Fabrication of 2D Photonic Crystal Slab Waveguides using Near-Field Phase-Shifting Contact Lithography and Interference Lithography

• Main Authors: Cai-Xia Yan, 晏彩霞
• Other Authors: Lon A. Wang
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/19848773817601451034

碩士 === 國立臺灣大學 === 電機工程學研究所 === 95 === 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.