Delamination of polyimide/Cu films under mixed mode loading

Organic passivation layers are used as coatings in semiconductor devices for protection of metallization films against a variety of environmental effects. Polyimides (PI) have been used successfully as conformable protection layers on aluminium and also recently on copper metallization. While adhesion properties of Cu interconnects to compliant polymer substrates have been investigated so far, studies on PI/Cu passivation layers are scarce. In this study the adhesion strength of polyimide passivation layer to Cu film stacks on Si has been studied by using different fracture mechanic methods including four point bending, double cantilever beam and single lap shear tests. The focus is investigation of the dependency of the critical energy release rate to the mode mixity obtained by different testing techniques and evaluation of the delamination data using analytical models and by means of FEA and cohesive zone modelling.     

Breakdown characteristics of gallium arsenide

This paper presents a comparison of the experimentally measured breakdown characteristics of high-purity gallium arsenide epitaxial layers with the theoretical calculations reported in the literature. The experimental data has been obtained by forming gold Schottky barrier diodes on material grown by using two different liquid phase epitaxial growth techniques. Good agreement is observed between the measured data and the breakdown voltages calculated by Lee and Sze[4] for     

Molybdenum germanide ohmic contact to n-GaAs

GeMo refractory ohmic contacts for n-type GaAs with a specific contact resistivity as low as 10-6?cm2 have been obtained on 1018cm-3 epitaxial layers. This low resistivity was obtained by contact annealing under As overpressure. Contacts using As-doped Ge layers and annealed without As overpressure have also been realised; in this case the obtained resistivity was 5 × 10-6?cm2. The ohmic contact formation resulted from the creation of an n + layer by Ge overdoping and the formation of a molybedenum germanide stable phase.     

Electrochemical capacitance voltage profiling of the narrow band gap semiconductor InAs

InAs is a narrow band gap compound semiconductor with potential applications in infra-red detectors and high speed transistors. In order to facilitate device design using this material, it is essential that carrier concentration profiles be accurately known. Capacitance-voltage (CV) profiling is often employed for this purpose. Due to surface Fermi level pinning, it is difficult to form metal Schottky contacts to InAs layers, making conventional CV profiling difficult. Electro-chemical CV (ECV) measurements have been successfully performed on InAs epilayers grown by molecular beam epitaxy on GaP. A solution of 0.2 M EDTA with 0.2M NaOH and 10–20% by volume of ethylenediamine acts both as an etchant and as a Schottky contact to InAs. The profiles obtained for undoped InAs layers were compared to Hall effect data, and showed good agreement. ECV profiling of thick layers with p- and n-type doped regions is also demonstrated.     

Three-layer 1.3 µm In1-xGaxAsyP1-ylasers with quaternary confining layers

Improvements in the surface morphology of InGaAsP DH wafers were obtained with addition of small amounts of Ga and As in the confining layers. This method was used to improve interface flatness between active and confining layers, consequently improving wafer yield and reproducibility. Three-dimensional lattice-mismatch data of the confining layers were determined in detail using simultaneous multiple Bragg diffraction of X-rays. In all wafers tested, independent of the active layer thickness, the maximum threshold current density Jthwas at most 60 percent higher than Jthminimum. The minimum normalized threshold current density obtained by us-3.4 kA/cm²μmis to our knowledge the lowest reported to date. Low resistance contacts-differential series resistance of 1 to 2 Ω for 10 μm SiO2stripe-geometry contact-can consistently be directly applied to tile top confining layer, thus dispensing with file need of a cap layer. CW operation at room temperature has been achieved with these three-layer devices.     

Laser oscillation at 3-4 µm optically pumped InAs1-x-ySbxPy

Quaternary InAs1-x-ySbxPy) and ternary InAs1-xSbxhave been grown on InAs substrates using liquid phase epitaxy. The quaternary layers are lattice matched to InAs fory = 2.2x, and have bandgaps greater than InAs. The ternary layers have lower bandgaps than InAs, but have larger lattice constants. Reasonable quality growth has been obtained up tox = 0.15where the luminescence peak is shifted to ∼4 from 3.1 μm and the lattice mismatch is ∼0.01. Optically pumped laser emission at 3.1 μm has been observed from 77 to 100 °K using an InAs active layer with InAs1-x-ySbxPyclading layers. Laser emission at 3.9 μm has been observed from 77 to 125 °K using a InAs1-xSbxactive layer, withxsim 0.13, and InAs cladding layers. Laser emission from intermediate ternary compositions has also been observed.     

