Liquid immersion lithography tools with NA=1.3 are being applied for hp4x node device and beyond. As the typical DOF has been reduced to 100 nm or less for this hyper-NA exposure, precise consideration of the error factors that lead to DOF reduction is required. The BFD (Best Focus Difference between pattern kinds) induced by resist stack is one of the error factors yet to be solved. In this work, the BFD induced by resist stack was studied through simulation and experiment by decomposing it into the following three components: One induced by the "refraction" effect, one induced by the "reflection" effect and one induced by the "process" effect. Each BFD was evaluated by simulation to make a BFD budget. Experimental verification was also performed, which confirmed BFD of 25 nm and it was found that over 30 % of the observed BFD was induced owing to resist stack. Based on this result, we discuss a method for controlling the BFD by utilizing projection lens aberration and review the design flow of resist stacks with antireflection coatings.

Date Published: 16 March 2009
PDF: 10 pages
Proc. SPIE 7274, Optical Microlithography XXII, 72741H (16 March 2009); doi: 10.1117/12.813367

Published in SPIE Proceedings Vol. 7274:
Optical Microlithography XXII
Harry J. Levinson; Mircea V. Dusa, Editor(s)