Significant effort has been directed in recent years towards the realization of immersion lithography at 193nm
wavelength. Immersion lithography is likely a key enabling technology for the production of critical layers for 45nm and
32nm design rule (DR) devices. In spite of the significant progress in immersion lithography technology, there remain
several key technology issues, with a critical issue of immersion lithography process induced defects. The benefits of the
optical resolution and depth of focus, made possible by immersion lithography, are well understood. Yet, these benefits
cannot come at the expense of increased defect counts and decreased production yield. Understanding the impact of the
immersion lithography process parameters on wafer defects formation and defect counts, together with the ability to
monitor, control and minimize the defect counts down to acceptable levels is imperative for successful introduction of
immersion lithography for production of advanced DR's. In this report, we present experimental results of immersion
lithography defectivity analysis focused on topcoat layer thickness parameters and resist bake temperatures. Wafers were
exposed on the 1150i-α-immersion scanner and 1200B Scanner (ASML), defect inspection was performed using a DUV
inspection tool (UVisionTM, Applied Materials). Higher sensitivity was demonstrated at DUV through detection of small
defects not detected at the visible wavelength, indicating on the potential high sensitivity benefits of DUV inspection for
this layer. The analysis indicates that certain types of defects are associated with different immersion process parameters.
This type of analysis at DUV wavelengths would enable the optimization of immersion lithography processes, thus
enabling the qualification of immersion processes for volume production.
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