Sheet Resistance Data Research Articles

Machine Learning Aided Optimization of P1 Laser Scribing Process on Indium Tin Oxide Substrates

Present study employes a picosecond laser (532 nm) for selective P1 laser scribing on the indium tin oxide (ITO) layer and subsequent fine‐tuning of P1 scribing conditions with machine learning (ML) techniques. Initially, the scribing is performed by varying different laser parameters and further evaluate them via an optical microscope and two probe resistivity measurements. The corresponding scribing width and sheet resistance data are used as input databases for ML analysis. The classification and regression tree (CART)‐based ML analysis revealed that median pulse energy <5.7 μJ insufficient to separate the adjacent scribing regions. While pulse energy >5.7 μJ, APL > 35%, LSO > 46%, and processing speed ≥1250 mm s−1 gives ≥16 μm of scribing width. Further, the decision tree (DT) analysis showed that pulse energy of ≥8.1 μJ, and LSO ≥ 37% are required for electrically isolated lines. The feature importance score suggests that laser fluence and pulse energy determined the scribing width, whereas electrical isolation strongly depends on LSO and processing speed. Finally, the ML achieved conditions experimentally validated and reassessed via scanning electron microscope, and atomic force microscopy aligns well with optical microscope measurements.

Ellipsometric Study on the Uniformity of Al:ZnO Thin Films Deposited Using DC Sputtering at Room Temperature over Large Areas.

Al-doped ZnO combines high transparency and conductivity with abundant and non-toxic elements; making it suitable for optoelectronic devices with large-scale applications. In order to check the quality of the material deposited over large areas, spectroscopic ellipsometry is a powerful technique that allows the determination of various optical and electrical parameters by applying suitable oscillator models. This technique is used here to obtain sheet resistance and visible transmittance data at several equidistant points of Al:ZnO thin films deposited using DC sputtering on 15 cm × 15 cm glass substrates. Independent measurements using other optical (spectrophotometry) and electrical (four point probe) methods show analogous visible transmittance but somewhat higher resistance values than those obtained with ellipsometry, which is explained by the contribution of grain-boundary scattering compared to in-grain properties provided using ellipsometry. However, the mapping of the data gives a similar spatial distribution to the different types of measurement; therefore, proving the capacity of ellipsometry to study with a single tool the uniformity of the optical and electrical characteristics of large areas.

Direct-write formation of integrated bottom contacts to laser-induced graphene-like carbon

We report a simple, scalable two-step method for direct-write laser fabrication of 3D, porous graphene-like carbon electrodes from polyimide films with integrated contact plugs to underlying metal layers (Au or Ni). Irradiation at high average CO2 laser power (30 W) and low scan speed (∼18 mm s)−1 leads to formation of ‘keyhole’ contact plugs through local ablation of polyimide (initial thickness 17 μm) and graphitization of the plug perimeter wall. Top-surface laser-induced graphene (LIG) electrodes are then formed and connected to the plug by raster patterning at lower laser power (3.7 W) and higher scan speed (200 mm s)−1. Sheet resistance data (71 ± 15 Ω sq.)−1 indicates formation of high-quality surface LIG, consistent with Raman data which yield sharp first- and second-order peaks. We have also demonstrated that high-quality LIG requires a minimum initial polyimide thickness. Capacitance data measured between surface LIG electrodes and the buried metal film indicate a polyimide layer of thickness ∼7 μm remaining following laser processing. By contrast, laser graphitization of polyimide of initial thickness ∼8 μm yielded devices with large sheet resistance (>1 kΩ sq.)−1. Raman data also indicated significant disorder. Plug contact resistance values were calculated from analysis of transfer line measurement data for single- and multi-plug test structures. Contacts to buried nickel layers yielded lower plug resistances (1-plug: 158 ± 7 Ω , 4-plug: 31 ± 14 Ω) compared to contacts to buried gold (1-plug: 346 ± 37 Ω , 4-plug: 52 ± 3 Ω). Further reductions are expected for multi-plug structures with increased areal density. Proof-of-concept mm-scale LIG electrochemical devices with local contact plugs yielded rapid electron transfer kinetics (rate constant k 0 ∼ 0.017 cm s−1), comparable to values measured for exposed Au films (k 0 ∼0.023 cm s)−1. Our results highlight the potential for integration of LIG-based sensor electrodes with semiconductor or roll-to-roll manufacturing.

