Plasma Science in Development of industrial Etching and Depostion Tools: The Presence of Normal Modes Above a Capacitive Plasma Applicator

Capacitively-coupled plasma glow discharges are extensively used for materials processing
in numerous industrial applications, and microelectronics fabrication in particular. Considerable
research has been performed on plasma sheaths and standing waves over a capacitive applicator
which typically holds the processed substrate (e.g., a semiconductor wafer). Normal modes of
standing waves in the plasma potential, Vp, have been observed over the entire surface of a dualfrequency
capacitive applicator immersed in an inductively-generated rf glow discharge. An
emissive probe used to measure the plasma potential is located 0.95 cm above the applicator and
moved by a two‐dimensional drive system. The heater current to the probe is switched off during
the 100 μs measurement to eliminate uncertainties due to the heater voltage. Vp is mapped at 208
spatial locations and digitized at 1 GHz. An electrically floating probe is located 1.84 cm above the
center of applicator to afford a means to generate correlation functions for the detection of waves
in the low temperature plasma. The observed normal modes in potential exist at several
frequencies and can be expressed as summations of Bessel functions much like the vibrational
modes in circular membranes and plates. The modes are most likely excited by the oscillations of
the plasma‐sheath interface including harmonic oscillations arising from the nonlinear
mechanisms governing the sheath dynamics. As the frequency is increased, the order of the
normal modes is postulated to increase as these modes are likely determined by the impedance
terminating conditions on the chamber surfaces. The implications of these observations on
industrial plasma equipment will be discussed.
Dr. Michael S. Barnes started his career at IBM developing plasma processing technology
for manufacture of semiconductor integrated circuits. He then joined Lam Research Corp. and
Applied Materials, Inc. leading the development of new plasma etch and plasma chemical vapor
deposition (CVD) products that have since generated billions of dollars in revenues. More recently
Dr. Barnes was General Manager for High Density Plasma CVD at Novellus Systems, Inc., and is
now Chief Technical Officer of Intevac, Inc., a leading supplier of plasma equipment for
manufacturing hard disk drives and semiconductor integrated circuits. He is inventor on over 75
patents and served on the National Research Council Plasma Sciences Committee. Dr. Barnes
received his B.S., M.S., and Ph.D. in Electrical Engineering from The University of Michigan.