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Beryllium oxide (BeO) is a wurtzite structured, large bandgap (E g > 8 eV) material of significant interest as an alloying agent and cladding dielectric in various oxide based optoelectronic devices. The success of such devices is highly reliant on bandgap and band alignment engineering to achieve sufficient charge carrier and optical confinement for device operation. In this regard, we have utilized x-ray photoemission spectroscopy (XPS) to determine the valence band offset (VBO) between atomic layer deposited (ALD) BeO and a (001) oriented magnesium oxide (MgO) substrate. The BeO VBO with MgO (001) was determined to be 0.1 ± 0.15 eV. Applying the rules of commutativity and transitivity for band alignment, we additionally predict the BeO VBO with other conductive oxides such as ZnO, Ga2O3, and InGaZnO4, to be 1.15 ± 0.3 eV, 0.3 ± 0.2 eV, and 0.9 ± 0.2 eV, respectively.

We report high and low-frequency electrically detected magnetic resonance measurements and near-zero-field magnetoresistance measurements on radiation-induced leakage currents in irradiated Si/SiO2 metal-oxide-silicon (MOS) structures. This study identifies the chemical and physical nature of atomic-scale defects involved in radiation-induced leakage currents in SiO2 using an analytical technique. Our results suggest that trap-assisted tunneling through these Si/SiO2 structures involves Pb centers (silicon dangling bonds at the Si/SiO2 interface), rather than only ${E}$ ’ centers (oxygen vacancies in the SiO2 film). We utilize simulations of the defects’ resonance spectra to provide further evidence for the involvement of interface Pb centers in the radiation-induced leakage currents. These simulations also explore the possibility of additional ${E}$ ’ center involvement in the radiation-induced leakage currents.

While numerous thermal conductivity investigations of amorphous dielectrics have been reported, relatively few have attempted to correlate to the influence of processing conditions and the resulting atomic structure. In this regard, we have investigated the influence of growth conditions, post deposition curing, elemental composition, atomic structure, and nano-porosity on the thermal conductivity for a series of organo-silicate (SiOCH) thin films. Time-domain thermoreflectance (TDTR) was specifically utilized to measure thermal conductivity while the influence of growth conditions and post deposition curing on composition, mass density, atomic structure, and porosity were examined using nuclear reaction analysis (NRA), Rutherford backscattering spectroscopy (RBS), Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), ellipsometric porosimetry (EP), and positronium annihilation lifetime spectroscopy (PALS). Analytical models describing the thermal conductivity dependence on mass density and vol% porosity were found to generally over-predict the measured thermal conductivity, but improved agreement was obtained when considering only the heat carrying network density determined by FTIR. Ashby’s semi-empirical relation, which assumes only 1/3 of the heat carrying bonds are aligned to the heat transport direction, was also found to reasonably describe the observed trends. However, the thermal conductivity results were best described via a model proposed by Sumirat (J Porous Mater 9:439 (2006)) which considers the effect of both vol% porosity and phonon scattering by nanometer sized pores. Post-deposition curing was additionally observed to increase thermal conductivity despite an increase in nano-porosity. This effect was attributed to an increase in the Si–O–Si network bonding produced by the cure.

Radiation damage in materials is an important reliability issue in applications ranging from microelectronic devices to nuclear reactors. However, the influence of atomic structure and specifically topological constraints on the ion damage resistance of amorphous dielectrics has until recently been largely neglected. We have investigated the 120 keV He + ion damage resistance for a series of amorphous hydrogenated silicon carbide (a-SiC:H) thin films. Changes in elemental composition and atomic structure induced by He + ion irradiation were monitored using nuclear reaction analysis, Rutherford backscattering spectroscopy, transmission Fourier-transform infrared spectroscopy, and transmission electron microscopy while changes in mechanical properties were investigated using nanoindentation measurements. We show that for 120 keV He + ion doses producing up to one displacement per atom, significant hydrogen loss, bond rearrangement, film shrinkage, and mechanical stiffening were induced for films with mean atomic coordination (〈 r 〉) ≤ 2.7, while comparatively minor changes were observed for films with 〈 r 〉 > 2.7. The observed radiation hardness threshold at 〈 r 〉 rad > 2.7 is above the theoretically predicted rigidity percolation threshold of 〈 r 〉 c = 2.4. Based on the observed elimination of terminal C H bonds and Si CH 2 Si linkages, the higher radiation hardness threshold is interpreted as evidence that these bonds are too weak to function as constraints in high-energy ion collisions. Eliminating these constraints increased 〈 r 〉 c to 2.7, in agreement with the observed 〈 r 〉 rad = 2.7. These results demonstrate the key role of topological constraints in ion damage resistance and provide additional criteria for the design of ion-damage-resistant amorphous materials.

Owing to a unique combination of low density, high mechanical stiffness, and high neutron capture cross section, boron rich solids are of interest for a number of applications ranging from fusion shielding and neutron absorbing materials to solid state neutron detection. In many of these applications, the boron containing materials may be exposed to extreme temperatures and thermal gradients where heat dissipation is a significant concern. While there have been several reports of the thermal conductivity for crystalline boron solids, comparitively little is known regarding the thermal conductivity for amorphous boron thin films used in many nuclear applications. In this investigation, we report time-domain thermoreflectance (TDTR) measurements for a series of plasma deposited boron rich thin films with nominal compositions of a-B:H and a-BP:H. The results were compared to additional measurements performed on a-C:H films with similar mass density and which are also utilized as fusion plasma shielding materials. The values of thermal conductivity determined by TDTR for the a-B:H and a-BP:H films ranged from 1 to 2 W/mK. These values are reduced relative to those reported for crystalline boron (4–400 W/mK) but compare well to those obtained for a-C:H (0.5–1.5 W/mK).

