The mechanisms of self-diffusion and dopant impurity diffusion in silicon have been the subject of intense debate since the 1960’s. Until the mid-1980’s, there was only limited experimental information and virtually no theory. In the last five years, however, first-principles calculations of many key quantities and new experimental data have led to significant progress. This paper traces the major theoretical advances and the key experimental data that have resolved many controversies and have provided a fairly comprehensive picture of diffusion processes. Theory has also recently provided detailed microscopic information about the diffusion of interstitial hydrogen.

We have investigated, via parameter-free calculations, the effects of hydrostatic and nonhydrostatic strains on the energetics of defect formation and self-diffusion in silicon. The three microscopic mechanisms, vacancy, interstitial, and concerted exchange, have very similar activation enthalpies at zero pressure but exhibit different behavior with hydrostatic pressure. Our results suggest that experiments performed at different pressures can determine the relative contributions of each of these mechanisms. The calculations also show that the neutral Si vacancy has a negative relaxation volume, with the nearest neighbors of the vacancy relaxing inwards, in contrast to the Si (111) surface. Large nonhydrostatic strains, which are present in e.g. Si/GexSi1-x pseudomorphic heterostractures, substantially reduce the formation energy of the tetrahedral interstitial, but do not affect the formation energy of the vacancy. These findings suggest that, aside from being another useful tool for the investigation of self-diffusion in Si, nonhydrostatic strain may significantly affect annealing and impurity diffusion in strained heterostructures. In particular, the interstitial-assisted impurity diffusion may proceed more rapidly in Si lattice-matched to GexSi1-x, but be slowed down in GexSi1-x lattice-matched to Si. The compressed GexSi1-x layers may thus act as diffusion barriers for impurities diffusing with help of native interstitials, such as B or P.

It has been reported that diffusion of substitutional dopant atoms in silicon occurs during the formation of transition-metal suicides at temperatures below 300°C. By observing the diffusion enhancements of buried marker layers of Sb-, Ga-, Ge-, and B-doped silicon layers, we provide solid experimental evidence that the diffusion enhancement induced by Pd2Si formation at low temperatures is due to point defects generated by the suicide reactions. Diffusion enhancement is observed at temperatures as low as 200°C. We have found the surprising result that diffusion is asymmetric: diffusion occurs preferentially towards the suiciding interface.

This paper deals with an analysis of the oxynitridation and direct nitridation experiments of Fahey et al.(1984[1]). The inconsistencies in the evaluation of the fiactional component of diffusion for aisenic are discussed. Using a recently developed diffusion model an explanation for the diffusion data for arsenic is given. The standard equation for analyzing diffusion under nonequilibrium conditions is shown to lead to erroneous results. A consistent treatment must account for the concentrations of arsenic, point defects and arsenic point defect pairs. Pair formation kinetics must be included. Values are presented for the diffusion constants DIAs, DVAS, and the reaction constants kIAs, kVAs depending on the fractional interstitial component of diffusion .

Reported calculations of the diffusion coefficient of silicon self interstitials vary over several orders of magnitude at temperatures of interest for integrated circuit fabrication. In this work, we measure the enhanced diffusion of phosphorus buried layers while interstitials are injected at a wafer surface via thermal oxidation. The starting substrates were either float-zone silicon or Czochralski silicon with a pre-treatment to precipitate excess oxygen. The samples were prepared by implantation of phosphorus followed by the growth of a 40-60µm epitaxial layer. They were then etched anisotropically from the frontside or backside to yield membrane structures. Local oxidation was performed at 1100°C on either the frontside or backside of each wafer and buried layer diffusion was monitored, yielding information about interstitial diffusion in silicon and it’s dependence on bulk properties.

