Epitaxial Growth of Implanted Amorphous Si

The series of spectra presented in Fig. 10.4 shows the reduction in thickness of the amorphous layer as a function of anneal time for a (100) Si sample held at 550°C. This data demonstrates that the regrowth originates at the interface between the amorphous layer and the underlying single crystalline Si and proceeds to the surface. The interface on (100) Si shifts to the surface linearly with time, indicating a uniform regrowth velocity. 

Channeling measurements have been used to study the epitaxial regrowth of Ge and Si crystals amorphized by ion implantation for a variety of crystal orientations (Csepregi et al. 1977). These studies have shown that, with the exception of (111) orientated Si crystals and samples cut within 16° of the (111) direction, the amorphous/crystal interface moves with a constant velocity toward the surface (at a fixed annealing temperature) and maintains a laterally uniform front. 

Measurements of the growth velocity, vg of the crystal-amorphous interface are shown in Fig. 10.6. The measured velocities extend over nearly ten orders of magnitude and can be characterized by a single-activation energy, EA = 2.76 eV, (Olson and Roth 1988) so that 

The presence of high concentrations of implanted dopants influences the epitaxial growth rate. As shown in Fig. 10.7, concentrations of phosphorus at levels greater than 0.1 atomic percent (5 x 1019 cm3) cause an increase in the growth rate. This increase is similar to the increase in the diffusion coefficient of dopants, which is attributed to an increase in the vacancy concentration in heavily doped Si, where the Fermi level is near the conduction or valence-band edges. The concentration of vacancies in Si depends on the charge state of the vacancy. The neutral vacancy concentration [Vx] (Mayer and Lau 1990) is given by 

A square bracket notation indicates concentrations. The equilibrium concentration of neutral vacancies in Si is independent of the position of the Fermi level, and so there is no reference to the Fermi energy in (10.2). For Si, Hlv = 3.6eV for a neutral vacancy and the term Sly = 1.1 K, which gives the first expeditional term a value of 3, and N= 5.0 x 1022 cnT3 (the concentration of Si lattice sites), 

Measurements of the growth velocity as a function of temperature indicate that the growth process is thermally activated, with an activation energy of about 

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Fig. 10.6. Growth rate versus 1/kT for solid-phase epitaxial regrowth of implanted amorphous Si on (100) Si (from Olson and Roth 1988)...

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