bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-time spectroscopic ellipsometry as an in-situ probe of the growth dynamics of amorphous and epitaxial crystal silicon for photovoltaic applications
Authors: Levi D.H. , Teplin C.W. , Iwaniczko E. , Yan Y. , Wang T.H. , Branz H.M.
Published: June 2019

In this paper we report on our work using in-situ real time spectroscopic ellipsometry (RTSE) to study the dynamics of hot-wire chemical vapor deposition (HWCVD) of hydrogenated amorphous silicon (a-Si:H) and epitaxial crystal silicon (epi-Si) for photovoltaic applications. We utilize RTSE as both an in-situ diagnostic and a postgrowth analysis tool for a-Si:H/crystalline silicon heterojunction (SHJ) solar cells and epi-silicon films grown by HWCVD. RTSE enables precise thickness control of the 3 to 10 nm thick layers used in the SHJ devices, as well as monitoring crystallinity and surface roughness in real time. With the assistance of in-situ RTSE feedback we have achieved a photovoltaic energy conversion efficiency of 17% on an Al-backed p-type float-zone c-Si wafer. Open-circuit voltages above 650 mV indicate excellent passivation of the c-Si surface by the a-Si:H intrinsic layer. We have used RTSE to obtain information on the degree of crystallinity and the electronic and optical properties of films as a function of deposition conditions. RTSE has indirectly indicated the persistence of a hydrogen layer at the interface between the a-Si:H layer and the crystal silicon substrate. Absorption spectra determined by RTSE have provided guidance in device optimization.

We are also applying in-situ RTSE to study the dynamics of HWCVD growth of epi-Si. The goal of this work is to develop low-temperature methods for growing 2-10 μmthick layers of c-Si on c-Si seed layers on glass for solar cell applications. This study presents unique challenges for RTSE, as perfect epitaxial growth of c-Si on a c-Si wafer would produce no change at all in the RTSE spectra. We have found that by monitoring the pseudo-dielectric function in real time during growth we gain immediate feedback on the breakdown of epi-Si growth. Post-deposition analysis of the RTSE data provides quantitative information on the percent of c-Si and a-Si versus film thickness. The RTSE analysis has been confirmed by cross sectional TEM. Based on the rapid feedback provided by RTSE we have surpassed the previous HWCVD maxiumum of 200 nm of epi-Si growth, achieving a maximum thickness of 500 nm of epi-Si. TEM analysis has shown that micron-sized areas of these films achieve 1000 nm of epi-Si thickness.
Development of Deposition Phase Diagrams for Thin Film Si:H and Si1-xGex:H Using Real Time Spectroscopic Ellipsometry
Authors: Podraza N. J. , Ferreira G. M. , Wronski C. R. , Collins R. W.
Published: June 2019

The growth of hydrogenated silicon (Si:H) and silicon-germanium alloys (Si1-xGex:H) by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) substrates has been studied by real time spectroscopic ellipsometry (RTSE). The motivation is to develop deposition phase diagrams that can provide greater insight into the optimization of amorphous Si1-xGex:H (a-Si1-xGex:H) for multijunction photovoltaics. In initial studies, the phase diagram for bottom cell a-Si1-xGex:H (Eg ˜ 1.4 eV) is found to exhibit fundamental similarities to that for Si:H when both materials are prepared under standard PECVD conditions that optimize pure a-Si:H. These similarities suggest directions for optimizing a-Si1-xGex:H by identifying conditions under which a smooth, stable surface is obtained to the largest possible bulk layer thickness. In phase diagram development for PECVD Si1-xGex:H on c-Si, it has been found that the highest surface stability and smoothest surfaces are obtained using cathodic deposition (self bias: ˜-20 V) with a H2-dilution level just below that of the amorphous-to-(mixed-phase microcrystalline) [→(a+μc)] transition for a thick layer. Due to the promising nature of these results, full phase diagrams are compared for cathodic and anodic Si1-xGex:H as well as for cathodic and anodic Si:H, all on c-Si substrates. The cathodic phase diagram for Si1-xGex:H reveals a narrow range of significant improvement in surface structural evolution near the →(a+μc) transition, and for a-Si:H reveals an extension of the ultrasmooth protocrystalline regime to a much wider range of thickness.
Threshold Voltage Optimization with Ion Shower Implantation for Polysilicon Thin-film Transistors
Authors: Choi B. D. , Choi D. C. , Im C. Y. , Choi K. H. , Yu C. H. , Kakkad R. , Chung H. K.
Published: June 2019

In this paper, we present the results of ion shower implantation to adjust threshold voltages on ELC (excimer laser crystallized) poly silicon thin film transistors. We observed that the threshold voltages of poly Si TFT strongly depended on the shower implantation dose, not the shower implantation energy for the 500 Å-thick active silicon layer. The threshold voltages for the reference, dose 5×1011 cm-2, and 1×1012 cm-2 cases were 0.30V, 1.25V, and 2.04V, respectively. We conclude that the threshold voltage can be appropriately adjusted by tuning the dose of the counter doping shower implant and its DIBL can still be suppressed to within an acceptable level.
PECVD grown hydrogenated polymorphous silicon studied using current transient spectroscopies in PIN Diodes
Authors: Tripathi Vibha , Mohapatra Y. N. , Roca i Cabarrocas P.
Published: June 2019

