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Simulation study of illumination effects in high-NA EUV lithography

机译：高NA EUV光刻中照明效果的模拟研究

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Current EUV exposure systems employ a numerical aperture (NA) of 0.3.3. This relatively small NA is a consequence of geometrical design limitations of all reflective projection systems with a 4× demagnification in the orthogonal x- and y-directions of the image plane. Anamorphic imaging, which employs different demagnification in horizontal (y) and vertical (x) direction can increase the NA to a value of 0.55. The consequences of using anamorphic high-NA imaging system have to be studied by rigorous methods. Since the range of illumination angles of the anamorphic system is different in x and y directions, one way to understand the involved phenomena, is to investigate and compare the impact of illumination angles for both the high-NA 4×8× anamorphic system at 0.55NA and the lower-NA 4×4× system at 0.33NA. We employ fully coherent that is single source point illumination and imaging to study the impact of the illumination direction on the most relevant lithographic metrics. These metrics include the resulting feature size or critical dimension (CD), the feature position, a local contrast or the normalized image log slope (NILS) and the best-focus position of the projected images. In this study, aerial images from a uniformly-distributed grid of 230 illumination positions were computed and analyzed. The results of the simulation study confirmed that larger illumination angles cause more pronounced shadowing effects and significant variations of the position and feature size versus the illumination direction. The larger demagnification direction of the anamorphic system involves a smaller object-side angular spread of the illumination direction, resulting in less pronounced variation of CD and position versus the illumination direction compared to the isomorphic system. Both systems exhibit a drop of the NILS for more oblique angles. However, the larger image side angles of the high-NA system result in more pronounced polarization effects, which reduce the NILS values compared to that of the lower NA system. The high NA achieved by anamorphic imaging increases the importance of 3D mask effects in EUV lithography.2 It is not a priori known, which of these 3D mask effects can be attributed to the absorber or the multilayer part of the mask. A hybrid mask simulation approach addresses this question. In the second part of this study, simulations using an hybrid of real and ideal mask elements were performed in an attempt to understand their individual effects of the mask elements and which mask element contributes to which of the observed effects.
机译：当前的EUV曝光系统采用0.3.3的数值孔径（NA）。相对较小的NA是所有反射投影系统的几何设计限制的结果，这些反射投影系统在像平面的正交x方向和y方向上具有4倍的缩小率。在水平（y）和垂直（x）方向上采用不同放大倍率的变形成像可以将NA增加到0.55的值。使用变形高NA成像系统的后果必须通过严格的方法进行研究。由于变形系统的照明角度范围在x和y方向上不同，因此了解所涉及现象的一种方法是研究和比较照明角度对高NA 4×8×变形系统在0.55时的影响。 NA和下层NA 4×4×系统的值为0.33NA。我们采用完全相干的单源点照明和成像技术来研究照明方向对最相关的光刻指标的影响。这些度量包括生成的特征尺寸或关键尺寸（CD），特征位置，局部对比度或归一化图像对数斜率（NILS）以及投影图像的最佳聚焦位置。在这项研究中，对来自230个照明位置的均匀分布网格的航拍图像进行了计算和分析。仿真研究的结果证实，较大的照明角度会导致更明显的阴影效果，并且位置和特征尺寸随照明方向的变化也很大。变形系统的较大放大倍数方向涉及照明方向的较小的对象侧角度扩展，与同构系统相比，导致CD和位置相对于照明方向的变化较小。两种系统都表现出NILS下降，倾斜角度更大。但是，高数值孔径系统的较大图像侧角会导致更明显的偏振效应，与较低数值孔径系统的偏振角相比，NILS值会降低。通过变形成像获得的高数值孔径提高了3D掩模效应在EUV光刻中的重要性。2尚不清楚，这些3D掩模效应中的哪一个可归因于掩模的吸收层或多层部分。混合掩模仿真方法解决了这个问题。在本研究的第二部分中，使用真实和理想蒙版元素的混合进行了模拟，以试图了解它们各自对蒙版元素的影响以及哪个蒙版元素对观察到的效果做出了贡献。

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