Reactive interdiffusion between a lead-free solder and Ti/Ni/Ag thin-film metallizations

The reactive interdiffusion between a Sn-3.0wt.%Ag-0.7wt.%Cu solder and thin-film Ti/Ni/Ag metallizations on two semiconductor devices, a diode and a metal-oxide-semiconductor field-effect transistor (MOSFET), and a Au-layer on the substrates are studied. Comprehensive microanalytical techniques, scanning electron microscopy, transmission electron microscopy (TEM), and analytical electron microscopy (AEM) are employed to identify the interdiffusion processes during fabrication and service of the devices. During the reflow process of both diode and MOSFET devices, (1) the Ag layer dissolves in the liquid solder; (2) two intermetallics, (Ni,Cu)₃Sn₄ and (Cu,Ni)₆Sn₅, form near the back metal/solder interface; and (3) the Au metallization in the substrate side dissolves in the liquid solder, resulting in precipitation of the (Au,Ni,Cu)Sn₄ intermetallic during solidification. During solid-state aging of both diode and MOSFET solder joints at 125°C and 200°C, the following atomic transport processes occur: (1) interdiffusion of Cu, Ni, and Sn, leading to the growth of a (Ni,Cu)₃Sn₄ layer until the Ni layer is completely consumed; (2) interdiffusion of Au, Cu, Ni, and Sn through the (Ni,Cu)₃Sn₄ layer and unconsumed Ni layer to the Ti layer to form a solid solution; and (3) further interdiffusion of Au, Cu, Ni, and Sn through the (Ni,Cu)₃Sn₄ layer to from an (Au,Ti,Ni,Cu)Sn₄ layer. The growth of the latter layer continues until the entire Ti layer is consumed.     

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.     

Diffuse diffracted features and ordered domain structures in GalnP layers grown by organometallic vapor phase epitaxy

Transmission electron diffraction (TED) and transmission electron microscope (TEM) studies have been made of organometallic vapor phase epitaxial Ga_xIn_1−xP layers (x ≈ 0.5) grown at temperatures in the range 570–690°C to investigate ordering and ordered domain structures. TED and TEM examination shows that the size and morphology of ordered domains depend on the growth temperature. The ordered domains change from a fine rod-like shape to a plate-like shape as the growth temperature increases. The domains are of width 0.6∼2 nm and of length 1∼10 nm. Characteristic diffuse features observed in TED patterns are found to depend on the growth temperature. Extensive computer simulations show a direct correlation between the ordered domain structures and such diffuse features. A possible model is suggested to describe the temperature dependence of the ordered domain structure.     

Study on stacking faults and microtwins in wide bandgap II-VI semiconductor heterostructures grown on GaAs

ZnMgSSe and ZnSSe layers grown on GaAs substrates with GaAs buffer layers by molecular beam epitaxy have been examined by transmission electron microscopy (TEM). The depth level at which paired triangular stacking faults are nucleated in the ZnMgSSe/GaAs heterostructure has been investigated by using the plan-view TEM technique. It has been found that in the ZnMgSSe/GaAs heterostructure the nucleation of the paired stacking faults occurs within a range of depth which starts at the II-VI/GaAs interface and ends at a level that is above the interface by about 120 nm. The dominant type of defects in ZnSSe layers, which have the single triangular shape, has been identified to be microtwins by high resolution TEM.     

原位生成(Al2O3)p/(Al-4wt.%Mg)复合材料的TEM观察

本文用TEM研究了原位反应方法制备的Al2O3增强铝基复合材料，发现在Al-4wt.%Mg基复合材料中的尖晶石型反应产物MgAl2O4以“界面AgAl2O4”，“弥散MgAl2O4”和“晶内MgAl2O4”三种形态存在，原位生成的Al2O3以“晶内MgAl2O4”为衬底形核长大，并在界面富集形成“界面MgAl2O4”。     

Morphology and defect structures of GaSb islands on GaAs grown by metalorganic vapor phase epitaxy

