ULSI中Cu互连线的显微结构及可靠性

观察了ULSI中大马士革结构的Cu互连线的晶粒生长和晶体学取向.分析了线宽及退火对Cu互连线显微结构及电徙动的影响.Cu互连线的晶粒尺寸随着线宽的变窄而减小.与平坦Cu膜相比,Cu互连线形成微小的晶粒和较弱的 (111) 织构.300℃、30min退火促使Cu互连线的晶粒长大、(111) 织构发展,从而提高了Cu互连线抗电徙动的能力.结果表明,Cu的扩散涉及晶界扩散与界面扩散,而对于较窄线宽的Cu互连线,界面扩散成为Cu互连线电徙动失效的主要扩散途径.     

铜互连线静水应力的有限元模拟

本文根据工业上使用的铜大马士革互连线尺寸建立了三维有限元模型,模拟计算了铜大马士革互连线中对应力诱导形成空洞很关键的静水应力分布,对比分析了不同低k介质、阻挡层材料和互连线深宽比对静水应力的影响。研究结果表明,静水应力受k介质、阻挡层材料和互连线深宽比影响很大,静水应力在铜大马士革互连线中分布不均匀且最大应力出现在互连线表面。     

集成电路铜互连线及相关问题的研究

论述了Cu作为互连金属的优点、面临的主要问题及解决方案,介绍了制备Cu互连线的双镶嵌工艺及相关工艺问题,讨论了Cu阻挡层材料的作用及选取原则,对低k材料的研究的进展情况也了简要的介绍。     

AFM加工的Ti纳米氧化钛线的直线度分析

为了与微电子加工工艺相结合,基于Ti氧化线的纳米电子和光电器件需要加工μm级长的Ti氧化线。Ti氧化线的直线度决定了加工的纳米器件的形状,从而影响纳米器件的工作特性。在偏置电压8 V、扫描速度0.1μm/s的条件下,在7μm×7μm的范围内从左到右每隔1μm加工了6条5μm长的Ti纳米氧化线,研究了针尖磨损和压电陶瓷扫描器等因素对加工的Ti氧化线的直线度的影响,原子力显微镜(AFM)扫描范围的中间位置加工的Ti氧化线的高度和宽度的一致性与直线度最好。     

纳米材料的几种扫描探针显微表征方法

扫描探针显微镜（SPM）作为一种广泛应用的表面表征工具,不仅可以表征三维形貌,还能定量地研究表面的粗糙度、孔径大小和分布及颗粒尺寸,在许多学科均可发挥作用.以纳米材料为主要研究对象,综述了国外最新的几种扫描探针显微表征技术,包括扫描隧道显微镜（STM）、原子力显微镜（AFM）和近场扫描光学显微镜（SNOM）等方法,展示了这几种技术在纳米材料的结构和性能方面的应用.     

互连线和CMOS模型对性能影响的分析

在集成电路中,全局互连线的设计是关键.分析了互连线RC和RLC模型的不同特性;针对互连线与CMOS器件级联的电路进行分析.分析了集成电路中互连线和CMOS的模型对性能的影响,并给出了基于HSPICE软件的仿真结果.仿真结果表明,不同互连线和CMOS模型对系统传输特性有一定影响.     

大马士革镶嵌结构对Cu膜微结构及应力的影响

通过TEM、SEM、XRD和EBSD,观察了Cu互连线和平坦Cu膜的微观结构。采用薄膜应力测试分布仪和二维面探测器XRD,测量了平坦Cu膜和Cu互连线的应力,计算了Cu薄膜热应力的理论值。凹槽侧壁成为互连线新的形核区域,并且在平行于侧壁的方向形成较弱的(111)织构。与平坦膜相比,互连线晶粒尺寸明显变小(、111)织构较弱,且存在大量Σ3和Σ9晶界。平坦膜和互连线分别表现出压应力和张应力。降温过程产生的热应力为互连线的主要应力。     

