Effects of 72Ge/74Ge preamorphization combined with sub-keV boron implantation in pMOSFET fabrication

Abstract

The reduction of transient enhanced diffusion (TED) and suppression of short-channel effect (SCE) are very critical for the formation of ultra shallow junctions required for deep sub-micron devices. This article reports the nanoscale gate length of p-type metal–oxide-semiconductor field-effect transistor (pMOSFET) technology using 72Ge/74Ge germanium preamorphization implantation (Ge PAI) upon the (100)-oriented silicon substrates. It is demonstrated that the channeling can be eliminated by the formation of a Ge-implantation induced thin amorphous layer near the surface prior to boron implantation. Optimizing the amorphous layer thickness by controlling a high 72Ge/74Ge ratio, the device performance of pMOSFETs can be enhanced. In addition, the optimum conditions of Ge PAI would help the confinement of boron ions to avoid the channeling phenomenon. It is also found that the thin Ge PAI amorphous layer formed by a low 72Ge/74Ge ratio would cause the degradation of threshold voltage (Vth) roll-off characteristics, Ion/Ioff ratio and the fluctuation of 62.14% in gain factor, as compared to that formed by a high 72Ge/74Ge ratio. It is attributed to a thinner Ge amorphous layer that has a weak ability to suppress the channeling tail of boron, as compared to a thicker Ge amorphous layer at the same implanted doses and acceleration energies among various 72Ge/74Ge ratios.