Abstract
The moisture barrier properties of stacked graphene layers on Cu surfaces were investigated with the goal of improving the moisture barrier efficiency of single-layer graphene (SLG) for Cu metallization. SLG with large grain size were stacked on Cu surfaces coated with CVD-SLG to cover the grain-boundaries and defective areas of the underneath SLG film, which was confirmed to be oxidized by Raman spectroscopy measurements. To evaluate the humidity resistance of the graphene-coated Cu surfaces, temperature humidity storage (THS) testing was conducted under accelerated oxidation conditions (85 °C and 85% relative humidity) for 100 h. The color changes of the Cu surfaces during THS testing were observed by optical microscopy, while the oxidized Cu into Cu2O and CuO was detected by X-ray photoelectron spectroscopy (XPS). The experimental results were accord with the results of first-principle simulation for the energetic barrier against water diffusion through the stacked graphene layers with different overlap. The results demonstrate the efficiency of SLG stacking approach against moisture for Cu metallization.
Highlights
Copper (Cu) interconnects, which are used in large-scale integrated circuits (LSIs), require a barrier layer to prevent Cu diffusion, which leads to degradation in the Si carrier lifetime
Regarding the previous report of moisture barrier properties of single-layer graphene (SLG)-coated Cu surface[20], we reproduce this experiment again, and found that some areas of Cu surface were oxidized after 100 h of temperature and humidity storage (THS) testing, as shown in the relative O/Cu atomic concentration ratios investigated by X-ray photoelectron spectroscopy (XPS) (Fig. 1)
The results suggest that when graphene does not completely protect the Cu surface from moisture, the oxidation of the defective areas is enhanced by the graphene coating
Summary
Copper (Cu) interconnects, which are used in large-scale integrated circuits (LSIs), require a barrier layer to prevent Cu diffusion, which leads to degradation in the Si carrier lifetime. We reported that CVD-grown single-layer graphene (SLG) can serve as an efficient impermeable film to prevent the diffusion of moisture. We have confirmed that the oxidized areas in the SLG-coated Cu were corresponding to the grain-boundaries or defective structures of graphene by Raman spectroscopy measurements. For improvement in the resistance of graphene-coated Cu to prevent the oxidation from moisture, we report an artificial stacking SLG layers on CVD-SLG/Cu into double-layer graphene (DLG) to eliminate the Cu oxidation through the defects and grain boundaries of the underneath SLG, as in the second experiment. TLG is a highly efficient barrier that uniformly prevents oxidation on the Cu film surface by covering the cross-points of grain boundaries in DLG. We discuss the mechanism of improvement by the first-principles simulation of overlapping graphene films result in an increased energetic barrier against the water diffusion through the different length of graphene overlap
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