Conformal doping strategy for fin structures: tailoring of dopant profile through multiple monolayer doping and capping layer control

Monolayer doping (MLD) has attracted attention as a next-generation doping method because of its great potential for conformal doping of non-planar nanostructures. However, fundamental limitations are identified in conformal doping of fin structures using conventional MLD process, and fin structures doped with conventional MLD presents a poor dose conformality (surface concentration ratio between the side-wall and the top of the fin) of 0.32. The poor dose conformality is mainly caused by the hydrogen-terminated silicon surface formed differently depending on the orientation of each face of the fin structure and the capping layer deposited with low step coverage on the fin structure. As a strategy to overcome the limitations without increasing process complexity, multiple-MLD for dose compensation and capping layer thickness control for adjusting the dopant diffusivity are proposed. These methods are found to be effective in tailoring doping profiles on each face of the fin structure with a fine dose controllability from about 70% to 200%. Finally, it is demonstrated that the proposed approach allows conformal doping of the fin structure with a high surface concentration of 5 10²⁰ atoms cm^-3 and an excellent dose conformality of 0.98.