漸變式折射複合光學薄膜技術

摘要：本文探討漸變式折射複合光學設計及製程技術，利用反應式磁控濺鍍製程製備漸變折射率光學薄膜，並分析高低折射率材料之光學常數及殘留應力特性。使用具較低吸收及低殘留應力條件下之單層膜製程，製備AlNxOy薄膜及分析其光學常數及殘留應力特性。另製備漸變折射率光學濾光片，且使該漸變折射率光學濾光片具有良好之光學特性及低的殘留應力值。採用鋁靶做為起始的材料，調整濺鍍功率、氮氣或氧氣之氣體流量等製程參數，亦探討同時通入氮氣及氧氣製備AlNxOy光學混合薄膜，並使用電漿迴授控制方式監控氮氧化鋁電漿製程。

Abstract：This work investigates a composite optical design with progressive refraction index and process technology to manufacture the films. The optical films with gradient refractive index were prepared by reactive magnetron sputtering process. The optical constants and residual stress properties of the high and low refractive index materials were characterized. Processes with low absorption and low residual stress were used to prepare various single layer thin films, AlNxOy, and their optical constants and residual stress properties were analyzed. Optical filter with gradient refractive index was then prepared, and the optical filter has good optical characteristics and low residual stress value. An aluminum target was used as the starting material to prepare AlNxOy optical films, and the effects of sputtering power, the gas flow of nitrogen or oxygen, and other process parameters were discussed. Plasma feedback control method was used to monitor the aluminum oxide plasma process. We look forward to establishing the technology of gradient refraction optical filter to make light tablets generate better optical characteristics and with the low of residual stress.

關鍵詞：漸變折射、反應式磁控濺鍍、皺波濾光片
Keywords：Gradient Refraction、Reaction Type Magnetron Sputter、Rugate Filter

漸變式折射複合光學設計
傳統光學濾光片使用高低折射率膜堆疊的設計，需要有初始設計才有辦法得到與目標光譜相近的結果，新光學濾光薄膜製鍍方式可採用混合薄膜（composite film）的技術，除具有能改善單一材料的物理及化學特性外，亦能使用折射率漸變光學濾光片。在多層膜光學濾光片設計中，如以正弦函數分佈的混合膜設計取代傳統高折射率及低折射率材料結構，此種類型的帶止濾光片一般稱為皺波濾光片（rugate filter）[1-3]，過去Southwell利用耦合波理論之型式，導出折射率變化若為一正弦函數如圖1，其數學公式如式（1）所示：

式中n_a為平均折射率，n_P為最高與最低折射率之差，Φ為膜層在基板上的相位。若此波型有S週期，每一週期之光學厚度為帶止濾光片之中心波長λ₀的二分之一，則可得帶止濾光片其半寬度為