First Demonstration of Vertically Stacked Gate-All-Around Highly Strained Germanium Nanowire pFETs

This paper reports on 45-nm fin pitch strained p-type Ge gate-all-around devices fabricated on 300-mm SiGe strain-relaxed-buffers (SRB). By improving the process integration flow, excellent electrical performance is demonstrated: the $Q$ factor is increased to 25 as compared to our previous work, $I_{ \mathrm{\scriptscriptstyle ON}} = \textsf {500}~\mu \text{A}/ \mu \text{m}$ at $I_{ \mathrm{\scriptscriptstyle OFF}} = \textsf {100}$ nA/ $\mu \text{m}$ is achieved, approaching the best published results on Ge finFETs. Good negative-bias temperature instability reliability is also maintained, thanks to the use of Si-cap passivation. The process flow developed for the fabrication of the single Ge nanowire (NW) is adapted and vertically stacked strained Ge NWs featuring 8-nm channel diameter are successfully demonstrated. A systematic analysis of the strain evolution is conducted on both single and double Ge NWs after the most challenging steps of the process integration flow: 1.7-GPa uniaxial-stress is demonstrated along the Ge wire, which originates from the lattice mismatch between the Ge source/drain and the Si0.3Ge0.7 SRB.