Hydrogenated polymorphous silicon (pm-Si:H) has steadily emerged as a potential replacement of hydrogenated amorphous silicon. Possible changes in the density of gap states due to the presence of crystallites is of central importance in understanding steady state and dynamic characteristics of devices using these materials. We have studied a-Si:H and pm-Si:H grown by PECVD at optimized conditions through the measurement of the steady state reverse current and their transients in PIN devices. The transients are analyzed using isothermal spectroscopic techniques such as Time Analyzed Transient Spectroscopy (TATS), and high resolution Laplace DLTS as a function of temperature. In case of a-Si:H, we obtain the expected signature of emission from a broad density of states in the form of stretched exponentials. In contrast the corresponding spectra for pm-Si:H are dominated by nearly exponential fast current decay processes with discrete energies between 0.20 and 0.26 eV. It is shown that the study of the density of states by dynamic methods such as transient techniques reveal features not accessible to steady state measurements.
Ge Growth on Nanostructured Silicon Surfaces
Authors: Vanamu Ganesh , Datye Abhaya K. , Zaidi Saleem H.
Published: June 2019

We report highest quality Ge epilayers on nanoscale patterned Si structures. 100% Ge films of 10 μm are deposited using chemical vapor deposition. The quality of Ge layers was examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution x-ray diffraction (HRXRD) measurements. The defect density was evaluated using etch pit density measurements. We have obtained lowest dislocation density (5×105 cm-2) Ge films on the nanopatterned Si structures. The full width half maximum peaks of the reciprocal space maps of Ge epilayers on the nanopatterned Si showed 93 arc sec. We were able to get rid of the crosshatch pattern on the Ge surface grown on the nanopatterned Si. We also showed that there is a significant improvement of the quality of the Ge epilayers in the nanopatterned Si compared to an unpatterned Si. We observed nearly three-order magnitude decrease in the dislocation density in the patterned compared to the unpatterned structures. The Ge epilayer in the patterned Si has a dislocation density of 5×105 cm-2 as compared to 6×108 cm-2 for unpatterned Si.
Polycrystalline GeC Thin Films Deposited Using a Unique Hollow Cathode Sputtering Technique
Authors: Soukup R. J. , Ianno N. J. , Schrader J. S. , Dalal V. L.
Published: June 2019

Experimental results on thin films of the new material GexC1-x, deposited by a unique dual plasma hollow cathode sputtering technique are presented. The mostimportant contribution of this work is that it shows that by using non-equilibrium growth conditions resulting from the hollow cathode technique, one can grow Group IV materials which cannot otherwise be grown using normal CVD or MBE processes. The sputtering is accomplished by igniting a dc plasma in the Ar and H2 gases which are fed through Ge and C nozzles.

The GeC films are grown on etched Si (100), on Si with the native oxide and on glass. The films grown on glass were quite disordered, but the films grown on both types of Si substrates were very ordered in nature. This order has been characterized using Xray diffraction (XRD) and Raman spectroscopy.

Films with as much as 8% C have been deposited. In order to produce useful GexC1-x films, the C must bond to the Ge at lattice sites. Evidence of this desired GeC bond has been seen using Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, and XRD.
Characterization of the Silicon-Based Thin Film Multi-Junction Solar Cells
Authors: Hishikawa Yoshihiro
Published: June 2019

Technical issues for the performance characterization of silicon-based thin-film multi-junction devices, such as the a-Si/thin-film c-Si structure, are discussed. The measured spectral response of each component cell is affected by the shape of the I-V curves of the component cells under color bias light, as well as the applied bias voltage. This paper describes procedures for correcting the measured spectral response. High-fidelity solar simulators, which incorporate Xe lamp(s) and halogen lamps that simulate AM1.5G standard sunlight, are very useful for characterizing the I-V curves of the multi-junction devices. They can accurately reproduce the current generated in each component cell and the I-V curve of the devices under standard sunlight, with a simple spectral adjustment procedure, thanks to their basic good spectral fidelity to standard sunlight. The irradiance dependence of the I-V curve is important for translating the I-V curve under different irradiance conditions. Although translation is not straightforward for multi-junction devices, the experimental results of the present study suggest that it is possible under spectral conditions where the relative value of the photocurrent among the component cells is constant. Determination of the I-V curve of each component cell based on the I-V curves of the multi-junction devices is also mentioned.
Structure of microcrystalline solar cell materials: What can we learn from electron microscopy?
Authors: Luysberg M. , Houben L.
Published: June 2019

Microcrystalline silicon and its group IV alloys are widely explored as absorber layers in thin film solar cells. Despite the extended research in recent years the fundamental understanding of the relation between macroscopical properties, i.e. electrical and optical properties, and the microstructure is poor. Clearly, the structure of microcrystalline materials, consisting of a phase mixture between “amorphous” material, crystalline grains, and voids, is complex. To demonstrate the strengths and limitations of transmission electron microscopy on microcrystalline materials, we will discuss different techniques employed to investigate grain sizes and morphologies, crystallographic orientations, amorphous volume fractions, and lateral arrangements of crystallites. In particular, we focus on the potential for analyzing the structure of grain boundaries and the amorphous phase in microcrystalline silicon and silicon carbide by the most advanced techniques in atomic resolution imaging in the transmission electron microscope.
Microcrystalline and Nanocrystalline Silicon: Simulation of Material Properties
Authors: Biswas R. , Pan B. C. , Selvaraj V.
Published: June 2019