A good candidate for replacing the inert platinum (Pt) electrode in the well-behaved Cu/TaOx/Pt resistive RAM memory cell is ruthenium (Ru), already successfully deployed in the CMOS back end of line. We benchmark Cu/TaOx/Ru device against Cu/TaOx/Pt and investigate the impact of embedment of Cu/TaOx/Ru on two different substrates, Ti(20nm)/SiO2(730nm)/Si and Ti(20nm)/TaOx(30nm)/SiO2(730nm)/Si, on the cell's electrical performance. While the devices show similar switching performance at some operating conditions, there are notable differences at other operation regimes shedding light on the basic switching mechanisms and the role of the inert electrode. The critical switching voltages are significantly higher for Ru than for Pt devices and can be partly explained by the work function difference and different surface roughness of the inert electrode. The poorer switching properties of the Ru device are attributed to the degraded inertness properties of the Ru electrode as a stopping barrier for Cu+ ions as compared to the Pt electrode. However, some of the degraded electrical properties of the Ru devices can be mitigated by an improved integration of the device on the Si wafer. This improvement is attributed to the suppression of crystallization of Ru and its silicidation reactions that take place at elevated local temperatures, present mainly during the reset operation. This hypothesis has been corroborated by extensive XRD studies of multiple layer systems annealed at temperatures between 300K and 1173K.

High-dielectric constant (high-k) gate oxides and low-dielectric constant (low-k) interlayer dielectrics (ILD) have dominated the nanoelectronic materials research scene over the past two decades, but they have recently reached a state of maturity and perhaps the limits of their scaling. Based on this, there is a need for a systematic review summarizing not only the historic research and achievements on high-k and low-k dielectrics, but also emerging device applications as well as an outlook of future challenges.We begin by first reviewing the factors that drove the emergence of low-k and high-k materials in nanoelectronics as ILD and gate dielectric materials, respectively, and the challenges and limits these materials ultimately approached in terms of permittivity scaling.We then illustrate that gate dielectric and ILD applications represent just a small fraction of the numerous dielectrics utilized in present day nanoelectronic products where permittivity scaling is now being increasingly demanded for materials such as dielectric spacers, trench isolation, and etch stopping layers. We conclude by examining the numerous new applications for dielectric materials that are emerging as the semiconductor industry transitions to novel patterning schemes, prepares for life post CMOS scaling, and explores ways to natively embed device functionality in the metal interconnect. For the former, we specifically examine the “colorful”requirements for the various enabling dielectric hard mask and spacer materials utilized in pitch division-multi-pattern processes and then discuss the role that selective area deposition of dielectrics and metals could play in reducing the complexity of such patterning processes. For the latter, we review the use of both high-k and low-k dielectrics in various metal-insulator-metal (MIM) structures as Fermi level de-pinning layers, tunnel diodes, and back-end-of-line (BEOL) compatible capacitive and resistive switching random access memory (ReRAM) elements.We further examine how dielectrics can hinder or aid new forms of computing such as quantum and neuromorphic in reaching their full potential. In conclusion, we find that while the field of dielectrics has a long history, it remains vibrant with numerous exciting new and old research vectors awaiting further exploration.© 2019 The Electrochemical Society.

Amorphous solids are traditionally assumed to set the lower bound to the vibrational thermal conductivity of a material due to the high degree of structural disorder. Here, were demonstrate the ability to increase the thermal conductivity of amorphous solids through ion irradiation, in turn, altering the bonding network configuration. We report on the thermal conductivity of hydrogenated amorphous carbon implanted with C+ ions spanning fluences of 3 × 1014-8.6 × 1014 cm-2 and energies of 10-20 keV. Time-domain thermoreflectance measurements of the films' thermal conductivities reveal significant enhancement, up to a factor of 3, depending upon the preirradiation composition. Films with higher initial hydrogen content provide the greatest increase, which is complemented by an increased stiffening and densification from the irradiation process. This enhancement in vibrational transport is unique when contrasted to crystalline materials, for which ion implantation is known to produce structural degradation and significantly reduced thermal conductivities.

Hydrogenated amorphous dielectric thin films are critical materials in a wide array of technologies. In this work, we present a thorough investigation of the thermal conductivity of hydrogenated amorphous silicon nitride $(a\text{\ensuremath{-}}{\mathrm{SiN}}_{x}:\mathrm{H})$, a ubiquitously used material in which the stoichiometry plays a direct role in its functionality and application. In particular, through chemical, vibrational, and structural analysis in tandem with thermal conductivity measurements on chemically variant silicon nitride films, we show that hydrogen incorporation into silicon nitride disrupts the bonding among silicon and nitrogen atoms, and directly impacts the thermal conductivity, leading to as much as a factor of 2.5 variation in heat transfer. This variability, driven by the change in hydrogen content, is fundamentally related to the changes in the average atomic distances, as we experimentally measure with selected-area electron diffraction and computationally show with molecular dynamics simulations. This, combined with our evidence of chemical and spatial fluctuations on the order of average atomic pair distances, leads us to conclude that the vibrational heat transport in $a\text{\ensuremath{-}}{\mathrm{SiN}}_{x}:\mathrm{H}$ is primarily dominated by diffusonlike modes. The results presented in this work combined with our extensive review of prior reports on the thermal conductivity of $a\text{\ensuremath{-}}{\mathrm{SiN}}_{x}:\mathrm{H}$ films resolves discrepancies in decades of prior literature and facilitates a more universal understanding of the vibrational heat transport processes in hydrogenated amorphous silicon nitride.

The remarkable advancement of CMOS electronics over the past two decades has been greatly aided by innovations allowing dielectric scaling across both ends of the permittivity spectrum. This paper describes how new dielectric innovations beyond permittivity scaling will allow both the extension of Moore’s law for another decade and usher in an array of new devices and computational paradigms.

