Transmission electron microscopy investigations of damage induced by high energy helium implantation in 4H-SiC

摘要

In 4H-SiC, damage created by helium implantation at high fluence (5×10~(16) ions cm~(-2)) and high energy (1.6 MeV) was studied using different techniques of electron microscopy all along the ion path. Around the end of range, conventional transmission electron microscopy was used to observe the fine microstructure of defects in the as-implanted and 1500℃ annealed samples. No bubbles were found in the as-implanted sample while numerous cavities with different shape, size and density are present after annealing. The amorphous-crystalline (a/c) transition region was checked by high resolution transmission electron microscopy. The strain profile, determined using the large angle convergent beam electron diffraction, shows a strong correlation with the nuclear stopping curve given by SRIM simulation. The dilatation of the c axis measured all along the ion path is in agreement with the value of the observed swelling. Relaxation volumes for interstitial and vacancy do not cancel. After annealing the cavity parameters are found to be dependent on both the helium density and the as-implanted microstructure.