Capabilities and Limits to Form High Aspect-Ratio Microstructures by Molding of Borosilicate Glass

Abstract

This paper presents an experimental study of capabilities to fabricate high aspect-ratio microstructures in glass. The fabrication was done by molding borosilicate glass in deep silicon trenches created by deep reactive ion etching in silicon and releasing the structures by potassium hydroxide (KOH) and Xenon difluoride (XeF2) etching of the Si mold. Subsequent over-etching of the glass can also be used to increase the aspect ratio of the glass structures. By using this molding method, glass structures have been successfully fabricated achieving an aspect ratio of 42:1, a height of 212 $\mu \text{m}$ , and vertical sidewall angle up to 89.7°. We also investigated the effect of molding parameters (heat treatment time, temperature, and pressure) on the process capabilities and limitations for defect free structures. This work demonstrates the capabilities to fabricate high aspect-ratio glass structures that cannot be achieved by conventional etching techniques to date, opening new perspectives for the use of glass in MEMS and microfluidics.