Metallic masking materials are promising candidates for plasma-based pattern transfer into low-k materials for fabricating integrated circuits. Improving etching selectivity (ES) between the low-k and hardmask material requires a fundamental understanding of material erosion in fluorocarbon (FC) plasmas. The authors have previously reported on the erosion mechanism and plasma parametric dependencies of Ti etch in FC discharges. The present work focuses on elucidating differences in the erosion behavior between Ti and TiN hardmasks. The authors studied erosion of Ti, TiN, and organosilicate glass (OSG), a reference low-k material, in CF4/Ar and C4F8/Ar plasmas. Changes in surface composition, FC surface reaction layer thicknesses, erosion rates, and corresponding ES were established by x-ray photoelectron spectroscopy and in situ ellipsometry. The authors found that the erosion stages and plasma parameter dependent surface compositions were similar for Ti and TiN. The previously established dependence of Ti erosion rates on FC layer thickness and energy deposition on the hardmask surface by ions generally holds for TiN as well. However, TiN etch rates (volumetric removal rates) and etch yields (atomic removal rates) were increased by a factor of 1–1.4 compared to Ti. This difference can be explained by the rapid removal of N from the TiN surface, increasing the Ti atom number density at the surface above values of the Ti hardmask. The resulting increase in surface reactivity is in good agreement with the enhanced erosion rates compared to Ti. Differences in erosion rates have a direct impact on the ES and the highest ES relative to OSG (up to 15) were achieved for Ti hardmasks in CF4/Ar plasmas with low ion energy.

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