Yi-Lung Cheng

Pulsed Electrodeposition of CuInSe2 Thin Films onto Mo-Glass Substrates

In this study, copper indium selenide (CIS) films were deposited by pulsed electrodeposition with multi potentials to control the atomic ratio of the CIS film and improve the deposition uniformity. It was found that smaller duty cycle and pulsed period enhanced the cathodic current due to ion replenishment. The results show that the Cu/In ratio was significantly influenced by reverse voltage of pulsed electrodeposition. The uniformity of the CIS films can be improved by proper reverse voltage. The deposition rate did not decrease in direct proportion to the duty cycle because the plating current was enhanced by the pulse effect. The pulsed deposited CIS film with optimized composition show smaller grain size, smoother microstructure, and less secondary phase than constant deposited film.

Effect of Annealing on the Microstructure and Electrical Property of RuN Thin Films

Ruthenium (Ru) and ruthenium nitride (RuN) thin films have been investigated as candidates for barrier layers in copper (Cu) damascene processes. In order to study the thermal stability of the Ru and RuN films, the as-deposited films were annealed by rapid thermal annealing (RTA), and the film resistance was real-time measured by a four-point probe, which was embedded in the RTA tool. The X-ray diffraction data show that the grain size of Ru decreased with the increase of the nitrogen (N) content. The Ru phases gradually changed to the RuN phases, and the resistivity of the RuN films decreased with annealing time due to nitrogen effusion. Discontinuous RuN films were found when the annealing temperature was higher than 800°C and then caused a poor Cu diffusion barrier property. We also demonstrated that the Cu film could be directly electroplated on the RuN films with adequate adhesion.

Competition of Electromigration Reliability in Copper and Nickel-Silicide

In this study, electromigration (EM) characteristics of Cu line and nickel (Ni)-silicide on Cu-line/W-via/Ni-silicide structure were compared. The experimental results revealed that EM competition of Cu line depletion and Ni-silicide migration depends on the length of Cu line and the stress current density. For a longer Cu line or stress at a higher current density, the failure time of Cu-line depletion is lower than that of Ni-silicide migration because the failure mode is Cu-line depletion. On the other hand, as the length of Cu line is decreased and stressed at a lower current density, the failure mode is transferred to Ni-silicide migration due to a stronger back-stress effect in a shorter Cu line. The critical current densities (j c ), activation energy (E a ), and current density exponent (n) values for Cu-line depletion mode and Ni-silicide migration modes were characterized, which are used to predict the EM lifetime at normal operation conditions. The results indicated that although the failure time of Ni-silicide migration mode is lower than that of Cu-line depletion mode for a shorter Cu line at a higher stress temperature, Ni-silicide migration with a higher activation energy ( ~ 1.7 eV) results in a longer EM lifetime at a lower operation temperature.

Effect of Electron Flow Direction and Via Number on Electromigration Mechanism for Copper Dual Damascene Interconnects

In this study, the effects of the via number and the current direction on electromigration characteristics in the dual-damascene Cu lines have been investigated. The results reveal an interesting difference in electromigration behavior of electron up- and down-flow directions on the multi-via structures. Increasing the via number results in a higher electromigration failure time and then reaches saturation for electron up-flow case. As for electron down-flow direction, the failure time is independent of the via number. Moreover, the failure time of Cu lines with via structure is lower than that without via structure. A higher current density at the triple junction site in the inner via is the possible mechanism, resulting in a shorter failure time and via-number independent. These observed effects are specific to Cu dual-damascene structures and can provide great technological implications in electromigration improvement.