Cu/Ta/SiO_2/Si多层结构的纳米压痕研究

利用磁控溅射方法在Si衬底上沉积钽层以及铜层,并利用纳米压痕技术对Cu/Ta/SiO_2/Si多层膜结构进行了硬度和弹性模量的表征,研究发现多层膜结构的硬度随着薄膜厚度的增加而降低,然而弹性模量与膜厚之间并没有这样的关系。利用聚焦离子束（FIB）工艺将纳米压痕区域剖开,并通过透射电子显微镜（TEM）表征发现在纳米压痕过后,钽以及二氧化硅界面有了明显的分层现象,这一点表明层与层之间较弱的键合在相对大的负荷下遭到了破坏。     

电流密度对电-热耦合下微焊点界面形貌的影响北大核心CSCD

针对电子封装器件中Cu/焊料/Ni焊点结构的电-热耦合效应问题,通过回流焊工艺制备Cu/Sn3.0Ag0.5Cu-0.01BP/Ni微焊点,在焊点电-热耦合实验平台上进行了四种电流密度下的热电应力实验。采用SEM和EDS研究了电流密度对电-热耦合下微焊点界面形貌的影响,探讨了阴极和阳极两侧电迁移行为以及IMC层生长机制。结果表明,当电子从阴极Cu端流向阳极Ni端时,在电子流的作用下Cu原子的移动速度加快,并阻碍阳极界面Ni原子流向Cu端。单纯热时效状态下,阳极和阴极界面厚度增长缓慢,而高电流密度下则快速增厚。无电流时,阳极端生成(Cu_(x),Ni_(y))_(6)Sn_(5)的驱动力来源于Cu、Ni两端之间的温度梯度和浓度梯度;当电-热耦合产生效应时,相对于温度梯度和浓度梯度,电流应力逐步起主导作用,改变了阴极和阳极界面IMC层的主生长机制。     

MEMS多层结构的热应力分析

温度载荷能够引起MEMS多层薄膜结构发生翘曲和分层等失效模式,而界面应力则是引起这些失效的直接原因。根据Suhir.E的双金属带热应力分布理论,对温度载荷作用下MEMS界面中的剪应力和剥离应力的分析表明,这两种应力随着与界面中心距离的增大呈指数增加,在界面端处达到最大值。界面应力与材料热膨胀系数和所加载温度呈线性相关,另外还与两材料层的厚度密切相关。以铜/铬组成的双层结构为例,利用Matlab数值仿真研究了界面应力与材料层厚度的关系,结果表明,界面应力与两材料层厚度比有关,当铜层和铬层厚度比为1.5时,层间剪应力和剥离应力均较小,可有效提高MEMS结构的可靠性,降低分层失效的概率。     

Cu/Ta/SiO_2/Si多层膜纳米压痕与压痕下微观结构的研究

Cu/Ta/SiO2/Si多层膜结构是目前集成电路制造工艺中的常见结构,其硬度与弹性模量通过纳米压入技术测得。为了表征纳米压痕下的形变微观区域,采用聚焦离子束加工出压痕截面,同时进行扫描电子、扫描离子显微观察,发现样品衬底发生开裂,多层膜结构出现分层现象。TEM分析表明分层出现在Ta/SiO2界面,说明这是该结构的一个薄弱环节。     

Cu/Ta/SiO2/Si多层膜纳米压痕下微观结构的研究

Cu/Ta/SiO2/Si多层膜结构是目前集成电路制造工艺中的常见结构,其硬度与弹性模量通过纳米压入技术测得.为了表征纳米压痕下的形变微观区域,采用聚焦离子束加工出压痕截面,同时进行扫描电子、扫描离子显微观察,发现样品衬底发生开裂,多层膜结构出现分层现象.TEM分析表明分层出现在Ta/SiO2界面,说明这是该结构的一个薄弱环节.     

