Remote plasma-enhanced atomic layer deposition of metallic TiN films with low work function and high uniformity

Abstract

Thermal stability of metal/n-GaN contact is critical for its applications in microelectronic and optoelectronic devices. Metal Ti is generally used to make Ohmic contact on n-GaN after high temperature annealing, and the key factor is to form TiN at the interface. To reduce the processing temperature and improve the reliability, metallic titanium nitride (TiN) thin film has been proposed to substitute traditional metals (such as Ti) in the contact structures, due to its low work function and high blocking effect. For this novel approach, the first step is to fabricate high quality TiN films. Here, the authors adopted remote plasma-enhanced atomic layer deposition method to deposit TiN films under well-controlled conditions. Stoichiometric TiN films (Ti:N ∼ 1:1) with low oxygen contamination (<5%) have been deposited uniformly on 2 in. substrates in a large temperature range of 250–400 °C. The work function of TiN films is quite low (∼3.7 ± 0.1 eV) compared to metal Ti (∼4.33 eV), and almost independent to the growth temperature and substrates. Strong Fermi edge and high conductivity indicate excellent metallic property of the TiN films. This study of TiN film growth paves the way to establish a low temperature process and improve the thermal stability of Ohmic contacts for wide band gap semiconductor-based devices.