LIF measurement of Ar+ motion above a biased wafer in a plasma etching reactor

We studied the motions and energy distribution of argon ions in an inductively coupled plasma (ICP) etching tool, by the method of laser induced fluorescence (LIF). The silicon wafer clamped to a chuck at the bottom of the chamber was biased with a 1 MHz 1–1.2 kV peak-to-peak sinusoidal voltage. The plasma is formed with a 2 MHz ICP coil pulsed at 10 Hz. Sheath thickness was measured at different phases of the bias waveform. Ion energy distribution functions and the two-dimensional flow pattern were studied near the center and edge of the wafer, with / without wafer bias, at different switch-on time of wafer bias. Significant vortex flows were observed near the wafer edge. Experiments in which the wafer was biased in the plasma afterglow resulted in a narrow distribution of ion energy close to the bias voltage at the vicinity of the wafer, and the ion incident angle on the wafer was the smallest.