NH3 and NO interaction with Si(100)-(2 x 1) surfaces

In Situ Infrared Absorption Study of Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride

Despite the success of plasma-enhanced atomic layer deposition (PEALD) in depositing quality silicon nitride films, a fundamental understanding of the growth mechanism has been difficult to obtain because of lack of in situ characterization to probe the surface reactions noninvasively and the complexity of reactions induced/enhanced by the plasma. These challenges have hindered the direct observation of intermediate species formed during the reactions. We address this challenge by examining the interaction of Ar plasma using atomically flat, monohydride-terminated Si(111) as a well-defined model surface and focusing on the initial PEALD with aminosilanes. In situ infrared and X-ray photoelectron spectroscopy reveals that an Ar plasma induces desorption of H atoms from H-Si(111) surfaces, leaving Si dangling bonds, and that the reaction of di-sec-butylaminosilane (DSBAS) with Ar plasma-treated surfaces requires the presence of both active sites (Si dangling bonds) and Si-H; there is no reaction on fully H-terminated or activated surfaces. By contrast, high-quality hydrofluoric acid-etched Si₃N₄ surfaces readily react with DSBAS, resulting in the formation of O-SiH₃. However, the presence of back-bonded oxygen in O-SiH₃ inhibits H desorption by Ar or N₂ plasma, presumably because of stabilization of H against ion-induced desorption. Consequently, there is no reaction of adsorbed aminosilanes even after extensive Ar or N₂ plasma treatments; a thermal process is necessary to partially remove H, thereby promoting the formation of active sites. These observations are consistent with a mechanism requiring the presence of both undercoordinated nitrogen and/or dangling bonds and unreacted surface hydrogen. Because active sites are involved, the PEALD process is found to be sensitive to the duration of the plasma exposure treatment and the purge time, during which passivation of these sites can occur.

Nitric oxide oxidation of a Ta encapsulating Si cage nanocluster superatom (Ta@Si16) deposited on an organic substrate; a Si cage collapse indicator

Stepwise oxidative reaction of a Ta-encapsulating Si₁₆ caged nanocluster superatom upon exposure to nitric oxide is investigated by monitoring N 1s core level signals.

Dehydrohalogenation Condensation Reaction of Phenylhydrazine with Cl-Terminated Si(111) Surfaces

Formation of stable organic-inorganic contacts with silicon often requires oxygen- and carbon-free interfaces. Some of the general approaches to create such interfaces rely on the formation of a Si-N bond. A reaction of dehydrohalogenation condensation of Cl-terminated Si(111) surface with phenylhydrazine is investigated as a means to introduce a simple function to the surface using a -NH-NH₂ moiety as opposed to previously investigated approaches. The use of substituted hydrazine allows for the formation of a stable structure that is less strained compared to the previously investigated primary amines and leads to minimal surface oxidation. The process is confirmed by a combination of infrared studies, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry investigations. Density functional theory is utilized to yield a plausible surface reaction mechanism and provide a set of experimental observables to compare with these data.

Spontaneous N incorporation onto a Si(100) surface

Initial nitridation of the Si(100) surface is investigated using photoemission, ion-scattering and ab initio calculations. After dissociation of NO or NH3, nitrogen atoms are found to spontaneously form a stable, highly coordinated N[triple bond]Si(3) species even at room temperature. The majority of the N species is incorporated into the subsurface Si layers occupying an interstitial site, whose atomic structure and unique bonding mechanism is clarified through ab initio calculations. This unusual adsorption behavior elucidates the atomistic mechanism of initial silicon nitride formation on the surface and has important implication on the N-rich layer formation at the SiO(x)N(y)/Si interface.