We have simulated nano-crystalline silicon and microcrystalline silicon structures with varying crystallite volume fractions, using molecular dynamics simulations. The crystallite regions reside in an amorphous matrix. We find the amorphous matrix is better ordered in nanocrystalline-Si than in the homogenous amorphous silicon networks, consistent with the observed higher stability of H-diluted films. There is a critical size above which the crystallites are stable and may grow. Sub-nm size crystallites in the protocrystalline phase are found to reduce the strain of the amorphous matrix. We simulated micro-crystalline silicon with a substantial crystallite volume fraction. Microcrystalline structures exhibit a crystalline core surrounded by an amorphous shell with similarities to silicon nanowires. We find a relatively uniform H distribution in the amorphous region and a crystal-amorphous phase boundary that is not welldefined.
Effects of Post Annealing and Material Stability on Undoped and n+ nc-Si:H Films Deposited at 75 °C Using 13.56 MHz PECVD
Authors: Lee Czang-Ho , Sazonov Andrei , Nathan Arokia
Published: June 2019

The effects of post-deposition annealing and material stability of undoped and n+ nanocrystalline silicon (nc-Si:H) films deposited at 75 °C using standard 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) have been investigated. Electrical, structural, and chemical composition properties of the films at ambient atmosphere were studied before and after the thermal annealing. The dark conductivity (σd) in all films demonstrated high stability against prolonged ambient atmosphere exposure, which can be attributed to stable hydrogen passivation of the grain boundaries. On the other hand, in undoped nc-Si:H films, the σd increases by more than one order of magnitude after annealing in ambient atmosphere, followed by a decrease below the as-grown value. Depending on the annealing temperature, the σd can drop as low as 10-8 S/cm. In n+ nc-Si:H films, the decrease in the σd was lower. However, in undoped nc-Si:H films capped by an amorphous silicon nitride (a-SiN:H), this was not observed. In all films, no significant change in the film microstructure before and after annealing was detected. However, a small decrease in the hydrogen content (CH) accompanied by an increase in the oxygen content (CO) was observed in uncapped undoped nc-Si:H films. It was therefore concluded that the σd is affected by oxygen desorption due to annealing and its absorption from the ambient atmosphere. Based on experimental results, we propose a possible model in terms of hydrogen effusion-assisted oxygen absorption.
Characterization of Silicon thin Film Deposited by E-Beam Evaporator for Flexible Display
Authors: Song In-Hyuk , Han Sang-Myeon , Park Jung-Hyun , Han Min-Koo
Published: June 2019

The structure and crystal growth of the silicon thin film deposited by e-beam evaporator have been studied with use of scanning electron microscopy (SEM), x-ray diffraction and transmission electron microscopy (TEM). The silicon thin film is deposited at room temperature for flexible display. It is found that the silicon film deposited by e-beam evaporator has polysilicon structure by scanning electron microscopy (SEM). SEM image also shows that grain size of the silicon film is about 50nm. X-ray diffraction of the silicon thin film represents that the orientation of the silicon film is (201). We have also investigated the structure and the crystal growth of the silicon film after the silicon film is irradiated by XeCl excimer laser with various energy densities. Transmission electron microscopy shows that the irradiated silicon thin film has low intra-grain defects and sharp grain boundary.
Electron Field Emission from SiC/Si Heterostructures Formed by Carbon Implantation into Silicon and Etching of the Top Silicon Layer
Authors: Xing Yumei , Zhang Jihua , Yu Yuehui , Song Zhaorui , Shen Dashen
Published: June 2019

High intensity electron field emissions were obtained from SiC/Si heterostructures formed by high temperature carbon implantation into silicon and subsequently etching of the top silicon layer. Implantation processes were performed at 700 °C with a dose of 3.0 to 8.0 x 1017 ions/cm2. Post-implantation annealing in argon at 1250 °C for 5h was done for partial samples. β-SiC precipitates were easily formed and embedded in silicon at the interface of SiC/Si heterostructures during high temperature carbon implantation for all samples. The densely distributed small protrusions led to efficient electron emission. Implantation dose scarcely impacted the electron emission characteristics when it reached to a definite value. After annealing, the density of protrusions at the interface of SiC/Si heterostructures became smaller since β-SiC precipitates were grown into larger sizes, which caused to a relatively inefficient electron emission.
Excimer Laser Crystallized HWCVD Thin Silicon Films: Electron Field Emission
Authors: Shaikh M. Z. , O'Neill K. A. , Persheyev S. K. , Rose M. J.
Published: June 2019

Thin silicon films deposited using the Hot-Wire Chemical Vapor Deposition (HWCVD) technique are studied here for the effect of XeCl excimer laser crystallization on their structural, optoelectronic, and electron field emission properties. Excimer Laser Annealing (ELA) of the silicon thin films indicated increased dark conductivity and reduced optical gap. Encouraging Field Emission (FE) results were obtained from XeCl excimer laser processed HWCVD films on Cr, V, Mo, and Ti backplanes. Geometric field enhancement factors from surface measurements and Fowler-Nordheim Theory (FNT) were compared. FE thresholds were also found to be particularly influenced by the backplane material.
GaAs Growth on Micro and Nano Patterned Ge/Si1-XGeX and Si Surfaces
Authors: Vanamu Ganesh , Datye Abhaya K. , Dawson Ralph L. , Zaidi Saleem H.
Published: June 2019

