Evolution of strain and mechanical properties upon annealing in He-implanted 6H-SiC

The effects of annealing temperature on strain and mechanical property changes of 6H-SiC implanted with helium ions at 600 K to doses of 3 × 1015 cm−2, 1 × 1016 cm−2 and 3 × 1016 cm−2 and at an ion energy of 100 keV were investigated by using high-resolution X-ray diffraction (XRD), nano-indentation and transmission electron microscopy (TEM). Strain increases with increasing displacements per atom (dpa). Strain relaxation in terms of changes in Δd/d exhibited a linear decrease with increasing annealing temperature ranging from 873 K to 1473 K for 30 min in vacuum. The relaxation activation energies of the strains were estimated by Arrhenius law to be in the range of 0.4–0.7 eV. Irradiation-induced hardening was observed via nano-indentation measurements as a function of annealing. The hardness of the highly damaged layer decreased monotonically with increasing annealing temperature for the samples implanted with He ions to doses of 3 × 1015 cm−2 and 1 × 1016 cm−2, and where no helium bubbles were formed in the damaged layer. The hardness of the damaged layer initially decreased and then increased with increasing annealing temperature from 600 K to 1073 K for the sample implanted He ions to a dose of 3 × 1016 cm−2, where numerous helium bubbles were formed in the damaged layer. The TEM results suggest that the growth of helium bubbles emits interstitials upon annealing. These interstitials agglomerate into stacking faults and dislocation loops, which increase the hardness.