Close coupled resonant aperture inserts for waveguide filteringapplications

A two-layer frequency selective surface (FSS) is used as a very compact and lightweight transverse waveguide filter element. A narrow-hand transmission response is produced from two layers, which, otherwise, in isolation would exhibit a broadband response. Measured results are compared with theoretical data obtained from a Transmission Line Matrix (TLM) based modeling method. Reduction in the passband bandwidth of a factor of four has been achieved using the proposed structure     

High quality thick epitaxial films for power semiconductor devices

High quality epitaxial layers with low defect levels are the key to fabrication of high voltage power devices. Growth of 100 μm thick epitaxial layers has been performed using a thermally driven chemical vapor deposition process. Three important parameters that have significant influence on epitaxy quality have been identified: substrate surface condition, reactor system cleanliness, and deposition process. The prerequisite p-n-p structure of a 6 kV thyristor was fabricated using 100 μm thick epitaxial layers to form the p-base. Defect density (hillocks and dislocations) in epitaxial layers has been correlated with the breakdown voltage of the p-n-p structure. It was found that an order of magnitude improvement of the defect level was obtained using well polished substrates instead of poorly polished substrates. Further improvement was achieved with the use of an etched reactor system before epitaxial growth, resulting in the reduction of defect density by another order of magnitude. A new cycled process, consisting of successive H₂ purges and deposition steps, is proposed that effectively reduces the defect level by an additional factor of 4, as compared with the conventional continuous deposition process. Specular epitaxial layers without spikes were obtained. Experimental results showed that for thick epitaxial films (100 μm), a susceptor with round-bottomed depressions provides higher dislocation density than one with flat-bottomed depressions, leading to a lower breakdown voltage of test devices.     

Characterization of closed space vapor transport GaP epitaxial layers

The growth of homoepitaxial GaP layers using Te-doped GaP as source material has been obtained by the so-called closed space vapor transport technique. The photoluminescence study shows that these layers, when grown under optimized thermodynamical conditions, have both a large luminescence efficiency and the same optical quality as the ones obtained by liquid phase epitaxy. The variation of the luminescence properties with the conditions of growth has been investigated. Both electron paramagnetic resonance and deep level transient spectroscopy detect the presence of deep levels that are not observed in liquid phase epitaxy materials.     

Optical anisotropy in thin films of poly(3,4-ethylenedioxythiophene)–poly(4-styrenesulfonate)

Anisotropic optical constants spectrum of spin-coated thin films of poly(3,4-ethylenedioxythiophene)–poly(4-styrenesulfonate) (PEDOT–PSS) from 200 to 1700 nm were determined using variable-angle spectroscopic ellipsometry and polarized intensity transmission data together with absorption spectroscopy. PEDOT–PSS was found to be very anisotropic, uniaxial with the optic axis parallel to the surface normal. The result is in good agreement with results obtained of chemically polymerized PEDOT layers doped with toluenesulfonate. By adding sorbitol to the PEDOT–PSS dispersion before spin-coating, layers with a higher conductivity were obtained. A detailed study was made of the optical response of these layers in comparison to the PEDOT–PSS prepared from dispersions without sorbitol. The optical anisotropy is important to consider when using PEDOT–PSS in optoelectronic devices, such as polymer light-emitting diodes and photovoltaic devices.     

Low temperature InP/Si technology: from Si substrate preparation toepitaxial growth

InP layers have been grown on Si(001) substrates by using a low temperature process, both for the Si surface preparation (400°CSi<550°C) and for the growth process itself (T_g <350°C) using solid source atomic layer molecular beam epitaxy. Strain-free InP on Si layers, with an etch pit density of ~1-2×10⁷ cm^-2, showing an excellent morphology and good optical quality have been obtained using a buffer layer involving strain layer superlattices (SLS) of elastically dissimilar materials. This result implies an actual advancement towards monolithic integration of III-V devices to conventional CMOS-Si circuits     

Atomic layer epitaxy of InP

In this work we will discuss the growth conditions for ALE of InP. Growth experiments were carried out in a LP-MOCVD system with a fast switch gas manifold. InP layers were deposited by pulsing TMIn and PH₃, using Argon as carrier gas. A self limiting growth rate at 1 ML/cycle has been obtained with a substrate temperature as low as 320-360° C. InP epitaxial layers were grown on GaAs and InP substrates, and on GaInAs(P) layers previously deposited by conventional MOCVD. Selective area epitaxy on InP using a Si₃N₄ mask was also demonstrated. Results of this study are very encouraging for hybrid MOCVD/ALE growth of In-based compounds.     

Si衬底上无坑洞3C-SiC的外延生长研究

在冷壁式不锈钢超高真空系统上 ,利用低压化学气相淀积 (LPCVD)方法在直径为 5 0 mm的单晶 Si(1 0 0 )和 Si(1 1 1 )晶向衬底上生长出了高取向无坑洞的晶态立方相碳化硅 (3 C-Si C)外延材料 ,利用反射高能电子衍射 (RHEED)和扫描电镜 (SEM)技术详细研究了 Si衬底的碳化过程、碳化层的表面形貌及缺陷结构 ,获得了界面平整光滑、没有空洞形成的 3 C-Si C外延材料 ,并采用 X-射线衍射 (XRD)、双晶 X-射线衍射 (DXRD)和霍尔(Hall)测试等技术研究了外延材料的结构和电学特性     

