Effects of B18Hx+ and B18Hx dimer ion implantations on crystallinity and retained B dose in silicon

Abstract

The effects of B18Hx+ and B18Hx dimer ion (B36Hy+) implantations on Si crystallinity and the retained B dose in Si were investigated using B18Hx bombardment and compared with the effects of B+ implantation. Crystallinity was estimated for the implantation dose using molecular dynamic simulations (MDSs) and was quantified using the optical thickness obtained from spectroscopic ellipsometry. The authors focused on the crystallinity at a low B dose and compared the amorphized zones predicted by MDS for B18Hx+ implantation with those measured using transmission electron microscopy; the predicted and measured results were in reasonable agreement. The authors then used their understanding of B18Hx bombardment to discuss the process for the generation of larger amorphized zones and thicker amorphized layers, as observed in B36Hy+ implantation. The retained B dose and the sputtering were examined with secondary ion mass spectroscopy, focusing on a comparison of the retained B and the sputtering of Si and SiO2 surfaces. The retained B dose was lower for B18Hx+ and B36Hy+ implantations, with and without surface SiO2, than for B+ implantation, although no sputtering was observed. The reduction of the retained B dose was more severe in the samples with SiO2. The origin of the differences between Si and SiO2 surfaces was considered to be Si melting; this was predicted by the MDSs, and observed indirectly as flat B profiles in the Si region. To examine the effects of both crystallinity and retained B dose on the electrical characteristics, the sheet resistance (RS) was measured. The RS for B18Hx+ implantation was lower than that for B+ implantation at both B doses studied. Additionally, the B36Hy+ implantation under conditions that produced a thicker amorphized layer led to lower RS than B18Hx+ implantation. These results indicate that both the amorphized layer and the amorphized zone contribute to the activation of more B atoms.