离轴照明技术(OAI)是极紫外光刻技术中提高光刻分辨率的关键技术之一。为了实现考虑掩模阴影效应情况下离轴照明的优化选择，构造了一种新型实现OAI曝光的成像模型。将照射到掩模上的非相干光等效为一系列具有连续入射方向的等强度平行光，基于阿贝成像原理分别对掩模进行成像，最终在像面进行强度叠加实现OAI方式下空间成像的计算；并通过向投影系统函数添加离焦像差项实现不同离焦面上空间成像计算。该模型极大地简化了OAI条件下对掩模阴影效应的计算，提高了成像质量计算效率。结合光刻胶特性及投影曝光系统焦深设计要求，以显影后光刻胶轮廓的侧壁倾角为判据，获得了采用数值孔径为0.32的投影系统实现16 nm线宽黑白线条曝光的最优OAI参数。

Off-axis illumination (OAI) is one of the key technologies to enhance the resolution in extremely ultraviolet lithography (EUVL). For the optimizing of OAI specifications involving shadowing effect of mask, a novel model of OAI imaging is presented. It divides the incoherent incident light into a series of parallel light beams with numerical continuous directions, imaging the mask to the wafer plane with each of these beams based on Abbe imaging principle, and finally takes the superposition of the intensities to achieve OAI exposure in EUVL. Images at various defocus planes are equivalently achieved via adding extra defocus aberration into projection system. The model facilitates the simulation of the mask shadowing effect effectively. Then adapting the sidewall angle of the developed photoresist for criterion, the optimum specifications of OAI style are obtained for the exposure of 16 nm half-pitch dense line and space under the consideration of properties of photoresist and depth of focus requirement of the projection system with numerical aperture of 0.32.