Frequency tuning for pulsed radio frequency plasma processing

#The present application for patent is a continuation of U.S. Non-Provisional application Ser. No. 15/403,021, entitled “FREQUENCY TUNING FOR PULSED RADIO FREQUENCY PLASMA PROCESSING” filed Jan. 10, 2017, which is a continuation of U.S. Non-Provisional application Ser. No. 14/320,268, entitled “FREQUENCY TUNING FOR PULSED RADIO FREQUENCY PLASMA PROCESSING” filed Jun. 30, 2014, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.

#The present disclosure relates generally to pulsed radio frequency power. In particular, but not by way of limitation, the present disclosure relates to systems, methods and apparatuses for frequency tuning a power generation system for igniting and sustaining a plasma load in a plasma processing chamber.

#Plasma processing of a substrate often calls for radio frequency (RF) power to be used to sustain the plasma, and sometimes this RF power is provided in a pulsed envelope. During each pulse, frequency tuning of the RF power can be used to optimize power delivery (e.g., by impedance matching). Existing tuning algorithms call for the tuned frequency at the end of a pulse to be used at the start of a subsequent pulse. Yet, the tuned frequency at an end of a pulse is often not well-tuned at the start of a subsequent pulse, leading to a large impedance mismatch at a start of many pulses. This impedance mismatch can disrupt processing recipes or even damage the substrate being processed.

#Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by referring to the following detailed description and to the appended claims when taken in conjunction with the accompanying drawings:

#FIG. 1 illustrates a power generation system providing pulsed RF power to a plasma chamber via a matching network, where the pulsed RF power uses a fixed initial RF frequency at a start of each pulse.

#FIG. 2 illustrates the impedance mismatch that can result when traditional frequency tuning methods are used.

#The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

#For the purposes of this disclosure, “pulsed RF power” is RF power having a power envelope that is pulsed. In other words, multiple periods of RF power are delivered, followed by a period of no power, followed by another set of period of RF power (or a pulse).

#To avoid the impedance mismatch that the prior art sees at the start of many pulses, this disclosure describes systems, methods, and apparatus where an initial RF frequency at the start of each pulse is dictated not by the tuned frequency at an end of a preceding pulse, but by a fixed value that remains the same from pulse to pulse. Further, this initial RF frequency can be determined prior to a processing run using a dummy substrate or other means. While this fixed initial RF frequency will still see some impedance mismatch at the start of each pulse due to unavoidable variations at the start of any pulse, the mismatch will on average be far less than seen in the prior art (e.g., compare FIGS. 2 and 3).