Shen-Qi Xie

Duplication of nanoimprint templates by a novel SU-8/SiO2/PMMA trilayer technique

In this work, a trilayer technique used in the nanoimprint lithography process to replicate the templates is developed. The SU8/SiO2/PMMA trilayer was used. The photosensitive epoxy (SU8 resist) which has a low glass transition temperature was used as the imprint layer. Polymethylmethacrylate (PMMA) was used as the transfer layer. A SiO2 layer is placed between the SU8 and PMMA to act as a protective layer due to its strong resistance to oxygen reactive ion etching. By optimizing imprint and etching processes, master templates with minimum feature size of 150 nm and period of 300 nm can be successfully duplicated.

APPLICATIONS OF NANOIMPRINT LITHOGRAPHY FOR BIOCHEMICAL AND NANOPHOTONIC STRUCTURES USING SU-8

Nanoimprint lithography (NIL) technology has aroused great interests in both academia and industry due to its high resolution, low-cost, and high-volume nanopatterning capability. And as an expoxy resin-based negative amplified photoresist, SU-8 is an ideal candidate for NIL because of its low-glass-transition temperature, low-volume shrinkage coefficient, and good optical properties. In this reviewing paper, we highlight the major technical achievements in NIL on epoxy resin and its applications for bio- and nanophotonic structures. NIL was also applied for the duplication of imprint templates, originally fabricated by e-beam lithography (EBL) followed by reactive ion etch (RIE), using a SU-8/SiO2/PMMA tri-layer technique. And nanoimprint properties were systematically investigated for optimization. The developed nanoimprint process for different applications indicates promising industrial potentials in the next generation lithography resolution.

Design and fabrication of Bragg reflectors based on SU-8

We report the design and fabrication of two kinds of distributed Bragg reflectors (DBRs). One is a Bragg filter which introduces a periodic height modulation in part of a waveguide, and the other is a horizontal DBR with a deeply patterned grating structure in a waveguide at a freespace wavelength of 1.55 um (the propagation loss of quartz fiber used in optical communication is lowest around 1.55 um wavelength) based on a Si/SiO2/SU8/air structure. The transfer matrix theory was used to calculate the spectral response of the Bragg filter and its dependence on the height modulation and the grating length. In addition, a multilayer film reflection theory was applied to simulate reflection spectrum of the DBR and estimate the least number of pairs of DBR mirrors needed for almost 100% (¿ 99.6%) reflection. Based on the simulation results, we designed and successfully fabricated these two types of DBRs with Si/SiO2/SU8/air structures.

Development of novel SU-8 based nanoimprint lithography

We present two kinds of novel nanoimprint lithography techniques based on SU-8 photoresist with single layer and tri-layer approaches. The imprint templates with high aspect ratio were first fabricated by electron beam lithography (EBL) and reactive ion etch (RIE), and then duplicated by the SU-8/SiO2/PMMA tri-layer technique we developed. Imprint properties such as pressure and temperature are determined to fabricate different nanostructures with various imprint depth. The developed processes, which provide us the capability to fabricate both imprinted nanostructures on resist and transferred nanopatterns on substrate with high volume and low cost, are further applied in producing high density gratings, planar chiral photonic metamaterials, and nanofluidics channels.