Studies of boron diffusivities on (001) and (110) substrate orientation in Si and Ge along vertical/out-of plane and lateral/in-plane directions study

Abstract

Systematic investigation on boron diffusivities along different diffusion directions in Si and Ge substrates is presented in this work. Dopant diffusivities along vertical and lateral directions are extracted experimentally with nano-meter-resolution from secondary ion mass spectroscopy measurement and capacitance–voltage measurement on a test pattern, respectively. The results show that boron diffusivities in Ge are smaller than in Si along random diffusion directions and substrate orientations (~0.84× in (001)/<001>, ~0.86× in (110)/<110>, ~0.78× in (001)/<110>, and ~0.875× in (110)/<1-10>). Moreover, boron diffusivities on the (110)-oriented substrate are also found to be higher ~1.33× than in (001)-oriented substrate. An interesting finding in this work is that wafer orientation, (001) or (110), plays a more important role than the substrate material in boron diffusion along the vertical direction, while the substrate material is more important than wafer orientation for diffusion in lateral direction. Combination with this observation and the understanding of the lateral dopant diffusion playing the more important role for the device junction design than the vertical dopant diffusion, Ge channel device can provide not only the higher mobility than Si channel device but also the higher capability to further retard the boron diffusion with the better short channel control along the lateral dopant diffusion direction, especially in the advanced FinFET structure having two (110) substrate orientation surfaces with looser crystal lattice density and larger dopant diffusivity.