有机／无机光电探测器的AFM和XPS分析

采用真空蒸发沉积，在室温下制备了PTCDA／p—Si有机／无机异质结样品。对其表面用原子力显微镜(AFM)研究表明，PTCDA薄膜具有岛状形态结构。经X光电子能谱(XPS)分析表明，在PTCDA分子中，C原子有两种束缚能态，其结合能力分别为285．3eV和288．7eV；O原子与C原子相邻，一些O原子通过双键与C原子相结合，另外的O原子则通过单键与2个C原子相结合。经Ar^ 束溅射研究界面电子状态表明，随溅射时间增加，C1s和O1s峰逐渐减弱，而Si 2p和Si 2s峰渐渐增强。C1s和Si 2p谱峰随着溅射时间的增加而逐渐向低束缚能力方向移动。由于荷电效应和碳硅氧烷(C—Si—O)及SiO2的存在，Ols谱峰随溅射时间的增加先向高束缚能方向移动，然后向低束缚能方向移动。     

扫描近场声显微镜用于光盘表面薄膜结构的研究

介绍了一种将超声检测技术与扫描探针显微技术相结合的扫描近场声显微镜（SNAM）,并利用该装置对CD—R光盘表面薄膜进行了检测,得到了其平整印刷面的SNAM图像,与原子力显微镜（AFM）测得的凹槽数据面形貌吻合。文中介绍了这种SNAM的结构、基本工作原理和检测方法,并给出了具体的实验结果。     

Textural and microstructural transformation of Cu damascene interconnects after annealing

Influence of annealing on the textural and microstructural transformation of Cu interconnects having various line widths is investigated. Two types of annealing steps have been considered here: room temperature over 6 months and 200°C for 10 min. The texture was determined by x-ray diffraction (XRD) of various cross-sectional profiles after electropolishing, and the surface, microstructure, and grain boundary character distribution (GBCD) of Cu interconnects were characterized using electron backscattered diffraction (EBSD) techniques. In order to analyze a relationship between the stress distribution and textural evolution in the samples, microstresses were calculated with decreasing line widths at 200°C using finite element modeling (FEM). In this investigation, it was found that the inhomogeneity of stress distribution in Cu interconnects is an important factor, which is necessary for understanding textural transformation after annealing. A new interpretation of textural evolution in damascene interconnects lines after annealing is suggested, based on the state of stress and the growth mechanisms of Cu electrodeposits.     

Three-dimensional simulation of microstructure evolution in damascene interconnects: Effect of overburden thickness

Microstructure in the damascene interconnects evolves with the overburden layer, an excessive metal layer over trenches. We present the results of three-dimensional simulation, which show the effects of overburden thickness on microstructure evolution in a trench. When the thickness of the overburden is less than half of the trench depth, for a trench with the aspect ratio of unity, the microstructure in the trench tends to evolve into a bamboo structure. This effect is discussed in terms of grain sizes in the trench and those in the overburden. The thinner overburden layer would have smaller grains, of which growth is limited by its thickness. Such small-sized grains in the overburden are not likely to grow into the trench, which hardly make grain boundaries in the trench. Meanwhile, the grains from the trench are able to continue growth inside the trench, resulting in a bamboo structure. Overburden thickness affects the reliability and the electrical performance of the damascene copper interconnects. Optimization of overburden thickness is required to minimize these effects.     

Damageless Cu chemical mechanical polishing for porous SiOC/Cu interconnects

Both chemical and mechanical damages to porous SiOC film should be minimized in the Cu-CMP (chemical mechanical polishing) process for the 32-45 nm node Cu interconnect process. This paper first discusses chemical damage that occurs during direct CMP on a porous SiOC film. We found that the k-value increase after direct CMP was caused by the surfactants added to the cleaning chemicals to suppress watermark generation on the hydrophobic SiOC film surface. The surfactants assisted water molecule diffusion into the pores by improving the wettability of the film surface. N₂ annealing after direct CMP removed moisture inside the pores and restored the k-value increase. Second, the paper discusses low-pressure electro-CMP (e-CMP) technology that we developed to reduce mechanical stress on the porous SiOC film. A high removal rate and good planarization performance were obtained by optimizing the cathode area of the electro-cell and carbon material of the e-CMP pad.     

