Surface damage versus defect microstructures in He and H ion co-implanted Si3N4/Si

Cz n-type Si (1 0 0) wafers with a top Si3N4 layer of about 170 nm in thickness were sequentially implanted with 40 keV He ions at a fluence of 5 × 1016/cm2 and 35 keV H ions at fluences of 1 × 1015, 5 × 1015 and 1 × 1016/cm2, respectively. Creation and evolution of surface damage as well as micro-defects have been studied. Our results clearly show that production of surface damage depends strongly on both the H implant fluence and annealing temperature. Only blistering or localized exfoliation of the top Si3N4 layer has been observed for post H implantation at fluences of 1 × 1015 and 5 × 1015/cm2 upon 800 °C annealing. However, serious surface exfoliation has been found for the 1 × 1016/cm2 H co-implanted samples after annealing at 450 °C and above. The exfoliation occurs at a depth of about 360 nm from the surface, which is obviously larger than the He or H ion range. Moreover, the exfoliated craters show clear two-step structures. Cross-sectional transmission electron microscopy (XTEM) observations reveal formation of micro-cracks in Si bulk and along the original interface, which is mainly responsible for the observed surface phenomena. The formation mechanism of micro-cracks has been discussed in combination of He and H implant-induced defects, impurities as well as their interactions upon annealing.