Author(s): Frazer, TD; Knobloch, JL; Hernandez-Charpak, JN; Hoogeboom-Pot, KM; Nardi, D; Yazdi, S; Chao, W; Anderson, EH; Tripp, MK; King, SW; Kapteyn, HC; Murnane, MM; Abad, B | Abstract: Ultrathin films and multilayers, with controlled thickness down to single atomic layers, are critical for advanced technologies ranging from nanoelectronics to spintronics to quantum devices. However, for thicknesses less than 10 nm, surfaces and dopants contribute significantly to the film properties, which can differ dramatically from that of bulk materials. For amorphous films being developed as low dielectric constant interfaces for nanoelectronics, the presence of surfaces or dopants can soften films and degrade their mechanical performance. Here we use coherent short-wavelength light to fully and nondestructively characterize the mechanical properties of individual films as thin as 5 nm within a bilayer. In general, we find that the mechanical properties depend both on the amount of doping and the presence of surfaces. In very thin (5-nm) silicon carbide bilayers with low hydrogen doping, surface effects induce a substantial softening - by almost an order of magnitude - compared with the same doping in thicker (46-nm) bilayers. These findings are important for informed design of ultrathin films for a host of nano- and quantum technologies, and for improving the switching speed and efficiency of next-generation electronics.

Intermediate phases represent the so called “sweet spot” in amorphous material systems where the bond stretching and bond bending constraint forces are equally balanced by the total degrees of freedom in the system. They are sometimes also referred to as “Boolchand” phases in recognition of the seminal contributions of Dr. Punit Boolchand to the study of these materials. In a prior publication (King et al., J. Non-Cryst. Solids 379 (2013) 67), we presented possible evidence for the existance of an intermediate (i.e. “Boolchand”) phase in amorphous hydrogenated silicon carbide (a-SiC:H) with a wide range in mean atomic coordination (〈r〉 = 2.4 − 2.7). Support for such a wide phase window was based primarily on a correlation between the post plasma deposition bi-axial film stress and 〈r〉. However, we demonstrate in the present article that the apparent width of the Boolchand intermediate phase window in the prior study was inflated due to two competing film stress contributions, and that the true range in 〈r〉 for the phase window is substantially narrower. Specifically, opposing tensile and compressive film stress components were identified to arise during the plasma enhanced chemical vapor deposition (PECVD) of a-SiC:H. The tensile film stress component was attributed to film/substrate thermal contraction mismatch on cooling from the deposition temperature, while the compressive stress component was attributed to ion bombardment of the a-SiC:H growth surface during PECVD. In the prior study, the energy of the ions during PECVD was primarily modulated by the addition of a low frequency bias to the plasma and was intentionally utilized to produce films with varying compressive stress and 〈r〉. In the present study, the low frequency bias was removed from the PECVD of a-SiC:H and instead the deposition pressure was varied to produce films with varying 〈r〉 and exclusively tensile stress. Through detailed analysis of the tensile bi-axial film stress and Young's modulus dependence on 〈r〉, we found conclusive evidence that the film-substrate thermal contraction mismatch was the dominant film stress component in this case and that the magnitidue of the tensile stress was purely due to rigidity percolation in the a-SiC:H film. We therefore conclude that in our previous study the balance of the tensile and compressive stress components resulted in the deceptive appearance of a potentially wide Boolchand intermediate phase window for a-SiC:H. Based on the a-SiC:H films generated in the present study where only the tensile stress component was significant, we have found the window for a possible intermediate phase to be greatly narrowed at Δ〈r〉 ≤ 0.05.

In the last two decades, significant progress has been made on developing new nanoscale mechanical property measurement techniques including instrumented indentation and atomic force microscopy based techniques. The changes in the tip-sample contact mechanics during measurements uniquely modify the displacement and force sensed by a measurement sensor and much effort is dedicated to correctly retrieve the sample mechanical properties from the measured signal. It turns out that in many cases, for the sake of simplicity, a simple contact mechanics model is adopted by overlooking the complexity of the actual contact geometry. In this work, a newly developed matrix formulation is used to solve the stress and strain equations for samples with edge geometries. Such sample geometries are often encountered in today’s nanoscale integrated electronics in the form of high-aspect-ratio fins with widths in the range of tens of nanometers. In the matrix formulation, the fin geometries can be easily modeled as adjacent overlapped half-spaces and the contact problem can be solved by a numerical implementation of the conjugate gradient method. This method is very versatile in terms of contact geometry and contact interaction, either non-adhesive or adhesive. The discussion will incorporate a few model examples that are relevant for the nanoscale mechanics investigated by intermittent contact resonance AFM (ICR-AFM) on low-k dielectric fins of high-aspect-ratio. In such ICR-AFM measurements, distinct dependence of the contact stiffness was observed as a function of the applied force and distance from the edges of the fins. These dependences were correctly predicted by the model and used to retrieve the mechanical changes undergone by fins during fabrication and processing.

To reduce the RC (resistance–capacitance) time delay of interconnects, a key development of the past 20 years has been the introduction of porous low-k dielectrics to replace the traditional use of SiO2. Moreover, in keeping pace with concomitant reduction in technology nodes, these low-k materials have reached thicknesses below 100 nm wherein the porosity becomes a significant fraction of the film volume. The large degree of porosity not only reduces mechanical strength of the dielectric layer but also renders a need for non-destructive approaches to measure the mechanical properties of such ultra-thin films within device configurations. In this study, surface Brillouin scattering (SBS) is utilized to determine the elastic constants, Poisson’s ratio, and Young’s modulus of these porous low-k SiOC:H films (∼ 25–250 nm thick) grown on Si substrates by probing surface acoustic phonons and their dispersions.

The microstructure and mechanical properties of amorphous silicon oxycarbide (SiOC) before and after irradiation were investigated using Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), nuclear reaction analysis and nano-indentation. SiOC films of different compositions were subjected 1 displacement per atom (dpa) He+ irradiation. The irradiation results in a decrease of Si O Si bond angle and an increase of average coordination number. These microstructure variations are associated with increases of hardness and Young's modulus. Our findings reveal that mechanical properties correlate with the Si O Si bond angle and average coordination number in irradiated amorphous SiOC alloys.

