Impact of isofocal bias on MEEF management

Abstract

The Mask Error Enhancement Factor (MEEF) is an important consideration for determining the best mask bias used in conjunction with Optical Proximity Corrections (OPC). Reducing MEEF, increasing process window, and minimizing through pitch proximity bias are all factors that need to be addressed when optimizing OPC and illumination. These simulations determine the interaction between isofocal bias with the sign (positive or negative) and the magnitude of the mask bias that reduces the MEEF for 130nm lines/spaces in DUV resist. Ideally, bias applied in this manner minimizes the through pitch print bias, thereby increasing the overlap of the individual process windows, and hence the common process window. Incorporating the current technique of varying mask bias through pitch to minimize MEEF and increase common process latitude, we correlate the isofocal bias to the sign of the mask bias for optimal MEEF reduction.