Barrier layer effect of tantalum on the electromigration in sputtered copper films on hydrogen silsesguioxane and SiO2

As IC devices scale down to the submicron level, the resistance-capacitance (RC) time delays are the limitation to circuit speed. A solution is to use low dielectric constant materials and low resistivity materials. In this work, the influence of underlying barrier Ta on the electromigration (EM) of Cu on hydrogen silsesquioxane (HSQ) and SiO₂ substrates was investigated. The presence of a Ta barrier not only improves the adhesion between Cu and dielectrics, but also enhances the crystallinity of Cu film and improves the Cu electromigration resistance. The activation energy obtained suggests a grain boundary migration mechanism and the current exponent calculated indicates the Joule heating effect.     

A microprocessor based autoscanner for electromigration studies in thin films

Mass transport due to electromigration can be estimated if the diffusion coefficientD and the electromigration effective charge numberZ* are known. Neutron activated tracer scanning method determine the radioactivity at different positions. An automatic scanning system for determining the radioactive concentration profiles developed using a microprocessor is described in this paper. Using the radioactive concentration profiles the electromigration shift is determined. From this shift the electromigration effective charge numberZ* is calculated. The system developed was tested for tin thin films.     

Electromigration effects in aluminum alloy metallization

An investigation of electromigration-induced failure in aluminum alloy films, with the major emphasis on aluminum-copper-silicon, was conducted. Flash evaporation was utilized for alloy deposition and yielded aluminum-copper films having electromigration resistance comparable to that of such films prepared by other techniques. Results for aluminum-copper-silicon and aluminum-copper were similar indicating the passive role of silicon in the presence of copper. Additions of four weight percent copper resulted in near-optimum electromigration resistance. In addition, hot-substrate deposition was beneficial in attaining greater lifetime. For films deposited on unheated substrates, or having lower copper contents, heat treatment seriously degraded electromigration resistance. Heat treatment effects were considered to be a consequence of copper redistribution. Lifetime decrease at large copper contents and possible saturation at large thicknesses were interpreted in terms of clustering of CuAl₂ precipitates. The superior reliability of copper-alloyed metallization when compared with aluminum or aluminum-silicon was clearly demonstrated. Lifetime improvement could be accounted for by the increased activation energy for the failure process in the aluminum-copper alloys.     

深亚微米SoC中的电源/地网络设计

随着芯片集成度的不断提高,其上所消耗的功率也在不断增加,因此,电源/地网络设计的可靠性与有效性就成为了SoC设计中一个关键性的问题.以往的设计中,通常都是由设计师根据经验进行电源/地网络的设计,因而可能导致设计效率的降低,延长了芯片的上市时间.针对这个问题,本文首先介绍了IR压降和电迁移现象的产生原因及其影响因素.其次,提出了一种方法,在芯片物理设计的初始阶段,就对其电源/地网络进行可靠的估算,并在估算的基础上进行电源/地网络的设计,从而在设计的早期确保了电源分配的可靠性,提高了设计效率.最后,本文通过一个DSP＆CPU芯片的设计实例,介绍了该方法的使用,并获得了良好的效果.     

铝互连线的电迁移问题及超深亚微米技术下的挑战

铝互连线的电迁移问题历来是微电子产业的研究热点，其面临的电迁移可靠性挑战也是芯片制造业最持久和最重要的挑战之一.从20世纪90年代开始，超深亚微米(特征尺寸≤0.18 μm)铝互连技术面临了更加复杂的电迁移可靠性问题.从电迁移理论出发，分析概括了铝互连电迁移问题的研究方法，总结了上世纪至今关于铝互连电迁移问题的主要经验；最后结合已知的结论和目前芯片制造业现状，分析了当前超深亚微米铝互连线电迁移可靠性挑战的原因和表现形式，提出了解决这些问题的总方向. 关键词： 电迁移 铝互连 微结构     

