利用奈米球微影術製作抗反射結構之研究

Abstract

抗反射鍍膜(Antireflective coating)或抗反射結構(Antireflective structure)廣泛的用於相機的透鏡系統、顯示器的螢幕、光學元件或太陽能電池、有機發光二極體等光電元件。因為當光線入射上述元件時，其表面會發生反射。反射光線會造成透鏡中的耀光、顯示器螢幕的眩光、減少太陽能電池的光電轉換效率以及降低有機發光二極體的發光效率。傳統上解決反射的方式是在表面鍍上一層低折射率的介電質薄膜，利用薄膜上下界面的破壞性干涉來消除反射光線。但利用單層鍍膜來消除反射光線的方式，只能消除特定波長或是某一狹窄區間的波段的光線。而利用在表面製作奈米突起陣列的方式，可以消除較廣波段的反射。 在本研究中，建立了一套流程，利用奈米球微影術在石英玻璃表面上製作奈米突起陣列。首先使用200奈米以及600奈米大小的聚苯乙烯奈米球，利用自組裝技術在石英玻璃的表面製作單層奈米球陣列當作遮罩。隨後在CF4的電漿環境下對含有遮罩的石英玻璃進行活性離子蝕刻，可得奈米突起陣列。奈米突起的表面形貌藉由不同的蝕刻時間可控制為類斑點狀(spot-like)、截錐狀(truncated cone-shaped)及類拋物面狀(paraboloid-like)。在固定的CF4氣體流率及壓力下，週期為200奈米且具有類拋物面的奈米突起其深寬比可達1.35，週期為600奈米的類拋物面的奈米突起深寬比則為1.15。當突起的表面近似拋物面時，相較於其他形狀的突起有較好的抗反射效果。 此外，我們也利用模擬驗證當OLED基板表面具有類拋物面突起奈米陣列是否能增加OLED的發光功率。研究中利用FullWAVETM作為模擬的軟體，並使用有限時域差分法(Finite-difference time-domain)，模擬具有不同週期跟高度的類拋物面突起奈米陣列的發光效率。研究結果顯示當奈米陣列的週期為200奈米、高度為600奈米(深寬比=3)的時候，發光效率可增加14%。

When the light impinges the interface between two different media, some of light is reflected at interface. The reflection creates many problems, such as flare and glare, and may reduce the performance of electro-optical devices. Traditionally, a coating of dielectric thin film with low refractive index was used to reduce the reflection. But the coating can only suppress the reflection in a single or narrow-band wavelength. However, the reflection can be reduced in broadband, if the surface has nanoscale protuberance arrays. In this study, we developed a process to fabricate the protuberance arrays on quartz surface using nanosphere lithography and two different polystyrene (PS) sphere sizes, 600 nm and 200 nm. First, the polystyrene sphere arrays can be prepared on the quartz surface by a self-assembly technique. The protuberance arrays on quartz surface were then fabricated by CF4 reactive ion plasma etching under the masking of polystyrene sphere. Different profiles of protuberances such as spot-like, truncated-cone, and paraboloid-like shapes can be made and controlled by etching time. At fixed CF4 flow rate and pressure, the aspect ratio of paraboloid-like protuberance arrays of 200 nm in period is about 1.35 and 1.15 for 600 nm PS sphere arrays as a mask. In addition, the quartz surface with paraboloid-like profile arrays is found to show better transmittance than other structures. Simulations were also carried out to assess if the paraboloid-like profile arrays on the quartz surface have the potential to enhance the light power in OLED. The light power of OLED as a function of different period and height in the paraboloid nanostructure was calculated using FullWAVETM, a finite-difference time-domain (FDTD) simulator. When the period of protuberance is 200 nm and the aspect ratio of protuberance is 3, the light power of OLED substrate with paraboloid-like protuberance arrays shows 14% increase.