高精度奈米級共平面移動台之研製

Abstract

隨著科技業不斷進步，產品持續朝微小化發展，因此具微奈米高精度平台需求被視為當下重要議題。本論文針對奈米級共平面平台提出一系列關鍵技術其中包含：零阿貝共平面平台設計，強健控制系統，高解析度感測器，即時訊號校正與細分，定位誤差校正與誤差補償系統建置。 為了兼顧效率和驅動解析度，同時考慮結構精簡化要求，本研究採用一種基於壓電陶瓷元件的超音波馬達HR4（Nanomotion Co.）作為驅動器。該馬達提供交流、脈衝與直流三種驅動模式，分別提供毫米、微米、奈米級長度驅動。為補償平台運動中時變的磨擦力，控制系統根據感測器迴授訊號，以自調式類神經即時調整PID控制器參數，並利用大小行程驅動與各種軌跡控制來驗證系統定位精度。 第三代共平面平台利用具奈米精度之線性繞射光柵干涉儀做為各軸位移量的感測器。為達到高精度定位控制，以誤差補償表為策略來消除平台中系統性誤差。此誤差補償表之建立乃利用雷射干涉儀進行定位誤差校正，並搭配四象限感測器校正光軸以確保無餘弦誤差。實驗結果證實，補償後全行程20 mm內定位誤差可達到±20 nm，標準差為12 nm。 改良式共平面平台是由多自由度量測系統來進行X與Y軸位移量測，該量測系統由波長補償麥克森干涉儀、雙軸自動視準儀與波長補償模組所組合而成，為了符合奈米級量測精度，發展一套麥克森干涉儀的反射鏡直線度對位方式，並針對即時波長補償建立一套數學模式，經實驗驗證其多自由度系統的波長穩定度可達 。更重要的，多自由度系統不僅在X與Y軸向具備奈米級量測精度，也可同時量測移動軸向的俯仰角和偏擺角，所以Z軸上阿貝誤差也因此得以補償。另外自動視準儀在定距離±30 arc sec量測時，精度為±0.3 arc sec。 由於幾何誤差對於高精度奈米共平面平台影響甚劇，因此在改良式共平面平台上，定位誤差、直線度誤差、垂直度誤差與角度誤差皆可由多自由度量測系統量測得出，另外平面鏡形貌也利用兩組多自由度系統分離出，因此該體積誤差可被自動補償。最後，結果驗證此共平面平台可達到奈米級精度與解析度並且適合應用於如微奈米三次元量測儀，微型曝光機與微機械加工之應用。

With the continuing trend toward device miniaturization in many engineering and scientific fields, the need to accomplish highly-precise stage at the micro- or nanoscale has emerged as a critical concern. This research presents a series of key technologies with nanometer level co-planar X-Y stages including Abbe free co-planar stage development, robust motion control scheme, high-resolution sensor, real-time signal correction and subdivision, positioning error calibration and error compensation system established. For the driving resolution and efficiency, as well as the simplification requirement, a piezoelement-based ultrasonic motor HR4 (Nanomotion Co.) is employed in this study. The motor drive provides three main driving modes, namely AC, Gate and DC, for millimeter, micrometer and nanometer displacements, respectively. To compensate for the effects of the variable friction force during stage motion, the gains of the PID controller used to regulate the stage motion are tuned adaptively by a self-tuning neuro-PID based on the feedback signals. The positioning accuracy of the proposed system is evaluated by performing large and small stroke and a series of contouring experiments. The 3rd generation of co-planar stage, the displacement of each axis stage is sensed using a linear diffraction grating interferometer (LDGI) with a nanometer resolution. Furthermore, to obtain a high accuracy positional motion, the error compensation strategy is implemented to eliminate the systematic errors of the stage with error budget. The error budget is obtained by positioning error calibration using a laser interferometer, which optical axis is detected by a quadrant photodetector (QPD) to ensure no cosine error. The positioning error can be controlled to ±20 nm with standard deviation 12 nm after implementing error compensation. In the modified co-planar stage, the x- and y-axis coordinates are measured using the MDFMS which comprising a wavelength-corrected Michelson interferometer, a dual-axis autocollimator and wavelength compensator. In order to meet the requirement for a nanometer level measurement, the method for straightness of mirror in Michelson interferometer and alignment procedures have been developed. Moreover, a mathematical model for real time wavelength correction has been proposed and experimental results show that the MDFMS has a normalized wavelength stability of less than 10-6. Importantly, the MDFMS not only enables the x- and y-axis coordinates to be measured with a nanoscale precision, but also enables the pitch and yaw errors of each axis to be detected such that the Abbe errors in the z-direction can be compensated. Moreover, the autocollimator has an accuracy of ± 0.3 arc-sec over the range of ± 30 arc-sec. Besides, the performance of a high-precision co-planar stage is extremely sensitive to the effects of volumetric accuracy. In the modified co-planar stage, this 6-DOF capability can measure the positioning error, straightness error, squareness error and angular errors of the X and Y motions. In addition, the shape error of the mirror can also be separated by using two MDFMS. The volumetric error compensation can also be done automatically. The results demonstrate that the co-planar stage achieves a nanometer level of accuracy and resolution and is therefore a suitable solution for micro-CMM, micro-lithography and micro-machining applications.