基于多级次同步叠加干涉的光栅标记对准测量机理研究

The continuous improvement of the advanced lithography device and related technology has put forward higher technical requirements for the future lithographic alignment measurement performance. However, it is difficult to take into account the problem of measuring precision and measuring range simultaneously, and the interference noise in the system limits the measurement precision. Aiming the problems above, a grating mark alignment measurement method based on multi-diffraction-order simulataneous aliasing interferometry is studied in this subject. The highest measurement accuracy in this method is obtained by the interference signal formed of the highest diffraction order, and the measurement range is extended by the interference signal formed of the lower diffraction orders simultaneously. This subject analyzes the transformation path of the alignment information in signals of all the diffraction orders. The simultaneous generation principle of multi-order interference measurement signals is researched. This method can simultaneous generate and measure the coarse and fine alignment measuring signals with multiple scales periods, the higher measurement precision and the larger measurement range are satisfied, thus effectively avoid the effects of multi-order measuring signal cannot be generated simultaneously on measurement results in traditional alignment technology. Secondly, a method of reducing the interferometric noise based on phase modulated interference system is proposed. The temporal coherence of the light source is controlled by the phase modulation of the light source. The interferometric noise signal with extra optical path introduced by the spurious reflection is suppressed. This project will provide an early exploration for the further improvement of the level of the advanced lithography equipment and ultra precision equipment technology in China.

尖端光刻装备与相关技术的不断进步对未来光刻对准测量性能提出了更高的技术需求。针对现有对准测量技术中普遍存在的测量精度与测量范围难以兼顾以及干涉噪声影响的问题。本项目探索一种基于多级次同步叠加干涉的光栅标记对准测量机理，利用最高衍射级次形成的干涉测量信号实现最高精度的对准测量，并利用其它级次干涉测量信号进行测程扩展，揭示各级次干涉信号间标记对准测量信息的转移途径，研究多个尺度不同周期干涉测量信号的同步生成理论，同步进行对准位置粗测/精测以兼顾测量精度和测量范围，克服传统方法中多级次信号无法同步测量导致的原理误差；其次，为防止干涉噪声制约测量精度，提出一种基于光源相位调制的干涉噪声抑制方法，通过光源相位调制实现光源时间相干性的周期性变化控制，在不影响正常干涉测量信号的前提下，对寄生反射引入的具有额外光程差的干涉噪声信号进行抑制。本项目将为我国尖端光刻装备与精密仪器水平的进一步提升提供先期探索。

本项目旨在面向光刻机对准技术中的急迫需求，研究基于多级次同步叠加干涉的光栅标记对准测量技术，以及多级次测量信号中对准相位信息的分离和提取，同时结合光源调制技术抑制干涉系统中寄生反射引入噪声，解决测量精度、测量范围难以兼顾的问题，为实现我国自主研发光刻机中的高性能对准测量奠定理论基础。主要研究内容如下：.建立了基于光栅标记多衍射级次同步叠加干涉的对准测量方法，对多级次混叠干涉对准测量信号进行了分析并构建完整理论模型，确定对准测量相位信息的传递过程，通过光栅对准标记衍射形成的多个不同空间频率的对准测量干涉信号，利用逐级精化理论对多衍射级次对准测量结果进行整合。分析及实验结果表明，该方法可实现大范围、快速、高精度对准测量，对光栅标记13个级次对准测量信号进行同步探测并对其中第1和第9级测量信号进行融合，对于光栅标记单一位置重复测量的标准差最小达到2.53nm。.针对现有对准测量系统中由于寄生反射引入的干涉噪声以及光源漂移背景噪声等问题，提出了一种基于光源外调制的测量系统噪声抑制方法，利用通过光源的相位调制实现光源时间相干性的控制，其相干性在不同光程差下呈现为有周期变化。通过控制调制参数可以对寄生反射引入的具有额外光程差的噪声干涉信号进行抑制，而不影响正常测量干涉信号。同时，利用光源的振幅调制和解调方法实现背景噪声和光源漂移引入的低频噪声信号的有效抑制。.最后，搭建基于多级次同步混叠干涉的光栅标记对准测量方法的实验系统并进行实验验证与分析。结合多级次测量结果在其测量范围内实现了光栅标记高精度对准测量。采用激光干涉仪与对准测量系统进行同步比对，在多个不同标记位置上重复测量结果与干涉仪的测量结果对比误差不大于11.27nm。引入光源调制系统后，多位置重复对准测量性能得到明显提升（调至后最小标准差3.72nm，最大标准差6.23nm；调制后最小标准差2.33nm，最大标准差4.63nm）.在项目的资助下，累计发表SCI论文7篇，申请中国发明专利1项。