We show heteroepitaxial growth of GaAs on Ge/SiGe grown on nanometer-scale grating structures. Conventional lithography techniques were combined with reactive ion and wet-chemical etching to fabricate 1-D patterns of silicon posts. The quality of the GaAs layers was investigated using high-resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), photoluminescence (PL) and etch pit density (EPD) measurements. Our results show significant improvement in the quality of heteroepitaxial layers grown on nano patterned structures compared to those on the unpatterned silicon. The optical quality of the GaAs/Ge/SiGe on nano-scale patterned silicon was comparable to that of single crystal GaAs.
High-Temperature Nanoindentation Measurement for Hardness and Modulus Evaluation of Low-k Films
Authors: Ye Jiping , Kojima Nobuo , Shimizu Satoshi , Burkstrand James M.
Published: June 2019

A high-temperature nanoindentation measurement method has been developed for evaluating the hardness and modulus of low-k films when the temperature is raised from R.T. to 200°C. Thermal stability and chemical changes due to heating were investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetry-differential thermal analysis, and by thermal desorption spectroscopy, respectively. Two different classes of low-k materials, organic polyarylence ether film and methyl-hydrogen-silsesquioxane film, were examined. The hardness and modulus of the former film during heating increased due to water desorption in the lower temperature range, and then decreased due to the evolution of hydrocarbon gas from some unreacted components or solvent residuals in the higher temperature range. In regard to the latter film, the hardness and modulus of a specimen (A) having a higher hydrocarbon content decreased during heating and reached the lowest value at 200°C and then constantly remained at the lowest levels during cooling. In contrast, no significant changes in hardness and modulus were observed for a specimen (B) having a lower hydrocarbon content in either the heating or cooling process. The reduction of the hardness and modulus of specimen A was attributed to thermal decomposition of most of its Si-CH3 and SiH/SiH2 chains. These results revealed that the temperature dependence of the hardness and modulus of low-k films is significantly affected by physical and/or chemical changes during heating due to moisture absorption, thermal evolution of organic residuals and thermal decomposition, rather than other factors such as thermal stress.
Integration of a Polymer Etch Stop Layer in a Porous Low K MLM Structure
Authors: Smith Gregory C. , Henis Neil , McGowan Richard , White Brian , Kraatz Matthias , Satyanarayana Sri , Hosali Sharath , Liu Youfan , Pfeifer Klaus
Published: June 2019

Two level metal structures were fabricated to test the efficacy of using an organic low K etch stop layer (OESL) in order to lower the effective dielectric constant for intralayer capacitance. The organic etch stop layer's intrinsic capacitance of 3.3 compares with that of silicon carbide (∼ 5) which constitutes the control of the experiment. This reduction represents a reduction of effective dielectric constant for the stack of about 10% to about 3.0. The process was optimized so as to achieve yield of via chains of a million 130 nm diameter vias, and effective K was measured. The target of 3.0 was achieved using this process. Interpenetration of the organic etch stop with the MSQ porous low K material was observed.
Nanoscale Observation of Dielectric Damage to Low k MSQ Interconnects from Reactive Ion Etching and Ash Treatment
Authors: Gross Todd S. , Yao Shaoning
Published: June 2019

Electrostatic force microscopy (EFM) was used to measure the extent of dielectric damage from plasma processing of nanoporous, low k methyl silsesqioxane (MSQ) interconnect structures with approximately 50 nm spatial resolution. Single level patterns were formed in 200 nm thick MSQ films by reactive ion etching (RIE) and were subsequently backfilled with an MSQ layer that was not exposed to plasma to act as a reference. The backfill was performed on as-etched structures with the photoresist intact and on structures in which the photoresist was removed by an oxygen plasma (ash) treatment. The EFM images on cross sections and feather sections show that the damage from the RIE penetrated ∼100 nm in from the sidewall and that the redeposited polymer had a higher k than the MSQ (k∼2.2). The etched and ashed MSQ exhibits a higher dielectric constant than the reference MSQ if it was exposed to water and has nearly the same dielectric constant as the reference with no water exposure. This suggests that the damage from the ash acts to make the MSQ hydrophilic.
Observation of Intrusion Rates of Hexamethyldisilazane During Supercritical Carbon Dioxide Functionalization of Triethoxyfluorosilane Low-k Films
Authors: Capani P.M. , Matz P.D. , Mueller D.W. , Kim M.J. , Walter E.R. , Rhoad J.T. , Busch E.L. , Reidy R.F.
Published: June 2019

Water adsorption by porous low-k silica films results in increased dielectric constants and is often due to silanol groups on the pore surfaces. Reacting the silanols with silylating agents (e.g., hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS)) in supercritical CO2 (SC-CO2) can increase film hydrophobicity and can remove adsorbed water. In porous methylsilsesquioxane (MSQ) films (average pore size ∼ 3-4nm), it has been determined that supercritical silylation reactions do not substantially penetrate beyond the film surface.1,2 In this work we have examined the supercritical penetration behavior of silylating agents in low-k films with larger pore sizes (5-10nm). The depth and extent of reactants was determined by in situ infrared spectroscopy (FTIR), and surface hydrophobicity was examined by contact angle experiments.
Effect of Plasma Treatment and TMCTS Vapor Annealing on the Reinforcement of Porous low-k Films
Authors: Kohmura Kazuo , Tanaka Hirofumi , Oike Shunsuke , Murakami Masami , Ono Tetsuo , Seino Yutaka , Kikkawa Takamaro
Published: June 2019

