Dynamic nanometer alignment for nanofabrication and metrology

Future generations of IC fabrication depend in part on continued improvements in lithography. To meet the lithographic challenges posed by 25- nm lithography, a novel through-the-mask, interferometric imaging alignment method is described that has demonstrated detectivity below 1 nm. Approximately x-ray alignment and exposure system was constructed which incorporates this "Interferometric Broadband Imaging" (IBBI) alignment scheme. 18BI employs complementary grating and checkerboard-type alignment marks on mask and wafer, respectively. Interference fringes are imaged onto a CCD camera when viewing the marks at a Littrow angle of 15 degrees. Alignment is signified by the spatial phase discontinuities between two identical sets of interference fringes that move in opposite directions as the mask is translated relative to the wafer. The robustness of IBBI was verified by demonstrating that the relative spatial phase is not affected when overlayers of resist, polysilicon, or aluminum cover the alignment marks. Further verification of robustness was found when the illuminating and viewing beams traversed long optical paths through air, glass, and helium. It is significant that JBBJ measurements are made external to a helium enclosure through the above optical paths, since this allows continuous observation of alignment during exposure. Feedback stabilization was developed to nullify the effects of thermal drift and mechanical disturbances during exposure. Over several hours the relative position of the mask and wafer was demonstrated to be locked to within [sigma]=1.4 nm.

Department dc:contributor.department

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

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

1998

Author dc:creator

• Moon, Euclid E. (Euclid Eberle), 1965-

Advisor dc:contributor.advisor

• Henry I. Smith.

• 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/1721.1/41799

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/41799