Beam alignment and image metrology for scanning beam interference lithography : fabricating gratings with nanometer phase accuracy

We are developing a scanning beam interference lithography (SBIL) system. SBIL is capable of producing large-area linear diffraction gratings that are phase-accurate to the nanometer level. Such gratings may enable new paradigms in fields such as semiconductor pattern placement metrology and grating-based displacement measuring interferometry. With our prototype tool nicknamed "Nanoruler", I have successfully patterned, for the first time, a 400 nm period grating over a 300 mm-diam. wafer, the largest that the tool can currently accommodate. By interfering two small diameter Gaussian laser beams to produce a low-distortion grating image, SBIL produces large gratings by step-and-scanning the photoresist-covered substrate underneath the image. To implement SBIL, two main questions need to be answered: First, how does one lock the interference image to a fast-moving substrate with nanometer accuracy? Secondly, how does one produce an interference image with minimum phase nonlinearities while setting and holding its period to the part-per-million (ppm) level? My thesis work solves the latter problem, which can be further categorized into two parts: period control and wavefront metrology. Period control concerns SBIL's ability to set, stabilize and measure the image grating period. Our goal is to achieve control at the ppm level in order to reduce any related phase nonlinearity in the exposed grating to subnanometers. A grating beamsplitter is used to stabilize the period. I demonstrate experimental results where the period stabilization is at the 1 ppm level. An automated beam alignment system is built. The system can overlap the beam centroids to around 10 [mu]m and equalize the mean beam angles to better than 2 [mu]rad (0.4 arcsec), which translates into a period adjustability of 4 ppm at 400 nm.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Chen, Carl Gang, 1972-

Advisor dc:contributor.advisor

• Mark L. Schattenburg.

• Electrical Engineering and Computer Science.

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/1721.1/16950

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/16950