As optical lithography approaches the 0.25 micrometers performance level, overlay performance approaches 75 nanometers (nm). This in turn requires alignment systems to work to tighter budgets. This paper presents the theory of operation behind the AXIOM off-axis alignment system. We have examined the advantages of using the AXIOM system, and have implemented a trade-off strategy. Our discussion includes an overview of the AXIOM alignment sensor head (sensor head) system. We also provide the benefits of the sensor's broadband incoherent light source illumination when used to achieve process insensitivity. In addition, we provide the benefit of being a bright and dark field system. We performed modeling to evaluate how various alignment targets interact with illumination. Modeling assessments highlighted the advantages of separately detecting the left and right diffracted order of a target. The sensor head can examine a target by using both bright field, left and right orders simultaneously. Examining a target helps us obtain more information and further reduces process sensitivity. Finally, we verified performance with multilevel data and compared it to industry standards.

Date Published: 7 June 1996
PDF: 14 pages
Proc. SPIE 2726, Optical Microlithography IX, (7 June 1996); doi: 10.1117/12.240980

Published in SPIE Proceedings Vol. 2726:
Optical Microlithography IX
Gene E. Fuller, Editor(s)