MCM-D多层金属布线互连退化模式和机理

介绍了MCM-D多层金属互连结构的工艺及材料特点，并就Cu薄膜布线导体的结构特点和元素扩散特性。说明了多层布线互连退化的模式和机理，以及防止互连退化的技术措施，实验分析表明，Au/Ni/Cu薄膜布线结构的互连退化原因是，Cu元素沿导带缺陷向表层扩散后，被氧化腐蚀，导致互连电阻增大，而Cu元素在温度应力作用下向PI扩散，导致PI绝缘电阻下降。     

互连宽度对铜互连应力可靠性的影响

基于Cu的随动强化模型,用二维有限元分析方法,模拟分析了不同互连宽度对Cu互连热应力分布的影响。研究发现,当互连尺寸减小到一定宽度后,静水应力先减小,后略有增加;随线宽的减小,等效塑性应变的最大值逐渐减小,塑性应变最大值的位置由Cu互连上界面处转向Cu互连上界面边角处,而发生等效塑性应变的区域先减小后增加。讨论了在不同Cu互连结构条件下,应力状态和塑性应变对Cu互连可靠性的影响。     

菊花链Cu/Cu3Sn/Cu互连凸点电迁移仿真研究

多物理场耦合作用下产生的电迁移现象成为影响键合结构可靠性的关键问题。建立了菊花链键合封装结构的三维有限元模型,研究了电-热-力交互作用下键合结构的温度分布、电流密度分布及应力分布。发现在连接线与凸点相连的位置容易发生电流聚集效应,从而导致此处出现温度升高及热应力增大的现象。此外,仿真分析了2～12 mV输入电压和20～100μm凸点间距对键合结构的电迁移失效的影响。发现对于20μm间距的凸点,输入电压超过8 mV时会发生电迁移失效。对于间距超过40μm的凸点,输入电压超过4 mV时会发生电迁移失效。结果表明,20μm间距的凸点电迁移可靠性高,为凸点结构设计及电迁移的实验研究提供了参考。     

集成电路Cu互连线的XRD研究

对硫酸盐体系中电镀得到的Cu镀层,使用XBD研究不同电沉积条件、不同衬底和不同厚度镀层的织构情况和择优取向.对比了直流电镀和脉冲电镀在有添加剂和无添加剂条件下的织构情况.实验结果表明,对于在各种条件下获得的1 μm Cu镀层,均呈现(111)晶面择优,这样的镀层在集成电路Cu互连线中有较好的抗电迁移性能.     

45nm双大马士革Cu互连逆流电迁移双峰现象及改善

集成电路中金属连线的逆流电迁移(EM)的双峰失效现象在45 nm双大马士革低k材料铜布线工艺中变得尤为突出,介绍了由于空洞存在于连接电路导致电迁移的早期失效,总结出两个早期失效的主要原理:分别是空洞形成在通孔以及浅槽与通孔的斜面,这是由于淀积扩散阻挡层和铜工艺在上述两个地方存在弱点,越薄的扩散阻挡层厚度对EM越不利。因为偏薄的扩散阻挡层不利于阻挡铜扩散,尤其在通孔的侧壁和边角斜面,这样在测试电迁移的高温大电流下,铜在通孔侧壁和边角斜面处易扩散而形成空洞,最终导致芯片失效。实验表明可以通过优化双大马士革结构通孔以及浅槽与通孔的斜面的长宽比(AR)减少消除这些弱点。介质层(ILD)的厚度,浅槽的深度以及通孔的关键尺寸可以作为调节AR的主要方法。     

SiC MOSFET栅极电参数退化机理及耦合关系

栅极一直是SiC MOSFET可靠性研究的重点,栅极老化过程中电参数之间的耦合关系对栅极可靠性研究有至关重要的作用。为此,搭建了能够同时监测阈值电压和栅极漏电流的高温栅偏(HTGB)试验平台。研究了HTGB下阈值电压和漏电流的退化趋势和影响,基于氧化层注入电荷量深入分析了两者之间的耦合关系。结果表明,热应力对载流子隧穿影响较为明显,对陷阱捕获的载流子影响相对较小,而场强则对两者均具有显著的影响。此外,提出了减小阈值电压漂移对SiC MOSFET均流特性影响的方法,指出了栅极漏电流下降现象的本质是栅极陷阱充电,并给出了栅极老化过程中漏电流失效基准值选取的方法。该研究结果为深入理解SiC MOSFET的栅极失效机理提供了理论指导。     

