Systems and methods for use of low frequency harmonics in bias radiofrequency supply to control uniformity of plasma process results across substrate

Abstract

First, second, third, and fourth radiofrequency (RF) signal generators generate first, second, third, and fourth RF signals, respectively, having first, second, third, and fourth frequencies, respectively. The second and third frequencies are different specified harmonics of the first frequency. The fourth frequency is at least two orders of magnitude larger than the first frequency. An impedance matching system controls impedances for the first, second, third, and fourth RF signal generators. A control module is programmed to control: A) a first phase difference between the first and second RF signals, B) a second phase difference between the first and third RF signals, C) a first voltage difference between the first and second RF signals, D) a second voltage difference between the first and third RF signals. The first and second phase differences and the first and second voltage differences collectively control a plasma sheath voltage as a function of time.