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This article reports Si-passivated Ge nFinFETs with significantly improved GmSAT/SSSAT and positive bias temperature instability (PBTI) reliability enabled by an improved replacement metal gate (RMG) high- ${k}$ last process. SiO2 dummy gate oxide (DGO) deposition on Ge fin is shown to form (Si x )Ge1- x O y , which is, compared to a pure SiO2, more difficult to remove completely during the dry clean prior to the gate-stack formation. By extending the DGO removal clean, improved PBTI reliability, reduced ${D}_{{\text {IT}}}$ , and increased electron mobility are demonstrated. Moreover, by suppressing the Ge channel oxidation through the choice of less-oxidizing DGO or inserting an Si-cap layer prior to the DGO deposition, a greatly improved long-channel electron mobility is obtained at a scaled fin width. Finally, together with the PBTI maximum ${V}_{{\text {OV}}}$ of 0.13 V, the best GmSAT/SSSAT of 5.4 is achieved, which is today’s record value among the sub-100-nm- ${L}_{g}$ n-channel Ge Fin and gate-all-around nanowire FETs. These results clearly show the importance of the pre-gate-stack channel surface preparation on the scaled Ge FinFETs to benefit from a previously optimized Si-passivated Ge gate-stack.

With the continuous miniaturization and increasing complexity of the devices used in nanotechnology, there is a pressing need for characterization techniques with nm-scale 3D-spatial resolution. Unfortunately, techniques like Secondary Ion Mass Spectrometry (SIMS) fail to reach the required lateral resolution. For this reason, new concepts and approaches, including the combination of different complementary techniques, have been developed in over the past years to try to overcome some of the challenges. Beyond the problem of spatial resolution in a 3D SIMS experiment, one is also faced with the impact of changes in topography during the analysis. These are quite difficult to identify because they originate from the different sputter rates of the various materials and or phases in a heterogeneous system and are notorious at the interfaces between organic and inorganic layers. As each of these materials will erode at a different velocity, accurate 3D-analysis will require means to establish a spatially resolved relation between ion bombardment time and depth. Inevitably such a nonhomogeneous erosion will lead to the development of surface topography. The impact of these effects can be overcome provided one can capture the time and spatially dependent surface erosion (velocity) with high spatial resolution during the course of a profiling experiment. Incorporating a Scanning Probe Microscope (SPM) unit which provides topography measurements with high spatial resolution, into a SIMS tool (e.g., Time of Flight (ToF) SIMS) with means to alternate between SPM and SIMS measurements, is one approach to meet that demand for complementary topographical information allowing accurate 3D chemical imaging. In this paper, the result of integrating a SPM module into a ToF-SIMS system is presented illustrating the improvements in 3D data accuracy which can be obtained when analyzing complex 3D-systems. ispartof: ANALYTICAL CHEMISTRY vol:92 issue:16 pages:11413-11419 ispartof: location:United States status: published

We have demonstrated Ge nFinFETs with a record high $\text{G}_{\text{mSA}\Gamma}/\text{SS}_{\text{SAT}}$ and PBTI reliability by improving the RMG high-k last process. The SiO 2 dummy gate oxide (DGO) deposition and removal processes have been identified as knobs to improve electron mobility and PBTI reliability even with a nominally identical Si-passivated Ge gate stack. Surface oxidation of Ge channel during the DGO deposition is considered to impact the final gate stack. By suppressing the Ge channel surface oxidation, increasing mobility with decreasing fin width is obtained, whereas PBTI reliability, $\text{D}_{\text{IT}}$ of scaled fin as well as high-field mobility are improved by extending the DGO in-situ clean process, resulting in the record $\text{Gm}_{\text{SAT}}/\text{SS}_{\text{SAT}}$ of 5.4 at 73 nm Lg.

Gallium nitride (GaN) grown on Si by metalorganic chemical vapor deposition was analyzed using high-resolution, high-energy x-ray photoelectron spectroscopy (HAXPES). The HAXPES spectra of GaN obtained using monochromatic Cr Kα radiation at 5414.7 eV include a survey scan (Al Kα) and high-resolution spectra of Ga 3d, Ga 2p3/2, Ga 3p, Ga LMM, N 1s, C 1s, and O 1s.

Layers composed of binary blends of a polymer and a fullerene derivative are at the heart of bulk heterojunction organic photovoltaic cells. The efficiency and stability of these devices critically depend on the distribution of the polymer and fullerene materials within the blend layer. Whereas time-of-flight secondary ion mass spectrometry, particularly in combination with cluster ion beams, has frequently been used to probe similar organic materials, the quantification of the results is often missing due to a lack of understanding of all the parameters influencing the measurement results. This study contributes to improved quantification by exploring the role of the bulk composition and interfacial material on parameters such as sputtering yield, mass fragmentation, and ionization. We show that the argon cluster sputtering yields of these materials may be described by two widely acknowledged sputtering yield relationships. Their fitting parameters depend on the layer composition in a manner that is consistent with a lower energy required for sputtering of layers with higher fullerene derivative content. Similarly, we show that changes in composition impact the ion yields nonlinearly, which is an important source of quantification uncertainty. We provide evidence that, for the case of the fullerene derivative mixed with different donor materials, the matrix effect (i.e., the deviation from a linear response) correlates linearly with the electronegativity of the species in the donor material. Finally, with respect to the quantification of the composition at the interface with the substrate, we present a charge transfer mechanism that describes observed enhancements of the secondary ion intensities. ispartof: Journal of Physical Chemistry C vol:120 issue:49 pages:28074-28082 status: published

The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O3) or oxygen (O2) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH4) at 500 °C. After O3 exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH4 reactants, allowing more time for surface diffusion. After O2 exposure, the O atoms are present in the form of SiOx clusters. Regions of hydrogen-terminated Si remain present between the SiOx clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness.

