Ink feed trench etch technique for a fully integrated thermal inkjet printhead

Abstract

A monolithic inkjet printhead formed using integrated circuit techniques is described. A silicon substrate has formed on its top surface a thin polysilicon layer in the area in which a trench is to be later formed in the substrate. The edges of the polysilicon layer align with the intended placement of ink feed holes leading into ink ejection chambers. Thin film layers, including a resistive layer, are formed on the top surface of the silicon substrate and over the polysilicon layer. An orifice layer is formed on the top surface of the thin film layers to define the nozzles and ink ejection chambers. A trench mask is formed on the bottom surface of the substrate. A trench is etched (using, for example, TMAH) through the exposed bottom surface of the substrate and to the polysilicon layer. The etching of the polysilicon layer exposes fast etch planes of the silicon. The TMAH then rapidly etches the silicon substrate along the etch planes, thus aligning the edges of the trench with the polysilicon. A wet etch is then performed using a buffered oxide etch (BOE) solution. The BOE will completely etch through the exposed thin film layers on the topside and underside of the substrate, forming ink feed holes through the thin film layers. The trench is now aligned with the ink feed holes due to the polysilicon layer.