Ge and Zn atoms were introduced into the unirradiated regions of Si at 150°C and GaAs wafers at 50°C, respectively by using the electron-beam doping method. The surfaces of Si and GaAs substrates were covered partially by the overlayers of Ge and Zn sheets, respectively. The only surfaces of the Ge and Zn sheets were irradiated locally. with high energy electrons at 7MeV with the fluences of 5×1017 – 1×1018 electrons cm-2 . Even at a distance of ~10mm from the irradiated overlayers in the Si and GaAs substrates, Ge and Zn atoms respectively, whose interstitials may migrate the unirradiated regions, were detected by SIMS measurements. PL signal due to band-to-acceptor (ZnGa ) transition at 1.48eV becomes observable after annealing at 800°C for 20mm in the unirradiated GaAs region, which is separated from Zn sheet by nearly 10mm.

Czochralski silicon has been heated in a H-plasma at temperatures in the range 300-450°C, and compared with furnace annealed material. Plasma treatments produce enhanced rates of oxygen diffusion jumps, loss of oxygen from solution and formation of thermal donor centres. The available evidence indicates that atomic hydrogen catalyses the enhancements via the oxygen diffusion rate. Donor concentrations greater than 1017cm-3 have been observed in samples heated in a plasma at 350°C. Doubts have been raised about dimer formation being the primary mechanism for oxygen loss in furnace anneals at 350°C, but invoking enhanced diffusion leads to a conflict with stress dichroism data.

We extend our earlier model which was proposed to explain tails in the diffusion profiles of high concentration boron and phosphorus in silicon. Our quasi-steady-state approach is generalized here to include both vacancies (V) and interstitials (I) at equivalent levels. I-V recombination is regarded as near local equilibrium, occurring through reactions of the defects with defect-impurity pairs. This approach leads to the well-known plateau, kink and tail in high surface concentration P diffusions in Si and to the less well recognized tails in B as well. Our extended model, in its simplest form, allows a more complete and less restrictive treatment of Au diffusion in Si. An important advantage is the direct inclusion of these defect-impurity interactions and the resulting gradients in the defect concentrations.

By grouping high and low temperature diffusivity measurements in boron-doped silicon, a new diffusivity law for chromium in the 20–1050 °C temperature range has been established. High temperature diffusivities were deduced from erfc fits of chromium-boron pair profiles measured by means of Deep Level Transient Spectroscopy in chromium-plated substrates, after annealing for a short time in a lamp furnace. Low temperature diffusivities were derived from the association time constants of the chromium-boron pairing reaction in chromium-contaminated specimens. The whole data points were well fitted using the following expression for the diffusion coefficient: D= 2.6×10-3 exp(-0.81 ± 0.02 eV/kT). Because of the wide 1/T interval available, the migration enthalpy value is more accurate than the previous determinations using only high temperature diffusivity results.

Diffusion studies of mono and bilaycrs of transition-metal films on silicon showed that the formation of η′ —Cu3Si lowers the formation temperature of subsequently forming ReSi2 by 400°C. This is due to the creation of a large amount of silicon self-interstitials accompanying the formation of the copper suicide, which lowers the activation energy for silicon diffusion. The generalization of this result - stating that the formation of all suicides, in which the volume density of silicon is much larger than in elementary silicon injects silicon self-intcrstitials into the silicon lattice - gives new insight into suicide formation, silicide-cnhanccd dopant diffusion and the self-diffusion of silicon itself6.

The precipitation of copper and (radioactive) cobalt at low energy grain boundaries in polycrystalline silicon and bicrystals is investigated. The metals are diffused in from a surface source between 800 - 1000 °C and the precipitation after cooling down is studied by TEM (for Cu) and Mößbauer spectroscopy (for Co). The precipitates are metal suicides. For copper it is shown that they appear in form of colonies containing hundreds of precipitates with a particle size between 5-60 nm. In the grain boundary they nucleate preferentially at dislocations and steps. The distribution and size of the precipitates depend on the cooling rate after the diffusion. In the vicinity of the grain boundary the volume is depleted from the impurities.

By combining RBS/channeling, Mössbauer spectroscopy, and TEM measurements on implanted Sn in Silicon, the solid solubility has been determined at 1025°C, 1075°C, and 1188°C to be respectively, 6.1 , 4.8 , 3.1·1020 cm-3.