We report on a study that offers fundamental physical insight into an important phenomenon in solid state device physics, tunneling in Si/SiO2. We observe near-zero field magnetoresistance via spin-dependent trap-assisted-tunneling in both unpassivated and passivated Si/SiO2 and 28Si/28SiO2 metal–insulator–semiconductor (MIS) capacitors. A previous report, which utilized electrically detected magnetic resonance and NZFMR on these devices, indicates a surprising conclusion: the observed trap-assisted tunneling spectra are dominated by silicon dangling bonds back bonded to silicon at the Si/SiO2 interface, Pb0 and Pb1 centers. In this study, the four sets of samples are virtually identical, apart from the presence or absence of either 1H and 29Si. We observed a substantial narrowing of the NZFMR response with the removal of 29Si nuclei and a substantial broadening with the addition of 1H. Since superhyperfine interactions between 29Si nuclei Pb at the Si/SiO2 interface are a full order of magnitude stronger than such interactions involving silicon dangling bonds defects (E′ centers) within the oxide, the NZFMR results strongly suggest a response dominated by Si/SiO2 interface trap defects. With the introduction of 1H magnetic nuclei to the interface after a forming gas anneal, linewidths and lines shapes of Si/SiO2 and 28Si/28SiO2 MIS capacitors were nearly identical. However, the amplitude of the NZFMR response is greatly reduced by the introduction of hydrogen by a fraction about equal to the reduction in the interface trap density. Our results further indicate that the rate limiting step in trap-assisted tunneling is the interface to oxide trapping event.

We report on electrically detected magnetic resonance (EDMR) and near-zero-field magnetoresistance (NZFMR) measurements observed through spin-dependent trap-assisted-tunneling on unpassivated Si/SiO2 metal–insulator–semiconductor capacitors comparing those containing silicon of natural isotopic abundance and silicon depleted of 29Si. Although our measurements involve monitoring the spin-dependence of the trap-assisted-tunneling current responsible for leakage across the oxide, the EDMR spectra resemble that of a combination of Pb0 and Pb1 silicon dangling bonds sites at the Si/SiO2 interface. Additionally, we observe a substantial narrowing of the NZFMR response with the removal of 29Si nuclei. The breadth of the NZFMR response is strongly influenced by hyperfine interactions. Since superhyerfine interactions between 29Si nuclei and silicon dangling bonds at the Si/SiO2 interface are a full order of magnitude stronger than such interactions involving silicon dangling bonds defects (E′ centers) within the oxide, the NZFMR results also strongly suggest a response dominated by Si/SiO2 interface trap defects. These results collectively suggest very strongly that the leakage currents that we observe involve tunneling from Si/SiO2 Pb dangling bonds to defects within the oxide. Our results thus offer fundamental insight into technologically important phenomena involving oxide leakage currents in metal–oxide–semiconductor devices such as stress induced leakage currents and time dependent dielectric breakdown.

In our previous work (ECS Trans.75 (32), 13-23, 2017), we have compared the electric performance of Cu/TaOx/Ru and Cu/TaOx/Pt devices finding that the performance of the Ru device is far inferior to that of the Pt device. The poor resistive switching (RS) properties of the Ru device were imputed to the greatly degraded inertness properties of the Ru electrode as a stopping barrier for Cu drift-diffusion. The degraded inertness of the Ru electrode, in turn, has been attributed to larger Cu surface and/or Cu bulk diffusion in Ru than in Pt. The result is surprising as both Pt and Ru are known to be excellent diffusion barriers for Cu in CMOS backend applications. Here, we have manufactured two nominally identical Cu/TaOx/Ru devices, though, differently embedded on the Si wafer. While Ru device A has been manufactured on oxidized Si wafers with 730 nm SiO2 followed by 20 nm of Ti, 55 nm of Ru, 25 nm of TaOx, and 150 nm of Cu, Ru device B has been manufactured in the same way except that a 30 nm TaOx layer has been inserted between SiO2 and Ti layers. Electrical analysis shows that the RS behavior of the two devices is markedly different. Thus the way, nominally identical RS devices are embedded into a technology module has a major impact on the intrinsic device performance. We have identified three major reasons for this disparity. First, the layers of Ti and Ru involved are very thin (20nm and 55 nm). Second, during resistive switching local temperatures at the filament during the form/set and reset operations can exceed 600oC i.e. far higher than the maximum temperature which CMOS backend may experience when the underlying processor is in operation. This temperature is estimated to be ~120oC. Indeed, up to 120oC and above, amorphous Ru remains an excellent diffusion barrier for Cu. The third reason is the crystallinity phase of Ru thin layers that depends on the deposition method and the subsequent ‘unintended’, i.e. related to the RS, local anneals. We find that Ru device A can be switched a limited number of times at high compliance currents Icc (~0.5mA) while the device B at such Icc levels shows either volatile filament formation or when a filament forms, it is permanent. Conversely, at Icc of ~5uA Ru device B shows fairly good RS behavior, while Ru device A shows mostly volatile behavior. Besides Icc, the other critical parameter is the ramp rate rr during the voltage sweep. Both parameters determine effectively the thermal budget during the set and reset operations and are thus responsible for: 1) chemical reactions taking place between the thin metal and dielectric layers and formation of chemical compounds. 2) Cu surface diffusion on the Ru electrode and Cu penetration through the Ru electrode which appears to include compound formation of Ru2Si3 and Cu3Si in case of Ru device A. Therefore, the declared purpose of inserting the TaOx layer between SiO2 and Ti was to prevent those silicidation reactions. In this work, we show that reports in the literature on a number of Ru metallization issues such as: a) thin Ru amorphous films crystallize into a polycrystalline phase at ~550oC; b) observation of a strong diffusive penetration of Cu through the increased number of grain boundaries within Ru layer at 475oC; c) Ru transforms into a less dense Ru2Si3 at ~500oC; d) Ru2Si3 triggers Cu3Si formation at low temperature (~200oC) and degrades the barrier functionality of Ru electrode, are indeed correlated with the differences between the device I-V characteristics of the two Ru devices. Because of the chemical reactions triggered by high local temperatures during cell switching, the Ru devices show new properties over the stable Pt devices. In contrast to Pt devices, the voltage ramp rate has a major impact on the resistance of the on-state, Ron, in the Ru devices: lower ramp rate leads to a higher Ron values because the forming filament is exposed for a longer time to elevated temperatures and suffers from Cu out-diffusion. The observation that Ron in Ru device A is significantly higher than in the Ru device B at the same Icc and rr values, demonstrates that Ru electrode in Ru device B has better inertness properties than in the Ru device A. In summary, this work shows that nominally same device with excellent characteristics in a specific experimental environment, may show vastly degraded characteristics when embedded into a module such as CMOS metallization backend – an issue that has largely been disregarded so far.