For patterned TiN/silicon oxide/low-k dielectric stack, fluorinated etch residues were detected on the TiN surface, the dielectric sidewall and bottom, regardless of the low-k material used in the stack. XPS results showed that they consisted of polymer-based (CFx) residues deposited on trench sidewall and bottom, and metal-based (TiFx) residues mainly deposited on top surface. In terms of post-etch residue removal, the efficiency of various wet clean solutions can be clearly distinguished for CFx, and TiFx using the same patterned porous low-k stack. These results also demonstrate that the removal of both TiFx and CFx residues generated during the plasma is possible in one step with optimized chemical and process.

The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga–S and As–S bonds at the GaAs–thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 °C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of O (0.05 ML coverage) and C (about 3% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al2O3 on this surface occurs via the formation of Al–S bonds without introducing a...

Solution processed polymer (donor) and fullerene (acceptor) bulk heterojunctions are widely used as the photo active layer in organic solar cells. Intimate mixing of these two materials is essential for efficient charge separation and transport. Identifying relative positions of acceptor and donor rich regions in the bulk heterojunction with nanometer scale precision is crucial in understanding intricate details of operation. In this work, a combination of Ar(+)2000 gas cluster ion beam and scanning probe microscopy is used to examine the lateral and vertical phase separation within regio-regular poly(3-hexylthiophene)(P3HT):phenyl-C60-butyric acid methyl ester (PCBM) bulk heterojunction. While the Ar(+)2000 gas cluster ion beam is used as a sputter tool to expose the underneath layers, scanning probe microscopy techniques are used to obtain two-dimensional (2D) electrical maps (with sub-2 nm lateral resolution). The electrical mapping is decoded to chemical composition, essentially producing lateral and vertical maps of phase separation. Thermal stress causes large PCBM-rich hillocks to form, and consequently affecting the balance of P3HT:PCBM heterojunctions, hence a negative impact on the efficiency of the solar cell. We further developed a method to analyze the efficiency of exciton dissociation based on the current maps and a loss of 20% in efficiency is observed for thermally degraded samples compared to fresh un-annealed samples.

Epitaxial Si-O superlattices consist of alternating periods of crystalline Si layers and atomic layers of oxygen (O) with interesting electronic and optical properties. To understand the fundamentals of Si epitaxy on O atomic layers, we investigate the O surface species that can allow epitaxial Si chemical vapor deposition using silane. The surface reaction of ozone on H-terminated Si(100) is used for the O deposition. The oxygen content is controlled precisely at and near the atomic layer level and has a critical impact on the subsequent Si deposition. There exists only a small window of O-contents, i.e. 0.7–0.9 atomic layers, for which the epitaxial deposition of Si can be realized. At these low O-contents, the O atoms are incorporated in the Si-Si dimers or back bonds (-OSiH), with the surface Si atoms mainly in the 1+ oxidation state, as indicated by infrared spectroscopy. This surface enables epitaxial seeding of Si. For O-contents higher than one atomic layer, the additional O atoms are incorporated in the Si-Si back bonds as well as in the Si-H bonds, where hydroxyl groups (-Si-OH) are created. In this case, the Si deposition thereon becomes completely amorphous.

[Co/Ni] multilayers with perpendicular magnetic anisotropy (PMA) have been researched and applied in various spintronic applications. Typically the seed layer material is studied to provide the desired face-centered cubic (\textit{fcc}) texture to the [Co/Ni] to obtain PMA. The integration of [Co/Ni] in back-end-of-line (BEOL) processes also requires the PMA to survive post-annealing. In this paper, the impact of NiCr, Pt, Ru, and Ta seed layers on the structural and magnetic properties of [Co(0.3 nm)/Ni(0.6 nm)] multilayers is investigated before and after annealing. The multilayers were deposited \textit{in-situ} on different seeds via physical vapor deposition at room temperature. The as-deposited [Co/Ni] films show the required \textit{fcc}(111) texture on all seeds, but PMA is only observed on Pt and Ru. In-plane magnetic anisotropy (IMA) is obtained on NiCr and Ta seeds, which is attributed to strain-induced PMA loss. PMA is maintained on all seeds after post-annealing up to 400$^{\circ}$C. The largest effective perpendicular anisotropy energy ($K_U^{\mathrm{eff}}\approx 2\times10^5$J/m$^3$) after annealing is achieved on NiCr seed. The evolution of PMA upon annealing cannot be explained by further crystallization during annealing or strain-induced PMA, nor can the observed magnetization loss and the increased damping after annealing. Here we identify the diffusion of the non-magnetic materials from the seed into [Co/Ni] as the major driver of the changes in the magnetic properties. By selecting the seed and post-annealing temperature, the [Co/Ni] can be tuned in a broad range for both PMA and damping., Comment: 9 pages, 11 figures

Interpretation of time-of-flight (TOF)-SIMS spectra of organic molecules could be difficult because of the presence of a high number of secondary ion peaks; this often requires the use of data analysis methods to simplify the TOF-SIMS measurements. In this study, we will demonstrate that the gentle-SIMS method could be applied to more easily interpret the TOF-SIMS spectra of organic solar cell materials. Various conditions of the primary ion beam were used to generate the gentle-SIMS spectra from pure layers of two materials, i.e. PC70BM and PCDTBT. It will be shown that by using specific conditions of the primary ion column, the corresponding molecular ion or characteristic peaks of the pure organic materials are highlighted. Results obtained on an organic layer prepared from a mixture of both materials will be also discussed.

