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5 September 2001 Contact holes: optical area measurement predicts printability and is highly repeatable
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Proceedings Volume 4409, Photomask and Next-Generation Lithography Mask Technology VIII; (2001)
Event: Photomask and Next Generation Lithography Mask Technology VIII, 2001, Kanagawa, Japan
Small contact holes are the most difficult structures for microlithography to print because their sizes match the resolution of the stepper. Thus a mask hole that is a little too small won't print at all. It is widely accepted that the size of the contact hole on the wafer is controlled by the total light flux that gets through the contact hole on the mask. This is demonstrated by the fact that normal small contact holes print round on the wafer, no matter what shape they were on the mask. Therefore it is the area, not the shape that affects the wafer print. Contact holes have traditionally been measured in height and width. Recently, technology has been introduced to estimate corner rounding, so that a combination of height, width, and corner rounding could be used to estimate the area of the contact. Th introduction of the flux-area technique allows direct measurement of the optical area of features as small as (lambda) /4, e.g. 0.15(mu) using visible light. These measurements have been shown to be linear, repeatable, and highly correlated to what prints on the wafer. This study examines the accuracy and repeatability of optical contact hole area measurements using visible light and I-line illumination with the AVI Metrology system. A test mask is designed and printed by Photronics. It is measured with the AVI Photomask Metrology system taking images from a KLA353uv inspection system and a Zeiss AIMS tool, and a SEM. The mask is then printed at LSI Logic on a 0.25micrometers process. The contact sizes on the wafer are measured on a SEM. Results show that optical measurements from the AVI system correlate to the printed contact size as well as SEM measurements of the mask, and twice as well as conventional optical measurements. Furthermore, optical mask measurements at the mask shop and the fab correlate within 20nm despite the use of different wavelengths, and measurement with and without pellicles.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Glen W. Scheid, Darren Taylor, and Peter Fiekowsky "Contact holes: optical area measurement predicts printability and is highly repeatable", Proc. SPIE 4409, Photomask and Next-Generation Lithography Mask Technology VIII, (5 September 2001);


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