R. F. Lever

Kinetics of compound formation in thin film couples of Al and transition metals

Intermetallic coumpound formation at metal–metal interfaces was observed for thin film couples of Al and transition metals such as Cr, Ti, Hf, Zr, Co, Ta, Pd, and Pt. The Al–Cr system was investigated in some detail using a conductance method and nuclear backscattering for reaction‐rate measurements. The compounds CrAl7 and Cr2Al11 were identified and their growth was found to be diffusion controlled. The temperature dependence of the rate constant for CrAl7 obeyed an Arrhenius plot from 300° to 450 °C with an activation energy of 1.91±0.1 eV. The Al‐rich phases of the remaining transition metals were investigated; the compounds either exhibited a planar interface with parabolic growth kinetics or an irregular interface with nonparabolic growth. An empirical relationship involving the melting point and stability of the compounds was proposed to explain the different growth kinetics.

Arsenic Clustering in Silicon

Large decreases in the conductivity of arsenic‐doped silicon have been observed during 500–970°C heat treatments. The rate of conductivity change depends upon the prior quenching rate from diffusion temperature to room temperature. These conductivity changes are reversed by higher‐temperature treatments. The relationship between the electrically active arsenic, as calculated from the conductivity, and the total arsenic is shown to be consistent with a model of substitutional arsenic atoms being nonionized when in a cluster or in a complex involving one or more vacancies.

Surface enrichment of copper due to keV Xe sputtering of an Al-Cu mixture

A surface enrichment of Cu due to keV Xe sputtering of Al‐Cu mixtures has been observed by high‐energy He ion backscattering and by Auger electron spectroscopy. The complementary nature of these two methods provides information on the total Cu enrichment (4.5×1015/cm2) and depth of the altered layer (∼300 A).

Boron diffusion in silicon at high concentrations

Depth profiles measured by secondary ion mass spectrometry have been used to compare boron diffusion from three different sources for temperatures ranging from 850 to 1050 °C. The sources included boron in situ doped and ion‐implanted polycrystalline silicon as well as vapor using an evacuated capsule with highly doped powder. The junction depths and surface concentrations demonstrated little source dependence. Boltzmann–Matano analysis has been used to show that the concentration dependence of the diffusivity on source was minimal. We have clearly shown that conventional models of boron diffusion cannot fit the experimental data or the Boltzmann–Matano results, regardless of source. A new model has been used to describe the boron diffusion profiles more accurately.

Anomalous growth of HfAl3 in thin films

Anomalous growth of HfAl3 is observed on 400°C annealing of evaporated thin‐film samples consisting of 900 A aluminum, on 1000 A hafnium, 6000 A aluminum and SiO2 substrates. A continuous layer of HfAl3 forms at the aluminum–hafnium interface nearer the surface, but not at the deeper interface. The surface HfAl3 layer then continues to grow, fed by diffusion of underlying aluminum through the intervening hafnium layer. Needlelike precipitates of HfAl3 are formed along the underlying aluminum grain boundaries. Observations are made by nuclear backscattering, Auger electron spectroscopy, and transmission electron microscopy. Similar behavior is observed in Al–Zr–Al layers.

The steady‐state model for coupled defect‐impurity diffusion in silicon

We extend and generalize 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 important details such as 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, with no additional ad hoc assumptions. Our extended model, in its simplest form, allows a more complete and less restrictive treatment than the usual models of Au in‐diffusion in Si. An important advantage is the direct inclusion of these defect‐impurity interactions and the resulting gradients in the defect concentrations, which are ignored in even the latest versions of popular process simulation programs, such...

A low energy limit to boron channeling in silicon

Both experimental profiles and Monte Carlo simulations have shown that a channeling tail is unavoidable in the implantation of boron into silicon at 5 keV, even though high‐index channeling does not occur. A model is proposed to explain this disappearance of high‐index channeling at low energies, based on simple geometrical considerations of ion deflections predicted by a binary collision potential.

Diffusion of boron into polycrystalline silicon from a single crystal source

Boron was outdiffused at 900 °C from single crystal silicon into undoped chemical vapor deposited polycrystalline silicon. Boron concentration profiles measured by secondary ion mass spectrometry showed preferential segregation into the polysilicon with a segregation coefficient of 0.7. Pileup of boron at grain boundaries due to migration of boron ions in the interface field during the diffusion process can account for some of the observed segregation.

Interference of arsenic diffusion by argon implantation

Abstract In the study of ion implantation, electrically active ions or noble gas ions are often used for damage study, range profiling, etc. Very seldom are both electrically active ions and noble gas ions implanted at about the same depth. In the work reported here, argon and arsenic ion implants and their interference in diffusion were studied by using backscattering, electrical measurements, and transmission electron microscopy (TEM). Several unexpected phenomena were observed. First, when both Ar and As are implanted in high doses (about 1016/cm2), at depths around a few hundred nanometers, the Ar significantly hampers the As diffusion, and the As prevents the outdiffusion of the Ar. The interference occurs regardless of which ion is implanted first. Second, when Si wafers uniformly doped with about 4 × 1019 As/cm3 are ion-implanted with log16 Ar/cm2 at 130 keV, the As atoms stay uniformly distributed. When the sample is annealed at a temperature between 900 and 1100°C in a nitrogen ambient, however, ...

Radiation Damage of 50–250 keV Hydrogen Ions in Silicon

Damage distributions in [001] Si crystals bombarded with a fluence of 1016 to 1017/cm2 at 50 keV to 250 keV H+ ions at temperatures below 600° C were measured using high energy He+ channeling. The nature of the damage was investigated by transmission electron microscopy (TEM). Different defect types are formed at different target temperatures, e.g. microblisters located on {111} planes exist between 100°C and 450°C. With higher fluences or post-implantation anneal the Si surface becomes visibly blistered.