Material Removal and Wear Behaviour of Copper Thin Film in Ambient Air and Wet Environment by Nanoindenter

Abstract

This paper aims to investigate the scratching behaviour of copper thin film in dry and wet environments by nanoindenter using conical indenter. The material removal mechanism of the complex chemical mechanical polishing (CMP) process is viewed as single abrasive scratch wear considering the effect of the wet environment. The experimental scratches are performed on Hysitron TI 980 Triboindenter in constant load mode as well as ramp load mode. The experimental results show that for a given force, the scratch depth in slurry environment sample is significantly larger than that in the DI water environment sample, due to the presence of soft passivation in the slurry environment. Consequently, the wear rate in the slurry environment is significantly larger than wear rates in the air and DI water environment. The wear rate in the slurry environment is five times larger than those in ambient air and DI water environments. A similar trend is reflected by the instantaneous specific energy evaluation for all conditions. In comparison to ambient conditions, the slurry environment requires 78% less and the DI water environment require 17% more instantaneous specific energy for unit volume material removal, at a given scratch depth. The ease of material removal in the slurry environment is supported by the significant decrease in Scratch hardness of the copper thin film sample passivated in the slurry environment. The progression of the coefficient of friction is studied concerning the nano deformation mechanism in the copper thin film in all environments. The stick-slip behaviour is observed for the copper thin film in wet environment. An explicit scratch hardness model with consideration of elastic recovery is developed for constant load mode scratching to access the scratch hardness of the copper thin film. The computed scratch hardness of copper thin film in ambient, DI water and slurry comes out to be 1.875 GPa, 1.948 GPa and 0.996 GPa respectively. X-ray photoelectron spectroscopy (XPS) analysis is performed to characterize the copper thin film surface before and after passivation in DI water and slurry. Results of this study of deformation during scratching of the passivation layer on copper thin film can be applied to develop and analyze the advanced node copper CMP process.