Better on wafer performance and mask manufacturability of contacts with no or non-traditional serifs

Abstract

In the course of using Optical Proximity Correction (OPC) to optimize contact printing, the obvious solution is not always the correct solution. This paper will explore two different types of contact layers, with two different sets of objectives. In the first type of contact layer, the primary objective is to achieve consistent area uniformity. For these designs, use of contacts without serifs over contacts with traditional corner serifs will result in a mask that has a lower data volume input to the mask writer and an easier time in inspection and repair. We also show that on the wafer, this simpler style of OPC will result in lower variation of area and CD. In second type of contact layer, there are additional complicating factors over the first type of contact layer in that these mask designs include layouts with different sizes of contacts that must be printed simultaneously. As contacts get pushed close together on corner to corner type spacing, traditional serifs will be more likely to drive mask inspection issues and high mask error enhancement factor (meet). One way to address this is with OPC that employs inverse serifs, with the center fragment of the rectangle pushed out and the corners pushed in. This approach reduces meef and provides better image parameters for lower variability through process window. However, this solution does not lend itself to very aggressive correction to achieve aggressive contact aspect ratios. We compare these different OPC strategies (squares, traditional corner serifs and inverse corner serifs) and describe the strengths and weaknesses of each approach.