設計並製作高效率圓極化熱輻射發射器以及黃光微影製程二次曝光對準測試

Abstract

本論文旨在開發在中紅外波段具圓極化之熱輻射發射器，基於金屬/介電質/金屬(metal-insulator-metal, MIM)之三明治結構，藉由優化頂層金的幾何結構與旋轉角度來達到四階相位排列。首先，利用模擬軟體設計在不同的二氧化矽的厚度下，改變上層金屬結構分別為長方形與V字型的幾何形狀，去分析兩種結構的反射頻譜以及相位響應，找到了在200 nm二氧化矽厚度下，長方形與V字型的反射率達0.5、兩者相位差為93度的結構來組成具四階相位響應的圓極化熱輻射發射器設計。接著使用黃光製程來完成樣品的製作，並利用傅里葉轉換紅外光譜儀量測比對實驗與模擬結果是否吻合。根據廣義斯乃爾定律，出射光的角度取決於結構的空間相位梯度分布，因此我們進一步量測比較樣品在不同角度下的發射強度，判斷其發射是否符合理論設計。發現由於製程上的誤差，製作出的V字型樣品其斜邊長度會使得反射值增加到0.9，相位值提升至240，因此需提升製作樣品的精細度。我們接著開發黃光微影二次曝光的技術，測試的結構為光柵圖案，藉由不同的間距進行測試，測試的實際間距為100 nm到800 nm左右，針對光罩設計和基板進行改善，以及在對準時改進位移平台和旋鈕的問題，最後也進行了第二次曝光的秒數測試，實驗後發現間距最小可以達到800 nm左右，也讓光柵的解析度可以更好。未來也可以對不同的結構去進行二次對準的實驗，讓設計的結構可以複雜化，結構設計的限制也可以更小。The thesis aims to develop a mid-infrared circularly polarized thermal emitter based on the designs of a metal-insulator-metal (MIM) structure. We first optimize the geometry of the top-layered gold micro-structures and rotate them to achieve a four-level metasurface. First, the simulation software is utilized to design the top-layered gold structures including rectangular- and V-shaped structures and analyzed the reflection and phase responses of these structures under different oxide layer (SiO2) thicknesses. Then, we designed a four-level circularly-polarized thermal emitter using optimized rectangular- and V-shaped structures with reflection of 0.5 and a phase difference of 93o between then under an oxide thickness of 200 nm. Next, we fabricate samples using photolithography and measure spectra with Fourier-transform infrared spectroscopy. We compare the results with simulations. Based on generalized Snell's law, emission angles rely on the metasurface's phase distribution. We measure sample emission at different angles to check if it deflects as intended. However, deviations between fabricated samples and the designed structures exist, We observed that a shorter inclined side of the V-shaped structure we produced resulted in increased reflectance to 0.9 and a phase value of 240. Therefore, we require enhanced precision in sample fabrication. To address this, secondary exposure in photolithography are conducted using a grating pattern structure with varying gap sizes ranging from approximately 100 nm to 800 nm. We try to improve the designs of photomask and substrate conditions, along with the adjustment in the alignment platform and rotation knob during alignment. The results indicate that the minimum gap size can reach around 800 nm, leading to improved grating resolution.