bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Field Emission Behavior of Carbon Nanotubes with Different Sources
Authors: Lin Mark Ching-Cheng , Lai M.S. , Lai H. J. , Yang M. H. , Wei B.Y. , Li A. K.
Published: June 2019

The field emission properties of carbon nanotubes (CNTs) from various sources are investigated for the application of field emission displays. Comparisons are made between graphite with Ni metal as catalyst and polycyclic aromatic hydrocarbon as precursor by the arc discharge method. Cathode deposits are examined using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) to determine microstructure. Carbon structure is studied using Raman spectroscopy. Electron field emission characteristics are measured with the diode method at 10-6 torr pressure. In this study, SEM micrographs of cathode deposits show dense random fiber-like carbon nanotubes. The HRTEM images clearly exhibit characteristic features of multiwalled carbon nanotubes. Microstructural investigation provides evidence that both the metal catalyst and the precursor can be used to synthesize carbon nanotubes. The Raman spectrum shows a stronger peak at about 1580 cm-1 indicating formation of a well-graphitized carbon nanotube. The degree of carbon nanotube graphitization is high and is in good agreement with the HRTEM result. From field emission measurements, the lowest onset field is about 1.0 V/μm and can be attributed to highly sharp tips and the high density of carbon nanotubes. Based on microstructure characterization and field emission measurements, the influence on field emission properties including turn on voltage and threshold voltage of carbon nanotubes synthesized from different sources is discussed.
Development of “New Abrasive-Free Copper CMP Solutions” BASED on Electrochemical and Film Analysis Method
Authors: Amanokura Jin , Kamigata Yasuo , Habiro Masanobu , Suzuki Hiroshi , Hanazono Masanobu
Published: June 2019

Abrasive-free Cu CMP solutions have been developed to reduce micro-scratches and obtain minimized dishing and erosion properties. During the development of the solutions, some electrochemical examinations were performed. One of the most instructive knowledge was obtained through the Tafel plot. Other attractive data were obtained through Cu complex film analysis. On the basis of these studies were developed and released newly formulated abrasive-free Cu CMP solutions with a high Cu removal rate and excellent topography performance. Mechanism of polishing by applying abrasive-free Cu CMP solutions is also discussed in this paper.
Topography Reduction During Barrier CMP Improved Due to Tantalum Oxidation
Authors: Lefevre Paul , Ina Katsuyoshi , Sakai Kenji , Tamai Kazusei , Rader Scott
Published: June 2019

Barrier CMP can reduce the topography generated during Cu CMP. In case of selective barrier CMP slurry like 1:10:1, it is expected that the topography reduction could not exceed the Ta thickness. Some recent observations made at Fujimi show that the topography reduction can be twice larger than the Ta thickness without dielectric loss. This paper presents the chemical mechanical phenomenon that is responsible for this 40 to 50 nm topography reduction during barrier CMP. At the end of the Cu CMP, Ta is exposed to oxidizer. This process can oxidize an important part of the Ta barrier which becomes Ta2O5 according to Pourbaix diagram [1]. Ta2O5 can be as much as 2.3X thicker than original Ta layer. This phenomenon explains why topography reduction can be twice higher than initial Ta thickness. This mechanism explains why after Cu CMP it is likely to have more than 30 nm dishing on copper lines. The last and more important consequence is that this reduces final topography and total copper metal loss at the same time by about 30 nm. Obviously very high selectivity Cu CMP slurry (Cu:Ta ∼ 1000:1) is necessary to have neither Ta erosion nor Ta2O5 erosion during copper CMP. High selectivity slurry is required during barrier CMP in order to reduce the loss of copper and Dielectric during Barrier CMP.
Pad Conditioning and Pad Surface Characterization in Oxide Chemical Mechanical Polishing
Authors: Lawing A. Scott
Published: June 2019

An understanding of the pad surface state and its effect on the polishing process is critical to a more fundamental understanding of Chemical Mechanical Polishing (CMP). Vertical Scanning Interferometry has been shown to be a useful tool to monitor the pad surface state. In this paper, various techniques for analyzing pad surface data obtained using interferometry are described. The pad surface state can be modified through the manipulation of process and pad conditioner design parameters. Many of the parameters extracted from interferometry data show strong correlations with corresponding polish data. A careful analysis of these complementary data can yield significant insight into the mechanisms of CMP processes.
Effect of Temperature and Temperature Uniformity on Plasma and Device Stability
Authors: Ganguly G. , Bennett M.S. , Carlson D.E. , Arya R.R.
Published: June 2019

We have investigated the changes in the cathode potential in a dc discharge of silane and hydrogen used to deposit the intrinsic layer of p-i-n type solar cells at deposition rates from 1 to 10Å/s with the superstrate temperature at 200°C and 250°C. Under plasma conditions that lead to higher deposition rates (5-10Å/s), fluctuations of the cathode potential which are suggestive of the formation and de-trapping of particulates in/from the plasma, are observed at 200°C but disappear at 250°C. Improvement of the temperature uniformity over the plasma region from 1.7°C/cm to 0.7°C/cm removes the fluctuations of the cathode potential even at 200°C, indicating that the particulates are formed predominantly at the plasma boundary. Consequently, the stability of solar cells with i-layers deposited at ~10Å/s in the center of the plasma region at the same superstrate temperature improved by 26% suggesting that multiple silicon containing molecules diffuse from the edge to the center of the plasma region.
Temperature Dependence of a Hydrogen Doublet Site in Light-Soaked a-Si:H From 1H NMR
Authors: Su T. , Taylor P. C. , Ganguly G. , Carlson D. E.
Published: June 2019

