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 Sinanocone 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.

High-rate etching of silicon oxide and nitride using narrow-gap high-pressure (3.3 kPa) hydrogen plasma

“…Etching rates of SiO x and SiN x films were determined from the variation of Si emission intensity in OE spectra. As described previously [17], the etching rate of Si by H 2 plasma is much higher than those of SiO x and SiN x . As a result, the Si emission intensity in the OE spectrum increases rapidly when the overlying films are removed and the Si substrate starts to be etched.…”

“…The experimental equipment for plasma etching used in this study has been described in a previous paper [17]. A schematic of a plasma treatment region is shown in figure 1.…”

“…In the indirect flow (IF) setup, the H 2 gas was introduced from a chamber sidewall 70 mm from the electrode, as shown in figure 1(b). The H 2 gas flow [17]. rate (F H ) was varied from 1.5 to 5.0 standard liters per minute (slm) under DF conditions and fixed at 1.5 slm under IF conditions.…”

“…Throughout plasma etching, the plasma was monitored by optical emission (OE) spectroscopy. Details of OE spectroscopy measurements were described in our previous paper [17]. Etching rates of SiO x and SiN x films were determined from the variation of Si emission intensity in OE spectra.…”

“…Schematic of etching reaction systems for (a) direct flow (DF) and (b) indirect flow (IF). Details of the experimental setup have been presented in a previous study[17].…”