Deep reactive ion etching (DRIE) is becoming a more popular method to etch deep structures (>10 µm) in silicon for unique MEMS, BioMEMs, and microelectronics applications. DRIE tools commonly rely on the Bosch process where deep structures are anisotropically etched in cyclic process with a reactive plasma of sulfur hexafluoride (SF6) etching followed by passivation with octafluorocyclobutane (C4F8) polymerization. Unfortunately, SF6 is one of the most potent greenhouse gases with a global warming potential of 22,800 times that of CO2 and the gas remains stable in the atmosphere for 3,200 years. Stricter regulations limit the use of SF6 in manufacturing and other fluorine species are under investigation as potentials replacements.
Electrochemical etching with hydrofluoric acid of other nonaqueous fluoride salts presents a faster and lower cost alternative to the Bosch process along with a more manageable environmental impact. In this talk we discuss the electrochemical etching of deep structures in silicon including the etch chemistry and voltammeric behavior of silicon in these electrolytes.