Search

Small amounts of copper were added to enhance the adhesion and minimize agglomeration of Ag thin films on SiO2 substrates. Comparison of texture profiles between Ag and Ag(Cu) thin films showed that Cu additions enhanced (111) texture in Ag thin films. For the case of Ag film, (111) texture was enhanced mainly by recrystallization of amorphous regions during annealing. In addition to the recrystallization, (111) texture enhancement in Ag(Cu) film attributes to the dissociation of grains with other crystallographic orientations.

Substrate surface roughness effects on Ag film texture were investigated using pole figure analysis. X-ray diffraction results confirmed that Ag thin films on smooth SiO2 substrates had strong {111} texture when compared with Ag films on PEN. It was noted that the difference of strain energy density (δEε) in Ag film on PEN (0.039 MPa) was almost 5 times greater than that on SiO2 (0.0084 MPa). The comparison between surface and strain energies revealed that the {111} texture of Ag thin film on SiO2 was explained by minimization of the surface energy and the weaker {111} texture of Ag on PEN was a result of reduced diffusion length of Ag adatoms on the rough PEN surface.

This work investigates the mechanical properties of ITO on PEN substrates as a function of processing conditions, including rf power, substrate temperature, and substrate treatment. The best mechanical performance is obtained from high substrate temperature and low rf power. Plasma treatment gases also influence mechanical properties, with mixture of nitrogen and hydrogen gases producing the best results. This work provides an initial understanding of the impact of sputter process conditions on film's mechanical performance.

A study of the effects of C and Ge additions on the Cu catalyzed oxidation of Si has been performed. It was found that the addition of Ge alone resulted in a marked slowdown in the rate of oxygen incorporation; during the first three days of the experiment the rate of oxygen incorporation was 25 times higher in the Si reference sample. The Ge was incorporated into the oxide. Small amounts of C added to the SiGe compound have a more pronounced effect. Carbon concentrations of less than 2% prevent oxidation of SiGeC for periods of at least one month. Copper enhanced oxidation of Si(100) has produced oxides of several hundred nanometers in under one month.

We examined whether smokers who purchased low-taxed cigarettes from American Indian reservations had lower quit attempt and cessation rates than did smokers who purchased cigarettes from full-price outlets. Smokers who bought cigarettes from American Indian reservations were half as likely to make a quit attempt and had a nonsignificant trend toward lower cessation rates (20% vs 10%) compared with those who bought full-priced cigarettes. Interventions that reduce price differentials are suggested to maximize the public health benefit of cigarette excise taxes.

Thin encapsulated silver films have been prepared on oxidized silicon by nitridation of ∼200‐nm‐thick Ag–19 at. % Ti alloy films and Ag(120 nm)/Ti(22 nm) at 300–700 °C in an ammonia ambient. The encapsulation process has been studied in detail by Rutherford backscattering, and scanning Auger and secondary‐ion‐mass spectrometry, which showed that Ti‐nitride and Ti‐oxide‐silicide formation take place at the surface and the Ag–Ti/SiO2 interface, respectively. Four‐point‐probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Resistivity values of ∼4 μΩ cm were measured in encapsulated Ag alloy films with initial low Ti concentrations. The annealed bilayer structure had minimal Ti accumulations in Ag and the resistivity values were comparable to that of the as‐deposited Ag (∼3 μΩ cm).

TiAl based thin-films possess high oxidation-resistance and high melting points, making them possible candidates for application in electronics. The behavior of the films upon exposure to various temperatures is of interest for such application. In the present study, Ti37Al63 thin films were deposited onto SiO2 substrates using RF magnetron sputtering from a compound target. Anneals were performed in vacuum at temperatures ranging from 400 °C to 700 °C. The phases and microstructural behavior of the films were evaluated as a function of annealing. Microstructural behavior was correlated with resistivity changes in the films. The behavior of Ti-Al films as potential under-layers for silver metallization was also evaluated. The Ti-Al was observed to enhance the thermal stability of pure Al thin-films. The results are relevant for potential application of the films to electronics.

The thermal stability and electrical resistivity of Ag(Al) alloy thin films on SiO2 are investigated and compared to pure Ag thin films by performing various analyses: Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and four-point probe. The susceptibility to agglomeration of Ag on SiO2 layer is a drawback of Ag metallization. Ag(Al) thin films show good thermal stability on SiO2 layer without any diffusion barrier. The films are stable up to 600 °C for 1 hour in vacuum. Electrical resistivity of as-deposited Ag (5 at % Al) thin film is slightly higher than that of pure Ag thin film. However, the resistivity of Ag(Al) samples annealed at high temperatures (up to 600 °C for 1 hour in vacuum) remains constant due to the improvement of thermal stability (large reduction of agglomeration). This finding can impact metallization for thin film transistors (TFT) for displays, including flexible displays, and high-speed electronics due to lower resistivity value compared to Cu thin film.