We investigate the temperature dependence of an additional 1H NMR signal that appears in aSi:H at T = 7 K only after light soaking. This “doublet” signal is attributed to a pair of hydrogen atoms approximately 2.3 Å apart. We present the first lineshape of this doublet, and we examine the spin-lattice relaxation from 6.5 K to 20 K at a magnetic field of about 3.5 T. At low temperatures, the spin-lattice relaxation time of these paired hydrogen sites has a strong dependence on temperature, which is probably the result of some form of local motion.
Towards Microcrystalline Silicon n-i-p Solar Cells with 10% Conversion Efficiency
Authors: Feitknecht L. , Droz C. , Bailat J. , Niquille X. , Guillet J. , Shah A.
Published: June 2019

High-performance microcrystalline and amorphous silicon solar cells are the key elements for a successful combination to form the “micromorph” tandem cell [1,2]. A microcrystalline silicon (μc-Si:H) solar cell in the n-i-p configuration was fabricated by the VHF PE-CVD deposition process. The cell has a conversion efficiency exceeding 9% (VOC=520 mV, FF=73%, JSC=24.2 mA/cm2). This result was achieved by a successful combination of the following elements: first a fine-tuning of the silane concentration (SC) in hydrogen feedstock gas used for deposition of the intrinsic  absorber layer, second, the incorporation of an optimised back-reflecting substrate into the cell; and, third, the ideal combination of each of these key-components.

Compared to earlier results with n-i-p-type μc-Si:H solar cells, a substantial increase in VOC was now obtained, while maintaining reasonable JSC-values. Earlier investigations on the role of the i-layer material had revealed a trade-off between cells with high JSC but low VOC or cells of low JSC and high VOC. In the present contribution the authors now show the successful combination of a cell with an acceptable VOC and good JSC generation in the long-wavelength region (above 700 nm). This is mainly because of suitable light-diffusing back-reflectors which perform well with respect to both, optical and electrical aspects.
Influence of Laser Annealing on Hydrogen Bonding in Disordered Silicon Thin Films
Authors: Nickel N. H. , Brendel K.
Published: June 2019

The influence of laser dehydrogenation and crystallization of hydrogenated amorphous silicon (a-Si:H) on H bonding is investigated. Depending on the deposition temperature the amorphous starting material contains a H concentration of up to 44 at.%. Laser crystallization lowers the H content significantly. Fully crystallized poly-Si contains H concentrations of up to 17 at.%. This reservoir of hydrogen can be used to passivate additional grain boundary defects by annealing the specimens at low temperatures in vacuum. Information on hydrogen bonding is obtained from hydrogen effusion measurements.
Light and Thermally Induced Metastabilities in Nanocrystalline Silicon
Authors: Mandal N. P. , Agarwal S. C.
Published: June 2019

Light soaking for short durations and thermal quenching produce metastable states having a higher dark current, higher photo current, a larger photoluminescence and a smaller electron spin resonance signal in porous silicon (PS). Long exposures, however, have the opposite effect. All metastabilities can be removed by annealing at 150°C (1 h), but not by exposure to infrared light. Micro-Raman spectroscopy shows the presence of a-Si:H in the PS sample. However, a closer look shows that our results can not be explained in terms of a-Si:H alone. Our experiments suggest that structural changes involving the movement of hydrogen present on the surface of PS or on PS/a-Si:H interface may be responsible for these effects.
Correlation Between the Tunnelling Oxide and I-V Curves of MIS Photodiodes
Authors: Águas H. , Pereira L. , Goullet A. , Silva R. , Fortunato E. , Martins R.
Published: June 2019

In this work we present results of a study performed on MIS diodes with the following structure: substrate (glass) / Cr (2000Å) / a-Si:H n+ (400Å) / a-Si:H i (5500Å) / oxide (0-40Å) / Au (100Å) to determine the influence of the oxide passivation layer grown by different techniques on the electrical performance of MIS devices. The results achieved show that the diodes with oxides grown using hydrogen peroxide present higher rectification factor (2×106)and signal to noise (S/N) ratio (1×107 at -1V) than the diodes with oxides obtained by the evaporation of SiO2, or by the chemical deposition of SiO2 by plasma of HMDSO (hexamethyldisiloxane), but in the case of deposited oxides, the breakdown voltage is higher, 30V instead of 3-10 V for grown oxides. The ideal oxide thickness, determined by spectroscopic ellipsometry, is dependent on the method used to grow the oxide layer and is in the range between 6 and 20 Å. The reason for this variation is related to the degree of compactation of the oxide produced, which is not relevant for applications of the diodes in the range of ± 1V, but is relevant when high breakdown voltages are required.
Numerical Simulation of the Influence of the Gap State of a-Si:H on the Characteristics of a-Si:H p-i-n/OLED Coupling Device
Authors: Wu Chunya , Chen Yousu , Li Juan , Yang Guanghua , Yang Huidong , Zhou Zhenhua , Zhao Ying , Meng Zhiguo , Geng Xinhua , Xiong Shaozheng , Zhang Lizhu , Wang Qi
Published: June 2019

