Optimization of thermal loads in TSV fabrication process based on real-time micro deformation process analysis of copper

Abstract

A real-time micro deformation process of copper in through silicon Vias(TSVs) was revealed for optimizing thermal loads of TSV preparation technologies based on the dynamic real-time measurement system (DRMS) and the finite element method(FEM). The change of copper ’ s protrusion in TSVs with temperature, tested by the DRMS, was considered to be the important criteria. An axial symmetry TSV basic model was built to simulate the copper’s micro-mechanical responses under these different thermal loads. The results of FEM match well with the experiment curve in both shape and value, because the creep of TSV-Cu can be precisely described when n is 5. FEM results show that slow linear heating has smaller protrusion than fast linear heating heating and step heating can make further improvement. Besides, relatively fast cooling enhances reliability for it reducing the risk of crack in interface between TSV-Cu and BEOL. Creep plays a key role in copper’s deformation revealed by simulation, since larger heating rate easily causes stress accumulation in the heating stage, and larger stress leads to larger creep deformation, naturally the protrusion under fast heating is larger than that under slow heating. By the above simulation and experimental methods, the real-time thermal deformation process and micro-morphology of TSV was understood in detail, thus the thermomechanical reliability of TSV was improved by optimization of thermal load.