The oxidation of amorphous Si0.65Ge0.27C0.08 and single‐crystal Si0.63Ge0.36C0.01 in wet ambient at 700 and 900 °C has been studied using Rutherford backscattering spectrometry and transmission electron microscopy. A reference sample of Si0.63Ge0.37 was also oxidized in order to determine the influence of carbon on the oxidation behavior. The low C content alloy behaved similar to the SiGe alloy: uniform Si1‐xGexO2 was obtained at 700 °C whereas SiO2 was formed at 900 °C, and Ge piled up underneath the oxide. In both cases, carbon was not detected in the oxide layer. The amorphous Si0.65Ge0.27C0.08 alloy behaved significantly different at both oxidation temperatures in comparison with the crystalline Si0.63Ge0.36C0.01 and Si0.65Ge0.37. Negligible oxidation occurred at 700 °C whereas SiO2 was obtained at 900 °C and the rejected Ge distributed uniformly throughout the SiGeC alloy. It is proposed that fast Ge diffusion during oxidation at 900 °C resulted from diffusion at grain boundaries, since crystallizat...

In our recent report associating community demographics and tobacco outlet density in Erie County, New York,1 we stated that no other studies had been performed examining this topic. After our original submission date, work was published by Laws et al,2 who found that the percentage of all businesses that sold tobacco in 10 Massachusetts neighborhoods was strongly inversely correlated with the average per capita income of those neighborhoods and that the resident populations of the lower-income neighborhoods were predominantly African American or Latino. Therefore, by the publication date of our report, our statement was no longer correct, and the work of Laws et al should be recognized. The important point is not whose paper was published first, but rather that 2 independent studies found similar results. There seems to be little dispute over the observation that tobacco-selling retail outlets are disproportionately located in poor neighborhoods. The implication for public health is that zoning rules to limit the proliferation of tobacco outlets to eliminate this disparity should be seriously considered.

Four monolithic transformers and an inductor are fabricated in a 5 metal CMOS process with varying number of turns and metal thicknesses. The S-parameters are measured from 500 MHz to 5.5 GHz, and equivalent lumped element models are extracted to calculate the differential quality factor vs. frequency. The transformers demonstrated significantly higher quality factors peaking at higher frequencies compared to the inductor.

In recent years, a substantial amount of research has been focused on identifying suitable interfacial layers in organic light-emitting diodes and organic solar cells which has efficient charge transport properties. In this work, a very thin layer of AgOx is deposited on top of the ITO layer along with PEDOT:PSS and is observed that the solar cells having the AgOx interfacial layer showed a 28% increase in power conversion efficiency in comparison to that of the control cell. The enhancement in efficiency has been ascribed to improvements in fill factor as well as the increase in shunt resistance and decrease in the series resistance of the solar cells. An equivalent circuit model is also provided to understand the changes in the series and shunt resistances in the AgOx modified devices.

For the benefit of reducing capacitance in multilevel interconnect technology, low-k dielectric HSQ (hydrogen silsesquioxane) has been used as a gapfill material in Al-metallization- based non-etchback embedded scheme. The vias are consequently fabricated through the HSQ layer followed by W plug deposition. In order to reduce the extent of via poisoning and achieve good W/Al contact, thin Ti/TiN stack films are typically deposited before via plug deposition. In this case, HSQ makes direct contact with the Ti layer. The reliability of the Ti/HSQ structures at elevated temperatures has been systematically studied in this work by using a variety of techniques. These results are also compared with those from Ti/TEOS (Tetraethylorthosilicate) structure, where TEOS is a conventional intra-metal dielectric. When the temperature is below 550 °C, a significant number of oxygen atoms are observed to diffuse into the titanium layer. The primary source of oxygen is believed to come from the HSQ film. When the temperature is above 550 °C, HSQ starts to react with Ti. At 700 °C, a TiO/Ti5Si3/HSQ stack structure forms. The Ti/HSQ system exhibits a higher reactivity than that of the Ti/TEOS system.

