運用中空錐狀微管設計與開發貝索光束加工平台之研究

Abstract

傳統光學系統中，為增加其空間解析度，除了採用短波長光源外，還可藉由提高透鏡的數值孔徑的方式，皆可提高系統的空間解析度，而光學系統的焦深同時也被前述兩項參數所影響，光學繞射極限同時也指出了空間解析度與焦深的相互連動關係。換言之，在傳統光學系統中，一旦設定了空間解析度，焦深也自動地被決定了。 從突破光學繞射極限的構想出發，回顧近場光學的方法，近場的光學特性雖可輕易達到超越繞射極限的聚焦光點，但其焦深過短以及近場高度控制問題，都是此方法不易被材料加工領域廣泛應用的原因。過去，本研究團隊曾提出以次波長單圓環孔徑結構製作金屬薄膜上，在遠場產生具有次波長聚焦能力的貝索光束，並應用於曝光微影以及材料鑽孔，以製作奈微米的高深寬比結構。 運用團隊內近期之拉伸中空微管微影曝光的前導性研究為基礎，同時以一系列拉伸中空微管與次波長單圓環孔徑結構歷年來研究的比較來進行探討，本論文結合近場及遠場光學的概念，從討論中空微管的光線耦合方式出發，進而透過時域有限差分法電磁模擬、光強實驗以及曝光微影實驗，深入探討中空微管漸縮後的尺寸大小對此種光學頭出光特性的影響，研究結果中發現中空錐狀微管的尖端管壁厚度為影響次波長貝索光束產生的重要因素，而尖端的直徑大小則會影響貝索光束的焦點位置及焦深長度，同時也對光束偏極態是否影響微管出光特性做研究，最後結合石英音叉，並以簡易之SFM技術做為近接或碰觸感測，建立出一次波長貝索光束加工平台，最終在自製的加工平台上，以光阻為感光材料，製作出高深寬比的孔洞，經過多次實驗，乃能初步製作出奈微米尺寸的高深寬比光阻孔洞，也成功的顯示出運用本論文所提出的創新發明架構建構次世代奈微米加工機的契機。

In traditional optical system, the spatial resolution was defined by the wavelength of incident light and the numerical aperture of lens. Using shorter wavelength incident light or higher numerical aperture lens, the spatial resolution of optical system can be improved. The depth of focus also depends on the above-mentioned two parameters. The diffraction limit actually implies that the spatial resolution and the depth of focus are coupled. In other words, once the spatial resolution is set, the depth of focus is automatically pre-determined in traditional optical systems. This thesis started from the idea of trying to break the diffraction limit. The near-field optical methods were reviewed as they had been proposed to achieve super-resolution in near-field. But the extremely short depth of focus associated with near-field system makes the distance control between tip and sample in near-field a major reason prevents us from using near-field system for general material machining. Our research group proposed a subwavelength annular aperture on metallic film that enables Bessel light beam, which maintains a subwavelength focusing ability while achieving tens of micron of depth of focus in the far-field region, for lithography process and material machining or drilling with a hope to produce high aspect ratio structures with ease. Following the preliminary studies of using tapered hollow micro-tube to do the lithography process and a series of correlation discussion between tapered hollow micro-tube and subwavelength annular aperture, the subject of this research combined the near-field and the far-field optics concepts by using tapered hollow micro-tube. Started from discussing the approaches for coupling the incident light into the hollow micro-tube, this thesis studied and verified the tip size of tapered hollow micro-tube could affect the emitted light beam properties by FDTD simulations, intensity profile and lithography experiments. The results showed the tube’s thickness on tapered hollow micro-tube tip was an important factor for generating subwavelength Bessel light beam. The tip diameter size could also change the focal length and depth of focus. Moreover, if the incident light polarization state will affect the characteristics of emitted light beam will also be studied. Finally, integrating quartz tuning fork and simple SFM technique to do tip approach or contact sensing, a subwavelength Bessel light beam machining system was successfully established to produce nano/micro high aspect ratio holes on photoresist. These results finally shed lights on adopting the innovative configuration and processing parameters developed in this thesis to design next generation nano/micro machine tool.