A simple doping method to fabricate a very thin channel body of the p-type FinFETs with a 20 nm gate length by solid-phase-diffusion (SPD) process was developed. Using the poly-boron-films (PBF) as a novel diffusion source of boron and the rapid thermal annealing (RTA), the p-type sourcedrain extensions of the FinFET devices with a threedimensional structure were doped. The junction properties of boron doped regions were investigated by using the $p^+-n$ junction diodes which showed excellent electrical characteristics. Single channel and multi-channel p-type FinFET devices with a gate length of 20-100 nm was fabricated by boron diffusion process using PBF and revealed superior device scalability.