Thermal Stresses in Passivated AlSiCu-Lines From Wafer Curvature Measurement

Abstract

AbstractA wafer curvature technique was used to measure the mechanical stresses during thermal cycling and the isothermal stress relaxation in passivated Ti/TiN/AlSi(l%)Cu(0.5%)-lines (aspect ratio: 0.92) in the in-plane directions, parallel and perpendicular to the lines. The evaluation of the measured curvature data is explained in detail. The evaluation procedure was tested with the help of passivated SiO2-lines in which the stresses can be calculated because both, the SiO2-lines and the passivation, behave elastically. Comparision to elastic Finite-Element-Method calculations show excellent agreement. The main results are: a)During thermal cycling all stresses in the AlSiCu-lines vary linearly with temperature without significant hysteresis. The stress parallel to the lines is higher than perpendicular to the lines. X-ray stress data from the same sample confirm the wafer curvature data and show, additionally, that the stresses in the two directions perpendicular to the lines are equal.b)The isothermal stress relaxation depends strongly on the temperature with a maximum at 250°C. Void formation and growth probably control the observed relaxation.