Current Transport and Maximum Dielectric Strength of Silicon Nitride Films

Measurements of current-voltage characteristics have been performed on Au-Si3N4-Mo and Au-Si3N4-Si (degenerate substrate) structures of various nitride-film thicknesses from 300 Å to 3000 Å and over a range of temperatures. The films are deposited by the process of reaction of SiCl4 with NH3. It is found that at any given temperature and electric field, the current transport is essentially independent of the substrate material, the film thickness, or the polarity of the electrodes. It is proposed that the current-transport mechanisms are bulk controlled rather than electrode controlled. The conduction-current density, J, is the sum of three contributions: J = J1+J2+J3, where J1∼E exp −qφ1 − (qE/πε0εd) ½/ kT, J2∼E2 exp (−E2/E), and J3∼E exp (−qφ3/kT). At high fields and high temperatures J1 dominates the current conduction (the Poole-Frenkel effect or internal Schottky effect) ; one obtains a barrier height of (1. 3±0. 2) V for φ1 and a value of 5. 5±1 for the dynamic dielectric constant εd. At high fields and low temperatures J2 dominates as a result of field ionization of trapped electrons (presumably from the same centers as for J1) into the conduction band; one obtains a value for the field E2 of the order of 6×107 V/cm. At low fields and moderate temperatures J3 dominates because of the hopping of thermally excited electrons from one isolated state to another yielding Ohmic characteristics and a thermal-activation energy qφ3 of about 0. 1 eV. At low temperatures the maximum dielectric strength approached ∼107 V/cm. At high temperatures where J1 dominates the current conduction, the maximum dielectric strength, which is limited by thermal instability, decreases as (φ1 − CT) 2, where C is a function of the thermal conductivity of the nitride films.