During the past decade, the semiconductor industry has experienced an unprecedented paradigm shift toward focused materials screening in order to keep pace with the rapid rate of device scaling dictated by Moore’s Law. In addition, new device architectures have evolved that place greater demands on physical characterization techniques to interrogate subtle materials intermixing at buried interfaces. In this chapter, we demonstrate the general utility of HAXPES to probe sample materials representative of advanced semiconductor devices, thereby elucidating specific bonding configurations that limit electrical performance. HAXPES provides several distinct advantages for the analysis of advanced semiconductor devices; notably, the ability to probe structures of technologically relevant thicknesses and to tune the photoelectron depth sensitivity to measure changes with depth. Studies presented here include the influence of anneal temperature on transistor high-k gate dielectric layers deposited on both Si and high mobility SiGe and InGaAs substrates, substrate passivation processes, novel low resistivity metal contact formation, and the oxygen redistribution phenomenon associated with advanced memory structures. As materials and devices continue to evolve, it is clear that HAXPES will play a significant role in the successful integration of advanced devices into high volume manufacturing.

The local symmetries around the Hf sites in thin films of Hf1−x Zr x O2/Si(100) were probed using grazing incidence extended X-ray absorption fine-structure spectroscopy (EXAFS). The effects of the Zr incorporation on the local crystal symmetries were investigated using Hf L3 EXAFS at the Beamline X23A2 of the Brookhaven National Laboratory. The Zr ratios in the various films were set to between 0.0 and 1.0. Significant changes in the local environment were observed for x = 0.25 or greater values. For x = 0.0, the film local structure around Hf sites remain in the equilibrium monoclinic phase as referenced from our previous studies on HfO2 thin films on Si(100). When Zr is introduced, tetragonal symmetry around the Hf atom appears and becomes dominant at x = 0.63. Using the EXAFS theoretical simulations and non-linear least-square fit results, the fractions of the monoclinic versus tetragonal phases were identified in each film.

Reducing defects at III-V/high-k interfaces is essential for optimizing devices built on these materials. Here, the role of an interfacial AlN process at In0.53Ga0.47As/ZrO2 interfaces is investigated by hard x-ray photoelectron spectroscopy (HAXPES) and capacitance/voltage (C-V) measurements. C-V measurements show a significant reduction in the density of interface traps with the interfacial AlN process and a capping TiN layer. To elucidate the specific role of the AlN process, blanket films with various deposition processes are compared. The AlN process alone (without subsequent dielectric deposition) reduces InGaAs oxide levels below the HAXPES detection limit, even though the AlN is ultimately found to be oxidized into AlOx with only trace N incorporation, yet AlN passivation provides a lower Dit (density of interface traps) when compared with an H2O-based Al2O3 deposition. The AlN process does not passivate against re-oxidation of the InGaAs during an O3 based ZrO2 deposition process, but it does provide passivation against As-As development during subsequent TiN deposition. The role of chemical defects in the C-V characteristics is also discussed.

The nature of chemical bonding at graphene–metal interfaces is intriguing from a fundamental perspective and has great relevance for contacts to novel spintronics and high-frequency electronic devices. Here, we use near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in conjunction with Raman spectroscopy and first-principles density functional theory to examine chemical bonding and perturbation of the π-electron cloud at graphene–metal interfaces. Graphene–metal bonding has been contrasted for graphene interfaced with single-crystalline metals, polycrystalline metal foils, and with evaporated metal overlayers and is seen to be strongest at the last noted interface. Strong covalent metal-d-graphene-π hybridization and hole doping of graphene is observed upon deposition of Ni and Co metal contacts onto graphene/SiO2 and is significantly stronger for these metals in comparison to Cu. Of single-crystalline substrates, the most commensurate (111) facets exhibit the strongest interactions with the graphene lattice. First-principles electronic structure simulations, validated by direct comparison of simulated spectra with NEXAFS measurements, suggest that metal deposition induces a loss of degeneracy between the α- and β-graphene sublattices and that spin-majority and spin-minority channels are distinctly coupled to graphene, contributing to splitting of the characteristic π* resonance. Finally, the electronic structure of graphene is found to be far less perturbed by metal deposition when the π cloud is pinned to an underlying substrate; this remarkable behaviour of “sandwich” structures has been attributed to electronic accessibility of only one face of graphene and illustrates the potential for anisotropic functionalization.

