| AVS 55th International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1-WeM |
| Session: | Plasma-Surface Interactions in Materials Processing I |
| Presenter: | F.L. Buzzi, University of Wisconsin-Madison |
| Authors: | F.L. Buzzi, University of Wisconsin-Madison Y.H. Ting, University of Wisconsin-Madison A.E. Wendt, University of Wisconsin-Madison |
| Correspondent: | Click to Email |
Ion bombardment provides a key benefit in plasma etching for microelectronics fabrication and other materials processing applications. A sheath electric field accelerates ions into the substrate so they strike at normal incidence, contributing energy and reactive species to enable anisotropic etch profiles. The energy of the bombarding ions is a significant parameter, and is typically controlled coarsely by adjusting the time-averaged sheath voltage through the application of a sinusoidal bias voltage to the substrate electrode. The sinusoidal voltage waveform produces a broad “bimodal” ion energy distribution (IED) at the substrate, with two ion flux maxima, at respective energies considerably above and below the average. In order to deconvolve the effect of ions of multiple energies bombarding the substrate simultaneously, we have manipulated the waveform of the bias voltage to produce two ion flux maxima. By systematically tailoring the shape of the waveform, the energies and relative fluxes of the two IED peaks are varied independently over a 100 to 500 eV range in a fluorocarbon-based helicon plasma, while silicon dioxide and photoresist etch rates are monitored. Fluorocarbon plasmas create a competition between deposition and etching on the substrate surface, so that with a single IED peak at 100 eV, net deposition is observed, while etching with a monotonically increasing etch rate is observed for a single peak in the 200 to 500 eV range. Two experiments were conducted in which a 100 eV IED peak was combined with a higher energy peak, varying the energy and relative flux of the high energy peak, respectively. In both cases, a relatively small contribution of high energy ions clearly leads to considerable etch rate enhancement, higher than predicted by a linear combination of single peak etch rates at the two energies. We attribute this to the effect of high energy ion bombardment on the chemical composition at the substrate surface, altering the competition between etching and deposition. When net deposition is suppressed, 100 eV ions will interact with the underlying substrate to more effectively enhance etching. The etch rate data provide evidence that for the process examined, a high energy group of ions, comprising as little as 25% of the total flux. produces this suppression, enabling lower energy ions to contribute to etching reactions. These results highlight the significance of the shape of the IED on plasma process outcomes.