Nitride film deposition by femtosecond and nanosecond laser ablation in low-pressure nitrogen discharge gas

Abstract

Thin films of TiN and BN are deposited by femtosecond and nanosecond laser ablation in a vacuum chamber with N 2 gas discharge at 0.8 mTorr. Use of these activated gas conditions guarantees stoichiometric incorporation of nitrogen in the films. Properties of the deposited films are compared for the two different laser pulse durations. Ultrafast (fs) pulses are at a wavelength of 780 nm and the nanosecond pulses at 355 nm. The film growth is monitored with in situ RHEED, which provides information on the crystal quality of the films during growth. In addition to single-layer films of TiN being grown on silicon, a superlattice of BN/TiN was also fabricated. The TiN films were observed to form first as cubic phase single-crystal material that converted to polycrystal as the film thickness increases. These polycrystals exhibited textured orientation for the nanosecond pulsed depositions but were a randomly oriented fine-grained structure for the femtosecond pulses. The alternating multi-layers of TiN/BN exhibited interesting features that were complicated by surface roughness in the film. However, cross-sectional HRTEM demonstrated that a region of cubic phase BN was present in between two of the cubic phase TiN layers. It is thought that this results from a domain epitaxial relationship between the two materials. Such behavior is expected to be of great potential interest in the fabrication of uniform c-BN films by epitaxial growth.