激光沉积制备SiCp/Cu梯度涂层残余应力分析

利用ANSYS有限元软件对激光沉积过程中Si Cp/Cu梯度涂层的残余应力进行数值模拟。建立该梯度涂层的有限元分析模型,探讨梯度分布因子和涂层单层层厚对Si Cp/Cu梯度涂层残余应力的影响。结果表明:较大的残余应力主要分布在梯度涂层与基体的界面边缘位置;当梯度涂层层数为4,梯度分布因子为1,单层厚度为0.6 mm时,Si Cp/Cu梯度涂层有较好的残余应力缓和效果。根据优化结果采用激光沉积法制备的Si Cp/Cu不同梯度层之间界面较为清晰,结合良好;与均质涂层相比,其硬度和耐磨性分别提高了23.2%和5.2%。     

Cu/低k芯片铜引线键合中应力状态的数值分析

新型Cu/低k芯片以其优异的性能逐步替代Al/SiO2芯片在微纳米器件中得到越来越多的应用。但由于其抗变形能力和强度较低,在引线键合中容易发生损坏。为研究Cu/低k芯片键合中的应力特征和失效机理,建立了Cu/低k芯片与传统Al/SiO2芯片铜引线键合过程的有限元分析模型,计算并对比分析了两种芯片中的应力状态。结果表明:芯片内应力在键合初期快速增长,随后继续增加,但增速变缓;键合过程中高应力区位于铜微球与芯片接触区边缘的下方,呈环形分布;振动中劈刀所在侧高应力区的范围及应力值明显大于另一侧;Cu/低k芯片中应力主要集中于Cu/低k层,Al/SiO2芯片中应力主要集中于劈刀所在侧的Si基板内。键合过程中应力在Cu/低k层的高度集中是新型芯片更易发生分层和开裂失效的根本原因。     

微电子封装界面强度的复合模式弯曲测试

设计了一种复合模式界面开裂测试装置,通过改变加载臂长来实现作用在试样裂纹尖端的不同应力模式。以试验测得的临界载荷及对应位移、裂纹扩展长度为条件,建立与测试装置对应的有限元模型,计算裂纹尖端模式角及在此模式角下的临界能量释放率。结果表明,装置所测试的模式角为7°～78°,以此为参数,可预测微电子封装界面强度。     

温度应力对MEMS器件分层失效的影响规律

通过分析MEMS器件多层结构界面裂纹疲劳扩展的影响因素及温度应力对界面疲劳的影响机理,建立了温度应力对分层失效影响的理论模型,并建立了双材料结构层的有限元分析模型,研究了温度应力对界面裂纹疲劳扩展的影响规律。研究结果表明:在温度应力作用下,裂纹易沿界面方向扩展;温度幅值升高,裂纹疲劳扩展速率呈指数关系增大;裂纹从形成初期到扩展至分层失效的过程中历经较慢扩展、相对平稳扩展和快速扩展三个阶段。     

温度应力对MEMS器件分层失效的影响规律

通过分析MEMS器件多层结构界面裂纹疲劳扩展的影响因素及温度应力对界面疲劳的影响机理,建立了温度应力对分层失效影响的理论模型,并建立了双材料结构层的有限元分析模型,研究了温度应力对界面裂纹疲劳扩展的影响规律。研究结果表明:在温度应力作用下,裂纹易沿界面方向扩展;温度幅值升高,裂纹疲劳扩展速率呈指数关系增大;裂纹从形成初期到扩展至分层失效的过程中历经较慢扩展、相对平稳扩展和快速扩展三个阶段。     

Identification of crack path of inter- and transgranular fractures in sintered silicon nitride by in situ TEM

Inter- and/or transgranular crack paths in sintered silicon nitride (Si3N4) during fracture were investigated by in situ straining experiments in a transmission electron microscope at room temperature, using a high-precision micro-indenter. By this technique, cracks introduced in an in situ manner were observed to propagate in the grain interior and along grain boundaries. High-resolution electron microscopy (HREM) observation revealed that the crack propagation takes place at an interface between Si3N4 grains and an intergranular glassy film (IGF) in the case of intergranular fractures. According to the results by previous molecular dynamics simulations, a number of dangling bonds are present at the Si3N4/IGF interface, which should result in the observed fracture behavior at the interface. On the other hand, the crack path introduced during transgranular fracture of Si3N4 grains was found to be sharp and straight. The observed crack propagated towards [1120] inside the Si3N4 grain with the crack surface parallel to the (1100) plane. The HREM observations of crack walls revealed them to be atomically flat. The atomic termination of the crack walls was identified in combination with image simulations based on atomic models of the cleaved crack walls.     

