Research On Low Temperature Thermocompression Bonding Technology Based On Nanoporous Cu

3D Packaging based on TSV has many advantages such as high speed interconnection andhigh density integration; it has been accepted as the next generation technology for packaging.Bonding is one of the key processes to achieve3D packaging and now Cu-Cuthermocompression bonding is the mainly bonding technology which has well electricalinterconnection, excellent path for thermal transfer and high mechanical reliability. Howeverconventional Cu-Cu thermocompression bonding need high temperature(350℃～400℃),high pressure which has adverse impact on the performance of temperature sensitivelycomponent and structure, increasing the thermal stress of package and decreasing thereliability of product, so achieving low temperature bonding is very important for3Dpackaging. As we known, nanomaterials have many attractive properties such as large surfaceto volume ratio, high surface activity and size-dependent melting of nanoparticles, so it’spotential to realize low temperature bonding using nanomaterials or nanostructures asbonding layer. With the simple process and tunable for nanoporous dimension, now selectivedealloying is the mainly method to fabricate nanoporous structure. In this article, nanoporousCu is fabricated on silicon substrate by selective dealloying, and then using this nanoporousCu as bonding layer to realize low temperature bonding. The detailed contents are as follows:(1) Analyze the foundation of low temperature thermocompression bonding based onnanoporous Cu which has large surface to volume ration, high surface activity andsize-dependent melting of nanoparticles, also it’s softer than bulk Cu which isbeneficent to thermocompression bonding;(2) Study three different methods of fabricating nanoporous Cu: Heat-alloying method、Electroplate-alloying method and Sputter-alloying method. According to the SEMimages and XRF analysis, nanoporous Cu with dimension ranging from20nm to 100nm has been fabricated on silicon substrate and the dimension of nanoporous Cuincrease with the concentration rising of dealloying solution, extending of dealloyingtime and increasing of Cu content. Also compare the difference between threemethods;(3) Roughness of electroplated alloy surface is below100nm; Nanoindenter test showthat the Young ’ s Modulus of nanoporous Cu after dealloying5h is one-Sixth of thebulk Cu which demonstrate nanoporous Cu is softer than the bulk Cu;(4) Achieve low temperature thermocompression bonding with the bonding temperatureat280℃,bonding pressure at1.4KN and the bonding dwell time is120min.Nointerface is observed on the bonding cross-section by SEM view, also no voids arefound in the bonding layer by SAM test. Study the influence of bonding temperature,pressure and dwell time to bonding quality. Tensile strength test show that bondingstrength with nanoporous Cu is much bigger than the one without nanoporous Cu, thisresult also demonstrate the superiority of low temperature thermocompressionbonding with nanoporous Cu.