Investigation on Resistance Oscillation Induced by Direct Current Electromigration

在铝互连的直流电迁移测试中，经常观察到电阻的突变（acr），如阶跃和振荡。acr的互连宽度与平均Al晶粒尺寸相当。对这些电阻振荡进行了集中的研究，发现电阻振荡有两种类型：向下尖峰和向上尖峰。这些尖峰进一步分为准周期尖峰和随机尖峰。对电流密度依赖性、局部性和非局部性的研究强烈表明，向上和向下的峰值的起源有很大的不同。向下的尖峰是发生在几μ m范围内的局部现象，向上的尖峰是发生在几千μ m以上范围内的非局部现象。向下的尖峰的频率随着电流密度的增加而急剧增加，而向上的尖峰的幅度则急剧增加。向下的尖峰极有可能对应于湮灭和单一空洞形成的交替，基于高电阻区域（如空位簇）周围电流迂回效应的模型很好地解释了频率对电流密度的依赖。向上尖峰的机制仍有待澄清，然而，一种可能的机制可能与由于位错动力学（如爬升、产生和湮灭）引起的互连应力脉动有关。

Abrupt changes in resistance (ACRs) such as steps and oscillations are frequently observed during DC electromigration testing of Al interconnections. ACRs are observed in a interconnection which width is as large as the mean Al grain size. In vestigations are concectrated to these resistance oscillations, and it is revealed that there are two types in resistance oscillations : downward spikes and upward spikes. These spikes are further classified into quasi-periodic ones and random ones. Investigations on the current density dependence and locality and non-locality strongly suggest that origines of the upward spikes and the downward spikes are quite different. The downward spikes are local phenomena which occur within a range of several mu m, while the upward spikes are non-local phenomena which occurs in a range extending to more than several thousands mu m. A frequency of the downward spikes drastically increases with an increase in the current density, on the other hand, an amplitude increased drastically in the case of the upward spikes. It is most likely that the downward spikes correspond to the alternation of annihilation and formation of a single void, and a modeling based on the current detour effect around a high-resistance region such as a vacancy cluster well explains the current density dependence of the frequency. The mechanisms of the upward spikes are remained to be clarified, however, one possible mechanism may relate to pulsating of stress of the interconnection due to dislocation dynamics such as climb, generation and aninhilation.