Kinetics Of Solid Phase Epitaxy Research Articles

Solid-phase epitaxial growth of the correlated-electron transparent conducting oxide SrVO3

$\mathrm{SrV}{\mathrm{O}}_{3}$ thin films with a high figure of merit for applications as transparent conductors were crystallized from amorphous layers using solid phase epitaxy (SPE). Epitaxial $\mathrm{SrV}{\mathrm{O}}_{3}$ films crystallized on $\mathrm{SrTi}{\mathrm{O}}_{3}$ using SPE exhibit room-temperature resistivities as low as $5.2\ifmmode\times\else\texttimes\fi{}{10}^{--5}$ and $2.5\ifmmode\times\else\texttimes\fi{}{10}^{--5}\phantom{\rule{0.16em}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$, residual resistivity ratios of 2.0 and 3.8, and visible light transmission maxima of 0.89 and 0.52 for film thicknesses of 16 and 60 nm, respectively. $\mathrm{SrV}{\mathrm{O}}_{3}$ layers were deposited at room temperature using radiofrequency sputtering in an amorphous form and subsequently crystallized by heating in a controlled gas environment. The lattice parameters and mosaic angular width of x-ray reflections from the crystallized films are consistent with partial relaxation of the strain resulting from the epitaxial mismatch between $\mathrm{SrV}{\mathrm{O}}_{3}$ and $\mathrm{SrTi}{\mathrm{O}}_{3}$. A reflection high-energy electron diffraction study of the kinetics of SPE indicates that crystallization occurs via the thermally activated propagation of the crystalline/amorphous interface, like SPE phenomena in other perovskite oxides. Thermodynamic calculations based on density functional theory predict the temperature and oxygen partial pressure conditions required to produce the $\mathrm{SrV}{\mathrm{O}}_{3}$ phase and are consistent with the experiments. The separate control of deposition and crystallization conditions in SPE presents possibilities for the crystallization of transparent conductors in complex geometries and over large areas.

Solid-phase epitaxy of a cavity-shaped amorphous alumina nanomembrane structure on a sapphire substrate

A stripe-shaped cavity structure was formed with amorphous alumina membrane on a sapphire substrate and its solid phase epitaxy (SPE) to crystalline sapphire membrane was investigated by transmission electron microscopy (TEM). The SPE process occurred through two-stage phase transformation from amorphous to γ-Al2O3 and subsequently to α-Al2O3. SPE of γ-Al2O3 at around 780 °C was initiated from the interface between amorphous alumina and sapphire substrate with an epitaxial relationship of [0 0 0 1]sapphire//[1 1 1]γ-Al2O3. Besides SPE, it was observed that nanocrystalline γ-Al2O3 were formed in the upper part of the membrane after an incubation time. The subsequent phase transformation of the alumina membrane from γ- to α- Al2O3 was observed at higher temperatures above 920 °C. The SPE of α-Al2O3 began at the corner region of the membrane and proceeded along the whole membrane. The whole alumina membrane was successfully transformed into single crystalline α-Al2O3 by SPE after annealing at 1063 °C for 2.5 h. The SPE kinetics was investigated by precise measurement of the thicknesses of epitaxially transformed γ- and α-Al2O3 layers in TEM images, resulting in activation energies of 3.1 eV and 3.9 eV for the SPE from amorphous to γ-phase and that from γ- to α-phase, respectively.

Recent Insights In Solid Phase Epitaxy of Silicon and Germanium

The crystallization of amorphous layers via solid phase epitaxy (SPE) is commonly used in semiconductor device fabrication to activate dopants. The kinetics of SPE depend on temperature, dopant and impurity concentration, hydrostatic pressure and crystallographic orientation. The effect of H on SPE in both Si and Ge is discussed. Numerical simulations are performed to model the H diffusion, the moving amorphous/crystalline interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. A significant fraction of the H escapes from the a-Si layer during SPE and becomes trapped at end of range defects. The light-emitting properties of these defects are investigated. Finally, the formation of germanides via SPE is discussed.

