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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)也有一定程度的改善。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。
Off-axis illumination (OAI), as an important resolution enhancement technique (RET), not only improves lithographic resolution but also improves the depth of focus (DOF) to a certain extent. For a particular mask pattern, what kind of off-axis illumination mode is used to maximize photolithographic imaging performance is a major research topic. The optimum illumination mode is obtained through the optimized design method. The optimized algorithm is the steepest descent method, and the evaluation function is the lithography process window. Process window contains three aspects of information: imaging accuracy, exposure, depth of focus. These three aspects are described respectively by the spatial image performance, and the three functions are weighted to obtain a comprehensive evaluation function. The description avoids the complicated photoresist model and the evaluation function value can be quickly and accurately solved. The results show that the evaluation function of the spatial image performance can better reflect the performance of the actual process window, the reasonable choice of weights, and the optimization of the process window Lighting mode has a significant improvement on the performance of the process window.