Electromigration measuring techniques for grain boundary diffusion activation energy in aluminum

The activation energy E_g for electromigration along aluminum grain boundaries has been examined intensively by many authors and different methods. However, the common techniques yield very contradictory results, with E_g ranging between 0.3 and 1.2 eV. For clarifying these contradictions, the present work examines the validity of the different test methods and their basic assumptions. It is shown that for most of these techniques the test quantity being measured is given by time dependent divergences which cause local stripe variations from scarcely detectable voids up to stripe interruptions. This means that constant conditions are not maintained during the test period, thus yielding more or less incorrect activation energies. A well defined measurement of the mass transport and the activation energy is practicable only if the divergence of the electromigration is both constant for a fixed test condition and proportional to the flux for different test conditions. Additionally, all other diffusion terms except electromigration must be negligible, especially the diffusion term based on pressure gradients. These preconditions are satisfied for the direct measurement of the drift velocity of an aluminum front on a TiN stripe, proper test conditions provided. That is why this technique is applied here extensively for clarifying several contradictions. Other techniques were performed for comparison yielding different results. The here obtained valid values of E_g and their variation between 0.43 and 0.47 eV are smaller than generally reported, even for extremely different evaporation and sputtering conditions. In contrast to former results obtained by improper test methods, the activation energy is temperature independent in the examined temperature range between 140 and 280°C, and E_g is not dependent on grain size even for most different fabrication conditions, yielding grain sizes from 0.3 up to 3 μm.     

原子探针层析方法研究690合金晶界偏聚的初步结果

利用脉冲电解抛光的方法制备了含有晶界的三维原子探针（3DAP）针尖样品,用原子探针层析方法（APT）研究了杂质原子在690合金晶界附近的偏聚情况。结果表明：样品经过固溶处理并在500℃～0.5 h时效后,碳化物仅在部分有利于形核的晶界位错纠结处析出,大小为5～10 nm。用三维原子探针可观察到晶界处杂质原子的偏聚现象,C主要偏聚在晶界附近1个原子层内,Si和P偏聚在晶界附近约2个原子层的厚度内。根据这些元素的偏聚数据,讨论了它们发生偏聚时的规律。     

Bulk electromigration by eliminating grain boundary mass flow in continuous aluminum lines

Starting from electromigration threshold in single segments of narrow large-grained lines, grain boundary mass flow was eliminated in continuous Al lines. Mass flow divergences proceeding from grain boundaries on bonding pads were suppressed by another threshold, which is given by the test current per Al thickness. Narrow test lines should be free of tensile stress, which can produce premature failure. Lifetime tests were performed at 200°C with current densities of 8 × 10⁵ A/cm². The averaged stripe width was 1.3 μm. Within 16400 hours no failure occurred, due to homogeneous bulk electromigration.     

EBSD研究取向硅钢晶粒取向和晶界结构

采用扫描电镜结合EBSD技术分析了取向硅钢初次再结晶晶粒的取向和晶界结构。初次再结晶晶粒中以30°～55°的大角晶界为主,Goss取向晶粒含量小于5%,且经常生长在（111）〈112〉取向的晶粒周围。同时测定了二次再结晶晶粒的实际取向,并计算出与Goss取向的取向差关系。     

Effect of doping concentration on the grain boundary trap density and threshold voltage of polycrystalline SOI MOSFETs

PolySOI MOSFETs have been fabricated on undoped and doped polycrystalline silicon films and characterized to study the effect of doping on grain boundary passivation. The grain boundary trap density (N_ST) and threshold voltages have been extracted experimentally to evaluate the extent of grain boundary passivation by the dopants. Charge sheet model based on the effective doping concentration has been employed to analytically estimate the threshold voltages using the experimentally determined grain boundary trap density and grain size (L_g) as model parameters. The variation of threshold voltages with increasing doping concentration for the range of N_A ? (N_ST/L_g) has been studied both by simulation and experiments and the results are presented. Analytically estimated threshold voltages and experimental results show that the threshold voltage falls with increase in the dopant concentration and that this effect is indeed due to the reduction in N_ST as a result of the grain boundary passivation by the dopants.     

Electromigration lifetime improvement of copper interconnect by cap/dielectric interface treatment and geometrical design

A significant improvement of electromigration (EM) lifetime is achieved by modification of the preclean step before cap-layer deposition and by changing Cu cap/dielectric materials. A possible mechanism for EM lifetime enhancement was proposed. Cu-silicide formation prior to cap-layer deposition and adhesion of Cu/cap interface were found to be the critical factors in controlling Cu electromigration reliability. The adhesion of the Cu/cap interface can be directly correlated to electromigration median-time-to-failure and activation energy. Effects of layout geometrical variation and stress current direction were also investigated.     