Hydrogen refinement during solid phase epitaxy of buried amorphous silicon layers

The effect of hydrogen on the kinetics of solid phase epitaxy (SPE) have been studied in buried amorphous Si layers. The crystallization rate of the front amorphous/crystalline (a/c) interface is monitored with time resolved reflectivity. Secondary ion mass spectrometry (SIMS) is used to examine H implanted profiles at selected stages of the anneals. The H retardation of the SPE rate is determined up to a H concentration of 2.3×1020 cm−3 where the SPE rate decreases by 80%. Numerical simulations are performed to model the H diffusion, the moving a/c interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. The segregation coefficient is estimated to be 0.07 at 575 °C. A significant fraction of the H escapes from the a-Si layer during SPE especially once the two a/c interfaces meet which is signified by the lack of H-related voids after a subsequent high temperature anneal.

Hydrogen in amorphous Si and Ge during solid phase epitaxy

Studies into the effect of hydrogen on the kinetics of solid phase epitaxy (SPE) in amorphous Si (a-Si) and Ge (a-Ge) are presented. During SPE, H diffuses into surface amorphous layers from the surface and segregates at the crystalline–amorphous interface. Some of the H crosses the interface and diffuses into the crystalline material where it either leaves the sample or is trapped by defects. H segregation at concentrations up to 2.3 × 10 20 H/cm 3 is observed in buried pha-Si layers with the SPE rate decreasing by up to 20%. H also results in a reduction of dopant-enhanced SPE rates and is used to explain the asymmetry effects between the SPE velocity profile and the dopant concentration profile observed with shallow dopant implants. Conversely, H diffusion is enhanced by dopants in a-Si. These studies suggest that H diffusion and SPE may be mediated by the same defect. The extent of H in-diffusion into a-Ge surface layers during SPE is about one order of magnitude less that that observed for a-Si layers. This is thought to be due to the lack of a stable surface oxide on a-Ge. However, a considerably greater retarding effect on the SPE rate in a-Ge of up to 70% is observed. A single unifying model is applied to both dopant-enhanced SPE and H diffusion processes.

Dopant enhanced H diffusion in amorphous silicon and its effect on the kinetics of solid phase epitaxy

Dopant enhanced H infiltration into surface amorphous Si ( a-Si) layers formed by ion implantation is reported. Dopant enhanced H in-diffusion is observed for both B and P implant profiles in a-Si and the effect of this enhanced in-diffusion on the kinetics of solid phase epitaxial (SPE) crystallization is quantified. Near-surface dopant profiles were formed by multiple energy ion implantation. Anneals were performed in air over the temperature range 500–640 ° C. Secondary ion mass spectrometry (SIMS) analysis of partially annealed samples reveals that implanted dopants enhance the in-diffusion of H thereby increasing its concentration at depths well beyond the dopant implanted region. The effect of an enhanced H concentration on crystallization rates via SPE is monitored using time resolved reflectivity. Boron is found to enhance both H diffusion and SPE to a much greater extent than P. Possible links between the SPE and H diffusion mechanisms are discussed and the possibility of applying SPE models to H diffusion is explored. Implications for the formation of shallow junctions are also considered.

Combinatorial Studies of Switching and Solid-Phase Crystallization in Amorphous Silicon

AbstractCombinatorial approaches are successfully applied for the optimization of electric write-once, thin-film Si antifuse memory devices, as well as for studying the solid-phase epitaxy kinetics of amorphous silicon on c-Si. High forward, low reverse current thin film Si diode deposition recipes are selected using cross-strips of different combinations of amorphous and microcrystalline doped layers, as well as a thickness-wedged intrinsic a-Si:H buffer layer. By studying switching in thickness-wedged a-Si:H layers, it is found that switching requires both a critical field and a critical bias voltage across the metallic contacts. Solid-phase epitaxy speed has a non-linear dependence on the film thickness, which is easily observed by optical image monitoring and analysis in wedged a-Si:H films on c-Si wafers.