蓝色荧光粉的退化机理

ＰＤＰ中的蓝色荧光粉是ＢＡＭ单相和Ｂａ－β氧化铝的混合体。蓝色荧光粉的退化主要是位移氧附近的深能态电子陷阱。这种电子陷阱增加了非辐射发射,退化了发光强度维持系数。用大上离子像Ｓｒ＾２＋、Ｅｕ＾２＋来代替Ｂａ＾２＋离子,可以使发光亮度维持系数显著改进。     

铜互连电迁移可靠性的研究进展

综述了近年来铜互连电迁移可靠性的研究进展;讨论了电迁移的基本原理、常用研究方法及主要失效机制;探讨了改善铜互连电迁移性能的各种方法,如铜合金、增加金属覆盖层及等离子体表面处理。最后,指出了铜互连可靠性研究中存在的问题。     

ULSI Cu互连CoSiN扩散阻挡薄膜的研究

CoSiN薄膜可以作为超大规模集成电路Cu布线互连材料使用。利用磁控溅射技术制备了CoSiN/Cu/CoSiN/SiO2/Si薄膜,利用四探针测试仪、薄膜测厚仪、原子力显微镜、X射线光电子能谱仪等来检测多层膜电阻率、薄膜厚度、表面形貌、元素含量及价态等。考察亚45 nm级工艺条件下CoSiN薄膜对Cu的扩散阻挡性能。实验结果表明,在氩气气氛条件下经500℃,30 min热退火处理后多层膜的电阻率和成分没有发生明显变化,CoSiN薄膜能够保持良好的铜扩散阻挡性能;经600℃,30 min热退火处理后,Cu大量出现在表面,CoSiN薄膜对Cu失去扩散阻挡性能。     

制备Cu互连悬空结构的新型工艺研究

为了降低集成电路中的互连延迟,采取了一种新型的集成电路Cu互连工艺,以掩膜电镀的方法制备Cu互连的叠层结构,借鉴MEMS工艺的牺牲层技术,用浓磷酸对Al2O3牺牲层进行湿法刻蚀,不仅在互连金属间介质层而且在层内介质层都形成了以空气为介质的Cu互连悬空结构.用一种叉指测试结构对以空气和聚酰亚胺为介质的互连性能进行了比较,结果表明,采用空气介质减小了互连线耦合电容,为进一步降低集成电路的互连延迟提供了途径.     

Electromigration Failure Mechanism in Sn-Cu Solder Alloys with OSP Cu Surface Finish

Organic solderable preservative (OSP) has been adopted as the Cu substrate surface finish in flip-chip solder joints for many years. In this study, the electromigration behavior of lead-free Sn-Cu solder alloys with thin-film under bump metallization and OSP surface finish was investigated. The results showed that severe damage occurred on the substrate side (cathode side), whereas the damage on the chip side (cathode side) was not severe. The damage on the substrate side included void formation, copper dissolution, and formation of intermetallic compounds (IMCs). The OSP Cu interface on the substrate side became the weakest point in the solder joint even when thin-film metallization was used on the chip side. Three-dimensional simulations were employed to investigate the current density distribution in the area between the OSP Cu surface finish and the solder. The results indicated that the current density was higher along the periphery of the bonding area between the solder and the Cu pad, consistent with the area of IMC and void formation in our experimental results.     

Electromigration properties of electroless plated Cu metallization

The electromigration properties of electroless plated copper films have been evaluated under DC stress conditions. The formation of microvoids and the diffusion of copper through the seed layer caused an increase of the line resistance in the initial stage of the stressing. The current density dependence and the activation energy of the lifetime were determined     

Electromigration studies on Sn(Cu) alloy lines

The Cu alloying effect in the Sn(Cu) solder line has been studied. The Sn0.7Cu solder line has the most serious electromigration (EM) damage compared to pure Sn and Sn3.0Cu solder lines. The dominant factor for the fast EM rate in Sn0.7Cu could be attributed to the relatively small grain size and the low critical stress, i.e., the yielding stress of the Sn0.7Cu solder line. Also, we found that the shortest Sn0.7Cu solder line, 250 μm, has the most serious EM damage among three solder lines of different lengths. The back stress induced by EM might not play a significant role on the EM test of long solder lines. A new failure mode of EM test was observed; EM under an external tensile stress. The external stress is superimposed on the stress profile induced by EM. As a result, the hillock formation was retarded at the anode side, and void formation was enhanced at the cathode.     