The initial nucleation of GaSb on (001) GaAs substrates by metalorganic vapor phase epitaxy has been investigated using transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). TEM results showed that the GaSb islands experience a morphological transition as the growth temperature increases. For growth at 520°C, the islands are longer along the [110] direction; at 540°C, they are nearly square, and at 560°C, they are longer along the direction. Possible mechanisms are proposed to describe such a transition. TEM and HREM examination showed that lattice misfit relaxation mechanisms depend on the growth temperature. For the sample grown at 520°C, the lattice mismatch strain was accommodated mainly by 90° dislocations; for the sample grown at 540°C, the misfit strain was relieved mostly by 90° dislocations with some of 60° dislocations, and for the sample grown at 560°C, the strain was accommodated mainly by 60° dislocations which caused a local tilt of the GaSb islands with respect to the GaAs substrate. The density of threading dislocations was also found to be dependent on the growth temperature. Mechanisms are proposed to explain these phenomena.     

Microstructural development and critical currents in long-length (Tl,Bi)−(Sr,Ba)−Ca−Cu−O wires

Synthesis of long Tl−Ba−Ca−Cu−O wires has been achieved byin situ synthesis techniques. Substitutions of Bi for Tl and of Sr for Ba were found to greatly enhance formation of the superconducting phase. Detailed microstructural characterization was performed on wires processed under various conditions in order to elucidate the reaction mechanisms. In addition, microstructural studies were carried out to investigate the beneficial effects of uniaxial compression on critical current density. It was found that thein situ reaction follows a “natural” two-powder process with early formation of Tl-1212. This reaction pathway provides a mechanism for sintering and crack healing and protects existing Tl-1223 for regrowth. Intermediate heat treatment allows more complete advantage to be taken of the above processes, while subsequent pressing increases the density and promotes grain alignment with minimum damage. Further heat treatment sinters grains and allows completion of the transformation to Tl-1223. Elements of this process have been incorporated in a sandwich-type geometry using plate-like grains to promote additional grain alignment.     

纳米级高压扫描电子束曝光技术

通过简单添加一些附件,将一台带有扫描附件的商用透射电子显微镜改造为一台高压扫描电子束曝光机,以研究高压下高分辨率、高深宽比抗蚀剂图形曝光及邻近效应的影响。重点介绍了如何获得一个高分辨率的电子光学系统,并利用此系统初步进行了曝光实验,在120nm厚的PMMA胶上获得了53nm线宽的抗蚀剂图形,表明此装置可用于纳米图形的制作。     

Structural study of GaN grown on (001) GaAs by organometallic vapor phase epitaxy

Detailed transmission electron microscope (TEM) and transmission electron diffraction (TED) examination has been performed on organometallic vapor phase epitaxial GaN layers grown on (001) GaAs substrate to investigate microstructures and phase stability. TED and TEM results exhibit the occurrence of a mixed phase of GaN. The wurtzite (α) phase grains are embedded in the zinc-blende (β) phase matrix. It is shown that there are two types of the wurtzite GaN phase, namely, the epitaxial wurtzite and the tilted wurtzite. The tilted wurtzite grains are rotated some degrees ranging from ∼5° to ∼35° regarding the GaAs substrate. A simple model is presented to describe the occurrence of the mixed phases and the two types of the wurtzite phase.     

Study of threading dislocations in the plan-view sample of SiGe/Si(001) superlattices by transmission electron microscopy

Interfacial defects due to a mismatch of 1.378% between substrate and epilayer were examined in a Si_0.67Ge_0.33/Si(001) superlattice by transmission electron microscopy (TEM). Plan-view specimens from the superlattice were prepared to investigate the defects in the structure. It was observed that 60°C-type misfit dislocations associate with point contrast on and at their ends. This point contrast was found to represent threading dislocations by using tilt experiments in the microscope. Consequently, stereo electron microscopy was used to examine the threading dislocations. It was discovered that the threading dislocations are not on the {111} slip planes but can be almost parallel to the [001] zone axis.     