Integrating nanometer sized pores into low-k ILD films is one of the approaches to lower the RC signal delay and thus help sustain the continued scaling of micro-electronic devices. While increasing porosity of porous dielectrics lowers the dielectric constant (k), it also creates many reliability and implementation issues. One of the problems is the little understood metal ion drift in porous media. Here, we extend the rigorous simulation method of Cu diffusion in porous dielectrics based on elementary jump probabilities (presented at 231st ECS Spring Meeting 2017 [1]) to include the ion drift in electric fields and explore the conditions for metal filament formation in porous media. The present atomistic approach allows a consistent co-implementation of Cu diffusion and Cu ion drift in electric field by lowering and raising of the diffusion activation energy Ea along the electric field Eel direction as exp(-(Ea ±1/2qlEel)/kT), where l is the elementary jump distance, q is the elementary electronic charge, "-" denotes the enhancement factor in the field direction and "+" the retardation factor against the field. Our analysis of resistive switching behavior in porous dielectrics [2] shows that electric fields responsible for Cu filament formation are in excess of 106 V/cm. At such high fields, the drift transport based mobility (m) concept where drift velocity v=m´Eel is no longer valid since the required inequality Eel<< kT/(ql) = 1.2´105 V/cm for T=300K and l=21 A, does not hold, and, consequentially, all modeling methods based on drift-diffusion continuum equations fail to describe ion drift adequately. As described in [1] as a numerical method the diffusion tensor technique (4th rank tensor in 2D, 9th rank in 3D) has been used with elementary diffusion/drift jump probabilities at each lattice site. Simulation shows that the Cu drift transport across porous materials depends more on the type of morphology than on the level of porosity. Three different basic pore morphologies are considered: 1) columnar pores laterally oriented to the Cu transport, 2) Columnar pores vertically oriented to the Cu transport, and 3) Uniform distribution of pores of the same size across the dielectric. For all morphologies, the porosity is varied between 0% and 47%. We find that, for spherical pores distributed more or less uniformly, the effective drift transport of Cu across dielectric at a room temperature comes to a stop at a porosity of around 40%. At room temperature, uniform spherical pore morphologies at certain porosity levels will block the drift transport of Cu across the dielectric entirely. However, for the same pore morphology at elevated temperatures, the relative jump frequency enhancement factor caused by the electric field is considerably reduced and now the increased lateral jump frequencies, owing to pure diffusion, help circumnavigate the pores causing a significant surge of drift transport of Cu ions. This is important technologically in CMOS back-end Cu lines when those are operated at high currents or at high switching frequencies. Under such circumstances, the local temperature of the dielectric may rise significantly over the room temperature. We have performed atomistic drift-diffusion simulations in the temperature interval between 27 oC and 400 oC. We find that although the relative electric field enhancement factor has been substantially reduced, the increased lateral jump frequencies give rise to a significant drift transport of Cu ions across the porous dielectric. One consequence of this is that resistive switching in porous media is facilitated by rising temperature which may pose a reliability issue. In case of columnar pore morphology, when the electric field is aligned to the main pore orientation, the so called “channeling effect” [1] is simply enhanced by the drift component. However, the drift enhancement factor is decreasing with increasing temperature. In most of morphologies, the increasing temperature makes the drift-diffusion transport more efficient. However, in the case of the columnar morphology with its main orientation perpendicular to the electric field, the effective drift-transport may decrease with the increasing temperature. The reason for this unusual transport retardation at elevated temperatures is the deflection of the Cu ions due to increase of lateral movement into the quasi-trapping regions between the columnar pores which weakens the overall perpendicular drift diffusion transport from the Cu electrode to the counter-electrode. In our simulation grain boundary diffusion can be accommodated as a particular embodiment of interconnected pore morphology. [1] R. Ali et al, “Modeling and Simulation of Cu Diffusion in Porous low-k Dielectrics’ 231stECS Spring MTG, 2017 [2] Y. Fan et al, “Characterization of Porous BEOL Dielectrics for Resistive Switching”, 229th ECS Spring MTG, 2016

The exploitation of nanoscale size effects to create new nanostructured materials necessitates the development of an understanding of relationships between molecular structure, physical properties and material processing at the nanoscale. Numerous metrologies capable of thermal, mechanical, and electrical characterization at the nanoscale have been demonstrated over the past two decades. However, the ability to perform nanoscale molecular/chemical structure characterization has only been recently demonstrated with the advent of atomic-force-microscopy-based infrared spectroscopy (AFM-IR) and related techniques. Therefore, we have combined measurements of chemical structures with AFM-IR and of mechanical properties with contact resonance AFM (CR-AFM) to investigate the fabrication of 20–500 nm wide fin structures in a nanoporous organosilicate material. We show that by combining these two techniques, one can clearly observe variations of chemical structure and mechanical properties that correlate with the fabrication process and the feature size of the organosilicate fins. Specifically, we have observed an inverse correlation between the concentration of terminal organic groups and the stiffness of nanopatterned organosilicate fins. The selective removal of the organic component during etching results in a stiffness increase and reinsertion via chemical silylation results in a stiffness decrease. Examination of this effect as a function of fin width indicates that the loss of terminal organic groups and stiffness increase occur primarily at the exposed surfaces of the fins over a length scale of 10–20 nm. While the observed structure–property relationships are specific to organosilicates, we believe the combined demonstration of AFM-IR with CR-AFM should pave the way for a similar nanoscale characterization of other materials where the understanding of such relationships is essential.

We explore some aspects of the optimization of amorphous semiconductors as well as low- and high-dielectric-constant (low-/high-k) materials viewed purely from the perspective of percolation and topological constraint theories. We specifically illustrate how percolation, constraint theory, and mean network coordination, 〈r〉, play underlying roles in determining the electrical and mechanical properties of amorphous semiconducting and dielectric materials as well as interfaces that are important for modern micro-/nanoelectronic devices.