We investigate the capabilities and limitations of performing (quantitative) in-depth composition analysis of polymer:fullerene blends, using time-of-flight SIMS with large Arn+ clusters. These blends constitute an important class of organic solar cell materials, whose performance and reliability critically depend on the blend’s physicochemical properties at the nanoscale. We investigate the effect of Ar cluster size n, kinetic energy E and E/n on the secondary ion and sputter yields and evaluate the Ar beam-induced damage in these layers. On the basis of this, the ideal experimental conditions are derived that allow us to investigate matrix effects and variations in sputter yields as function of polymer:fullerene compositions. We demonstrate that time-of-flight SIMS is capable to retrieve quantitative in-depth information in common polythiophene, polycarbazole,and fullerene blends.

Self-assembled monolayers (SAMs) derived from 11-cyanoundecyltrichlorosilane precursor are deposited in vapor phase and characterized on ultra-low- k Chemical Vapor Deposition (CVD) dielectric films ( k = 2.0) with open porosity up to 50% and pore diameter as large as 3.5 nm. Two surface preparation methods, such as Ar/H 2 and Ar/N 2 plasma pretreatments, are investigated and the pore sealing efficiency after SAM deposition is quantified from the experimental determination of open porosity and pore size measurements derived from toluene adsorption isotherms. In parallel, low- k damage is evaluated after surface preparation and SAM deposition by XPS depth profiling and by monitoring the change in refractive index, thickness and k value together with the –CH 3 and –CH 2 normalized FTIR peak areas vs. the pristine dielectric. Subsequently, a 10 nm HfO 2 thin film was deposited by Atomic Layer Deposition (ALD) in order to assess the pore-sealing capability of the proposed approach. When combining surface activation, SAM deposition and ALD, it was possible to accomplish a wide range of pore sealing. By adequate optimization, it was possible to obtain complete pore sealing after ALD, without precursor penetration into the porous low- k film, but at the expense of a 37% k increase for a 90 nm dielectric thickness.

Spin-on-diffussant (SoD) processing as a doping technique in two-dimensional semiconductors shows a general process compatibility with materials such as MoS2 and WSe2. The characteristic Raman modes in chemical vapor deposition-grown MoS2 are retained after a phosphorus-based SoD processing at temperatures up to 1000 °C; the evolution of the characteristic Raman peaks with SoD processing indicates a reduction in the intrinsic electron concentration. Electrical measurements show a corresponding p-type shift in the MoS2 MOSFET transfer characteristics and indicate possible oxidation of MoS2 by the SoD processing. Both these effects correlate with XPS measurements which confirm the diffusion of phosphorus atoms into MoS2 and increased atomic percentage of Mo oxide after SoD processing. The p-type shifts in the electrical characteristics correspond to a maximum of 2.4 × 1012 cm–2 change in the intrinsic carrier concentration. Repeating the experiment on WSe2 flake devices leads to similar trends: an increased p-type and a decreased n-type conduction indicating p-type doping and a significant increase in the OFF-state leakage current.Spin-on-diffussant (SoD) processing as a doping technique in two-dimensional semiconductors shows a general process compatibility with materials such as MoS2 and WSe2. The characteristic Raman modes in chemical vapor deposition-grown MoS2 are retained after a phosphorus-based SoD processing at temperatures up to 1000 °C; the evolution of the characteristic Raman peaks with SoD processing indicates a reduction in the intrinsic electron concentration. Electrical measurements show a corresponding p-type shift in the MoS2 MOSFET transfer characteristics and indicate possible oxidation of MoS2 by the SoD processing. Both these effects correlate with XPS measurements which confirm the diffusion of phosphorus atoms into MoS2 and increased atomic percentage of Mo oxide after SoD processing. The p-type shifts in the electrical characteristics correspond to a maximum of 2.4 × 1012 cm–2 change in the intrinsic carrier concentration. Repeating the experiment on WSe2 flake devices leads to similar trends: an increased...

Medium energy ion scattering (MEIS) using, typically, 100–200 keV H+ or He+ ions derives it ability to characterise nanolayers from the fact that the energy after backscattering depends (i) on the elastic energy loss suffered in a single collision with a target atom and (ii) on the inelastic energy losses on its incoming and outgoing trajectories. From the former the mass of the atom can be determined and from the latter its depth. Thus MEIS yields depth dependent compositional and structural information, with high depth resolution (sub-nm near the surface) and good sensitivity for all but the lighter masses. It is particularly well suited for the depth analysis of high-k multilayers of nanometer thickness. Accurate quantification of the depth distributions of atomic species can be obtained using suitable spectrum simulation.\ud \ud In the present paper, important aspects of MEIS including quantification, depth resolution and spectrum simulation are briefly discussed. The capabilities of the technique in terms of the high depth resolution layer compositional and structural information it yields, is illustrated with reference to the detailed characterisation of a range of high-k nanolayer and multilayer structures for current microelectronic devices or those still under development: (i) HfO2 and HfSiOx for gate dielectric applications, including a TiN/Al2O3/HfO2/SiO2/Si structure, (ii) TiN/SrTiO3/TiN and (iii) TiO2/Ru/TiN multilayer structures for metal–insulator–metal capacitors (MIMcaps) in DRAM applications.\ud \ud The unique information provided by the technique is highlighted by its clear capability to accurately quantify the composition profiles and thickness of nanolayers and complex multilayers as grown, and to identify the nature and extent of atom redistribution (e.g. intermixing, segregation) during layer deposition, annealing and plasma processing. The ability makes it a valuable tool in the development of the nanostructures that will become increasingly important as device dimensions continue to be scaled down.

