The development of pellicles for 157 nm lithography includes not only the determination of appropriate materials, but also the minimization of pellicle-induced distortions contributing to overlay error. In particular, the attachment of the pellicle to the reticle surface can cause both out-of-plane and in-plane distortions (OPD and IPD) which contribute to pattern placement errors. This research focused on identifying the mechanical characteristics of thin-film pellicles, and the effect of bonding the pellicle frame to the reticle. Several different pellicle designs and films were analyzed and compared, using experimental, analytical, and finite element (FE) methods. The pellicle film stress was determined via two experimental procedures. The first, a resonant frequency test, identified the natural frequencies and mode shapes. The film stress values were subsequently determined from their relation to the frequencies. In the second procedure, static measurements of the displaced shape due to applied loads were taken using an MTI Fotonic Sensor. The film stresses from these independent measurements were between 200 and 300 kPa. The effect of the pellicle bonding was determined interferometrically by measuring the change in OPD of the reticle. The OPD values corresponded to IPD magnitudes of approximately 10 to 20 nm. These distortions were also simulated with FE models to replicate the mounting process. Using these methods, alternative mounting schemes, procedures, and materials can be developed, tested, and analyzed to reduce distortions in future designs.

Date Published: 22 January 2001
PDF: 10 pages
Proc. SPIE 4186, 20th Annual BACUS Symposium on Photomask Technology, (22 January 2001); doi: 10.1117/12.410695

Published in SPIE Proceedings Vol. 4186:
20th Annual BACUS Symposium on Photomask Technology
Brian J. Grenon; Giang T. Dao, Editor(s)