Topological constraint theory (TCT) has revealed itself to be a powerful tool in interpreting the behaviors of amorphous solids. The theory predicts a transition between a “rigid” overconstrained network and a “floppy” underconstrained network as a function of connectivity or average coordination number, 〈r〉. The predicted results have been shown experimentally for various glassy materials, the majority of these being based on 4-fold-coordinate networks such as chalcogenide and oxide glasses. Here, we demonstrate the broader applicability of topological constraint theory to uniquely coordinated amorphous hydrogenated boron carbide (a-BC:H), based on 6-fold-coordinate boron atoms arranged into partially hydrogenated interconnected 12-vertex icosahedra. We have produced a substantial set of plasma-enhanced chemical vapor deposited a-BC:H films with a large range of densities and network coordination, and demonstrate a clear threshold in Young's modulus as a function of 〈r〉, ascribed to a rigidity transition. We investigate constraint counting strategies in this material and show that by treating icosahedra as “superatoms,” a rigidity transition is observed within the range of the theoretically predicted 〈r〉c value of 2.4 for covalent solids with bond-stretching and bond-bending forces. This experimental data set for a-BC:H is unique in that it represents a uniform change in connectivity with 〈r〉 and demonstrates a distinct rigidity transition with data points both above and below the transition threshold. Finally, we discuss how TCT can be applied to explain and optimize mechanical and dielectric properties in a-BC:H and related materials in the context of microelectronics applications.

International audience; Stoichiometric silicon nitride films were deposited by low-pressure chemical vapor deposition from the SiHCl3-NH3-H2-Ar system in a hot wall reactor at pressures ranging from 0.3 to 2 kPa. The films are amorphous for deposition temperatures up to 1000 °C and crystalline, in the α-form, at 1200 °C and above. A method for evaluating the internal stresses based on the curvature of the silicon substrate wafer and the resulting silicon Raman peak shift was developed. Some amorphous films exhibit high internal tensile stresses that can lead to cracking during deposition depending on the mechanism and effective precursors involved. Residual stresses can thus be reduced and cracking avoided by, in descending order of importance, reducing the concentration of reactive gases through dilution, increasing the deposition temperature and decreasing the total pressure. The effects of these parameters on the intrinsic stresses were related to the amount of residual hydrogen successively incorporated and thermally released during the growth of the coating according to the Noskov's model.

Beryllium oxide (BeO) is a wurtzite structured, large bandgap (E g > 8 eV) material of significant interest as an alloying agent and cladding dielectric in various wide band gap oxide based optoelectronic devices. The success of such devices is highly reliant on bandgap and band alignment engineering to achieve sufficient charge carrier and optical confinement for device operation. In this regard, we have utilized x-ray photoemission spectroscopy (XPS) to determine the valence band offset (VBO) between atomic layer deposited (ALD) BeO and a magnesium oxide (MgO) substrate with (001) orientation. The BeO VBO with MgO (001) was determined to be 0.1 ± 0.15 eV. Applying the rules of commutativity and transitivity for band alignment, we additionally predict the BeO VBO with other wide bandgap conductive oxides such as ZnO, Ga2O3, and InGaZnO4, to be 1.15 ± 0.3 eV, 0.3 ± 0.2 eV, and 0.9 ± 0.2 eV, respectively. Utilizing the reported bandgaps for ALD BeO and the conductive oxides, we find a Type I band alignment with CBOs > 1 eV in all cases. BeO is therefore a promising dielectric for oxide based optoelectronic and high-frequency, -power, and -temperature device applications

In this study, we report on the thermal conductivity of amorphous carbon generated in diamond via nitrogen ion implantation (N 3 + at 16.5 MeV). Transmission electron microscopy techniques demonstrate amorphous band formation about the longitudinal projected range, localized approximately 7 μm beneath the sample surface. While high-frequency time-domain thermoreflectance measurements provide insight into the thermal properties of the near-surface preceding the longitudinal projected range depth, a complimentary technique, steady-state thermoreflectance, is used to probe the thermal conductivity at depths which could not otherwise be resolved. Through measurements with a series of focusing objective lenses for the laser spot size, we find the thermal conductivity of the amorphous region to be approximately 1.4 W m − 1 K − 1, which is comparable to that measured for amorphous carbon films fabricated through other techniques.

We investigate the possibilities of measuring the band gap of a variety of semiconductors and insulators by reflection electron energy loss spectroscopy without additional surface preparation. The band gap is a bulk property, whereas reflection energy loss spectroscopy is generally considered a surface sensitive technique. By changing the energy of the incoming electrons, the degree of surface sensitivity can be varied. Here, we present case studies to determine the optimum condition for the determination of the band gap. At very large incoming electron energies recoil effects interfere with the band gap determination, whereas at very low energies surface effects are obscuring the band gap without surface preparation. Using an incoming energy of 5 keV a reasonable estimate of the band gap is obtained in most cases.

The recent development of the photothermal induced resonance (PTIR) technique has enabled atomic force microscope based infrared (AFM-IR) spectroscopy and imaging to be achieved at the nanometer scale. However, a direct correspondance between PTIR/AFM-IR and more traditional Fourier transform IR (FTIR) spectroscopy has been prohibited for nanometer scale features due to Rayleigh diffraction constraints that limit the latter to few micron spatial resolution. In this regard, we have overcome this challenge by fabricating 1 cm2 arrays of 90 nm wide fins in a nano-porous low dielectric constant (i.e. low-k) amorphous hybrid inorganic-organic silicate material using standard nano-electronic fabrication techniques. With these structures, we demonstrate both a general correspondance between AFM-IR, FTIR, and Germanium attenuated total reflection (GATR) IR spectroscopy, as well as differences in the sensitivities that these techniques exhibit to the nanoscale variations in chemical structure induced in the low-k dielectric by the nanopatterning method. To further illustrate the sensitivity of AFM-IR to changes in chemical structure with nanometer resolution, the nanopatterned low-k dielectric was exposed to additional oxidizing plasma ash cleans post patterning. Focusing on the Si-CH3 deformation band at ∼1275 cm−1, both the AFM-IR, FTIR and GATR measurements show a clear reduction in the concentration of terminal methyl groups in the low-k dielectric as the oxidation potential of the plasma ash clean increased. These results further establish the power of AFM-IR to perform nanoscale IR spectroscopy and demonstrates a stronger correspondance between AFM-IR and well-known micron scale IR techniques such as FTIR and GATR.

