High performance poly Si junctionless transistors with sub-5nm conformally doped layers by molecular monolayer doping and microwave incorporating CO2 laser annealing for 3D stacked ICs applications

Abstract

A junctionless (JL) fin thin film transistor (FinTFT) with a novel shell doping profile (SDP) formed by a damage-free conformal molecular monolayer doping (MLD) method and a combination of microwave annealing (MWA) and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser spike annealing (COLSA) is demonstrated and studied. MWA drives in and partially activates the MLD dopants; the resultant SDP features an ultra-shallow depth (<; 5nm) and an abrupt steepness (<; 0.8 nm/dec). The dopant activation of the devices experienced MLD and MWA is further enhanced by the nonmelting COLSA without dopant diffusion, and which can also avoid fin deformation and recover surface defects left by fin patterning. Thanks to the enhanced dopant activation by COLSA, the SDP-FinTFTs overall exhibit better performance than the SDP-FinTFTs without COLSA and the conventional implanted (imp) FinTFTs in terms of subthreshold swing (S.S.), on-currents (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> by 160% compared to the SDP-FinTFTs without COLSA) and on/off current ratio (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> ) for 3D stacked ICs applications. Our results reveal the potential of the proposed SDP formed by MLD, MWA and COLSA enabling a JLFinTFT showing excellent performance.