Investigation of phosphoric acid-catalyzed silver-assisted chemical etching for upgrading metallurgical grade silicon to solar grade silicon

Abstract

Purifying metallurgical-grade silicon (MG-Si) to solar-grade silicon (SoG-Si) is crucial for achieving optimal performance and purity. Traditional silicon refinement processes are costly, energy-intensive, and environmentally harmful. In this study, we introduce a silver-assisted chemical etching (Ag-ACE) process for purifying silicon kerf loss (SKL), using phosphoric acid (H₃PO₄) as an oxidizing agent to replace the conventional hydrogen peroxide (H₂O₂). This approach effectively reduces bulk material into fine particles, increasing the surface area for easier removal of metal and non-metal impurities. The transformation of impurities and their byproducts on the silicon surface were analyzed using field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectroscopy (ICP-MS). All investigations were conducted before and after treatment with each etchant, including Ag-ACE. Our results demonstrate remarkable removal efficiencies for aluminum (Al), iron (Fe), and nickel (Ni). This breakthrough highlights the potential of Ag-ACE using H₃PO₄ for efficient metal impurity removal and high yield rates. The leaching results indicate that different concentrations of the oxidizing agent H₃PO₄@0.5 M < 1.0 M < 1.5 M effectively remove impurity contaminants. The major impurities in silicon, such as Fe, Al, and Ni, were significantly reduced by the Ag-ACE process, increasing the purity of MG-Si from 99.55% to 99.99%. The yield of silicon was calculated based on the recovery of silicon powder after Ag-ACE treatment.