A study of the formation of nanometer-scale cavities in helium-implanted 4H-SiC

In this work, the annealing behavior of microstructures in 4H-SiC helium-implanted at about 500 K to moderate doses (2.5-5)×10¹⁶ ionscm^-2 is studied by combining transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). It is found that a low concentration of planar clusters of helium bubbles in ring structures was formed in a narrow range of dose in a well-defined depth region of the specimens on annealing above 973 K. The formation of the bubble layer is associated with remarkable distortion and deformation in the matrix. A simple model based on the frozen matrix assumption was developed to study the production of defects in SiC below the temperature of vacancy mobility. We found that the main features of the depth distribution of the bubble layer can be understood using this model if assuming the planar clusters of bubbles evolve from vacancy clusters larger than a critical size through an intermediate stage of helium platelets.