Deep etching of Zerodur glass ceramics in a fluorine-based plasma

The etching of glass is still much more challenging than the deep etching of silicon. But in contrast to pure silica, most glasses are complex alloys of serval oxides including aluminium oxide. For this reason, it is quite difficult to find suitable high-rate deep dry etching processes and related masking materials. For extremely temperature-insensitive micromechanical systems it is of interest to use zero-expansion glass ceramics such as Zerodur. But the microstructure of Zerodur consists of crystalline and amorphous phases and shows a high percentage of Al2O3-bonds. This makes plasma etching challenging. Here, deep etching of Zerodur only in a fluorine-based plasma for micro-technical applications is investigated. Different process parameters such as the physical power and gas mixtures of the ICP-RIE-process have been varied. Etch rates of about 250 nm/min and sidewall angles of approximately 71° were reached with a nickel mask and the etch gas SF6. The achieved total etching depth is as large as 150 μm resulting in a release of microelements such as springs and gears from a Zerodur wafer.