A method of fabricating high step alignment marks on a twin-well integrated circuit. An alignment mark photoresist pattern is formed overlaying the nitride layer using lithography technique. The nitride layer is partially etched to form a nitride alignment pattern using the alignment mark photoresist pattern as a mask. After the formation of N-well and P-well regions using lithography technique, the N-doped and P-doped impurities are subject to a thermally drive in process to activate and form N-well and P-well regions, respectively. At the same time, the pad oxide layer overlaying the N-well and P-well regions and the region not covered by the nitride alignment pattern is converted to a thermal oxide layer. The thermal oxide layer can be removed to reveal a recessed portion on the surface of the P-type silicon substrate, whereby the thickness of the nitride layer plus the depth of the recessed portion causes high step alignment marks to be formed.
A process of etching a semiconductor substrate and forming a trench which becomes a positioning mark on the semiconductor substrate, forming a burying film to fill the trench, forming a mask layer having an aperture to expose the trench, introducing an impurity to the trench with the mask layer used as the mask, and recessing the burying film in the trench which becomes the positioning mark.
A method for making a semiconductor structure, includes patterning a photoresist layer to form both a zero marks pattern and a well implant mask pattern. The photoresist layer is on a region of a substrate.