The influence of different wet chemical treatments (HCl, H₂SO₄, NH₄OH) on the composition of InP surfaces is studied by using synchrotron radiation photoemission spectroscopy (SRPES). It is shown that a significant amount of oxide remains present after immersion in a NH₄OH solution which is ascribed to the insolubility of In³⁺ at higher pH values. Acidic treatments efficiently remove the native oxide, although components like Pᴼ, Inᴼ and P(2±Δ)+ suboxides are observed. Alternatively, the influence of a passivation step in (NH₄)₂S solution on the surface composition was investigated. The InP surface after immersion into (NH₄)₂S results in fewer surface components, without detection of Pᴼ and P(2±Δ)+ suboxides. Finally, slight etching of InP surfaces in HCl/H₂O₂ solution followed by a native oxide removal step, showed no significant effect on the surface composition.

The surface chemistry and the interface formation during the initial stages of the atomic layer deposition (ALD) of Al2O3 from trimethylaluminum (TMA) and H2O on InP(100) were studied by synchrotron radiation photoemission spectroscopy and scanning tunneling microscopy. The effect of the ex situ surface cleaning by either H2SO4 or (NH4)2S was examined. It is shown that the native oxide on the InP surface consisted mainly of indium hydrogen phosphates with a P enrichment at the interface with InP. After a (NH4)2S treatment, S was present on the surface as a sulfide in both surface and subsurface sites. Exposure to TMA led to the formation of a thin AlPO4 layer, irrespective of the surface cleaning. The surface Fermi level of p-type InP was found to be pinned close to midgap after H2SO4 cleaning and moved only slightly further toward the conduction band edge upon TMA exposure, indicating that the AlPO4/InP interface was rather defective. (NH4)2S passivation led to a Fermi level position of p-type InP close ...

The atomic layer deposition of titanium oxide TiO2 on ruthenium and oxidized ruthenium with titanium methoxide as metal precursor and H2O and O3 as oxidant was investigated by Rutherford backscattering (RBS) and time of flight secondary ion mass spectrometry (TOFSIMS). An ultra-thin layer of TiO2 deposited a priori with H2O plays the role of protection of Ru(Ox) substrates against etching by O3. Information about thin films (~3 nm) interfacial reactions, thickness and structure was brought by Medium Energy Ion Scattering Spectroscopy (MEIS) and X-ray absorption spectroscopy (XAS) measurements. The growth enhancements observed in the first stages of the deposition depends on the pre-treatment (pre-oxidation, H2O based interlayer thickness) of the Ru substrate. Thick films (~14 nm) were analyzed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The as deposited TiO2 films are crystalline with rutile structure, as resulted from structural analyzes. However, the presence of small amounts of anatase was detected by soft X-ray absorption spectroscopy (XAS) and is strongly influenced by the surface pre-treatment of the Ru substrate. The electrical properties (equivalent oxide thickness and leakage current density) correlate with a different rutile/anatase ratio present in the films.

In this study, the gentle SIMS (G-SIMS) method has been applied to organic solar cell materials. Various primary ion conditions were used to generate the G-SIMS spectra; monoatomic and cluster sources with different energies were tested. It is shown that the G-SIMS concept helps to identify both PCBM and P3HT materials through the enhancement of molecular and characteristic ions of the two molecules. Copyright © 2012 John Wiley & Sons, Ltd.

In back-end of line processing, the polymer deposited on the dielectric sidewalls during the etch must be removed prior to subsequent processing steps to achieve high adhesion and good coverage of materials deposited in the etched features [1,. Typically, this is done by a combination of short plasma treatment and diluted wet clean, or by wet cleans alone. On the one hand, for porous dielectric stacks, a mild plasma treatment that preserves the integrity of the low-k dielectrics would not be sufficient to efficiently remove this residue. Furthermore, aqueous cleaning solutions is not efficient to achieve a complete removal without etching the underlying layer. Hence appropriate wet clean chemistries are needed to dissolve/decompose these polymers without etching the dielectric. On the other hand, analytical techniques available for direct characterization of sidewall polymer are limited. For a fast screening of potential chemistries capable of dissolving/removing polymer residues generated during the low-k etch, a fluoropolymer deposited on a blanket, checkerboard low-k substrate was used as a model polymer. In our recent study [, using X-ray photoelectron spectroscopy (XPS), it was shown that the polymer was composed of CF, CF2, and CF3 groups. This model polymer was found to be very similar to the polymer residue generated during the etch of the low-k stack using similar plasma. The present study mainly focused on the effect of UV treatment and the concentration of active component in wet clean solution on the structure change of the polymer and the enhancement of polymer removal.

Downscaling of the metal-insulator-metal capacitor (MIMCAP) for Dynamic Random Access Memory (DRAM) requires the introduction of high permittivity dielectrics. MIMCAP structures formed with RuO"2/Ru as bottom electrode, rutile TiO"2 as dielectric and TiN as top electrode are described. Ozone (O"3) is needed as oxidant in the TiO"2 atomic layer deposition (ALD) process in order to obtain the rutile phase (permittivity>80), while anatase TiO"2 (permittivity ~40) is obtained with H"2O. As O"3 etches the ruthenium substrate, an ultra-thin interlayer of TiO"2 was first grown with H"2O, followed by the thick TiO"2 layer deposited with O"3. In order to minimize the content of anatase in the TiO"2 layer, responsible for a reduced dielectric constant, we investigate the effect of scaling down the thickness of the protective H"2O based inter-layer on the equivalent oxide thickness (EOT) and leakage current density (J"g). The four times reduction in thickness without affecting the integrity of the ruthenium substrate resulted in a significant decrease of both EOT and J"g.

