AVS 57th International Symposium & Exhibition
    Plasma Science and Technology Wednesday Sessions
       Session PS1-WeA

Paper PS1-WeA1
VUV-Induced Bond Scission and Site-Specific Nitridation in Organosilicate Glass: Bulk and Surface Effects

Wednesday, October 20, 2010, 2:00 pm, Room Aztec

Session: Plasma Surface Interactions (Fundamentals & Applications) II
Presenter: S. Behera, University of North Texas
Authors: S. Behera, University of North Texas
J. Lee, University of California-Berkeley
S. Gaddam, University of North Texas
S. Pokharel, University of North Texas
D.B. Graves, University of California-Berkeley
J.A. Kelber, University of North Texas
Correspondent: Click to Email
In-situ XPS and ex-situ FTIR have been used to characterized the effects of ionizing vacuum ultraviolet (VUV— 147 nm) photons on the surface composition of organosilicate glass (OSG; k = 3.0). VUV irradiation is an important component of the plasma environment, and both the types and kinetics of VUV- induced effects must be understood in order to accurately control and model plasma effects. Irradiation was carried out in vacuum (10-6 Torr), and in the presence of 10-4 Torr NH3 so that NH3 reactions with VUV-induced reactive sites would cause chemical shifts in XPS core level spectra, permitting a more detailed characterization of photo-induced chemistry. The effects of photo-excited gas phase species are negligible under these conditions, as confirmed by experiments with the light path parallel to the surface. FTIR and XPS data after photoirradiation in vacuum indicate photon-induced Si-C and Si-O bond scission. Lifetimes of bulk Si reactive sites are ~ 6 days, as determined by Si-OH, but ~ minutes at surface sites due to reaction with chamber ambient. Core level XPS spectra recorded after irradiation in the presence of NH3 show similar effects, but with nitridation at Si sites, and not at carbon sites. Si-C/Si-O bond breaking and C-C bond formation obey first order kinetics. At longer exposure times, the nitridation process saturates while the Si-C/Si-O bond scission and C-C bond formation processes do not, consistent with photo-induced surface densification inhibiting NH3 diffusion into the solid. However, similar increases in surface carbon intensity were observed for photoirradiation of SiO2 with ~ 1 monolayer of surface carbon, indicating that reaction of background gases with surface reactive sites may also be a factor. Preferential Si-N bond formation and absence of C-N bond formation were also reported1 for OSG bombardment by Ar+ in the presence of NH3 and suggest fundamentally different dissociation pathways/kinetics at Si vs. C sites created by either ion bombardment or ionizing photoirradiation. C-C and C-H bond dissociation enthalpies are larger than those of Si-H or Si-C bonds, but smaller than that of Si-O, so this site specificity is not readily explainable on the basis of bond strengths alone.

1J. A. Wilks and J. A. Kelber, Applied Surface Science 255 (2009) 9543

Acknowledgements: This research was supported by the Semiconductor Research Corporation under Task IDs 1862.001 and 1862.002.