Periodic Error Elimination Through New Displacement Measuring Interferometer Design

本研究的研究目标是构建、测试和验证位移测量干涉仪设计的新概念。新的外差(双频)干涉仪设计将消除目前限制传统配置精度的周期性误差。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线偏振态和偏振相关光学元件来分离。由于光学和光偏振的固有缺陷，由于频率并不只沿着其预定的路径传播，所以会发生混频。误差表现为运动过程中测量的位移相对于真实值的周期性(或周期性)振荡，通常幅度为几纳米。在新的设计中，这两个频率是使用声光调制器产生并在空间上分离的。通过消除干涉仪内部重叠和混频的可能性，消除了周期性误差。主要的教育目标是开发团队授课的研究生研讨会课程，其中将包括：1)创意写作；2)技术写作；3)口头陈述；4)提案写作。新的设计理念将把位移测量精度提高到亚纳米级，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，在集成电路生产的分步阶段，改进的定位精度是不断推动提高特征密度以及随后的计算能力的重要组成部分。除了研究方面的好处，教育的影响还包括通过研讨会课程提高研究生的沟通能力和创造力。

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.