利用聚焦離子束製作之Fresnel微透鏡

Abstract

隨著資訊科技的進步，高容量及高速度的資料存取的需求和重要性亦顯著增加，而光儲存科技在裡面扮演著極為重要的角色，其中，對於光儲存系統的效能，光學讀取頭的設計有著舉足輕重的影響力。 微型化和輕量化的要求推動了更小更輕的光學資料儲存系統的發展；近年來，微機電製程技術在IC半導體產業的快速進展之下有了重大的發展，而利用微光機電技術製作之微光學讀取頭乃是實現可攜式且高容量的光儲存系統的途徑之一。在本研究中，微光學讀取頭是由微光學平台及固定在雙軸致動器的聚焦透鏡所組成的，其中的聚焦透鏡正是本論文研究的主要方向。 本論文中所提及到的微透鏡有兩種：一種為直接利用聚焦離子束蝕刻氮化矽薄膜所製作出來的Fresnel微透鏡，此種微透鏡是以氮化矽做為材質；而另一種則是利用接觸式的黃光微影技術，配合著聚焦離子束所產生的灰階光罩，所製作出來的Fresnel微透鏡，此種微透鏡是以正光阻AZ4620為材質，而灰階光罩的材質則是以氮化矽為主。 關於微透鏡及灰階光罩的表面形貌和厚度大小已經設計完成，而其製作程序亦於此論文中被提出；另外，利用原子力顯微鏡進行其二維及三維的量測。對直徑大小為20微米的氮化矽微透鏡進行量測，其數值孔徑約為0.64，近似於DVD讀取頭的規格要求。本研究的最終目標是欲在微光學讀取頭中，實現一個整合於微光學平台之微透鏡，而其直徑大小為600微米，數值孔徑為0.65。

With the progress of information technology, the demand and importance of high capacity and high speed data storage systems rise significantly. In data storage systems, optical data storage technology plays a key role. Moreover, the design of optical pick-up heads has great influence in the performance of the optical data storage system. The requirement of miniaturization and lightness pushes the development of more miniaturized and lighter optical data storage system. Recently, the Micro Electro Mechanical Systems (MEMS) technology has been developed greatly with the rapid progress in the IC semiconductor industry. Micro optical pick-up heads fabricated by Micro-Opto-Electro-Mechanical System (MOEMS) technology can be used to realize portable high-capacity optical storage systems. In this research, the micro optical pick-up head is composed of a micro optical bench and a focusing lens mounted on a two-axis actuator. The study of focusing lenses is the major topic in this thesis. Two kinds of focusing lenses are proposed in this thesis. One is the Fresnel microlens in silicon nitride fabricated by focused ion beam (FIB) milling. The other one is the Fresnel microlens in positive photoresist AZ4620 produced through the contact-mode photolithography with the FIB-milled gray scale mask in silicon nitride. The profile and thickness of the microlenses and gray-scale masks have been designed. The fabrication process has also been proposed. 2D and 3D profiles of the lenses and masks were measured by the atomic force microscopy (AFM). For the microlens in nitride with a diameter of 20 μm, the numerical aperture (N.A.) of the lens was measured as 0.64, close to the specification of a DVD optical pick-up head. The ultimate target of this research is to realize a focusing microlens with a diameter of 600 μm and N.A. of 0.65, integrated with the micro optical bench in a micro pick-up head.