1/f noise, hydrogen transport, and latent interface-trap buildup in irradiated MOS devices

A large, delayed increase is observed in the postirradiation 1/f noise of Oki pMOS transistors prior to the onset of latent interface-trap buildup. Both effects are evidently due to similar thermally activated processes involving hydrogen. The increased noise through irradiation and anneal is found to be caused not only by the generation of defects at or near the Si/SiO₂ interface, but also by an apparent transition from buried to surface channel conduction. This is evidently triggered by the passivation of dopants in the Si by hydrogen transport during irradiation and anneal. Switched bias annealing confirms many of these effects are reversible. Three types of hydrogen transport are identified in MOS oxides: dispersive transport leading to “two-stage” interface-trap buildup, retarded transport leading to latent interface-trap buildup, and blockaded transport leading to proton confinement in SiO₂. The nature of the transport appears to correlate with O vacancy density and the temperature at which hydrogen is incorporated into the SiO₂ . Implications are discussed for enhanced bipolar low dose rate response, the sensitivity of pMOS dosimeters, and protonic nonvolatile memory elements