High-Performance P-Type Germanium Tri-Gate FETs via Green Nanosecond Laser Crystallization and Counter Doping for Monolithic 3-D ICs

Abstract

This paper proposed a fabrication of p-type Germanium (Ge) tri-gate field-effect transistors (Tri-gate FETs) via green nanosecond laser crystallization (GNSLC) and counter doping (CD). By using the GNSLC, the nano-crystalline-Ge (nc-Ge) with a grain size of 80 nm could be turned into polycrystalline Ge (poly-Ge) with that of above $1 ~\mu \text{m}$ . With the increase of laser power, the improved crystallinity and lower hole concentration of poly-Ge were also verified by Raman spectra and Hall measurement. To fabricate the high-performance Ge Tri-gate FETs, the chemical-mechanical planarization (CMP) and counter doping (CD) process would further be utilized. The CMP process eliminated the surface roughness of poly-Ge while the CD process decreased the hole concentration of poly-Ge or even converted that into an N-type one. The effect of the CD on the performance of p-type Ge Tri-gate FETs was further investigated. Consequently, the GNSLC Ge Tri-gate FETs showed threshold voltage (Vth) of −0.41 V, ION of $7.10\times 10\; ^{-6}$ , and IOFF of $1.28\times 10\; ^{-9}$ respectively, indicating better crystallinity of the Ge channel.

Keywords

• Monolithic 3D integration
• polycrystalline Ge (poly-Ge)
• tri-gate field-effect transistors (Tri-gate FETs)
• green nanosecond laser crystallization (GNSLC)
• counter doping (CD)