J.S. Williams

Ion-beam-induced crystallization and amorphization of silicon

Thin amorphous silicon layers can be produced in crystalline silicon substrates by ion-implantation. Subsequent ion-irradiation at elevated temperatures can induce such layers to either crystallize epitaxially or increase in thickness, layer by layer. This paper examines these processes and their dependence on substrate temperature and ion-irradiation parameters. It is shown that both processes, epitaxial crystallization and layer-by-layer amorphization, are controlled by ion-beam induced defect production at, or near, the crystalline/amorphous interface. The competition between defect production (determined by the ion flux and rate of nuclear energy deposition) and dynamic defect annealing (determined by the substrate temperature) is shown to play an important role in determining whether the layer crystallizes or amorphizes. Possible models for the observed behavior are discussed.

Characterization of damage in ion implanted Ge

It has been observed that ion implantation into Ge at room temperature creates severe surface craters extending several thousand angstroms into the surface, and results in the incorporation of large quantities of C and O impurities (∼50 impurities/ion). This effect has a strong temperature dependence and essentially disappears for implantations performed at liquid nitrogen temperature. The systematics of this effect are presented, preliminary annealing results are cited, and possible mechanisms are discussed.

Low‐temperature epitaxial regrowth of ion‐implanted amorphous GaAs

Glancing‐angle Rutherford backscattering and channeling techniques have been used to investigate the regrowth of Ar+‐ion‐implanted amorphous layers on (100) GaAs. Under carefully controlled implant conditions, amorphous GaAs layers can be recrystallized epitaxially at temperatures below 250 °C. However, the regrowth process is complex, with the crystalline quality and regrowth rate most dependent on implant dose.

Ion implantation in GaAs

Recent advances in the understanding of the relationship between implanted dopant solubility and electrical activity in GaAs are reviewed and direct lattice configuration measurements explaining these results are presented. The nature of residual defects remaining after activation annealing of GaAs, in particular rapid thermal annealing, are discussed, along with a review of the application of ion beams in promoting compositional disordering of GaAs-AlAs superlattices. The outstanding problems remaining in the use of ion implantation technology for GaAs are also detailed.

Substitutional solid solubility limits during solid phase epitaxy of ion implanted (100) silicon

High resolution channeling techniques have been used to investigate the maximum nonequilibrium solid solubility which can be achieved during low‐temperature (⩽600 °C) epitaxial regrowth of high‐dose antimony and indium implanted (100) silicon. The substitutional impurity concentration is observed to increase with implant dose and saturate at a limiting concentration well above the maximum equilibrium solid solubility for antimony or indium in silicon. Observed correlations between the measured solubility limits, epitaxial regrowth rates, and intriguing impurity redistribution effects suggest that impurity size and attendant lattice strain at the crystal‐amorphous interface may determine the substitutional solubility limit for low‐temperature annealing, where impurity diffusion lengths are negligible during the time of epitaxial recrystallization.

Thin‐film adhesion changes induced by electron irradiation

The adhesion of thin films of gold, sputter deposited onto silicon, is shown to be improved by subsequent irradiation with 5–30‐keV electrons. The similarities between electron and heavy ion irradiation effects suggest a common (electronic) origin for the change in interfacial bonding.

Impurity‐stimulated crystallization and diffusion in amorphous silicon

An amorphous‐to‐polycrystalline silicon transformation and concomitant In redistribution have been observed in In‐implanted silicon at temperatures well below those at which solid phase epitaxial growth or random crystallization is observed in undoped films. The process is extremely rapid and exhibits a strong dependence on both In concentration and temperature. It is proposed that the In redistribution and accompanying silicon crystallization are mediated by molten, In‐rich precipitates in amorphous silicon.

DIFFUSION OF IMPLANTED IMPURITIES IN AMORPHOUS SI

The diffusion coefficients of Cu, Ag and Au have been measured in implanted, amorphous Si. The temperature dependences over the range 150–600° C are characterized by Arrhenius relationships with activation energies for Cu, Ag and Au of 1.25, 1.6 and 1.4 eV, respectively. Diffusion is concentration dependent. The diffusion coefficients correlate remarkably well, when extrapolated to high temperatures, with the corresponding slower or “substitutional-like” diffusion coefficients in crystalline Si.

Solid phase epitaxial regrowth phenomena in silicon

Abstract The recrystallisation of ion implanted amorphous layers on silicon is a simple activated process which proceeds epitaxially on the underlying bulk silicon at temperatures of around 600°C. However, detailed recrystallisation studies have revealed some interesting crystal growth phenomena which can be conveniently classified into processes occurring at either low or high implanted concentrations. An overview of the various high and low dose regrowth observations are given in this review. Particular attention is given to two aspects which have been the subject of recent investigation, namely, (a) the influence of electronic processes on epitaxial growth, and (b) the formation and stability of supersaturated solid solutions of implanted dopants in silicon.

Ohmic contacts produced by laser‐annealing Te‐implanted GaAs

We report the formation of Ohmic contacts to high‐dose (∼1016 cm−2) Te‐implanted n‐type GaAs annealed with a Q‐switched Nd : YAG laser. The annealing results in a Te concentration greater than 10 times the equilibrium solubility and the formation of free Ga at the surface. Ohmic contacts of specific contact resistance rc≃2×10−5 Ω cm2 were obtained by first removing the surface Ga by an HCl etch and then backsputtering to remove 50 A of GaAs, thereby exposing a surface of high Te concentration.