Effect of heat treatment on the stress and structure evolution of plasma deposited boron nitride thin films

Boron nitride (BN) thin films are deposited at 573 K by plasma enhanced chemical vapor deposition (PECVD) with ammonia (NH3) and hydrogen diluted diborane (15% B2H6 in H2) source gases. UV–visible and Fourier transform infrared (FTIR) spectroscopies together with surface profilometry are used for the film characterization. These films are hydrogenated (BN:H) whose hydrogen content is pursued following the 1.5 h annealing process at 748 K, 923 K and 1073 K under nitrogen atmosphere. Hydrogen escape with the rising annealing temperature is observed together with increases of the compressive stress, band gap and Urbach energies. Films are composed of the hexagonal BN (h-BN) clusters that grow dominantly parallel to the substrate surface with some non-parallel planes at the edges of the clusters, which are embedded in an amorphous tissue (the so-called turbostratic structure, t-BN). Annealing seems to promote non-parallel planes, thus creating more stressful and distorted network. Most of hydrogen atoms are removed from the film annealed at 1073 K and wurtzite BN (w-BN) phase is formed with volume fraction of 57%. As a consequence or in parallel of hydrogen reduction, high compressive stress causes the cracking of the films.