We present an overview of the National Institute of Standards and Technology beamline X24A at the National Synchrotron Light Source at Brookhaven National Lab and recent work performed at the facility. The beamline is equipped for HAXPES measurements, with an energy range from 2.1 to 6 keV with Si(1 1 1) crystals. Recent measurements performed at the beamline include non-destructive depth dependent variable kinetic energy measurements of dielectric and semiconductor films and interfaces for microelectronics applications, band alignment at buried interfaces, and the electronic structure of bulk-like materials. The design and operation of the current beamline will be discussed, as well as the future NIST beamline at NSLS II. (C) 2013 Elsevier B.V. All rights reserved.

We report optical characterization of the conduction band offset (CBO) between atomic-layer-deposited single crystal BeO and Si using internal photoemission (IPE) and internal multi-photon photoemission (IMPE), and of the valence band offset (VBO) using synchrotron x-ray photoelectron spectroscopy. The IPE/IMPE measurements indicate a CBO of 2.31 ± 0.1 eV for 10 nm thick as-deposited oxides. For samples subjected to post-deposition anneal in N2 at 600 °C and 900 °C, it increases to 2.54 ± 0.1 eV and 2.61 ± 0.1 eV, respectively. The VBO is stable at 4.14 ± 0.2 eV for both as-deposited and annealed samples.

The information on the subtle local structural modifications around the Hf atom in HfO2 high-k dielectric stacks has been demonstrated to be crucial in determining the resulting electronic properties of the complementary metal oxide (CMOS) devices. In this work, using extended X-ray-absorption fine structure (EXAFS) spectroscopy, the local structural characterization of Hf-based advanced gate stacks thin films were investigated. The thin film stacks used in this project are Al2O3 capped HfO2 thin films deposited on silicon substrates. EXAFS simulations and fits were applied to the data in order to extract crucial structural modifications on these films upon postdeposition annealing (PDA). The local crystal symmetry and coordination around the Hf atom were investigated under various annealing conditions. Specifically, in Hf-based dielectric thin films on silicon substrates capped with Al2O3 layers, the local crystal symmetry, and coordination around the Hf atom were investigated under various annealing conditions. The questions addressed are the effects of various annealing mechanisms to the diffusion mechanisms in the cap layers and modifications on the emerging local structures around the Hf atom. The diffusion of Al into HfO2 films were monitored through the EXAFS simulations. The non-linear least-squares fitting to the EXAFS data revealed that the PDA in NH3 (or N-2) ambient after HfO2 deposition had prevented Al diffusion to the HfO2 layers. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A study of resonant photo-absorption features in high-k dielectric film stacks using vacuum ultraviolet spectroscopic ellipsometry demonstrates that all optically observable dielectric-related defects are located in the interfacial SiO2 layer rather than in the bulk high-k film. The defects, located at 2.9 eV, 3.6 eV, 3.9 eV, and 4.75 eV within the bandgap of this bottom interface, are found to be strongly affected by processing conditions. These results are supported by both electrical and physical characterization measurements that identify a consistent trend in the evolution of charge trapping defects for samples subjected to identical processing conditions. In addition, evidence is provided correlating the optically active 2.9 eV defect to positively charged oxygen vacancies in the bottom interfacial layer that have recently been proposed as contributing to the flatband voltage roll-off phenomenon. The close connection between these results and both ab initio calculations and experimental findings substantiate the use of spectroscopic ellipsometry as a unique characterization method for identifying process-induced defects during development and fabrication of dielectric film stacks.

Charge redistribution at graphene/dielectric interfaces is predicated upon the relative positioning of the graphene Fermi level and the charge neutralization level of the dielectric. The authors present an angle-resolved near-edge x-ray absorption fine structure (NEXAFS) spectroscopy investigation of single-layered graphene transferred to 300 nm SiO2/Si with subsequent deposition of ultrathin high-κ dielectric layers to form graphene/dielectric interfaces. The authors’ NEXAFS studies indicate the appearance of a distinct pre-edge absorption for graphene/HfO2 heterostructures (but not for comparable TiO2 and ZrO2 constructs). The hole doping of graphene with substantial redistribution of electron density to the interfacial region is proposed as the origin of the pre-edge feature as electron depletion renders part of the initially occupied density of states accessible for observation via NEXAFS spectroscopy. The spectral assignment is validated by calculating the NEXAFS spectra of electron- and hole-doped graphene using density functional theory. In contrast, a similarly sputtered metallic TiN layer shows substantial covalent interfacial hybridization with graphene.

