Effect of boron on the resistivity of compensated 4H-SiC

High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 10⁴ Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.     

Verification of models for fabrication of Arsenic source-drains in VLSI MOSFET's

The understanding of the effects of both low- and high-temperature anneals of arsenic implanted into silicon is critical in the calculation of p-n junction profiles of sources and drains in short-channel MOSFET's. The work reported here uses a sample matrix of arsenic implanted into silicon over a wide range of fluences and annealed in both the low- and high-temperature regimes. This matrix of samples was measured by means of Rutherford Backscattering Spectrometry (RBS), spreading resistance (Rsp), and Secondary Ion Mass Spectrometry (SIMS). The measurement techniques are compared with each other, with the predictions of ion-implantation models, and with the annealing/diffusion models. Comparison of the RBS data from more than one experiment indicates that high-quality quantitative analysis requires more complex calibration data for the detector than is usually available. The Rsp data obtained on the low-temperature annealed samples did not yield reasonable arsenic profiles, both with respect to the peak location and profile shape. The measurement technique which was most consistent with theoretical models and most reproducible from one experimenter to another is the SIMS technique. Calculations of the annealed profiles were found to be in agreement with the SIMS data, at temperatures greater than 900°C, when the form used by Fair was employed. A large adjustment in the parameters of the charge vacancy reaction is necessary; a much smaller adjustment is required in the parameters of the extrinsic diffusion reaction. The accuracy obtained here is typical of much available data and is sufficiently accurate for 2-µm MOS device characterization, but not sufficient for submicrometer devices.     

Experimental studies of metal/InP interfaces formed at room temperature and 77K

Metal/InP interfaces were formed at room temperature (RT = 300K) and low temperature (LT = 77K). A high leakage current was observed for the RT processed metal/InP samples due to its low barrier height (0.35–0.55 eV). An extremely low leakage current and high barrier height (up to 0.96 eV) were achieved when Au and Pd Schottky contacts to n-InP were produced at low temperature. Photoluminescence spectroscopy, Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), and secondary ion mass spectroscopy (SIMS) were used to study the metal/InP interfaces. Photoluminescence spectra showed that there was less surface state density in LT samples. The RT processed sample showed more O and C in the surface region of an Au/InP structure than the same sample processed at LT in the AES spectra. The phosphide out-diffusion was observed in RT processed samples by ESCA. A possible P:O layer on the metal side of the LT processed sample was found by SIMS. Extensive chemical and structural analysis indicated that LT process caused the metal film to be continuous at 50 Å, much better than in standard RT processing.     

Atomic Cobalt Vacancy-Cluster Enabling Optimized Electronic Structure for Efficient Water Splitting

Vacancies created on a surface can alter the local electronic structure, thus enabling a higher intrinsic activity for the evolution of hydrogen and oxygen. Conventional strategies for vacancy engineering, however, have a strong focus on non-metal sulfur/oxygen defects, which have often overlooked metallic vacancies. Herein, evidence is provided that cobalt vacancies can be atomically tuned to have different sizes to achieve cobalt vacancy clusters through controlling the migration of iridium single atoms. The coalescence of Co vacancy clusters at the surface of an IrCo alloy results in an increased d-band level and eventually compromises H adsorption, leading to enhanced electrocatalytic activity toward the hydrogen evolution reaction. In addition, the Co vacancy clusters can improve the electronic conductivity with respect to the oxidized Co surface, which substantially aids in strengthening the adsorption of oxygen intermediates toward an effective oxygen evolution reaction at a low overpotential. These collective effects originate from the Co vacancy cluster and specifically enable highly efficient and stable water splitting with a low total overpotential of 384 mV in alkaline media and 365 mV in an acidic environment, achieving a current density of 10 mA cm^–2.     

Positronics and nanotechnologies: Possibilities of studying nanoobjects in critical engineering materials using positron annihilation spectrometry

It is shown that positron annihilation spectroscopy (PAS) is one of the efficient methods for determining the sizes of nanodefects (vacancies, vacancy clusters); free volumes of pores; cavities, and voids; their concentrations and the chemical composition at the annihilation site (location) in nanomaterials and other critical engineering materials. A brief review of experimental studies of nanodefects in porous silicon, silicon, and quartz monocrystal irradiated by protons as well as quartz powders are given.     

