Structure and chemical composition of BN thin films grown by pulsed-laser deposition (PLD)

BN thin films are grown on Si(100) substrates in a pulsed-laser deposition (PLD) process using a pulsed CO2 laser, a hexagonal-phase BN (h-BN) target, and N2 as processing gas. The effect of RF power coupled to the substrate during PLD is investigated. Films are analysed using optical microscopy and micro-Raman and X-ray photoemission spectroscopies. They are generally composed of a fine-grained matrix in which particles 10–100 μm in size are embedded, with the morphology and chemical composition dependent on the lateral position on the film surface relative to the laser-induced plasma plume from the target. The roughness and contaminant concentration (B2O3, elemental B, and boron-oxynitride) are largest nearest the plasma-affected region. The matrix material over the entire film surface exhibits weak, broad spectral structures, indicating an amorphous structure. Certain regions have in addition h-BN Raman peaks that are shifted by up to 15 cm−1 to lower wave numbers relative to crystalline h-BN due to strain built in during deposition. No peaks characteristic of cubic BN or B2O3 are found. Positions further from the plasma-affected region show stronger peaks, implying more crystalline order. The highest degree of crystallinity is reached for deposition with RF power applied to the substrate mainly during the laser pulses, as opposed to deposition with power applied between pulses or to deposition without RF power. In general, embedded particles have more intense Raman peaks than the surrounding matrix, comparable in strength to those of the target, suggesting that they arise from material ejection.