The Protrusion Behaviors in Cu-TSV During Heating and Cooling Process

The Cu protrusion phenomena and thermal stresses in TSV structures were studied using finite element analysis. When the TSV model was heated from 25°C to 100°C, 200°C, 300°C, 400°C and then cooled down to 25°C, the change of the Cu protrusion height was estimated as a function of annealing temperature. It is concluded from the protrusion height-temperature hysteresis curve that Cu shows a combination of reversible thermal expansion and irreversible plastic deformation which cannot be recovered after annealing the Cu protrusion. The plastic deformation has been found to initiate at the top of the Cu and Si-via interface because of the large mismatch in the coefficients of thermal expansion. The thermally induced plastic flow causes Cu protrusion in the TSV. The simulation and experimental values of Cu protrusion height are respectively 0.93 μm and 1.02 μm at 400°C, showing the validity of the present model.