Collaborative Research: Wavelet Analysis of Periodic Error for Improved Displacement Metrology

这笔赠款将使新的基础研究位移测量干涉。在这里要研究的外差或双频系统中，从移动目标反射的一个频率的激光相对于从固定目标反射的第二频率的激光的相移用于确定需要亚纳米定位精度的应用中的位移。该研究的目的是应用小波分析技术来表征周期性误差，这是由两个光频率的混合，并导致非累积定位误差的数量级为几个纳米。Wavelet提供了一种新的方法来分析信号的周期性错误;他们以前被用于图像压缩，语音识别和医疗应用。需要使用小波，而不是更传统的傅立叶变换方法，因为在非恒定速度条件下，周期误差随时间变化。此外，当使用保偏光纤将激光传送到干涉仪光学器件时，误差幅度是时变的。这是一种常见的情况，因为通常需要将产生热量的激光源与测量平台隔离。如果成功，这项研究将能够提高计量能力，并随后在纳米科学领域取得新的技术进步。这项研究有望改善测量技术（位移测量干涉法），提供最高的性能，在精度，分辨率和范围。该传感器对于半导体制造业至关重要，例如，在反馈控制系统中使用该传感器来相对于光刻光学器件定位硅晶片。对可实现的线宽（以及最终的芯片处理速度）的一个限制是载物台定位精度。其他应用包括传感器校准和材料去除机器。

This grant will enable new fundamental research into displacement measuring interferometry. In the heterodyne, or two-frequency, systems to be studied here, the phase shift in laser light of one frequency reflected from a moving target relative to laser light of a second frequency reflected from a fixed target is used to determine displacement in applications requiring sub-nanometer positioning accuracy. The objective of the research is to apply wavelet analysis techniques to characterize periodic error, which is caused by mixing of the two light frequencies and leads to non-cumulative positioning errors on the order of several nanometers. Wavelets provide a new approach to signal analysis for periodic error; they have previously been used in image compression, voice recognition, and medical applications. The use of wavelets, rather than the more traditional Fourier transform approach, is required because periodic error varies with time under non-constant velocity conditions. Additionally, the error amplitude is time-varying when polarization-maintaining fibers are used to deliver the laser light to the interferometer optics. This is a common occurrence because it is generally desired to isolate the heat-generating laser source from the measurement platform.If successful, this research will enable improved metrology capabilities and, subsequently, new technological advancements in the nano-science field. This research promises to improve the measurement technique (displacement measuring interferometry) that offers the highest performance in terms of accuracy, resolution, and range. This transducer is critical to the semiconductor manufacturing industry, for example, where it is used in a feedback control system to position the silicon wafer relative to the lithographic optics. One limitation on the achievable linewidth (and, ultimately, the chip processing speed) is the stage positioning accuracy. Other applications include transducer calibration and machines for material removal.