大马士革铜互连线织构的研究

采用EBSD研究了不同线宽和退火前后Cu互连线的织构和晶界特征分布.Cu互连线均具有多重织构,其中(111)织构强度最高.沉积态样品在室温下发生了自退火现象,并出现了一些异常长大的晶粒.随高宽比降低和退火处理,Cu互连线晶粒尺寸变大,(111)织构得到加强,而具有较低应变程度的织构与(111)织构强度的比例下降.沉积态样品出现了(111)<112>和(111)<231>织构组分.退火后,出现了(111)<110>组分,而且(111)<112>和(111)<231>组分得到增强.Cu互连线以大角度晶界为主,其中具有55°～60°错配角的晶界和∑3晶界比例最高,35°～40°的错配角和∑9晶界次之.随高宽比增加和退火处理,∑3晶界比例逐渐升高,∑9晶界比例下降.     

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.     

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。     

低碳冲压钢板静态再结晶行为的研究

利用背散射电子衍射(EBSD)技术和X射线衍射(XRD)对SPCD冷轧钢板缓慢升温退火工艺下的再结晶取向特征、织构的形成规律及与形变织构的关系进行研究,并与快速加热退火工艺下的IF钢再结晶取向特点进行对比。结果表明:宏观织构显示冷轧态下{111}〈112〉形变织构稳定存在,随后的再结晶过程中γ线上存在{111}〈112〉与{111}〈110〉织构的竞争,其中再结晶初期{111}〈112〉织构占主导,后期{111}〈110〉吞食{112}〈110〉和{001}〈110〉织构进而取代{111}〈112〉作为γ线织构的主导取向;不同取向新晶粒具有不同的再结晶形核地点:{111}〈110〉新晶粒主要在{112}〈110〉和{111}〈112〉形变晶粒的晶界处形核;{111}〈112〉新晶粒主要在相同取向的形变晶粒内形核;而{110}〈001〉新晶粒主要在{111}〈112〉形变晶粒的形变带内形核。     

Cu互连线显微结构和应力的AFM及SNAM分析

在ULSI中采用Cu互连线代替Al以增加电子器件的传输速度和提高器件的可靠性，Cu的激活能约为1．2eV，而Al的激活能约为0．7eV,Cu互连线寿命约为Al的3－5倍。Cu大马士革互连线的制备工艺为：在硅衬底上热氧化生成的SiO2上开出凹槽，在凹槽中先后沉积阻挡层Ta和晶种层Cu，然后由电镀的Cu层将凹槽填满，最后采用化学机械抛光将凹槽外多余的Cu研磨掉，Cu互连线的尺寸为：200um长，0．5μm厚，宽度分别为0．35，0．5，1至3μm不等，部分样品分别在200℃，300℃和450℃下经过30min退火。利用原子力显微镜（AFM）和扫描近场声学显微镜（SNAM），同时获得形貌像和声像，分别了Cu大马士革凹槽构造引起的机械应力和沉积引起的热应力对Cu互连线显微结构及可靠性的影响，SNAM是在Topometrix公司AFM基础上建造的实验装置，实验采用的机械振动频率在600Hz-100kHz之间。分析测试结果如下：1．AFM和SNAM可以实现对微米和亚微米特征尺寸的Cu互连线的局域应力分布和显微结构的原位分析。2．采用AFM，TEM、XRD观察和测试了Cu互连线的晶体结构，分析了大马士革凹槽工艺 对Cu晶粒尺寸及取向的影响。平坦的沉积态Cu膜的晶粒尺寸约为100nm；而由大马士革工艺制备的凹槽中的Cu互连线的晶粒尺寸约为70－80nm，凹槽结构抑制了晶粒生长，平坦的沉积态Cu膜有较强的（111）织构；而凹槽中的Cu互连线的（111）织构减弱，（200）和其它的晶体取向分量增强。3．SNAM声阻尼信号对材料局域应力的变化敏感，SNAM声图衬底可显示出局域应力的分布，在沉积态的Cu互连线声图中，金属和SiO2介电层的界面处像衬度强，表明该处为应力较高的区域，而在退火后的Cu互连线的声图中，金属和SiO2介电层的界面处像衬度弱，表明退火后该处应力减小，我们对Cu膜进行了宏观应力的测试，退火后应力值从沉积态的661MPa减少至359Mpa，这与SNAM声成像的结果相符合。     

直流和脉冲电镀Cu互连线的性能比较

针对先进纳米Cu互连技术的要求,比较了直流和脉冲两种电镀条件下Cu互连线的性能以及电阻率、织构系数、晶粒大小和表面粗糙度的变化.实验结果表明,在相同电流密度条件下,脉冲电镀所得Cu镀层电阻率较低,表面粗糙度较小,表面晶粒尺寸和晶粒密度较大,而直流电镀所得镀层(111)晶面的择优程度优于脉冲.在超大规模集成电路Cu互连技术中,脉冲电镀将有良好的研究应用前景.     

