Thermal stability of a-SiNx:H films deposited by plasma electron cyclotron resonance

Abstract

We analyze the influence of rapid thermal annealing on Al/SiNx:H/Si structures with a nitrogen to silicon ratio of 1.55 in the insulator bulk. The SiNx:H is deposited by the electron cyclotron resonance plasma method and the films were annealed at temperatures ranging from 300 to 1050 °C. We have related the changes of the interface trap density with those of the insulator bulk density of dangling bonds, resistivity, and breakdown field. A sharp dip in the dangling bond density is observed at moderate annealing temperatures, from 1.8×1018 cm−3 for the as-deposited film down to 9.6×1016 cm−3 at the point of inversion of the trend between 500 and 600 °C. The density of interface states is also reduced in this range of temperatures from 3.6×1011 to 1.2×1011 eV−1 cm−2. Resistivity and breakdown field are maintained in the range 5×1014–5×1015 Ω cm and 6.4–6.6 MV/cm, respectively, up to a temperature of 600 °C. We attribute the improvement of the interface characteristics and the decrease of dangling bonds to a thermal relaxation and reconstruction of the SiNx:H lattice and its interface with the silicon substrate. For temperatures above this threshold the electrical properties suddenly deteriorate and the density of dangling bonds increase. At even higher temperatures (above 900 °C) a release of hydrogen from N–H bonds takes place.