缺陷对极紫外掩模多层结构反射场的扰动研究

Study of Defect Perturbation in Reflective Field of EUV Mask Multilayer

极紫外光刻掩模具有特殊的多层膜堆叠的反射式结构,在工艺制造过程中极易产生缺陷,引起多层膜结构变形,从而对掩模反射场产生干扰。这种掩模缺陷是制约极紫外光刻技术发展的难题之一。建立了含有缺陷的极紫外掩模多层膜结构模型,在此基础上采用时域有限差分(FDTD)法分析了缺陷尺寸和缺陷位置对掩模多层膜结构反射场分布的影响。结果表明,多层膜结构反射场受干扰程度是缺陷的高度和宽度综合作用的结果,并且与缺陷结构的平缓程度有关。反射场受干扰程度也与缺陷在多层膜结构内部的高度位置有关,引起多层膜结构靠近底层变形的缺陷对反射场的影响较小,而引起多层膜结构靠近顶层变形的缺陷对反射场有明显的干扰。

Extreme ultraviolet(EUV)lithography system uses a reflective mask structure with multilayers of Mo/Si,but defects can easily occur in the surface of substrate or in the process of depositing multilayer.Even a small defect can cause a large disturbance to the reflected field of mask.Manufacture of defect-free EUV mask is one of the most critical challenges for EUV lithography.In this paper,a multilayer structure model of ultra-ultraviolet mask with defects was established,and the influence of defect size and location on the reflection field distribution of mask multilayer structure was analyzed by finite difference time domain(FDTD)method.The results show that the interference degree of the reflection field of the multilayer structure is the result of the combination of the height and width of the defects,and is related to the smoothness of the defect structure.The interference degree of the reflection field is also related to the height of the defects in the multilayer structure.The defects that cause the multilayer structure to be deformed near the bottom have little influence on the reflection field,while the defects that cause the multilayer structure to be deformed near the top have obvious interference on the reflection field.