Cu Surface Characterization after Wet Cleaning Processes

In damascene architecture, widely used both in flash memories and in DRAM as interconnect scheme since 90 nm node, copper surface is exposed after via etch. A deep understanding of the effect of different wet cleanings on Cu surface is therefore mandatory, not only to ensure an efficient post etch polymer removal, but also to provide a better surface termination, capable to minimize Cu oxidation kinetic and to reduce the growth of Cu-rich precipitates which may negatively effect contact resistance. In this work we have analyzed the Cu surface after processing with several cleaning chemistries -often present in BEOL cleaning processes- using XPS (X-ray Photoelectron Spectroscopy) and ToF-SIMS (Time of Flight – Secondary Ion Mass Spectroscopy), fast and powerful techniques widely used in Cu surface characterization [1]. In addition, the evolution of the surface with storage time has been monitored using the same techniques, in order to better understand the effect of the different cleaning chemistries. XPS has been proven to be very sensitive to monitor Cu oxidation, while ToF-SIMS has been used to reveal organic species adsorbed on the surface.