Frequency tuning for dual level radio frequency (RF) pulsing

A method for processing a substrate using a dual level pulsed radio frequency (RF) plasma, comprising:

• alternately providing RF energy to a plasma in a process chamber at a first power level and a second power level, wherein the first and second power levels are different and non-zero, wherein the RF energy provided at the first power level has a first frequency and is provided for a first period of time, wherein the RF energy provided at the second power level has a second frequency and is provided for a second period of time;
• tuning the first frequency of the RF energy during the first period of time and the second frequency of the RF energy during the second period of time to reduce a reflected power of the RF energy and storing a last known tuned value of the first frequency and the second frequency;
• and
• when switching between power levels, setting an initial frequency of the RF energy to the last known tuned value of the first frequency or the second frequency.

A method for processing a substrate using a dual level pulsed radio frequency (RF) plasma, comprising:

• providing RF energy having a first frequency and a first power level for a first period of time to a plasma formed in a process chamber, wherein the first power level is non-zero;
• during the first period, tuning the first frequency to a first tuned frequency to minimize RF power reflected from the plasma;
• subsequently providing RF energy having a second frequency and a second power level for a second period to the plasma, wherein the second power level is non-zero and different than that first power level;
• during the second period, tuning the second frequency to minimize RF power reflected from the plasma;
• and
• subsequently providing RF energy having the first tuned frequency and the first power level for a third period to the plasma.