Curing of polyimide and the effect of the TEOS SiO2 barrier layer on the electromigration of sputtered Cu with polyimide passivation

The curing process of polyimide and the electromigration of copper films with polyimide (PI) passivation are studied. Thermal analysis of polyimide suggests that imidization completes at ∼200°C with an endothermic reaction associated with the breaking of the C-OH and N-H bonds as revealed by Fourier transformation infrared spectroscopy (FTIR). Although there is 89.8% weight loss when PI is heated from 20°C to 200°C, outgassing of PI passivation is still observed at higher temperatures. Carbon, nitrogen, and oxygen atoms diffuse into Cu during thermal processing of PI/Cu films. The tetraethyl orthosilicate (TEOS) SiO₂ films are used as the barrier layer between PI and Cu to retard the poisoning of Cu. The effect of TEOS SiO₂ film on electromigration of Cu is investigated.     

Electrical characteristics of low temperature polysilicon TFT with a novel TEOS/oxynitride stack gate dielectric

This investigation is the first to demonstrate a novel tetraethylorthosilicate (TEOS)/oxynitride stack gate dielectric for low-temperature poly-Si (LTPS) thin film transistors (TFTs), composed of a plasma-enhanced chemical vapor deposition (PECVD) thick TEOS oxide/ultrathin oxynitride grown by PECVD N/sub 2/O-plasma. The stack oxide shows a very high electrical breakdown field of 8.4 MV/cm, which is approximately 3 MV/cm larger than traditional PECVD TEOS oxide. The field effective mobility of stack oxide LTPS TFTs is over 4 times than that of traditional TEOS oxide LTPS TFTs. These improvements are attributed to the high quality N/sub 2/O-plasma grown ultrathin oxynitride forming strong Si/spl equiv/N bonds, as well as to reduce the trap density in the oxynitride/poly-Si interface.     

Electrical properties of ZnO Nano-particles embedded in polyimide

The ZnO nano-particles were made in the polyimide dielectric matrix by using the chemical reaction between the zinc metal film and polyamic acid. The concentration of the ZnO particle is about 1.5×10¹² cm⁻², with average size below 10 nm, and its shapes are almost spherical. Then, the polyimide layer is a stable dielectric material with a dielectric constant of 2.9. To investigate the electrical properties of ZnO particles in the polyimide insulator film, we fabricated a metal-insulator-semiconductor (MIS) structure and measured capacitance-voltage (C-V) with temperature modulation. At room temperature, C-V hysteresis with a voltage gap of 2.8 V appeared in the MIS structure using SiO₂/Si substrate. As the measuring temperature decreased, the C-V curves were shifted slightly to the accumulation region with gate bias. It was considered that the electrical charging may occur dominantly in nanoparticles, having only a few defects at the interface of the polyimide/SiO₂ and the polyimide/ZnO.     

Electrical and interface properties of Au/DNA/n-Si organic-on-inorganic structures

The effect of the thickness and coverage rate of a DNA film on the electrical and interface properties of Au/DNA/n-Si organic-on-inorganic structures has been investigated. The thin film properties of the DNA deposited on n-Si wafer were characterized by atomic force microscopy. The effect of the thickness and coverage rate of the DNA layer was investigated by evaluating electrical parameters, such as the barrier height, ideality factor, series resistance, and interface state density. The thickness and coverage rate of the DNA layer significantly affects the electrical properties of the Au/DNA/n-Si organic-on-inorganic structures. The interface state density properties of the Au/DNA/n-Si diodes were determined by conductance technique. The results show that the interface state density decreases with decrease in both film thickness and coverage rate of the DNA in an acetate buffer, modifying the electronic parameters of the Au/DNA/n-Si diodes.     

