Measurements and modeling of ion energy distributions in high-density, radio-frequency biased CF4 discharges

Abstract

Models of ion dynamics in radio-frequency (rf) biased, high-density plasma sheaths are needed to predict ion bombardment energies in plasma simulations. To test these models, we have measured ion energy distributions (IEDs) in pure CF4 discharges at 1.33 Pa (10 mTorr) in a high-density, inductively coupled plasma reactor, using a mass spectrometer equipped with an ion energy analyzer. IEDs of CF3+, CF2+, CF+, and F+ ions were measured as a function of bias frequency, bias amplitude, and inductive source power. Simultaneous measurements by a capacitive probe and a Faraday cup provide enough information to determine the input parameters of sheath models and allow direct comparison of calculated and measured IEDs. A rigorous and comprehensive test of one numerical sheath model was performed. The model, which includes a complete treatment of time-dependent ion dynamics in the sheath, was found to predict the behavior of measured IEDs to good accuracy over the entire range of bias frequency, including complicated effects that are observed when the ion transit time is comparable to the rf bias period.

Ion energy distribution measurements in rf and pulsed dc plasma discharges

“…The characteristic frequency of the damping is the ion plasma frequency ω i . For consistency with other models Soblewski et al [29] have also derived their expression in terms of τ i . The result of [29], expressed in terms of the variables defined in this paper, is…”

“…An analytical expression for E for all values of τ i /τ rf is also given by Sobolewski et al [29] which uses the rf sheath model described in [37]. This model is solved in terms of the ion plasma frequency at the sheath edge rather than the ion transit time.…”

“…The IEDF generated by an oscillating, collisionless rf sheath has been solved analytically by a number of authors [28][29][30].…”

“…In section 2 the experimental setups are described. In section 3 a simple circuit model of the rf CCP discharge, similar to that used by Kohler et al [26,27], is introduced and a number of analytical models of the IEDF in rf sheaths [28][29][30] are summarized. These models are combined with the measured IEDFs in the CCP reactor to estimate other important plasma parameters.…”

Challenges of Tailoring Surface Chemistry and Plasma/Surface Interactions to Advance Atomic Layer Etching

“…In the recent past, the focus of plasma etch equipment has been on the ability to minimize damage and/or increase etch pattern fidelity by means of either tailoring ion energy distributions or reducing the average electron temperature of the plasma. For example, early work by Sobolewski 7 and Wendt 8 demonstrated the ability to modify ion energy distribution functions via plasma frequency or pulsed DC bias modulation to enable ion extraction with either narrow or broad energy distributions. This work was further expanded upon with the exploration of multi-frequency drive electrodes, 9,10 the inclusion of DC superposition [DCS] 11,12 and/or more elaborate plasma pulsing combinations of both source and/or bias powers to reduce ion energy and/or enable charge balance.…”