Numerical Analysis of the Reliability of Cu/low-k Bond Pad Interconnections Under Wire Pull Test: Application of a 3D Energy Based Failure Criterion

Abstract

Due to size reduction in die manufacturing and introduction of brittle dielectric materials, crack related failures occur currently, mainly in interconnect levels. By means of Finite Element (FE) simulations, an energy based failure criterion named Nodal Release Energy (NRE) Method, inspired by the so-called Area Release Energy (ARE) one developed by Philips Applied Technologies, is used to numerically predict the mechanical related failures. More precisely, the failure index is applied to investigate wire bonding induced peeling. In this paper, the NRE method is presented and its added value to forecast delamination failures in a typical microelectronics stack is demonstrated.The NRE method is related to fracture mechanics and founded on propagation approach. Two FE calculations are used to evaluate the energy quantity: an uncracked and cracked one. In the latter model, a virtual crack is inserted. Aiming to compare the NRE values with known physical quantities experimentally measured such as critical adhesion energy, a relation bridging the gap from NRE to the Energy Release Rate is given. This relation is based on the crack extension method and relates to Griffith theory. The accuracy of the NRE method is investigated through comparisons with 2D and 3D analytical cases. Results show that the method provides a good approximation. The NRE behaviour with respect to key numerical parameters will be studied.At last, a typical bond pad structure under a wire pull test is simulated. Both stress and energy based analyses are carried out. The critical interface is investigated with both post processing methods. Results based on the energy criterion show that delamination interface is in agreement with experimental observations, in contrast to stress based values. However, it is also shown that simulation results can depend on the prescribed crack length, suggesting a accurate definition of the cracked model. The main assumptions done in this study are discussed, trying to define the associated uncertainties, particularly residual stress and crack morphology features. Finally, the added insights provided by NRE method and its ability to help in design and process development for advanced IC technologies are demonstrated.

3D Multi Scale Modeling of Wire Bonding Induced Peeling in Cu/Low-k Interconnects: Application of an Energy Based Criteria and Correlations with Experiments

“…Note that the numerical parameters to be used, the sensitivity and the ability to link this value with the energy release rate has been previously validated; and additional insights compared to a standard stress based analysis have been demonstrated [18] Finite Element Models Multi level models The three dimensional bonding model consists of a silicon die containing the interconnect layers, the gold wire and ball, and the capillary. The simulated die stack is seven copper metal levels (7ML) including five low-k levels and the two others containing classical silicon dioxide dielectric.…”

“…Furthermore, micro-crack is highly suspected at the early stage of peeling failure, which is initiated at the many interfaces of metal layer and low-k dielectric. Hence, the targeted failure mode, which is brittle delamination, is related to fracture mechanics and specific energy based numeric tools are developed [18,19]. The so-called Nodal Released Energy (NRE) post processing procedure is based on the computation of energetic quantity from the nodal solution.…”

Package induced low-k delaminations: Numerical developments and experimental investigations to address FEBE compatibility fracture phenomena.

“…This method is quite attractive since both the nucleation and the propagation are included in the model. The second one has been in-house developed, the named Nodal Release Energy (NRE) method [9] (inspired from Area Release Energy technique [10]) has demonstrated its robustness and efficiency through similar applications [11][12]. However, since a virtual crack must be initially assumed, only propagation phenomenon is addressed by this method.…”

Study on failure mode and mechanism of bond pad under Cu ball bonding process using wire pull test and finite element modeling

“…However, failure criterion and failure mode are still unknown even wire bond induced stress can be monitored. Finite element analysis (FEA) of wire bonding can lead to the possibility for virtual experiment, leading to an improved knowledge of how parameters influence the bonding process and damage mechanisms [6][7][8][9].…”