AVS 51st International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThA

Paper PS-ThA2
Mechanisms of Etching in the Presence of Depositing Species: Molecular Dynamics Simulations of Silicon Etching in Fluorocarbon Plasmas

Thursday, November 18, 2004, 2:20 pm, Room 213A

Session: Plasma-Surface Interaction
Presenter: J.J. Vegh, University of California, Berkeley
Authors: J.J. Vegh, University of California, Berkeley
D. Humbird, University of California, Berkeley
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
The fundamental mechanisms of plasma etching in the presence of depositing species, a very common situation in industrial practice, remains poorly understood at the atomistic level. Recent MD simulations of silicon etching in the presence of small FC ions and neutral radicals, F atoms, and Ar@super +@ have consistently failed to reproduce experimental observations of simultaneous Si etching and the presence of relatively thick FC film on the surface. Simulations of FC film formation alone, without Si etching, can easily be observed with small unsaturated FC ions at energies below about 100 eV, and thermal CF and CF@sub 2@ are observed to deposit alone or in the presence of low energy ion bombardment (@<=@50 eV). Si etching is observed in the presence of higher energy ions, especially Ar@super +@, and most readily in the presence of thermal F. However, the combination of significant Si etch, coupled with dominant FC signal in simulated surface XPS measurements, has proven elusive using only small FC species. Even at relatively high neutral to ion ratio (e.g. 90:9:1 CF/F/Ar@super +@), only a thin FC film develops during Si etch, and the XPS is dominated by the C-C/Si peak. We conclude that simultaneous FC film and Si etch requires heavier, unsaturated FC neutrals and/or ions. These large, polymeric species are created by ion impact or neutral F attack within a deposited FC film. In other words, the FC film can be etched in the form of large products that redeposit on the surface to maintain the film. We demonstrate that simultaneous FC film and Si etch requires that the FC film have minimal cross-linking and be relatively weakly bound to the surface. We highlight the role of ion impact in locally removing substantial amounts of FC film material, exposing the underlying Si to etch species.