Microstructural effects on the 1/f α noise of thin aluminum based films

The 1 /f^α noise was measured on a variety of Al-based thin metal films with widely varying microstructure using an ac bridge technique. The magnitude of the current noise in response to a small, non-destructive ac signal was found to vary several orders of magnitude between 0.01 and 10 Hz and was correlated to the microstructural differ-ences of the films. These differences have a strong affect on film lifetimes as measured in an accelerated electromigration test. Variation in microstructure was accomplished by different deposition temperatures and annealing parameters, and verified using TEM micrographs. Following fabrication, the current noise magnitude was measured and found to be sensitive to film width and grain size. The use of this technique to discriminate differences in film microstructure is discussed along with the correlations between ex-cess noise and the quality of the thin film as a metallic interconnection.     

电迁移致SnAgCu微焊点强度退化及尺寸效应研究

在100℃温度下,对直径为300μm、高度为100,200和300μm的Sn-3.0Ag-0.5Cu钎料微焊点施加密度为1×104A/cm2的直流电流。通电48h后,利用DMA对电迁移作用后微焊点拉伸强度的变化进行了研究。结果表明,电迁移作用导致微焊点拉伸强度明显退化,且退化程度随微焊点高度的减小而减弱。其中,高度为300μm的微焊点的平均拉伸强度由初始态的44.4MPa降至27.8MPa,下降了37.4%。电迁移还导致微焊点的断裂由延性变为延性与脆性相结合的模式。     

焦耳热作用下共晶锡铋焊点电迁移特性

电迁移可以引发芯片内部互连金属引线(单一元素)中的原子或离子沿电子运动方向移动.但是,在共晶锡铋焊点中,组成的元素为锡和铋而非单一元素.由于铋原子和锡原子在高电流密度下具有不同的迁移速率,因此共晶锡铋钎料具有独特的电迁移特性.实验中采用的电流密度为104A/cm2,同时焦耳热会引发焊点温度从25升高至49℃,富铋相在此温度下会发生明显粗化,除此之外,铋原子会首先到达正极界面处并形成坚硬的阻挡层,使得锡原子的定向运动受到阻碍,最终,富锡相会,凸起,其与负极界面问会有凹谷形成.     

The microstructure,mechanical stress,texture, and electromigration behavior of Al-Pd alloys

As the minimum feature size of interconnect lines decreases below 0.5 urn, the need to control the line microstructure becomes increasingly important. The alloy content, deposition process, fabrication method, and thermal history all determine the microstructure of an interconnect, which, in turn, affects its performance and reliability. The motivation for this work was to characterize the microstructure of various sputtered Al-Pd alloys (Al-0.3wt.%Pd, Al-2Cu-0.3Pd, and Al-0.3Nb-0.3Pd) vs sputtered Al-Cu control samples (Al-0.5Cu and Al-2Cu) and to assess the role of grain size, mechanical stress, and crystallographic texture on the electromigration behavior of submicrometer wide lines. The grain size, mechanical stress, and texture of blanket films were measured as a function of annealing. The as-deposited film stress was tensile and followed a similar stress history on heating for all of the films; on cooling, however, significant differences were observed between the Al-Pd and Al-Cu films in the shape of their stress-temperature-curves. A strong (111) crystallographic texture was typically found for Al-Cu films deposited on SiO₂. A stronger (111) texture resulted when Al-Cu was deposited on 25 nm titanium. Al-0.3Pd films, however, exhibited either a weak (111) or (220) texture when deposited on SiO₂, which reverted to a strong (111) texture when deposited on 25 nm titanium. The electromigration lifetimes of passivated, ≈0.7 μm wide lines at 250°C and 2.5 × 10⁶ A/cm² for both single and multi-level samples (separated with W studs) are reported. The electromigration behavior of Al-0.3Pd was found to be less dependent on film microstructure than on the annealing atmosphere used, i.e. forming gas (90% N₂-10%H₂) annealed Al-0.3Pd films were superior to all of the alloys investigated, while annealing in only N₂ resulted in poor lifetimes.