# Recent Advances in Black Silicon Surface Modification for Enhanced Light Trapping in Photodetectors
## 3 Dry Methods for Black Silicon Fabrication
### Reactive Ion Etching (RIE)
#### 3.1.2 Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE)  
The fabrication of BSi can also be achieved through the utilization of the inductively coupled plasma reactive ion etching (ICP-RIE) process. Typically, this process employs \(SF_{6}\) as the primary etchant gas. The introduction of O\({}_{2}\) into the process serves to promote the formation of silicon oxyfluorides (SiOF\({}_{2}\)), which serves as an efficient passivation layer. Consequently, this enables an anisotropic etching process, resulting in the formation of randomly distributed needle-like nanostructures [58].  
A pioneering study by [PERSON] et al. ICP-RIE was employed to fabricate BSi on hemispherical Si lenses with a radius of 12.7 mm, enabling the first-ever examination of nanostructures on such highly curved surfaces [58]. By systematically adjusting the etching parameters, including a critical etching pressure of 2 Pa and gas flows of \(SF_{6}\) and O\({}_{2}\) at 60 sccm, the team successfully replicated diverse structural morphologies akin to those achievable on flat Si samples. The uniformity and orientation of these structures across the lens surface were meticulously analyzed through SEM. Optical reflectance measurements validated the findings, confirming uniformity and demonstrating significantly reduced reflectance, pivotal for the augmentation of optical systems performance in infrared and terahertz technologies. This study not only opens new avenues for applying BSi in nonpla  
Figure 3: An SEM image of BSi (as grassy-looking residuals) on the etch profile due to micro-masking caused by excess polymer from increased \(C_{4}F_{8}\) pulse time and incomplete O\({}_{2}\) plasma etching.  
nar device architectures but also underscores the adaptability and potential of ICP-RIE for advanced manufacturing processes.  
The large-area tomography technique integrates plasma focused ion beam and SEM, which could characterize BSi morphologies over expansive areas up to 320 \(\upmu\)m\({}^{2}\)[59]. A quantitative two-dimensional (2D) dopant mapping with an optimized SEM was employed for dopant contrast imaging (SEMOCI), capable of effectively analyzing textured surfaces like BSi. The direct integration of these morphological characterizations with optical properties via FDTD simulations provides a robust framework for enhancing BSi applications in photovoltaics and sensor technologies, which aimed to boost their performance and efficiency.  
A temperature of \(-5\,\mathrm{\SIUnitSymbolCelsius}\) and a pressure of 20 mTorr were utilized in our prior work and \(SF_{6}\)/O\({}_{2}\) flow rates of 85/18 sccm. The RF and Induced Coupled Plasma (ICP) powers were set at 100 W and 300 W, respectively. We employed a planar ICP source and a capacitively coupled radiofrequency (RF) source to enable precise control of ion energy independently of plasma density, a crucial factor in producing uniform nanostructures that is essential for high-quality BSi. These specific parameters were strategically selected based on extensive research correlating them with the successful fabrication of BSi with desired morphological and optical properties. Creating BSi via ICP is a sophisticated process that requires a comprehensive understanding of the etching environment to consistently produce it for advanced applications. Its distinctive surface properties make BSi particularly advantageous for PV applications, where it can improve the efficiency of photodetectors [60].