Superconducting fluctuations and giant negative magnetoresistance in a gate-voltage tuned two-dimensional electron system with strong spin-orbit impurity scattering

We present a quantitative theory of the gate-voltage tuned superconductor-to-insulator transition (SIT) observed experimentally in the 2D electron system created in the (111) interface between crystalline ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ and ${\mathrm{La}\mathrm{Al}\mathrm{O}}_{3}$. Considering two fundamental opposing effects of Cooper-pair fluctuations---the critical conductivity enhancement, known as paraconductivity, and its suppression associated with the loss of unpaired electrons due to Cooper-pairs formation---we generalize the standard thermal fluctuations theory to include interaction between fluctuations within the self-consistent field approximation and quantum tunneling between mesoscopic superconducting puddles within a phenomenological approach. Relying on the quantitative agreement found between our theory and a large body of experimental sheet-resistance data, we conclude that spin-orbit scatterings, via significant enhancement of the interaction between fluctuations, strongly enhance the sheet resistance peak at high fields and reveal anomalous metallic behavior at low fields, due to mixing of relatively heavy electron bands with a light electron band near a Lifshitz point. The large enhancement of the interaction between fluctuations at high fields, where the sheet resistance is strongly amplified, is shown to result in localization of Cooper-pair fluctuations within mesoscopic puddles.

Tc depression and superconductor-insulator transition in molybdenum nitride thin films

We have studied that the Tc depression and the superconductor-insulator transition (SIT) in molybdenum nitride (MoN) thin films. Thin films were fabricated by reactive DC magnetron sputtering method onto (100) MgO substrates in the mixture of Ar and N2 gases. Several dozen MoN thin films were prepared in the range of 3 nm < thickness d < 60 nm. The resistance was measured by a DC four-probe technique. It is found that Tc decreases from 6.6 K for thick films with increase of the normal state sheet resistance and experimental data were fitted to the Finkel’stein formula using the bulk superconducting transition temperature Tc0 = 6.45 K and the elastic scattering time of electron τ = 1.6 × 10−16 s. From this analysis the critical sheet resistance Rc is found about 2 kΩ, which is smaller than the quantum sheet resistance RQ. This value of Rc is almost the same as those for 2D NbN films. The value of τ for MoN films is also the similar value for NbN films 1.0 × 10−16 s, while Tc0 is different from that for NbN films 14.85 K. It is indicated that the mechanism of SIT for MoN films is similar to that of NbN films, while the mean free path ℓ for MoN films is larger than that for NbN films.

Experimental investigation of change in sheet resistance and Debye temperatures in metallic thin films due to low-energy ion beam irradiation

We present a systematic experimental investigation of low-energy (0–1 kV) ion irradiation induced changes in sheet resistivity and Debye temperatures in metallic nano-films of Ag, Cu and Al of thickness d/λo ∼ 2–5, where d is the film thickness and λo is the bulk mean free path, as a function of ion beam induced defects and impurities in a controlled manner. Ions of both atomic (Ne, Ar and Kr) and molecular (H2, N2) gases are employed in the investigation and the number of defects and impurities in the nano-film can be varied in a controlled manner by varying the ionic mass number (1–84) and beam fluence (8.7 × 1015–1.4 × 1016 ions cm−2). Low-temperature measurements are carried out for pristine and irradiated films to obtain the residual sheet resistance (RRS). An empirical formula relating the variation of RRS with beam fluence and ionic mass number is proposed for the first time. The change in RRS is due to the large diffusion of the impurities inside the nano-films as confirmed from energy dispersive x-ray spectroscopy. The Debye temperature (ΘD) is determined from Bloch–Grüneisen fitting of the temperature variation of sheet resistance data and it is found that ΘD decreases with increase in both fluence and ionic mass number arising primarily from the change in bulk modulus of the nano-film.

