[OPTICAL REVIEW Vol. 2, No. 3 (1995) 207-210]
A New Imaging Method with a Spatial Filter for Incoherent Stream*
Naomasa SHIRAISHI1 and Koichi MATSUMOTO2
11st Designing Department, IC & LCD Equipment Division, 22nd Optical Designing Department, NIKON Corporation, Nishi-Ohi, Shinagawa-ku, Tokyo, 140 Japan
(Accepted March 2, 1995)
A new imaging method using an incoherent-type pupil filter: SFINCS (Spatial Filter for INCoherent Stream) is presented. The new filter divides the imaging beam into several incoherent beams at the pupil plane thereby enlarging the depth-of-focus (DOF). The capabilities of SFINCS are studied by simulations and several ways to realize the method are also discussed. The experimental results show that SFINCS has excellent DOF expanding capabilities for a point-image such as a hole pattern in VLSI lithography, and that 1.7 μm DOF is obtained with a 0.30 μm hole pattern by an i-line projection lens with 0.57 NA (numerical aperture).
Key words : photolithography, resolution, depth-of-focus, pupil filter, incoherence