Mechanisms and energetics of hydride dissociation reactions on surfaces of plasma-deposited silicon thin films

High-Resolution Electron Ionization Mass Spectrometry of Stannane: Deconvolution of Superimposed Fragmentation Patterns

In a pulsed laser plasma driven extreme ultraviolet (EUV) light, tin droplets undergo evaporation, eventually depositing on different surfaces. The removal of surface bound tin is commonly achieved with a hydrogen plasma, resulting in the formation of stannane (SnH4). The mechanisms leading to the formation and decomposition of stannane remain incompletely understood. To analyze these mechanisms mass spectrometrically, a reference is crucial, necessitating a high-resolution and thoroughly characterized mass spectrum of stannane. In this paper, a high-resolution 70 eV electron ionization (EI) mass spectrum of stannane is presented. The mass spectrum comprises all ten natural isotopes of the stannane fragments generated through EI. Utilizing the custom analysis program RASP, the relative distribution of fragments is calculated from the isotopically superimposed mass signals, offering crucial insights into the occurring processes. Furthermore, the dependence of fragment formation on ion source pressure and temperature was determined.

Disilane chemisorption on Si(x)Ge(1-x)(100)-(2 x 1): molecular mechanisms and implications for film growth rates

At low temperatures, hydrogen desorption is known to be the rate-limiting process in silicon germanium film growth via chemical vapor deposition. Since surface germanium lowers the hydrogen desorption barrier, Si(x)Ge((1-x)) film growth rate increases with the surface germanium fraction. At high temperatures, however, the molecular mechanisms determining the epitaxial growth rate are not well established despite much experimental work. We investigate these mechanisms in the context of disilane adsorption because disilane is an important precursor used in film growth. In particular, we want to understand the molecular steps that lead, in the high temperature regime, to a decrease in growth rate as the surface germanium increases. In addition, there is a need to consider the issue of whether disilane adsorbs via silicon-silicon bond dissociation or via silicon-hydrogen bond dissociation. It is usually assumed that disilane adsorption occurs via silicon-silicon bond dissociation, but in recent work we provided theoretical evidence that silicon-hydrogen bond dissociation is more important. In order to address these issues, we calculate the chemisorption barriers for disilane on silicon germanium using first-principles density functional theory methods. We use the calculated barriers to estimate film growth rates that are then critically compared to the experimental data. This enables us to establish a connection between the dependence of the film growth rate on the surface germanium content and the kinetics of the initial adsorption step. We show that the generally accepted mechanism where disilane chemisorbs via silicon-silicon bond dissociation is not consistent with the data for film growth kinetics. Silicon-hydrogen bond dissociation paths have to be included in order to give good agreement with the experimental data for high temperature film growth rate.

Molecular mechanisms for disilane chemisorption on Si(100)-(2 x 1)

The dissociative chemisorption of disilane is an important elementary process in the growth of silicon films. Although factors governing the rate of film growth such as surface temperature and disilane flux have been extensively studied experimentally by a large number of groups, the molecular mechanism for disilane adsorption is not well established. In particular, although it is generally held that chemisorption occurs via silicon-silicon bond dissociation, there have been a number of suggestions that silicon-hydrogen bond dissociation also occurs. We consider this issue in detail hereby examining a number of different paths that disilane can take to chemisorb. In addition to silicon-silicon bond dissociation paths, we examine three different mechanisms for silicon-hydrogen bond dissociation, for each path considering both adsorption at interdimer and intradimer sites. The calculated barriers are critically compared to experimental data. We conclude that silicon-hydrogen bond dissociation is likely, finding two zero barrier paths for chemisorption at interdimer sites, and a precursor-mediated path with a low barrier. We also find two precursor states, and show that each can lead to chemisorption via either silicon-silicon or silicon-hydrogen bond dissociation. Finally, we calculated the barriers for reaction of coadsorbed disilyl and hydrogen to form gas phase silane. Our calculations are performed using density-functional theory within a planewave ultrasoft pseudopotential methodology. We traced the reaction paths with the nudged-elastic band technique.