The influence of the density of gap states and the band gap width of the intrinsic a-Si:H active layer on the characteristics of a-Si PIN/OLED coupling pair was analyzed by a-Si:H PIN/OLED CAD simulation model. The CAD simulation model was carried out based on a-Si PIN Hack & Shur model and OLED TCL transport model. At the same band gap width, for the intrinsic a-Si:H active layer with the higher density of gap states, the reverse current of a-Si PIN trended to be saturated at the higher reverse bias voltage. As a result, I-V curve of a-Si PIN/OLED around the turn point Vt became smoother with the increase of the density of gap states. At the same state density, the light induced current of a-Si PIN increased against the band gap width, assuming the input light had the same spectrum as AM1.5 solar light. Thus the luminance emitted from OLED increased with the decrease of the band gap width because OLED belongs to the light-emitting device controlled by current. The simulation results also showed that the influence of the state density intensified with the increase of the band gap of a-Si:H.
Area-Dependent Switching in Thin Film-Silicon Devices
Authors: Hu Jian , Jackson Warren , Ward Scott , Stradins Pauls , Branz Howard M. , Wang Qi
Published: June 2019

We report on the area dependence of switching in both Cr/p+a-Si:H/Ag(Al) and Cr/p+μc-Si/Ag(Al) filament switches. The doped amorphous (a-Si:H) or microcrystalline (μc-Si) thin Si layers are made by hot-wire chemical vapor deposition. The device active region area (A) is varied over 5 orders of magnitude, from 10-7 to 10-2 cm2, using photolithographically defined Ag and Al top contacts. Before switching, the resistance of 100-μm2 devices is normally about 100 kΩ for μc-Si and 10 GΩ for a-Si:H. After switching with applied current ramps, the resistance decreases to a few hundred ohms in all a-Si devices and to a few thousands ohms in μc-Si devices. In both μc-Si and a-Si:H devices, the switching voltage (Vsw) decreases with increasing device area according to Vsw ~ V0-αln(A/A0) with α=0.3V for a-Si:H and α=0.04V for μc-Si. For both materials, the switching current roughly obeys the power law Isw ∞ Aβ with β~1. A statistical model is proposed to explain the area scaling of the switching voltage and relate the parameters to the material properties.
Properties of Silicon Nitride Films Prepared by Combination of Catalytic-Nitridation and Catalytic-Cvd
Authors: Izumi A. , Kikkawa A. , Higashimine K. , Matsumura H.
Published: June 2019

This paper reports about the interface of silicon nitride (SiNx) formed on Si(100) prepared by combination of catalytic-nitridation and catalytic-vapor deposition method in a catalytic chemical vapor deposition system. It is found that flat interface of SiNx/Si(100) is formed by inserting nitridation layer before growing the SiNx films.
High-rate (> 1nm/s) and low-temperature (< 400°C) deposition of silicon nitride using an N2/SiH4 and NH3/SiH4 expanding thermal plasma
Authors: Hong J. , Kessels W.M.M. , Sanden M.C.M. van de
Published: June 2019

High-rate (> 1 nm/s) and low-temperature (50– 400°C) deposition of silicon nitride (a-SiNx:H) films has been investigated by the expanding thermal plasma (ETP) technique using SiH4 as Si-containing and N2 or NH3 as N-containing precursor gases. The structural, optical and electrical properties of the a-SiNx:H films have been studied by elastic recoil detection, spectroscopic ellipsometry, infrared spectroscopy, dark conductivity measurements and atomic force microscopy. The film properties of the ETP deposited a-SiNx:H films in this low-temperature range are discussed in terms of deposition rate, atomic composition, UV-VIS optical and IR vibrational properties, conductivity, and surface topography of the films.
Switch-On Transients And Static Characteristics Of Polymorphous And Amorphous Silicon Thin-Film Transistor
Authors: Tripathi V. , Mohapatra Y. N.
Published: June 2019

Hydrogenated polymorphous silicon (Pm-Si:H) being an admixture of amorphous and ordered phase silicon shows improved optical and electrical properties due to the presence of nanocrystallites. In order to compare the dynamic and steady state electrical properties in a-Si:H and pm-Si:H, bottom gate Thin Film Transistors (TFT) of these materials were fabricated with SiO2 as the insulating layer. The active materials were deposited using plasma-enhanced chemical vapor deposition (PECVD) by varying pressure, temperature and hydrogen dilution. Transfer characteristics of TFTs made using pm-Si:H show lower leakage current, higher on-current and sharper volt per decade change as compared to similar TFTs made from a-Si:H. Density of states in pm-Si:H as calculated from field effect conductance using incremental method is observed to be an order of magnitude lower than in a-Si:H based devices. To compare dynamic characteristics, we studied the switch-on transient characteristics of polymorphous and amorphous silicon TFTs by pulsing the gate to different voltages in the temperature range of 150-300K. The switch-on transients are trap limited with overall better switching characteristics for pm-Si:H samples. An initial rising transient in case of pm-Si:H is activated with an effective energy of 0.3 eV. The origins of transients are interpreted in terms of trap limited carrier dynamics and charge redistribution within the distribution of localized states.
Dependences of Structural Parameters on the Characteristics of Poly-Si Thin-Film Transistors after Plasma Passivation
Authors: Yu Cheng-Ming , Huang Tiao-Yuan , Lei Tan-Fu , Lin Horng-Chih
Published: June 2019

