利用近場相位移微影術及干涉微影術製作二維光子晶體波導

Abstract

本論文將探討如何結合近場相位偏移微影及干涉微影兩種技術製作出二維週期性結構的光子晶體波導。 我們將具有特定圖案及厚度的光阻，以PDMS (聚二甲基矽氧烷) 材料翻製成軟性光罩，再將此成型之PDMS光罩貼附在塗佈光阻的基板上，同時以汞燈光源作近場相位偏移曝光製作二維光子晶體的缺陷波導，再將光阻之圖案轉移到鉻金屬層，利用此技術最小可製作出約100奈米的線寬。另外在已有鉻金屬線的基板上塗佈光阻，並利用波長351奈米的氬離子雷射以干涉微影技術，將基板旋轉90度作二次曝光，製作出二維週期性結構的光阻圖案。鍍上鉻金屬後用金屬剝離的方式把光阻圖案轉移到鉻金屬層。我們選擇絕緣層上覆矽(Silicon on insulator， SOI)為波導材料，以鉻金屬為乾蝕刻擋罩，SOI最上層的非晶矽蝕刻後即可得到二維光子晶體波導。 結合以上兩種技術，可快速製作出大面積的二維光子晶體波導，相較於電子束直寫法可節省成本、時間，並解決雷射直寫法及傳統微影術的線寬極限。

This thesis describes an approach to fabricate a 2-dimensioinal photonic crystal waveguide by combining near-field phase-shifting contact lithography and interference lithography. The elastomeric phase mask is fabricated by casting and curing the prepolymer of PDMS (Polydimethylsiloxane) against photolithographically patterned lines of photoresist on a silicon substrate. We then expose the UV light through the elastomeric phase mask onto the photoresist to perform photolithography in the near field of the mask for fabricating the 2-dimensional photonic crystal waveguides. These waveguiding patterns are transferred to the underlying chromium layer by chemical wet etching. Critical dimensions as small as 100 nm can be fabricated by this method[1]. Then photoresist is spun onto the substrate which contains the chromium lines and exposed to 351 nm wavelength of argon ion laser to perform the interference lithography. Square or triangular lattice of 2D photoresist patterns can be achieved by simply rotating the substrate to specific angle to perform multiple exposures. These photoresist patterns are transferred to the deposited chromium layer by liftoff process. Silicon on insulator (SOI) is chosen to be waveguiding material because its index contrast is high enough to support a guided Bloch mode in photonic crystal waveguides. The desired patterns were transferred to a-Si (the top layer of SOI) by dry etching. Combining the above two methods, 2-dimensional photonic crystal waveguide can be fabricated rapidly. When compared with the high cost and slow e-beam writing technique, the above two methods are economically and technically advantaged. It also overcomes the diffraction limit of conventional mask photolithography and line width limited issue of direct laser beam writing technique.