Paper PS1-FrM4
Surface Modifications of Ultralow Dielectric Constant Materials Exposed to Plasmas under Sidewall-like Conditions

Friday, October 24, 2008, 9:20 am, Room 304

Fluorocarbon (FC)/Ar based capacitively coupled plasmas (CCP) are widely used for dielectric etch in back-end-of-line (BEOL) processes. During formation of via/trench structures, highly polymerizing FC radicals deposit on via/trench sidewalls in parallel with ion-assisted etching of the dielectric. Since porous ultralow dielectric constant κ (ULK) dielectrics for 45 nm technologies or below are sensitive to plasma damage, FC thin film deposition on sidewalls is examined for its potential to protect ULK against plasma damage during subsequent process steps, e.g. photoresist ashing. For conditions where a small gap, high-aspect ratio structure in conjunction with blanket ULK films is used to simulate surface chemistry aspects of trench sidewalls we find that a thin (~1-3 nm) FC film deposits on the ULK surface and protects the ULK material against damage from other neutrals species, e.g. fluorine. The dependence of protection efficiency on FC film thickness and FC etching chemistry is discussed. The small gap geometry neglects the effect of scattered ions on ULK sidewalls, which potentially may produce surface modifications of actual ULK via/trench sidewalls. We attempted to address the effect of scattered ions, by examining ULK surface portions additionally bombarded by ions deflected at the edge of the gap structure. Fluorocarbon film deposition rates and composition were studied for these surface regions. The influence of these ULK surface modifications on ULK damage during photoresist mask stripping will be evaluated as a function of gap structure geometry, plasma chemistry and ion energy.