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Ultra-thin high-k layers based on HfO2, or Hf-silicates in combination with sub-nanometer SiO2, show much promise in their use as Si-compatible gate dielectrics. XPS has been applied on a range of HfO2/SiO2 and HfSiOx(60%Hf)/SiO2 films on Si(100), before and after decoupled plasma nitridation (DPN) at 1073 K. The treatment of the data was optimized in order to determine individual layer thicknesses of the multilayer stack taking into account the measured nitrogen content of the nitrided films. The procedure adhered to the prescriptions of ISO18118:2004(E) for the calculations of inelastic mean free paths (IMFP) and elastic corrections thereof, using film material properties, like densities and band gaps. Effective attenuation lengths (EAL) were taken throughout as 90% of the respective IMFP, whereas an appropriate set of empirical relative sensitivity factors (RSF) was used. The XPS-derived thicknesses were compared with corresponding values obtained from medium-energy ion scattering (MEIS) measurements on the same series of specimens in combination with energy spectrum simulation to provide quantitative layer information with sub-nanometer resolution. The XPS and MEIS results exhibit very good agreement on the deduced layer structures within the respective experimental uncertainty, and both sets are consistent with the grown nominal layer parameters of the high-k nanofilms. Copyright © 2010 John Wiley & Sons, Ltd.

Nitrogen depth profiling in a high-k gate stack structure, SiON/HfO2/SiON/Si(0 0 1) was performed by high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The nitrogen depth profile is determined so that both the HRBS spectrum and the angular dependence of the XPS yield are reproduced. The obtained nitrogen profile is compared with the result of high-resolution elastic recoil detection (ERD) which is the most reliable technique for depth profiling of light elements. The agreement between the result of the present combination analysis and that of high-resolution ERD is fairly good, showing that the present combination analysis is a promising method for the analysis of light elements.

Composition depth profiling of HfO(2) (2.5 nm)/SiON (1.6 nm)/Si(001) was performed by three diffetent analytical techniques: high-resolution Rutherford backscattering spectroscopy (HRBS), angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and high-resolution elastic recoil detection (HR-ERD). By comparing these results we found the following: (1) HRBS generally provides accurate depth profiles. However, care must be taken in backgroud subtraction for depth profiling of light elements. (2) In the standard AR-XPS analysis, a simple exponential formula is often used to calculate the photoelectron escape probability. This simple formula, however, cannot be used for the precise depth profiling. (2) Although HR-ERD is the most reliable technique for the depth profiling of light elements, it may suffer from multiple scattering, which deteriorates the depth resolution, and also may cause a large background.

Report on the 47th IUVSTA Workshop ‘Angle-Resolved XPS: the current status and future prospects for angle-resolved XPS of nano and subnano films’ A. Herrera-Gomez,a,b∗ J. T. Grant,c P. J. Cumpson,d† M. Jenko,e F. S. Aguirre-Tostado,b C. R. Brundle,f T. Conard,g G. Conti,h C. S. Fadley,i J. Fulghum,j K. Kobayashi,k L. Kover,l H. Nohira,m R. L. Opila,n S. Oswald,o R. W. Paynter,p R. M. Wallace,b W. S. M. Wernerq and J. Wolstenholmer

Using reference-free X-ray fluorescence analysis (XRF) in different geometries carried out in the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin various nanolayered systems have been investigated. As an example the investigation of Hf containing thin oxide layers is shown. For comparison reasons these samples have been also measured by X-ray reflectometry (XRR) in the PTB laboratory and by other partners within the ANNA project, which confirmed the thickness of the Hf containing top layers determined by XRF within their respective uncertainties. The XRF spectra were deconvolved employing the detector response functions to deduce the intensity of the corresponding Hf L3 fluorescence lines. The investigation of nanolayered systems especially in the lower energy range shows advantages, like different absorption conditions which allow for better dynamics and the suppression of the silicon fluorescence signal from the substrate, but needs more effort in determining the respective fundamental parameters.

We present a detailed characterization of thin high-k Hf-based dielectric/SiO2 stacks on Si by electrical measurements (capacitance - voltage (C-V) and current-voltage (I-V)), structural analysis using transmission electron microscopy (TEM) and compositional analysis using medium energy ion scattering (MEIS). We show that the electrical results are consistent with and can be explained by the structural and compositional results. Specifically, the structural results show that the effect of nitridation of the films using a decoupled plasma nitridation method is an increase in SiO2 thickness, which results in a capacitance and leakage current decrease, revealed by the electrical measurements. Nitridation also reduces the density of interface traps for these samples. The reduction is more effective in the case of nonstoichiometric hafnium silicate films (HfSiOx) than in the case of HfO2.

The effect of tetramethyl ammonium hydroxide (TMAH) used as additive in organic solvent (N-methyl pyrrolidone, NMP) on removal efficiency of post-etch photoresist was investigated on both blanket substrate and single damascene structures. In contrast to plasma ashing, photoresist removal using NMP/TMAH combined with megasonics showed no carbon depletion and no significant change in k-value. Mixing TMAH with NMP enhanced photoresist removal efficiency with respect to pure NMP. Photoresist removal using NMP/TMAH resulted in lower low-k capacitance (lower k-value) compared with that of plasma ashing process, due to the removal of the damaged layer generated during plasma etching. As a consequence of the removal of the damaged layer, a CD change was observed. The CD loss was estimated to be about 7nm for 1% TMAH, and became negligible for 0.1% TMAH. Analysis of low-k sidewall using angle-resolved X-ray photoelectron spectroscopy showed that solvent mixture containing TMAH also removed sidewall residues generated by the etch plasma.