Sn-8Zn-3Bi无铅焊料的表面改性

采用液相法用有机物改性剂对Sn-8Zn-3Bi焊料进行表面包覆改性,以改善焊料的润湿性能及抗氧化性能。对包覆样品进行了红外光谱表征。考察了样品的抗氧化性、润湿性能和存储性能。结果表明:采用液相法可以实现在Sn-8Zn-3Bi焊料表面包覆有机物。以有机物C为改性剂,且用量为2%(质量分数)时得到的改性样品的润湿角θ为7.8°,铺展面积S为108.83mm2,而未被改性的焊料θ为10.74°,S为93.40mm2。     

Cleaning and passivation of the Si(100) surface by low temperature remote hydrogen plasma treatment for Si epitaxy

This paper presents the results of a study of the hydrogen-passivated Si(100) surface prepared by a remote hydrogen plasma treatment which serves the dual purpose of cleaning and passivating the Si(100) surface prior to low temperature Si epitaxy by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD). The remote hydrogen plasma treatment was optimized for the purposes of cleaning and passivation, respectively. To achieve a clean, defect-free substrate surface, the remote hydrogen plasma process was first optimized using Transmission Electron Microscopy (TEM) and Auger Electron Spectroscopy (AES). For hydrogen passivation, the substrate temperature was varied from room temperature to 250° C in order to investigate the degree of passivation as a function of substrate temperature by examining the amount of oxygen readsorbed on the substrate surface after air exposure. Low temperature Si expitaxy was subsequently performed on the air-exposed substrates without further cleaning to evaluate the effectiveness of the hydrogen passivation. It was found that better Si surface passivation is achieved at lower substrate temperatures as evidenced by the fact that less oxygen is observed on the surface using AES and Secondary Ion Mass Spectroscopy (SIMS) analyses. The amount of readsorbed oxygen on the H-passivated Si surface after a two hour air exposure was found to be as low as 0.1 monolayer from SIMS analysis. Using Reflection High Energy Electron Diffraction (RHEED) analysis, different surface reconstructions ((3 × 1) and (1 × 1)) were observed for H-passivated Si surfaces passivated at various temperatures, which was correlated to the results of AES and SIMS analyses. Epitaxial growth of Si films at 305° C was achieved on the air-exposed Si substrates, indicating a chemically inert Si surface as a result of hydrogen passivation. A novel electron-beam-induced-oxygen-adsorptiom phenomena was observed on the Hpassivated Si surface. Scanning Auger Microscopy (SAM) analysis was performed to study the reaction kinetics as well as the nature of Si—H bonds on the H-passivated Si surface. Preliminary results show that there is a two-step mechanism involved, and oxygen adsorption on the H-passivated Si surface due to electron beam irradiation may be due to the formation of O-H groups rather than the creation of Si—O bonds.     

Stress relaxation and creep of 12 to 35 μm copper foil

Stress relaxation and creep of the electrodeposited and rolled copper foils, 12-35 μm thick, are investigated near yield stress and near room temperature. The stress relaxation does not obey a logarithmic time law; the creep appears to follow a power function. These deviations from the expected logarithmic behavior are thought to be caused by very small grain size, unstable non-equilibrium defect structure and extensive micropore population (vacancies and vacancy clusters) typical of the electrodeposit. Relaxation and creep are significantly lower for the rolled (than for the electrodeposited) foil. Decreasing the electrode-posit thickness has an effect of enhancing relaxation and creep, attributable to a limited nucleation on the cathode surface and consequent generation of microvoids between growth clusters in the vicinity of the substrate. The foil thickness effect on creep and stress relaxation is not observed for the rolled foil, which is prone to embrittlement and stiffening at about 323K.     

