PHYSICAL MODELING OF ELECTRICAL AND DIELECTRIC PROPERTIES OF HIGH-k Ta2O5 BASED MOS CAPACITORS ON SILICON

In this paper we present an integral physical model for describing electrical and dielectric properties of MOS structures containing dielectric stack composed of a high-k dielectric (with emphasize on pure and doped Ta2O5) and an interfacial silicon dioxide or silicon oxynitride layer. Based on the model, an equivalent circuit of the structure is proposed. Validity of the model was demonstrated for structures containing different metal gates (Al, Au, Pt, W, TiN, Mo) and different Ta2O5 based high-k dielectrics, grown of bare or nitrided silicon substrates.The model describes very well the I-V characteristics of the considered structures, as well as frequency dependence of the capacitance in accumulation. Stress-induced leakage currents are also effectively analyzed by the use of the model

Manufacturable process and tool for high performance metal/high-k gate dielectric stacks for sub-45 nm CMOS & related devices

Off state leakage current related power dominates the CMOS heat dissipation problem of state of the art silicon integrated circuits. In this study, this issue has been addressed in terms of a low-cost single wafer processing (SWP) technique using a single tool for the fabrication of high-κ dielectric gate stacks for sub-45 nm CMOS. A system for monolayer photoassisted deposition was modified to deposit high-quality HfO2 films with in-situ clean, in-situ oxide film deposition, and in-situ anneal capability. The system was automated with Labview 8.2 for gas/precursor delivery, substrate temperature and UV lamp. The gold-hafnium oxide-aluminum (Au-HfO2-Al) stacks processed in this system had superior quality oxide characteristics with gate leakage current density on the order of 1 x 10-12 A/cm2 @ 1V and maximum capacitance on the order of 75 nF for EOT=0.39 nm. Achieving low leakage current density along with high capacitance demonstrated the excellent performance of the process developed. Detailed study of the deposition characteristics such as linearity, saturation behavior, film thickness and temperature dependence was performed for tight control on process parameters. Using Box-Behnken design of experiments, process optimization was performed for an optimal recipe for HfO2 films. UV treatment with in-situ processing of metal/high-κ dielectric stacks was studied to provide reduced variation in gate leakage current and capacitance. High-resolution transmission electron microscopy (TEM) was performed to calculate the equivalent oxide thickness (EOT) and dielectric constant of the films. Overall, this study shows that the in-situ fabrication of MIS gate stacks allows for lower processing costs, high throughput, and superior device performance

Hafnium oxide-based dielectrics by atomic layer deposition

In 2007 there was an important change in the architecture of nanotransistors - the building blocks of modern logic and memory devices. This change was from utilising thermally grown silicon dioxide as a dielectric to so-called high-_ hafnium oxide dielectrics grown by atomic layer deposition. The _rst production logic devices of this era used a hafnium oxide dielectric layer deposited by thermal atomic layer deposition; using HfCl4 and H2O as the precursors. Present day fabrication makes use of hafnium oxide-based atomic-layer-deposited dielectric _lms. The latest nanotransistor devices utilise a third generation hafnium oxide-based dielectric material. This thesis examines hafnium oxide-based thin _lm dielectric materials prepared by thermal atomic layer deposition on silicon substrates. Speci_cally the enhancement of the dielectric response of hafnium oxide by the addition of other elements is examined. Two ternary materials systems were deposited by thermal atomic layer deposition and analysed: titanium-hafnium oxide and cerium-hafnium oxide. Hafnium oxide _lms were deposited to be used as measurement benchmarks. Cerium oxide _lms were also deposited and analysed in their own right as potential dielectric layers. The hafnium oxide and both ternary deposition experiments used (MeCp)2Hf(OMe)(Me) as the hafnium precursor. The titanium-hafnium oxide growth used Ti(iOPr)4 as a titanium source and the cerium oxide and cerium-hafnium oxide work utilised Ce(mmp)4 as a cerium source. Post-deposition specimen sets consisted of an as-deposited sample, a sample spike-annealed in N2 at 850 _C and a sample annealed for 30 minutes at 500 _C. These annealing regimes were performed to mimic typical gate-_rst and gate-last transistor processing steps. The compositions and thicknesses of the _lms were measured using medium energy ion scattering. The structure of the _lms was analysed by X-ray di_raction and Raman spectroscopy. Capacitance-voltage and current density- _eld measurements were taken from fabricated MOS capacitor specimens to assess the dielectric response of the _lms. X-ray di_raction and Raman measurements showed that un-doped HfO2 had monoclinic crystallinity as-deposited and after the two annealing regimes. The dielectric constant and leakage current density, 17 and 1.7_1

Effect of thermal annealing treatments on the optical and electrical properties of aluminum-doped, amorphous, hydrogenated silicon carbide thin films

