A recessed channel MOSFET with plasma-grown silicon oxynitride gate dielectric

Fabrication and electrical characterization of a recessed channel n-MOSFET on a p on p⁺ epi-layer and with plasma-grown silicon oxynitride (SiON) as the gate dielectric, are reported. This non-planar MOSFET structure was devised to have suppressed short channel effects; and the effects of plasma-grown SiON on the device characteristics were studied. The proposed structure was fabricated by using anisotropic wet etching to etch the channel and by using solid phase diffusion to form the source and drain. The gate silicon oxynitride layer (thickness 7nm) was fabricated by nitridation of pre-grown SiO₂ in a nitrogen plasma. The pre-oxide was also grown by oxidation of Si in oxygen plasma. Plasma-grown gate SiON showed higher breakdown strength over plasma-grown SiO₂. MOSFETs (L/W=2.2μm/22μm) with plasma nitrided gate SiON demonstrated higher on-state currents compared with devices with plasma-grown gate SiO₂. The improved on-state currents are related to increased channel carrier mobility which is supposed to be due to interface property improvements brought about by plasma nitridation.