High temperature annealing of mnos devices and its effect on si-nitride stress, interface charge density and memory properties

Abstract

The effects of high temperature annealing in N2 and H2 ambients upon the following properties of MNOS devices have been investigated: Si-nitride stress, etch rate, index of refraction, fixed interface charge and fast surface state density, memory window and charge retention at elevated temperatures. The CVD Si-nitride and Si-oxynitride films were deposited at temperatures as low as 610°C with a NH3/SiH4 ratio of 1000:1, the heat treatments were performed in the temperature range from 640°C to 1130°C. A similar N2-annealing behavior was found for film stress and flatband voltage. The film stress increased with increasing annealing time and temperature while the interface charge density changed from high positive values (QN/q = 4 × 1012cm−2) after nitride deposition at 610°C to high negative values (QN/q = -4 × 1012cm−2) after annealing at 930°C, The fast interface state density increased while the charge retention time was drastically reduced. The changes of the properties by N2 annealing are mainly attributed to decomposition of SiH and NH bonds. Minor effects were obtained by annealing in H2 and the drastic changes caused by N2 annealing could be reversed to a great extent by subsequent H2 annealing. Finally the different effects of deposition and annealing temperature on the propertiesare discussed .