Microstructural characterization of Si wafers processed by multi-wire sawing of hot pressed silicon powder based ingots

Abstract

The purpose of this work is to verify the possibility to process highly doped Si supporting substrates using a 2-step process: (i) sintering of a low-cost Si powder based ingot using hot pressing and a ELKEM Silgrain material as a feedstock; and (ii) wafering of such ingots using multi-wire sawing technique similar to that, which is used for cast multi-Si or Cz-Si grown ingots. Moreover, the possibility to dope Si powder ingot at sintering temperatures below melting point of Si, using a mixture of Si and boron powders to fabricate highly conductive Si wafers is verified as well. The slurry technique has been chosen for multi-wire sawing of sintered Si powder based ingots. Surface properties of Si powder based substrates as well as their chemical composition have been studied by optical microscopy imaging and energy-dispersive X-ray spectroscopy (EDX). Although the overall concentrations of oxygen, carbon and possibly also metal impurities, which are initially present in a low-cost Si feedstock, are too high to achieve acceptable semiconducting properties, it is concluded, that sintered Si powder based wafers have high enough conductivity (resistivity ∼0.001 Ω cm) to serve as supporting substrates for low cost Si wafer equivalent structures.