A model is proposed to describe the temperature dependence of the aluminum oxynitride (AlxOyNz) diffusion barrier formation during a silver self-encapsulation process. These barrier layers form in the temperature range of 500-725 °C during anneals of the Ag/Al bilayers on oxidized Si substrates in an ammonia ambient. Experimental results show that temperature has a significant effect on the kinetics of this process. In this investigation, the diffusion of Al atoms through the Ag layers during self-encapsulation process is modeled using an analytical solution to a modified diffusion equation. This model shows that higher anneal temperatures will minimize the retardation effect by i) reducing the chemical affinity between Al and Ag atoms, and ii) allowing more Al atoms to surmount the interfacial energy barrier between the metal layer (Ag) and the newly formed AlxOyNz diffusion barriers. The theoretical predictions on the amount of segregated Al atom correlate well with experimental results from Rutherford backscattering spectrometry. This model in addition confirms the self-passivation characteristics of AlxOyNz diffusion barriers formed by Ag/Al bilayers annealed between 500∼725 °C.

Silver has been explored as a potential candidate for future advanced interconnects due to its lowest electrical resistivity, when compared with Al and Cu. As in the case of Cu metallization, an additional layer between the Ag film and underneath dielectric is necessary in order to improve adhesion and to block the diffusion of Ag atoms. In this study, thin aluminum oxynitride (AlxOyNz) diffusion barriers have been formed in the temperature range of 400-725 °C by annealing Ag/Al bilayers on oxidized Si substrates in ammonia ambient. Rutherford backscattering spectrometry showed that the out-diffused Al reacted with both the ammonia and oxygen in the ambient and encapsulated the Ag films. Higher process temperatures and thinner original Al layers showed to improve the resistivity of the encapsulated Ag layers. The resulting Ag resistivity values are ∼1.75 ± 0.35 µΩ-cm. The thermal stability test of these diffusion barriers showed that these barriers sustained the interdiffusion between Cu and Ag up to 620 °C at least for 30 min in either vacuum or flowing He-0.5% H2. This temperature is a 200°C improvement over previously reported values for the self-encapsulated Cu and Ag films. X-ray diffraction spectra showed no formation of any high resistive intermetallic compounds, i.e., Ag3Al, Ag2Al, and AlAg3.

HSQ (hydrogen silsesquioxane) is one of the promising low-k materials used in VLSI technology as an intra-metal dielectric to reduce capacitance-related issues. Like any other dielectrics, the integration of HSQ in multilevel interconnect schemes has been of considerable importance. In this study, the compatibility of HSQ with different nitride barrier layers, such as PVD and CVD TiN, PVD TaN, and CVD W2N, has been investigated by using a variety of techniques. The refractory metal barriers, Ti and Ta, are also included for a comparison. The degradation of HSQ films indicates a strong underlying barrier layer dependence. With CVD nitrides or refractory metals as barrier, HSQ exhibits a better structural and property stability than that with PVD nitrides. The possible mechanisms have been discussed to account for these observations.

The failure mechanisms arising from the instability in operation of indium gallium zinc oxide based thin film transistors (TFTs) upon prolonged real application stresses (bias and illumination) have been extensively studied and reported. Positive and negative gate bias conditions, along with high photonic energy wavelengths within visible light spectrum are used as stress conditions. The increased carrier concentration due to photonic excitation of defects within bandgap and ionization of deep level vacancies is compensated by the reduction in off currents under illumination due to the trapping of carriers in the intermetal dielectric. Band lowering at the source-channel junction due to accumulation of negative carriers repelled due to negative gate bias stress further causes high carrier flow into the channel and drives the devices into failure. The defect identification during failure and degradation assisted in proposing suitable low temperature post processing in specific ambients. Reliability tests a...

Polyimides prepared from oxydiphthalic anhydride and diamine precursors can be photosensitive. The thermal, mechanical, and dielectric properties of the polyimide films have been characterized with various techniques. The thermal decomposition temperature of the cured film is 520 °C, and the coefficient of thermal expansion is 20 × 10−6/°C. The polymer chemistry and processing conditions result in a low stress (in situ during the curing and cooling cycles. Pads of 6 μm were patterned through the photosensitive polyimide at a sensitivity of 110 mJ/cm2 to i-line wavelength. The polyimide films exhibit anisotropy with an in-plane refractive index of 1.74 and an oul-of-plane index of 1.62 measured at 632.8 nm wavelength. This indicates a preferred orientation of polymer chains in the film plane. The estimated dielectric anisotropy should be considered a major factor for device design and optimization.

The texture in polycrystalline Ag thin films prepared by e-beam evaporation has been characterized by an x-ray diffraction technique as a function of underlayers and encapsulation temperatures. The Ag films deposited on Ti layers showed a strong fiber texture with a fiber axis parallel to the film normal, whereas an almost random orientation was observed in the Ag films on Cr layers. This underlayer dependence of texture is associated with the lattice match between Ag and underlayer metal. In addition to texture, the Ag films on Ti also exhibited a texture component, which is the result of twinning of -oriented grains. After the encapsulation process, the texture in the Ag films on Ti was significantly improved, as evidenced by an increased (111) diffraction intensity and a slightly narrower space distribution of the texture along the fiber axis. The highly textured Ag films are expected to exhibit an improved electromigration resistance.