The local structural characterization of novel contact materials (nickel silicides) on N-2(+) implanted Si(100) substrates have been performed using Extended X-ray-Absorption Fine-Structure Spectroscopy (EXAFS). The crystal phases of nickel silicides that are stabilized on Si (100) substrates (NiSi or NiSi2) upon varying implantation and post deposition annealing conditions were identified. The questions addressed are whether the final stabilized crystal phases of the nickel silicide layers could be identified and the fraction of the various crystal symmetries could be determined. The identification of the stabilized crystal phases in the nickel silicide formation process is crucial, as it was shown that a Si rich Ni silicide layer at the NiSix/Si interface causes a significant reduction in the electron Schottky barrier height (SBH). EXAFS analyses using experimental and theoretical references were performed on nickel silicide thin films on silicon substrates exposed to different N-2(+) ion doses prior to nickel deposition and silicidation processes. Using EXAFS analyses, the stabilized phases (e. g. NiSi vs. NiSi2, etc.) and their ratios were determined. EXAFS was proved to be sensitive to the subtle modifications of the crystal structures introduced by these modifications in the processing conditions. EXAFS analyses of the experimental reference structures (NiSi, NiSi2 powder samples) clearly exhibited the robust differences in the Fourier Transformed (FT) EXAFS data in the first shell region. EXAFS fits using theoretical structures corresponding to NiSi and NiSi2 symmetries have successfully identified the distinct crystal phases present in nickel silicide thin films subjected to different doses of N-2(+) ion implantation. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Hard x-ray photoelectron spectroscopy (HAXPES) was performed on In0.53Ga0.47As/Al2O3 gate stacks as deposited and annealed at 400 °C, 500 °C, and 700 °C to test for out-diffusion of substrate elements. Ga and As core-level intensities increase with increasing anneal temperature, while the In intensity decreases. HAXPES was performed at two different beam energies to vary the surface sensitivity; results demonstrate Ga and As out-diffuse into the Al2O3 film. Analysis suggests the presence of an interlayer containing Ga and As oxides, which thickens with increasing anneal temperature. Further diffusion, especially of Ga, into the Al2O3 film is also observed with increasing anneal temperature.

We report significant improvements in the high-k/In0.53Ga0.47As interface quality by controlling atomic layer deposition (ALD) oxidizer chemistry. A step-by-step correlation between electrical data and chemical reactions at the high-k/InGaAs interface has been established using synchrotron photoemission. AsOx, GaOx, and In2O3 formed during unintentional ALD surface oxidation and the increase of As-As bonds are responsible for degrading device quality. A better quality H2O-based high-k gate stack is evidenced by less capacitance-voltage (CV) dispersion (14% in ZrO2), smaller CV hysteresis (37% in Al2O3 and 47% in ZrO2), fewer border traps (Qbr) (96% in Al2O3 and 25% in ZrO2), and lower mean interface traps density (Dit) (91% in Al2O3 and 29% in ZrO2). Improvements in Id and Gm therefore have been achieved by replacing O3 with H2O oxidizer. Our work suggests that H2O-based high-k is more promising than O3-based high-k. These results positively impact the industry's progress toward III-V CMOS at the 11nm node.

X-ray photoelectron core level spectroscopy, secondary ion mass spectroscopy, spectroscopic ellipsometry, and extended x-ray absorption fine structure measurements have been employed to distinguish the effects of Al and N diffusion on the local bonding and microstructure of HfO2 and its interface with the Si substrate in (001)Si/SiOx/2 nm HfO2/1 nm AlOx film structures. The diffusion of Al from the thin AlOx cap layer deposited on both annealed and unannealed HfO2 has been observed following anneal in N2 and NH3 ambient. Both N2 and NH3 subsequent anneals were performed to decouple incorporated nitrogen from thermal reactions alone. Causal variations in the HfO2 microstructure combined with the dependence of Al and N diffusion on initial HfO2 conditions are presented with respect to anneal temperature and ambient.

Hf-based dielectric films are susceptible to formation of charge trapping, performance-limiting point defects, making improved characterization of these defects a high priority of research on high-k dielectrics. Here we report noninvasive optical characterization of defect spectra and charge trapping kinetics in Si/SiO2/Hf1−xSixO2 film stacks using internal multiphoton photoemission and time-dependent electrostatic field-induced second-harmonic (TD-EFISH) generation. Oxygen vacancy defects unique to as-deposited HfO2 films are identified by resonant two-photon ionization of the 3.24 eV transition from their occupied mid-gap ground states to conduction-band-edge excited states and subsequent tunneling of the photoelectrons to the Si substrate. These defects are found to be located within the HfO2 bulk, and to be quenched upon annealing or silication of the high-k dielectric layer. Charge trapping in Hf-silicate samples is found to be dominated by traps at the oxide surface. Trapping rate is nearly independent of excitation wavelength and alloy composition. By contrast, trap lifetimes are found to be as much as two orders of magnitude shorter in Hf-silicate surfaces than at HfO2 surfaces.