The starting point for describing the electrostatic operation of any semiconductor device begins with a band diagram illustrating changes in the semiconductor Fermi level and the alignment of the valence and conduction bands with other interfacing semiconductors, insulating dielectrics and metal contacts. Such diagrams are essential for understanding the behavior and reliability of any semiconductor device. For metal interconnects, the band alignment between the metal conductor and the insulating intermetal and interlayer dielectric (ILD) is equally important. However, relatively few investigations have been made. In this regard, we have investigated the band alignment at the most common interfaces present in traditional single and dual damascene low- k /Cu interconnect structures. We specifically report combined X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy (REELS) measurements of the Schottky barrier present at the ILD and dielectric Cu capping layer (CCL) interfaces with the Ta(N) via/trench Cu diffusion barrier. We also report similar measurements of the valence and conduction band offsets present at the interface between a-SiN(C):H dielectric CCLs and low- k a-SiOC:H ILDs (porous and non-porous). The combined results point to metal interfaces with the CCL having the lowest interfacial barrier for electron transport. As trap and defect states in low- k dielectrics are also important to understanding low- k /Cu interconnect reliability, we additionally present combined electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) measurements to determine the chemical identity and energy level of some electrically active trap/defect states in low- k dielectrics. Combined with the photoemission derived band diagrams, the EPR/EDMR measurements point to mid-gap carbon and silicon dangling bond defects in the low- k ILD and CCL, respectively, playing a role in electronic transport in these materials. We show that in many cases the combined band and defect state diagrams can explain and predict some of the observed reliability issues reported for low- k /Cu interconnects.

For hydrogenated amorphous silicon oxide (a-SiO:H) layers applied to crystalline Si heterojunction solar cells, we have studied the correlations between the dielectric function and local bonding states using spectroscopic ellipsometry and high-sensitivity infrared spectroscopy. In particular, systematic characterizations have been made on both a-SiO:H and hydrogenated amorphous silicon carbide (a-SiC:H) layers prepared at similar conditions. In a-Si 1− x O x :H and a-Si 1− x C x :H layers, the increase in the alloy content x leads to the significant reduction in the amplitude of the dielectric functions due to microvoid formation. The infrared spectra reveal that the local bondings in the a-SiO:H are dominated by SiH 2 and SiH m (O 4−m ) (m ≤ 2) at high x , whereas the local bonding states of the a-SiC:H alloy can be interpreted as a mixture of SiH 2 and CH n (n = 2, 3). The amplitude of the a-SiO:H dielectric functions shows a clear relationship with a total amount of SiH m (O 4−m ) in the network, indicating that the significant microvoid formation in a-SiO:H layers is most likely triggered by the generation of SiH 2 (O 2 ) and SiH(O 3 ). Our results indicate that, compared with the C atom, the O atom increases the band gap of a-Si:H more effectively while suppressing the H incorporation in the amorphous network.

Building nonvolatile memory directly into a CMOS low-k/Cu interconnects would reduce latency in connectivity constrained computational devices and reduce chip’s footprint by stacking memory on top of logic. In the relentless drive to lower the interconnect time delay, porous low-k dielectrics are being currently explored. In this paper, porous dielectrics are being electrically characterized and their suitability for resistive switching (RS) assessed. Metal-Insulator-Metal (MIM) structures have been manufactured with bottom Cu electrode and with top island-shaped W or Pt counter-electrode. The porous dielectric was a-SiC:H or a-SiOC:H with level of porosity varying between 8% to 25%. The thickness of the porous dielectric is 20 nm and the dielectric constant k varied between 3.1 (@ 8% porosity) and 2.5 (@25% porosity). Some devices have a 2 nm SiCN diffusion barrier (DB), either at the Cu or W/Pt electrode or at both electrodes. The SiCN layers serve a dual-purpose: i) to prevent Cu diffusion, and ii) to prevent Cu, W, and Pt protrusion into pores and voids of porous dielectrics. A bulk majority of devices has been found conductive from the beginning and less than 10% - only those with at least one DB - displayed RS behavior. The intrinsic conductive state has been found to scale with the area of the top island electrode, and its temperature coefficient of resistance (TCR) has been found to be TCR=0.0028 K-1. Both findings are consistent with high concentration of Cu in the dielectric indicating bulk conduction. This means that porous dielectrics are vulnerable to metal diffusion and even two diffusion barriers of 2 nm are marginal in arresting Cu diffusion. When subjected to resistive switching, the intrinsic resistance Rint was found to be dependent on the applied compliance current Icc. Rint decreases linearly with increasing Icc when Icc is smaller than a critical value Icc(crit), typically 10 mA; for Icc larger than Icc(crit) Rint is constant. This finding is explained with improved ionization of copper and more homogenous Cu distribution through out the dielectric. The RS behavior was tested in two modes: a) positive bias applied, and b) negative bias applied to Cu electrode, while W/Pt electrode are being grounded. At positive bias, a few samples displayed resistive behavior where a Cu filament could be formed, and subsequently reset and set several times. Thus, as a proof of concept, it has been demonstrated that resistive switching can be realized in porous dielectrics. It has been found that devices with W electrode showed superior behavior compared to Pt devices. Best resistive switching behavior was found with dielectric of 25% and with both SiCN barriers at Cu and at W electrode. The filament formation at positive and negative bias results in different type of a filament. Filaments formed at positive bias applied to Cu electrode are Cu filaments and filaments formed at negative bias are attributed to defects or broken bonds of the dielectric matrix. Measurements of temperature coefficient of resistance (TCR) have confirmed that both types of filaments have substantially different TCR coefficients. TCR of the filaments created at positive and negative bias has been measured and found to be 0.0031 K-1 for positive and 0.0021 K-1 for the negative bias, respectively. TCR=-0.0031K-1 has been found to be characteristic of Cu filaments in Cu/TaOx/Pt devices, and TCR=0.0021K-1 is consistent with oxygen vacancy filaments in the same devices. Hence, filaments with 0.0031K-1 have been identified with Cu filaments and filaments with 0.0021K-1 with defect filaments. Those devices that have shown resistive switching were found to be sensitive to the level of Icc. For Icccc>1 mA, the on-state was non-volatile. In many cases, the non-volatile state was a permanent one, i.e. the device could not be reset. Devices that were not conductive from the beginning were subjected to a 5 min anneal at 40 oC, 60 oC, and 100 oC. The electrical measurements confirm that with increasing temperature more and more samples became intrinsically conductive; at 100 oC all the samples (including those with two diffusion barriers) became intrinsically conductive. These results confirm that the devices suffer from excessive Cu diffusion at the manufacturing stage of the devices. Surprisingly, it has been also found that – for those devices that displayed resistive switching – the forming voltage increased with increasing level of porosity. The present study gives good insights and establishes a solid data base for further improvement of the implementation of porous dielectrics into CMOS BEOL.