Cu/Nb微观复合线材中Cu沿径向的织构研究

本文利用电子背散射衍射(EBSD)技术,对含不同铌芯丝数的Cu/Nb微观复合线材中的Cu沿径向的织构进行了表征。结果表明:复合线材在拉拔过程中,各层织构存在差异,织构种类由表及里减少,且主要向平行于拉拔方向的<111>丝织构聚集;对于复合不同道次的样品,在相同部位,变形量大的线材内部织构更集中于<111>织构组分。     

低碳冲压钢板静态再结晶行为的研究

利用背散射电子衍射(EBSD)技术和X射线衍射(XRD)对SPCD冷轧钢板缓慢升温退火工艺下的再结晶取向特征、织构的形成规律及与形变织构的关系进行研究,并与快速加热退火工艺下的IF钢再结晶取向特点进行对比.结果表明:宏观织构显示冷轧态下{111}〈112〉形变织构稳定存在,随后的再结晶过程中γ线上存在{111}〈112...     

退火温度对铝互连线热应力的影响

采用二维面探测器X射线衍射(XRD)测量1μm和0.5μm厚Al互连线退火前后的残余应力.沉积态Al线均为拉应力,且随膜厚的增加而减小.沿长度方向的应力明显高于宽度方向的应力,表面法线方向应力最小.250℃退火2.5h后,互连线在各方向上的应力都减弱,其中1μm Al线应力减弱幅度高于0.5μm互连线.采用电子背散射衍射(EBSD)方法,测量退火前后Al互连线(111),(100),(110)取向晶粒的IQ值.退火后平均IQ值提高,互连线残余内应力随之减小.EBSD分析结果与XRD应力测试结果相符合.     

退火温度对铝互连线热应力的影响

采用二维面探测器X射线衍射(XRD)测量1μm和0.5μm厚Al互连线退火前后的残余应力.沉积态Al线均为拉应力,且随膜厚的增加而减小.沿长度方向的应力明显高于宽度方向的应力,表面法线方向应力最小.250℃退火2.5h后,互连线在各方向上的应力都减弱,其中1μm Al线应力减弱幅度高于0.5μm互连线.采用电子背散射衍射(EBSD)方法,测量退火前后Al互连线(111),(100),(110)取向晶粒的IQ值.退火后平均IQ值提高,互连线残余内应力随之减小.EBSD分析结果与XRD应力测试结果相符合.     

Microstructure and reliability of copper interconnects

The effects of texture and grain structure on the electromigration lifetime of Cu interconnects are reported. Using different seed layers, (111)- and (200)-textured CVD Cu films with similar grain size distributions are obtained. The electromigration lifetime of (111) CVD Cu is about four times longer than that of (200) CVD Cu. For Damascene CVD Cu interconnects, the electromigration lifetime degrades for linewidths in the deep submicron range because the grains are confined as a result of conformal deposition in narrow trenches. In contrast, electroplated Cu has relatively larger grains in Damascene structure, resulting in longer electromigration lifetime than CVD Cu and no degradation for linewidths in the deep submicron range     

Influence of substrate on high-temperature behavior of copper film studied in situ by electron backscatter diffraction

Change in the in-plane orientation of (111) grains in the copper film was studied in situ by electron backscatter diffraction (EBSD) during its thermal treatment inside the scanning electron microscope (SEM). Two separate investigations were carried out each at different locations of the film. Both of the investigations showed the presence of (111) fiber texture with increased strengths of {111}〈112〉 and {111}〈110〉 orientations. During the first investigation, the {111}〈110〉 component became sharper relative to {111}〈112〉, while in the second investigation the sharpness decreased relative to {111} 〈112〉 with increasing temperature. No such changes in the in-plane orientation of the (111) grains were observed during the similar experiment carried out on the Cu film in freestanding condition. The role of silicon subtrate on influencing these changes has been proposed based on dislocation activity within the grains. The increase in the inclination of (111) planes to the specimen surface in {111}〈110〉 and {111}〈112〉 grains as a function of temperature was linked to the stress relaxation. The inclination of the (111) planes to the specimen surface leads to decrease in the sharpness of the (111) texture components. Finally, similar transformation in the texture of (111) grains in Cu damascene interconnects was investigated.     

