Mechanical characterization of CMOS metal layers

Abstract

This paper reports on the strain rate dependence of the mechanical properties of aluminum-based metallization layers. Evaporated Al, sputtered Al 99% Cu 1% , and multilayers of µm-thick Al 99% Cu 1% films separated by thinner TiN/Ti layers are characterized using the bulge test, the microcompression method and the microtensile technique. Elastic, ductile and fracture parameters are extracted for strain rates dε/dt between 10 -4 to 10 1 s -1 . The Young's modulus E of sputtered layers, 59 GPa, is marginally lower than that of evaporated films, 63 GPa. Both fracture strain ε max and strength σ max of sputtered Al, 5.5% and 79 MPa, respectively, show no significant variation with dε/dt, changing to ε max = 2.1 % and σ max = 200 MPa when such films are stacked with TiN/Ti layers. Regarding evaporated Al, the failure parameters depend strongly on the strain rate: ε max decreases from 33.2 to 1.3% and σ max increases from 153 to 380 MPa within the entire range of tested dε/dt values.