Ion motion above a biased wafer in a plasma etch tool.

The behavior of ions in the plasma are essential to the process of industrial etching. We studied the motions and energy distribution of argon ions in a 2 MHz inductively coupled plasma (ICP) etching tool, by the method of laser induced fluorescence (LIF). The silicon wafer posited at the bottom of the machine can be biased with a 1 MHz 1.2 kV peak-to-peak sinusoidal voltage. The plasma is formed with a 2 MHz ICP coil which, along with the wafer bias, can be pulsed on and off within 50 microseconds.. The experiment compares the cases of ion motion with and without wafer bias. For both of these cases the two diemsional flow pattern of ions is studied near the center and edge of the wafer. Significant vortex flows are observed near the wafer edge. Experiments in which the wafer is biased in the afterglow, that is when the ICP is off, results in a narrow distribution of ion energy close to the bias voltage close to the wafer. The angles at which ions strike the wafer is smallest under these conditions. The results are compared to simulations using the Hybrid Plasma Equipment Model code.