Impact of Phase Shifted Coil Currents on Plasma Uniformity

Plasma etching at sub-3x-nm nodes requires inductively coupled plasma (ICP) reactors to work within tight uniformity constraints. The characteristic donut shape of the ICPs is, however, visible on the wafer in a 20-60 mTorr range due to reduced plasma diffusion. Phase shifting of the coil currents in an ICP source has been used to improve plasma uniformity. Images of plasma properties with and without phase shift of coil currents are presented.