Dynamic damage analysis of thin film stacked structures for microelectronic devices

Abstract

In the context of the megatrends of remote working, the development of artificial intelligence, and electric vehicle applications, there is a great demand for betterperforming and multi-functional integrated circuit (IC) chips to fill the technology gaps.Moreover, the demand for package minimization and rapid production of power electronic products have raised a serious concern about the robustness of thin-film stacked structures in the bond pad of IC chips, especially in the processes of wirebonding, wafer probing, and die ejection.Recently, hard copper (Cu) wires have been widely applied to replace traditional soft gold (Au) wires in the wire-bonding process. It is not only because the price of Cu wires is more competitive than that of Au wires, but also Cu wires possess superior electrical, mechanical, and thermal properties over Au wires. However, the dynamic contact between the Cu free air ball (FAB) and the bond pad surface leads to excessive deformation and thus significant damage or failure in the brittle substrate beneath the top metallization pad of IC chips. Moreover, the damaged sites are invisible, which makes it difficult to predict their occurrences. Hence, this research aims to study the dynamic deformation and damage behavior of the thin-film stacked structure during high strain-rate indentation loading through experimental, statistical, and analytical methods.First, a dynamic strain-rate (DSR) model has been developed for analyzing the dynamic response of a thin-film stacked structure consisting of a top metallization layer (copper-titanium CuTi) and an intermediate dielectric layer (silicon nitride Si3N4) on the Si substrate at varying loading rates. In the DSR model, the exponential indentation strain rate-time history is established by maintaining the constant ratio of the Abstract X instantaneous loading rate to load (Ṗ/P) in the indentation tests. The relationship between the indentation strain rate and indentation strain at different Ṗ/P was analyzed for characterizing the DSR model. The indentation stress-strain curves at different testing protocols were plotted to investigate the rate-dependent behaviors of the thinfilm stacked structure. Second, DSR indentation tests integrated with the acoustic emission (AE) sensingtechnique were conducted on a Si (100) wafer to investigate the phase transformation at low and high Ṗ/P. The occurrence of phase transformation was detected by an AE event and corresponds to an onset load. It was found that high Ṗ/P leads to a decrease in the phase transformation threshold, which could be attributed to an increase in the shear stress with increasing strain rates. The activation volume V* for the onset of phase transformation was determined based on two methods of the strain rate sensitivity and the nucleation theory-based model. Both analysis methods yield comparable V* and well proximate the size of the nucleated β-Sn phase, suggesting that the phase transformation is predominantly induced by shearing under the non-hydrostatic condition. Moreover, an incre...