| 摘要: | 本論文的主要內容為氮化矽波導組成微環形共振腔的模擬分析、製程與量測結果。其中模擬分析是針對設計不同錐度的傳輸波導(bus waveguide)從而增加耦合效應(coupling effect)；在製程上本論文是以傳統的紫外光光刻技術加上正光阻反轉進行曝光、顯影，進而做出微環形共振腔；最後在量測上會量測氮化矽微環形共振腔之共振現象。
第一部分在模擬上會以時域有限差分(Finite-Difference Time-Domain, FDTD)的方法分析，首先會先分析傳輸波導中單面錐度(single-side taper)與雙面錐度(double-side taper)，不同錐度寬度(taper width)下其橫向電場模態(transverse electric mode, TE)分佈，並且在不同錐度長度(taper length)，固定錐度寬度，探討波導傳播損耗，最後在不同的錐度寬度、間隙(gap)、環形波導半徑(ring-waveguide radius)的情況下，分析其耦合效應。
第二部分在製程上由於傳統紫外光光刻技術最大的問題是曝光解析度的問題，所以會以接觸式曝光的情況下，改變曝光時間，觀察光罩上波導寬度、間隙與顯影後的波導寬度、間隙差異；我們特別在光罩上設計正光阻區、負光阻區，並選擇AZ5214光阻液當作製程光阻，由於AZ5214光阻液本身為正光阻，加上通過反轉曝光的方法能達到負光阻的效果，所以能在光罩的正光阻區與負光阻區完成曝光，最後分析兩者的差別。
第三部分在量測上會量測氮化矽微環形共振腔的共振現象，並且分析其自由光譜範圍(free spectral range)，最後擬合模擬求出本質品質因數(intrinsic quality-factor)。
最後部分會探討其未來發展，在紫外光光刻上，此章節會利用雙重圖形(double patterning)避免干涉現象，在製程上做出共振腔具有亞微米解析度的耦合間隙。
;This thesis discusses the simulation analysis, waveguide fabrication, and measurement of silicon nitride micro-resonators. The simulation analysis is aimed at designing different tapered-bus waveguides to increase the coupling effect; for fabrication, this thesis addresses the conventional ultraviolet lithography technology with reverse baking of a positive photoresist for exposure and development. Finally, the cavity resonance of the silicon nitride micro-resonator will be measured and discussed.
First, we simulate waveguide propagation by the method of Finite-Difference Time-Domain. First, the fundamental transverse electric waveguide mode of the single-side-tapered and double-side-tapered bus waveguide will be analyzed under different taper widths and taper lengths. We will both analyze the waveguide propagation loss, and the coupling between waveguide and resonators under different taper widths, gaps, and resonator radius.
Second, we study the micro-resonator fabrication with conventional ultraviolet (UV) lithography, which typically has the exposure resolution limited by 1 μm. With contact exposure, the exposure time will be discussed and the fabrication optimization for waveguide width and gap will be given. In this thesis, we design both a positive photoresist region and a negative photoresist region on the mask. A positive photoresist- AZ5214 is selected to pattern the waveguide when it can also be served as a negative photoresist by the method of reverse baking. We will discuss the patterned waveguides on both regimes.
In the third part, the cavity resonance of the fabricated silicon nitride micro- resonator will be evaluated in the wavelength-dependent transmission measurement; and the corresponding free spectral range will be analyzed. We will also show the measured intrinsic quality-factor for the resonators.
Last, to overcome the lithography limitation of UV patterning and enhance the coupling between waveguide and resonators, double patterning will be introduced to avoid the optical interference during lithography. The fabricated resonator shows submicron resolution for the coupling gap. |
