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随着半导体制造步入1xnm技术节点时代,光刻机中的对焦控制精度需要达到几十纳米。在纳米精度范围内,硅片上的集成电路(IC)工艺显著影响调焦调平系统的测量精度。基于实际的调焦调平光学系统模型和三角法、叠栅条纹法测量原理,建立工艺相关性误差模型。研究表明,工艺相关性误差主要来源于测量光在光刻胶涂层内部的多次反射。选取3种光刻胶仿真分析发现,不同光刻胶的工艺相关性误差随光刻胶厚度的变化趋势相同,随测量光入射角(45°~85°)的增大而减小。在实验验证平台上分别测量7种工艺硅片,实验测量值与理论模型计算值差异统计平均值小于6nm。结果表明,光刻机中调焦调平系统的测量光有必要采用大入射角度,同时提高光刻胶的涂胶均匀性,以减少工艺相关性误差。
With the era of semiconductor manufacturing entering the 1xnm technology node, the accuracy of the focus control in lithography needs to reach tens of nanometers. Integrated circuit (IC) processes on silicon significantly affect the accuracy of the focusing and leveling system at nanometer accuracy. Based on the actual focusing and leveling optical system model and trigonometry and moire measurement principle, a process-dependent error model was established. Research shows that the process-dependent errors mainly come from the multiple reflections of the measuring light inside the photoresist coating. The simulation analysis of the three kinds of photoresists showed that the process-related errors of different photoresists vary with the thickness of the photoresist, and decrease with the incident angle (45 ° ~85 °) of the measuring light. Seven kinds of process wafers were measured on the experimental verification platform respectively. The statistical mean difference between experimental and theoretical models was less than 6 nm. The results show that it is necessary to adopt a large incident angle to measure light of the focusing and leveling system in the lithography machine, and at the same time improve the uniformity of photoresist coating to reduce the process-related errors.