Residual stress estimation in damascene copper interconnects using embedded sensors

Mechanical stress in damascene copper/low-k interconnects has been studied by means of micro-rotating sensors embedded in chips and directly integrated in CMOS process flow. A new hinge sensor design has been elaborated and a new analytical model of the mechanical equilibrium of sensors is validated. These sensors allow the study of the average residual stress as a function of the line width in a range from few hundred nanometers to several microns. It was found that the residual stress increases from 290 to 850 MPa in, respectively, 2 and 0.25 μm wide lines. This trend shows a yield stress increase with the line width reduction. Copper grains microstructure change between large and narrow lines is probably one of the reasons for yield stress and so residual stress increase. This microstructure change has been observed by means of Transmission Electron Microscopy (TEM) observations.     

Grain morphology of Cu damascene lines

The evolution of the grain structure through annealing of narrow damascene Cu interconnects is important for any further design of highly integrated circuits. Here we present a comprehensive transmission electron microscopy study of damascene lines between 80 nm and 3000 nm wide. Experimental results clearly indicate that morphology evolutions through annealing are strongly influenced by the line width. If the lines are wider than 250 nm a strong connection between the grain structure within the lines and the overburden copper is present at least after sufficient annealing. Once the lines are as small as 80 nm the grain structure within the lines are only weakly connected to the overburden copper grown above.     

高透过率、高分辨率纳米微探针的制备

介绍了一种用于近场扫描光学显微镜(SNOM)中的高透过率光纤探针的制作方法。采用氢氟酸腐蚀低掺杂的普通单模石英光纤,选取适当比例的腐蚀液,并通过激光消融的方法得到直径、圆锥角均十分理想、表面光滑的针尖,所获探针直径变化范围为80～200nm,锥度40°～81°,透过率3.5×10-3。     

Relationship between grain structures and texture of damascene Cu lines

The anisotropic spread of the central peak in a (111) pole figure by x-ray diffraction (XRD) was observed for damascene Cu lines of 0.18–2 μm in width and 0.5 μm in depth. The spread originates from the existence of slightly tilted (111) grains because of inclined sidewalls. The tilted (111) orientation is favorable only for polygranular clusters whose sidewall energies can be minimized simultaneously. Consequently, bamboo grains have an exact 〈111〉 orientation, while the polygranular clusters have a tilted 〈111〉 orientation. Using this concept, the volume fraction of the bamboo grains and polygranular clusters in the damascene Cu lines were quantified using the XRD pole plots.     

Thermomechanical response and stress analysis of copper interconnects

This study is devoted to thermomechanical response and modeling of copper thin films and interconnects. The constitutive behavior of encapsulated copper film is first studied by fitting the experimentally measured stress-temperature curves during thermal cycling. Significant strain hardening is found to exist. Within the continuum plasticity framework, the measured stress-temperature response can only be described with a kinematic hardening model. The constitutive model is subsequently used for numerical thermomechanical modeling of Cu interconnect structures using the finite element method. The numerical analysis uses the generalized plane strain model for simulating long metal lines embedded within the dielectric above a silicon substrate. Various combinations of oxide and polymer-based low-k dielectric schemes, with and without thin barrier layers surrounding the Cu line, are considered. Attention is devoted to the thermal stress and strain fields and their dependency on material properties, geometry, and modeling details. Salient features are compared with those in traditional aluminum interconnects. Practical implications in the reliability issues for modern copper/low-k dielectric interconnect systems are discussed.     

Nanotwin formation and its physical properties and effect on reliability of copper interconnects

Ultra-fine grained copper with a large amount of nano-scale twin boundaries has high mechanical strength and maintains normal electrical conductivity. The combination of these properties may lead to promising applications in future Si microelectronic technology, especially as interconnect material for air-gap and free-standing copper technologies. Based on first principles calculations of total energy and in-situ stress measurements, high stress followed by stress relaxation during the Cu film deposition seems to have contributed to nanotwin formation. Nanoindentation studies have shown a larger hardness for copper with a higher nanotwin density. The effect of Cu nanotwin boundaries on grain growth was investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The presence of a high density of nanotwin boundaries may improve the reliability of Cu interconnects.