The effects of NH3 and H2 plasma passivation on the characteristics of poly-Si thin-film transistors with source/drain extensions induced by a bottom sub-gate were studied. Our results show that significant improvements in device performance can be obtained by both passivation methods. Moreover, NH3-plasma-treatment appears to be more effective in reducing the off-state leakage, subthreshold swing, compared to H2 plasma passivation. NH3 plasma treatment is also found to be more effective in reducing the anomalous subthrehold hump phenomenon observed in non-plasma-treated short-channel devices. Detailed analysis suggests that all these improvements can be explained by the more effective passivation of the traps distributed in both the front and back sides of the channel by NH3 plasma treatment.
Photoelectron spectroscopic investigations of very thin a-Si:H layers
Authors: Schmidt M. , Schoepke A. , Milch O. , Lussky Th. , Fuhs W.
Published: June 2019

We report on a detailed study on gap-state distribution in thin amorphous silicon layers (a-Si:H) with film thicknesses between 5 nm and 20 nm on c-Si wafers performed by UV excited photoelectron spectroscopy (UV-PES). We measured how the work function, the gap state density, the position of the Fermi-level and the Urbach-energy depend on the layer thickness and the doping level of the ultra thin a-Si:H(n) layers. It was found, that for phosphorous doping the position of the Fermi level saturates at EF–EV=1.47 eV. This is achieved at a gas phase concentration of 10000 ppm PH3in the SiH4/H2mixture which was used for the PECVD deposition process. The variation of the doping level from 0 to 20000 ppm PH3addition results in an increase of the Urbach energy from 65 meV to 101 meV and in an increase of the gap state density at midgap (EV-Ei= 0.86eV) from 3·1018to 2·1019cm-3eV-1.
Determination of Defect Densities by Constant Photocurrent Method – Comparison of AC and DC Methods
Authors: Main Charlie. , Reynolds Steve , Zrinšća Ivica. , Merazga Amar
Published: June 2019

We report on discrepancies in the absorption spectrum of a-Si:H measured by DC and AC constant photocurrent methods (CPM). Our measurements reveal discrepancies in the absorption coefficient alpha, of up to an order of magnitude. DC measurement gives the higher value for alpha at photon energies below the Urbach tail. In this paper we examine free carrier generation paths in AC CPM, and the influence of these paths on the photocurrent frequency response to modulated sub-gap illumination. A simple kinetic model is used to attempt to explain quantitatively the differences in the photocurrent frequency response for sub- and super-gap excitation. At first sight the basic AC technique is of doubtful validity, even at exciting frequencies as low as 1 Hz, since maintaining a constant AC photocurrent does not guarantee a constant carrier lifetime. On the other hand, the DC method involves several parallel excitation paths, obfuscating attempts to extract a density of states from the absorption spectrum. We demonstrate that a simple variation of AC CPM can provide a more accurate means of determining the density of states than DC CPM.
Metastable Defects in the Amorphous Silicon-Germanium Alloys
Authors: Cohen J. David
Published: June 2019

This paper first briefly reviews a few of the early studies that established some of the salient features of light-induced degradation in a-Si,Ge:H. In particular, I discuss the fact that both Si and Ge metastable dangling bonds are involved. I then review some of the recent studies carried out by members of my laboratory concerning the details of degradation in the low Ge fraction alloys utilizing the modulated photocurrent method to monitor the individual changes in the Si and Ge deep defects. By relating the metastable creation and annealing behavior of these two types of defects, new insights into the fundamental properties of metastable defects have been obtained for amorphous silicon materials in general. I will conclude with a brief discussion of the microscopic mechanisms that may be responsible.
Temperature Dependence of the Decay of Optically Excited Charge Carriers in Amorphous Silicon
Authors: Whitaker J. , Taylor P. C.
Published: June 2019

We report the temperature dependence of the growth and decay of the optically induced electron spin resonance (LESR) on short and long time scales (10-3 s < t < 2500 s). This range of times spans the region between previously published photoluminescence and the LESR data. In addition, we examine the steady-state density of optically excited charge carriers as a function of temperature. These measurements lead to a better understanding of the band tail structure of amorphous silicon as well as the kinetics of the excitation and recombination processes.
Improvement of Gate Oxide Integrity in Low Temperature Poly Silicon TFT
Authors: Lee Seok-Woo , Nam Dae Hyun , Yoon Jin Mo , Seo Hyun Sik , Lim Kyoung Moon , Kim Chang-Dong
Published: June 2019

The electrical characteristics of SiH4-based PECVD gate oxide have been investigated with respect to gate oxide integrity (GOI) and its reliability. It was found that the GOI of poly-Si TFT integrated on glass substrate strongly depended on the charge trapping and deep level interface states generation under Fowler-Nordheim stress (FNS). By applying elevated temperature postanneal without vacuum break after the gate oxide deposition, highly reliable gate oxide was obtained. Under FNS, ID-VG curve showed severe shift and degradation of subthreshold slope, which were reduced by adopting post-annealed gate oxide. Besides, the TFT with post-annealed gate oxide showed around 10 times higher charge to breakdown than that of as-deposited gate oxide. Charge to breakdown of MOS capacitors were also studied. By applying post-annealed gate oxide, charge to breakdown drastically improved, which could be explained by reduced charge trapping under FNS.
Characteristics of Bottom Gate Thin Film Transistors with Silicon rich poly-Si1-xGex and poly-Si fabricated by Reactive Thermal Chemical Vapor Deposition
Authors: Shimizu Kousaku , Zhang JianJun , Lee Jeong-Woo , Hanna Jun-ichi
Published: June 2019

