Depth of focus enhancement for sub-<inline-formula><math display="inline" overflow="scroll"><mrow><mn>110</mn><mtext>-</mtext><mi>nm</mi></mrow></math></inline-formula> technology by using KrF double-exposure lithography

Abstract

Traditional double-exposure lithography (DEL) or double-patterning lithography (DPL) methodologies stem most from the resolution enhancement standpoint. A single mask with high feature densities is split into two exposure steps, each with lower feature densities that can be easily resolved. The DEL is proposed as the process window enhancement technology for sub-110-nm technology. Features with sparse pitches are printed by a first step of dense pitch exposures and a second exposure with dummy features removed. The pattern decomposition strategy described is similar to that of subresolution assisting features (SRAF). So it is compatible with the traditional rule-based SRAF implementation methodology. By comparing the depth of focus (DOF) of the 110-nm lithography process between the single exposure and the double exposure, it is found that the DOF for marginal features is extended by using double-exposure methodology, and thus extends the capability of KrF exposure tools. Furthermore, the link between the overlay performance and the overlap of the second exposure's trim slots over the first exposure is studied. The results show that the overlay control is within the KrF scanner capability. As a further study, the proposed double-exposure methodology for the 90-nm lithography process is evaluated.