Systems, methods, and apparatus for minimizing cross coupled wafer surface potentials

摘要

This disclosure describes systems, methods, and apparatus for reducing a DC bias on a substrate surface in a plasma processing chamber due to cross coupling of RF power to an electrode coupled to the substrate. This is brought about via tuning of a resonant circuit coupled between the substrate and ground based on indirect measurements of harmonics of the RF field level at a surface of the substrate. The resulting reduction in DC bias allows a lower ion energy than possible without this resonant circuit and tuning thereof.

主权项

1. A system for reducing a DC voltage on a substrate of a plasma processing chamber below a minimum otherwise established by cross-coupling from an RF power source, the system comprising:
an RF field level sensor configured to be arranged adjacent to, but not touching, a substrate being processed in the plasma processing chamber; a harmonics filter configured to:
couple to one or more RF power sources for a plasma processing chamber;receive a primary RF frequency from the one or more RF power sources;receive RF field level measurements from the RF field level sensor; andpreclude the passage of measurements of at least the primary RF frequency; a first tunable resonant circuit configured to couple between the substrate and ground; a surface voltage minimum tracker coupled to the harmonics filter and configured to:
receive measurements from the harmonics filter other than those of at least the primary RF frequency; anddetermine whether the first resonant circuit is to be tuned to a higher or lower resonant frequency in order to minimize the measurements from the harmonics filter; and a controller circuit coupled between the surface voltage minimum tracker and the first resonant circuit and configured to generate one or more control signals to increase or decrease a first resonant frequency of the first resonant circuit based on instructions from the surface voltage minimum tracker.