Effects of an aminosilane and a tetra‐functional epoxy on the physical properties of di‐functional epoxy/graphene nanoplatelets nanocomposites

The physical properties of difunctional epoxies would be improved by adding nanofillers and multifunctional epoxies. Therefore, in this study, a tetrafunctional epoxy was added to difunctional epoxy/GNPs nanocomposites. An aminosilane was used to improve the interfacial bonding between GNPs and the epoxy matrix. The physical properties of the epoxy/GNPs nanocomposites were investigated by DSC, TMA, DMA, and electrical resistivity test. The glass transition temperature and storage modulus of the nanocomposites increased with increasing GNPs content. Adding the aminosilane resulted in a marginal increase in the glass transition temperature of the nanocomposites. However, adding the tetrafunctional epoxy resulted in a considerable increase in the glass transition temperature, thermal dimensional stability, and storage modulus of the nanocomposites. SEM images of the fracture surfaces of the nanocomposites showed that the aminosilane improved the interfacial bonding. The aminosilane and tetrafunctional epoxy made the sheet resistance of the nanocomposites higher. The sheet resistance data showed electrical percolation at 1–2 phr of GNPs. POLYM. ENG. SCI., 54:969–976, 2014. © 2013 Society of Plastics Engineers

Gate Voltage Tuned Quantum Superconductor to Insulator Transition in an Ultrathin Bismuth Film Revisited

We explore the implications of Berezinskii–Kosterlitz–Thouless (BKT) critical behavior and variable-range hopping on the two-dimensional (2D) quantum superconductor–insulator (QSI) transition driven by tuning the gate voltage. To illustrate the potential and the implications of this scenario we analyze sheet resistance data of Parendo et al. taken on a gate voltage tuned ultrathin amorphous bismuth film. The finite size scaling analysis of the BKT-transition uncovers a limiting length L preventing the correlation length to diverge and to enter the critical regime deeply. Nevertheless the attained BKT critical regime reveals consistency with two parameter quantum scaling and an explicit quantum scaling function determined by the BKT correlation length. The two parameter scaling yields for the zero temperature critical exponents of the QSI-transition the estimates \(z\overline{\nu }\simeq 3/2\), z≃3 and \(\overline{\nu} \simeq 1/2\), revealing that hyperscaling is violated and in contrast to finite temperature disorder is relevant at zero temperature. Furthermore, \(z\overline{\nu }\simeq 3/2\) is also consistent with the two variable quantum scaling form associated with a variable-range hopping controlled insulating ground state.

FABRICATION AND THERMAL STABILITY OF A1CrTaTiNi/(A1CrTaTiNi)N BILAYER DIFFUSION BARRIER

The (AlCrTaTiNi)N and AlCrTaTiNi/(AlCrTaTiNi)N thin films were deposited on Si substrates as copper interconnects diffusion barriers by magnetron sputtering methods. The phase structure, phase composition and thermal stability at high temperature were investigated by XRD, EDS and SEM in this work, respectively. The results indicate that the gap could be observed between Cu and (AlCrTaTiNi)N layers when the samples were annealed at 500 for 30 min, and the Cu film fall off at 700 under visual conditions. The bonding properties of Cu and (AlCrTaTiNi)N layers can be improved by inserting a AlCrTaTiNi layer. The XRD patterns, SEM cross-sectional micrographs and sheet resistance data show that the AlCrTaTiNi/(AlCrTaTiNi)N bilayers is stable up to 800 .

Ultrathin Cr added Ru film as a seedless Cu diffusion barrier for advanced Cu interconnects

A 5nm thick Cr added Ru film has been extensively investigated as a seedless Cu diffusion barrier. High-resolution transmission electron microscopy micrograph, X-ray diffraction (XRD) pattern and Fourier transform-electron diffraction pattern reveal that a Cr contained Ru (RuCr) film has a glassy microstructure and is an amorphous-like film. XRD patterns and sheet resistance data show that the RuCr film is stable up to 650°C, which is approximately a 200°C improvement in thermal stability as compared to that of the pure Ru film. X-ray photoelectron spectroscopy depth profiles show that the RuCr film can successfully block Cu diffusion, even after a 30-min 650°C annealing. The leakage current of the Cu/5nm RuCr/porous SiOCH/Si stacked structure is about two orders of magnitude lower than that of a pristine Ru sample for electric field below 1MV/cm. The RuCr film can be a promising Cu diffusion barrier for advanced Cu metallization.

