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

We prepared 'black Si' with Si nanocone structures using a moderate-pressure H-2 plasma at 3.3 kPa with a minor air addition. The roles of N-2 and O-2 as additives in Si-nanocone formation were investigated. Air additives in H-2 gas are required to form Si oxynitride micromasks on the surface, and the O-2 concentration in the additive modifies the chemical and physical characteristics of the micromasks. When the additive in the H-2 gas was only O-2 , a relatively smooth sample surface or a low-aspect-ratio nanocone structure was formed. In contrast, the N-2 -only additive of H-2 gas resulted in a fine nanopillar structure with a low height. An O-2 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 H-2 plasma was three times higher than that of the SiNx film. In addition, an adequate additive O-2 concentration in the H-2 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.