Growth Optimization and Characterization of Reactively Sputtered Zirconium Nitride Thin Films for III-V Buffer Layer Applications

Abstract

Zirconium nitride (ZrN) thin films were deposited by reactive dc magnetron sputtering to assess the effects of processing conditions upon film properties. Processing conditions and parameters were optimized to generate films of completely oriented (111) ZrN on silicon to be used as buffer layers for the growth of gallium nitride A single and double Langmuir probe were used to determine trends in electron temperature, ion density, ionization fraction, and floating potential during reactive sputtering of zirconium in argon and nitrogen. Reactive gas concentration, deposition pressure, deposition temperature, cathode current, film thickness and substrate orientation were investigated as variable processing conditions. Four-point probe, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and x-ray diffraction (XRD) were used to characterize thin films produced.

The optimum growth conditions for the (111) oriented growth of ZrN, for this work, were found to occur during reactive magnetron sputtering at a deposition temperature of 500°C, a constant cathode current of 0.5 ampere, a deposition pressure of 15 mTorr, a reactive nitrogen gas concentration of 4% in argon, deposited on (111) oriented silicon, with a thickness on the order of 600 nanometers. Gallium nitride was then deposited on films of ZrN to assess the crystallinity of films produced. The lattice mismatch between (111) oriented ZrN and c-axis oriented GaN was calculated at 1.6%. Microscopic evaluation showed the films to be of columnar structure with dense grains and smooth surfaces.

A change in preferred orientation was noticed as a function of increasing film thickness and cathode current and was determined to be due to an increase in ion channeling and bombardment energy.