Thermal stability of the high-k/In0.53Ga0.47As interface has been analyzed by both physical and electrical methods for the first time. It has been found that As-O and In-O bonds decompose and Ga-O bonds form above 400°C, as shown by XPS and corroborated by TEM, SIMS and EDX. Electrically, this interface decomposition resulted in increased frequency dispersion (accumulation), C-V shift, and mobility degradation. These results provide additional insights into improving the III-V/high-k interface as a candidate for 11nm CMOS technology.

Electronic structure heterogeneities are ubiquitous in two-dimensional graphene and profoundly impact the transport properties of this material. Here we show the mapping of discrete electronic domains within a single graphene sheet using scanning transmission X-ray microscopy in conjunction with ab initio density functional theory calculations. Scanning transmission X-ray microscopy imaging provides a wealth of detail regarding the extent to which the unoccupied levels of graphene are modified by corrugation, doping and adventitious impurities, as a result of synthesis and processing. Local electronic corrugations, visualized as distortions of the π*cloud, have been imaged alongside inhomogeneously doped regions characterized by distinctive spectral signatures of altered unoccupied density of states. The combination of density functional theory calculations, scanning transmission X-ray microscopy imaging, and in situ near-edge X-ray absorption fine structure spectroscopy experiments also provide resolution of a longstanding debate in the literature regarding the spectral assignments of pre-edge and interlayer states.

The redistribution of nitrogen from silicon to the Si-SiO 2 interface due to thermal processing is investigated by Secondary Ion Mass Spectroscopy (SIMS) using Metal-Oxide-Semiconductor (MOS) capacitors. SIMS profiles of implanted atomic nitrogen concentration indicate a significant redistribution of the nitrogen, from the silicon to the oxide layer in response to variations of the steady state time and temperature parameters of Rapid Thermal Anneal (RTA) processing. RTA treatment, in N 2 ambient, over a temperature range of 750°C - 1100°C, results in a measured increase of the integrated nitrogen peak at the interface. High Frequency Capacitance Voltage (HFCV) measurements of an implanted (N/ 5 × 10 14 cm 2 /s / 26keV) and annealed (900°C / 10s) sample is compared with a control (without N implant) sample to determine the relative nitrogen abundance at the interface. This value corresponds to the increase in fixed oxide charge Q that produces a negative shift in the flat band voltage Vo under negative gate bias conditions.

Bulk and surface sensitive photoemission core line spectra have been acquired for Si and Ge following each step in the process sequence of Si0.7Ge0.3/2 nm HfO2/2.5 nm TaN/950 degrees C gate stack film systems. Extended x-ray absorption fine structure measurements have confirmed Ge segregation and pileup to form a Ge-rich layer at the SiGe surface during Si oxidation. Transmission electron micrograph cross-sections with electron energy loss element profiles have verified the effectiveness of plasma nitridation for restricting SiGe oxidation and achieving <1 nm equivalent oxide thickness with gate leakage current density equivalent to that of Si substrates without the necessity of a Si cap for oxidation control. (C) 2011 American Institute of Physics. [doi:10.1063/1.3651519]

A design-of-experiments methodology was implemented to assess the commercial equipment viability to fabricate the high-K dielectrics Ta 2 O 5 , TiO 2 and BST (70/30 and 50/50 compositions) for use as gate dielectrics. The high-K dielectrics were annealed in 100% or 10% O 2 for different times and temperatures in conjunction with a previously prepared NH 3 nitrided or 14 N implanted silicon surface. Five metal electrode configurations—Ta, TaN, W, WN and TiN—were concurrently examined. Three additional silicon surface configurations were explored in conjunction with a more in-depth set of time and temperature anneals for Ta 2 O 5 . Electrical characterization of capacitors fabricated with the above high-K gate dielectrics, as well as SIMS and TEM analysis, indicate that the post high-K deposition annealing temperature was the most significant variable impacting the leakage current density, although there was minimal influence on the capacitance. Further studies are required, however, to clarify the physical mechanisms underlying the electrical data presented.