Comprehensive surface and subsurface characterization of silicon wafer processed by Micro-EDM

Silicon wafers are extensively used in the semiconductor industry; however, their high hardness and inherent brittleness make precision machining challenging. In the present work, Micro-Electric Discharge Machining (Micro-EDM) was employed to machine low-resistivity silicon wafers. The study systematically investigates the influence of discharge energy (8-1280 μJ) on the surface and subsurface characteristics of the machined silicon wafers using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). The results revealed a progressive transition in the material removal mechanism from localized melting and vaporization at lower discharge energies to a combination of melting, vaporization, and stress-assisted brittle fracture with increasing discharge energy. EDS analysis confirmed the migration of copper and zinc from the brass tool electrode to the machined surface, whereas XPS identified the formation of oxidation and hydroxylation products on the silicon surface. Raman spectroscopy revealed machining-induced phase transformation and tensile residual stress resulting from intense plasma-induced thermal loading. The estimated residual stress remained below the tensile strength of silicon up to approximately 200 μJ, indicating a crack-free machining regime, and reached a maximum value of 1275 MPa at 1280 μJ. TEM further confirmed the transformation of monocrystalline silicon into polycrystalline silicon beneath the machined surface, while the underlying substrate retained its monocrystalline structure. These findings demonstrate that material removal during Micro-EDM of low-resistivity silicon is governed by localized melting, vaporization, and thermally induced stress-assisted brittle fracture, providing guidance for optimizing machining conditions and surface integrity.