Surface and subsurface integrity of monocrystalline silicon in impulse-discharge driven abrasive machining

Abstract

In abrasive machining of monocrystalline silicon, surface and subsurface behaviors are changed by the brittle-to-ductile removal transfer due to uncertain mechanical force, thus leading to surface micro-burr, surface roughness, subsurface residual stress, subsurface damage and so on. In mechanical diamond grinding, an impulse-discharge between wheel metal and semiconductor silicon is proposed to drive a loose-abrasive flow along with the flexible pressure for nano-scale surface removal, micro-scale mechanical removal and thermal modification. The formation behavior of abrasive-Si interface is researched to improve the surface and subsurface integrity by integrating modification, flexible removal and cut-copying. First, the surface formation procedure was modelled in relation to impulse-discharge energy, hydrodynamic pressure and loose-abrasive diameter, etc. Then, the dynamic characteristic of fixed-diamond, loose-abrasive machining as well as impulse-discharge machining was investigated in relation to the ductile-brittle transition. Finally, the surface integrity of monocrystalline silicon was investigated in hybrid machining. It is shown that the hybrid machined formation chain is formed in the abrasive-workpiece interface with cut-copying the surface profile. The impulse-discharge drives the loose-abrasive and modifies the interface by thermal ductile transition. The loose-abrasive obtains a removal force to eliminate the modified Si–O bond and expose the Si2p3/2, Si2p1/2 substrate with ductile formation. Decreasing the impulse-discharge energy and hydrodynamic pressure promote brittle to ductile transition for high surface and subsurface integrity. Accordingly, the surface integrity is subject to impulse-discharge energy, hydrodynamic pressure and loose-abrasive size. With the thermal tensile and abrasive driven effect of impulse-discharge, the residual compressive stress, surface micro-burr and subsurface damage thickness were decreased by 72 %, 65 % and 88 %, respectively. As a result, the mechanical cut-copying with impulse-discharge thermal modifying action and abrasive flow driving ensures the surface integrity and form accuracy in process.