Patterning with spacer for expanding the resolution limit of current lithography tool

Double Exposure Technology (DET) is one of the main candidates for expanding the resolution limit of current lithography tool. But this technology has some bottleneck such as controlling the CD uniformity and overlay of both mask involved in the lithography process. One way to solve this problem and still maintain the resolution advantage of DET is using spacers. Patterning with a spacer not only expands the resolution limit but also solves the problems involved with DET. This method realizes the interconnection between the cell and peripheral region by "space spacer" instead of "line spacer" as usually used. Spacer process involves top hard mask etch, nitride spacer, oxide deposition, CMP, and nitride strip steps sequentially. Peripheral mask was additionally added to realize the interconnection region. With the use of spacers, it was possible to realize the NAND flash memory gate pattern with less than 50nm feature only using 0.85NA (ArF).