Effect of semiconductor growth method and bulk doping on fermi level stabilization for aluminum and gold contacts on n- and p-GaAs(100)

Effects of substrate doping and growth method on interface deep level formation and Schottky barrier height were investigated using low-energy catho doluminescence and soft x-ray photoemission spectroscopy. Our results reveal that for Au/GaAs(100) contacts Fermi level (E_F) stabilization energy shows little sensitivity to either substrate growth technique or the type of doping, and Iles in the 0.37 to 0.47 eV range above the valence band maximum (E_v). In contrast, the E_F position at Al/GaAs(100) interfaces is highly sensitive to substrate growth method for n-type GaAs, but shows no significant difference between the epitaxial and melt-grown p-type GaAs. Furthermore, for a specific substrate dopant type and growth method, gold and aluminum produce barrier heights which differ by 0.05 to 0.50 eV, depending upon the substrate growth and dopant properties. Cathodoluminescence results demonstrate that discrete surface and interface states responsible for E_F stabilization at these metal/GaAs junctions are highly sensitive to the substrate growth technique, as well as to the specific metal contact. This work emphasizes that both substrate crystalline and electronic properties, as well as the adatom-specific interface chemistry are crucial for the electrostatic barrier height formation at metal/GaAs contacts.     

Determination of diffusion length and grain boundary recombination velocity by laser excitation

A new technique is developed here for accurately evaluating the diffusion length and the grain-boundary recombination velocity in a semiconductor bicrystal from photovoltage measurements taken by scanning of a laser "infinite line" parallel to the grain boundary. The present method can also be applied in semiconductor bicrystals of small diffusion length, in contrast to a previous scanning laser spot technique, which is limited by the spot size. Experimental application shows that the values of diffusion length and grain boundary recombination velocity measured with the present method are in very good agreement with the values measured in previous work in similar materials.     

Modification of the electron spectrum and vibrational properties of amorphous carbon by copper doping

The near-gap electron spectrum and the effective charge distribution in graphite-like carbon nanoclusters of simple geometry in a-C: H containing a single Cu atom are calculated in the tight-binding approximation. Only the coupling between π electrons of the constituent C atoms and one valence s electron of the Cu atom is taken into account. The binding energy of the Cu atom in the clusters and the static dipole moment of the clusters are calculated. The results are invoked to interpret the experimentally observed activation of the Raman G band in the IR spectrum of a-C: H: Cu as a consequence of a lowering of the symmetry of the graphite-like clusters due to copper intercalation. Experimental data on the time dependence of the G band intensity during isothermal annealing of a-C: H: Cu are presented. The data suggest the possibility of reversible transfer of Cu atoms between the impurity states in the copper-carbon clusters and the impurity states in the purely copper clusters. The average activation energies of direct and reverse transfer are estimated from the experiment. Fiz. Tekh. Poluprovodn. 32, 931–938 (August 1998)     

氧化铝陶瓷基板化学镀铜金属化及镀层结构

通过化学镀铜在氧化铝陶瓷基板表面实现了金属化,采用SEM研究了镀铜层表面微观形貌以及热处理的影响,检测分析了金属化镀层附着力。结果表明:通过控制镀液中铜离子浓度以及铜沉积速率,在基板表面可形成均匀致密的铜金属化层;热处理后进一步提高镀层致密化和导电性,其方阻由3.6 mΩ/□降为2.3 mΩ/□。划痕法测试表明镀铜层与氧化铝陶瓷基板结合紧密无起翘,可以满足敷铜基板的要求。     

Grain boundary segregation in multicrystalline silicon: correlative characterization by EBSD,EBIC, and atom probe tomography

This study aims to better understand the influence of crystallographic structure and impurity decoration on the recombination activity at grain boundaries in multicrystalline silicon. A sample of the upper part of a multicrystalline silicon ingot with intentional addition of iron and copper has been investigated. Correlative electron‐beam‐induced current, electron backscatter diffraction, and atom probe tomography data for different types of grain boundaries are presented. For a symmetric coherent Σ3 twin boundary, with very low recombination activity, no impurities are detected. In case of a non‐coherent (random) high‐angle grain boundary and higher order twins with pronounced recombination activity, carbon and oxygen impurities are observed to decorate the interface. Copper contamination is detected for the boundary with the highest recombination activity in this study, a random high‐angle grain boundary located in the vicinity of a triple junction. The 3D atom probe tomography study presented here is the first direct atomic scale identification and quantification of impurities decorating grain boundaries in multicrystalline silicon. The observed deviations in chemical decoration and induced current could be directly linked with different crystallographic structures of silicon grain boundaries. Hence, the current work establishes a direct correlation between grain boundary structure, atomic scale segregation information, and electrical activity. It can help to identify interface–property relationships for silicon interfaces that enable grain boundary engineering in multicrystalline silicon. Copyright © 2015 John Wiley & Sons, Ltd.     

