I-line lithography offers the capability to achieve half-micron integrated circuit design rules. Such design rules require very good optical performance matched to resist process technology. Overlay performance at these design rules is also critical wit capability needed in the 100-150 nm region. Resolution and usable depth of focus (UDoF) need to be evaluated concurrently and are influenced by the lens design (wavelength, NA, focal plane deviation) as well as the resist processing technology. A simple model is presented to describe these inter-relationships. Experimental comparison of UDoF performance from 0.7 μm to 0.5 μm resolution is presented for several resist processes showing UDoF performance of greater than one micron for half-micron features. Half-micron capability on IC film stacks and topography with good UDoF is also demonstrated. The PAS 2500 alignment and positioning systems are compatible with the overlay requirements for half-micron design rules. Improved performance of the key subsystems is reported; notably the reproducibility of the phase grating alignment system and the positioning accuracy of the three axis XY stage system. The resulting improved single machine overlay from 37 steppers is 120 nm 3 σ. Improved machine to machine matching will be reported based upon the reduced single machine overlay, smaller lens distortions and an improved matching procedure. The distortion data of 19 Zeiss 58 lenses will be reported in terms of the difference between all possible pairs of lenses. Multiple machine overlay data will be given and the improvements from lens selection demonstrated.

Date Published: 25 July 1989
PDF: 16 pages
Proc. SPIE 1088, Optical/Laser Microlithography II, (25 July 1989); doi: 10.1117/12.953147

Published in SPIE Proceedings Vol. 1088:
Optical/Laser Microlithography II
Burn Jeng Lin, Editor(s)