A novel process of TMCTS vapor annealing combined with a plasma treatment has been developed for improving the mechanical strength of porous silica films having ultralow dielectric constant. When porous silica films annealed under 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) vapor were treated with argon plasma and then re-treated with TMCTS vapor, the mechanical strength (i.e., elastic modulus, hardness) of the films increased significantly. Results of Fourier transform infrared spectroscopy (FT-IR) suggested an accelerative effect resulted from the plasma treatment on the conversion of Si-CH3 and Si-H groups to Si-OH groups. The latter group appears to react faster with TMCTS from the second annealing to form cross-linked polymer network on the porous silica wall surfaces. The resulting cross-linked network is thought to keep the low permittivity and enhance the mechanical strength of the low-k films.
High Strength Low Dielectric Constant Aromatic Thermosets
Authors: Huang Yongqing , Economy James
Published: June 2019

Continuing miniaturization of microelectronic devices requires development of low dielectric constant materials to lower the RC delay, power dissipation and crosstalk noise. Although spin-on polymer dielectrics usually have better potential for extendibility to lower dielectric constant (k) values compared to chemical-vapor-deposited dielectrics, their low mechanical properties prevent them from being successfully integrated with copper metal lines.

Recent evaluation of a new thermosetting oligomer shows high thermal stability, low moisture pick-up and low dielectric constant. Techniques to optimize the solubility and spin coating characteristics of the oligomer have been developed. The thermally cured polymer displayed a thermal stability up to 480°C in nitrogen and 400°C in air. The cured polymer displayed a dielectric constant of 2.7 at 1 MHz and a breakdown strength larger than 230 V/μm. Nanoindentation testing showed that it had an extraordinarily high Young's modulus of 16.8 GPa and a hardness of 3.5 GPa. By use of porogens, a dielectric constant as low as 1.85 was obtained while still maintaining an acceptable high Young's modulus of 7.7 GPa and hardness of 2.0 GPa. Nanoscratch testing indicated that this material had good adhesion to the Si substrate, and Ta which is a diffusion barrier for copper. These results appear unique compared to all commercially available low-k candidates.
A Novel Organic Low-k Film Deposited by Plasma-Enhanced Co-Polymerization
Authors: Kunimi Nobutaka , Kawahara Jun , Kinoshita Keizo , Nakano Akinori , Komatsu Masashi , Kikkawa Takamaro
Published: June 2019

A new organic precursor was designed and synthesized in order to form polymer films having low dielectric constants by a plasma-enhanced co-polymerization (PCP) technology. The organic monomer features a large aliphatic hydrocarbon structure, tricyclodecane (TCD) group. Optimized polymer films deposited from the monomer had dielectric constants less than 2.5. A solid 13C-NMR spectrum showed that the TCD moiety in the precursor was included in the polymer without changing the structure. The effect of the deposition temperature on the film structure was studied by analyzing Raman spectra. It was revealed that the dielectric constant is strongly associated with sp2 carbon content in the TCD-based polymer films.
Analysis of Electromigration-Induced Void Motion and Surface Oscillations in Metallic Thin-Film Interconnects
Authors: Cho Jaeseol , Gungor M. Rauf , Maroudas Dimitrios
Published: June 2019

An analysis is presented of electromigration-induced migration and oscillatory dynamics of morphologically stable void surfaces based on self-consistent numerical simulations of morphological evolution of voids in metallic thin films. As the morphological stability limit is approached, the migration speed of a stable void deviates substantially from being inversely proportional to the void size, a well-known result that is rigorously valid in an infinite conductor with isotropic material properties. A non-linear shape function that includes both current crowding and diffusional anisotropy effects is used to rescale properly the void migration speed resulting in a universally valid relationship for the migration speed as a function of void size. Furthermore, in grains characterized by high symmetry of surface diffusional anisotropy, our analysis predicts the onset of stable time-periodic states for the void surface morphology that correspond to waves propagating on surfaces of voids that migrate along the metallic film at constant speeds.
The Effect of Immersion Sn coating on the Electromigration Failure Mechanism and Lifetimes of Cu Dual Damascene Interconnects
Authors: Yan Minyu , Tu King-Ning , Vairagar Anand V. , Mhaisalkar Subodh G. , Krishnamoorthy Ahila
Published: June 2019

In sub-micron dual damascene Cu interconnects, electromigration occurs mainly along the interfaces between Cu and dielectric cap layer. Many reports have shown that the interface of Cu/dielectric cap is the dominant diffusion path. In-situ electromigration experiments were carried out recently by A. V. Vairagar etal [APPL. PHYS. LETT., 85, 2502 (2004)] to investigate the electromigration failure mechanisms in the upper and lower layers in dualdamascene Cu test structures. It was found that electromigration-induced void first nucleates at locations which are far from the cathode, then moves along the Cu/dielectric cap interface in opposite direction of electron flow, and eventually causes void agglomeration at the via in the cathode end to open the interconnect. In the present study, immersion Sn (20 nm) was employed after CMP and before SiN deposition. All the samples, with a line-width of 0.28 um, were assessed by package level electromigration tests at 300°C under a current density of 3.6MA/cm2. We found that immersion Sn surface treatment effectively introduced the Cu-Sn bonding to the Cu/dielectric interface and has influenced electromigration along the Cu/dielectric interfaces. Failure analysis shows that the samples with these Sn processes have a median-time-to-failure almost 1 order of magnitude larger than the control samples. A careful characterization utilizing FIB and SEM cross-sectional images shows that the failure mechanism has changed due to the Sn surface treatments. After electromigration-induced void nucleation, its movement is blocked by the strong Cu-Sn bonding so that its growth is localized and occurs along grain boundaries. With the increased impedance to surface diffusion, failure analysis seems to indicate that grain boundary diffusion now participates in the void movement and growth, which is proposed to be the reason for the increased lifetime.
Influence of design parameters on dark current of vertically integrated a-Si:H diodes.
Authors: Miazza C. , Wyrsch N. , Choong G. , Dunand S. , Ballif C. , Shah A. , Blanc N. , Lustenberger F. , Kaufmann R. , Despeisse M. , Jarron P.
Published: June 2019