We report the low temperature growth (625 - 700 °C) of epitaxial silicon and silicon-germanium alloy films by vapor phase techniques with oxygen concentrations approximately 1020 cm-3. These concentrations are well above the accepted solid solubility for oxygen in silicon. The films, however, have excellent structural and electrical properties with virtually no stacking faults or “haze”. Infrared transmission analysis suggests the possible presence of OH, but the exact nature of the oxygen is not known.

In the substrate region underneath the antimony buried layer, an enhanced oxygen donor generation and a retardation of the oxygen precipitation were observed. Both phenomena can be explained by the vacancy mechanism in which the charged vacancies dominate at high temperatures. Based upon this hypothetical model, it is suggested that the intrinsic vacancy concentration could play a significant role in both oxygen thermal donor generation and oxygen precipitation in silicon.

The effect of high background doping (8×1019 - 5×1020 cm-3 ) on the diffusion of Ge and As in Si has been studied. A strong enhancement is found for As for donor concentrations higher than ~2×1020 cm-3 , but not for Ge. These experimental findings are discussed within the percolation model.

A kinetic modeling approach is used together with experimental studies to gain insight into the processes taking place during anomalous transient diffusion. A physical process analogous to B clustering is found to play an important role, even at B concentrations well below the solid solubility limit.

We have performed large scale computer simulations on the controversial issue of Au diffusion into Si at T = 1095° C. Using a Monte Carlo algorithm and a conveniently parametrized set of parameters, our computer program is capable of working out the macroscopic consequences of a variety of models, i.e. atom level assumptions, in an unbiased way and without the approximations introduced in analytic calculations.

When applied to the “kick-out” hypothesis, our results are dramatically at odds with the properties claimed by its proponents. Neither the profile of the Au substitutionals, nor the Au-interstitial profiles are in agreement with the analytically obtained results. The discrepancy becomes most pronounced when comparing the variation with time of the Au concentration in the center of the sample, which we find to be linear at all times, in contrast to the alleged t1/2 behavior. Moreover, the Au profile of a one-sided diffusion never becomes U-shaped, as experimentally observed.

A systematic theoretical and computational study is presented for the diffusion of point defects in a stressed cubic lattice. The study combines an atomistic description of point defect migration with a continuum model for point defect transport. Moment analysis of the macroscale transport equation gives expressions for the drift velocity and the diffusivity tensor of the point defects, which are calculated by a dynamic Monte Carlo simulation of the defect migration process. Results are presented for the case of diffusion under a constant force of interaction between the applied stress on the crystal and the defects. The continuum model gives the general constitutive model for stress-assisted point defect diffusion.

Amorphous Si/ amorphous Ge artificial multilayers were prepared by ion beam sputtering. Boron or gold impurities were introduced into the Si/Ge multilayers by ion implantation or during the sputtering deposition. Diffusion coefficients were determined by measuring the decrease in the intensity of the first order X-ray diffraction peak resulting from the composition modulation. It was found that the interdiflusion of Si and Ge in their amorphous phase can be enhanced by doping. The enhancement factor is independent of the degree of structural relaxation, as observed by the decrease of diffusivity with annealing time, of the amorphous phase. A model is proposed that describes this behavior in terms of electronic effects, introduced by the dopants, on the pre-existing structural defects governing diffusion.

The diffusivity of Au in amorphous Si (a-Si) has been determined in the temperature range 200-260°C using and Ar-ion sputter deposited artificial multilayered films of a-Si and a-Si(0.7at%Au) with repeat lengths between 44 and 48 Å. Diffusion on lengths scales of the order of interatomic spacings have been investigated. The Au diffusivity exhibits an Arrhenius temperature dependence with an activation enthalpy of 1.2eV and shows good agreement with extrapolations of higher temperature Au diffusion data obtained by Rutherford backscattering spectrometry (RBS) in ion-implanted, CVD, and sputter deposited a-Si. The measured Au diffusivity also shows a significant time dependence.