Stepper alignment mark formation with dual field oxide process

Abstract

A semiconductor photomask set for producing wafer alignment accuracy in a semiconductor fabrication process. The photomask set produces an alignment mark that is accurate for subsequent fabrication after undergoing a dual field oxide (FOX) fabrication process. Prior arts methods have traditionally covered the alignment marks with layers of oxide material. The method includes the steps of: (a) providing a first photomask member having mask portions for forming a plurality of first field oxide regions on a first region of a semiconductor substrate and also having a mask portion for forming an alignment marker; (b) providing a second photomask member having mask portions for forming a plurality of second field oxide regions on a second region of the semiconductor substrate and also having mask portions delineated for covering any first field oxide regions and alignment marker formed by using the first photomask member; (c) forming the first field oxide regions and the alignment marker utilizing the first photomask member; (d) covering the formed first field oxide regions and the alignment marker with a photoresist material by utilizing the second photomask member; (e) forming the second field oxide regions after utilizing the second photomask member; (f) facilitating wafer alignment accuracy by removing the photoresist material and exposing the alignment marker; and (g) aligning a semiconductor wafer by utilizing the exposed alignment marker. The mask set can be used in conjunction with stepper wafer alignment tools and is especially useful in forming a memory semiconductor product capable of performing block data erasure operations. The exposed alignment marker facilitates checking and testing mask misalignment during the fabrication process.