Abstract
The reliability issues of 0.25×0.25 μm2 contact structure had been studied in this work. Through the use of four terminal cross - bridge Kelvin structure and the TiN / Al - Si - Cu / TiN / TiSi2 / P+ - N contact structure to observed the behavior of contact structure, which before long time and large current density stressing was studied. There are different polarity stressing were used in the reliability test. Another reliability test was used thermal stressing addition to the contact structure and observed the failure exterior of contact structure. After both of positive and negative stressing, used AES depth profile analysts the property of material of contact structure. In this work, the 0.25×0.25μm2 contact resistance value was about 150 ~ 250Ω.The specific contact resistance was about 4.55 ~ 6×10-7 Ω-cm2. In the reliability tests, varied the direction of stress (include the positive and negative stress direction), stress current density, test wafer substrate temperature. The result of varied the direction of stress, the resistance value of both of the positive and negative stressing was decreased with stressing time increased. And when stressing current density large enough, the "step shape" changed of contact resistance value can clear observed. Both of stress current density and wafer substrate temperature were indirectly proportion to the contact life - time. From the positive thermal stressing, determined the activation energy is 0.66 eV. Before large current density stress, through the Auger electron spectroscopy (AES) to analysis the materials compose of depth profile of contact structure. Clearly, before the positive stressing, the titanium and nitrogen atoms of top layer of the contact structure were penetrated into the conduction layer (aluminum alloy). Contrary, before the negative stressing, the titanium and nitrogen atoms of the diffusion barrier were penetrated into the conduction layer. Both of the positive and negative stressing, the depth of atoms penetrated increased with stressing current density increased. The atoms penetrated of the negative stressing easier than positive stressing. The atoms penetrated phenomenon due to applied a large current density was induce electron drift velocity and when the momentum of electron large enough. The electron collision with the titanium or nitrogen atom, the mass transport was happen. Then titanium and nitrogen atoms were penetrated into the conduction layer.