离轴照明(OAI)作为一种重要的分辨力增强技术(RET)，不仅可以提高光刻分辨力，而且对焦深(DOF)也有一定程度地改善。针对特定的掩模图形，采用何种离轴照明模式能最大程度地改善光刻成像性能是主要研究的内容。通过优化设计的方法来获得最佳照明模式，采用的优化算法为最速下降法，采用的评价函数为光刻工艺窗口。工艺窗口包含三个方面的信息：成像精确度、曝光度、焦深。通过空间像性能对这三个方面分别做了描述，并将这三个函数加权得到综合评价函数，这种描述方法避免了复杂的光刻胶模型，评价函数值能快速准确地被求解。求解不同权值下的最佳照明模式及该照明模式对应的实际工艺窗口大小，结果表明，空间像性能描述的评价函数能较好地反映实际工艺窗口的性能，合理选择权值，优化得到的照明模式对工艺窗口性能有较大改善作用。

As an important resolution enhancement technology (RET), off-axis illumination (OAI) can not only improve lithography resolution, but also improve depth of focus (DOF) to some degree. Finding a best OAI mode to improve lithography performance for specific mask pattern is the main research content. The best OAI mode is obtained through optimum design method, using the steepest descent algorithm as the optimum method, and using process window as the evaluation function. The process window contains three information: image fidelity, exposure latitude and depth of focus. The three aspects are described by performance of aerial image, and the three functions are weighted to get a comprehensive evaluation function. The complex photoresist model is avoided, and the evaluation function value can be obtained quickly and accurately by the propsed method. The optimal OAI modes and actual process window are solved for different weights, and the results show that the actual performance of process window can be reflected by evaluation function described through aerial image, and the performance of process window can be improved greatly by using the optimal source obtained by selecting right weight.