Yihong Lu

Planar Bulk MOSFETs With Self-Aligned Pocket Well to Improve Short-Channel Effects and Enhance Device Performance

We present and demonstrate a self-aligned pocket well (SPW) structure used in planar bulk MOSFETs with a metal gate length of 25 nm and an effective channel length less than 20 nm. The SPW features a retrograde doping profile in vertical direction and a doping profile self-aligned with drain/extension in lateral direction. A novel process, called replacement spacer gate (RSG), is designed to avoid challenges in gate patterning and high-k metal gate filling. Planar bulk pMOSFETs, with SPW and halo doping, respectively, were simulated and fabricated adopting the RSG process. Due to its retrograde feature, the SPW can achieve low drain-induced barrier lowering (DIBL) along with low VT. Compared with halo doping with the same VT,sat at VDD = 0.8 V, despite no ION enhancement, the SPW reduces DIBL by 45% and enhances IEFF by 18%. Compared with halo doping with the same IOFF = 100 nA/μm at VDD = 0.8 V, the SPW structure reduces DIBL by 16%, enhances ION by 5%, and improves IEFF by 30%. In addition, with the self-aligned feature, the SPW does not deteriorate junction band-to-band tunneling (BTBT)

Mitigation of Reverse Short-Channel Effect With Multilayer TiN/Ti/TiN Metal Gates in Gate Last PMOSFETs

This letter investigates the mitigation of reverse short-channel effect (RSCE) using multilayer atomic layer deposition (ALD) TiN/PVD Ti/CVD TiN metal gates (MG) for the p-channel metal-oxide-semiconductor field-effect transistors fabricated the by gate-last process. It is found that work function (WF) of multilayer ALD titanium nitride/physical vapor deposition titanium/chemical vapor deposition titanium nitride (ALD TiN/PVD Ti/CVD TiN) MG in devices of short channels is larger than in devices of long channels. This mainly results from different ALD TiN crystal orientations for devices with different gate lengths, that is, TiN(100) for devices with short gate length, whereas TiN(111) for devices with long gate length. The WF of ALD TiN(100) is larger than TiN(111). Meanwhile, because of the property of PVD sputtering, the Ti layer is thinner in devices of short channels than in devices of long channels. Our results on MOSCAP show that the flat-band voltage (Vfb) for TiN MG with a Ti layer is reduced by 0.2 V. Taking all the aforementioned into account, Vth roll-up is suppressed as the gate length shrinks, leading to the mitigation of RSCE.