AVS 50th International Symposium
    Plasma Science and Technology Friday Sessions
       Session PS-FrM

Paper PS-FrM7
Molecular Dynamics Simulations of Silicon in Fluorocarbon Plasmas: Role of the Fluorocarbon Film as an Etchant Source

Friday, November 7, 2003, 10:20 am, Room 315

Session: Plasma-Surface Interactions: Etching
Presenter: D. Humbird, University of California at Berkeley
Authors: D. Humbird, University of California at Berkeley
D.B. Graves, University of California at Berkeley
X. Hua, University of Maryland, College Park
G.S. Oehrlein, University of Maryland, College Park
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We use MD simulations to examine fluorocarbon (FC) ions and radicals impacting Si and compare these simulations to new experimental results. During FC plasma etching of Si, Oehrlein and coworkers observe changes in surface chemistry as ion energy is increased above the threshold necessary for etching, and/or when a large fraction of the impinging ions are Ar@super +@. The F/C ratio of the film decreases and Si-C, C-C, and Si-F bonds all increase in number with the onset of etching. These results were interpreted to mean that F is driven from the FC film into the underlying Si, creating etch products. In simulations of Si etching with CF@sub x@@super +@ species with and without Ar@super +@, we observe a change in the composition of the FC film as the ion energy increases from a depositing to an etching level. The FC film formed at lower energy is comprised almost entirely of C-F@sub x@ groups. At higher energy (>50 eV), Si etching commences, C-F@sub x@ groups are greatly reduced, and SiF@sub x@ bonds form. The FC film becomes stratified, with Si-C at the surface of the film, and Si-F (the etch precursor) underneath. These results are in excellent agreement with XPS measurements of Si samples etched by FC plasmas. Oehrlein and co-workers concluded from their measurements that the FC film contains the etchant F. The simulations confirm that F can reach the Si by way of the FC film. We identify the mechanisms for ion-induced redistribution of F between the FC film and substrate.