On the Formation of Black Silicon Features by Plasma-Less Etching of Silicon in Molecular Fluorine Gas.

Bishal Kafle,Edward Duffy,Marc Hofmann,Ahmed Ridoy,Jochen Rentsch,Laurent Clochard,Eleni Miethig

doi:10.3390/nano10112214

Bishal Kafle, Edward Duffy + Show 5 more

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https://doi.org/10.3390/nano10112214

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Journal: Nanomaterials	Publication Date: Nov 6, 2020
Citations: 11	License type: CC BY 4.0

Affiliation: Fraunhofer Institute for Solar Energy Systems

Abstract

In this paper, we study the plasma-less etching of crystalline silicon (c-Si) by F2/N2 gas mixture at moderately elevated temperatures. The etching is performed in an inline etching tool, which is specifically developed to lower costs for products needing a high volume manufacturing etching platform such as silicon photovoltaics. Specifically, the current study focuses on developing an effective front-side texturing process on Si(100) wafers. Statistical variation of the tool parameters is performed to achieve high etching rates and low surface reflection of the textured silicon surface. It is observed that the rate and anisotropy of the etching process are strongly defined by the interaction effects between process parameters such as substrate temperature, F2 concentration, and process duration. The etching forms features of sub-micron dimensions on c-Si surface. By maintaining the anisotropic nature of etching, weighted surface reflection (Rw) as low as Rw < 2% in Si(100) is achievable. The lowering of Rw is mainly due to the formation of deep, density grade nanostructures, so-called black silicon, with lateral dimensions that are smaller to the major wavelength ranges of interest in silicon photovoltaics.

Highlights

The formation of high aspect ratio and/or large surface area sub-micron structures on silicon is of high interest for several applications, such as photovoltaics, micro-electro-mechanical systems (MEMS), photodetectors, and silicon anodes for lithium-ion batteries [1,2,3,4]
Statistical Variation of Process Parameters The statistical analysis of the experimental section was performed for the etch rate and surface reflection as the dependent variables
It was observed that a normal distribution assumption of the residuals is valid and analysis of variance (ANOVA) was used to analyse the output data

Summary

Introduction

The formation of high aspect ratio and/or large surface area sub-micron structures on silicon is of high interest for several applications, such as photovoltaics, micro-electro-mechanical systems (MEMS), photodetectors, and silicon anodes for lithium-ion batteries [1,2,3,4]. In silicon photovoltaics, the formation of submicron features on c-Si surface has received increased attention in the field of Si photovoltaics due to its ability to dramatically reduce the surface reflection to a very low value so that the wafer turns ”black” in appearance, a so-called black-silicon (B-Si). Application of such anti-reflective surfaces on single or monocrystalline silicon (mono-c-Si) and multicrystalline silicon (mc-Si) surfaces have shown an improved short-circuit current density (JSC) of solar cells due to a higher absorption of incident light [1,2,3]. This method has drawbacks, such as the need for multiple processing steps, the use of expensive process materials, cumbersome waste management, and a high likelihood of trace metal particles being present in the Si wafer

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