Compositional dependence of cation impurity gettering in Hg1−xCdxTe

Cation impurity gettering in Hg_1−xCd_xTe is described in the context of process models which include the interactions of the impurities and the dominant native point defects. Experimental results are presented using secondary ion mass spectroscopy (SIMS) profiles of Au redistribution in Hg_1−xCd_xTe (x = 0.2,0.3,0.4) following Hg anneals and ion mills, which are processes known to inject excess Hg interstitials. In either process, the IB impurity distributes preferentially to high vacancy regions. The junction depth of the low to high impurity transition is determined by SIMS. For Hg-rich anneals of Au-doped high vacancy concentration material, the impurity junction behavior with respect to anneal time and temperature is compared to that expected for type converted electrical junctions in vacancy-only material. For milled Au-doped Hg_0.7Cd_0.3Te with a high vacancy concentration, the impurity junction depths are approximately proportional to the amount of material removed, as was the case with x = 0.2 material. Hg anneal type-conversion rates are found to have a strong compositional dependence which compares favorably with the strong self-diffusion coefficient dependence on x-value. In contrast, the mill conversion rate has a weak x-value dependence. Effects of trace vs dominant Au levels compared to the background vacancy concentration are quantified. True decoration of intrinsic defect processes requires Au <<[Cation Vacancies].     

Si3N4无杂质空位诱导InGaAs/InP 量子阱结构带隙的蓝移

用光荧光谱和二次离子质谱的方法,研究了由Si3N4电介质薄膜引起的无杂质空位诱导InGaAs/InP多量子阱结构的带隙蓝移。实验中选用Si3N4作为电介质层,用以产生空位,并经快速热退火处理。实验结果表明,带隙蓝移同退火时间和退火温度有关,合理选用退火条件可以控制带隙的蓝移量。二次离子质谱分析表明,电介质盖层Si3N4和快速热退火导致量子阱中阱和垒之间互扩,这种互扩是导致带隙蓝移的主要原因。     

Effects of Ag and Al Additions on the Structure and Creep Properties of Sn-9Zn Solder Alloy

Creep behavior of the eutectic Sn-9Zn, Sn-9Zn-0.5Ag, and Sn-9Zn-0.5Al solder alloys was studied by impression testing under constant punching stress in the range of 60 MPa to 130 MPa and at temperatures in the range of 298 K to 370 K. Analysis of the data showed that, for all loads and temperatures, Sn-9Zn-0.5Al had the lowest creep rates and thus the highest creep resistance among all materials tested. The creep resistance of Sn-9Zn-0.5Ag was slightly lower than that of the Al-containing alloy. The enhanced creep behaviors of the ternary alloys are attributed to the presence of AgZn₃ and very fine Zn particles, which act as the main strengthening agents in the Sn-9Zn-0.5Ag and Sn-9Zn-0.5Al alloys, respectively. Assuming a power-law relationship between the impression rate and stress, average stress exponents of 6.9, 7.1, and 7.2 and activation energies of 42.1 kJ mol⁻¹, 42.9 kJ mol⁻¹, and 43.0 kJ mol⁻¹ were obtained for Sn-9Zn, Sn-9Zn-0.5Ag and Sn-9Zn-0.5Al, respectively. These activation energies are close to 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about 7, suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.     

Effects of Ce and La Additions on the Microstructure and Mechanical Properties of Sn-9Zn Solder Joints

The effects of rare-earth elements on the microstructure and mechanical properties of Sn-9Zn alloys and solder joints in ball grid array packages with Ni/Au(ENIG) surface finishes have been investigated. Metallographic observations showed that (Ce_0.8Zn_0.2)Sn₃ and (La_0.9Zn_0.1)Sn₃ intermetallic compounds appeared in the solder matrix of Sn-9Zn-0.5Ce and Sn-9Zn-0.5La alloys, respectively. Both fiber- and hillock-shaped tin whiskers were inhibited in the Sn-9Zn-0.5Ce solder, while tin fibers were still observed on the surface of oxidized (La_0.9Zn_0.1)Sn₃ intermetallics in Sn-9Zn-0.5La after air exposure at room temperature. Mechanical testing indicated that the tensile strength of Sn-9Zn alloys doped with Ce and La increased significantly, and the elongation decreased, in comparison with the undoped Sn-9Zn. The bonding strengths of the as-reflowed Sn-9Zn-0.5Ce and Sn-9Zn-0.5La solder joints were also improved. However, aging treatment at 100°C and 150°C caused degradation of ball shear strength in all specimens. During the reflowing and aging processes, AuZn₈ intermetallic phases appeared at the interfaces of all solder joints. In addition, Zn-rich phases were observed to migrate from the solder matrix to the solder/pad interfaces of the aged specimens.     