互连铝通孔电迁移特征及其可靠性研究

研究了超大规模集成电路铝互连系统中铝通孔的电迁移失效机理及其可靠性寿命评价技术.试验采用CMOS和BiCMOS两种工艺各3组的铝通孔样品,分别在三个温度、恒定电流的加速条件下试验,以通孔开路为电迁移失效判据,最后得到了在加速条件下互连铝通孔的电迁移寿命,其结果符合标准的威布尔分布,试验准确可行.通过电迁移模型对试验数据进行了拟合,得到了激活能、电流加速因子和温度加速因子,计算出了正常工作条件下通孔电迁移的寿命,完成了对铝通孔电迁移的研究和寿命评价.     

磁控溅射的TaN薄膜的扩散阻挡性能

用反应磁控溅射方法在SiO2/Si(100)衬底和Cu薄膜间溅射一层TaN阻挡层,测试不同N气分压及热处理温度下Cu/TaN/SiO2/Si薄膜的显微结构和电阻特性.同时利用微细加工技术加工了镂空的Cu互连叉指测试结构,研究了TaN薄膜在镂空的铜互连结构中的扩散阻挡性能.结果发现,在退火温度不超过400 ℃时,薄膜电阻率均低于80μΩ·cm,而当溅射N分压超过10%,退火温度超过400℃时,薄膜电阻率很快上升.低N气分压下(≤10%)溅射时,即使退火温度达到600 ℃,薄膜电阻基本不变.     

Electromigration of Cu/low dielectric constant interconnects

Electromigration in damascene Cu/low dielectric constant interconnects with overlayers of CoWP, Ta/TaN, SiN_x or SiC_xN_yH_z and Cu(Ti) interconnects capped with SiN_x was studied. The results showed that the migration fast path in the bamboo-like lines primarily occurred at the interface. Cu lines fabricated with various forms of TaN/Ta liner including PVD TaN, ALD TaN, and PVD body centered cubic α- or tetragonal β-Ta liners were also investigated. Both thin surface layers of CoWP or Ta/TaN and the addition of Ti in the Cu lines significantly reduced the Cu/cap interface diffusivity and remarkably improved the electromigration lifetime when compared with Cu lines capped with SiN_x or SiC_xN_yH_z. Activation energies for electromigration were found to be 1.9–2.4 eV, 1.4 eV, 0.85–1.1 eV, and 1.3 eV for the bamboo-like Cu lines capped with CoWP, Ta/TaN, and SiN_x or SiC_xN_yH_z, and Cu(Ti) bamboo lines capped with SiN_x, respectively. The structural phase of the Ta was found to have an insignificant effect on the Cu mass flow rate. A large via size, thicker liner and/or stable connected exposed liner can provide a longer lifetime and tighter lifetime distribution, at the expense of chip density or effective Cu line conductivity.     

基于弹性分组环的多环互联研究

现有的弹性分组环协议无法实现多环互联。提出了一种基于弹性分组环多环互联的数据转发和自动拓扑发现的实现方案,该方案充分利用弹性分组环协议草案中的扩展帧格式,采用类似多协议标签交换(MPLS)的一次路由、多次交换的思想,实现了跨环数据在多环互联弹性分组环中的高速传输,并且与现有的RPR协议之间有着良好的兼容性。     

Cu互连及其关键工艺技术研究现状

低介电常数材料和低电阻率金属的使用可以有效地降低互连线引起的延时.Cu因其具有比Al及Al合金更低的电阻率和更高的抗电迁移能力而成为新一代互连材料.论述了Cu互连技术的工艺过程及其研究发展现状.对Cu互连技术中的阻挡层材料、电化学镀Cu技术以及化学机械抛光技术等一系列关键工艺技术进行系统的分析和讨论.     

Discussion on the Mechanism of Electromigration from the Perspective of Electromagnetism

The mechanism of electromigration is discussed from the perspective of electromagnetism, rather than from the traditional view of momentum exchange owing to collisions between electrons and diffusing ions. It is suggested that, from the perspective of conservation of momentum, the momentum transferred to the diffusing ions is related to the Maxwell stress, and the effective charge is proportional to the density of the net charge within the volume element. It is also suggested that, from Poynting’s theorem, the energy associated with electromigration is related to the work done by the electric field, and the conversion of the nonelectrostatic energy from the electric power source into the chemical energy of the diffusion system. From both perspectives, the effective driving force can be shown to have a square dependence on the current density. Therefore, it is suggested that the effective charge number is linearly related to the current density.