The effects of percolation in nanostructured transparent conductors

Abstract

Optical Properties of Ultrathin Copper Thin Films Sandwiched between Nb-Doped TiO2 Films Studied with Spectroscopic Ellipsometry

Cu thin films sandwiched between Nb-doped TiO2 (NTO) thin films were grown on glass substrates using tilted-dual target DC magnetron sputtering deposition. The thicknesses of the top and bottom NTOs were nominally 30 nm, and the thicknesses of the Cu films (t) varied between 1.5 nm and 50 nm. We measured the ellipsometric angles (Ψ,Δ) of the NTO/Cu/NTO/glass by using spectroscopic ellipsometry and estimated the thicknesses and dielectric functions of the Cu films by using a multi-layer model analysis. Transmission electron microscopy measurements showed that the Cu layers evolved from aggregates of Cu nanoparticles to coalesced Cu thin films as the Cu film thickness increased. Sheet resistance data also showed that the t = 8 nm film was near the percolation threshold, suggesting that films thinner than 8 nm were aggregations of Cu nanoparticles that were not well-connected. The films thicker than 8 nm were above the percolation threshold. From the Drude model, we estimated the plasmon frequency (ωp) and the electron relaxation time (τ), which were found to increase with increasing film thickness. By applying standard critical point analysis to the second derivatives of the dielectric function spectra, we found several peaks near 1.5, 2.1, 2.5, 3.5, and 4.3 eV, and attributed to interband transitions. The peak energies (except 1.5 eV) matched to the band structure calculations of bulk Cu found in the literature.

Dose loss of phosphorus due to interface segregation in silicon-on-insulator substrates

The dose loss of phosphorus due to interface segregation in silicon-on-insulator (SOI) substrates was characterized by using sheet resistance. Bulk silicon and SOI wafers were implanted with phosphorus at a dose of 5×1014 cm−2, followed by annealing at 900 °C to produce phosphorus segregation at the SiO2–Si interface. The effectiveness of the mobility model for calculating sheet resistance and the reliability of parameters in interface segregation models were verified based on the sheet resistance data and the secondary ion mass spectrometry profiles of phosphorus in bulk silicon samples. The sheet resistance in SOI substrates was then simulated using the verified mobility model and interface segregation parameters. Simulation results indicate that the equilibrium segregation behavior at the interfaces in SOI samples is similar to that in bulk silicon samples. Moreover, the dose loss in SOI substrates is more significant than that in bulk silicon wafers owing to a larger interface area in the SOI substrates.

Silicon and selenium implantation and activation in In 0.53Ga 0.47As under low thermal budget conditions

Si and Se implantations have been systematically investigated in In 0.53Ga 0.47As. Different implant doses and various activation anneals with temperatures up to 700 °C have been examined. Raising Si implant dose from 1 × 10 14 to 1 × 10 15 cm −2 was found to increase the active doping concentration by about a factor of two. As confirmed by Transmission Electron Microscopy (TEM) and electrical measurements, the rest of the implanted Si ions remain as defects in the crystal and degrade the mobility. It was also confirmed from Secondary Ion Mass Spectrometry (SIMS) that the Si diffusivity in InGaAs is negligible up to 700 °C implant activation anneal making Si a suitable option for the formation of shallow junctions in InGaAs. The activation efficiency, sheet resistance, carrier density and mobility data of 25 keV Se and Si implanted InGaAs layers are also presented under various activation anneal temperatures.

Are There Fundamental Limitations on the Sheet Resistance and Transmittance of Thin Graphene Films?

From published transmittance and sheet resistance data, we have calculated a figure of merit for transparent, conducting graphene films; the DC to optical conductivity ratio, sigma(DC)/sigma(Op). For most reported results, this conductivity ratio clusters around the values sigma(DC)/sigma(Op) = 0.7, 4.5, and 11. We show that these represent fundamental limiting values for networks of graphene flakes, undoped graphene stacks, and graphite films, respectively. The limiting value for graphene flake networks is much too low for transparent-electrode applications. For graphite, a conductivity ratio of 11 gives R(s) = 377Omega/ for T = 90%, far short of the 10 Omega/ minimum requirement for transparent conductors in current driven applications. However, we suggest that substrate-induced doping can potentially increase the 2-dimensional DC conductivity enough to make graphene a viable transparent conductor. We show that four randomly stacked graphene layers can display T approximately 90% and 10 Omega/ if the product of carrier density and mobility reaches nmu = 1.3 x 10(17) V(-1) s(-1). Given achieved doping values and attainable mobilities, this is just possible, resulting in potential values of sigma(DC)/sigma(Op) of up to 330. This is high enough for any transparent conductor application.