Modeling the effect of hydrogen infiltration on the asymmetry in arsenic-enhanced solid phase epitaxy in silicon

The kinetics of solid phase epitaxy (SPE) in surface amorphous silicon layers doped with a single arsenic profile have been examined in relation to the generalized Fermi level shifting model of the SPE growth process. The model has been extended to include passivation by hydrogen of the defects responsible for SPE and∕or passivation of dopant atoms. A previous study has suggested that the asymmetry between the dopant-enhanced SPE rate and the arsenic concentration profile is due to the infiltration of hydrogen from the surface oxide. Theoretical calculations of the dopant-enhanced SPE rate compare well with experiment if it is assumed that the indiffusing hydrogen passivates some of the SPE defects and∕or some of the dopant atoms.

The kinetics of dopant-enhanced solid phase epitaxy in H-free amorphous silicon layers

The kinetics of intrinsic and dopant-enhanced solid phase epitaxy (SPE) have been measured in the H-free environment provided by buried amorphous Si layers formed by MeV ion implantation. The dopant-enhanced SPE kinetics were studied in buried a-Si layers containing uniform As concentration profiles produced by multiple energy ion implantation to doses spanning the concentration range 1–28×10 19 As/cm 3 and the crystallisation rates were measured over the temperature range 460–660°C using time-resolved reflectivity. The dopant-enhanced SPE data can be modelled by an extension of the Generalised Fermi Level Shifting model (GFLS) to take into account the degenerate semiconductor statistics on the crystalline Si side of the interface and by estimating the effect of band bending at the amorphous/crystalline (a/c) interface.

Kinetics of solid phase epitaxy in buried amorphous Si layers formed by MeV ion implantation

The kinetics of solid phase epitaxy have been measured in buried amorphous Si layers produced by ion implantation. Crystallization occurs simultaneously at both amorphous/crystalline interfaces of the buried layer. By collecting time resolved reflectivity data simultaneously at λ=1152 nm and λ=632.8 nm it is possible to accurately determine the crystallization rates at both interfaces. Both interfaces crystallize at a constant rate that is comparable to the intrinsic rate found for thick amorphous surface layers before rate retardation due to H infiltration has occurred. Thus, buried amorphous Si layers provide a suitable environment for studies of the intrinsic growth kinetics of amorphous Si.

A study of the effect of misfit-induced strain on the kinetics of solid phase epitaxy in the Si1−xGex on 〈001〉 Si system

In this paper we present the results of an experimental determination of the rate of solid phase epitaxical regrowth of amorphous Si1−xGex on 〈001〉 Si as a function of temperature and Ge concentration. Layers of chemical vapor deposited Si1−xGex roughly 200-nm thick containing 5.4, 11.6, and 17.0 at. % Ge were amorphized with a two-step process of 100 keV, followed by 200 keV, 29Si ion implantation. This procedure left the near surface region of the substrate, including the entire Si1−xGex film, amorphous to a depth of 380 nm. The epitaxical recrystallization of the alloy portion (5.4, 11.6, or 17 at. % Ge) of the amorphous layer results in the development of large lattice mismatch stresses (0.5–2 GPa). The rate of epitaxical regrowth of the amorphous material was studied with isothermal heating and in situ transmission electron microscopy observations. Isothermal annealing at temperatures between 476 and 602 °C show that, compared to pure unstrained Si, the rate of regrowth is decreased in strained alloys of Si1−xGex. Furthermore, we report that the activation energy for strained-layer regrowth of Si1−xGex is not a strong function of composition and, for all three compositions, was in the range 3.2±0.2 eV. This is significantly larger than the activation energy for the homoepitaxical regrowth of unstrained pure Si. Stress related origins of these observations are discussed.

