MECHANISTIC STUDIES OF PLASMA-SURFACE INTERACTIONS DURING NANOSCALE PATTERNING OF ADVANCED ELECTRONIC MATERIALS USING PLASMA
Oehrlein, Gottlieb S
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Photolithographic patterning of photoresist materials and transfer of these images into electronic materials using directional plasma etching techniques plays a critical role in the fabrication of integrated circuits. As critical device dimensions are reduced below 100 nm, precise control of the interactions of process plasmas with materials is required for successful integration. This requires a scientific understanding of plasma-surface interaction mechanisms that control the properties of the ultimate devices and ICs produced. Fluorocarbon discharges are commonly used for dielectric etching, e.g. SiO2. In this work we have studied surface-chemical aspects of the interaction of C4F8/Ar discharges with SiO2 and Si. Free fluorine atoms that are liberated from fluorocarbon species during ion bombardment are driven to the surface and react with the substrate, a process called defluorination. The defluorination is dependent on the plasma properties and the penetration of reactive species is limited within 10nm below the surface. Future device requires novel materials, i.e. nanoporous silica, to replace conventional SiO2.When some O atoms in Si-O matrix are replaced with nano cavities (pores), the plasma-induced modifications are extended to the deep subsurface region and the modification scale can be a few hundred nanometers. This modification is correlated with overall porosity and also strongly depends on plasma properties. O2 N2 and H2 discharges likely induce carbon depletion and material densification on nanoporous silica. Novel approach, i.e. shutter approach, is employed to study the issues of plasma processing of advanced photoresist materials at nanometer dimension. Hydrogen depletion, material densification and graphitization of these polymers are important processes during short exposure time with the plasma. High roughening rates are also observed within this time range. Subsequently, dedensification, i.e. surface roughening, dominates in the plasma-photoresist interactions. Depending on the molecular structures, the roughness scale can be well beyond the molecular size and RMS roughness does not saturate even after a long exposure time. For the etching of features, rough edges induced by initial plasma exposure on the top of the lines in the features form local masks and striations are formed on the sidewalls during long exposure times, which could lead failures of the devices.