Growth and Energy Bandgap Formation of Silicon Nitride Films in Radical Nitridation

Abstract

The surface profiles and energy bandgap of sub-nanometer-thick silicon nitride layers, which were formed by radical nitridation, were analyzed by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). According to the STM results, the surface roughness of the nitride layers depends only on substrate temperature regardless of radio frequency (RF) power, which indicates that the growth mode of the silicon nitride layer in radical nitridation is attributed to the surface silicon atom migration but does not depend on the types of nitrogen radical. In contrast, STS spectra show that the energy bandgap of the silicon nitride layer is significantly changed with not only substrate temperature but also RF power. The densities of nitrogen radicals were analyzed by absorption and emission spectroscopy, which suggests that the contribution of the excited-state nitrogen atoms to radical nitridation increases as RF power increases. The monolayer-thick nitride layer with both an atomically flat surface and a wide energy bandgap can be formed under appropriate conditions, because they are limited by different thermaly activated features.