Cast Monocrystalline Silicon: New Alternative for Micro- and Nano-electromechanical Systems

Casted silicon wafers dominate the current photovoltaic (PV) market due to much lower fabrication costs as compared to well-known Czochralski (Cz) –growth. Traditionally casted silicon ingots have been multicrystalline, but recent developments in casting technology have enabled also the growth of single crystalline (sc) silicon ingots. While the resulting sc-Si ingot quality is naturally high enough for PV, it is not sufficient for the integrated circuit (IC) industry, mainly due to the increased amount of intrinsic point defects and dislocations in comparison to Cz-Si. However, many applications that do not
have such stringent requirements for substrates, such as micro- and nano-electromechanical systems (MEMS, NEMS), could potentially find this material beneficial. Indeed, here we take the first step in studying the applicability of cast mono-Si for such applications. More specifically, we focus on advanced focused ion beam lithography combined with deep reactive ion etching for NEMS and wet etching for MEMS. Our results show that the quality of cast monoSi is high enough for successful patterning in both micro- and nanoscale. Sub-micron resolution is achieved and the Ga+ doses required for successful patterning are comparable to conventional Cz-Si. The preliminary results presented here thus show great promise for cast mono-Si as a low-cost alternative for micro- and nanoelectromechanical systems.