Planar defects in 4H-SiC PiN diodes

Using plan-view transmission electron microscopy (PVTEM), we have identified stacking faults (SFs) and planar defects in 4H-SiC PiN diodes subjected to electrical bias. Our observations suggest that not all planar defects seen in the PiN diodes are SFs. By performing diffraction-contrast imaging experiments using TEM, we can distinguish SFs from other planar defects. In addition, high-resolution TEM (HRTEM) imaging and analytical TEM have revealed that some planar defects consist of a 3-nm-wide SiC amorphous layer. Many of these planar defects are orientated parallel to {1 00} planes, whereas others are roughly parallel to the (0001) plane. The appearance of these planar defects suggests that they are grain boundaries.     

Al-Cr二元合金中的一个新正交相O-Al_(11)Cr_2

通过透射电镜原位观察,发现单斜η-Al11Cr2相在800℃保温2h后,其三个主带轴电子衍射图中的超点阵弱点逐渐减弱直至消失,且a轴和c轴所成的角度由91°变为90°,这些变化意味着单斜η-Al11Cr2相在加热后转变为一个新相,点阵参数为a=1.2428nm,b≈1.2658nm,c≈3．0456nm的体心正交相,命名为O-Al11Cr2.其[010]电子衍射图具有伪十次对称特点,因此也是一个十重对称准晶近似相.     

Nanoscale characterization of the silicon dioxide-silicon carbide interface using elemental mapping by energy-filtered transmission electron microscopy

Energy-filtered transmission electron microscopy (EFTEM) was used to study 6H-SiC/SiO₂ interfaces produced by thermal oxidation as a function of the oxidation conditions. Elemental maps of C and Si were used to calculate C-to-Si concentration profiles across the interfaces. Enhanced C/Si concentrations (up to ∼ 35%) were observed at distinct regions in samples oxidized at 1100°C for 4 h in a wet ambient. The data from a number of randomly selected regions indicate that re-oxidation at 950°C for 3 h significantly reduced, but did not eliminate, the amount of excess interfacial carbon.     

Electron microscopic study on residual defects of Al+ or B+ implanted 4H-SiC

The residual defects of Al⁺- or B⁺-implanted 4H-SiC were studied in combination with annealing temperature and implantation temperature using cross-sectional transmission electron microscopy technique. Noticeable defects structure is not observed before post-implantation annealing. But after annealing, a lot of black spots appear in the implanted layer. These black spots are composed of a dislocation loop, parallel to {0001} of 4H-SiC, and strained area at the upper and lower sides of the dislocation loop. This defect structure and its size do not depend on implantation temperature and implanted ion species. The size of defect area depends only on post-implantation annealing temperature. The size grows, when post-annealing temperature is raised.     

Transmission electron microscopy studies of defects in HgCdTe device structures grown by molecular beam epitaxy

Transmission electron microscopy (TEM) was used to evaluate the microstructure of molecular beam epitaxy (MBE) grown (211)B oriented HgCdTe films. TEM analysis of in-situ doped p-on-n and n-p-n device structures will be presented. Under fully optimized growth conditions the substrate-epilayer interface is free of threading dislocations and twins, and a high degree of structural integrity is retained throughout the entire device structure. However, under non-optimal growth conditions that employ high Hg/Te flux ratios, twins can be generated in the p-type layer of p-on-n device structure, resulting in roughness and facetting of the film surface. We propose a mechanism for twin formation that is associated with surface facetting. TEM evaluation of voids, threading dislocations and Te-precipitates in HgCdTe films are also discussed.     

