For the fabrication of microelectromechanical system devices, deep trench etching of borosilicate glass (Corning 7740) has been investigated using SF6/Ar inductively coupled plasma. Since borosilicate glass contains metal elements which produce nonvolatile fluorides, dry etching of its smooth surface is a difficult issue. In this article, requisite conditions for etching glass with a smooth surface and high mask selectivity have been discussed on the basis of the results of a comprehensive experimental study of the effects of substrate bias power and Ar addition on the removal of involatile fluoride residues deposited via the backscattering of etch products in the vicinity of the substrate surface. Under optimized etching conditions, deep trench etching of borosilicate glass to 32 μm depth and 15 μm width has been accomplished using 3-μm-thick chrome metal masks. © 2003 American Vacuum Society.