Electrical properties and interface chemistry in the Ti/3C-SiCsystem

Characterizations were performed to determine the properties of Ti contacts on 3C-SiC. Both titanium carbides and titanium silicides were studied carefully following heat treatments from 600 to 1000°C. The peak associated with titanium silicides in Auger Si spectrum is identified. Structural and chemical analyzes using AES, XPS, and XRD revealed how the electrical properties of the contacts correlate with the interface chemistry. It is found that while the carbide improves the ohmic behavior of the contacts, the cubic structure disilicide C49 TiSi ₂ formed at the interface at above 700°C is closely related to the lowering in the contact resistance. The barrier height decreases from 0.53 eV for as-deposited films to 0.44 eV due to annealing. The contacts maintained stable electrical characteristics after annealing at 600°C for extended periods of time     

Charges at a laser-recrystallized-polycrystalline-silicon/insulator interface

Capacitance-voltage characteristics have been measured to determine the interface properties at the back surface of a layer of laser-recrystallized polycrystalline silicon. The interface between the recrystallized poly-silicon and an underlying oxide layer can be characterized by an effective fixed-charge density and a fast-state density, both in the low-to-middle-10¹¹cm^-2range. Charge trapping at a polysilicon/silicon-nitride interface precludes the determination of a meaningful value of interface charge.     

Comprehensive dynamic analysis of wirebonding on Cu/low-K wafers

Comprehensive dynamic analysis is performed in this paper to simulate wirebonding on Cu/low-K wafers, which involves both the impact and the ultrasonic vibration stages. After the impact stage, the contact region between the pad and the gold ball is welded to allow subsequent ultrasonic vibrations to take place. Parametric studies are carried out to investigate structural responses of the Cu/low-K layer due to variation of the moduli of Cu/low-K components.     

Electrical properties at p-ZnSe/metal interfaces

In order to prepare low resistance ohmic contacts to p-ZnSn by the “deposition and annealing (DA)” technique which has been extensively used for GaAs and Si-based devices, formation of a heavily doped layer by the p-ZnSe/metal reaction is required. For p-ZnSe/Ni contacts, Ni and Se reacted preferentially at the ZnSe/Ni interface upon annealing at temperatures higher than 250°C. However, capacitance-voltage measurements showed that the net acceptor concentration (N_A-N_D) close to the p-ZnSe/Ni interface was reduced upon the Ni/ZnSe reaction, resulting in high contact resistance. For p-ZnSe/Au contacts, neither Au/ZnSe reaction nor reduction of the acceptor concentration were observed after annealing at temperatures lower than 300°C. This indicates that although the metal/p-ZnSe reaction is mandatory to prepare a heavily doped layer, the reaction induced an increase in the compensation donors in the p-ZnSe substrate. In order to increase the acceptor concentration in the vicinity of the p-ZnSe/metal interface through diffusion from the contact materials, Li or O which was reported to play the role of an acceptor in ZnSe was deposited with a contact metal and annealed at elevated temperatures. Ni or Ag was selected as the contact metal, because these metals were expected to enhance Li or O doping by reacting with ZnSe. However, the current density-voltage characteristics of the Li(N)/Ni and Ag(O) contacts exhibited rectifying behavior, and the contact resistances increased with increasing annealing temperature. The present results indicated that, even though the acceptor concentration in the p-ZnSe substrate increased by diffusion of the dopants from the contact elements, an increment of the compensation donors was larger than that of the acceptors. The present experiments indicated that preparation of low resistance ohmic contacts by forming a heavily doped intermediate layer between p-ZnSe and metal is extremely difficult by the DA technique.     

Mechanisms of interface trap-induced drain leakage current inoff-state n-MOSFET's

An interface trap-assisted tunneling and thermionic emission model has been developed to study an increased drain leakage current in off-state n-MOSFET's after hot carrier stress. In the model, a complete band-trap-band leakage path is formed at the Si/SiO₂ interface by hole emission from interface traps to a valence band and electron emission from interface traps to a conduction band. Both hole and electron emissions are carried out via quantum tunneling or thermal excitation. In this experiment, a 0.5 μm n-MOSFET was subjected to a dc voltage stress to generate interface traps. The drain leakage current was characterized to compare with the model. Our study reveals that the interface trap-assisted two-step tunneling, hole tunneling followed by electron tunneling, holds responsibility for the leakage current at a large drain-to-gate bias (V_dg). The lateral field plays a major role in the two-step tunneling process. The additional drain leakage current due to band-trap-band tunneling is adequately described by an analytical expression ΔI_d=Aexp(B_it/F). The value of B_it about 13 mV/cm was obtained in a stressed MOSFET, which is significantly lower than in the GIDL current attributed to direct band-to-band tunneling. As V_dg decreases, a thermionic-field emission mechanism, hole thermionic emission and electron tunneling, becomes a primary leakage path. At a sufficiently low V_dg, our model reduces to the Shockley-Read-Hall theory and thermal generation of electron-hole pairs through traps is dominant     

