近場光學讀取頭中奈米孔與固態浸沒透鏡整合製程之研究

Abstract

在近場光學紀錄系統中，微孔與固態浸沒透鏡（SIL）為常被用來克服光學繞射極以及限縮小光點的兩項技術。其中在微孔系統中，光點大小直接由微孔尺寸所決定，因此我們可藉由縮小微孔尺寸至奈米等級來得到極高解析度，然而由於奈米級微孔之光輸出效率極低，因此在記錄速度上一直無法有效提升。至於利用SIL，雖然所獲得的光點可較傳統光學記錄系統小，同時仍然可保持高光輸出效率，但其所得到之解析度卻不及微孔所能獲得的。根據以往研究指出，若將微孔與SIL結合，則由於入射於微孔的光功率密度增加，因此光出射效率相對得以提升。然而在組裝或黏合奈米孔與SIL/SSIL時，必然會產生對準誤差，但如何將奈米孔與SIL/SSIL準確結合則至今尚未有文獻討論。本論文之研究重點即是在利用奈/微米機電技術製作SIL/SSIL與奈米級微孔之整合結構，其中奈米孔是利用聚焦離子束蝕刻進行製作，而SIL/SSIL則是利用熱回流製程進行製作。為了克服對準誤差，本研究提出一種自我對準技術，其方法是利用在熱回流製程中表面張力所自行產生的自我調整機制。在微孔設計方面，論文中也將研究不同形狀之微孔對光輸出效率的影響。在此介紹圓形孔及C形孔。 在製作方面，SIL以及SSIL已製作成功，而其最大尺寸誤差皆在3％以內。在奈米孔方面，已製作出直徑103nm、148nm、329nm的圓孔以及尺寸303nm×205nm、223nm×105nm的C形孔。本研究並藉由掃瞄電子顯微鏡（SEM）證實所提出整合SIL/SSIL與奈米孔之自我對準技術的可行性。 在遠場量測結果中，與直徑329nm的圓孔比較，SIL與直徑329nm圓孔之整合元件在光輸出率上可增強約1.68倍，顯示SIL確實有增強奈米孔的光輸出效率，並進一步證實其整合SIL與奈米孔結構之自我對準技術的可行性。在C形孔量測方面，在保持相同光點大小之情形下，303nm×205nm的C形孔在光輸出效率上比直徑148nm圓孔提高14.325倍。與直徑148nm圓孔比較，直徑15μm的SIL與303nm×205nmC形孔之整合元件在光輸出率方面甚至可增強約24.438倍，顯示整合SIL與C形奈米孔可大幅提昇光學讀取性能。

For near-field recording systems, Aperture and Solid Immersion Lens（SIL） are two popular techniques to overcome light diffraction limit and reduce spot size. In aperture systems, seeing that light spot size is directly determined by aperture size, aperture systems can provide an ultra-high resolution by reducing the aperture size to nano-scale. However, nano-aperture suffers from low power throughput which results in the recording speed unable to be promoted. SIL systems, while can providing a smaller spot size than obtained in conventional optical recording systems with still maintaining high optical throughput, do not have the resolution observed from aperture probe systems. According to previous researches, nano-aperture combined with SIL/SSIL can improve the throughput owing to greater power densities at the aperture. However, the misalignment between the SIL/SSIL and nano-aperture always occurred in assembling or bonding step. How to align the nano-aperture and SIL/SSIL together precisely has not proposed yet. In this research, the purpose is concentrated on combination of SIL/SSIL and nano-aperture by Nano/Micro Electro-Mechanical Systems（N/MEMS） technology, where nano-aperture is fabricated with Focused Ion Beam（FIB）system and SIL /SSIL are formed by thermal reflowing process. In order to overcome the misalignment between SIL/SSIL and nano-aperture, a self-alignment technique based on self-modulation by surface tension during thermal reflowing process is proposed. About aperture designs, the influence of varied shapes of apertures at optical throughput is also studied. Here, circular apertures and C-shaped apertures are introduced. In fabrication results, SIL and SSIL are fabricated and the maximum error is less than 3% in comparison with the designed values. About nano-aperture, the diameter 103nm, 148nm, and 329nm of circular aperture and the dimensions 303nm×205nm and 223nm×105nm of C-shaped apertures are fabricated. The feasibility of self-alignment technique between SIL/SSIL and nano-aperture proposed in this research is also verified by Scanning Electron microscope（SEM）. From the measurement results of far-field system, the 15μm-diameter SIL/329nm-diameter circular aperture component has 1.68 times enhancement of throughput compared with 329nm-diameter aperture alone. This result shows that SIL can really enhance the light throughput of nano-aperture and the feasibility of self-alignment technique between SIL and nano-aperture is further verified. About measurement results of C-shaped apertures, the throughput of 303nm×205nm C-shaped aperture alone is 14.325 times larger than that of 148nm-diameter circular aperture alone, while maintaining a comparable near-field spot size. Even the throughput of 303nm×205nm C-shaped aperture/15μm-diameter SIL component can be enhanced by 24.438 times as compared with 148nm-diameter circular aperture alone. This result indicates that combination of SIL and C-shaped aperture can really greatly enhance the performance of near-field pick-up head.