Surface charge and power feedback and control using a switch mode bias system

An apparatus for providing a voltage comprising:

• a power supply configured to provide an asymmetric periodic voltage function to an output configured to couple to a substrate support, the asymmetric periodic voltage function having a positive voltage ramp, a first negative voltage ramp, and a second negative voltage ramp, having a duration, t2, between the first negative voltage ramp and a next positive voltage ramp;
• the power supply including a means to obtain a measure of ion current in a plasma processing chamber based upon monitoring of at least one of current or voltage during the duration, t2;
• the power supply including a means to obtain an estimate of surface charge accumulation, Qi, on a substrate held by the substrate support as a function of the ion current and the duration, t2;
• and
• the power supply comprising a controller configured to adjust the duration, t2, to achieve a desired surface charge accumulation, Qi, or to keep the surface charge accumulation, Qi, below a threshold.

A non-transitory, tangible processor readable storage medium, encoded with processor executable code to perform a method for providing a voltage, the method comprising:

• biasing a substrate in a plasma processing chamber, a waveform of the biasing comprising:
• (1) periodic positive pulses, and (2) a linearly decreasing voltage between each of the positive pulses, lasting for a duration, t2, and having a rate of decrease, dv/dt;
• calculating an ion current, II, from current measurements of the waveform during the duration, t2, or from the rate of decrease, dv/dt;
• calculating surface charge accumulation, Qi, that builds up during the duration, t2, from the ion current, II;
• comparing the surface charge accumulation, Qi, to a first threshold;
• and
• changing the duration, t2, when the surface charge accumulation, Q1, meets or exceeds the first threshold.