Role of O2 and N2 addition on low-reflectance Si surface formation using moderate-pressure (3.3 kPa) hydrogen plasma

Abstract

We prepared ‘black Si’ with Si nanocone structures using a moderate-pressure H2 plasma at 3.3 kPa with a minor air addition. The roles of N2 and O2 as additives in Si-nanocone formation were investigated. Air additives in H2 gas are required to form Si oxynitride micromasks on the surface, and the O2 concentration in the additive modifies the chemical and physical characteristics of the micromasks. When the additive in the H2 gas was only O2, a relatively smooth sample surface or a low-aspect-ratio nanocone structure was formed. In contrast, the N2-only additive of H2 gas resulted in a fine nanopillar structure with a low height. An O2 concentration in the additives of approximately 20% is desirable for black Si fabrication. In addition, the etching rate of the SiO2 film using moderate-pressure H2 plasma was three times higher than that of the SiNx film. In addition, an adequate additive O2 concentration in the H2 gas increased the atomic H density in the plasma. As a result, a Si surface with a very low light reflectance of less than 0.5% in the wavelength range of 380–830 nm was obtained.