Annealing and recrystallization of amorphous silicon carbide produced by ion implantation

Abstract

The annealing behavior of amorphous SiC layers produced by MeV Si implantation into 6H–SiC has been investigated systematically by means of step height measurements, x-ray diffraction, and optical microscopy. Two annealing stages are found. Each of them causes a specific densification of the amorphous layer. At temperatures between 250 and 700 °C both the rapidity and the low activation energy (184 meV) of the densification suggest that defect annealing processes are responsible for densification. Partial crystallization and changes of the amorphous network structure can be excluded as a possible reason for low temperature densification. Annealing at temperatures above 700 °C is characterized by a combination of defect annealing and recrystallization. The crystallization kinetics is analyzed in terms of the Johnson–Mehl–Avrami theory. It is shown that the crystallization mode changes with increasing temperature from nucleated growth at 800 °C to epitaxial growth at 1000 °C. The recrystallization generates stress in the layer which leads to surface cracking if the layer exceeds a critical thickness.

A Method to Improve Activation of Implanted Dopants in SiC

“…However, the remainder of the implanted region is not in registry with the bulk. Annealing appears to have resulted in formation of randomly oriented polycrystals, consistent with the results of Höfgen et al [8] that showed crystallization of α-layer in SiC yields a polycrystal with different polytypes. Even after annealing at 1200°C, there appears to be little preferential alignment of the polycrystals with the bulk except a small amount of epitaxial growth in the interfacial region.…”

“…Amorphous layers in Si crystallize during annealing by SPEG at the crystal-α interface to yield defect-free, single-crystal with the implanted dopant trapped substitutionally within the lattice, even at concentrations far exceeding solid solubility. Unfortunately, bulk nucleation during recrystallization of α-layers in SiC leads to the formation of a polycrystalline phase consisting of misoriented grains of different SiC polytypes [8]. In addition, stress generated during recrystallization leads to severe cracking within the layer extending into the substrate (substantially beyond the depth of the amorphous interface) and partial exfoliation of the surface.…”

Characterization of the ion-amorphization process and thermal annealing effects on third generation SiC fibers and 6H-SiC

“…However, little information concerning thermal annealing-induced mechanical failure is available for SiC. It has been reported that thermal stresses -arising from a mismatch between the coefficient of thermal expansion of the irradiated layer and the pristine substrate -are not responsible for the mechanical failure [37] and recrystallization-related stresses have been pointed out as the cracking and delamination cause [36,37]. In order to provide further information on how recrystallization is related to mechanical failure, several thermal annealing tests on ion-amorphized 6H-SiC single crystals have been conducted and observed at different temperature ramps via in situ E-SEM.…”

“…it has been reported that thermal annealing has an undesirable side effect. As shown in Figure 8, it induces mechanical failure of the ion-amorphized layers in single crystals SiC [25,36] and in HNS fibers [37]. However, little information concerning thermal annealing-induced mechanical failure is available for SiC.…”

“…0.36-0.65 25 to 2.1 36 eV, sustaining that recrystallizationrelated stresses are the underlying mechanism which induced mechanical failure.…”