Monitoring Sheath Voltages and Ion Energies in High-Density Plasmas Using Noninvasive Radio-Frequency Current and Voltage Measurements

Abstract

To obtain optimal results from plasma processing, the energy of ions incident on substrate wafers must be carefully controlled. Such control has been difficult to achieve, however, because no practical method exists for monitoring the energy distributions of ions at a wafer surface during processing. To solve this problem, we have developed a noninvasive, model‐based method for determining ion energy distributions (IEDs) that is suitable for use during actual processing in commercial plasma reactors. The method was validated by tests performed in argon and CF4 discharges at 1.3–3.1 Pa (10–23 mTorr) in an inductively coupled, high‐density plasma reactor, with radio‐frequency (rf) substrate bias at frequencies of 0.1 MHz to 20 MHz. Plasma potential waveforms and sheath voltages obtained from the noninvasive rf technique agreed well with independent measurements made using a capacitive probe. Ion energy distributions from the rf technique were in good agreement with distributions measured by ion energy analy...