Si–O–C-based amorphous or nanostructured materials are now relatively common and of interest for numerous electronic, optical, thermal, mechanical, nuclear, and biomedical applications. Using plasma-enhanced chemical vapor deposition (PECVD), hydrogen atoms are incorporated into the system to form SiOCH dielectric films with very low dielectric constants (k). While these low-k dielectrics exhibit chemical stability as deposited, they tend to lose hydrogen and carbon (as labile organic groups) and convert to SiO2 during thermal annealing and other fabrication processes. Therefore, knowledge of their thermodynamic properties is essential for understanding the conditions under which they can be stable. High-temperature oxidative drop solution calorimetry measurement in molten sodium molybdate solvent at 800°C showed that these materials possess negative formation enthalpies from their crystalline constituents (SiC, SiO2, C, Si) and H2. The formation enthalpies at room temperature become less exothermic with increasing carbon content and more exothermic with increasing hydrogen content. Fourier transform infrared spectroscopy (FTIR) spectroscopy examined the structure from a microscopic perspective. Different from polymer-derived ceramics with similar composition, these low-k dielectrics are mainly comprised of Si–O(C)–Si networks, and the primary configuration of carbon is methyl groups. The thermodynamic data, together with the structural analysis suggest that the conversion of sp2 carbon in the matrix to surface organic functional groups by incorporating hydrogen increases thermodynamic stability. However, the energetic stabilization by hydrogen incorporation is not enough to offset the large entropy gain upon hydrogen release, so hydrogen loss during processing at higher temperatures must be managed by kinetic rather than thermodynamic strategies.

A multiresponse 25 full factorial experiment is performed to investigate the effects of growth conditions (temperature, power, pressure, total flow rate, partial precursor flow rate) on the chemical, mechanical, dielectric, electronic, and charge transport properties of thin-film amorphous hydrogenated boron carbide (a-BxC:Hy) grown by plasma-enhanced chemical vapor deposition (PECVD) from ortho-carborane. The main and interaction effects are determined and discussed, and the relationships between properties are investigated via correlation analysis. The process condition with the strongest influence on growth rate is pressure, followed by partial precursor flow rate, with low pressure and high partial flow rate conditions yielding the highest growth rates. The atomic concentration of hydrogen (at.% H) and density are controlled primarily by temperature and power, with low temperature and power conditions leading to relatively soft, hydrogen-rich, low-density, porous films, and vice versa. The B/C ratio is controlled by temperature, power, pressure, and the power*pressure interaction, and is uncorrelated to hydrogen concentration. Thin-film dielectric and electronic structure properties, including high-frequency dielectric constant (e1), low-frequency/total dielectric constant (κ), optical band gap (ETauc/E04), and Urbach energy (EU), are correlated strongly with at.% H, and weakly to moderately with B/C ratio. These properties are dominated by the influence of temperature, with a second significant influence from the power*pressure interaction. The interaction of power and pressure leads to two opposite growth regimes—high power and high pressure or low power and low pressure—that can produce a-BxC:Hy films with similar dielectric or electronic structure properties. Charge transport properties also show a correlation with at.% H and B/C, but not with the electronic structure and disorder parameters, which suggests a complicated relationship between the two. The range of properties measured highlights the potential of thin-film a-BxC:Hy for low-κ dielectric and neutron detection applications, and suggests clear pathways for future material property optimization.

In this paper, 15N nuclear reaction analysis (NRA) for H is combined with 1.2 MeV deuteron (D) NRA which provides a simultaneous analysis for Li, Be, B, C, N, O and F. The energy dependence of the D NRA has been measured and used to correct for the D energy loss in film being analyzed. A 2 MeV He RBS measurement is made. Film composition is determined by a self-consistent analysis of the light element NRA data combined with an RBS analysis for heavy elements. This composition is used to simulate, with no adjustable parameters, the complete RBS spectrum. Finally, comparison of this simulated RBS spectrum with the measured spectrum provides a powerful check of the analysis.

To facilitate the design of future heterostructure devices employing two-dimensional (2D) materials such as molybdenum disulphide (MoS2) and hexagonal/sp2 boron nitride (BN), x-ray photoelectron spectroscopy (XPS) has been utilized to determine the valence band offset (VBO) present at interfaces formed between these materials. For MoS2 grown on a pulsed laser-deposited amorphous BN (a-BN) layer with sp2 bonding, the VBO was determined to be 1.4 ± 0.2 eV. Similarly, the VBO between the a-BN layer and the aluminum oxide (Al2O3) substrate was determined to be 1.1 ± 0.2 eV. Using the bandgaps established in the literature for MoS2, h-BN, and Al2O3, the conduction band offsets (CBOs) at the MoS2/a-BN and a-BN/Al2O3 interfaces were additionally calculated to be 3.3 ± 0.2 and 1.7 ± 0.2 eV, respectively. The resulting large VBOs and CBOs indicate BN and Al2O3 are attractive gate dielectrics and substrates for future 2D MoS2 devices.