In-situ XPS studies of Ar ion bombardment on organosilicate glass (OSG) films at ion kinetic energies between 500eV and 900eV demonstrate that such bombardment inhibits O2 plasma-induced carbon loss by forming an SiO2-like overlayer, and that the degree of protection correlates directly with increased ion energies, but not the thickness of SiO2 overlayer. Bombardment at 500eV results in a ~3 Å thick SiO2overlayer and subsequent O2 plasma treatment results in a slower rate of carbon loss from the surface region than observed for a vicinal film, but complete carbon removal is observed after 3 min O2plasma treatment under these conditions. In contrast, bombardment by a similar flux of 900eV ions results in a SiO2-like overlayer of similar average thickness, but with greatly inhibited rate of carbon loss upon subsequent O2 plasma exposure. Ar ion bombardment (900eV) in the presence of NH3 (1 x 10-6 Torr) results exclusively in Si-N rather than C-N bond formation, and dramatically increases the average thickness of the Si-O-N overlayer to 22 Å. The formation of this overlayer further reduces the rate of subsequent O2 plasma-induced carbon loss compared to 900eV Ar ions alone. These results indicate Ar ion bombardment causes Si-C bond scission. Subsequent NH3 reaction results in Si-N bond formation and inhibits Si-Si and Si-O-Si formation, increasing the thickness of the ion-induced damage overlayer. The data indicate that ion kinetic energies are a critical parameter in protective noble gas plasma treatments to inhibit O2 plasma damage, and also indicate that high energy ions alone can provide better protection against carbon loss when compared to plasmas or VUV photons.

 

Acknowledgement: This work was supported by the Semiconductor Research Corporation under Task ID 2071.002. The authors thank Novellus Systems Inc. for providing the low k samples. David Graves and Joe Lee are also acknowledged for stimulating discussions.