Polarity effect on failures of Ni and Ni(2)Si contacts on p(+)-Si and n(+)-Si under high current densities

Multilevel thin film structure is used for future very large-scale integration (VLSI) technology. In the multilevel structure, there are many contacts and vias of which the interfaces are planes of atomic flux divergence and are susceptible to electromigration failure. Most of the electromigration studies have merely addressed circuit failures along wires or at vias, very few focused on contacts. In this work, the stabilities of the Ni/n{dollar}sp+{dollar}-Si, Ni/Ni{dollar}sb2{dollar}Si/n{dollar}sp+{dollar}-Si, Ni/p{dollar}sp+{dollar}-Si and Ni/Ni{dollar}sb2{dollar}Si/p{dollar}sp+{dollar}-Si contacts against high current density were studied. A contact pair structure was used to study the failure behaviors of the cathode and the anode contacts. A strong polarity effect on contact failure was observed in the Ni/n{dollar}sp+{dollar}-Si, Ni/Ni{dollar}sb2{dollar}Si/n{dollar}sp+{dollar}-Si, Ni/p{dollar}sp+{dollar}-Si and Ni/Ni{dollar}sb2{dollar}Si/p{dollar}sp+{dollar}-Si contacts. Optical inspection was made in-situ for the study of failure times and the statistics of failure sites. Micro-beam Rutherford backscattering spectrometry (RBS) and Auger electron spectrometer (AES) depth profiling showing the reaction at the damaged contacts were presented. The current-induced silicide at the contact was identified to be epitaxial-NiSi{dollar}sb2{dollar} phase by plan-view transmission electron microscopy (TEM). The in-situ resistance data by the Kelvin structure showed that the resistance of the damaged contact increased with stressing time.; The electrical behavior of the p{dollar}sp+{dollar}-Si and the n{dollar}sp+{dollar}-Si channels was studied by applying current through the Si channel in the contact pair structure. The p{dollar}sp+{dollar}-Si and n{dollar}sp+{dollar}-Si were applied to current gradually to 100 mA. For the p{dollar}sp+{dollar}-Si, the resistance responded by increasing gradually to a maximum at the current defined as the critical current and then decreasing gradually. The resistance change with current was reversible. For the n{dollar}sp+{dollar}-Si, the resistance increased by less extent compared to the p{dollar}sp+{dollar}-Si and then dropped abruptly at the critical current. The resistance drop beyond the critical current was not permanent. Hysteresis in the resistance change of the n{dollar}sp+{dollar}-Si was observed; the critical currents upon ramp-up and ramp-down of current were different. The electrical behaviors in both p{dollar}sp+{dollar}-Si and n{dollar}sp+{dollar}-Si showed dependence upon temperature and channel size. The dependence of channel length and width has effected the critical current, the critical current density and the activation energy. We propose the high field effect for the resistance increase in regime I and the junction breakdown for the resistance decrease in regime II.; An ultra-fast lateral silicide formation in the p{dollar}sp+{dollar}-Si by high current densities was observed in the Ni and Cu on the p{dollar}sp+{dollar}-Si. The 140 {dollar}mu{dollar}m long silicide line was created in less than 1 second by applying instantaneously to a current of 80 mA or above, corresponding to a current density of about 10{dollar}sp6{dollar} A/cm{dollar}sp2.{dollar} The diffusivity of Ni or Cu in the Si is about 10{dollar}sp{lcub}-4{rcub}{dollar} cm{dollar}sp2{dollar}/sec, higher than the liquid diffusivity. We propose that the current-induced ultra-fast silicide formation be related to the electron-hole recombination and electromigration.