Demands on advanced exposure tools for ULSI applications have increased rapidly during the last few years. Overlay accuracy, one of the key subjects, has been under continuous development. In X-ray lithography the overlay is mainly determined by pattern displacement on X-ray masks, by process-induced wafer distortions and by stepper-related contributions, generated by a limited alignment accuracy and displacements during the pattern replication. It is the aim of this paper to characterize the stepper-related contributions to the overlay budget. For this purpose we investigated the overlay performance of vertical XRS-200 type X-ray steppers equipped with an advanced optical alignment system. Using a multiple exposure technique, a series of alignment experiments were performed on typical CMOS layers. The results show that the wafer chuck flatness has, beside the alignment accuracy, a major influence on the overlay accuracy.

Date Published: 9 July 1992
PDF: 10 pages
Proc. SPIE 1671, Electron-Beam, X-Ray, and Ion-Beam Submicrometer Lithographies for Manufacturing II, (9 July 1992); doi: 10.1117/12.136042

Published in SPIE Proceedings Vol. 1671:
Electron-Beam, X-Ray, and Ion-Beam Submicrometer Lithographies for Manufacturing II
Martin C. Peckerar, Editor(s)