Clustering of defects and impurities in hydrogenated single-crystal silicon

Data obtained to date on specific features of defect formation for hydrogenated single-crystal Si are analyzed. It was demonstrated that, in addition to other effects, interaction of H atoms with radiation defects and impurities leads to the formation of large clusters of three main types, namely, vacancy, interstitial, and impurity clusters. The main condition for formation of these clusters is the simultaneous presence of supersaturated solutions of H and defects in the sample. The interaction of H atoms with impurities and defects initiates the decomposition of the supersaturated solid solution of defects and impurities with the formation of precipitates. This leads to the formation of clusters, which are not observed in the absence of H. The mechanisms of formation and structure of clusters are discussed.     

钒注入制备半绝缘SiC的退火效应

对钒离子注入P型和n型4H-SiC制备半绝缘层的方法和特性进行了研究.注入层电阻率随退火温度的升高而增加,经过1 650℃退火后,钒注入p型和n型SiC的电阻率分别为1.6×1010Ω·cm和7.6×106Ω·cm.借助原子力显微镜对样品表面形貌进行分析,发现碳保护膜可以有效减小高温退火产生的表面粗糙,抑制沟槽的形成.二次离子质谱分析结果表明退火没有导致明显的钒在SiC中的再扩散.即使经过1 650℃高温退火,也没有发现钒离子向SiC表面外扩散的现象.     

Laser post-ionization improves surface analysis

Laser post-ionization (PI), a technique that overcomes the greatest handicap of secondary-ion mass spectroscopy (SIMS), namely, its susceptibility to matrix effects is discussed. The SIMS matrix effect is the often unknown relationship between the chemical composition of a solid and the secondary ion yield of an analyte in the sample, which is unpredictable and can vary as much as seven orders of magnitude. PI, which involves passing a laser beam parallel to, and just above, a surface undergoing stimulated desorption, solves the problem by decoupling the ionization and desorption steps. This allows the detection of secondary neutral species, which typically constitute more than 95% of the material removed from the surface during ion beam sputtering. This largely eliminates matrix effects because the chemical matrix generally has much less influence on the emission of charged particles. To compete with SIMS on sensitivity, PI methods efficiently ionize sputtered neutrals and detect those positionized particles. The nonresonant method of PI, which comes in two variations, nonresonant multiphoton and nonresonant single-photon ionization and is called SALI (surface analysis by laser ionization), is described, and its application to semiconductors is examined     

Features of defect formation under the thermal treatment of dislocation-free single-crystal large-diameter silicon wafers with the specified distribution of oxygen-containing gettering centers in the bulk

Possibilities of obtaining a defect-free layer in wafers of dislocation-free single-crystal silicon subjected to rapid thermal annealing (RTA) are analyzed. The application of RTA is based on the possibility of effectively affecting the distribution profile of the density of oxygen precipitates over the wafer thickness by means of controlling the distribution profiles of the vacancies and interstitial atoms. However, the solution of this important task encounters the problem of the appearance of large local stresses in the vicinity of the fastening supports of a large-diameter silicon wafer and its bending in the course of RTA, which are caused by its own weight. Using mathematical modeling of the three-dimensional stress-strain state and defect formation in large-diameter silicon wafers in the course of RTA, various methods of fastening the wafers are considered and the possibilities of lowering the stress-strain state of the silicon wafer are determined. A mathematical model taking into account the diffusion-recombination processes of vacancies and interstitial silicon atoms, as well as the formation of vacancy clusters is proposed to describe the defect formation in the course of RTA. Based on this model, temperature-temporal parameters of RTA, which correspond to the required (depleted near the surface) concentration profile of the vacancies and the density and size of the vacancy clusters over the wafer thickness, are determined (heating time, holding time at the highest temperature, the cooling rate of the wafer). The results of the calculations are verified for test samples using optical microscopy and transmission electron microscopy (OM and TEM).     