A study of cracking in GaN grown on silicon by molecular beam epitaxy

It is observed that GaN layers grown on silicon substrates often crack. The crack characteristics in hexagonal GaN films on Si(111) has been characterized using scanning electron microscopy and Nomarski optical microscopy. The effects of growth temperature, layer thickness, and V/III ratios on the cracking have been analyzed. The critical thickness for crack initiation was estimated using a simple theoretical model and is shown to have good agreement with experimental results. Crack-free GaN on Si(111) of thicknesses greater than one micron is possible by using low growth temperatures.     

脉冲激光沉积制备TiN/AlN多层膜的变形机理研究

本文采用纳秒脉冲激光沉积法在单晶硅试样表面制备了调制周期为20nm和200nm的TiN/AlN硬质多层膜,通过有限元模拟和纳米压痕方法研究了调制周期对多层膜的开裂机理的影响。结果表明:调制周期200nm时,载荷致使能量表层积累形成应力集中,一定程度后界面应变梯度劣化促使界面裂纹萌生、扩展。载荷继续增加后,主裂纹沿纵向扩展,其两侧也形成新的应力集中区,原有应力释放。薄膜应力近表层的应力集中超过多层膜的强度极限时,多层膜表层发生开裂。调制周期20nm时,加载诱导应力沿着AlN软膜向多层薄膜内部传递,能量在纵深方向累积储存,直至超过薄膜的屈服极限时,多层膜内部损伤失效。     

Crack-guided effect on dynamic mechanical stress for foldable low temperature polycrystalline silicon thin film transistors

In the thin film transistors (TFTs) device research for foldable display, the degradation effect by the mechanical stress is crucial. Here, the crack position is critical for TFT reliability. However, it is difficult to characterize the crack position due to the random generation of the crack by mechanical stress. In this paper, the crack-guided low temperature polycrystalline silicon (LTPS) TFT test structures are fabricated and the crack-guided effects on mechanical stress of the tested TFT structure are analyzed. To strain on the foldable LTPS TFTs, 50,000 cycles of tensile and parallel direction dynamic mechanical stresses were applied with 2.5-mm bending radius. Based on the results, the generating crack position can be guided and controlled and also TFT reliability for foldable display can be enhanced.     

光学非接触技术在两种岩样力学性能中的应用研究

为了解沿喀喇昆仑公路(314国道)沿线的岩石力学性能,对采自该公路(喀什地区段)沿线的片麻岩和灰白石英粉砂岩加工成标准试件并进行了三点弯曲强度实验。采用光学非接触变形测量技术以及试验机抗折试验,对两种试件分别进行了万能试验机加载并结合CCD(电荷耦合装置)摄像机采集并观测裂纹萌生、生成、演化的全过程,另外对两种试件进行了三点弯曲抗折强度的试验。结果得出试验中的片麻岩试件在受到弯曲应力作用下,会发生多裂纹萌生、生长,片麻岩岩样抗折强度略低于灰白石英粉砂岩,通过对两种岩样力学性能比较分析,得出试验中的片麻岩岩样的抗折断性能低于灰白石英粉砂岩的抗折断性能。     

Interfacial Fracture Investigation of Low-k Packaging Using J-Integral Methodology

In order to resolve the issues of RC time delay and high power consumption, IC chips with Cu/low-k interconnects are developed to meet the foregoing requirements. However, there is a high potential that in doing so it may contribute to interfacial cracks occurring or propagating between the copper metal and the low-k dielectric material as a result of poor adhesion and lower fracture toughness, which results from the inherent mechanical imperfection of low-k materials. This fracturing problem is one of the most urgent issues for the thermomechanical reliability of Cu/low-k interconnects, and it needs to be resolved urgently. For this reason, we propose a prediction methodology of finite-element analysis (FEA) based on J-integral value estimation to investigate the interfacial fracture opportunity of low-k packages. However, the J-integral calculation is path dependent and so crucial in FEA for a crack on an interface between dissimilar materials. Therefore, various paths with an integral contour surrounding the crack tip are considered to avoid a misunderstanding of the cracking energy. All the analytic results indicate that a rectangular contour with a proper ratio of length/width, and multilayers of element close to the delaminating surfaces, is suggested for obtaining a stable J-integral value. On the other hand, the proposed methodology has been validated by a four-point bending test and compared with the relative experimental data of multi-low-k dielectric films. Moreover, under a reliable integral contour path that crack driving force predicted using the type of interfacial crack constructed by means of the element death technique, it shows good agreement with the simulated results of embedding actual crack.     