In this work, a systematic study of the structural, optical and electrical properties of aluminum doped hydrogenated amorphous silicon carbide (Al-doped a-SiC:H) thin films grown by radio frequency magnetron sputtering is presented. The samples were grown using a high purity Al and SiC targets in a hydrogen-rich atmosphere and then were subjected to a rapid thermal annealing processes with temperatures of up to 600 °C. The film thickness ranged from 321 nm to 266 nm. The amorphous nature of the thin films was confirmed by X-ray diffraction measurements before and after the annealing treatments. Fourier transform infrared spectroscopy analysis revealed the different heteronuclear bonds present in the samples, whilst Raman spectroscopy showed the different homonuclear bonds present in the material. The evolution of the latter bonds with annealing temperature was assessed, showing a change in the structure of the thin film. Energy-dispersive X-Rays Spectroscopy confirmed the incorporation of aluminum in the amorphous silicon carbide matrix. UV-VIS Transmittance spectra revealed optical parameters such as Tauc energy bandgap, Iso-absorption energy bandgap and refractive index. Furthermore, the bandgap is also determined by means of a recently developed band-fluctuation model. In addition, electrical resistivity is determined by means of a four-probe Van Der Pauw method. Only the samples annealed at 600 °C exhibited contacts with an Ohmic behavior. The annealed films exhibited lower resistivities than the as-deposited ones, probably due to a thermal-induced reordering of the atoms. This reordering is shown in the variation of the Urbach energy which is related to an increase in the Si-C bond density, due to the dissociation of the hydrogen-related bonds.En este trabajo de tesis se presenta el estudio las propiedades estructurales y optoelectrónicas de carburo de silicio amorfo hidrogenado dopado con aluminio fabricado mediante pulverización catódica de radio frecuencia. Las muestras se fabricaron usando target de SiC y Al de alta pureza en atmosfera de hidrogeno. Luego las películas fueron calentadas hasta la temperatura de 600°C en un horno de rápido procesamiento térmico. La difracción de rayos X confirma la naturaleza amorfa de las películas. Los espectros de absorción infrarroja muestran los diferentes enlaces hetero-nucleares mientras que la espectroscopia Raman nos muestra los diferentes enlaces hononucleares presentes en la muestra. Se evaluó la evolución de los últimos enlaces con el tratamiento térmico, mostrando un cambio en la estructura del material. Espectroscopía de dispersión de energía de rayos X nos muestra la incorporación de aluminio en la matriz de carburo de silicio amorfo. Los espectros de transmitancia UV-VIS revelan parámetros ópticos tales como energía de Tauc, energía de Iso- absorción, energía de Tauc e índice de refracción. Además, el modelo de fluctuación de bandas desarrollado recientemente nos permite determinar los bordes de movilidad y energía de Urbach. Adicionalmente, el método de Van Der Pauw nos permite determinar el valor de la resistividad eléctrica de la muestra, solo a 600°C, donde se obtuvo un comportamiento óhmico mostrando baja resistividad eléctrica, probablemente debido a un reordenamiento de los átomos inducidos térmicamente. Este reordenamiento estructural se muestra en la variación de la energía de Urbach que está asociada con el aumento de la densidad de enlaces Si-C, debido a la disociación de los enlaces relacionados con el hidrogeno.Tesi

Investigation of high-K gate dielectrics for advanced CMOS application

Ph.DDOCTOR OF PHILOSOPH

Study on advanced gate stack using high-k dielectric and metal electrode

Ph.DDOCTOR OF PHILOSOPH

CONSIDERATION OF CONDUCTION MECHANISMS IN HIGH-K DIELECTRIC STACKS AS A TOOL TO STUDY ELECTRICALLY ACTIVE DEFECTS

In this paper conduction mechanisms which could govern the electron transport through high-k dielectrics are summarized. The influence of various factors – the type of high-k dielectric and its thickness; the doping with a certain element; the type of metal electrode as well as the measurement conditions (bias, polarity and temperature), on the leakage currents and dominant conduction mechanisms have been considered. Practical hints how to consider different conduction mechanisms and to differentiate between them are given. The paper presents an approach to assess important trap parameters from investigation of dominant conduction mechanisms

