AVS 46th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS+SS-WeA

Paper PS+SS-WeA6
Deposition and Etching Using Fluorocarbon Ions: Molecular Dynamics Simulations

Wednesday, October 27, 1999, 3:40 pm, Room 612

Session: Ion-Surface Interactions II
Presenter: C.F. Abrams, University of California, Berkeley
Authors: C.F. Abrams, University of California, Berkeley
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
SiO@sub 2@ etch processes use fluorocarbon (FC) plasmas to achieve selectivity to Si, SiN, and photoresist. FC plasmas deposit films which slow the etching of these surfaces compared to SiO@sub 2@. Further etch process optimization hinges on understanding these films. Specifically, the mechanisms of Si etching through the FC overlayer remain matters of speculation. We used molecular dynamics simulations of FC ions impacting Si surfaces to understand this process. We developed a Si-C-F interatomic potential as an extension of our C-F potential.@footnote 1@ We simulated ion impacts at normal incidence onto a:Si surfaces up to fluences of 4x10@super 16@ cm@super -2@. We examined the effects of ion composition (CF@sub x@ for x=1,2,3) and incident energy (50 @<=@ E@sub i@ @<=@ 200 eV). At low fluences, all ions deposit FC overlayers with significant Si incorporation. We found that CF ions result in net CF@sub x@ deposition, while CF@sub 3@ ions result in net Si etching with a steady-state overlayer thickness that increased with E@sub i@. For example, for 100 eV CF@sub 3@, we observed deposition of 2 equivalent monolayers of C up to a fluence of 4x10@super 15@ cm@super -2@, followed by Si etching (0.065 Si/ion) through a FC film with a steady thickness of 9.5 Å and F:C of 1.6. For CF@sub 2@, the resulting steady-state, deposition or Si etching, depended on E@sub i@, with deposition being favored at the lower energies. A striking result of the simulations is the dynamic character of the FC film during Si etching. Although the composition and thickness of the layer are unchanging at steady-state, F and C atoms are constantly depositing and then being etched by subsequent ion impacts. This `recirculation' of F and C through the overlayer appears to play a key role in Si etching. Mechanisms of both initial film deposition and steady-state etching by FC recirculation will be discussed. @FootnoteText@ @footnote 1@ J Tanaka, C F Abrams, D B Graves. Subm, 46th AVS Intl Sym, 1999.