Hybrid polyimide/Ta2O5/polyimide antiresonantreflecting optical waveguides

A hybrid polyimide/Ta₂O₅/polyimide antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW consists of fluorinated polyimide and tantalum pentoxide hybrid layers deposited on Si substrates. The propagation losses of the device are 0.6 and 2.6 dB/cm at 1.3 μm for TE and TM polarised lights, respectively     

固液界面纳米气泡的研究

在经典热力学理论中，室温下水中纳米气泡被认为是不能稳定存在的。近年来随着对疏水表面研究的深入，越来越多的现象暗示固液界面存在纳米气泡，并引起疏水长程作用力。目前直接探测固液界面纳米气泡的最有力手段是AFM，但它只能观察纳米气泡的形貌，无法对其进行直接定性，很有必要提供纳米气泡存在和来源的更直接证据。在云母表面进行乙醇和水替换形成纳米气泡，从成像条件和脱气对纳米气泡的影响两方面进行系统研究。不同成像模式和成像条件下AFM观察到的差异在一定程度上证明了观察到的就是纳米气泡。脱气实验结果表明，经脱气后乙醇和水形成纳米气泡的数量和概率明显降低，表明乙醇和水中溶解的气体是纳米气泡的来源，并为固液界面存在纳米气泡提供了更直接的证据。     

Transient analysis of the impact stage of wirebonding on Cu/low-K wafers

In this paper, transient mechanical responses of the Cu/low-K structure during the impact stage of the wirebonding process were investigated. Parametric studies were carried out to examine the effect of elastic moduli of different constituent materials on the potential of structural defect on the copper via and the pad. The analysis applied the explicit time integration scheme, which is feasible in dealing with the nonlinear transient structural behavior.     

Thermodynamic prediction of interface phases at Cu/solder joints

A thermodynamic method to predict the intermetallic compound which forms first at the substrate/solder interface during the soldering process has been suggested through calculations of metastable phase equilibria between the substrate and the liquid solder and by comparison of the driving forces of formation of individual intermetallic compound phases. It has been applied to the interfacial reaction between Cu substrate and Sn-Ag, Sn-Zn eutectic solders. The prediction from thermodynamic calculations was in good agreement with observed experimental results. The solid-state growth behavior of compound phases formed at the interface of Cu/Sn-Zn and Cu/Sn-Ag eutectic solder joints was explained and a schematic diffusion path suggested through calculated ternary phase diagrams.     

Gold nanoparticle superlattices self-assembled at a solid/liquid interface

Three-dimensional superlattices of gold nanoparticles were self-assembled at a highly oriented pyrolytic graphite (HOPG)/water interface under a strongly acidic condition. The surface of the gold nanoparticles is protected by mercaptosuccinic acid (MSA). The small angle X-ray diffraction (SAXD) pattern proved the presence of a large unit cell due to superlattice formation. The faceted morphology of the superlattices studied by scanning electron microscopy (SEM) was another indication of their crystalline nature. Scanning tunneling microscopy (STM) was used to investigate the surface image of the superlattices, demonstrating a well-ordered hexagonal arrangement of nanoparticles. Geometrical optimization using PM3 molecular orbital calculations suggested that CH/π interactions between the protonated form of MSA and HOPG surface would contribute to the initial-stage adsorption of the nanoparticles.     