Image and particle sensors based on thin film on CMOS (TFC) technology, where a-Si:H detectors are vertically integrated on top of a CMOS chip, basically provide high sensitivity and low dark current densities (Jdark). However, as shown in previous work and as confirmed by the actual measurements, Jdark values depend on the topology of the chip and on the detector structure used.

The present paper describes a systematic study carried out, both with test structures on glass and also with a dedicated CMOS test chip designed by CERN. The increase in Jdark is shown to be related to border effects, and especially on the detailed structure of the pixel periphery. In all cases, lower Jdark are obtained when one uses metal-i-p instead of n-i-p configuration detectors. Transferring these results to the standard TFC sensors used by them, the authors have obtained values of Jdark as low as 20 pA/cm2 at -1 V reverse bias.
Monolithic Integration of Electronics and Sub-wavelength Metal Optics in Deep Submicron CMOS Technology
Authors: Catrysse Peter B.
Published: June 2019

The structures that can be implemented and the materials that are used in complementary metal-oxide semiconductor (CMOS) integrated circuit (IC) technology are optimized for electronic performance. However, they are also suitable for manipulating and detecting optical signals. In this paper, we show that while CMOS scaling trends are motivated by improved electronic performance, they are also creating new opportunities for controlling and detecting optical signals at the nanometer scale. For example, in 90-nm CMOS technology the minimum feature size of metal interconnects reaches below 100 nm. This enables the design of nano-slits and nano-apertures that allow control of optical signals at sub-wavelength dimensions. The ability to engineer materials at the nanoscale even holds the promise of creating meta-materials with optical properties, which are unlike those found in the world around us. As an early example of the monolithic integration of electronics and sub-wavelength metal optics, we focus on integrated color pixels (ICPs), a novel color architecture for CMOS image sensors. Following the trend of increased integration in the field of CMOS image sensors, we recently integrated color-filtering capabilities inside image sensor pixels. Specifically, we demonstrated wavelength selectivity of sub-wavelength patterned metal layers in a 180-nm CMOS technology. To fulfill the promise of monolithic photonic integration and to design useful nanophotonic components, such as those employed in ICPs, we argue that analytical models capturing the underlying physical mechanisms of light-matter interaction are of utmost importance.
Infra-Red Photo-Detectors Monolithically Integrated with Silicon-Based Photonic Circuits
Authors: Bradley Jonathan D B , Jessop Paul E , Knights Andrew P
Published: June 2019

The development of monolithic silicon photonic systems has been the subject of intense research over the last decade. In addition to passive waveguiding structures suitable for DWDM applications, integration of electrical and optical functionality has yielded devices with the ability to dynamically attenuate, switch and modulate optical signals. Despite this significant progress, much higher levels of integration and increased functionality are required if silicon is to dominate as a substrate for photonic circuit fabrication as it does in the microelectronic industry. In particular, there exists a requirement for efficient silicon-based optical sources and detectors which are compatible with wavelengths of 1.3 and 1.5μm. While a great deal of work has focussed on the development of silicon-based optical sources, there has been less concentrated effort on the development of a simple, easily integrated detector technology. We describe here the design, fabrication and characterization of a wholly monolithic silicon waveguide optical detector, utilizing an integrated p+-u-n+ diode, which has significant response to optical signals at the communication wavelength of 1.54μm. Measurable infra-red response is induced via the controlled introduction of mid-gap electronic levels within the rib waveguide. This approach is completely compatible with ULSI fabrication. The requirement for the detectors to be integrated with a rib waveguide and hence the guarantee of a long optical signal-device interaction, results in electrical signals of several μAs, even for deep-levels with a small optical absorption cross-section. Further, the rise and fall time of the detectors is compatible with current monolithic, silicon device based, optical switching and modulation operating in the MHz regime. These results suggest that these detectors offer a cost-effective route to signal monitoring in integrated photonic circuits.
Making Wafer Bonding Viable for Mass Production
Authors: Tan Cher Ming , Yu Wei Bo , Jun Wei
Published: June 2019

Direct wafer bonding was performed under medium vacuum condition. High bonding strength (larger than 20 MPa) is achieved at the bonding temperature of only 400°C, and the annealing time for complete bonding is less than 5 hours. The bonding efficiency (percentage of the bonded area over entire wafer area) of the medium vacuum wafer bonding (MVWB) is also found to be better than the traditional wafer bonding.