Transmission electron microscopy (TEM) in both cross sectional and plan view is used to study the effect of annealing Ag-Ti bilayers deposited on SiO2/Si substrates in an NH3 ambient. The resulting structure, texture and grain size are investigated. Comparisons are made between films annealed at 400, 500 and 600 °C. Silver films show increasingly strong texture with annealing temperature while exhibiting a bamboo-like grain structure at 600 °C. Considerable grain growth with lateral grain sizes of up to 5 times the thickness of the Ag film is observed at 600 °C. The grains typically extend through the Ag film thickness. The Ti/SiO2 interface uniformity and the absence of voids at the substrate surface are positive indicators of the role of titanium as a good adhesion promoter. At 600 °C, a uniform TiN encapsulation layer is observed on the Ag surface.

Rapid processing and reduced end-of-range diffusion result from susceptor-assisted microwave (MW) annealing, making this technique an efficient processing alternative for electrically activating dopants within ion-implanted semiconductors. Sheet resistance and Hall measurements provide evidence of electrical activation. Susceptor-assisted MW annealing, of ion-implanted Si, enables more effective dopant activation and at lower temperatures than required for rapid thermal annealing (RTA). Raman spectroscopy and ion channeling analyses are used to monitor the extent of ion implantation damage and recrystallization. The presence and behavior of extended defects are monitored by cross-section transmission electron microscopy. Phosphorus implanted Si samples experience effective electrical activation upon MW annealing. On the other hand, when boron implanted Si is MW annealed, the growth of extended defects results in reduced crystalline quality that hinders the electrical activation process. Further comparison of dopant diffusion resulting from MW annealing and rapid thermal annealing is performed using secondary ion mass spectroscopy. MW annealed ion implanted samples show less end-of-range diffusion when compared to RTA samples. In particular, MW annealed P+ implanted samples achieve no visible diffusion and equivalent electrical activation at a lower temperature and with a shorter time-duration of annealing compared to RTA. In this study, the peak temperature attained during annealing does not depend on the dopant species or dose, for susceptor-assisted MW annealing of ion-implanted Si.

Susceptor-assisted microwave annealing enables effective dopant activation, at low temperatures, in ion-implanted Si. Given similar thermal budgets for microwave annealing and rapid thermal annealing (RTA), sheet resistances of microwave annealed Si, with either B+ or P+ implants, are lower than the values obtained using RTA. The fraction of dopants activated is as high as 18% for B+ implants and 64% for P+ implants. Dopant diffusion is imperceptible after microwave annealing, but significant after RTA, for P+ implanted Si samples with the same dopant activation. Microwave annealing achieves such properties using shorter anneal times and lower peak temperatures compared to RTA.

Herein the synthesis of Cu3Ge films by exposing Cu-Ge alloy films to microwave radiation is reported. It is shown that microwave radiation led to the formation of copper germanide at temperatures ca. 80 °C. The electrical properties of the Cu3Ge films are presented and compared for various annealing times. X-ray diffraction shows that the Cu3Ge films formed after microwave annealing is crystalline in the orthorhombic phase. Rutherford backscattering and X-ray photoelectron spectroscopy confirms the formation of copper oxide encapsulation layer. Despite the slight oxidation of Cu during the microwave anneal the lowest resistivity of Cu3Ge films obtained is 14 μΩ-cm.

Multilayer structures of TiO2/Ag/TiO2 have been deposited onto flexible substrates by room temperature sputtering to develop indium-free transparent composite electrodes. The effect of Ag thicknesses on optical and electrical properties and the mechanism of conduction have been discussed. The critical thickness (tc) of Ag mid-layer to form a continuous conducting layer is 9.5 nm and the multilayer has been optimized to obtain a sheet resistance of 5.7 Ω/sq and an average optical transmittance of 90% at 590 nm. The Haacke figure of merit (FOM) for tc has one of the highest FOMs with 61.4 × 10−3 Ω−1/sq.