In the fabrication of thin film transistors (TFTs), little attention has been paid to the polycrystalline silicon thin films prepared at low temperatures where the glass substrates are adopted so far. Since the film quality is not sufficient to achieve high mobility, e.g., over 50 cm2/Vs in spite of high benefit in their industrial fabrication. We have fabricated bottom gate TFTs with poly-Si and poly- Si1-xGex thin films deposited at 450°C by newly developed low-temperature LPCVD technique and characterized electrical characteristics of the TFTs: disilane and a small amount of either germanium tetrafluoride or fluorine were used as material gases and helium as carrier gas. Thermal annealing for dopant activation and atomic hydrogen treatment for defect passivation were carried out. We found that the defect elimination process is important for improving TFT performance significantly. Finally the mobility of p-channel and n-channel TFTs have attained 36.3-54.4 cm2/Vs and 57 cm2/Vs, respectively.
Bandtail Limits to Solar Conversion Efficiencies in Amorphous Silicon Solar Cells
Authors: Zhu K. , Yang J. , Wang W. , Schiff E. A. , Liang J. , Guha S.
Published: June 2019

We describe a model for a-Si:H based pin solar cells derived primarily from valence bandtail properties. We show how hole drift-mobility measurements and measurements of the temperature-dependence of the open-circuit voltage VOC can be used to estimate the parameters, and we present VOC(T) measurements. We compared the power density under solar illumination calculated with this model with published results for as-deposited a-Si:H solar cells. The agreement is within 4% for a range of thicknesses, suggesting that the power from as-deposited cells is close to the bandtail limit.
Evolution of Crystallinity in Mixed-Phase (a+μc)-Si:H as Determined by Real Time Spectroscopic Ellipsometry
Authors: Ferlauto A. S. , Ferreira G. M. , Koval R.J. , Pearce J.M. , Wronski C.R. , Collins R.W. , Al-Jassim M. M. , Jones K. M.
Published: June 2019

The ability to characterize the phase of the intrinsic (i) layers incorporated into amorphous silicon [a-Si:H] and microcrystalline silicon [μc-Si:H] thin film solar cells is critically important for cell optimization. In our research, a new method has been developed to extract the thickness evolution of the μc-Si:H volume fraction in mixed phase amorphous + microcrystalline silicon [(a+μc)-Si:H] i-layers. This method is based on real time spectroscopic ellipsometry measurements performed during plasma-enhanced chemical vapor deposition of the films. In the analysis, the thickness at which crystallites first nucleate from the a-Si:H phase can be estimated, as well as the nucleation density and microcrystallite cone angle. The results correlate well with structural and solar cell measurements.
P- and N-Type Microcrystalline SiC Fabricated by rf Plasma CVD with Ethane Gas
Authors: Toyama T. , Nakano Y. , Kosuge T. , Asano A. , Okamoto H.
Published: June 2019

We have been investigated p- and n-type microcrystalline Si1-xCx (μc-SiC) films fabricated by a conventional rf (13.56 MHz) plasma CVD method with a use of a new carbon source of C2H6 gas at a low substrate temperature on a glass substrate. The Si crystallites incorporated in μc-SiC films retain with a carbon content up to 9 at.%. Both of p- and n-type μc-SiC films show relative high dark conductivities of on the order of 10-3 S/cm with optical energy gaps, E04, of~2eV. In infrared spectra, any pronounced features due to C-Hn vibration mode are not found in C2H6-based μc-SiC films, which is different from the case of CH4-based μc-SiC films.
Hot-Wire Chemical Vapor Deposition for Epitaxial Silicon Growth On Large-Grained Polycrystalline Silicon Templates
Authors: Mason M. S. , Chen C.M. , Atwater H.A.
Published: June 2019

We investigate low-temperature epitaxial growth of thin silicon films on Si [100] substrates and polycrystalline template layers formed by selective nucleation and solid phase epitaxy (SNSPE). We have grown 300 nm thick epitaxial layers at 300°C on silicon [100] substrates using a high H2:SiH4 ratio of 70:1. Transmission electron microscopy confirms that the films are epitaxial with a periodic array of stacking faults and are highly twinned after approximately 240 nm of growth. Evidence is also presented for epitaxial growth on polycrystalline SNSPE templates under the same growth conditions.
Structural Evolution of Nanocrystalline Germanium Thin Films with Film Thickness and Substrate Temperature
Authors: Jordan William B. , Carlson Eric D. , Johnson Todd R. , Wagner Sigurd
Published: June 2019

The structure of germanium thin films prepared on glass by plasma enhanced chemical vapor deposition was characterized by Raman spectroscopy, atomic force microscopy (AFM) and field emission scanning electron microscopy (SEM). Crystallinity, surface roughness, and grain size were measured as functions of film thickness and deposition temperature. Grain nucleation was apparent for films as thin as 10 nm. Over the thickness range studied, grain size increased with film thickness, whereas average surface roughness started to increase with film thickness, but then remained fairly constant at approximately 1 nm for a film thickness greater than 25 nm.
Material Aspects of Reactively MF-Sputtered Zinc Oxide for TCO Application in Silicon Thin Film Solar Cells
Authors: Hüpkes Jürgen , Rech Bernd , Kluth Oliver , Müller Joachim , Siekmann Hilde , Agashe Chitra , Bochem Hans P. , Wuttig Matthias
Published: June 2019

