Patent ID: 8007990

Claim:
A method for increasing the planarity of a surface of a thick film layer after photoimaging and developing flow features therein for a micro-fluid ejection head, the method comprising: applying a negative photoresist layer to a device surface of a substrate, wherein the negative photoresist layer is derived from a multi-functional epoxy compound, a difunctional epoxy compound, a photoacid generator devoid of aryl sulfonium salts, an adhesion enhancer, and an aryl ketone solvent; heating the photoresist layer to remove at least a portion of the solvent; cooling the photoresist layer; etching a fluid feed slot through the substrate from a backside of the substrate opposite the device surface, wherein the heated and cooled photoresist layer serves as an etch stop to the etching; and thereafter imaging flow features in the photoresist layer; and developing the imaged photoresist layer to provide the plurality of flow features therein and the substantially planar thick film layer surface.