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       Session PS-FrM

Paper PS-FrM6
Characterization of Mass-Filtered CF@sub x@@super +@ Ion Beams for Surface Studies of Etching

Friday, November 2, 2001, 10:00 am, Room 104

Session: Diagnostics III
Presenter: M.J. Gordon, California Institute of Technology
Authors: M.J. Gordon, California Institute of Technology
K.P. Giapis, California Institute of Technology
Correspondent: Click to Email
Many ion beam systems used to probe plasma-surface interactions during etching are unable to deliver the tunable energy and high particle flux conditions that are typical of realistic processing plasmas. Some of the problems include inefficient ion production, space charge spreading of the beam resulting in very low fluxes, and a fixed plasma potential that requires the sample to be offset from ground in order to vary the beam energy. Furthermore, mass-filtering of the ion beam is required if the reaction dynamics of specific plasma species are to be understood. To create an improved ion source for etching studies, we have developed a mass-filtered ion beam system based on extraction of ions from an inductively coupled plasma (ICP) discharge. In our system, ions are extracted from an ICP discharge (13.56 MHz) using an accel-decel lens arrangement and injected into a transport line floating at -15 kV. The ion beam is mass filtered at high voltage using a magnetic sector, focused, and then decelerated to impinge on a grounded sample. Similar to biasing a wafer, capacitively coupled RF (15-30 MHz) from an auxiliary electrode is used to vary the ICP plasma potential and hence, vary the ion beam energy. Mass-filtered ion currents after focusing that approach 1 mA/cm@super 2@ can be obtained due to high ion densities in the ICP and beam transport at high voltage to avoid space charge spreading. This talk will focus on ion source design and beam characterization experiments for CF@sub x@@super +@ species extracted from ICP etching plasmas. The dependence of CF@sub 2@@super +@/CF@sub 3@@super +@ beam currents and ion energy distribution functions (IEDF's) on plasma pressure (1-10 mT) and RF inductive power (50-500W) were measured using a hemispherical energy analyzer located downstream of the sector magnet. In addition, the effect of capacitive RF bias power and frequency (15-30 MHz) on the plasma potential was investigated by monitoring the shift in the beam IEDF.