AN X-RAY-METHOD FOR DIRECT DETERMINATION OF THE STRAIN STATE AND STRAIN RELAXATION IN MICRON-SCALE PASSIVATED METALLIZATION LINES DURING THERMAL CYCLING

We describe a method for directly determining the strain state of pass ivated metal lines. Synchrotron radiation in the grazing incidence geo metry is used to directly measure the in-plane interplanar spacing alo ng the length and width of the lines, while the strain normal to the s urface of the line is measured using conventional diffraction methods. The entire strain state is thereby defined. Previous work has measure d out-of-plane reflections, fit them to a straight line as a trigonome tric function of the angle of orientation, and extrapolated to determi ne the principal strains. The equivalence of the two x-ray methods on the same sample is demonstrated at room temperature before and after t hermal cycling. For short time strain relaxation experiments during th ermal cycling, measurement of the three principal strains leads to the direct calculation of the stress relaxation. We apply the strain dete rmination technique to Al-0.5% Cu lines passivated with Si3N4 as the l ines are thermally cycled from room temperature to 450 degrees C and b ack. The strain state, stress state, and strain relaxation of the line s are calculated at several temperatures during thermal cycling.