EUV flare correction for the half-pitch 22nm node

Abstract

Extreme ultraviolet lithography (EUVL) is one of the most promising candidates for the next-generation lithography. For the adoption of EUVL, however, there are some technological issues to be solved. One of the critical issues is flare which is an undesirable scattered light that reduces the aerial image contrast leading to a reduction in the process window such as exposure latitude. Therefore, new methods to compensate for the anticipated flare effect have to be devised. At Selete, flare correction based on a flare point-spread function (PSF) is investigated. We succeeded in achieving a CD control of within a few nm over various pattern densities for the half-pitch (HP) 32-nm node. However, our estimation shows that the previous flare correction scheme could not meet the accuracy criteria of flare computation for HP 22-nm node. Therefore, we have modified the flare correction flow to implement a variable gridding for pattern-density calculation. The variable gridding based on the shape of a PSF enables highly accurate flare calculation within a reasonable runtime. Furthermore, we will use model-based OPC for HP 22-nm node, whereas we normally use rule-based OPC for HP 32- nm node. This is because the lithography process is reaching the low k1 regime. In this work, we investigate the feasibility of model-based OPC incorporating flare correction.