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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16nm线宽黑白线条曝光的最优OAI参数。
Off-axis illumination technology (OAI) is one of the key technologies for lithography resolution in EUV lithography. In order to realize the optimal choice of off-axis illumination considering the shadow effect of masks, a new imaging model to realize OAI exposure is constructed. The incoherent light impinging on the mask is equivalent to a series of equal intensity parallel light with continuous incident direction. The masks are respectively imaged based on Abbe’s imaging principle, and finally the intensity is superimposed on the image surface to realize the space imaging in the OAI mode The calculation of the spatial imaging on different out-of-focus surfaces is achieved by adding defocus aberration to the projection system function. The model greatly simplifies the calculation of the shadow effect of masks under OAI and improves the computational efficiency of image quality. Combined with the characteristics of photoresist and the design of focal depth of projection exposure system, the optimal OAI of 16nm line width black-and-white line exposure using projection system with numerical aperture of 0.32 was obtained based on the sidewall inclination of developed photoresist profile. parameter.