New optical metrology for masks: range and accuracy rivals SEM

Rand Cottle; Peter Fiekowsky; C. C. Hung; Sheng-che Lin

doi:10.1117/12.438380

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5 September 2001 New optical metrology for masks: range and accuracy rivals SEM

Rand Cottle, Peter Fiekowsky, C. C. Hung, Sheng-che Lin

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Proceedings Volume 4409, Photomask and Next-Generation Lithography Mask Technology VIII; (2001) https://doi.org/10.1117/12.438380
Event: Photomask and Next Generation Lithography Mask Technology VIII, 2001, Kanagawa, Japan

Abstract

Metrology is essential to success in all manufacturing processes. In microlithography metrology techniques have begun to shift from optical to SEM. In this paper we compare the capabilities of the new Flux-Area optical technique and of SEM techniques. SEM measurement has been increasing in mask shops because of the higher resolution it provides, despite disadvantages including damage to masks, charging effects, and inability to operate with pellicles. Optical measurements of photomasks are preferred because they are performed with light, in transmission. The success of virtual stepper software, which uses optical images in simulating stepper output, has demonstrated that optical images contain sufficient information to predict the results of even subwavelength lithography. Flux-Area measurement allows optical instruments to accurately measure features as small as (lambda) /6, or 0.08 (mu) using visible light (Fiekowsky and Selassie, 1999). It also allows the measurement of Optical Dimensions. This is the width of a line defined by the flux of light it transmits to the objective lens. In this study Flux-Area measurements of linewidths and contact are compared to SEM measurements and DUV AIMS microscope images. Results show that Flux-Area measurements are linear down to the smallest lines and holes tested, 0.23 (mu) and 0.4(mu) respectively. Thus the Flux-Area technique provides a practical alternative to SEM for metrology on current and future generation photomasks.

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Rand Cottle, Peter Fiekowsky, C. C. Hung, and Sheng-che Lin "New optical metrology for masks: range and accuracy rivals SEM", Proc. SPIE 4409, Photomask and Next-Generation Lithography Mask Technology VIII, (5 September 2001); https://doi.org/10.1117/12.438380

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