N ₂-plasma nitridation on Si(111): Its effect on crystalline silicon nitride growth

This study uses a combination of atom-resolved scanning tunneling microscopic and spectroscopic (STM/STS) techniques to investigate the effects of N ₂-plasma nitridation on a crystalline β-Si ₃N ₄ ultrathin film grown on the Si(111) substrate. The proposed two-step growth process, including N ₂-plasma nitridation followed by vacuum annealing both at high temperature (∼ 900 °C), can substantially improve the atomic and electronic structures of the β-Si ₃N ₄ having an atomically uniform morphology and stoichiometry. The effects of nitridation and post-annealing temperatures were examined by monitoring the morphological and electronic-structural evolutions of a non-stoichiometric surface. Moreover, the two-step N ₂-plasma nitridation process has extremely low activation energy and thus minimizes the thermal energy from the substrate for practical growth of β-Si ₃N ₄ ultrathin film.