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

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. refractive index) are tailorable in a wide spectral range between 250 and 1200 nm.