Amorphous Si — the role of MeV implantation in elucidating defect and thermodynamic properties

The role of MeV implantation in producing thick amorphous Si layers has been central in elucidating several of its properties. The recent use of MeV Si beams to produce very pure layers will be reviewed. The kinetics of solid-phase epitaxy have been measured for amorphous Si layers up to 5 μm thick and the activation energy found to be 2.70 ± 0.02 eV. Calorimetry measurements of such thick layers show an interfacial heat release due to crystallization of 13.4 ± 0.7 kJ/mol and a homogeneous heat release of 5.1 ± 1.2 kJ/mol. This homogeneous heat release, associated with relaxation, is due to the annihilation of defects in the amorphous structure. These defects have been studied by ion-bombarding 500°C annealed amorphous and single-crystal Si. The formation and annihilation properties of the defects in these two states are intriguingly similar. Defects saturate in previously annealed a-Si at ion doses ~ 0.02 dpa. The presence of the defects is also manifested in measurements of the density of amorphous Si which is (1.8 ± 0.1)% less dense than the crystal. The diffusion and solubilty of Cu, Zn, Pd, Ag, Pt and Au have been measured in amorphous Si and found to be very sensitive to defect population. The various experiments show that the intrinsic defect level in amorphous Si is 1–2 at.%

Kinetics of solid phase epitaxy in thick amorphous Si layers formed by MeV ion implantation

The kinetics of solid phase epitaxy (SPE) have been measured in MeV ion-implanted amorphous Si layers up to 5 μm thick. Epitaxial crystallization in these layers occurs at a constant rate throughout the entire film, without loss of interface planarity or competition from random nucleation or twin formation. The activation energy for SPE in thick layers is found to be 2.70 eV, in excellent agreement with the value determined previously in much thinner films. The SPE kinetics are shown not to depend on the implant dose for doses up to 1000 times the threshold for amorphization. The presence of water vapor in the annealing ambient during SPE results in the indiffusion of hydrogen and a concomitant reduction of the SPE growth rate at distances as great as 2 μm from the surface. This effect may have important implications for the development of a microscopic model of the SPE process in silicon.

The Effect of Hydrogen on the Kinetics of Solid Phase Epitaxy in Amorphous Silicon

AbstractThis paper discusses the intrusion of H into a-Si layers during solid phase epitaxy and the effect of this H on the growth kinetics. We show that during annealing in the presence of water vapor, H is continuously generated at the oxidizing a-Si surface and diffuses into the amorphous layer, where it causes a reduction in the epitaxial growth rate. The measured variation of growth rate with the depth of the amorphous/crystal interface is correlated with the concentration of H at the interface. The diffusion coefficient for H in a-Si is determined by comparing measured depth profiles with calculated values. Hydrogen intrusion is observed even in layers annealed in vacuum and in inert gas ambients. Thin (<;5000 Åthick) a-Si layers are especially susceptible to this effect, but we show that in spite of the presence of H the activation energy for SPE derived earlier from thin-layer data is in good agreement with the intrinsic value obtained from thick, hydrogen-free layers.

Present status of solid phase epitaxy of vacuum-deposited silicon

Results of recent studies of solid phase epitaxy (SPE) of amorphous Si films deposited in ultra-high vacuum are reviewed, including experimental aspects of conducting and investigation of SPE growth, SPE kinetics in intrinsic and doped Si films, application of SPE technique for growing highly-doped epitaxial layers with sharp profiles, and lateral SPE growth over oxide.

Laser-Induced Solid Phase Crystallization in Amorphous Silicon Films

ABSTRACTWe review recent work on the kinetics of laser-induced solid phase epitaxial crystallization of silicon as determined from time-resolved reflectivity measurements. Specific topics which are addressed include: the intrinsic kinetics of solid phase epitaxy (SPE) in ion-implanted and UHV-deposited films; SPE rate enhancement by implanted dopant atoms and the effects of electrical compensation on the SPE rate; and the temperature dependence of SPE and competing processes in samples containing impurity atoms at concentrations exceeding the solid solubility limit. The high temperature kinetics results are compared with predictions from transition state theory and are discussed with respect to a proposed depression in the amorphous Si melting temperature.