Micro-fluid ejection head containing reentrant fluid feed slots

Methods of micro-machining a semiconductor substrate to form through fluid feed slots therein. One method includes providing a semiconductor substrate wafer having a thickness greater than about 500 microns and having a device side and a back side opposite the device side. The back side of the wafer is mechanically ground to provide a wafer having a thickness ranging from about 100 up to about 500 microns. Dry etching is conducted on the wafer from a device side thereof to form a plurality of reentrant fluid feed slots in the wafer from the device side to the back side of the wafer.