A good dielectric layer on the GaAs substrate is one of the critical issues to be solved for introducing GaAs as a candidate to replace Si in semiconductor processing. In literature, promising results have been shown for Al2O 3on GaAs substrates. Therefore, atomic layer deposition (ALD) of Al2O3has been studied on GaAs substrates. We have been investigating the influence of the ALD process (thermal vs plasma-enhanced ALD) as well as the influence of the starting surface (no clean vs partial removal of the native oxide). Ellipsometry and total X-ray reflection fluorescence were applied to study the growth of the ALD layers. Angle-resolved X-ray photoelectron spectroscopy was used to determine the composition of the interlayer. Both processes were shown to be roughly independent of the starting surface with a minor dependence for the thermal ALD. Thermally deposited ALD layers exhibited better electrical characteristics based on capacitance measurements. This could be linked to the thinner interlayer observed for thermally deposited Al2 O3. However, the Fermi level was not unpinned in all cases, suggesting that more work needs to be done for passivating the interface between GaAs and the high- k layer. © 2009 The Electrochemical Society.

Reducing the energy of the primary ions will improve the depth resolution in SIMS depth profiling. At ultra low energies ( + ions, which are commonly used for their enhancement of negative secondary ion formation, and discuss the impact of these extreme conditions on the steady state surface concentration of cesium. In contrary to what is found from sputtering-based retention models, the steady state surface concentration of (retained) cesium on silicon reaches a maximum value in the order of 15 at%.

In advanced interconnect applications, the possibility to remove completely photoresist layers is one of the key points. To have the maximum removal efficiency, the selection of the needed chemistries is of first importance. To this end, the characterization of post-etched photoresists can be used to support that selection. The complete work includes the use of various spectroscopic and polymer characterization techniques. In the present paper, results obtained by time of flight-secondary ion mass spectrometry (ToF-SIMS), angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and Auger electron spectroscopy (AES) are presented for the characterization of post-etched photoresist used in photoresist mask patterning schemes.

The Physikalisch-Technische Bundesanstalt (PTB), Germany's national metrology institute, developed an alignment strategy to specify elemental depth profiling in vertical sidewall layers on structured wafers. For this purpose, PTB's irradiation chamber for 200 mm and 300 mm silicon wafers was used to combine total-reflection X-ray fluorescence (TXRF) and grazing incidence XRF (GIXRF) techniques by employing monochromatized undulator radiation of the BESSY II electron storage ring. 3-D test structures were fabricated to develop an optimal alignment strategy allowing for depth profiling in such nanolayers. The test structures consisted of silicon bars with widths/spacings either in the μm or in the nm range. In order to be able to differentiate the sidewalls more easily from the remainder of the structures, they were provided with an additional silicon nitride layer. Four structure types of different bar width and density parameters on two 200 mm silicon wafers were investigated. The alignment procedure developed in the present work consists of three main steps and allows for distinct excitation of multiple sidewalls of one kind. Information about depth-dependent sidewall contamination, layer thickness and composition can be obtained by this approach. First results obtained on these test structures demonstrate the application potential of this new technique. In principle, depth-dependent chemical speciation should also be possible using GIXRF in combination with near edge absorption X-ray fine structure (NEXAFS).

Atomic layer doping of phosphorus (P) and arsenic (As) into Si was performed using the vapor phase doping (VPD) technique. For increasing deposition time and precursor gas flow rate, the P and As doses tend to saturate at about 0.8 and 1.0 monolayer of Si, respectively. Therefore, these processes are self-limited in both cases. When a Si cap layer is grown on the P-covered Si(001), high P concentration of 3.7 × 1020 cm-3 at the heterointerface in the Si-cap/P/Si-substrate layer stacks is achieved. Due to As desorption and segregation toward the Si surface during the temperature ramp up and during the Si-cap growth, the As concentration at the heterointerface in the Si-cap/As/Si-substrate layer stacks was lower compared to the P case. These results allowed us to evaluate the feasibility of the VPD process to fabricate precisely controlled doping profiles.

A new method for the combination analysis of high-resolution Rutherford backscattering spectroscopy (HRBS) and angle-resolved X-ray photoelectron spectroscopy (AR-XPS) is proposed for accurate depth profiling of chemical states. In this method, attenuation lengths (ALs) for the photoelectrons are first determined so that the AR-XPS result is consistent with the HRBS result. Depth profiling of the chemical states are then performed in the AR-XPS analysis using the composition-depth profiles obtained by HRBS as constrained conditions. This method is successfully applied to Hf-based gate stack structures demonstrating its feasibility.

A ternary WN"xC"y system was deposited in a thermal ALD (atomic layer deposition) reactor from ASM at 300^oC in a process sequence using tungsten hexafluoride (WF"6), triethyl borane (TEB) and ammonia (NH"3) as precursors. The WC"x layers were deposited by a novel ALD process at a process temperature of 250^oC. The WN"x layers were deposited at 375^oC using bis(tert-butylimido)-bis-(dimethylamido)tungsten (^tBuN)"2(Me"2N)"2W (imido-amido) and NH"3 as precursors. WN"x grows faster on plasma enhanced chemical vapor deposition (PECVD) oxide than WC"x does on chemical oxide. WN"xC"y grows better on PECVD oxide than on thermal oxide, which is opposite of what is seen for WN"x. In the case of the ternary WN"xC"y system, the scalability towards thinner layers and galvanic corrosion behavior are disadvantages for the incorporation of the layer into Cu interconnects. ALD WC"x based barriers have a low resistivity, but galvanic corrosion in a model slurry solution of 15% peroxide (H"2O"2) is a potential problem. Higher resistivity values are determined for the binary WN"x layers. WN"x shows a constant composition and density throughout the layer.

