for Systems and Methods for Tuning an Impedance Matching Network in a Step-Wise Fashion for Multiple States of an RF Generator (USPTO 9711332)
The assignee for this patent, patent number 9711332, is
Reporters obtained the following quote from the background information supplied by the inventors: "Plasma systems are used to control plasma processes. A plasma system includes multiple radio frequency (RF) sources, an impedance match, and a plasma reactor. A workpiece is placed inside the plasma chamber and plasma is generated within the plasma chamber to process the workpiece. It is important that the workpiece be processed in a similar or uniform manner. To process the workpiece in a similar or uniform manner, it is important that the RF sources and the impedance match be tuned.
"It is in this context that embodiments described in the present disclosure arise."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Embodiments of the disclosure provide apparatus, methods and computer programs for tuning an impedance matching network in a step-wise fashion for multiple states of a radio frequency (RF) generator. It should be appreciated that the present embodiments can be implemented in numerous ways, e.g., a process, an apparatus, a system, a piece of hardware, or a method on a computer-readable medium. Several embodiments are described below.
"In a pulsing plasma system, e.g., a plasma system in which plasma that is generated or maintained by a pulsed RF signal that is generated by the RF generator, etc., a pulsing plasma has one set of RF powers in one state, e.g., S1, etc., and a second set of RF powers in a second state, e.g., S2, etc. Because the RF pulsing times are short, e.g., pulsing repetition rate is typically 100 hertz (Hz) to 10 kilohertz (kHz), etc., a motor driven variable capacitor of an impedance matching network cannot respond to the pulses of the RF signal and the variable capacitor is set to a compromise value that is the same for both the states.
"Some advantages of the herein described systems and methods include applying the step-wise fashion in which to tune a variable capacitance of the impedance matching network. In the step-wise fashion, during the state S1, an optimum value of an RF frequency of an RF signal generated by the RF generator for the state S1 and an optimum value of a combined variable capacitance of an impedance matching network for which a combination of voltage reflection coefficients for the states S1 and S2 at an input of a model system is minimum is calculated. Moreover, a local value of the RF frequency is determined for which the voltage reflection coefficient for the state S1 is a minimum. Furthermore, during the state S2, an optimum value of an RF frequency of the RF signal generated by the RF generator for the state S2 is calculated. Moreover, a local value of the RF frequency is determined for which the voltage reflection coefficient for the state S2 is a minimum. Instead of applying the optimum value of the combined variable capacitance, a step value of the combined variable capacitance is applied to the impedance matching network. The step-wise fashion is then repeated using the step value, the local value of the RF frequency for the state S1, and the local value of the RF frequency for the state S2 to apply another step value of the combined variable capacitance. The step value is incremented until an optimum value of the combined variable capacitance is reached. It is difficult to achieve an optimum value of the combined variable capacitance directly from a value at which the impedance matching network is operating at the same time an optimal value of the RF frequency is achieved. This is because it is difficult to control one or more variable capacitors of the impedance matching network with the same speed as that of controlling the RF generator. By using the step-wise fashion, optimal values of the variable capacitance and of the RF frequency are achieved.
"Further advantages include tuning to a compromise optimum value that has other than zero reflected power. For example, when plasma is pulsed between multiple states, a radio frequency of the RF signal that is generated by the RF generator changes quickly to have different values in the pulsing states, but a variable capacitor of an impedance matching circuit cannot. There are three variable parameters, e.g., an RF frequency of the RF signal in the state S1, an RF frequency of the RF signal in the state S2, and a position of a variable capacitor of the impedance matching network, etc., to tune four quantities, e.g., the real and imaginary parts of reflection coefficients in the state S1 and S2, etc. It is difficult to simultaneously achieve zero reflected power for both the pulsing state S1 and S2 so the compromise optimum value of a reflection coefficient is achieved for both the states S1 and S2. To obtain an optimum compromise, e.g., minimizing a quantity A*.GAMMA.(S1)+(1-A)*.GAMMA.(S2), where .GAMMA.(S1) and .GAMMA.(S2) are voltage reflection coefficients for the pulsing state S1 and S2, and A is a coefficient between 0 and 1, etc., a model system is used to find the position of the variable capacitor, and the two RF frequencies for the optimum compromise.
"Other aspects will become apparent from the following detailed description, taken in conjunction with the accompanying drawings."
For more information, see this patent: Howald, Arthur M.; Valcore, Jr., John C.; Fong, Andrew; Hopkins,
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