Fabrication of full intermetallic compound interconnects with single crystal (111) Cu under bump metallization

Abstract

This study focuses on the effect of single crystal (111) Cu substrate on the growth of IMC in full IMC micro-interconnects and the formation of Kirkendall voids at the interfaces in the single crystal (111) Cu/Sn/ electroplated Cu structure interconnects. From the top view morphologies of Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> grains, the regular arrays of the roof-type Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> grains were formed on the single crystals (111) Cu substrate after soldering at 300 ℃ for 10 s, which is different from the typical scallop-type Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> grains. It is quite significant for the manufacture of full IMC micro-interconnects in the electronic industry. From the cross-sectional microstructure by SEM, the asymmetric growth of interfacial IMCs was observed in the single crystal (111) Cu/Sn/ electroplated Cu interconnects after soldering at 300 ℃, evidenced by the growth rate of interfacial IMCs was slower on the single crystal (111) Cu substrates interface as compared with the electroplated Cu. At the same time, almost no Kirkendall voids were observed at the interface between Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn and single crystal (111) Cu and in the Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn layers after soldering at 250 ℃ and 300 ℃, meaning that using single crystal (111) Cu as the substrate can effectively reduce or even eliminate the formation of Kirkendall voids. We expect to form full IMC micro-interconnects without Kirkendall voids, which have better electrical, thermal and mechanical properties.