Silver doped cupric oxide thin films are prepared on polyethylene naphthalate (flexible polymer) substrates. Thin films Ag-doped CuO are deposited on the substrate by co-sputtering followed by microwave assisted oxidation of the metal films. The low temperature tolerance of the polymer substrates led to the search for innovative low temperature processing techniques. Cupric oxide is a p-type semiconductor with an indirect band gap and is used as selective absorption layer solar cells. X-ray diffraction identifies the CuO phases. Rutherford backscattering spectrometry measurements confirm the stoichiometry of each copper oxide formed. The surface morphology is determined by atomic force microscopy. The microstructural properties such as crystallite size and the microstrain for (−111) and (111) planes are calculated and discussed. Incorporation of Ag led to the lowering of band gap in CuO. Consequently, it is determined that Ag addition has a strong effect on the structural, morphological, surface, and optical properties of CuO grown on flexible substrates by microwave annealing. Tauc's plot is used to determine the optical band gap of CuO and Ag doped CuO films. The values of the indirect and direct band gap for CuO are found to be 2.02 eV and 3.19 eV, respectively.

Ag/Ti bilayer films deposited on silicon dioxide substrates were annealed in ammonia ambient in the temperature range of 400 - 600 °C. Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES) have shown that Ti segregates to both the surface to form a TiN(O) layer and to the Ti/SiO2 interface to form a Ti-oxide/Ti-silicide bilayer. The annealed bilayer structure had minimal Ti accumulations in Ag. Resistivity values of ˜2 μΩ-cm were obtained in encapsulated Ag bilayer films, which are comparable to that of the as-deposited. X-ray analysis confirmed the absence of intermetallic phase transformation.

Shallow contact metallization of SiGeC was studied in anticipation of this alloys use in low power applications. It has been shown that in the solid state reaction of Co on (100) Si, that Co is the moving species with proper annealing conditions. This prevents the formation of Kirkendal voiding in certain device structures. This work studies the Co and Ti metallization of SiGeC. A bilayer of 44 nm of Co on 7 nm of Ti, were electron beam evaporated onto epitaxially grown Si0.77Ge0.21C0.02. The samples were rapid thermal processed at 600 and 900 °C for up to two minutes in a nitrogen ambient. The analysis techniques used were Rutherford backscattering spectrometry which included the used of the 4.27 MeV 12C(α,α) 12C resonance reaction, glancing angle x-ray diffraction, During annealing at all temperatures, Co diffused through the Ti layer and formed CoSi. This phase was confirmed by x-ray diffraction. The Co displaced the Ti to the surface. At 600 °C, Ge diffused to the surface layer, while at 900 °C it was rejected back into the original SiGeC. The sample annealed at 600 °C was subsequently annealed at 900 °C. The Ge in the surface layer was rejected from the surface layer, diffused across the CoSi and back into the SiGeC.

Encapsulated Ag(Ti) films on oxidized silicon were obtained by nitridation of Ag(19 at.% Ti) alloys in NH3 at temperatures between 400-700°C for various times. Upon annealing Ti segregates to the surface and alloy/SiO2 interface to form a TiN(O) surface layer and a TiO/Ti5Si3 interfacial bilayer structure. Resistivity values of 2.5 μΩ-cm were measured in the encapsulated Ag alloys. The results suggest that resistivity is controlled by the residual Ti concentration.

In the present study, thin films of binary Ag–Cu alloys with different Cu content were prepared by a cosputtering technique and then annealed by microwave heating. The metallographic and electrical properties of the thin films were observed experimentally. It was found that the electrical performance of Ag–Cu thin films enhanced after microwave processing when compared to vacuum annealing. Based on the fact that Cu has a low solubility in Ag, it was chosen as the alloying element. The low solubility favored segregation of Cu at the surface and grain boundaries. This prevented Ag grain boundary diffusion and agglomeration. The as-deposited thin films were more resistive when compared to the microwave processed films. Comparison of the two postdeposition annealing techniques, microwave and vacuum, showed that microwave annealing is a clean, faster, and efficient process that can improve the electrical performance of Ag–Cu thin films. Results from this investigation demonstrated that microwave annealing is a suitable replacement of more expensive manufacturing techniques currently used in the field of interconnects technology.

Cu(90 nm)/Ti(20 nm) bilayers and Cu(Ti 27 at.%) alloy films were deposited on SiO2 and annealed in an NH3 ambient at temperatures 400–700° C for 30 min. During annealing Ti segregated to both the free surface and the alloy/SiO2 interface. At the surface Ti reacted with NH3 to form TiN, whereas at the interface the Ti reacted with the SiO2 to form a TiO/Ti5Si3 structure. High resolution energy dispersive x-ray analysis revealed the presence of interfacial Cu between the Ti-silicide and Ti-oxide layers at temperatures greater than 450°C. Using Cu-Ti alloy films enhanced the Si02 consumption rate by a factor of 3-4 compared to that of pure Ti. It is suggested that the interfacial Cu is responsible for the increased rate. It is plausible that an interfacial Cu2O component has a catalytic effect on the Ti- SiO2 reaction.

