Study on Ultra Shallow Junction n-MOS with 350°C Microwave Annealing for Activation of Phosphorus Dopants in Germanium

Abstract

In this study, low-energy microwave annealing is used to fabricate ultra-shallow junctions for less than 20 nm IC node applications in a potential material: Germanium (Ge). Germanium is a new promising material and might replace silicon in the future. A novel microwave annealing technique with two steps for the solid phase epitaxial recrystallization (SPER) and phosphorus dopants activation was applied to Germanium. The purpose of the first step, microwave annealing of 1.2 kW for 75 s, is to re-grow the amorphous layer and repair the destroyed crystal lattices caused by ion implantation. In the second-step of annealing, low-energy microwave, 0.9 kW (≈350°C) for 300 s, is used to activate the phosphorus dopants effectively without diffusion and de-activation. The target dopant activation concentration level will achieve 10²⁰ cm^-3. The sheet resistance will decrease to 78 ohm/sq. The low resistance after activating is reflected to the performance of the n-MOS device fabricated by the Ge substrate. The S. S. factor is 900 mV/dec, and the I_on/off ratio rise to 2.6×10¹. This has demonstrated that the two-step MWA has excellent control, significantly regarding leakage current.