US Patent 7560039 Methods of deep reactive ion etching

A method of substantially simultaneously forming at least two fluid supply slots through a thickness of semiconductor substrate from a first surface to a second surface thereof. The method includes the steps of applying a photoresist layer to the first surface of the semiconductor substrate. The photoresist layer is patterned and developed using a gray scale mask for a first fluid supply slot. The semiconductor substrate is then reactive ion etched, to form the at least two fluid supply slots through the thickness of the substrate. The first fluid supply slot is substantially wider than the second fluid supply slot, and the first and second fluid supply slots are etched through the substrate at substantially the same rate.