Molecular dynamics study of implant and damage formation in low-energy boron cluster ion implantation

Cluster ion implantation using decaborane (B₁₀H₁₄) has been proposed as a useful technique for shallow junction formation. In order to examine the characteristics and advantages of cluster ion implantation, molecular dynamics simulations of small B cluster and monomer implantation were performed. B₁, B₄ and B₁₀ are irradiated on Si (001) substrates with acceleration energy of 230 eV/atom so that B₄ and B₁₀ are accelerated with 0.92 keV and 2.3 keV, respectively. Those three show the same implant profile and implant efficiency, which agrees with the experimental result of B₁₀H₁₄ implantation. This result suggests that each B atom in a B cluster acts individually in similar way to a monomer ion. B clusters show the same properties in projection range and implant efficiency as the monomer whereas non-linearity is shown in damage formation. The number of displacements by one B atom once increases to the same maximum value for both a B cluster and a B monomer. However, the damage recovery process is different depending on the cluster size. Damage induced by B₁₀ recovers more slowly and 4 times as many displacements remain compared to B₁ 8 ps after impact. These displacements by B₁₀ clusters concentrate in the near surface region of the impact point, while the ones by B₁ reside around the implanted B atom as the end-of-range damage. This characteristic damage formation by B₁₀ cluster is expected to avoid transient-enhanced-diffusion of incident B atoms and achieve the formation of high-quality shallow p-type junction.