Al-doped ZnO films were deposited on glass in an in-line system by reactive mid-frequency (MF) magnetron sputtering. The influence of substrate position on the film properties as well as the relation between static and dynamic deposition are studied. All films showed low resistivity (<4x10-4 Ωcm) and excellent transparency (> 80 % in the visible region). The resistivity ρ for substrate positions above the sputter craters (race tracks) is up to a factor of two higher than on other positions where the smallest ρ is 1.9 x 10-4 Ωcm. Major differences in statically deposited films as a function of the position on the substrate are found for the structural film properties as characterized by x-ray diffraction (XRD) and etching behaviour. The different surface textures obtained after etching are directly related to variations in the short-circuit current densities of amorphous silicon p-i-n solar cells prepared on these etched ZnO:Al films.
The a-Si:H Growth Mechanism: Temperature Study of the SiH3 Surface Reactivity and the Surface Silicon Hydride Composition During Film Growth
Authors: Kessels W.M.M. , Barrell Y. , Oever P.J. van den , Hoefnagels J.P.M. , Sanden M.C.M. van de
Published: June 2019

We report on two experimental studies carried out to reveal insight into the interaction of SiH3 radicals with the a-Si:H surface as assumed essential in the a-Si:H growth mechanism. The surface reaction probability β of SiH3 on the a-Si:H has been investigated by spectroscopic means as a function of the substrate temperature (50 - 450°C) using the time-resolved cavity ringdown technique. The silicon hydrides –SiHx on the a-Si:H surface during deposition have been studied by the combination of in situ attenuated total reflection infrared spectroscopy and argon ion-induced desorption of surface hydrogen. For SiH3 dominated plasma conditions, it is found that the surface reactivity of SiH3 is independent of the substrate temperature with β = 0.30±0.03 whereas the silicon hydride composition on the a-Si:H surface changes drastically for increasing substrate temperature (from –SiH3 to =SiH2 to ≡SiH). The implications of these observations for the a-Si:H growth mechanism are addressed.
Effects of Excitation Frequency and H2 Dilution on Cluster Generation in Silane High-Frequency Discharges
Authors: Shiratani Masaharu , Koga Kazunori , Harikai Atsushi , Ogata Takanori , Watanabe Yukio
Published: June 2019

Reduction of cluster amount in silane discharges is the key to decreasing microstructure parameter Rα of a-Si:H films deposited with the discharges. The cluster amount is found to be reduced more than one order of magnitude using 60 MHz discharges instead of 28 MHz ones or using H2 dilution of an H2/SiH4 ratio of 5. The cluster-suppressed plasma CVD using 60 MHz discharges realizes deposition of a-Si:H films of Rα~ 0 at a fairly high rate of 0.55 nm/s. Moreover, a downstream cluster collection method of high sensitivity has been developed for detecting a small amount of clusters formed under deposition conditions of Rα < 0.01.
The Correlation of Adhesion Strength with Barrier Structure in Cu Metallization
Authors: Sekiguchi A. , Koike J. , Ueoka K. , Ye J. , Okamura H. , Otsuka N. , Ogawa S. , Maruyama K.
Published: June 2019

Adhesion strength in sputter-deposited Cu thin films on various types of barrier layers was investigated by scratch test. The barrier layers were Ta1-xNx with varied nitrogen concentration of 0, 0.2, 0.3, and 0.5. Microstructure observation by TEM indicated that each layer consists of mixed phases of β;-Ta, bcc-TaN0.1, hexagonal-TaN, and fcc-TaN, depending on the nitrogen concentration. A sulfur- containing amorphous phase was also present discontinuously at the Cu/barrier interfaces in all samples. Scratch test showed that delamination occurred at the Cu/barrier interface and that the overall adhesion strength increased with increasing the nitrogen concentration. A good correlation was found between the measured adhesion strength and the composing phases in the barrier layer.
Properties and Barrier Material Interactions of Electroless Copper used for Seed Enhancement
Authors: Witt C. , Pfeifer K.
Published: June 2019

The conventionally used sequence for copper damascene metallization consists of barrier deposition, physical vapor deposition (PVD) Cu seed and electroplated copper. Due to the limited step coverage of PVD copper, the extendibility of this sequence to feature dimensions below 90 nm is at risk. To reduce the risk of pinch-off of very small features, the PVD layer thickness will be reduced well below 100 nm, the drawback being poor seed coverage at the bottom of the features. Void free fill by electroplating is hence at risk by both pinch-off and discontinuous seed coverage (3-5). In this paper, the use of a conformal metal deposition method, electroless copper, to enhance PVD seed layers as thin as 10 nm is presented. It is demonstrated that sparse, discontinuous copper films provide a catalytic surface for electroless copper deposition. With electroless copper, void-free copper fill of 12.5 aspect ratio (AR) trenches (70 nm width) and 8.3 AR vias is achieved. Furthermore, 6 nm thin electroless copper films were integrated in a dual damascene process and electrically characterized. A yield of approximately 85% was achieved on via chains (360000 links, 0.25 by 1.1 μm vias), with 10 nm PVD seed. This was comparable to the yield when using 100 nm PVD seed. Hydrogen, generated as a byproduct during the electroless copper ion reduction, was found in the copper deposits as well as in the barrier films underneath. In some cases, spontaneous blistering in the plated copper film was observed, and is believed to be due to hydrogen incorporation. The interaction of electroless copper films with various barrier materials (PVD Ta, PVD TaN, CVD TiN(Si) and combinations) is discussed. Electromigration test results presented in this paper indicate that the failure mechanism is not qualitatively different from reference samples with the conventional PVD seed.
Electromigration Study of Cu Dual-damascene Interconnects with a CVD MSQ Low k Dielectric
Authors: Lu Xia , Lee Ki-Don , Yoon Sean , Matsuhashi Hideki , Lu Michael , Zhang Kai , Ho Paul S.
Published: June 2019