Qualitative description of the mechanism of MVWB is proposed in present work. It is believed that the medium vacuum can enhance the out-diffusion of the water molecules and other trapped impurities through the bonding interface which is porous initially. This enhanced diffusion speeds up the chemical reaction for the formation of Si-O-Si, and thus more bonding sites are available before the interface close-up. As a result, we observe an increase in bonding strength, bonding efficiency and the bonding speed.
Surface-Induced Recrystallization of Amorphous Calcium Carbonates to Oriented Calcite Crystals
Authors: Han T. Yong-Jin , Aizenberg Joanna
Published: June 2019

Enigmatic functions of amorphous calcium carbonates (ACC) are explored by inducing the formation and the stabilization of spherulitic ACC particles on self-assembled monolayers (SAM) of hydroxy-terminated alkanethiols on Au surface. We demonstrate that the stabilized ACC particles can be induced to crystallize on command to form oriented calcite crystals by introducing a nucleating surface by a means of a secondary SAM surface with carboxylate functionality.
Electropermeabilization of Mammalian Cells Visualized with Fluorescent Semiconductor Nanocrystals (Quantum Dots)
Authors: Sun Yinghua , Vernier P. Thomas , Wang Jingjing , Kuthi Andras , Marcu Laura , Gundersen Martin A.
Published: June 2019

Electroporation/electropermeabilization is a non-viral technique for gene transfection and drug delivery. Here, the transfer mechanisms were studied with fluorescent nanocrystals (quantum dots, QDs) in mammalian cells. Interactions of the cell membrane and nanoscale particles were visualized after electric pulse treatment. Responses of human multiple myeloma cells to nanocrystals were tracked for periods up to 7 days. Large particles do not cross the membrane directly after pulsing, even if the membrane is permeabilized to small molecules. Large QDs were trapped on the cell membrane for hours after electroporation and were gradually either excluded or internalized by cells. QD uptake efficiency depended on both particle size and membrane transport activity. These results, consistent with an electropermeabilization model, suggest that enhancing the interactions between the cell membrane and macromolecules may improve the transfer efficiency.
Aminopropyl Embedded Silica Films as Potent Substrates in DNA Microarray Applications
Authors: Saal Kristjan , Plaado Margo , Kink Ilmar , Kurg Ants , Kiisk Valter , Koževnikova Jevgenia , Mäeorg Uno , Rinken Ago , Sildos Ilmo , Tätte Tanel , Lõhmus Ants
Published: June 2019

Sol-gel derived silane hybrid films composing of (3-aminopropyl)trimethoxysilane–tetramethoxysilane (APTMS-TMOS) have been shown to have properties that make the films suitable for DNA microarray applications. The ability of the films to bind DNA was studied using aminated 25-mer oligonucleotide DNA and 1, 4-phenylenediisothiocyanate linker. The binding of DNA onto the films was shown to depend on films' composition i.e. the binding rate decreased with the decrease of APTMS content in the film. The arrayed primer extension (APEX) analysis showed reversed tendency – fluorescence signals of bound probes increased with the decrease of APTMS content in the film. The background noise was low and the fluorescent probes were clearly outlined. The density of functional amino groups on the films was estimated by fluorescence spectroscopy.
Superparamagnetic Flexible Substrates based on Submicron Electrospun Estane Fibers Containing MnZnFe-Ni Nanoparticles
Authors: Gupta Pankaj , Asmatulu Ramazan , Claus Rick , Wilkes Garth
Published: June 2019

Flexible field responsive superparamagnetic substrates were prepared by electrospinning a solution of elastomeric polyurethane containing ferrite nanoparticles (ca. 14 nm) of Mn-Zn-Ni. The flexible mats were characterized in terms of fiber morphology and magnetic properties. Field Emission Scanning Electron Microscopy (FESEM) indicated that the diameter of these composite fibers was ca. 300-500 nm. Furthermore, the back-scattered electron FESEM images indicated agglomeration of the nanoparticles at higher wt% (ca 17-26 wt%) loading in the electrospun fibers. The induced specific magnetic saturation and the relative permeability were found to increase linearly with increasing wt% loading of the ferrite nanoparticles on the submicron electrospun fibers. A specific magnetic saturation of 1.7 – 6.3 emu/g at ambient conditions indicated superparamagnetic behavior of these composite electrospun substrates. Additionally, dielectric constant values of the electrospun fibers were measured to be between 2.3 and 5.8.
Investigations on the Magnetic Properties of High-Coercivity Nd40Fe30Co15Al10B5 Bulk Amorphous Alloys
Authors: Bessais L. , Djëga-Mariadassou C. , Phuc N. X.
Published: June 2019

Nd40Fe30Co15Al10B5 bulk amorphous prepared by high energy milling shows a coercivity of 8.1 kOe with a Curie temperature of 645 K. The controlled nanocrystallization enhances the coercivity to 20 kOe and the remanence ratio is equal to 0.59. The coexistence of two crystalline magnetic phases, ferromagnetic Nd2(Fe,Co,Al)14B and antiferromagnetic Nd6(Fe,Co,Al)14 are revealed by x-ray diffraction, high-resolution transmission electron microscopy, magnetization measurements, and Mössbauer spectrometry. The grain size for optimal magnetic properties is around 30 nm. The nucleation process may play a leading role in the high magnetic behavior.
Two-Mode Magnetic Switching of a Ferromagnetic Nanowire-Granule-Array Embedded in a Porous Silicon Matrix
Authors: Rumpf K. , Granitzer P. , Krenn H.
Published: June 2019