Characterization of high-κ dielectrics on Germanium

This study explores and describes the interface properties of various high-k materials deposited on the Ge substrate. Deposition/ growth of these material films has been achieved using multiple techniques such as atomic layer deposition (ALD), molecular beam epitaxy and thermal growth. High dielectrics (k) materials based on metal (4d and 5d) such as Y2O3, ZrO2, HfO2, Ta2O5, and from the lanthanide series, La2O3 and Tm2O3 were deposited on germanium and characterized to find out interface quality and band offset between Ge substrate and the oxides. Additionally, Al2O3 was considered, both as an interface barrier layer and as a high –k layer. Material and interface characterization was done using atomic force microscopy (AFM), capacitance-voltage (C-V), current-voltage (I-V), Variable Angle Spectral Ellipsometry (VASE), X-Ray diffraction (XRD), and X-ray photoelectron Spectroscopy (XPS) including the post growth micro-structural and compositional analysis using high resolution transmission electron microscope (HRTEM). Various physical and electrical studies were performed based on the above mentioned characterization techniques. The high-k material / Ge interface has been studied systematically using XPS and VASE characterization, considering the effects of temperature and thickness during deposition. Two germanium interface engineering methods were developed and discussed: (i) germanate formation using La2O3 and Y2O3, and (ii) using Al2O3 and Tm2O3 as barrier layers, and S passivation for Ta2O5 films. Based on the physical and electrical characterization carried out in this work, Ge interface engineering using rare-earth material inclusion happens to be a promising route to fabricate Ge CMOS devices with high performance. This statement is supported by the fact that these high-k materials provide a defect free interface and reduce the possibility of unstable GeOx formation at the interface, hence improving the interface quality. Post deposition annealing effects on Tm2O3 has been analysed using XPS and VUV-VASE. The stack prepared for the purpose was of EOT (equivalent oxide thickness) ~5 nm Tm2O3/epi-Ge/Si. Study with Tm2O3 presented 3 main findings, i) Valence band offset estimation using Kraut’s method was consistent within the experimental error, and found to be 3.05 ± 0.2 eV, ii) the VBO for thermal GeO2/Ge stack was found to be matching with the recently reported value by Toriumi’s group. The value of conduction band offset was estimated to be higher than 1 eV, indicating the favorability of GeO2 as a passivation layer for Ge, iii) the reactivity of Tm2O3 on Ge was found to be even lower than that of Si, indicating the possibility of a desirable interface. This thesis further explores the use of hafnia and alumina with Sulphur (S) passivated and un-passivated Ge samples. For this purpose HfO2/Ge and Al2O3/Ge stacks were prepared using ALD technique. It was observed that using H2O with O plasma, reduces the purge time and gives low carbon incorporation from metals. Hence O plasma and H2O were used as oxidizing agents and the interface properties were studied systematically, which is a new contribution by this work. Further the effects of adding TiO2 contents to HfO2 layer on interface properties were studied, using Al2O3 (0.3 nm) as surface passivation.In this work the achieved EOT of HfO2 with the controlled introduction of TiO2 was ~ 1.3 nm, giving a leakage current as low as10-7 A/cm-2 at ±1 V, which is in the acceptable limits. Finally, Ta2O5 films were characterized on Ge for band line up with respect to Ge. The deposition of the films was done by ALD technique at 250 °C. The analysis was done on both S passivated and un-passivated samples. The band line up parameters were estimated using XPS and it was observed that the valence band offset for S passivated sample was 2.67 eV whereas it was 2.84 eV for un-passivated Ge sample. Ta2O5 reflected a band gap of 4.44 eV (estimated from the energy loss spectrum of O1 s core level) for a 20 nm thick film deposited by ALD. Hence this thesis will cover the high-k materials and their application as a gate oxide and also the passivation layer for Ge substrates for Ge CMOS devices

Perovskite oxynitride dielectrics

PhD thesisThe synthesis, crystal structures and dielectric properties of perovskite oxynitrides of the type LnTiO2N (Ln = La, Nd and mixtures) and ATaO2N (A = Ca, Sr, Ba and mixtures), have been investigated. The end-member oxynitrides and their associated LaxNd1-xTiO2N, CaxSr1-xTaO2N and BaxSr1-xTaO2N solid solutions were successfully prepared by ammonolysis of the appropriate precursor oxides at temperatures in the range 900-1200ºC. The complete range of LaxNd1-xTiO2N solid solution are orthorhombic perovskites, which show a small increase in unit cell parameters with increasing La content across the range. Compositions in the CaxSr1-xTaO2N series are tetragonal for x 0.6. BaxSr1-xTaO2N solid solutions are tetragonal for x 0.5. It was impossible to form any perovskite solid solution in the BaTaO2N-CaTaO2N series. Attempts were made to densify these oxynitrides by hot-pressing and spark plasma sintering, but a characteristic of all these oxynitride structures is that they are stable up to relatively low temperatures (1250oC) with decomposition occurring before any sintering can be achieved. A reducing environment is necessary to prevent oxidation, but this must not be too reducing to promote conversion of the transition metal into a lower oxidation state. As a result, fully dense samples were not obtained and dielectric property measurements could not be made on these samples. As an alternative, pure single phase LaTiO2N, NdTiO2N and LaxNd1-xTiO2N solid solutions were prepared as » 3 μm thick surface layers on dense pellets of the corresponding La2Ti2O7, Nd2Ti2O7 and (LaxNd1-x)2Ti2O7) oxides by ammonolysis. The bulk dielectric properties of these VI coated samples were then measured by LCR bridge techniques. The presence of an oxynitride layer significantly increased the measured dielectric constant of all samples, compared with the pure oxides, but a significantly higher dielectric loss was also observed. This lossy behaviour is believed to be due to the presence of a more conductive region of reduced La2Ti2O7 (of typical composition 2 2 7 La TiIV TiIIIO -x x -z ) situated immediately below the oxynitride layer, produced during synthesis by the presence of hydrogen in the nitriding ammonia atmosphere. The dielectric constant of all these oxynitrides was also measured in particulate form by impedance analysis of slurries and the dielectric constant calculated by a method of mixtures. Compared with the parent oxides, the dielectric constants were noticeably larger, ranging from 100-1500. These values are in reasonable agreement with the limited amount of data available in the literature, and show that this group of materials merits further exploration, providing easier synthesis routes can be developed, which also result in low loss final materials being obtained