Electromigration reliability in Cu dual-damascene interconnects with a CVD MSQ low k dielectric was investigated. Statistical studies were carried out using the critical length (LC) test structures containing multi-link line/via elements with varying line lengths. EM lifetime characteristics, critical current density-length product (jL)c, and failure mechanisms were discussed and compared with Cu/oxide structures. Our results suggested that the diffusion at the cap layer interface was the dominant mechanism for EM mass transport. The confinement effect, in terms of an effective modulus B, can be used to account for the shorter EM lifetime and smaller critical current density-length product (jL)c observed for Cu/CVD MSQ low k interconnects. Failure analysis by FIB confirmed the presence of multiple failure modes including voiding at the via bottom, Cu extrusion and delamination at Cu/cap layer interface.
Characterization of CVD TixCyNz Films Deposited as Diffusion Barriers for Cu on Low-k Dielectrics Methylsilsequiazane
Authors: Gau W.C. , Liu P.T. , Chang T.C. , Chen L.J.
Published: June 2019

Metal organic chemical vapor deposition (MOCVD) TixCyNz films were deposited by using tetrakis-dimethylamino-titanium (TDMAT) and NH3 as a reaction gas at temperatures from 325 to 400°C with multi-layer Ar/NH3 plasma treatment. Effects of annealing and Ar/NH3 plasma treatment on the microstructure, composition, and electrical properties of TixCyNz films were studied. By multi-layers plasma treatment, the resistivity of TixCyNz barriers decreased from 960 to 548 νΔ–cm and the concentration of oxygen in barrier films are also decreased. The integration of the TixCyNz with low-k methylsilsesquiazane (MSZ) was investigated through Cu/CVD-TixCyNz/SiO2 and Cu/CVD-TixCyNz /MSZ capacitors after being annealed in furnace at temperatures from 500 to 800°C. With thermal annealing in N2 ambient for 30 min, Cu/CVD-TixCyNz/ MSZ structure remains metallurgically stable up to 700°C.
Copper Oxidation Studied by In Situ Raman Spectroscopy
Authors: Schennach Robert , Gupper Andreas
Published: June 2019

The growing importance of copper in the semiconductor industry has led to a renewed interest in the properties and growth modes of copper oxides under a variety of conditions. While thermal oxidation of copper has been studied extensively over the last decades, recent surface studies seem to ignore the possible formation of Cu3O2. It has been shown earlier that thermal oxidation of copper leads to multilayer structures, which consist of CuxO, Cu2O, Cu3O2and CuO, depending on the oxidation conditions. These oxides were analysed ex situ using X-ray Photoelectron Spectroscopy (XPS) combined with depth profiling, Linear Sweep Voltammetry (LSV) and Galvanostatic Reduction (GR). In this work it will be shown that Raman Spectroscopy can be used to follow the formation of the different copper oxides in situ. The experiments were performed using a Raman Microscope with a sample heating extension, which enables in situ copper oxidation in air between room temperature and 300 Δ. Raman spectra were acquired in the range between 3000 Δcm-1to 150 cm-1. From these spectra one can see that Cu20 is formed between 70 Δ and 130 Δ, Cu302is formed between 150 Δ and 250 Δ and CuO starts to form at temperatures higher than 250 Δ.
Near-Threshold Electromigration of Damascene Copper on TiN Barrier
Authors: Meyer William K. , Solanki Raj , Evans David
Published: June 2019

Electromigration measurements of dual-damascene VLSI copper interconnect with sputtered TiN barrier was performed to measure both long-line (Jmax) performance and EM threshold (JLmax). Wafer-level stress of via chains with various segment lengths was combined with a statistical efficient experiment design to explore various conditions with minimum sample size. Resistance saturation was observed with exponential time constant corresponding to vacancy diffusivity. Time to opens failure by resistance increase follows Black's equation with current exponent n=1.90 and activation energy Ea=0.94 eV. Thermal gradients due to high current stress were characterized and accounted-for in acceleration models.
The Study of Modified Layers in SiCOH Dielectrics using Spectroscopic Ellipsometry
Authors: Worsley Marcus A. , Bent Stacey F. , Gates Stephen M. , Kumar Kaushik , Dalton Timothy , Hedrick Jeffrey C.
Published: June 2019

The current challenge in designing new low-k dielectrics is realizing sufficient mechanical and chemical stability such that the material can be integrated into current damascene schemes. The material of interest in this study is a nonporous SiCOH composite (carbon-doped silicon oxide, also known as organosilicate glass “OSG”) for use as an intermetal dielectric (IMD). During integration of this IMD, processing steps such as etch, resist strip and chemicalmechanical polishing for planarization may chemically alter the outer layer of the dielectric. Here, spectroscopic ellipsometry is used to characterize the modified layer of SiCOH films after exposure to different resist strip plasmas. The data are analyzed based on a 2-layer model, consisting of a carbon-deficient layer on the surface of the low-k SiCOH dielectric. This model is supported by XPS and FTIR data. The effects of two types of plasma etch chemistry on the formation of this modified layer were studied, and differences between the two chemistries were found. The 2-layer model accurately describes the modifications produced by the oxidizing plasma, but its description of the modified layer formed by the plasma involving nitrogen is not complete. A 3-layer model with an additional nitrogen-doped layer is suggested.
Observation of Grain Growth in Cu Films by In-Situ EBSD Analysis
Authors: Field D.P. , Nowell M.M. , Kononenko O.V.
Published: June 2019

