Current Transport and Maximum Dielectric Strength of Silicon Nitride Films

Abstract

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 {−q[φ₁ − (qE/πε₀ε_d)^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 ε_d. 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.