Electromigration early failure void nucleation and growth phenomena in Cu and Cu(Mn) interconnects

Abstract

Electromigration early failure void nucleation and growth phenomena were studied using large-scale, statistical analysis methods. A total of about 496,000 interconnects were tested over a wide current density and temperature range (j = 3.4 to 41.2 µmA/m2, T = 200 to 350°C) to analyze the detailed behavior of the current density exponent n and the activation energy Ea. The results for the critical V1M1 downstream interface indicate a reduction from n = 1.55±0.10 to n = 1.15±0.15 when lowering the temperature towards 200°C for Cu-based interconnects. This suggests that the electromigration downstream early failure mechanism is shifting from a mix of nucleation-controlled (n = 2) and growth-controlled (n = 1) to a fully growth-controlled mode, assisted by the increased thermal stress at lower temperatures (especially at use conditions). For Cu(Mn)-based interconnects, a drop from n = 2.00±0.07 to n = 1.64±0.2 was found, indicating additional effects of a superimposed incuba tion time. Furthermore, at lower current densities, the Ea value seems to drop for both Cu and Cu(Mn) interconnects by a slight, but significant amount of 0.1 - 0.2eV. Implications for extrapolations of accelerated test data to use conditions are discussed. Furthermore, the scaling behavior of the early failure population at the NSD=-3 level (F about 0.1%) was analyzed, spanning 90, 65, 45, 40 and 28 nm technology nodes

The need and opportunities of electromigration-aware integrated circuit design

“…Applications targeted for di erent use cases face di erent environmental conditions and quality goals. Among others, the JEDEC Solid State Technology Association (JEDEC) [13] and the Automotive Electronics Council (AEC) [2] released several standards on (1) how to characterize and to qualify a semiconductor technology with respect to intrinsic and extrinsic failure mechanisms and (2) how to scale technology and design parameters for speci c use cases. With respect to EM, these standards include JEP001A, JEP119A, JEP122H, JESD63, JESD87, JESD202 and AECQ-100.…”

“…The derivation of the parameters of the EM-failure model during technology characterization is done under temperature-accelerated conditions (JESD63, JESD202 [13]). Next, the current density j char used during the characterization of a particular layer and temperature T char must be scaled (using Black's Equation [6]) to one or more technology-speci c reference conditions j max,ref at T ref while considering reliability goals (Fig.…”

“…These use cases and operating phases are de ned in so-called "mission pro les". A mission pro le describes and links all environmental and operating conditions as well as functional loads which an application has to sustain during production, storage, shipping, assembly and operation [14,24]. For EM, the combinations of ambient temperature and the cumulated duration (e.g., 1000 h at 398 K + 300 h at 423 K) describe the relevant environmental conditions, whereas the terminal currents of a net represent functional loads.…”

“…The general approach for deriving "e ective" design rules (j max,e atT e ) for a particular layer is given as follows. The technology characterization provides the models and factors to scale the permitted current-density limit under consideration of reliability goals (CDF, lifetime) and varying operating temperatures (JESD63, JESD202 [13]). First, the particular temperatures and durations of all operating phases are used to calculate an EM-speci c e ective temperature T e using Black's Equation [6].…”

“…The detailed procedure to derive and scale current-density limits is beyond the scope of this tutorial paper due to space limitations. The procedure and the general mission-pro le-aware design approach is discussed in detail in [14] and [19].…”