Preparation and Characterization of Electroplated Cu/Graphene Composite

Cu and unoxidized graphene composite films were prepared by electroplating under room temperature. Graphene was added to the electrolyte of Cu to form composite materials to improve the performance of Cu for interconnection. Composite electrolyte containing high concentration of graphene (up to 0.5 g/L) was prepared by adding CTAB as surfactant. And ultrasound was also used to increase dispersion degree and reduce graphene agglomeration in electrolyte. Average coefficient of thermal expansion (CTE) of the composite films determined by thermo-mechanical analysis (TMA) shows a decrease from 17.3 ppm/K to 14.2 ppm/K from 260 K to 320 K, which reduce CTE by 18 % compared with Cu. CTE of the composite materials can be reduced to 10 ppm/K at 243 K, which is only 60 % of CTE of Cu. The thermal conductivity of the composite materials measured by phase sensitive transient thermo-reflectance (PSTTR) technique shows an improvement from 385 W/m.K to 468 W/m.K. CTE and thermal conductivity of the composite materials both decrease with the increase of current density. And they also both increase with the increase of graphene concentration. The composite materials also show good mechanical properties. The average hardness is 2.5 GPa, which is about 2 times of Cu. And the average elastic modulus is 145 GPa, which is 38 % higher than that of Cu. The resistivity of the composite materials is basically equivalent to that of pure Cu. Result of the experiment proved that the composite materials have better performance under low temperature conditions. The improvement of material properties makes composite materials have good application prospects for 3D interconnection in the near future.