US Patent 6932916 Semiconductor substrate with trenches of varying depth

A method for etching trenches having different depths on a semiconductor substrate includes providing a mask with first and second openings. The first and second openings are located where corresponding first and second trenches are to be etched. A slow-etch region, made of a slow-etch material, is provided above the substrate at a location corresponding to the second opening. When exposed to a selected etchant, the slow-etch material is etched at a rate less than the rate at which the semiconductor substrate is etched when exposed to the selected etchant.