Abstract: A method of fabricating a universal zero layer photomask of an integrated circuit is disclosed. With this method, only one universal zero layer mask is required for all the integrated circuit products; thus, the production cost can be reduced. In this method, the alignment marks and one or more vernier patterns are located near the edge of the effective exposure field of the wafer which takes up only a very small area of the wafer. Furthermore, the zero layer layout of the product also places the alignment marks and the vernier patterns in the same corner as the photomask. During the alignment, the wafer moves back and forth in both X and Y directions so as to match the previously recorded alignment marks positions on the mask.

Abstract: 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.

Abstract: A method of fabricating a twin-well integrated circuit device to implant the dopants directly through the nitride layer including steps of: The pad oxide layer and nitride layer are formed on a P-type semiconductor silicon wafer. Then, the alignment mark photoresist pattern is formed by the conventional lithography technique, where the alignment mark region is in clear field, while other regions are in dark field. Next, the nitride layer is patterned by plasma-etching technique to form the nitride alignment mark. The N-well region is formed by lithography and ion-implantation techniques. Thereafter, the P-well region is formed by lithography and ion-implantation methods again. Next, the active device region photoresist is formed by lithography technique. The nitride layer is partially etched to open the windows by plasma-etching technique. The P-well region photoresist is then formed, followed by the deep-implantation process.