Samples of Si1-x-YGexCy were analyzed with a triple axis high resolution x-ray diffractometer to produce reciprocal space maps. Films with compositions of approximately Si0.77Ge0.20C0.01 vvith thicknesses ranging from 120 nm to 750 nm were found to be pseudomorphic with a tetragonal distortion, εT, near 1%. The tetragonal distortion in pseudomorphic samples with compositions near Si0.47Ge0.50C0.03 with thicknesses ranging from 61 nm to 115 nm was found to be near 2%. The strain increased linearly with Ge concentration even though the Ge:C ratio remained nearly constant. The strain in samples with similar compositions was not a function of thickness. These strain measurements correlated well with results from ion channeling analysis.

Thin heteroepitaxial films of Si1-x-yGexCy have been grown on (100)Si substrates using atmospheric pressure chemical vapor deposition at 550 and 700°C. The crystallinity, composition and microstructure of the SiGeC films were characterized using Rutherford backscattering spectrometry (ion channeling), secondary-ion-mass-spectrometry and cross-sectional transmission electron microscopy. SiGeC films with up to 2% C were grown at 700°C with good crystallinity and very few interracial defects, while misfit dislocations at the SiGe/Si interface were observed for SiGe films grown under the same conditions. This difference indicates that the presence of carbon in the SiGe matrix increases the critical thickness of the grown layers. SiGeC thin films (>110 nm) with up to 3.5% C were grown at 550°C with good crystallinity. The crystallinity of the films grown at lower temperature (550°C) was less sensitive to the flow rate of the C source (C2H4), which enabled growth of single crystal SiGeC films with higher C content.

Single crystal Si0.63Ge0.36C0.01 and amorphous Si0.65Ge0.27C0.08 layers have been oxidized in a wet ambient at 700 °C and 900 °C. The oxide growth has been studied using Rutherford backscattering spectrometry and transmission electron microscopy. A reference sample of Si0.63Ge0.37 was also oxidized in order to determine the influence of C on the oxidation behavior. The lower C content alloy behaved similar to the SiGe alloy. Uniform Si1-xGexO2 was obtained at 700 °C whereas SiO2 was formed at 900 °C, and Ge piled up underneath the oxide. In both cases, C was not detected in the oxide layer. The amorphous Si0.65Ge0.27C0.08 alloy behaved significantly different at both oxidation temperatures in comparison with the crystalline Si0.63Ge0.36C0.01 and Si0.63Ge0.37. Negligible oxidation occurred at 700 °C whereas SiO2 was obtained at 900 °C and the rejected Ge distributed uniformly throughout the SiGeC alloy. It is proposed that fast Ge diffusion during oxidation at 900 °C resulted from diffusion at grain boundaries, since crystallization of the amorphous SiGeC layer occurred in conjunction with oxidation, leading to nucleation of ∼5 nm nanocrystals.

Silicon oxide films ( > 1μm ) were grown at room-temperature after low-energy copper-ion implantation of Si(100) substrates. The structural properties of the silicon oxide layer and the implanted silicon were characterized by Rutherford backscattering spectrometry and transmission-electron microscopy. During room temperature oxidation a portion of the implanted copper resided on the surface and a portion moved with the advancing Si/SiOx interface. This study revealed that the oxide growth rate was dependent on the amount of Cu present at the moving interface. The resulting oxide formed was approximately stoichiometric silicon dioxide.

Economic literature shows that smokers are responsive to the price of cigarettes and that African American and lower-income smokers are particularly price sensitive.1–4 Tobacco control policies that effectively restrict access and use of cigarettes will raise the cost of the cigarettes themselves as a result of increased costs in obtaining and using cigarettes. For example, zoning restrictions on the number of tobacco outlets in a given area will require smokers to travel greater distances, which has a cost associated with it, to obtain cigarettes. Studies in the alcohol literature indicate that reductions in the physical availability of alcohol products are associated with positive health and behavioral outcomes,5–8 especially in low socioeconomic areas.9,10 No such studies have been performed concerning tobacco retail outlet densities. Given this deficiency in the tobacco literature, we set out to determine whether tobacco outlets were more densely concentrated in areas with lower incomes and more African Americans.