Study of submelt laser induced junction nonuniformities using Therma-Probe

Submelt laser annealing is a promising technique to achieve the required sheet resistance and junction depth specifications for the 32 nm technology node and beyond. In order to obtain a production worthy process, it is important to minimize possible nonuniformities caused by the annealing process both at macroscopic and microscopic levels. In this work, the authors present high resolution Therma-Probe® measurements to assess the junction nonuniformity on 0.5 keV boron junctions and zoom in on the effect of temperature variations and multiple subsequent laser scans. The results are compared to standard and micro-four-point probe sheet resistance data, secondary ion mass spectrometry, and Hall measurements obtained during earlier studies. Besides the impact of the nonuniformities on the “conventional” thermal wave signal, they found a strong correlation to the dc reflectance of the probe laser (λ = 675 nm). The dc probe reflectance is dominated by free carriers and is highly correlated to the sheet resistance both on blanket wafers and on real device wafers.

Anomalous suppression of the transition temperature of superconducting nanostructured honeycomb films: Electrical transport measurements and Maekawa-Fukuyama model

We report electrical transport measurements made on thin superconducting niobium films perforated by an etched array of nanoscopic holes. The hole diameter in these ``honeycomb'' network films is comparable to the coherence length of the parent superconducting material. A series of 12 films, with varying hole depths, were measured. As the film thickness is decreased, an unusually large reduction of transition temperature is observed for the honeycomb films as compared to plain etched films of similar thicknesses. We report on a ${T}_{c}$ reduction in superconducting network films that is not due to an applied magnetic field. These observations are in contrast to previous reports based on Ginzburg-Landau theory analysis, which does not allow for any change in the transition temperature for perforated films in comparison to plain films. The Maekawa-Fukuyama (MF) model for two-dimensional (2D) superconductors is used to fit the sheet resistance data. The MF-2D model fits very well to the lightly etched samples, but an anomaly in ${T}_{c}$ reduction is observed for heavily etched samples. These deviations are analyzed on the basis of change in dimensionality using the Aslamozov-Larkin model.

Stress Characterization of Polycrystalline Silicon for Advanced CMOS Technologies

As advanced integrated circuit manufacturing moves through the 65nm technology node, we find that polycrystalline silicon (Poly-Si) films can be engineered to modulate the strain in the underlying channel for improved NMOS transistor performance in addition to fulfilling this primary function as the CMOS gate electrodes. In this paper, we study how the deposition conditions for Poly-Si films change the intrinsic stress. The effect of subsequent processing steps, such as ion implantation and rapid thermal annealing (RTA), on the Poly-Si stress are also measured. Poly-Si films deposited with different conditions are characterized by secondary ion mass spectrometry (SIMS) and sheet resistance. The results show that the compressive stress of columnar Poly-Si films deposited using disilane as the precursor has been reduced by 50% compared with films deposited using silane for the precursor. The stress measurement results confirm that the implant energy modifies the poly-Si film stress: the higher the energy, the lower the compressive stress. The SIMS and sheet resistance data indicate that the deposition conditions can affect the final Poly-Si dopant activation.

Boron pocket and channel deactivation in nMOS transistors with SPER junctions

In this paper, we demonstrate the consequences of extension junction formation by low-temperature solid-phase-epitaxial-regrowth in nMOS transistors. Atomistic simulations, experimental device results, sheet resistance, and scanning spreading resistance microscopy data indicate that the high concentration of silicon interstitials associated with the end-of-range defect band promote the local formation of boron-interstitial clusters, and thus deactivate boron in the pocket and channel. These inactive clusters will dissolve after the high concentration silicon interstitial region of the end-of-range defect band has been annihilated. This nMOS requirement is in direct opposition to the pMOS case where avoidance of defect band dissolution is desired, to prevent deactivation of the high concentration boron extension profile.

Kinetic analysis and correlation with residual stress of the Ni/Si system in thin film

AbstractReactive diffusion of the Ni/Si system has been studied by annealing nickel thin film on (100) silicon crystal. The measurement of the NiSi sheet resistance as a function of the annealing temperature and the type of annealing (Rapid Thermal Annealing and spike one) has been investigated. A kinetic model based on multiphase diffusion has been developed that fits experimental sheet resistance data. Residual stress in the thin film, measured by a curvature measurement technique, is correlated with the nature of the phases in the film. Finally the viscoplastic mechanical behavior of the Ni2Si and NiSi phases is analyzed in the case of low and fast thermal ramps.