Recrystallization, grain growth and crystallographic texture evolution in Cu films is an area of importance for IC interconnect fabrication as the film characteristics influence the resulting line microstructure. This study examines Cu films deposited by partially ionized beam deposition onto a sublayer of tantalum nitride and additionally onto alpha- C:H. The films were annealed in-situ in the SEM chamber and intermittent orientation imaging was used to characterize the grain growth and crystallographic texture evolution in the films. Both initial and final textures are weak in each of the films analyzed, but are a function of sublayer material and thickness. Grain size in the Cu films is significantly smaller for the tantalum nitride sublayer than for the á-C:H sublayer.
Wafer Thinning for Monolithic 3D Integration
Authors: Jindal A. , Lu J.Q. , Kwon Y. , Rajagopalan G. , McMahon J.J. , Zeng A.Y. , Flesher H.K. , Cale T.S. , Gutmann R.J.
Published: June 2019

A three-step baseline process for thinning of bonded wafers for applications in threedimensional (3D) integration is presented. The Si substrate of top bonded wafer is uniformly thinned to ~35 μm by backside grinding and polishing, followed by wet-etching using TMAH. No visible changes at the bonding interface and damage-free interconnect structures are observed after the thinning process. Both mechanical and electrical integrity of the bonded pairs are maintained after the three-step baseline thinning process, with electrical tests on wafers with multi-level copper interconnect test structures showing only a slight change after bonding and thinning. This thinning process works well for Si removal to an etch-stop layer, although present process uniformity is not adequate to thin bulk Si substrates. Other issues such as wafer breakage and edge chipping during Si thinning and their possible solutions are also addressed.
Some Aspects of the Materials Science of Low-K Integration
Authors: McGahay Vincent
Published: June 2019

The microelectronic industry's transition to low dielectric constant insulators in the wiring levels of integrated circuits has proven to be more difficult than expected. Materials properties are an integral part of the problem, as much for yield as for reliability. Unfortunately, many properties which are important for manufacturing robustness tend to degrade as the dielectric constant is lowered. Although materials properties are a useful guide to low-K manufacturability, inflexibility with regard to specifications could ultimately limit future progress. Application of basic principles of materials science to the integration of low-K dielectrics can give critical insight into the nature of the difficulties. Several examples of problems in low-K integration which benefit from such analysis are given.
Sequential Process Modeling for Determining Process-Induced Thermal Stress in Advanced Cu/Low-k Interconnects
Authors: Yang Kwanho , Waeterloos Joost J. , Im Jang-Hi , Mills Michael E.
Published: June 2019

The thermomechanical reliability of Cu/low-k interconnects, which is directly related to yield problems and premature device failures, has been a major issue. The development of a manufacturing process, which can satisfy the most stringent reliability standards, requires detailed information on the thermomechanical behavior of Cu/low-k interconnects. The thermomechanical behavior of Cu/low-k interconnects is complicated by the fact that processinduced thermal stresses are developed during the manufacturing process. A conventional finite element analysis (FEA) approach has some difficulties to model Cu/low-k interconnects that keep changing during process steps. Therefore, a sequential process modeling technique has been developed to simulate the interconnect behavior to substantially any level of detail and understand the complex thermomechanical behavior of Cu/low-k interconnects while being manufactured. In this paper, we briefly describe a sequential process modeling technique and demonstrate how we use the modeling technique to solve a Cu/SiC delamination problem in a Cu/SiLK* semiconductor dielectric dual damascene test structure.
Accelerated Oxidation of Hydrogen Silsesquioxane Thin Films Facilitated by an Organosilicone Resin Additive
Authors: Harkness Brian R. , Boisvert Ron , Deng Qian , Zhong Ben , Sun Jianing , Gidley David
Published: June 2019

It has been discovered that the incorporation of small amounts of hydrogen silsesquioxaneco-octadecyl silsesquioxane resin into hydrogen silsesquioxane films results in a significant modification of the thermally processed thin film properties compared to standard hydrogen silsesquioxane (HSQ) films derived from FOx ® solutions. These modifications included a doubling of the modulus and significant reduction in the remaining silyl hydride level. Key to the change in properties was an accelerated oxidation of the film during a one-minute hot plate bake step under a partial oxygen atmosphere. A systematic examination of a series of 5 to 30 weight percent resin additive formulations showed improved mechanical properties at lower additive levels but these were neutralized at higher levels by increasing levels of nanoporosity. It is hypothesized that the enhanced oxidation effect is the result of increased oxygen diffusivity into the film facilitated by the hydrocarbon component of the resin additive.
Structure and Properties of Polysilsesquioxanes and Copolymers for Ultra-Low Dielectric Films
Authors: Yoon Do Y. , Ro Hyun Wook , Park Eun Su , Lee Jin-Kyu , Kim Hie-Joon , Char Kookheon , Rhee Hee-Woo , Kwon Dongil , Gidley David W.
Published: June 2019

Polysilsesquioxanes (PSSQs) with the empirical formula (RSiO3/2)n have become very important as low-dielectric insulators for copper interconnects in the next-generation logic devices, but the detailed structure-property relationships were completely lacking. We have investigated the microstructure and functional properties of PSSQs with varying alkyl substituents and also PSSQ copolymers. As a result, significant advances have been made in the scientific understanding of PSSQ structures and significant improvements of key properties such as the crack resistance, mechanical modulus and hardness, and incorporation of nanometer-sized (<4 nm) porosity for ultra-low dielectric constants (<2.0).