Electrical properties and their thermal stability for silicon nitride films prepared by plasma-enhanced deposition

Abstract

The structural and electrical properties for plasma chemical vapor deposition amorphous silicon nitride films prepared from SiH4-N2-Ar mixtures have been investigated. Substrate temperature varied between 250 and 350 °C, and rf power density was set up in a range between 0.51 and 1.19 W/cm2 (13.56 MHz). Film composition changes toward a Si rich state with increasing substrate temperature or decreasing rf power density. Film density increases with increasing substrate temperature and rf power density. Film with a high degree of perfection (N/Si ratio=1.33 and density=3.2 g/cm3), is obtained at 350 °C and 1.19 W/cm2. Average electronic polarizability, dielectric strength, and Poole-Frenkel barrier height become smaller, stronger, and larger, respectively, when film structure approaches perfection. The electrical properties are degraded largely by annealing (700 °C, in a N2 gas), when as-grown films structure is far from perfection. This instability of electrical properties is attributed to the increase of trap density due to dehydrogenation and densification.