Monolithic integration of pseudomorphic power and low-noise HEMTs

Monolithic integration of pseudomorphic power and low-noise high electron mobility transistors (HEMTs) on a GaAs substrate has been demonstrated using specially designed multiple epitaxial layers. MBE-grown layers with three heterojunctions were selectively recessed to provide optimum structures for low-noise and power operations. At 18 GHz, a record power-added efficiency of 59% with 8 dB gain and 0.4 W/mm power density was obtained for the power HEMT. The low-noise device from the same slice achieved a noise figure of 1 dB with 9 dB associated gain at the same frequency.<>     

Indirect atmospheric measurements utilizing rake tropospheric scatter techniques—Part II: radiometeorological interpretation of rake channel-sounding observations

Successful remote sensing of the lower atmosphere's refractive-structure has been demonstrated using the Rake tropospheric scatter channel-sounding technique. The detected atmospheric structures show spatial refractive inhomogeneity in the form of discrete scattering layers at different heights. Detected layer heights and crosspath wind speeds were found to be in close agreement with U. S. Weather Bureau rawinsonde data from three surrounding locations. The analysis of the radio data was based on single scattering and assumed that Doppler shifts were due primarily to the horizontal crosspath wind. Certain detected layers exhibited azimuthal dependence in agreement with classical isotropic turbulence theory. Other layers of a specular nature produced radio data that are shown to agree with an anisotropic form of the refractive space correlation function. The degree of anisotropy for one experiment was evaluated from the radio data.     

Deposition of CuInSe2 films by a two-stage processutilizing E-beam evaporation

The deposition technique involves first depositing Cu and In metallic layers onto a substrate using the electron-beam evaporation method and then selenizing these layers in an H₂Se atmosphere. High-quality CuInSe₂ films of chalcopyrite phase have been obtained by this technique, and the films have been characterized by scanning electron microscopy, X-ray diffraction, electron microprobe, and resistivity measurements. Solar cells have been fabricated using these CuInSe₂ films, and active-area conversion efficiency values approaching 11% have been demonstrated for these devices     

Determination of the characteristic length of thickness fluctuations for a tunneling-thin insulator in MIS structures from electrical data

New methods for determining the “correlation length” for thickness fluctuations of a thin insulator film from data obtained in measurements of the electrical characteristics of MIS tunnel structures, i.e., without the use of microscopy, have been suggested and tested. One of these methods relies on statistical processing of electric current data for a random sample of structures. The other technique analyzes abrupt downward changes in current, observed in tests of devices under a sufficiently high bias. The methods have been tested on Al/SiO₂/Si tunnel structures. The resulting estimates of the characteristic scale of thickness fluctuations are compared with the data obtained in direct measurements of this scale for the same oxide layers.     

Ion-implantation and activation behavior of Si in MBE-Grown GaAs on Si substrates for GaAs MESFET's

The suitability of MBE-grown GaAs layers on Si substrates has been studied for ion-implanted GaAs MESFET technology. The undoped as-grown GaAs layers had a carrier concentration below 10¹⁴cm^-3. Uniform Si ion implants into 4-µm-thick GaAs layers on Si were annealed at 900°C for 10 s, using a rapid-thermal-annealing (RTA) system. Both the activation and the doping profile were similar to those obtained in bulk semi-insulating GaAs under similar conditions. The SIMS profiles of Si and As atoms near the GaAs/Si heterointerface were identical before and after the RTA process, indicating negigible interdiffusion during the implant activation. Dual implants of a shallow n+ layer and an n-channel layer were used to fabricate GaAs MESFET's with a recess-gate technology. Selective oxygen ion implantation was used for device isolation. The maximum transconductance obtained was 135 mS/ mm compared to typical values of 150-180 mS/mm obtained in our laboratory on GaAs substrates in similar device structures.     

Resolution of spreading-resistance measurements on shallow layers

The limited spatial resolution of spreading-resistance measurements made on shallow diffused layers is demonstrated both experimentally and theoretically. This effect seems to have been overlooked in the literature and may account for the discrepancies that are sometimes observed in profiles derived from spreading-resistance data obtained from bevelled surfaces.     

Structure and properties of high efficiencyZnO/CdZnS/CuInGaSe2 solar cells

Thin-film polycrystalline solar cells with the structure ZnO/CdZnS/CuInGaSe₂ fabricated with total area efficiencies of up to 12.5% under AM1.5 equivalent illumination and 10.5% under AM0 equivalent are discussed. These are among the highest total area efficiencies reported for polycrystalline thin-film solar cells. Current-voltage and quantum efficiency data for such a high-efficiency cell are given. Described are the deposition of the CuInGaSe₂ by physical vapor deposition in vacuum, the CdZnS by chemical deposition from solution, and the ZnO by reactive sputtering. The electrical and optical properties of the individual layers have been inferred from measurements on complete devices and on separate witness layers. Optical constants and thicknesses obtained for the device layers from these measurements are presented, and the requirements for optimizing the device efficiency are discussed