光柵位移干涉術

Abstract

本論文利用光柵干涉定位量測技術研製之平面繞射雷射編碼系統，此系統可直接量測二維位移，量測解析度達1奈米。傳統二維位移量測使用一雙交叉垂直的線性光學尺，兩光學尺的垂直度調校，相當困難。且光學尺的零件組裝對位也成為使用者的瓶頸。在所有調校中，光學讀頭與光柵間的對位是最大的問題。本論文採用共軛光路之雙繞射路設計，以單一二維光柵盤與單一入射光同時量測二維的位移，使兩干涉光點永不錯位從而達到光柵與光學讀頭對位的高容許差，光柵與光學讀頭的對位容差大於5°，且因為雙光路設計使訊號週期為光柵週期的四分之一。

本論文採用週期為1.6μm的二維光柵，訊號週期0.4μm，再利用四百倍的細分割技術使解析度達到1nm。與電容感測器比對，其誤差小於30nm，重複量測十次，其標準差優於8nm。

本論文將二維光學尺與壓電平台整合，以光學尺作為平台的回饋控制位移感測器，並應用於原子力顯微鏡系統之掃描，作為掃描用之載物台，成功掃描出二維光柵影像。

This thesis presents a planar diffractive laser encoder system (PDLENS), which serves as a two-dimensional position detection apparatus for precision machine applications with a measuring resolution of 1 nm. Traditional two-dimensional position detection uses a pair of linear encoders in crossed construction. However, it is difficult to align and keep the perpendicularity between this pair of encoders. The rigorous alignment tolerances among various components of the encoder system become a serious user adaptation bottleneck. Of all alignment tolerances, the head-to-scale alignment tolerance is the most important problem for applications. By using double-diffraction configuration, the PDLENS with a 2D grating exhibits much larger head-to-scale alignment tolerances (>±5°) than traditional linear encoder.

The 2D grating, which has period of 1.6μm in both the X and the Y directions provides a signal period of 0.4μm. Electronic interpolation with a factor of 400 leads to a measuring resolution of 1 nm. We measured a circle with radius of 1µm. The maximum difference between the measured values of capacitance displacement sensor and encoder is less than 30nm. This difference includes the intrinsic periodic error of 2D gratings, an inherent non-linearity of this positioning system, and noise of electronic circuit. The circle was measured 10 times for repeatability of encoder. The standard deviation of the repeatability measurements is better than ±8nm.