This investigation elucidates the influence of standalone-bias stress and standalone-illumination stress, and their combinatory effect on indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). Each phenomenon associated with illumination (wavelengths of 410, 467, 532 and 632 nm) and bias (Vg = ±20 V; Vd = 0, 20 V) stresses is categorized individually. Wavelengths below 532 nm are responsible for ionized vacancy creation, carrier generation and interface state creation while only gate stresses of +20 V create excessive charge trap states. Failure conditions are identified as gate stresses of −20 V with 410 nm illumination. An improvement in the Ion/Ioff ratio from 106 to 107 is due to increased charge contribution for on currents, and trapping of holes at the intermetallic dielectric near the source–channel junction in the off region. Upon stress removal TFTs exhibit incomplete recovery due to slow trapping of excited carriers from dielectric layers and inability created by the passivation layer to absorb oxygen for vacancy regeneration. The low-temperature fabrication and optimized post-fabrication anneal have created reduced defect and vacancy densities that make the IGZO TFTs more stable than the previous generation TFTs.

Different multilayer structures of Nb2O5/Ag/Nb2O5 have been deposited onto flexible substrates by sputtering at room temperature to develop an indium free transparent composite electrode. The effect of Ag thickness on the electrical and optical properties of the multilayer stack has been studied in accordance with the Ag morphology. The critical thickness of Ag to form a continuous conducting layer is found to be 9.5 nm. A new conduction mechanism has been proposed to describe the conduction before and after the critical thickness. The effective Hall resistivity of the optimized films is as low as 6.44 × 10−5 Ω-cm with a carrier concentration and mobility of 7.4 × 1021 cm−3 and 13.1 cm2 /V-s, respectively, at the critical Ag layer thickness. The multilayer stack has been optimized to obtain a sheet resistance of 7.2 Ω/sq and an average optical transmittance of 86% at 550 nm without any substrate heating or post-annealing process. The Haacke figure of merit (FOM) has been calculated for the films, and the multilayer with a 9.5 nm thick Ag layer has the highest FOM at 31.5 × 10-3 Ω−1, which is one of the highest FOM values reported for TCE deposited at room temperature on a flexible substrate.

We report on the enhanced performance of hybrid photovoltaic devices consisting of poly(3-hexylthiophene), (6,6)-phenyl C61 butyric acid methyl ester, and zinc oxide (ZnO) nanorod arrays grown on seedless indium tin oxide (ITO) glass in aqueous zinc chloride solution. Introduction of optimized-length ZnO nanorod arrays between hole injection and ITO layers increased photocurrent density from 8.0 to 8.8 mA/cm2 and fill factor from 42% to 47%. The absence of a seed layer significantly reduced incident light reflection on the ITO glass and resulted in an overall 10% increase in photocurrent. A photovoltaic device based on a ZnO nanostructure length of 100 nm exhibited a maximum power conversion efficiency of 2.4%, 15% higher than that of an equivalent device without ZnO nanorods.

A transparent conductive electrode of mixed titanium dioxide (TiO2−x)–indium tin oxide (ITO) with an overall reduction in the use of indium metal is demonstrated. When used in organic photovoltaic devices based on bulk heterojunction photoactive layer of poly (3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester, a power conversion efficiency of 3.67% was obtained, a value comparable to devices having sputtered ITO electrode. Surface roughness and optical efficiency are improved when using the mixed TiO2−x–ITO electrode. The consumption of less indium allows for lower fabrication cost of such mixed thin film electrode.

In this study, we investigated the possibility of fabricating flexible single-crystal Si-Pd diodes on polymer substrates using silver-filled conductive tape or epoxy. This simple technique mitigates the complexity of process-intensive metal-bonding schemes to achieve backside electrical contacts on semiconductor devices. The performance of such devices is evaluated while bent to a 1.2 cm radius of curvature. The longer-term stability of the devices fabricated is also briefly discussed.

We studied interfacial phase formation between copper and copper-alloy films on SiO2 in order to understand how to improve adhesion. CuCr and CuTi alloy and bilayer films on SiO2 were annealed from 400-600°C for 30 min in an N2 + H2 (5%) ambient. The bilayer systems exhibited refractory metal migration from the interface to the surface where they oxidized. In the CuTi bilayer system, an oxidized interfacial Ti layer was observed. Both CuCr and CuTi alloy systems exhibited refractory metal segregation to the interface and surface. Rutherford backscattering spectrometry and Auger electron spectroscopy were used for elemental depth profiling.

We investigate the nitridation of chromium films in an NH3 ambient at 500°C. Rutherford backscattering spectrometry using 2.0 MeV He2+ was utilized to determine the compositions of thick reacted layers and to provide calibration for the other techniques. In addition, analysis was performed using the 14N(α,α)14N resonance at 3.72 MeV in order to enhance sensitivity to nitrogen. Sputter-deposited TiN was used as a calibration for the cross section a for this resonance over the energy range 3.05-3.85 MeV and compared to the literature value. We find that analysis just above the peak in the resonance provides excellent sensitivity to N concentration in the nitride layers. This approach may be readily used in conjunction with 2.0 MeV backscattering to determine the overall composition and sample configuration. Auger electron spectroscopy was used to provide more depth sensitivity in compositional profiling and to monitor the oxygen impurity distribution. X-ray diffraction was used to identify phases in both as-deposited and annealed films.

