Pulsed laser deposition of non-stoichiometric silicon nitride (SiN_x) thin films

Abstract

Silicon nitride (SiN_x) thin films of various stoichiometries (x) were prepared on Si (100) substrates applying the Nd : YAG (λ=1064 nm) pulsed laser deposition (PLD) process in the “shaded off-axis” technique at room temperature. The specific arrangement of this technique with perpendicular target (Si) and substrate surfaces and a metallic screen in between guarantees very low particulate (droplet) deposition and, thus, excellent surface qualities. Compared to the usually used “on-axis” deposition technique consisting of a parallel arrangement of the target and substrate surface, the coating surface covered with particulates is about 100 times lower reaching a maximum of 0.2% on 400 nm thick films. The variation the N₂ partial pressure affects the nitrogen content and the silicon bonding structure of the films analysed by means of SIMS and XPS, respectively. As a consequence the optical properties (e.g.m refractive index) are tailorable in a wide spectral range between 250 and 1200 nm.