In this paper, we present methods of eliminating an overlay scaling error which is introduced when multi-layer resist (MLR) structures are imaged with a narrow bandwidth light source. Using the conventional box-in-box type mark, an intense interference fringe is produced around the box type mark and results in a scaling error on overlay reading. An optical interference effect combined with resist build-up of bottom PR is the origin of the scale error. Two methods have been tried to find a solution without changing the process. To remove the interference effects, a broad bandwidth light source was adopted so that clean and uniform images are obtained. On the other hand, to eliminate the resist build-up, narrow bar marks corresponding to the large box pattern have been generated to reduce the effect with the narrow bandwidth light source. Using the above methods we could realize accurate overlay measurement on MLR structures. The changes have been applied to a real DRAM process.

Date Published: 21 May 1996
PDF: 10 pages
Proc. SPIE 2725, Metrology, Inspection, and Process Control for Microlithography X, (21 May 1996);

Published in SPIE Proceedings Vol. 2725:
Metrology, Inspection, and Process Control for Microlithography X
Susan K. Jones, Editor(s)