The use of ion-beam techniques to enhance selected properties of bioactive materials, such as the adhesion of hydroxylapatite (HA) coatings on titanium-based substrates has been investigated. In this study, very thin HA films on titanium substrates were created by pulsed laser deposition techniques. Ion irradiations were carried out using 260-keV argon ions, with fluences of 0.25-50×1015ions/cm2, and at room temperature. Rutherford backscattering spectrometry was used to evaluate sample composition before and after irradiation. The amount of mixing was quantified by the mixing rate (the amount of atomic displacement due to an irradiation fiuence). This pilot data indicates that mixing was evident after sufficient ion irradiation. The ramification of this preliminary study has provided a quantitative measure of ion mixing as a potential prosthetic biomaterial surface modification technique.

The mixing of titanium overlayers with hydroxyapatite (HA) substrates via ion irradiation has been demonstrated. Analysis via secondary ion mass spectroscopy (SIMS) indicates an interfacial broadening of titanium and calcium of the implanted sample compared to that of the unimplanted sample. Attendant to the observed ion beam mixing of titanium into the HA, the oxygen signal of the titanium overlayer increases as a result of ion irradiation. It is supposed that this change is evident of diffusion through the metal layer and possibly from titania formation at the free surface and perovskite formation at the film/substrate interface. This possibility is consistent with thermodynamic predictions. Additionally, the force required to separate the film from the substrate increased as a result of ion irradiation, validating the continued study of ion beam processing of Ti/HA systems towards the improvement of long term fixation of implant devices.

Copper films generally exhibit poor adhesion on dielectrics. It has been shown that the addition of refractory metals promotes adhesion via an interfacial reaction or better wetting to the dielectric. We investigate the adhesion of Cu-refractory metal (Cr, Ti) alloy films and bilayers on various silicon oxide substrates (SiO2, PSG, BPSG) after annealing in the temperature range 400-600°C by conventional furnace using N2/H2 forming gas. Rutherford backscattering spectrometry (RBS) was used to determine the interfacial reaction characteristics. The efficacy of a variation of the standard Scotch™ tape testing was evaluated. We found that the combined Scotch™ tape/scribe adhesion test revealed excellent qualitative bonding information and could be correlated well to RBS characterization. We were able to optimize the sample configurations and chemical compositions to achieve the best adhering film.

Cu(Ti 27 at. %) and Cu(Cr 26 at. %) codeposited on silicon dioxide substrates were annealed in a flowing NH3 ambient at 400 - 600°C for 30 min. The Ti segregates to both the surface to form a TiN(O) layer and to the alloy/SiO2 interface to form a Ti-oxide/Ti-silicide bilayer. The Cr seems to migrate only to the free surface to form a CrNx layer. A 45 nm - thick Al film was deposited after nitridation, whereupon a second anneal was performed to evaluate these nitride layers as diffusion barriers. It was found that the Ti-nitride was stable up to 500°C as compared to Cr-nitride at 600°C.

Thick silicon dioxide films were prepared by room temperature oxidation of Si (100) and (11) induced by Cu3Si. This Cu3Si-enhanced oxidation process is accelerated by ultraviolet light irradiation. Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were employed to characterize the chemical and structural properties of the silicon dioxide layer underneath the oxidized Cu3Si surface layer. The resulting films of silicon dioxide are denser and stoichiometric when silicon oxidation proceeds under UV irradiation at room temperature. Compared with the oxidation in the Au/Si system, there are two distinguishing features of the Cu/Si system: (1) the formation of a silicon oxide layer in the interface between Cu and Si; and (2) room temperature growth of silicon dioxide with the thickness in the range of 1 micron.

Amorphous indium gallium zinc oxide (a-IGZO) thin films of the highest transmittance reported in literature were initially deposited onto flexible polymer substrates at room temperature. The films were annealed in vacuum, air, and oxygen to enhance their electrical and optical performances. Electrical and optical characterizations were done before and after anneals. A partial reversal of the degradation in electrical properties upon annealing in oxygen was achieved by subjecting the films to subsequent vacuum anneals. A model was developed based on film texture and structural defects which showed close agreement between the measured and calculated carrier mobility values at low carrier concentrations (2–6 × 1019 cm−3).