Electrodeposition Preparation Method And Mechanism Of Nano-copper Pillar Array Substrate For 3D Packaging

With the development of electronic devices towards miniaturization and multi-functionality,the packaging on the two-dimensional plane has been unable to meet the technical requirements,so people have turned their attention to three-dimensional integration technologies.Currently through silicon via(TSV)technology has won many attentions of the relevant scholars and industry,however,the big difference of thermal expansion coefficients between silicon,silicon dioxide,and copper may cause thermal mismatch problem,reducing the device reliability.This paper proposes to use nano-Cu pillar array filled anodic aluminum oxide(AAO)substrate prepared by electrodeposition to achieve three-dimensional high-density packaging interconnection.This paper mainly studied the preparation of nano-Cu pillar array filled AAO substrate by electrodeposition in order to realize high-density vertical interconnects in 3D packaging.Experiments were conducted using direct current deposition and pulse electrodeposition,respectively.Firstly,the influence of parameters such as current densities,temperature,deposition liquid composition,and electrodeposition time was investigated using direct current electrodeposition.The experimental results showed that the smaller the current density,the more uniform the current distribution in the AAO template,the higher the filling rate of the nano-Cu filled AAO template,and the stronger the Cu(110)preferred orientation of the prepared nano-Cu pillar array.The higher the temperature,the higher the filling rate of the nano-Cu pillar filled AAO template.However,if the temperature is too high,the template will be corroded.Compared with the high-acid and low-copper bath,the high-copper and low-acid bath is more conducive to the electrodeposition of nano-Cu pillar array in the AAO template.With the increase of electrodeposition time,the height of the nano-Cu pillar array in the AAO template gradually increases,but the increasing rate gradually decreases.The main problem in direct current electrodeposition is the overgrowth of copper blocks on the surface of the AAO template,which affects the uniformity of the nano-Cu pillar array.Next,the method of periodic pulsed electrodeposition was used to investigate the growth of nano-copper pillar array in six different modes of 25s/5s,20s/10 s,30s/15 s,20s/20 s,20ms/20 ms,and 10ms/30 ms.Experimental results showed that when the pulse frequency is the same,if the duty ratio is decreased,the growth of the copper blocks on the surface of the AAO template will be alleviated.When the duty ratio is the same,the smaller the frequency,the more uniform the growth of the nano-Cu pillar array in the AAO template and the better the growth quality.There is no obvious growth preferred orientation of the nano-Cu pillar array in the above six different periodic pulsed electrodeposition modes.A clean uniform nano-Cu pillar array filled AAO substrate was obtained under the conditions of current density 2 A/dm2,total electrodeposition time 6800 s,and electrodeposition temperature 30 °C with periodical pulse 20ms/20 ms electrodeposition.The difference in preferred growth orientation of nano-Cu pillar array under direct current electrodeposition and pulse electrodeposition was clarified using the relationship between the total surface energy and the aspect ratio of single nano-Cu pillar with different crystal orientations calculated by the theories of fracture bond model,surface energy anisotropy,and energy minimization.The mechanical,electrical and thermal properties of nano-Cu pillar array filled AAO substrate were tested.The results of the direct and indirect interconnection between the nano-Cu pillar array filled AAO substrate and the copper block showed that complete direct interconnection between copper and copper is difficult to achieve,but good metallurgical connection is achieved through the Sn Pb eutectic solder paste.The above experimental results showed that the nano-Cu pillar array filled AAO substrate is a low-cost and high-performance substrate that can be used for three-dimensional packaging.