Elastoplastic creep analysis of thermal stress and strain in aluminum interconnects of LSIs

Abstract

To study a thermally induced open‐failure mechanism of aluminum interconnects of LSIs, a three‐dimensional (3‐D) simulation using a finite element method was carried out. In this calculation, a creep strain increasing with time in addition to an elastoplastic strain was taken into account. Further, the effect of a manufacturing process on a stress and a strain induced in an aluminum layer was examined using a simulation for a subsequent stacking of oxide‐layer/aluminum film/protective layer on an Si chip. The condition for a 3‐D plasticity to occur was calculated in which case a strain was represented using the von Mises criteria. As a result, after the manufacturing process is completed, the stress is found to decrease significantly with time, while a plastic strain is kept constant. However, the creep strain responsible for the failure is found to increase. the temperature dependence of the creep strain also was studied. the three different results previously reported, i.e., the lifetime becomes shorter as the temperature rises, there is no temperature dependence, and the shortest lifetime is at about 150°C are all found to be possible. the calculation was applied to the multilayered interconnects and the creep strain is shown to decrease by more than a few tens percent in an aluminum layer.

Crystal-plasticity based thermo-mechanical modeling of Al-components in integrated circuits

“…As an exception, an isotropic elasto-plastic and temperature dependent material behavior with a yield stress of 120 MPa is used for the metallization plate in the study of the conductor paths, Section 4.1.2. A discrete data set of property-temperature-pairs is used as basis for the interpolation of material properties within a temperature range of 273 K 6 T 6 723 K [6,23]. In order to give an impression of the heterogeneity of the involved materials, Table 1 shows exemplarily the employed material properties for a temperature of 293 K.…”

“…Altogether 34560 finite elements are used for the model with wide conductor paths and 9350 finite elements for the model with narrow conductor paths. Table 1 Excerpt of material parameters (Young's modulus E, Poisson's ratio m, mass density q, heat conductivity k, specific heat c and thermal expansion coefficient a) based on [23,6] and adapted material parameters [6,30,31] …”

“…Additionally, the coefficient of thermal expansion a and Young's modulus E are treated as temperature dependent material parameters by using a discrete set of data for interpolation [6,23].…”

“…The few thermomechanical analyses available up to now were based on rather simple material models [8,[21][22][23]. http An attempt to simulate the thermo-mechanical behavior of aluminum interconnects using crystal plasticity was already presented by Povirk in 1995 [24].…”

On the Way to Zero Defect of Plastic-Encapsulated Electronic Power Devices—Part I: Metallization

“…4 was used, where the whole system was considered: a die pad, the MC, Si die, PI coating, dielectric layers, an Al plate, and a passivation layer. The layer thicknesses, basic constants, and material models used for the simulations are shown in Tables I and II. For the Al metallization, a bilinear kinematic (BKIN) hardening model with similar temperature dependence of the yield stress as described in [24] was applied. The corresponding stress/strain curves are shown in Fig.…”