双焦波带片干涉显微成像实现极紫外位相型掩模缺陷探测方法研究

In terms of the inspection of phase defect of extreme ultraviolet (EUV) mask, the image method of Dyson interferometric microscope with twin-focus zone plate is proposed. In this research project, the light intensity functions of interference field with the phase defect of 50-to-200-nm-wide and 2-to-10-nm-deep pit and that of the change in the Mo/Si multilayer membrane are constructed, which can be used for the design of phase function of the twin-focus zone plate to satisfy the ability of defect inspection. Further, the influence of the off-axis displacement and choose of the diffraction order for the devise of reflective or refractive twin-focus zone plate is analyzed. The inosculation of dual-phase function of twin-focus zone plate and the managing coding algorithm is researched. Dyson Interference microscopy imaging experiment system with twin-focus zone plate used to the inspection of mask phase defect is constructed. In this system, the twin-focus zone plate is employed as Dyson interference microscopy imaging component, and the phase reflection grating is employed as beam splitting component. This method has the advantages such as few elements, easy assembly and calibration (be convenient to position) and favorable reliability. This research could open up a new filed in the inspection of EUV mask defect, which can be applied to solve an unit technology for the very large scale integrated circuits (VLSI) manufacture and packaged technics study. Meanwhile, the development of the filed of shortwave optics and micro-nano-detection technology is promoted.

本项目针对EUV掩模位相缺陷的探测，提出Dyson型双焦波带片干涉显微成像方法，建立随50-200nm宽、2-10nm高缺陷大小和其在Mo/Si多层膜内的缺陷深度变化的干涉场光强函数，指导满足探测该缺陷能力的双焦波带片位相函数的设计，分析离轴量、衍射级次选用对反射/透射式双焦波带片设计的影响规律，研究双焦波带片双位相函数的融合与经济编码算法，建立用于位相缺陷探测的Dyson型双焦波带片干涉显微成像实验平台。该方法采用Dyson型双焦波带片作为干涉显微成像元件、位相型反射光栅作为分光元件，元件数量少、易于装校（具有定位指示）、可靠性好。它的研究将在EUV掩模缺陷探测方面开辟一个新的领域，为我国极大规模集成电路制造与成套工艺研究解决一项单元技术，推动短波光学与微纳检测领域的技术发展。

本课题采用Dyson型双焦波带片作为干涉显微成像元件、位相型反射光栅作为分光元件，元件数量少、易于装校（具有定位指示）、可靠性好。它的研究在EUV掩模缺陷探测方面开辟一个新的领域，为我国极大规模集成电路制造与成套工艺研究解决一项单元技术，推动短波光学与微纳检测领域的技术发展。. 为实现对EUV掩模缺陷的检测，本课题首先研究了掩模缺陷对入射场扰动机理，提出了散射偏振扰动理论的极紫外掩模位相缺陷检测方法，利用位相缺陷对偏振场的影响规律，通过检测位相缺陷引起光场强度变化，逆向映射得到位相缺陷参数。针对波带片的设计问题，提出了基于光线追迹和虚拟玻璃的位相型波带片设计方法、分区环形结构位相波带片设计方法以及组合波带片的设计方法，该方法不仅为波带片的设计打开了思路，还打破了现有加工条件的限制。针对材料对极紫外波段强吸收的特点，提出了基于位相光栅分光的双焦波带片干涉显微检测方法，该方法是一种基于镂空型位相光栅分光和偏轴型位相波带片聚焦的双焦波带片干涉显微检测方法，这些方法简化了系统结构，改善了缺陷定位精度和分辨率。针对极紫外波段可用透镜材料少的特点，本课题开展了无镜成像检测方法研究，提出了位相缺陷检测的交叠衍射无镜成像和多波长无镜成像方法；交叠衍射无镜成像技术具有光路简单、使用方便、成像范围可扩展、收敛速度快、抗噪声能力强等优点，研究中设计阵列扫描方案，移动样品实现全口径的采集图像，实现对全口径掩摸位相缺陷的检测。多波长无镜成像方法，通过波长扫描代替机械扫描，结合梯度加速相位恢复迭代算法，实现对位相缺陷的检测。研究结果表明：根据位相缺陷对入射场的扰动规律，采用无镜成像技术，据已知位置被缺陷调制后的相位信息，能够逆向映射到待测掩模上，获得位相缺陷的几何参数；结合阵列扫描技术，实现全口径、快速、高效的检测，是一种有效获得EUV掩模位相型缺陷的创新方法。. 本课题的研究成果可实现对EUV掩摸位相缺陷的检测，也可扩展到高精度光学系统中光学元件的缺陷检测。