Mask-aligner Talbot lithography using a 193 nm CW light source

We present and discuss Talbot mask-aligner lithography, relying on a continuous wave laser emitting at 193nm for the illumination. In this source, a diode laser at 772nm is amplified by a tapered amplifier in master-oscillator power-amplifier configuration and frequency-quadrupled in two subsequent enhancement cavities using lithium triborate and potassium fluoro-beryllo-borate nonlinear crystals to generate the emission at 193 nm. The high coherence and brilliance of such an illumination source is predestined for plane wave mask-aligner illumination, crucial in particular for high-resolution lithographic techniques such as Talbot lithography and phase-shift masks. Talbot lithography takes advantage of the diffraction effect to image periodic mask features via self-replication in multiples of the Talbot distance behind the photomask when exposed by a plane wave. By placing a photoresistcoated wafer in one of the Talbot planes, the mask pattern is replicated in the resist. Periodic patterns with diverse shapes are required for wire grid polarizers, diffraction gratings, and hole arrays in photonic applications as well as for filters and membranes. Using an amplitude mask with periodic structures, we demonstrate here with such a technique sub-micron feature sizes for various designs at a proximity gap of 20 µm.

Limitations of Proximity Lithography Printing

Krishnaparvathy Puthankovilakam

Photolithography is one of the earliest technologies used to transfer patterns to a substrate. It is also known as optical lithography since it uses light to transfer the pattern. The main exposure techniques exist in the industry are projection printing, contact printing, and proximity printing. Projection printing technology uses optical elements between mask and wafer to project the feature on the mask to the wafer. This is very expensive and delivers the highest resolution. In contact printing, the mask and wafer are in contact with each other and in proximity printing, the mask is kept at some proximity distance away from the wafer. Proximity printing is an easy and cost effective printing technique because the damage to the mask will be less and also no optical elements between mask and wafer are used. The main drawback of the proximity printing is the diffraction effect caused by the proximity gap between mask and wafer, which limits the resolution. The main objective of this thesis is to study the limitations of proximity printing and to increase its resolution. To study the limitations, different types of design strategies and verification methods are used in the thesis. First is the simulation technique which is performed with GenISys Layout LAB. This is specially designed for proximity printing. The software gives the aerial image and final resist pattern as output. The most interesting and important aspect is the second verification technique which is the experimental setup. A measurement setup has been built to study the light propagation from different masks and to study the aerial image at different proximity gaps. The setup is known as High Resolution Interference Microscopy (HRIM). The setup is basically a Mach- Zehnder interferometer having different light sources, sample plane and reference arm which are used according to the samples. The final verification is achieved using the mask aligner. Both the simulation and experiments are carried out using a special illumination optics called MO exposure optics from Süss MicroOptics. The thesis mainly focuses on the rule based optical proximity correction a technique which is a simple method for mass production. Correction structures are designed for one dimensional and two dimensional features in amplitude masks. Adding lines near the edge to improve the edge slope will be discussed as the one dimensional correction. The different intensity cutting planes and the comparison between simulation and experimental results will be discussed along with that. A unified correction structure is designed to solve corner rounding problem and will be studied as the two dimensional study. The structure is defined to print different line widths at single proximity gap on single exposure. Usually, all the structures in the amplitude mask are studied with their aerial image intensities at different proximity gaps. But, here the study extends to phase evaluation also. The measurement technique can measure both intensity and phase evolution from the mask structures. Phase evolution from amplitude correction features will be discussed and how the phase modulates the intensity patterns is also studied. The role of fundamental principles like phase singularities, phase shifts are also discussed to find its effects on proximity printing structures. The study also leads to the intensity and phase propagation from phase shifting mask (PSM) . The structure evaluated is a group of corners in PSM.

EPFL2017

Fabrication of planar chiral photonic meta-materials on SU- 8 using nanoimprint lithography technique

Yi-Chiang Sun, Shenqi Xie

We present a photonic meta-material with planar dielectric chiral structures on SU-8 realized using nanoimprint lithography (NIL). A Si template with chiral structure arrays was first fabricated by electron beam lithography (EBL) followed by reactive ion etch (RIE). The chiral pattern on the template was then transferred to a SU-8 layer spin coated on Pyrex using an in-house developed press. The imprint property of SU-8 under various pressures and temperatures was systematically studied. The optimized imprint process was successfully applied for the fabrication of planar chiral structure in SU-8. The periodically distributed chiral elements form a photonic crystal with the pitch of 4 μm. Optical diffraction of such kind of periodically arranged chiral structures in SU-8 has been observed for the first time.

2007

Nanophotonic crystals with chiral elements by a hot embossing process in SU-8

Yi-Chiang Sun, Shenqi Xie

We report a novel nanoprocess to fabricate 2D metallic and non-metallic nanophotonic crystals on SU-8 using hot embossing combining with a UV-curing process. The fabricated photonic crystals were characterized by optical diffraction experiments. Theoretical simulation of the light diffraction through such kind of artificial crystals agrees with the measured optical property very well, indicating that the developed fabrication technique is able to produce large area nanosize photonic crystals at economic costs. The success of this work not only provides scientists with a good opportunity to pioneer novel photonic physics in metallic and non-metallic chiral as well as photonic crystal systems, but also bridges the gap between laboratory and industrial application for mass production of photonic nanostuctures.

2008

Limitations of Proximity Lithography Printing

Krishnaparvathy Puthankovilakam

EPFL2017