A low-cost method has been developed to produce metallic, perpendicularly oriented ferromagnetic nanowires embedded in crystalline silicon. The mesoporous silicon structure consists of channels with a diameter of about 60 nm and about 30 μm in depth. The electrochemically prepared ferromagnetic nanosystem is a composition of granules and wires which leads to a peculiar magnetic behaviour. The interesting magnetic properties of this bimodal system are investigated by SQUID-magnetometry. The hysteresis loop shows two switching fields at different magnetic fields, one in the low field range and the other one in the high field range. The first switching field at about 500 Oe is due to the magnetization of the granules, the second switching field nearby 5 T (at room temperature) is caused by dipolar coupling of the nanowires which become single domain at high fields due to Bloch Wall motions. This promising ferromagnetic nanocomposite system is not only interesting in basic research but gives raise to a lot of silicon based applications like spin-injection devices and magnetic field sensors.
Characterization of Nanocones Grown During DC Magnetron Sputtering of an ITO Target
Authors: Conley J.F. , McClain D. , Jiao J. , Gao W. , Evans D. , Ono Y.
Published: June 2019

A low temperature method for uniform growth of In2O3 nanostructures on Si wafers that does not require separate catalyst materials or template-assistance is investigated. Nanostructures are uniformly deposited on either bare or SiO2 thin film coated Si substrates via DC magnetron sputtering at 200-400°C using a 90% In2O3 / 10% SnO2 (ITO) target. The nanostructures are approximately 500 nm long, sit atop an accompanying underlying 100 nm conductive film, and are conically shaped, with a diameter of about 80 nm at the base, tapering to a point that is capped with a spherical “ball”. X-ray diffraction (XRD) indicates a cubic In2O3 phase. Field emission from the tips is observed at a base pressure of 10-8 Torr with turn-on fields in a range between 45-75 V/cm and threshold fields from 64-105 V/cm. Nanocone growth is investigated with respect to O2 and Ar flow rates, temperature, power, pressure, wafer rotation, and time.
Short-Period Superlattice Structure of Sn-doped In2O3(ZnO)4 and In2O3(ZnO)5 Nanowires
Authors: Na Chan Woong , Bae Seung Yong , Park Jeunghee
Published: June 2019

Two longitudinal superlattice structures of In2O3(ZnO)4 and In2O3(ZnO)5 nanowires were exclusively produced by thermal evaporation method. The diameter is periodically modulated in the range of 50-90 nm. They consist of one In-O layer and five (or six) layered Zn-O slabs stacked alternately perpendicular to the long axis, with a modulation period of 1.65 (or 1.9) nm. These superlattice nanowires were doped with 6-8 % Sn. X-ray diffraction pattern reveals the structural defects of wurtzite ZnO crystals due to the In/Sn incorporation. High-resolution X-ray photoelectron spectrum suggests that In/Sn withdraw the electrons from Zn, and enhance the number of dangling-bond O 2p states, resulting in the reduction of band gap. Photoluminescence exhibit the peak shift of near band edge emission to the lower energy as the In/Sn content increases.
Morphology and Properties of Tetraleg ZnO Nanostructures Fabricated by Zn-Powder Evaporation without Catalysts at Lower Temperature
Authors: Zhang Yue , Huang Yunhua , He Jian , Dai Ying , Wang Sen , Zhou Cheng
Published: June 2019

By simply controlling temperature and atmosphere, tetraleg ZnO nanostructures with different morphologies and sizes have been fabricated respectively through pure zinc powder evaporation without catalysts at temperature of 600∼800 oC. The growth mechanisms of the nanostructures were proposed and discussed. Photoluminescence spectra showed a UV and green emission peaks at room temperature. Field emission measurements revealed that the turn-on field is very low and the emission current density is relative to the morphology and size. Such ZnO nanostructures are likely to be candidates as building blocks for constructing photonic and field emission crystals.
Nonaqueous Synthesis of Barium Titanate Nanocrystals in Acetophenone as Oxygen Supplying Agent
Authors: Niederberger Markus , Garnweitner Georg
Published: June 2019

Solvothermal reaction of a mixture of metallic barium and titanium isopropoxide in acetophenone leads to the formation of barium titanate nanocrystals. XRD measurements prove the presence of cubic BaTiO3 with traces of BaCO3 as side product. According to TEM investigations, the particles exhibit a nearly spherical particle shape with diameters ranging from 10 to 15 nm. However, due to the lack of any stabilizers, the particles are slightly agglomerated. NMR analysis of the obtained reaction solution shows that aldol condensation reactions of acetophenone and in situ formed acetone provide the water necessary for inducing crystallization and nanoparticle formation.
Perspective on Submicron-Resolution Three-Dimensional X-Ray Structural Microscopy to Address Mesoscale Materials Microstructure and Evolution Issues
Authors: Larson B. C. , Yang Wenge
Published: June 2019

This paper provides a perspective on submicron-resolution three-dimensional x-ray structural microscopy for the investigation of materials microstructure and evolution on mesoscopic length scales. Microstructure and thermal/stress induced microstructure evolution at the length scale of the local crystal grains, grain boundaries, triple junctions, and dislocation patterning are known to play critical roles in determining the physical properties of materials. Large scale computer simulations and multi-scale modeling are making significant progress on the nanoscale and detailed mesoscale computations are becoming increasingly tractable as new methods are developed. X-ray structural microscopy with submicron resolution now provides a (previously missing) direct experimental link between theory and computations and the mesoscopic behavior of materials microstructure.