CD uniformity improvement of dense contact array in negative tone development process
2015
Layout pattern density impacts mask critical dimension uniformity (MCDU) as well as wafer critical dimension
uniformity (WCDU) performances in some aspects. In patterning the dense contact array with negative tone
development (NTD) process, the abrupt pattern density change around the array edge of a NTD clear tone reticle arises
as a very challenging issue for achieving satisfactory WCDU. Around the array boundary, apart from the MCDU greatly
impacted by the abrupt pattern density change, WCDU in lithographic process is also significantly influenced by the
optical flare and chemical flare effects.
This study investigates the pattern density effect induced MCDU and WCDU variations. Various pattern densities are
generated by the combination of fixed array pattern and various sub-resolution assist feature (SRAF) extension regions
for quantifying the separated WCD variation budget contributed by MCD variation, chemical flare effect and optical
flare effect. With the proper pattern density modulation outside the array pattern on a clear tone reticle, MCD variation
across array can be eliminated, optical flare and chemical flare effects induced WCD variation is also greatly suppressed.
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