Physics of Amorphous Silicon–Carbon Alloys

The crystallization of undoped amorphous silicon films deposited by low‐pressure chemical vapor deposition in the temperature range 580–530 °C and annealed from 550 to 950 °C has been studied by transmission electron microscopy. The average grain size of the crystallized films depends on the annealing temperature and the deposition conditions. The nucleation rate of new grains during annealing decreases as the deposition temperature decreases from 580 to 545 °C and/or when the deposition rate increases. The final grain size is also influenced by the annealing temperature with the largest grain size obtained at low annealing temperatures. A simple model is described which explains the dependence of grain size on the annealing temperature. An average grain size of 500 nm has been obtained in a 200‐nm film deposited at 545 °C and annealed at 550 °C.

Large grain polycrystalline silicon by low‐temperature annealing of low‐pressure chemical vapor deposited amorphous silicon films

Measurements of monosilicon (SiHn) and disilicon (Si2Hn) radicals at the cathode surface of dc discharges in silane and silane‐argon mixtures are reported. Silyl radical density per decomposed silane was constant for fixed flow conditions over a range of powers and silane‐argon ratios. The relative densities for other monosilicon radicals SiHn/SiH3 decreased with increased fraction of silane in silane‐argon mixtures. The density of disilicon radicals was observed to be comparable to some of the monosilicon radicals, with Si2H2 and Si2H4 the dominant Si2Hn species. Formation and destruction reactions are discussed for these radicals, disilane, and the deposited film. We deduce that disilane is formed primarily on surfaces and that sputtering is a significant source for radicals near the cathode.

Mono‐ and disilicon radicals in silane and silane‐argon dc discharges

▪ Abstract Hydrogenated amorphous silicon (a-Si:H) exhibits a metastable light-induced degradation of its optoelectronic properties that is called the Staebler-Wronski effect, after its discoverers. This degradation effect is associated with the relatively high diffusion coefficient of hydrogen and the changes in local bonding coordination promoted by hydrogen. Reviewed are the fundamental aspects of the interplay between hydrogen and electronic energy states that form the basis of competing microscopic models for explaining the degradation effect. These models are tested against the latest experimental observations, and material and preparation parameters that reduce the Staebler-Wronski effect are discussed.

Development in Understanding and Controlling the Staebler-Wronski Effect in a-Si:H

We present a thorough study of the microstructure, texture, intrinsic stress, surface, and interface morphology of transition metal nitride (mainly TiN but also CrN) films grown on Si by reactive sputter deposition, with emphasis to the mechanisms of adatom migration on the surface and subplantation of energetic species. In order to study the effects of adatom mobility and the subplantation probability we vary the ion energy and growth temperature. For the experimental part of this work we used nondestructive, statistically reliable x-ray techniques (diffraction, reflectivity, scattering). The x-ray results are compared and correlated with supporting data of in situ spectroscopic ellipsometry as well as Monte Carlo simulations of the irradiation effects and surface diffusion of adatoms. We found that the texture and the surface and interface morphology are sensitive to the mechanism of dissipation of the impinging ions. If the energy is enough to overcome the subplantation threshold (∼50eV), then the film...

Surface kinetics and subplantation phenomena affecting the texture, morphology, stress, and growth evolution of titanium nitride films

Structure and crystal growth of undoped, as‐deposited, and annealed silicon films prepared by chemical vapor deposition (CVD) and low‐pressure chemical vapor deposition (LPCVD) of silane have been studied with use of x‐ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM). The grain size and a complete texture analysis are performed on CVD films grown at atmospheric pressure and temperature range 600≤Td≤805 °C, LPCVD films grown in the pressure range 0.1≤Pd≤2 Torr and temperature range 500≤Td≤650 °C and annealed amorphous CVD and LPCVD films near Ta=600 °C. We obtain systematically amorphous, strong 〈220〉 polycrystalline, and inhomogeneous partially crystallized films 〈111〉 or 〈311〉 oriented depending on the deposition conditions. The presence of a given texture is explained by a model which takes into account the specific free surface energies of the starting equilibrium forms and the extinction of some crystalline planes by {111} slow growing facets. The appearance of the 〈220〉 tex...

Structure and crystal growth of atmospheric and low-pressure chemical-vapor-deposited silicon films

The kinetic hydrogen exodiffusion and its temperature dependence in amorphous silicon prepared by glow discharge of silane has been studied using conductivity, electron paramagnetic resonance, $^{11}\mathrm{B}\ensuremath{\rightarrow}\ensuremath{\alpha}$ nuclear reaction, and infrared absorption measurements. Comparison of the results obtained with these techniques shows the existence of two principal stages in the H exodiffusion. The hydrogen evolution for $T\ensuremath{\le}500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ is controlled by a diffusion process with a diffusion coefficient $D$. $D$ is thermally activated; $D={D}_{0}{e}^{\frac{\ensuremath{-}{E}_{D}}{{k}_{B}T}}$ with ${D}_{0}=4.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{2}$/${\mathrm{s}}^{\ensuremath{-}1}$ and ${E}_{D}=1.5$ eV (where ${k}_{B}$ is the Boltzmann constant). The hydrogen evolution above 500\ifmmode^\circ\else\textdegree\fi{}C is controlled by a first-order process. The activation enthalpy and entropy are, respectively, $\ensuremath{\Delta}{H}_{2}=3.4$ eV and $\ensuremath{\Delta}{S}_{2}=7.8{k}_{B}$. The fact that the EPR signal appears during the second stage and that $\ensuremath{\Delta}{H}_{2}$ is equal to the Si-H bound energy is a direct evidence that EPR signal is associated with the breaking of this bond. We then deduce an exodiffusion model assuming that hydrogen atoms can be bound in two sorts of centers. A possible configuration of H occupying such sites in the amorphous network is proposed.

K. Zellama

Papers

Structure and crystal growth of atmospheric and low-pressure chemical-vapor-deposited silicon films

Possible configurational model for hydrogen in amorphous Si:H. An exodiffusion study

Crystallization study of chemically vapour-deposited amorphous silicon films by in situ x-ray diffraction

Influence de l'état de la surface sur les propriétés optiques de couches minces de silicium amorphe hydrogéné déposées par “glow discharge”

Evolution of the optical gap during hydrogen exodiffusion in a-Si: H prepared by glow-discharge decomposition of silane