Research On Preparation And Reliability Of Nanotwinned Copper Interconnect Materials For Microelectronic Packaging

Semiconductor packaging devices are developed towards the direction of miniaturization and multi-function,which led to the reduction in package size and increase in interconnection density.And it becomes a great challenge on the reliability of interconnected materials for microelectronic packaging.In 2004,Lu Ke reported that nanotwinned copper obtained by pulse electrodeposition,which had characteristics of high fracture strength and high elongation.In addition,nanotwinned copper also has advantages,including high conductivity and excellent resistance to electromigration（EM）,which is regarded as a promising material applied in advanced packaging technologies such as UBM,RDL and Cu P.Due to the complex process and low production efficiency of pulse electrodeposition,direct current electrodeposition was adopted to prepare high（111）-oriented nanotwinned copper,and its application in wafer-level packaging was further studied.Firstly,the influence of copper sulfate concentration,chloride ion concentration,the plating solution temperature on the microstructure and mechanical properties of nanotwinned copper were investigated.In detail,with the increase of the copper sulfate concentration in the plating solution,the thickness of transition layer decreased,the proportion of nanotwinned region had slightly increased.The mechanical properties was relatively stable despite the minor change in microstructure with increased concentration of copper sulfate.As the chloride ion concentration of the plating solution increases,the（111）texture coefficient continues to increase.Also,the proportion of columnar region and twin density increased when the concentration of hydrochloric acid increased,and reached a maximum value at 30μl/L.When the concentration further increased,the columnar grains was refined to equiaxed grains,and the strength was slightly decreased due to the change of twin density.Obvious influence of bath temperature on the microstructure was observed.When the temperature increased,microstructure of equiaxed grains was changed to columnar grains,and the twin density was firstly increased then decreased.The overall fracture strength shows a downward trend with increased temperature.In order to examine the performance of electrolyte for the microelectronic packaging,nanotwinned copper was electrodeposited on wafer substrate.The influence of sputtering Cu seed layer on the growth behaviour of nanotwinned copper were investigated.It was found that the higher（111）ratio of seed layer was beneficial to reduce the thickness of transition layer and increase the proportion of（111）ratio of electroplated nanotwinned copper films.Furthermore,the thermal stability and filling capacity were studied on the optimized substrate.As deduced from the hardness measured before and after heat treatment,the nanotwinned copper had a superior thermal stability.The recrystallization temperature of nanotwinned copper（350℃）was much higher than that of commercial copper（200℃）.In addition,nanotwinned copper was deposited on the substrate patterned with RDLs in different line width.By comparing the uniformity and flatness of the RDL deposited with the commercial copper plating solution,it was found that the nanotwinned copper plating solution has better filling performance.Finally,the comparison study of nanotwinned copper films and RDLs were further performed.The evolutions of microstructure and mechanical properties during high temperature and high humidity test（85℃ and 85% RH）and temperature cycling test were observed.It was revealed that,nanotwinned copper showed a better anti-oxidation ability under high temperature and high humidity environment and a similar performance under thermal cycling environment.