The AIMS^TM-45, when used in scanner mode, can emulate image intensity as seen in resist on the wafer at scanner illumination conditions. We show that this feature makes AIMS^TM-45 well-suited to analyze patterns treated with inverse lithography. We have used an inverse lithography technique by Mentor Graphics, to treat a random contact hole layout (drawn at minimal pitch 115nm) for imaging at NA 1.35. The combination of the dense 115nm pitch and available NA of 1.35 makes Quasar illumination necessary, and the inverse lithography treatment automatically generated optimal (model-based) Assist Features (AF) for all geometries in the design. The mask, after inverse lithography treatment, has CH patterns with numerous AF of different sizes and orientations, and is a challenge for both mask making and mask qualification. We have analyzed the inverse lithography masks with the model-based AF using an AIMS^TM-45 aerial image measurement tool, and compare the results of the AIMS^TM-45 to wafer data obtained after exposure on an ASML XT:1900i. A first benefit of AIM^TM-45 is that the most meaningful quantity (image in resist) is generated without the intermediate steps of doing multiple reticle SEM measurements followed by extensive simulation. A second point of interest is that the AIMS^TM-45 generates image intensities, which allows a direct validation of the intensity-driven inverse litho conversion. Both features prove the value of the AIMS^TM-45 for analyzing inverse litho masks and geometries.

Date Published: 17 October 2008
PDF: 11 pages
Proc. SPIE 7122, Photomask Technology 2008, 71221E (17 October 2008); doi: 10.1117/12.801559

Published in SPIE Proceedings Vol. 7122:
Photomask Technology 2008
Hiroichi Kawahira; Larry S. Zurbrick, Editor(s)