Evolution of mechanical properties of SiC under helium implantation

Mechanical property changes of 4H-SiC implanted at room temperature with helium ions at fluences ranging from 7 x 1015 to 1 x 1017 cm-2 and at an ion energy of 50 keV were investigated by using nano-indentation tests and subsequent atomic force microscopy investigations. Degradation of the mechanical properties of the near-surface due to helium implantation was analysed and correlated with the microstructure evolution examined through transmission electron microscopy cross-section and X-ray diffraction experiments. Up to 1 x 1016 He+ cm-2 no significant change in mechanical properties is seen whereas a normal strain profile of few percents is generated all along the ion path. Nevertheless, the as-created implantation damage enhance the dislocation nucleation. At intermediate fluences, when a buried amorphous layer is created, the hardness curve against penetration depth can be divided into three stages showing 'constraining coating' effects. When the entire part of the implanted crystal is amorphous a decrease of about 50% is measured for hardness value