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Volume device manufacturing using immersion lithography is widely accepted as the solution for patterning IC features
below 40 nm half pitch. In order to ensure high yield and steady productivity tight control of defectivity is essential. A
major source of defects and tool contamination is the particles introduced by incoming wafers. Particles can be
categorized in two groups: particles attached to wafer surface or residues on the wafer edge. Surface or edge peeling of
topcoats can also be a source of particle. Adhesion force between topcoat or topcoat-less (TC-less) resist and wafer is
one of the most important parameter for particle reduction. Peeling test results proved that TC-less resist has better
adhesion performance than topcoat. One of the most commonly used adhesion promoting material is
hexamethyldisilazane (HMDS). Application condition of this material is an important factor in preventing wafer edge
and surface topcoat peeling. Studies have shown lower temperature and longer application of HMDS shows better
adhesion result. Maintaining a clean wafer surface is also a very important factor for particle reduction. Pre-rinse, which
can rinse off particles before exposure, was evaluated and the efficiency was confirmed. Edge particles are more
effectively reduced by pre-rinse, because weakly attached topcoat and wafer edge residues were effectively removed by
pre-rinse. For further particle reduction, edge residue reduction and cut line roughness improvement were evaluated and
their effectiveness was confirmed. Lower cut position achieved improved particle counts on both topcoat and TC-less
resist; more frequent contact between water and cut-line can weaken the adhesion and consequently peel off topcoat or
TC-less resist. Finally the relationship between defectivity and hydrophobicity is analyzed, high Receding Contact Angle
(RCA) showed better defectivity result. Topcoat and TC-less process is compared for each defectivity reduction
methodology and for each category TC-less process always showed lower defectivity level and less sensitivity to process
conditions, indicating that TC-less process is safer and more robust than topcoat process.
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