Periodic Error Elimination Through New Displacement Measuring Interferometer Design

本文的研究目的是构建、测试和验证一种位移测量干涉仪设计的新概念。新的外差（双频）干涉仪设计将消除周期性误差，目前限制了传统配置的精度。周期误差是“偏振编码”的结果，其中两个共线光学频率在干涉仪内使用垂直的线性偏振状态和偏振相关光学分离。由于光学和光偏振的固有缺陷，混频器的发生是因为频率不只是沿着它们预定的路径传播。在运动过程中，误差表现为测量位移在真实值附近的周期性（或周期性）振荡，通常具有几纳米的振幅。在新的设计中，使用声光调制器产生两个频率并在空间上分离。通过消除干涉仪内部的重叠和混频的可能性，消除了周期性误差。主要教育目标是开发一个团队授课的研究生研讨会课程，包括：1)创意写作；2)技术写作；3)口头陈述；4)提案写作。新的设计概念将把位移测量精度提高到亚纳米水平，适用于各种应用，包括光刻步进工作台、机床和坐标测量机的位置反馈。例如，在集成电路生产的步进阶段，提高定位精度是不断推动增加特征密度和随后的计算能力的重要组成部分。除了研究方面的好处，教育方面的影响还包括通过研讨会课程提高研究生的沟通技巧和创造力。

The research objective of this study is to construct, test, and verify a new concept for displacement measuring interferometer design. The new heterodyne (two frequency) interferometer design will eliminate periodic error, which currently limits the accuracy of traditional configurations. Periodic error is the result of "polarization coding", where the two collinear optical frequencies are separated within the interferometer using perpendicular linear polarization states and polarization-dependent optics. Due to inherent imperfections in the optics and light polarizations, mixing occurs because the frequencies do not travel only along their intended paths. The error appears as a cyclical (or periodic) oscillation of the measured displacement about the true value during motion, typically with an amplitude of several nanometers. In the new design, the two frequencies are generated and spatially separated using an acousto-optic modulator. By removing the potential for overlap and frequency mixing within the interferometer, periodic error is removed. The primary education objective is development of a team-taught graduate seminar course that will include: 1) creative writing; 2) technical writing; 3) oral presentation; and 4) proposal writing.The new design concept will improve displacement measurement accuracy to the sub-nanometer level for various applications, including position feedback for lithographic stepper stages, machine tools, and coordinate measuring machines. In stepper stages for integrated circuit production, for example, improved positioning accuracy is an important component in the continuous push toward increased feature density and, subsequently, computing power. In addition to the research benefits, education impacts will include improved communication skills and creativity for graduate students through the seminar course.