ION ENERGY BIAS CONTROL APPARATUS
This disclosure describes systems, methods, and apparatus for operating a plasma processing chamber. In particular, a periodic voltage function combined with an ion current compensation can be provided as a bias to a substrate support as a modified periodic voltage function. This in turn effects a DC bias on the surface of the substrate that controls an ion energy of ions incident on a surface of the substrate. A peak-to-peak voltage of the periodic voltage function can control the ion energy, while the ion current compensation can control a width of an ion energy distribution function of the ions. Measuring the modified periodic voltage function can provide a means to calculate an ion current in the plasma and a sheath capacitance of the plasma sheath. The ion energy distribution function can be tailored and multiple ion energy peaks can be generated, both via control of the modified periodic voltage function.
1 . A plasma processing apparatus comprising:
a substrate support bias supply providing a periodic voltage function;
an ion current compensation component providing an ion current compensation that is combined with the periodic voltage function to form a modified periodic voltage function that is provided to the substrate support and thereby effects a DC voltage on a surface of the substrate opposite to the substrate support, which in turn controls an ion energy of ions incident on the surface of the substrate opposite to the substrate support, the modified periodic voltage function having:
a first portion comprising a rapidly increasing voltage;
a second portion comprising a substantially constant voltage; and
a third portion comprising:
a sloped voltage having a starting voltage that is a voltage step, ΔV, below the substantially constant voltage, the voltage step, ΔV, corresponding to the ion energy, and a slope, dV 0 /dt, controlled by the ion current compensation; and
a controller to control ion current, I I , as a function of the effective capacitance, C 1 , and the slope, dV 0 /dt.