A numerical procedure for simulating delamination growth on interfaces of interconnect structures

A fracture mechanics based numerical approach is developed for modeling delamination growth on materials interfaces in integrated circuit (IC) interconnects. In this approach, the heterogeneous interconnect structures neighboring the cracked interface are approximated by homogenized layers with transversely isotropic elastic properties. Evolution of the interface crack under fatigue condition is modeled by using an incremental approach, in which the fracture mechanics parameters including the strain energy release rate, the normalized stress intensity factors and phase angles are first estimated by post-processing finite element solutions. The fracture mechanics parameters along the curvilinear front of the interface crack are then substituted into a steady-state fatigue crack growth model for obtaining the crack growth increments. The process is repeated to simulate subsequent crack growth for predicting interconnect structural reliability under fatigue condition. The evolution of an interface corner crack in a back-end-of-line (BEOL) Cu/low-k interconnect structure under temperature cycling condition is considered as an application example of the procedure.     

The Effect of He Implantation on the Tensile Properties and Microstructure of Cu/Fe Nano‐Bicrystals

In situ uniaxial tensile experiments on as‐fabricated and helium‐implanted 100 nm‐diameter Cu/Fe bicrystals unearth the effect of individual face‐centred‐cubic/body‐centred‐cubic (fcc‐bcc) interfaces on improving radiation‐damage tolerance and helium absorption. Arrays of nanotensile specimens, each containing a single Cu grain in the bottom half and a single Fe grain on top, were fabricated by templated electron‐beam lithography and electrodeposition. Helium is implanted at 200 keV to a dose of 10¹⁴ ion/cm² nominally into the interface region. High‐resolution, site‐specific transmission electron microscopy (TEM) and through‐focus analysis reveal that the interfaces are nonplanar and contain ≈5 nm‐spaced He bubbles with diameters of 1–2 nm. Nanomechanical experimental results show that the irradiated samples exhibit yield and ultimate tensile strengths more than 60% higher than the as‐fabricated ones, while they retain comparable ductility. Tensile failure always occurs gradually, along the interfaces, with no noticeable shape localization. The absence of brittle failure in He‐irradiated metals might be explained, in part, by the inability of the small He bubbles to serve as sufficient stress concentrators for cracking. In addition, the non‐orthogonal orientation of the interfaces with respect to the loading axes results in the development of both normal‐ and shear‐stress components. Tensile loading along the pillar axes may cause those interfacial regions subjected to normal stresses to detach, while the inclined regions, subjected to shear, to carry plastic deformation until final fracture.     

Application of an asymmetrical four point bend shear test to solder joints

The asymmetrical four-point bend shear (AFPB) test method was used to measure the shear strength and creep properties through the stress relaxation experiments using three different Pb-free solder joint compositions in an assolidified condition. Since it was difficult to shear the uniform specimens and the local bending usually occurs at the inner loading points, the notches were introduced at the joint line to preferentially weaken this region. The stress analysis by finite element modeling showed that the straight notches transform the parabolic shear stress distribution in the uniform specimen into a relatively uniform shear distribution along the bond line in the notched specimens. Therefore, the shear strength results from the notched specimens are expected to be much more accurate. Experiments showed that both the Sn-3.6Ag-1Cu (wt.%) and Sn-3.6Ag-1Cu-0.45Co joints have superior strength and creep properties as compared to the Sn-3.5Ag joint. However, there was no statistical difference between the shear strength of the Sn-3.6Ag-1Cu and Sn-3.6Ag-1Cu-0.45 Co joints. Moreover, the difference between the creep resistance of these two types of joints was small.     

3D IC受热载荷作用下的数值模拟

针对基于硅通孔技术的3D IC在工作过程中的受热问题,利用热弹性力学理论建立了三维有限元数值模拟分析模型,对结构进行了热分析,同时探讨了器件由此产生的热应力.计算结果表明,由芯片到底面的热通路为散热的主要通道,其它表面的对流条件对热场分布影响不大;芯片与通孔接触面的边角处有应力集中,在热载荷的长期、交变作用下容易发生开...