Thin dysprosium-, scandium-, and hafnium-based oxide dielectric films are deposited by atomic vapor deposition (AVD) using tris(6-ethyl-2,2-dimethyl-3,5-decanedionato) dysprosium [Dy(EDMDD)3], tris(6-ethyl-2,2-dimethyl-3,5-decanedionato) scandium [Sc(EDMDD)3], and bis(tert-butoxide) bis(methoxymethyl propanoxide) hafnium [Hf(OtBu)2(mmp)2] as precursors. Spectroscopic ellipsometry (SE), Rutherford backscattering (RBS) spectrometry, and X-ray photoemission spectroscopy (XPS) demonstrate good control of the thickness and composition of the films. In particular, ternary and quaternary oxide alloys of any desired composition are grown. X-ray diffraction (XRD) shows that the (Dy0.5Sc0.5)2O3 films are amorphous as grown, whereas the (Dy0.5Hf0.5)4O7 and (Sc0.5Hf0.5)4O7 films are crystalline. The crystal structures of DyxHf1–xOy and ScxHf1–xOy change from monoclinic to cubic around x∼0.1.

The effect of postdeposition anneals in various ambients on negative bias temperature instability (NBTI) in metal-organic chemical-vapor-deposited HfSiO(N) stacks is investigated. The nitrided stacks, either by anneal or decoupled plasma nitridation (DPN) followed by a postnitridation anneal in O2 or N2 (DPN + O2 and DPN + N2 ), are more degraded by NBTI than the nonnitrided ones (O2, N2 anneal, and as deposited stacks). Moreover, none of the nitrided stacks reaches the 10-year NBTI lifetime, while the lifetime for the nonnitrided ones is larger than 10 years. Nitrogen profiles measured by X-ray photoelectrons spectroscopy and charge-pumping-current data show a relation between nitrogen location and positively charged defects in the gate stack. The additional NBT degradation in nitrided stacks is due to filling or generation of nitrogen-related defects by holes that are injected from the channel.

The replacement of poly-silicon by metallic compounds in the gate stack leads to the search of metals with suitable work function. However, it is observed that thermal budget has a large influence on the effective work functions of several metals. In this paper, we investigated the possible modification of the chemical states by physical analysis techniques (XPS, ERD, SIMS) by studying investigating the chemistry of the high-k oxide/metal interface. We show that in the case of the TiN/TaN/HfO2/SiO2/Si stack, several modifications occur upon 1000{degree sign}C N2 annealing: Increase of the nitrogen content of the TaN, interdiffusion of the Ti and TaN, and formation of Ta2O5 at the TaN/HfO2 interface.

Angle resolved XPS (ARXPS) is a powerful tool for the determination of the thickness of ultra-thin films. In the case of high-k dielectric layers, the technique is capable of measuring the thickness of both the high-k layer and intermediate layers of silicon dioxide or metal silicate. The values for layer thickness are in close agreement with those generated by a variety of other techniques. As well as knowing the thickness of these layers, it is important to determine whether the layers are continuous or whether the coverage of the high-k layer is only partial. Using ARXPS, a method has been developed to determine whether the coverage of the high-k material is continuous and, if not, to calculate the fraction of the surface that is covered. The method is described with reference to the layers of Al2O3 grown on SiO2 using atomic layer deposition (ALD). The method is then applied to HfO2 layers produced using ALD on silicon wafers whose surfaces had received three different types of surface treatment. The way in which the layers grow and the nature of the resulting layer were found to depend upon the pre-treatment method. For example, growth on a thermal silicon dioxide surface resulted in complete coverage of HfO2 after fewer ALD cycles than layers grown on an H-terminated surface. The results from ARXPS are compared with those obtained from ToF SIMS that have been shown earlier to be a valuable alternative to the LEIS analysis [1] .

The analysis of thin films in the range of 10 nm and less has become very important in microelectronics. The goal of this article is an evaluation of low-energy TOF-ERDA (time-of-flight elastic recoil detection analysis) in comparison with low-energy SIMS (secondary ion mass spectrometry) and HRBS (high-resolution Rutherford backscattering spectrometry), using a thin SiO 2 /Si 3 N 4 /SiO 2 stack as a test vehicle. Comparisons are made on the depth resolution, its loss as a function of depth and the quantification accuracy.

To facilitate selective removal of the gate dielectric towards the gate electrode, wet etch characteristics of HfSiOx and HfSiOx(N) in acidified HF solutions were determined as function of several process parameters. Etch behavior of Hf- silicates was found to be little influenced by the various CVD deposition processes. The top part (0-2 nm) of thick Hf- silicate layers etched similar to as-deposited thin layers (< 2nm) while the bulk part was etching significantly slower. However, etch rates were strongly dependent on composition (lower for Hf-rich silicates). Also, the removal rate of HfSiOx (N) was mainly depending on the amount of incorporated nitrogen and crystallization temperature. Thermally nitrided layers were easier to remove compared to plasma nitrided layers. Post nitridation anneals at high temperature in nitrogen environment decreased the etch rate. After removal, Hf concentrations below 1e11 at/cm2 for most of the HfSiOx(N) layers under study were observed after a short (typically a few seconds) etch process in a single wafer spin cleaning tool.

