Measurements of hydrogen in metal-oxide-semiconductor structures using nuclear reaction profiling

Abstract

We report depth profiles of the hydrogen concentrations in metal-oxide-semiconductor structures measured using the nuclear reaction profiling technique with a 6.4-MeV 15N beam. In both conventionally grown and ultra-dry thermal oxide samples with aluminum or gold gate metal, a peak of hydrogen concentration is observed at the metal/SiO 2 interface. The amount of hydrogen at this interface varied from sample to sample in the range 2-6×1015 H/cm 2, which was at least 20 times as much as in the SiO2 layers. By continued irradiation with the measuring beam, most of this hydrogen was detrapped from the metal/SiO2 interface and diffused into the SiO2. The detrapping occurred much more rapidly in samples made with Al metallization than in Au gate or unmetallized samples. The data can be fitted by a model in which hydrogen is detrapped from the metal/SiO2 interface by the beam, then diffuses into the SiO2. Redistribution of hydrogen was found to continue until it was uniformly distributed throughout the SiO2, with a residual peak of strongly trapped hydrogen remaining at the metal/SiO2 boundary. At the same time the concentration of hydrogen in the SiO2 increased from an initial low level to about 4×1020 cm-3, depending on the amount of hydrogen initially at the Al/SiO2 interface.