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Scatterometry Control for Multiple Electron Beam Lithography

Authored by: Yoann Blancquaert a, Nivea Figueiro b, Thibault Labbaye a, Francisco Sanchez b, Stephane Heraud b, Roy Koret c, Matthew Sendelbach d, Ralf Michel b, Shay Wolfling c, Stephane Rey a, Laurent Pain a | SPIE 2017, February 1, 2017

ABSTRACT
The evaluation of scatterometry for monitoring intended variations in innovative scatterometry targets that mimic nonuniformities
potentially caused by multibeam Maskless Lithography (MEB-ML2) is presented. Specialized scatterometry
targets consisting of lines and spaces were produced that have portions exposed using the nominal, or POR (Process of
Record), dose, and portions exposed with a slightly different dose. These exposure plans created targets with different
line CDs (critical dimensions). Multiple target designs were implement, each with a different combination of magnitude
of CD shift and size of the region containing lines with a shifted CD. The scatterometry, or OCD (Optical Critical
Dimension), spectra show clear shifts caused by the regions with shifted CD, and trends of the scatterometry results match
well with trends of the estimated CD as well as the trends produced by measurements using a critical dimension scanning
electron microscope (CD-SEM) system. Finally, the OCD results are correlated to the CD-SEM measurements. Taking
into account resist morphology variations across the wafer, correlations between OCD and CD-SEM of the weighted
average CD across the various targets are shown to be very good. Correlations are done using the rigorous TMU analysis
methodology. Due to the different targeted CD values within each scatterometry structure, a new methodology for
estimating the error of the CD-SEM measurements for nominally non-uniform targets is presented.
Keywords: scatterometry, alternative lithography, e-beam lithography, multibeam, multiple e-beam, dose variation,
TMU, TMU analysis