Quantitative TEM of point defects in Si

We review the use of transmission electron microscopy (TEM) to provide a quantitative measurement of both vacancy and interstitial clusters in ion-implanted silicon. Interstitials agglomerate into rod-like defects on 131I) planes, and the evaporation of these defects can be directly correlated to the diffusion enhancements observed during annealing of ion-damaged silicon. Vacancy clusters are easily detected in TEM once they have been labelled using a Au-diffusion technique. The combination of the two approaches provides a quantitative test for models of implantation and annealing in silicon. Detailed models for point defect behaviour, which include Ostwald-ripening and the surface recombination velocity, reproduce all of the crucial features of the observed defect annealing.     

Investigation of distribution and redistribution of silicon in thin doped gallium-arsenide layers grown by molecular beam epitaxy on substrates with (100), (111)Ga, and (111)As orientations

The distribution of silicon in GaAs was investigated by secondary-ion mass spectrometry (SIMS) before and after the thermal annealing of thin doped GaAs layers grown by molecular beam epitaxy on substrates with (100), (111)Ga, and (111)As orientations. The surface relief pattern of the grown epitaxial films was studied by atomic-force microscopy both inside and outside the ion-etching crater developed during the SIMS analysis. Features of the surface relief inside the crater are revealed for various orientations. Changes observed in the shape of doping profiles are explained both by the features of the development of the surface relief during the ion etching accompanying the SIMS analysis and by an accelerated diffusion of Si over the growth defects.     

Intermetallic reactions in Sn-8Zn-20In solder ball grid array packages with Au/Ni/Cu and Ag/Cu pads

During the reflow process of Sn-8Zn-20In solder joints in the ball grid array (BGA) packages with Au/Ni/Cu and Ag/Cu pads, the Au and Ag thin films react with liquid solder to form γ₃-AuZn₄/γ-Au₇Zn₁₈ and ε-AgZn₆ intermetallics, respectively. The γ₃/γ intermetallic layer is prone to floating away from the solder/Ni interface, and the appearance of any interfacial intermetallics cannot be observed in the Au/Ni surface finished Sn-8Zn-20In packages during further aging treatments at 75°C and 115°C. In contrast, ε-CuZn₅/γ-Cu₅Zn₈ intermetallics are formed at the aged Sn-8Zn-20In/Cu interface of the immersion Ag BGA packages. Bonding strengths of 3.8N and 4.0N are found in the reflowed Sn-8Zn-20In solder joints with Au/Ni/Cu and Ag/Cu pads, respectively. Aging at 75°C and 115°C gives slight increases of ball shear strength for both cases.     

Study of deep level defect behavior in undoped n-InP (1 0 0) after rapid thermal annealing

The effects of rapid thermal annealing on deep level defects in the undoped n-type InP with Ru as Schottky contact metal have been characterized using deep level transient spectroscopy (DLTS). It is observed that the as-deposited sample exhibit two deep levels with activation energies of 0.66 and 0.89 eV. For the samples annealed at 300 °C and 400 °C, a deep level is identified with activation energies 0.89 and 0.70 eV, respectively below the conduction band. When the sample is annealed at 500 °C, three deep levels are observed with activation energies 0.25, 0.32 and 0.66 eV. Annealing of the sample at 300 °C, orders the lattice of as-grown material by suppressing the defect 0.66 eV (A1) which is found in the as-deposited sample. The trap concentration of the 0.89 eV deep levels is found to be increased with annealing temperature. The deep level 0.32 eV may be due to the lattice defect by thermal damage during rapid thermal annealing process such as vacancies, interstitials and its complexes, indicating the damage of the sample after annealing at 500 °C. The defects observed in all the samples are possibly due to the creation of phosphorous vacancy or phosphorous antisite.