A.P. Pogany

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.

Ion beam induced epitaxial crystallisation of silicon

Abstract It is shown that epitaxial crystallisation of amorphous silicon layers can be induced by irradiating samples with energetic light ions at temperatures in the range 673–723 K. This epitaxial process is shown not to be a consequence of macroscopic beam heating. Under certain irradiation conditions Rutherford backscattering/channeling analysis suggests that the regrown silicon is nearly perfect single crystal but TEM analysis, while confirming epitaxial growth, reveals the presence of extended defects which result from the elevated temperature helium bombardment. Evidence is presented to support the view that ion beam induced epitaxy is a consequence of mobile, ion irradiation induced defects created at, or near, the crystal-amorphous interface.

Colloidal Au and Ag precipitates formed in Al2O3 by ion implantation and annealing

Abstract Ion implantation and thermal annealing have been used to create localized regions containing a high density of colloidal Au or Ag precipitates in Al2O3. These colloidal precipitates give rise to dramatic optical absorption effects through surface plasmon resonance absorption. Strong optical absorption is observed at 2.25 eV for Au implanted Al2O3 and at 2.75 eV for Ag implanted Al2O3 after annealing. Preliminary measurements of the third-order nonlinear optical susceptibility are discussed also.

Characterisation of MeV neon damage in silicon

Abstract Ion backscattering (RBS)/channeling and transmission electron microscopy (TEM) have been combined to characterise the radiation damage produced in crystalline silicon during irradiation with 1.5 MeV Ne + . The resulting damage structures and distributions are found to be a sensitive function of substrate temperature. In particular, for temperatures between 20 and 300°C the disorder is found to increase gradually from the surface to a peak at the projected ion range, whereas, for temperatures greater than 300°C the disorder is observed to have a very distinctive distribution, consisting of a narrow band of extended defects at the projected ion range but with the surface region essentially defect free to depths of ~ 1.4 μm. This latter structure has been employed to obtain an accurate measure of the channeled to random stopping power ratio (0.53 ± 0.05) for 3 MeV He + incident along a 〈001〉 silicon axial direction.

An investigation of phase formation by high dose silicon ion implantation into nickel

Abstract Structural changes and phase transitions during 1017–1018 ions/cm2 silicon ion implantation (at 100 keV) into nickel and subsequent annealing have been studied. Single crystal Ni samples were examined by Rutherford backscattering spectrometry and channeling (RBS-C) and reflection high energy electron diffraction (RHEED). Polycrystalline samples were thinned after ion implantation for TEM (transmission electron microscope) observations which included in situ annealing at temperatures up to 800°C. The structural changes were found to be critically dependent on the Si concentration which builds up with increasing implantation dose. Partial amorphization occured at intermediate doses higher than 1 × 1017 ions/cm2 and a complete amorphous layer formed at a nominal dose of 4.5 × 1017 ions/cm2 or above. The in situ annealing of selected prethinned specimens revealed a variety of nickel silicide phases depending on annealing conditions. This behaviour is discussed in terms of the availability of Ni supply during the annealing.

Dechanneling analysis of disorder in (100) gallium arsenide

Abstract The methods of transmission electron microscopy and high resolution RBS/channeling with MeV energy He + ions have been applied to a study of defect structures in ion implanted (100) GaAs. Implant conditions (substrate temperature 102 K, implants of 100 keV Te + to fluences between 4×10 13 and 2×10 14 cm −2 ) and anneal schedule (15 min at 623 K) were chosen to promote the formation of twins in the near-surface region of the epitaxial regrowth layer. TEM diffraction patterns and dark field micrographs from the annealed samples gave evidence for twinning on {111} planes. The residual amorphous layer thickness was estimated to be less than 2 nm for all cases. Rutherford backscattering spectra were recorded for He + ion channeling in the [001] direction and dechanneling characteristics determined for a range of ion beam energies. From the combined analyses a picture emerges of a regrowth layer rich in twins, initially with the 〈221〉 directions of the twins parallel to the 〈001〉 directions of the original crystal, but becoming progressively misoriented towards the surface.

Effect of heat treatment on the properties of gallium‐implanted polycrystalline silicon

Polycrystalline silicon films deposited on silicon dioxide were partially amorphized by implantation with 100 keV gallium ions to a dose of 6×1015 cm−2. These films were then subjected to various heat treatments at 580 and 900u2009°C using conventional furnace or rapid thermal heating techniques. Sudden drops in sheet resistance occurred at lower temperatures with little change upon further heating. However, the high‐temperature annealed specimen shows only an increase in sheet resistance with time. An explanation of these changes is proposed in terms of a liquid phase melting mechanism taking place during the crystallization of the amorphized near‐surface layer. Transmission electron microscopy and Rutherford backscattering observations support this explanation.

Characterization of Structural Changes and Defects in Ion Bombarded GaAs

In-situ time resolved reflectivity, Rutherford backscattering and channeling and transmission electron microscopy have been employed to characterise the evolution of Ar + ion implantation damage in GaAs as a function of ion dose at various irradiation temperatures. Specific reflectivity signatures have been identified and characterised in terms of observed structural changes to the GaAs. Reflectivity provides a simple and convenient means of monitoring damage build up during ion implantation. In contrast to accepted models for amorphous phase formation in semiconductors, GaAs has been observed to undergo a sudden transformation from a crystal containing a dense network of extended defects to an amorphous phase under elevated temperature irradiation conditions.

Ion-Beam-Induced Damaging and Dynamic Annealing Processes in Silicon

We have employed high resolution ion channeling and TEM methods to investigate the damage production and dynamic annealing processes which take place in (100) silicon bombarded at elevated temperatures. Two important observations have arisen from our results i) We have observed an amorphisation process for Sb-implanted silicon at 250°C which is more akin to amorphisation processes in metals, whereby the impurity (Sb) appears to influence the stability of amorphous zones associated with individual ion tracks. ii) We have demonstrated that previously amorphised layers in silicon can be recrystallised through a solid phase epitaxial process by subsequent bombardment with He + , Ar + and Sb + ions at substrate temperatures of 300–400°C, which are significantly below normal thermal regrowth temperatures of >500°C.

Ion-beam-induced amorphization/crystallization during buried oxide layer formation

Abstract Residual disorder in crystalline and preamorphized Si substrates implanted with 150 keV O ions has been investigated. Ion-beam-induced amorphization and crystallization was studied as a function of ion dose, energy deposition density per ion and implantation temperature. The competition between defect production and dynamic annealing has been demonstrated by the reversible displacement of a planar amorphous/crystalline interface under keV ion irradiation.