Sneha Gaddam

Fundamental mechanisms of oxygen plasma-induced damage of ultralow-k organosilicate materials: The role of thermal P3 atomic oxygen

Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), and ab initio density functional theory-based molecular dynamics simulations demonstrate fundamental mechanisms for CH3 abstraction from organosilicate films by thermal O(P3). Ex situ FTIR analysis demonstrates that film exposure to thermal O(P3) yields chemical changes similar to O2 plasma exposure. In situ XPS indicates that exposure to thermal O(P3) yields O/OH incorporation in the organosilicate film concurrent with carbon loss from the surface region. These results are consistent with simulations indicating specific low kinetic barrier (<0.1 eV) reactions resulting in concurrent Si–C bond scission and Si–O bond formation.

Interaction of vacuum ultraviolet light with a low-k organosilicate glass film in the presence of NH3

In situ x-ray photoemission spectroscopy (XPS) and ex situ Fourier transform infrared spectroscopy (FTIR) were used to characterize effects on organosilicate films of 147 nm irradiation in the presence of 10−4 Torr NH3. XPS and FTIR data indicate SiO and SiC bond scission, with nitridation only at Si sites. Photoirradiation causes the surface layer to become enriched in sp2 carbon. FTIR spectra of silanol formation upon exposure to ambient indicate reactive sites in the bulk have lifetimes of up to six days. XPS data indicate lifetimes of ∼minutes for surface states. Nitrogen uptake passivates with longer exposure times, indicating surface densification.

Effects of He and Ar ion kinetic energies in protection of organosilicate glass from O2 plasma damage

In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Fourier transform infrared studies of He plasma and Ar+ ion bombardment pretreatments of organosilicate glass demonstrate that such pretreatments inhibit subsequent O2 plasma-induced carbon loss by forming a SiO2-like damaged overlayer, and that the degree of protection correlates directly with increased ion kinetic energies, but not with the thickness of the SiO2 overlayer. This thickness is observed by XPS to be roughly constant and <1 nm regardless of ion energies involved. The data indicate that ion kinetic energies are an important parameter in protective noble gas plasma pretreatments to inhibit O2 plasma-induced carbon loss.

Surface cleaning for enhanced adhesion to packaging surfaces: Effect of oxygen and ammonia plasma

The effects of direct plasma chemistries on carbon removal from silicon nitride (SiNx) and oxynitride (SiOxNy) surfaces have been studied by in-situ x-ray photoelectron spectroscopy (XPS) and ex-situ contact angle measurements. The data indicate that O2 and NH3 capacitively coupled plasmas are effective at removing adventitious carbon from silicon nitride (SiNx) and Si oxynitride (SiOxNy) surfaces. O2 plasma treatment results in the formation of a silica overlayer. In contrast, the exposure to NH3 plasma results in negligible additional oxidation of the SiNx or SiOxNy surface. Ex-situ contact angle measurements show that SiNx and SiOxNy surfaces exposed to oxygen plasma are initially more hydrophilic than surfaces exposed to NH3 plasma, indicating that the O2 plasma-induced SiO2 overlayer is highly reactive toward ambient. At longer ambient exposures (≳10 h), however, surfaces treated by either O2 or NH3 plasma exhibit similar steady state contact angles, correlated with rapid uptake of adventitious carbo...

Organosilicate glass dielectric films with backbone carbon: Enhanced resistance to carbon loss in plasma environments

X-ray photoelectron spectroscopy (XPS) data indicate that organosilicate glass (OSG) films with backbone carbon (Si-R-Si) exhibit significantly enhanced resistance to carbon loss upon exposure to either atomic oxygen (O(3P)) or to vacuum ultraviolet light in the presence of O2 (VUV+O2) - important factors in O2 plasma environments-compared to films with terminal methyl groups (Si-CH3). These results and comparisons to ab initio molecular dynamics (AIMD) simulations indicate films with backbone carbon exhibit fundamentally different Si-C bond-breaking mechanisms, with more resistance to carbon loss, compared to those with terminal methyl groups.

Direct growth of graphene on nitride and oxide substrates

We have directly grown monolayer and few layer graphene on h-BN(0001), MgO(111), and Co3O4(111) by a variety of methods, including chemical or physical vapor deposition (CVD, PVD), or molecular beam epitaxy (MBE). Such capability is critical to the development of graphene charge- and spin-based devices. In each case, the interactions of graphene with the substrate give rise to distinct graphene properties with significant device implications. These effects include substantial n-type doping (graphene/monolayer h-BN(0001)), formation of a 0.5-1eV band gap (graphene/MgO(111), and magnetic polarization of the graphene conduction electrons (graphene/Co3O4(111)). The results on BN and MgO have significant implications for the formation of field effect transistor (FET)-like devices, while the results on Co3O4(111) suggest the feasibility of room temperature spin valves with high magnetoresistance and very low power demands.