Mechanical alloying of FeCo Nanocrystalline magnetic powders

Mechanical alloying of the Fe₅₀Co₅₀ equiatomic-magnetic alloy from elemental powders has been studied. Two milling speeds of 200 rpm and 300 rpm were used to process these powders. The as-milled powders were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The mixing of Fe and Co was completed in 200 min at a milling speed of 300 rpm; however, an increase in saturation magnetization was observed up to 10-h milling, indicating an increase in compositional homogeneity as a function of milling time. These findings were also reflected in the XRD results. During the milling of Fe and Co at 300 rpm, an increase of powder size was observed after 100-min milling. Further milling at 300 rpm led to a reduction in powder size; the decrease of powder size was more effective when milling was conducted at 200 rpm. This was attributed to a difference in the milling mechanisms dominating at these two speeds. The TEM observation showed that a banded microstructure was observed in the as-milled powders. The banded structure consists of grains, many of which show texture effects. After further milling, the banded structure became finer, then randomly arranged, and finally disappeared.     

异质外延立方氮化硼薄膜的微结构研究

利用离子束辅助沉积技术在金刚石薄膜衬底上制备立方氮化硼薄膜,傅立叶变换红外谱的结果表明,在高度(001)织构金刚石薄膜衬底上沉积的立方氮化硼薄膜是纯的立方相,而在多晶金刚石薄膜衬底上制备的立方氮化硼薄膜中还含少量的六角氮化硼。高分辨透射电镜的分析表明,在金刚石晶粒上异质外延的c-BN直接成核于金刚石衬底,界面没有六角氮化硼过渡层;而在含有大量缺陷的晶粒边界,存在六角氮化硼的成核与生长。     

有机电致发光器件的新型薄膜封装技术研究

针对有机电致发光器件(OLED)在空气中水汽和O2作用下寿命下降的问题,提出一种对OLED进行薄膜封装方法。封装薄膜由电子束蒸镀Al2O3薄膜和原子层沉积(ALD,atomic layer deposition)Al2O3薄膜相结合形成。利用Ca薄膜电学测试方法测定封装薄膜的水汽透过率(WVTR)。具体实现方法是,采用玻璃作为衬底,在100nm的Al电极上蒸镀200nm的Ca膜,然后对整个系统进行薄膜封装,只留出Al电极的一部分作为探针接触电极。实验发现,采用电子束蒸镀结合ALD的Al2O3薄膜封装,Ca薄膜变成透明的时间比未封装或采用单一结构封装得到了延长。为了检验薄膜封装效果,制作了一组绿光OLED,器件结构为ITO/MoOX(5nm)/mMTDATA(20nm)/NPB(30nm)/Alq3(50nm)/LiF(1nm)/Al,实验结果表明,本文提出的薄膜封装方法对器件进行封装,器件的寿命得到了延长。     

Effects of shock-induced defect density on flux pinning in melt-textured YBa2Cu3O7−δ

To introduce a high density of homogeneously distributed defects in YBa₂Cu₃O_7−δ (Y123), melt textured samples were shock-compacted at pressures up to 12.6 GPa (126 Kbar) at orientations favorable to slip along the basal planes.¹ Shock compressing melt-textured Y123 results in a nearly uniform detect density which is two to three orders of magnitude higher than in unshocked melt-textured material. However, the intergranular critical current density in bulk samples (J_c ^b) decreases by two orders of magnitude in the as-shocked state. This decrease in J_c ^b is attributed to microfractures. However, if the shocked disk is annealed in O₂ then ground, sieved, and magnetically aligned, J_c for H τ c-axis (J_c ^ab) is enhanced two to three times over the unshocked value. This indicates that the increase in dislocations density does increase flux-pinning.     

Metalorganic vapor phase epitaxial growth and structural characterization of GaAs/InP heterostructures

Highly mismatched GaAs epitaxial layers with thickness ranging from 15 nm to 7 μm have been grown on InP substrates by atomospheric pressure metalorganic vapor phase epitaxy. Layers thinner than 30 nm exhibited 3-D growth mechanism; in the thicker layers, the islands coalesced and then the growth followed the layer by layer mechanism. The elastic strain and the extended defects have been studied by high resolution x-ray diffraction and transmission electron microscopy, respectively. The common observation of planar defects, misfit, and threading dislocations in the layers has been confirmed. The results on the elastic strain release have been discussed on the basis of the equilibrium theory.