The TRIDYN collisional computer simulation has been modified to account for emission of ionic species and molecules during sputter depth profiling, by introducing a power law dependence of the ion yield as a function of the oxygen surface concentration and by modelling the sputtering of monoxide molecules. The results are compared to experimental data obtained with dual beam TOF–SIMS depth profiling of ZrO2/SiO2/Si high-k dielectric stacks with thicknesses of the SiO2 interlayer of 0.5, 1, and 1.5 nm. Reasonable agreement between the experiment and the computer simulation is obtained for most of the experimental features, demonstrating the effects of ion-induced atomic relocation, i.e., atomic mixing and recoil implantation, and preferential sputtering. The depth scale of the obtained profiles is significantly distorted by recoil implantation and the depth-dependent ionization factor. A pronounced double-peak structure in the experimental profiles related to Zr is not explained by the computer simulation, and is attributed to ion-induced bond breaking and diffusion, followed by a decoration of the interfaces by either mobile Zr or O.

Ultra thin Al2O3 and HfO2 films (UP to similar to6 nm) were deposited on SiO2/Si wafers by atomic layer chemical vapour deposition (ALCVD(TM,1)) and studied by exsitu X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The thickness of these high-k layers (including the thickness of the interfacial SiO2 film) were determined by XPS and compared to the ellipsometry values. No silicate was detected at the interface. The XPS results for the bandgap (6.7 eV for Al2O3 and 5.25 eV for HfO2) are in good agreement with the SE measured values (6.26 eV for Al2O3 and 5.78 eV for HfO2). The growth rate of the high-k oxide layers and the effective attenuation length (EAL) of Si2p electrons in them were estimated; the measured EAL (2.75 nm in Al2O3 and 2.3 nm in HfO2) are in fair agreement with the NIST database values. (C) 2004 Elsevier B.V. All rights reserved.

Ultrathin (a few nm) mixed HfO2/Al2O3 oxides deposited by ALCVD on Si substrates were analyzed with low energy (250 eV) Cs- and Xe+ ions by ToF-SIMS in the dual beam mode. The analysis beam was 15 keV Ga+. Several layers were measured, with different metal ratios (Hf:Al) and different number of deposition cycles. We observed a significant enhancement of the Al (and AlOx clusters) signal at the surface along with a Hf (and HfOx clusters) depletion at the film surface. However, the thinnest films were found to contain much more Hf than the thickest ones. Several ion ratios were used (e.g. HfO+/AlO+ or HfO2-/AlO2-) in order to quantify the Hf:Al concentration ratio in the films. We found that these ratios correlate well with each other. with the metal deposition ratio, and with XPS ratios, enabling us to reconstruct the Al and Hf composition variation in the film. (C) 2004 Elsevier B.V. All rights reserved.

Due to its numerous advantages ToF-SIMS profiling has often been used in the analysis of high-k dielectrics. However, profiling high-k gate stacks induces a number of artifacts such as preferential sputtering, tailing of the metal peak in the substrate, interfacial peaks, etc. In this work, we investigated a number of sputtering conditions (Ar, Xe, Ga, energy ranging from 350 eV to 15 keV) in order to determine the most favorable sputtering condition which minimizes these artifacts. The results show that the tail of the Hf in the Si is only marginally dependent on the sputtering conditions suggesting another mechanism than collisional mixing. It also shows that even if the influence on the tail is limited, Xe profiling is far superior to Ar profiling in terms of depth resolution for the rest of the profile. Finally, this work also shows that partially oxidizing sputtering conditions lead to heavily distorted profiles.

In order to increase performance in advanced MOS devices, alternative gate insulators with high electrical permittivity are investigated to replace SiO2. Recent developments include the presence of nitrogen in or around the HfO2 stack. It is thus important to be able to acquire knowledge of the depth distribution of the nitrogen in the layers with enough accuracy. This remains a real challenge for SIMS due to varying matrices in which the nitrogen is distributed. We first present results obtained with Xe and Cs profiling. We determined the “best to use” clusters in order to retrieve the maximum information of the data. In the second part, we investigate some less standard operational mode of SIMS profiling. For instance, it has also long been considered that the detection of MCs+ clusters suffers from less matrix effect and could thus be advantageous for this kind of analysis, where the Cs surface concentration is reduced by the use of Xe–Cs co-sputtering. We also introduce a new method in order to increase the sensitivity to nitrogen by using a “carbon-based” flooding and using the CN− cluster detection.

Measuring HfO 2 /Si stacks by secondary ion mass spectroscopy (SIMS) has become a common task in the semiconductor industry. However, when analyzing these stacks with an oxygen beam, a strong impact of the experimental conditions on the Hf + signal as well on the Si signal can be observed. In order to understand these effects, we investigated the effect of oxygen on the depth profiling of these stacks using an Atomika 4500. In this paper, the ionization probability of Hf sputtered from a HfO 2 /Si stack as well a Hf implantation in Si is measured for different beam incidence angles and energies. It is shown that basically two physical mechanisms are responsible for the Hf signal intensities. The first part of the signal can be correlated with the impact of oxygen on the Hf ionization degree, in line with the classical bond-breaking theory. The second mechanism is more difficult to define, but appears linked to the emission of Hf into a different (neutral, molecules?) emission channel, thereby reducing the available Hf for detection as Hf + . Finally, a very strong influence of Hf on the Si and Si-cluster ions is reported.