Monolayer-level controlled incorporation of nitrogen in ultrathin gate dielectrics using remote plasma processing: Formation of stacked “N–O–N” gate dielectrics

Abstract

A low thermal budget approach to monolayer-level controlled incorporation of nitrogen in ultrathin gate dielectrics using 300 °C, remote plasma processing is discussed. Incorporation of approximately 1 ML of nitrogen at the ${\mathrm{Si–SiO}}_2$ interface in an $\mathrm{“N–O”}$ structure has been achieved by remote plasma-assisted oxidation of the Si surface followed by ${\mathrm{N}}_{\mathrm{2}}\mathrm{/He}$ remote plasma nitridation, each at a process pressure of 0.3 Torr. The interface nitridation reduces direct and Fowler–Nordheim tunneling by at least one order of magnitude, independent of film thickness. Incorporation of nitrogen at the top surface of the oxide in a concentration equivalent to about 1–2 molecular layers of silicon nitride in an $\mathrm{“O–N”}$ structure has been accomplished by ${\mathrm{N}}_{\mathrm{2}}\mathrm{/He}$ remote plasma nitridation at 300 °C, but at a reduced process pressure of 0.1 Torr. Top surface nitridation has been shown to prevent boron diffusion out of $p^{+}$ poly-Si gate electrodes during high-temperature activation anneals, e.g., at 1000 $°$ C. Combining interfacial and top surface nitridation processes resulted in a $\mathrm{“N–O–N”}$ structure that was effective in reducing tunneling leakage currents and suppressing boron out-diffusion from $p^{+}$ poly-Si gate electrodes.