Multilevel interference lithography--fabricating sub-wavelength periodic nanostructures

Periodic nanostructures have many exciting applications, including high-energy spectroscopy, patterned magnetic media, photonic crystals, and templates for self-assembly. Interference lithography (IL) is an attractive method for fabricating such structures, as it offers several advantages including large exposure area and high spatial-phase coherence. However, the spatial resolution of IL is limited, and the smallest attainable period is roughly half the wavelength of the light used. To overcome this wavelength-limited resolution, we have developed a multilevel interference lithography process that is capable of fabricating sub-wavelength periodic nanostructures over large areas. In this process, multiple grating levels with different phase-offsets are overlaid and spatial-phase aligned to a common reference grating. Each grating level is pattern-transferred into a single hard mask layer, resulting in spatial-frequency multiplication. To ensure high grating overlay accuracy, each grating level is aligned to the reference grating with various interferometric techniques. In addition, an image-reversal process with plasma etch trimming was developed to control the linewidth of each grating level to nanometer-repeatability. Extensive optical simulations using rigorous coupled-wave analysis were used to examine the intensity distribution of exposures over multilayer periodic structures. The immediate goal of this work is to extend the wavelength-limited resolution of interference lithography with high precision metrology and well-controlled fabrication processes. Using this multilevel process, we have successfully fabricated 50 nm-period gratings using light with 351.1 nm wavelength. This process presents a general scheme for overlaying periodic nanostructures, and can be used to fabricate more complex 2D and 3D geometries.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Chang, Chih-Hao, 1980-

Advisor dc:contributor.advisor

• Mark L. Schattenburg.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/46481

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/46481