Degradation of the surface passivation of plasma-assisted ALD Al2O3under damp-heat exposure

The effect of humidity on boron diffused and undiffused silicon samples passivated by aluminum oxide (Al2O3) synthesized by plasma-assisted atomic layer deposition (PA-ALD) is investigated. It is found that samples exposed to a saturated humidity ambient show a much higher degradation rate than those exposed to 85% relative humidity (RH). The surface recombination velocity Seff increased by 25% for RH = 85% but by more than two orders of magnitude for 100% RH after 10 days of exposure. Moreover, the electrical resistance of Al2O3 film also decreased significantly following saturated humidity exposure. PECVD SiNx:H capping layers are effective at protecting Al2O3 films from damp-heat stress. Two degradation regimes are proposed to explain the degradation: (i) initial reversible degradation at shorter time exposures, which is ascribed to the loss of field effect passivation; (ii) severe degradation after longer term exposure, which is believed to be due to a substantial loss of chemical passivation with the generation of new species from the reaction of Al2O3 and water. The second regime was only observed for saturated humidity conditions.