When things go pear shaped: contour variations of contacts

Clemens Utzny

doi:10.1117/12.2013911

10 April 2013 When things go pear shaped: contour variations of contacts

Clemens Utzny

Proceedings Volume 8681, Metrology, Inspection, and Process Control for Microlithography XXVII; 868109 (2013) https://doi.org/10.1117/12.2013911
Event: SPIE Advanced Lithography, 2013, San Jose, California, United States

Abstract

Traditional control of critical dimensions (CD) on photolithographic masks considers the CD average and a measure for the CD variation such as the CD range or the standard deviation. Also systematic CD deviations from the mean such as CD signatures are subject to the control. These measures are valid for mask quality verification as long as patterns across a mask exhibit only size variations and no shape variation. The issue of shape variations becomes especially important in the context of contact holes on EUV masks. For EUV masks the CD error budget is much smaller than for standard optical masks. This means that small deviations from the contact shape can impact EUV waver prints in the sense that contact shape deformations induce asymmetric bridging phenomena. In this paper we present a detailed study of contact shape variations based on regular product data. Two data sets are analyzed: 1) contacts of varying target size and 2) a regularly spaced field of contacts. Here, the methods of statistical shape analysis are used to analyze CD SEM generated contour data. We demonstrate that contacts on photolithographic masks do not only show size variations but exhibit also pronounced nontrivial shape variations. In our data sets we find pronounced shape variations which can be interpreted as asymmetrical shape squeezing and contact rounding. Thus we demonstrate the limitations of classic CD measures for describing the feature variations on masks. Furthermore we show how the methods of statistical shape analysis can be used for quantifying the contour variations thus paving the way to a new understanding of mask linearity and its specification.

Citation Download Citation

Clemens Utzny "When things go pear shaped: contour variations of contacts", Proc. SPIE 8681, Metrology, Inspection, and Process Control for Microlithography XXVII, 868109 (10 April 2013); https://doi.org/10.1117/12.2013911

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KEYWORDS

Critical dimension metrology

Shape analysis

Metrology

Extreme ultraviolet

Principal component analysis

Scanning electron microscopy

Statistical analysis

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