Planarization of emitter-base structure of heterojunction bipolartransistors by doping selective base contact and nonalloyed emittercontact

The authors report an n-p-n heterojunction bipolar transistor (HBT) with a planar (and thus passivated) emitter-base structure fabricated using a simple, low-temperature technique. They use a nonalloyed emitter contact facilitated by δ-doping grown at the surface of the sample, so that the cap layer is only 75 Å thick. The base is contacted by depositing Au-Zn or Au-Be on the surface and alloying at 420°C for 10 s, resulting in an ohmic contact with the base and rectifying contact with the emitter. The authors present large-emitter area (50-μm diameter) HBTs with homogeneous-doped bases (gain of 170) and δ-doped bases (10¹⁴ cm^-2, gain of 20). Upon reducing the emitter size of the latter to 3×8 μm the gain increased to 30, demonstrating excellent surface passivation     

Electronic structure,carrier mobility and device properties for mixed-edge phagraphene nanoribbon by hetero-atom doping

Phagraphene, a new carbon allotrope, was proposed recently. We here select a mixed-edge phagraphene ribbon to study B-, N-, and BN-doping effects respectively on the geometric stability, electronic structure, carrier mobility, and device property. Calculations show that the energetic and thermal stability for these ribbons are very high. With different doping types and doping sites, the bandgap size of a ribbon may be nearly unchanged, increased, or decreased as compared with the intrinsic ribbon, and even become a metal, thus presenting fully tunable electronic structures. For this, the charge transfer shifting edge bands and the new formed hybridized bands due to doping play a crucial role. More interestingly, doping at different positions can regulate the carrier mobility of ribbon, and the difference of two orders of magnitude for hole mobility can be generated by BN-doping. In addition, the study on device property shows that there is a prominent negative differential resistance characteristics occurring in a BN-doped ribbon device. These findings are meaningful for understanding the doping effects on electronic properties of phagraphene nanoribbons.     

The Synthesis and band gap changes induced by the doping with rare-earth ions in nano-SnO2

A series of pure and Eu-doped (5%, molar ratio) nano-SnO₂ are prepared by a hydrothermal methods. The crystalline phase, morphologies and band gap of doped and pure samples are systematically studied. The nanosheets, nanorods and nanospheres are obtained by different ways for a further investigation. Doping Eu³⁺ in nano-SnO₂ could change the particle size, crystallinity, morphology, and band gap obviously. The doped samples present the trend of agglomerate, but the morphology is very similar among the samples, which are doped with different kinds of the rare-earth ions. It is interesting that the band gap of SnO₂ decreases as Eu³⁺ ions are added which is helpful in the design of functional nanomaterials such as optical, electrical materials.     

Extension of HRTEM resolution by semi-blind deconvolution method and Gerchberg-Saxton algorithm: application to grain boundary and interface

A generalized maximum entropy method coupled with Gerchberg-Saxton algorithm has been developed to extend the resolution from high-resolution TEM image(s) for weak objects. The Gerchberg-Saxton algorithm restores spatial resolution by operating real space and reciprocal space projections cyclically. In our methodology, a generalized maximum entropy method (Kullback-Leibler cross entropy) dealing with weak objects is used as a real space (P1) projection. After P1 projection, not only are the phases within the input spatial frequencies improved, but also the phases in the next higher frequencies are extrapolated. An example of semi-blind deconvolution (P1 project only) to improve the resolution in SiC twin boundary is shown. The nature of the bonding in this twin boundary is Si-C but it was rotated 180 degrees along the boundary normal. The optimum solution from P1 projection can be further improved by a P2 projection. The square roots of diffraction intensities from a diffraction pattern are then substituted to complete a cycle operation of the Gerchberg-Saxton algorithm. Application examples of Gerchberg-Saxton algorithm to solve the atomic structure of defects (2 x 1 interfacial reconstruction and dislocation) in NiSi2/Si interfaces will be shown also.     

