AVS 56th International Symposium & Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS-ThP

Paper PS-ThP12
Tailoring of Substrate RF Bias Voltage Waveform for Arbitrary Energy Distributions of Bombarding Ions in Plasma Processing: Ion Energy Measurements

Thursday, November 12, 2009, 6:00 pm, Room Hall 3

Session: Plasma Science Poster Session
Presenter: X.V. Qin, University of Wisconsin-Madison
Authors: X.V. Qin, University of Wisconsin-Madison
Y.-H. Ting, University of Wisconsin-Madison
A.E. Wendt, University of Wisconsin-Madison
Correspondent: Click to Email
In plasma etching of semiconductors for integrated circuit fabrication, positive ions are accelerated by a sheath electric field directed towards the substrate, where, upon impact at normal incidence, they enhance etching to produce anisotropic feature profiles. Varying the amplitude of a sinusoidal bias voltage waveform applied to the substrate electrode may be used to coarsely control the average energy of bombarding ions through its affect on the dc component of the sheath voltage, but the sinusoidal waveform also produces a broad spectrum of ion energies under typical process conditions. A bias voltage waveform with its shape tailored for the purpose of producing ion energy distributions (IED) with one or two groups of ions with a narrow spread around selected energies has been previously utilized to highlight the significant role of the IED in fluorocarbon-based etching. Presented here are direct IED measurements made with an ImpedansTM retarding field energy analyzer situated on the biased electrode. Measurements in a 10 mTorr helicon argon plasma in which ion flux and ion energy at the substrate are independently controlled clearly demonstrate the ability to predictably produce arbitrary IEDs at the substrate by tailoring the shape of the bias voltage waveform. Results to be presented for sinusoidal (500 kHz-10 MHz) and tailored (500 kHz) waveforms are compared to predictions based on computation of ion trajectories through the sheath electric field (assumed to instantaneously follow the Child-Langmuir Law), in order to evaluate the accuracy and limitations of this method. For the sinusoidal waveform, the expected broad, bimodal IED is produced, with a reduction in IED width with increasing frequency in agreement with model predictions. Under conditions where the sheath transit time of the ions is short compared to the RF bias period and where ion motion in the sheath is collisionless, tailoring of the waveform produces one or two peaks in the IED, and in the latter case, the energies and relative fluxes of the two peaks can be varied independently through waveform shaping.
*Support from the Lam Research Corporation and the UW NSF MRSEC are gratefully acknowledged.