Chemical and structural stabilities of SiN_x nano-scale islands formed by ionized N₂ gas at room temperature

Si-based nano-scale islands (NSIs) were formed by means of ionized N ₂ gas at room temperature (RT) on silicon substrates. The chemical states of the formed samples were found to be resolved to the intermediate states of SiN_x and the chemically stable state of Si ₃N₄ through the observation of Si 2p and N 1s core-level spectra obtained by X-ray photoelectron spectroscopy. The height of, the lateral size of, and the inter-distance between the NSIs were estimated to be 1.4-4.2 nm, 28-35 nm, and 30-39 nm, respectively, by atomic force microscopy analysis. The height, the lateral size, and the inter-distance decreased as the exposure time of the ionized gas increased beyond 30 min. After annealing at 700°C for 60 min, the height, the lateral size and the inter-distance increased to 4.7-6.6 nm, 36-55 nm, and 58-78 nm, respectively. The chemical compositions were stabilized to the chemically stable state of Si₃N₄ and meta-stable intermediate states of SiN_x. This long-time annealing behavior of the NSIs observed in this work is different from that in the case of thermally grown silicon nitride in nitrogen gas atmosphere in which the intermediate states and other interfacial states are rapidly destroyed during high temperature treatment.