Transport properties of copper indium aluminum selenide thin films deposited by successive Ionic layer adsorption and reaction

Cu(InAl)Se₂ (CIAS) thin films have been prepared by successive ionic layer adsorption and reaction (SILAR) technique on well-cleaned glass substrates. The structure, composition, morphology, optical, electrical, and Hall effect studies of prepared thin films have been studied. X-ray diffraction studies confirmed the polycrystalline nature of the thin films with a chalcopyrite structure. Scanning electron microscopy studies revealed that the morphology of the prepared films was smooth, dense, uniform, and granular. Composition of various constituents such as Cu, In, Al, and Se in the CIAS films has been determined from energy dispersive x-ray analysis. Optical properties have been studied in detail from the transmittance spectra in the visible and near infrared region and the optical transition has been found to be direct and allowed with the band gap of around 1.16–1.50 eV. Electrical analysis helps to identify that in high temperature region the conductivity is attributed due to thermal excitation of the charge carriers from grain boundaries to the neutral region of the grains. Transport properties of CIAS thin films have been studied in the temperature range 298–398 K and the transport parameters are evaluated and reported in this paper in detail.     

N- type doping of gallium antimonide and aluminum antimonide grown by molecular beam epitaxy using lead telluride as a tellurium dopant source

Lead telluride was used as a “captive” source of tellurium (Te) for the n-type doping of gallium antimonide (GaSb) and aluminum antimonide (AlSb)grown by molecular beam epitaxy. Controllable carrier concentrations from 1.2 x 10¹⁶ to 1.6 x 10¹⁸ cm^-3 were obtained. High room-temperature Hall mobilities of 4200 cm²/V · s were measured for the low-doped GaSb samples. In the growth temperature range of interest, doping ef-ficiencies are approximately 50% of those in GaAs. For GaSb, SIMS data show that the Te incorporation decreases significantly at growth temperatures above 500° C. How-ever, in AlSb, there is no significant reduction in the incorporation of Te up to at least 650° C. In contrast, the Te incorporation into AlSb decreases at low temperatures. There is also some evidence of surface segregation in AlSb. Contrary to other doping studies, increasing the Sb : Ga flux ratio was found to reduce the Te incorporation.     

陶瓷电子元件局部化学镀铜电极的性能及结构

采用含钯的催化浆料活化法,实现了陶瓷表面的局部化学镀铜。扫描电子显微镜观察结果表明均匀分散的钯纳米颗粒起到了催化铜沉积的作用,镀铜层光滑平整、颗粒大小均匀。X-射线光电子能谱(XPS)和X-射线衍射(XRD)测试结果表明镀层是具有晶态结构的纯铜镀层。对化学镀铜后的陶瓷电子元件进行物理性能和电性能测试,其结果均满足工业要求。     

四波混频与在液晶中光场感生的螺旋结构

本文用扩散-弛豫方程,最一般地处理了考虑到物质激发、弛豫及扩散后的四波混频问题。除讨论物质激发的弛豫及扩散过程对一般简并及二重简并四波混频的影响外,重点分析了两个相对传播的圆偏振光在一般非线性介质中感生的具有螺旋结构的激发,以及这种结构的双折射特性及其稳态与瞬态行为;指出了用这种结构的双折射特性测量一般非线性介质中激发的弛豫参数及扩散系数的可能性。本文还特别将以上分析方法应用于液晶材料,指出用上述的感生螺旋结构可以测量液晶中的一系列材料参数。当把这种分析方法应用于胆甾型液晶时,本文还预言了一个很有意思的“共振”效应。亦即当由激光感生的螺旋结构的螺距与液晶材料的固有螺距相等时或接近相等时,螺旋结构的激发最为有效。在此预言的基础上,指出了用此方法测量胆甾型液晶相变前固有螺距的可能性。此外还预言了相变点由于光场激发的可能变化。     

钝化层和铝电极浆料共烧结制备硅太阳能电池背电极

提出了一种新的硅太阳能电池背场结构及其形成方法,在硅片背面先制备一层氮化硅膜,然后再印刷背面铝电极,通过钝化层和铝电极浆料共烧结制备硅太阳能电池背场结构。在常规铝浆中添加易于同氮化硅反应的高活性玻璃粉,对比了钝化层厚度、玻璃粉种类和含量对氮化硅层的烧蚀效果以及对背电极硅片间接触电阻的影响。当铝浆中高活性玻璃粉添加量为质量分数4%,氮化硅厚度10 nm时,比常规铝浆在无钝化膜的硅片上制备的电池最高效率高出约0.26%。