Photomask pattern inspection using transmitted light and/or reflected light is commonly used for Die to Die or Die to Database comparison method. We have applied the differential interference contrast method to phase defect inspection for alternating phase shifting mask (Alt-PSM). The key parameters for optics are resident phase in an interferometer, shearing direction and distance between two spots, which are determined by Nomarski prism design. Firstly, we studied defect image contrast by simulation. Chrome edge defects are more detectable than isolated center defects from the simulation result. Next, we configured a reflective type, differential interference optics using an Ar ion laser as a light source. A test mask having 70-degree phase defects on 520, 600, and 720 nm CD are inspected. Edge defects down to 520nm CD were detectable compared with conventional reflective method.

Date Published: 5 September 2001
PDF: 12 pages
Proc. SPIE 4409, Photomask and Next-Generation Lithography Mask Technology VIII, (5 September 2001); doi: 10.1117/12.438389

Published in SPIE Proceedings Vol. 4409:
Photomask and Next-Generation Lithography Mask Technology VIII
Hiroichi Kawahira, Editor(s)