Boron diffusion in ion-implanted and annealed single-crystal and amorphized Si is compared to determine the effect of amorphization on the initial transient boron motion reported for single crystal. The boron was implanted at 20 keV and at doses of 1×1015 and 3×1015cm−2. The Si was either preamorphized or postamorphized to a depth of 320 nm by implantation of Si ions at three different energies. In the amorphized samples the entire boron profile was always contained within this distance. The samples were annealed by furnace or rapid thermal annealing to 900–1100 °C with or without a preanneal at 600 °C. The initial rapid diffusion transient in the tail region of the boron profile was observed in all the crystal samples. This transient was totally absent in the amorphized samples. This is manifest by careful comparison of boron concentration profiles determined by secondary ion mass spectrometry of single-crystal and amorphized samples after annealing. For anneals where significant motion occurs, the profiles of the amorphized samples could be fit with a computational model that did not include anomalous transient effects. It is proposed that excess interstitials cause the transient diffusion in the case of the crystalline samples. The source of interstitials is believed to be provided by the thermal dissolution of small clusters that are formed by the implantation process. They exist for only a short time, during which they enhance the boron diffusion. Since there is no enhanced diffusion in the amorphous region that regrows to single crystal, apparently interstitial clusters are neither produced by nor do they survive the regrowth process in that region. In addition, the interstitials generated by the damage beyond the amorphous-crystalline boundary are prevented from entering the regrown region by the dislocation loops formed at that boundary which act as a sink consuming the interstitials diffusing toward the surface.

Ge segregation at SiGe/Si heterointerfaces has been studied for films deposited by atmospheric pressure chemical vapor deposition (APCVD), ultrahigh vacuum CVD (UHV/CVD) and molecular beam epitaxy (MBE). Profiles were taken by secondary-ion-mass-spectroscopy (SIMS) of samples grown with these techniques at the same growth temperatures and Ge concentrations. The MBE grown profiles are dominated by segregation of Ge into the Si top layer in the temperature range from 450 to 800 °C. SiGe/Si interfaces deposited by UHV/CVD at elevated temperatures are smeared, but at 515 °C and below the interfaces are abrupt within the resolution of the SIMS. Heterostructures grown by APCVD show abrupt interfaces and no indication of Ge segregation in the investigated temperature range from 600 to 800 °C. Surface passivation by hydrogen appears to be responsible for the suppression of the Ge segregation in CVD processes.

Epitaxial Si has been grown selectively on oxide-patterned substrates from 850 down to 600 °C for the first time in the Si-Cl-H system at atmospheric pressure. Si deposition was achieved by hydrogen reduction of dichlorosilane in an ultraclean system using a load lock. Epitaxy was achieved at low temperatures only when the hydrogen was purified to remove traces of H2O and O2 implying that an oxygen-free environment is the most important factor controlling epitaxy at low temperatures. Cross-sectional transmission electron micrographs reveal perfect crystallinity in the epitaxial layer and a totally clean and featureless interface between epitaxy and substrate.

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We have measured the resonant tunneling current-voltage I(V) characteristics of strained p-Si/Si 1Ϫx Ge x double-barrier microstructures ranging from 1.0 to 0.1 m in lateral extent. The bias spacing between resonant current peaks in the I(V) reflects the energy separation of the Si 1Ϫx Ge x quantum well subbands, which is partially determined by the strain. As the lateral size of the structures decreases, we observe consistent shifts in the I(V) peak spacing corresponding to strain energy relaxation of ϳ30% in smaller structures. An additional I(V) fine structure is observed in the 0.1 m device, consistent with lateral quantization due to nonuniform strain.

Resonant tunneling measurements are used to probe the inhomogeneous strain in individual SiGe quantum dots. Current–voltage characteristics of strained Si/SiGe resonant tunneling diodes of diameter D⩽0.25 μm exhibit additional fine quasi-periodic structure in the resonant peaks. The fine structure is consistent with lateral quantization in the SiGe quantum well due to in-plane confining potentials arising from inhomogeneous strain, which we calculate by finite element techniques for various D. Quenching of the fine structure by a magnetic field is consistent with the effective length scale of the strain-induced potential.

n and p-Type doping of epitaxially grown Si over the temperature range from 850~ to as low as 550~ was investigated in an atmospheric pressure reactor. P, As, and B could be incorporated into single-crystal silicon at levels exceeding the solid solubility at growth temperatures to levels greater than 1 • 102~ 3. Remarkably, each of the hydride dopant sources, PH3, ASH3, and B2H6, dramatically enhanced the growth rate of Si from dichlorosilane (DCS) at lower temperatures. Such results are unprecedented for the growth of Si from dichlorosilane (DCS) (which has been restricted to higher growth temperatures until recently) and for growth from Sill4 (which has been practiced over a wide range of temperatures). Growth was carried out primarily from DCS in H2 carrier gas, although some experiments utilizing Sill4 were performed, in order to explore the mechanisms responsible for growth rate enhancement of doped films. Instrumental in achieving these results has been the ultraclean, load-locked atmospheric pressure reactor, which permits high-quality epitaxial growth at temperatures not previously obtainable with DCS. Thus utilizing conventional Si and dopant sources in an unconventional regime, doping behavior suitable for advanced device structures was obtained.

Short time annealing has recently become of interest in silicon processing as a technique to activate ion implanted dopants, remove defects, and regrow amorphized silicon, with minimal diffusion of the dopant atoms. Short time annealing is carried out using a variety of energy sources ranging from arc lamps and resistance heaters with heating times of a few tens of seconds, to laser, electron, and ion sources with heating times of a few milliseconds down to nanoseconds. The annealing processes are grouped according to the time durations of the anneal and with reference to the thermal response time of the silicon. These are designated as adiabatic for < 10−6 sec; thermal flux for 10−6–10−2 sec, and isothermal for > 10−2 sec. Processes in the adiabatic regime result in surface melting, regrowth of silicon free of extended defects, and complete dopant activation. However, the dopant diffuses throughout the melt zone. In the thermal flux and isothermal annealing regimes the dopant can be activated, and amorphous silicon regrown epitaxially with little dopant diffusion. In the limited results reported to date, the complete removal of extended defects has not been achieved. Further investigation may yield new results in extended defect removal.