基于正交实验法的Cu/Ta/TEOS碱性抛光液的优化

研究了碱性阻挡层抛光液中各组分对Cu、Ta和正硅酸乙酯(TEOS)去除速率的影响。通过单因素实验分别考察了磨料、FA/OⅡ螯合剂、KNO3和FA/OⅡ表面活性剂质量分数和H2O2体积分数对Cu、Ta和TEOS去除速率的影响,再结合正交实验研发了磨料质量分数为20%、FA/OⅡ螯合剂质量分数为2%、H2O2体积分数为0.1%,KNO3质量分数为1.5%、FA/OⅡ表面活性剂质量分数为2%的碱性阻挡层抛光液,该抛光液的Cu、Ta和TEOS的去除速率选择比为1∶1.47∶1.65。对4片12英寸(1英寸=2.54 cm)65 nm铜互连图形片的M4层进行阻挡层抛光,结果显示,铜沟槽内剩余铜膜厚度约为300 nm (目标值),图形片表面缺陷数目在10颗左右,碟形坑和蚀坑深度分别由52.3 nm和40 nm降至19.9 nm和18.4 nm,铜的表面粗糙度由4.4 nm降至1.9 nm。     

Observation of high interface state densities at the silicon/oxide interface for low doped polysilicon/oxide/silicon capacitor structures

In this work, we present new observations noted in the capacitance–voltage behaviour of polysilicon/oxide/silicon capacitor structures. As the active doping concentration reduces in the polysilicon layer, an anomalous capacitance–voltage behaviour is measured which is not related directly to depletion into the polysilicon gate. From examination of the frequency dependence of the capacitance–voltage characteristic, in conjunction with analysis and simulation, the anomalous capacitance–voltage behaviour is explained by the presence of a high density of near-monoenergetic interface states located at the silicon/oxide surface. The density and energy level of the interface states are determined. Furthermore, the work presents a mechanism by which the polysilicon doping level can impact on the properties of the silicon/oxide interface.     

Effective recombination velocity at the NN+ interface

The effective recombination velocity S_nn⁺ at the nn⁺ interface in buried layer (nn⁺p) and n epi-n⁺ substrate structures has been studied using a model which takes into account the retarding outdiffusion region, recombination and bandgap narrowing. The variation of S_nn⁺ with diffusion length and bandgap narrowing has been estimated taking into consideration their doping-dependence. An attempt has been made to explain the wide range in the reported values for S_nn⁺ using the results of this study.Results indicate clearly the difference between the S_nn⁺ of the two structures. This difference arises from the collection by the p-substrate which accounts for a significant part of the S_nn⁺ of the buried layer structure over a wide range of values of diffusion length. This collection component of S_nn⁺ is sensitive to bandgap narrowing.On the other hand, the S_nn⁺ of the nn⁺ structure is largely determined by the recombination in the outdiffusion region which is sensitive mainly to the value of diffusion length in that region. The component of S_nn⁺ representing recombination in the n⁺ substrate is sensitive to bandgap narrowing. The present study indicates the dependence of S_nn⁺ on the structure and processing of the devices in which the nn⁺ interface occurs.     

Electrical modeling of interface roughness in thin filmelectroluminescent devices

If two dielectric materials with different permittivities are in contact with each other and the interface between them is rough, then the electric field near this interface will be very inhomogeneous. In thin film electroluminescent devices, light is generated when electrons move back and forth in the phosphor layer under the influence of a strong ac electric field. At high electric fields, the electrons trapped in deep states at the interface between phosphor and insulator layer tunnel into the conduction band of the phosphor. This tunnel process is very sensitive to the electric field at the interface, so for a rough interface the electron flow will be very inhomogeneous. The relation between the interface roughness and the inhomogeneous charge transfer in thin film electroluminescent devices is investigated, based on an analytical flux tube model. The importance of the inhomogeneous current for the use of gray levels and aging is discussed     

高介电常数栅介质/二氧化硅界面偶极子成因研究

The formation of an electric dipole at the high-k/SiO2 interface is quantitatively analyzed. The band lineups and physical origin of dipole formation at the high-k/SiO2 interface are explained by the dielectric contact induced gap states(DCIGS). The charge neutrality level(CNL) of the DCIGS, which represents a distribution of high-k and SiO2 contact induced gap states, is utilized to study the dipole moment. The charge transfer due to different CNLs of high-k and SiO2 is considered as the dominant origin of dipole formation. The theoretically calculated dipole strengths of high-k/SiO2 systems based on this model are in good agreement with the experimental data.