Immersion defectivity study with volume production immersion lithography tool for 45 nm node and below
2008
Volume production of 45nm node devices utilizing Nikon's S610C immersion lithography tool has started. Important to
the success in achieving high-yields in volume production with immersion lithography has been defectivity reduction. In
this study we evaluate several methods of defectivity reduction. The tools used in our defectivity analysis included a
dedicated immersion cluster tools consisting of a Nikon S610C, a volume production immersion exposure tool with NA
of 1.3, and a resist coater-developer LITHIUS i+ from TEL. In our initial procedure we evaluated defectivity behavior
by comparing on a topcoat-less resist process to a conventional topcoat process. Because of its simplicity the topcoatless
resist shows lower defect levels than the topcoat process. In a second study we evaluated the defect reduction by
introducing the TEL bevel rinse and pre-immersion bevel cleaning techniques. This technique was shown to
successfully reduce the defect levels by reducing the particles at the wafer bevel region. For the third defect reduction
method, two types of tool cleaning processes are shown. Finally, we discuss the overall defectivity behavior at the 45nm
node. To facilitate an understanding of the root cause of the defects, defect source analysis (DSA) was applied to
separate the defects into three classes according to the source of defects. DSA analysis revealed that more than 99% of
defects relate to material and process, and less than 1% of the defects relate to the exposure tool. Material and process
optimization by collaborative work between exposure tool vendors, track vendors and material vendors is a key for
success of 45nm node device manufacturing.
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