Texture and electromigration lifetime improvements in layered Al-alloy metallization with underlying Ti by controlling water adsorption on SiO2 substrates

The effect of residual gas constituents and substrate temperature during Ti sputtering on the texture of TiN/Ti films deposited on SiO₂/Si substrates has been investigated. The Ti(002) and TiN(111) preferred texture of the films deposited at 350°C was found to be improved drastically by increasing the H₂O partial pressure from 1×10⁻⁹ to 3×10⁻⁸ Torr. Both of the Ti(002) and TiN(111) textures showed a similar H₂O partial pressure and substrate temperature dependence because of the epitaxial transfer between these planes. The improved Ti(002) texture was attributed to the self-assembly of Ti atoms on the SiO₂ surface, which had a low surface free energy due to the formation of surface OH groups. Two kinds of layered Al-alloy interconnects, AlSiCu/Ti/TiN/Ti and AlCu/TiN/Ti, were fabricated with the highly textured TiN/Ti film, and their Al(111) texture and electromigration lifetime were then evaluated. It was confirmed that both of the interconnects have strong Al(111) texture and longer EM lifetimes.     

Electromigration-Induced Plasticity: Texture Correlation and Implications for Reliability Assessment

Plastic behavior has previously been observed in metallic interconnects undergoing high-current-density electromigration (EM) loading. In this study of Cu interconnects, using the synchrotron technique of white-beam x-ray microdiffraction, we have further found preliminary evidence of a texture correlation. In lines with strong (111) textures, the extent of plastic deformation is found to be relatively large compared with that of weaker textures. We suggest that this strong (111) texture may lead to an extra path of mass transport in addition to the dominant interface diffusion in Cu EM. When this extra mass transport begins to affect the overall transport process, the effective diffusivity, D _eff, of the EM process is expected to deviate from that of interface diffusion only. This would have fundamental implications. We have some preliminary observations that this might be the case, and report its implications for EM lifetime assessment herein.     

Relationship between microstructure and electromigration damage in unpassivated PVD copper damascene interconnects

The microstructure of unpassivated PVD copper interconnects has been determined by electron backscatter diffraction technique (EBSD) inside a scanning electron microscope (SEM), and the appearance and growth of voids and hillocks during the electromigration testing has been observed in situ inside the SEM. The EBSD measurement indicates a strong <111 > texture for the tested line and a high angle boundary fraction of more than 70%. The comparison of the EBSD maps and the SEM images of the defect formation due to electromigration shows that the voids are formed mainly at the sidewall and after blocking grains. These images indicate that the diffusion paths are both the interface and the grain boundaries.     

Microstructural characterization of inlaid copper interconnect lines

The microstructure of inlaid Cu lines has been quantified as a function of annealing conditions, post-plating, and post-CMP. The grain size distribution was measured using the median intercept method, crystallographic texture was characterized by pole figure analysis, and mechanical stress was determined using x-ray diffraction. The median grain size and mechanical stress level increase with increasing anneal temperature. The crystallographic texture is independent of the anneal temperature and is predominantly (111) with a small fraction of sidewall-nucleated (111) grains. The (111) grains nucleated from the trench bottom have a preferred in-plane orientation. The grain growth in the trench is independent of that in the overburden.     

Texture investigation of copper interconnects with a different line width

To understand the effect of line width on textural and microstructural evolution of Cu damascene interconnect, three Cu interconnects samples with different line widths are investigated. According to x-ray diffraction (XRD) results, the (111) texture is developed in all investigated lines. Scattered {111}〈112〉 and {111}〈110〉 texture components are present in 0.18-μm-width interconnect lines, and the {111}〈110〉 texture was developed in 2-μm-width interconnect lines. The directional changes of the (111) plane orientation with increased line width were investigated by XRD. In addition, microstructure and grain-boundary character distribution (GBCD) of Cu interconnect were measured using electron backscattered diffraction (EBSD) techniques. This measurement demonstrated that a bamboo-like microstructure is developed in the narrow line, and a polygranular structure is developed in the wider line. The fraction of ∑3 boundaries is increased as the line width increases but is decreased in the blanket film. A new interpretation of textural evolution in damascene interconnect lines after annealing is suggested, based on the state of stress and growth mechanisms of Cu deposits.