Thin films of boron nitride (BN): investigation by laser ablation and characterization

Abstract

In this study, we have prepared BN thin films deposited on a silicon substrate using the laser ablation technique. The irradiation of boron nitride target by a NdYAG laser (with two wavelengths: 532 and 266 nm) and by an excimer laser (193 and 248 nm) leads to films which are characterized by Fourier Transform Infra-Red spectroscopy, and mainly by X-ray Photoelectron spectroscopy (XPS) and laser microprobe coupled with mass spectrometry (LAMMA). In a first step, we have investigated the laser-target interactions by XPS spectroscopy and LAMMA microprobe, in this last case, we compare the spectra both in positive and negative modes obtained by analysis of the different films (realized by laser ablation deposition at 266 nm) with those of reference materials: BN (target used for the films synthesis) and B<SUB>2</SUB>O<SUB>3</SUB> (oxide which could be formed in laser ablation experiment). The results underline the role of the oxygen traces in the synthesis vacuum chamber leading to a film in which oxygen is inserted in the boron nitride lattice but not under the B<SUB>2</SUB>O<SUB>3</SUB> structure. On the other hand, the XPS analysis of the films realized at 532 and 266 nm show that the boron is found in two different states: the first one corresponds to the boron bound to nitrogen (BN) and the second one is attributed to the elementary boron with oxidation state zero. All the analysis performed on the films prompt us to conclude that elementary boron detected by XPS experiments is formed during laser ablation leading to nitrogen deficient films. Finally, we show that the laser ablation of the boron nitride target with the 248 nm laser wavelength allows to obtain a thin film in which the boron is detected in only one state of binding (boron bound to nitrogen) by XPS spectroscopy. The profitable effect of the 248 nm laser irradiation on the stoichiometry of the obtained BN film could be due to the Band-Gap absorption phenomena.