AVS 46th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS2-ThA

Paper PS2-ThA3
Method for Ion Energy and Ion Energy Distribution Functions Control at the Substrate during Plasma Processing

Thursday, October 28, 1999, 2:40 pm, Room 609

Session: Pulsed Plasmas
Presenter: S.-B. Wang, University of Wisconsin, Madison
Authors: S.-B. Wang, University of Wisconsin, Madison
A.E. Wendt, University of Wisconsin, Madison
Correspondent: Click to Email
A new method is proposed for control of ion energy and ion energy distribution functions (IEDF) at the substrate during plasma processing. In contrast to the conventional approach of applying a sinusoidal voltage of variable amplitude and frequency to the substrate electrode, the new technique has a variety of advantages and provides a much greater degree of energy control by instead using a specially tailored waveform consisting of a periodic pulse or short high frequency burst in combination with a slow ramp. This rather adaptable technique for controlling the ion energy distribution function has important implications for selectivity and feature profile control in plasma etching, as well as film quality in plasma enhanced chemical vapor deposition (PECVD). In addition, it can be used to non-invasively measure the ion energy flux bombarding the substrate, and, therefore, can serve as a real-time indicator for etching process control and a real-time monitor for the drifting of plasma conditions during plasma processing. A time-dependent spherical-shell plasma fluid model is used to simulate different bias voltage waveforms and different area ratios for powered and grounded electrodes, and thus demonstrate the mechanisms of this method in producing a narrow IEDF of precisely controlled energy, independent of ion mass. Experiments in a helicon plasma using this method of substrate bias confirm predictions of sheath voltage evolution. Taking plasma noise into consideration, an IEDF with a single peak and full width at half maximum of 8 eV is expected for a 20 mTorr argon plasma, independent of the value of DC self-bias.