Ina Hideki, Takeda Mitsuo
Department of Information and Communications Engineering, Laboratory for Information Photonics and Wave Signal Processing, The University of Electro-Communications, Chofugaoka, Chofu, Tokyo, Japan.
Appl Opt. 2007 Jun 10;46(17):3485-92. doi: 10.1364/ao.46.003485.
To satisfy the increasing demand for extremely tight overlay accuracy in semiconductor manufacturing processes, all the measurement error factors in alignment systems and overlay measurement tools need be identified and eliminated. The principle of most alignment systems is based on image processing of target marks on the wafer under bright-field illumination. Although the phenomenon that the sensitivity to the alignment error varies with the step height (SH) of the mark has been known and used for evaluating the performance of the alignment optics, no investigation has been made into the origin and the physical mechanism of the phenomenon. We propose a simplified optical model that can account for the origin of the asymmetric image and clarify its relation to the SHs. The model is validated with simulation and experimental results. The improved performance of an alignment system using marks with optimally designed SHs is demonstrated.
为满足半导体制造工艺中对极高套刻精度日益增长的需求，需要识别并消除对准系统和套刻测量工具中的所有测量误差因素。大多数对准系统的原理基于明场照明下晶圆上目标标记的图像处理。尽管对对准误差的敏感度随标记的台阶高度（SH）变化这一现象已为人所知并用于评估对准光学器件的性能，但尚未对该现象的起源和物理机制进行研究。我们提出了一个简化的光学模型，该模型可以解释不对称图像的起源，并阐明其与台阶高度的关系。通过仿真和实验结果对该模型进行了验证。展示了使用具有优化设计台阶高度的标记的对准系统的改进性能。
