Swelling of SiC under helium implantation

Single crystals 4H-SiC were implanted with 50 keV helium ions at temperatures up to 600 deg. C and fluences in the range 1x1016-1x1017 cm-2. The helium implantation-induced swelling was studied through the measurement of the step height. The different contributions of swelling were determined by combining simulations of x-ray diffraction curves and transmission electron microscopy observations. At room temperature, amorphization occurs between 1 and 2x1016 cm-2, inducing the decrease in density of about 15%. For high-temperature implants, amorphization does not occur. The strain profiles show saturation in the near-surface region, indicating that a threshold concentration of defects is reached. All the additional point defects created during the implantation have been supposed to annihilate. In the region of high-energy deposition density, the value of strain increases with fluence up to values larger than 6%. The elastic contribution to swelling has been obtained by integration of the strain profile determined by x-ray diffraction simulations. Then, the contribution of helium bubbles to the step height is found to be linear with the fluence: 0.8 nm/1016 He/cm2