AVS 49th International Symposium
    Plasma Science Thursday Sessions
       Session PS-ThA

Paper PS-ThA3
Profile Evolution During Fluorocarbon Plasma Etching of Low-k Porous Silica@footnote 1@

Thursday, November 7, 2002, 2:40 pm, Room C-103

Session: Dielectric Etch II
Presenter: A. Sankaran, University of Illinois at Urbana-Champaign
Authors: A. Sankaran, University of Illinois at Urbana-Champaign
M.J. Kushner, University of Illinois at Urbana-Champaign
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To achieve shorter RC-delay times in integrated circuits low-k dielectric materials are being investigated for interconnect wiring. Porous silica is a promising candidate. Profile evolution and maintenance of critical dimensions during plasma etching of porous silica are problematic due to the exposure of open pores. To investigate these issues, reaction mechanisms for fluorocarbon plasma etching of porous silicon-dioxide have been developed and incorporated into the Monte-Carlo Feature Profile Model (MCFPM) which was modified to address these two-phase systems. To focus on issues related to the morphology of porous materials, the porous silica in the model was treated as stoichiometric SiO@sub 2@. Pores are randomly distributed in the SiO@sub 2@ to have a specified average pore radius and volume fraction (porosity). Fluxes to the substrate were obtained from the Hybrid Plasma Equipment Model for inductively coupled plasmas sustained in CHF@sub 3@, C@sub 2@F@sub 6@ and C@sub 4@F@sub 8@. The surface reaction mechanisms for these chemistries were validated by comparison to experiments.@footnote 2@ Etch rates and tapering of high aspect ratio features were investigated as a function of bias voltage and diluents (e.g., Ar). We found that etch rates for porous silica materials are generally higher than for SiO@sub 2@ even when accounting for the smaller mass density, though etch rates do not necessarily scale linearly pore size or porosity. Scaling parameters (e.g., more tapering with larger polymerizing fluxes) observed for solid SiO@sub 2@ are generally applicable to the porous materials. Removal of polymer from exposed pores was also investigated using O@sub 2@ plasmas. @FootnoteText@ @footnote 1@Work supported by Semiconductor Research Corp. and National Science Foundation. @footnote 2@Oehrlein et al. JVST A 17, 26 (1999); 18, 2742 (2000)