Method of forming self-aligned mask ROM

摘要

A method of forming a self-aligned mask ROM. Gate stacks that serve as word lines are formed over a substrate. Each gate stack includes a gate oxide layer, a gate conductive layer and a gate cap layer. Spacers are next formed on the sidewalls of the gate stacks. An insulation layer is deposited over the substrate and the gate stacks. The insulation layer is planarized to expose the gate cap layer. A patterned photoresist layer is formed over the insulation layer to expose the ion implant regions needed for programming. Using the patterned photoresist layer as an etching mask, the gate cap layer within each ion implant region is removed to expose the gate conductive layer using an etchant with high etching selectivity. Using the patterned photoresist layer as an implant mask, ions are implanted into the substrate via the ion implant regions so that the mask ROM is programmed. Finally, the photoresist layer is removed.