Source/drain engineering for MOSFETs with embedded-Si:C technology

Embedded silicon carbon alloy (e-Si:C) technology for source and drain (S/D) is expected to improve nMOSFET drive current. The distribution and activation characteristics of arsenic in Si:C film and the interfacial solid-phase reaction of the Ni/Si:C system were studied with the aim of achieving the maximum improvement of the characteristics of e-Si:C S/D. It was clarified that the active carrier concentration of Si:C decreased with increasing carbon concentration compared to the control Si. There is concern that the low doping activation in Si:C increases series resistance of e-Si:C S/D nMOSFETs and degrades the performance gain expected from the strain effect.     

Enhanced strain relaxation induced by epitaxial layer growth mode of MgO thin films

Growth of MgO films on silicon substrate was conducted by KrF excimer pulsed-laser ablation system. Two kinds of growth mode were revealed in situ by reflection high energy electron diffraction. It was found that the layer growth mode of MgO thin films could remarkably reduce the misfit strain originated from the different lattice constant and thermal expansion coefficiency between MgO films and Si. An enhanced strain relaxation was discovered for MgO films, which were grown with the layer growth mode, in the film thickness range of 40-100 nm. The value of critical thickness for the formation of misfit dislocation agrees well with the calculated one. This exceptional phenomenon should be ascribed to the layer growth mode of epitaxial MgO films.     

Pulsed-laser crystallization and epitaxial growth of metal-organic films of Ca-doped LaMnO3 on STO and LSAT substrates

Ca-doped LaMnO₃ (LCMO) thin films have been successfully prepared on SrTiO₃ (STO) and [(LaAlO₃)_0.3-(SrAlTaO₆)_0.7] (LSAT) substrates using the excimer laser assisted metal-organic deposition (ELAMOD) process. The crystallization and the epitaxial growth of the amorphous metal-organic LCMO thin films have been achieved using a KrF excimer laser irradiation while the substrates were kept at constant temperature of 500 °C. Epitaxial films were obtained using laser fluence in the interval of 50-120 mJ/cm². The microstructure of the LCMO films was studied using cross-section transmission electron microscopy. High quality of LCMO films having smooth surfaces and sharp interfaces were obtained on both the STO and the LSAT substrates. The effect of the laser fluence on the temperature coefficient of resistance (TCR) was investigated. The largest values of TCR of the LCMO grown on the LSAT and the STO substrates of 8.3% K⁻¹ and 7.46% K⁻¹ were obtained at different laser fluence of 80 mJ/cm² and 70 mJ/cm², respectively.     

Heavy atomic-layer doping of B in low-temperature Si epitaxial growth on Si(1 0 0) by ultraclean low-pressure chemical vapor deposition

Electrical characteristics of B atomic-layer doped Si epitaxial films on Si(1 0 0) formed by B atomic-layer formation on Si(1 0 0) at 180 °C and subsequent capping Si deposition at 500 °C using ultraclean low-pressure chemical vapor deposition were investigated. From evaluation results of carrier concentration in the films, by low-temperature SiH₄ exposure at 180-300 °C before the capping Si deposition at 500 °C, 70% improvement of B electrical activity was confirmed, and it is suggested that lowering the temperatures for B atomic-layer formation on Si(1 0 0) as well as SiH₄ exposure before the capping Si deposition is effective to suppress B clustering and to achieve B atomic-layer doped Si films with extremely high carrier concentration.     

Thermochemical process in preparation of ZnO film by TFA-MOD method

The excess weight loss due to the evaporation of zinc compound is observed in the growth of ZnO film by trifluoroacetate metalorganic deposition (TFA-MOD) method. Higher temperature (>90 °C) aging and/or addition of monoethanolamine (MEA) are effective to prevent the evaporation of zinc compound and increase the yield of ZnO. The mechanism of preventing evaporation is that zinc trifluoroacetate is hydrolyzed into Zn₄O(CF₃COO)₆. A three-dimensional structure of Zn₄O(CF₃COO)₆ is proposed. It is shown that higher temperature aging does harm to the surface morphology of ZnO films. The addition of MEA reduces the required aging temperature thus improves the surface morphology.     

MBE growth of SiGe with high Ge content for optical applications

The molecular beam epitaxy is a powerful technology for integrating optoelectronic devices in standard Si microelectronics. The MBE growth of high speed germanium detectors is discussed. The necessary lattice accommodation between Si and Ge is realized by an ultra thin virtual substrate. Contact layers with very high doping concentration and very sharp transitions are grown with special doping strategies. As special growth method the differential epitaxy allows the growth of epitaxial layers in oxide windows.     

Structural optimization of HfTiSiO high-k gate dielectrics by utilizing in-situ PVD-based fabrication method

We investigated the optimum structure for Ti-containing Hf-based high-k gate dielectrics to achieve EOT scaling below 1 nm. TiO₂/HfSiO/SiO₂ trilayer and HfTiSiO/SiO₂ bilayer structures were fabricated by a newly developed in-situ PVD-based method. We found that thermal diffusion of Ti atoms to SiO₂ underlayers degrades the EOT-J_g characteristics. Our results clearly demonstrated the impact of the trilayered structure with TiO₂ capping for improving EOT-J_g characteristics of the gate stack. We achieved an EOT scaling of 0.78 nm as well as reduced gate leakage of 7.2 × 10⁻² A/cm² for a TiO₂/HfSiO/SiO₂ trilayered high-k dielectric while maintaining the electrical properties at the bottom interface.     

Growth and thermal stability of epitaxial BiFeO3 thin films

We have investigated the oxygen pressure and the temperature dependence on BiFeO₃ thin films deposited on SrTiO₃ substrates by pulsed laser deposition. Reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM) and X-ray diffraction measurements indicate that high-quality epitaxial thin films are obtained for and T=650 °C. Outside of this pressure-temperature window, parasitic peaks attributed to β-Bi₂O₃ appear. We find an increase of the out-of-plane lattice parameter with oxygen pressure that we ascribe to Bi-deficiency due to its high volatility at low pressure. Ex-situ anneals have been performed and results show that as-grown single-phase BiFeO₃ thin films degrade after annealing, whereas as-grown BiFeO₃ containing impurity phases evolve toward a single-phase structure. These experiments demonstrate that parasitic phases can stabilize compounds which are usually unstable in air at elevated temperatures.     

Device and performance parameters of Cu(In,Ga)(Se,S)2-based solar cells with varying i-ZnO layer thickness

In pursuit of low-cost and highly efficient thin film solar cells, Cu(In,Ga)(Se,S)₂/CdS/i-ZnO/ZnO:Al (CIGSS) solar cells were fabricated using a two-step process. The thickness of i-ZnO layer was varied from 0 to 454 nm. The current density-voltage (J-V) characteristics of the devices were measured, and the device and performance parameters of the solar cells were obtained from the J-V curves to analyze the effect of varying i-ZnO layer thickness. The device parameters were determined using a parameter extraction method that utilized particle swarm optimization. The method is a curve-fitting routine that employed the two-diode model. The J-V curves of the solar cells were fitted with the model and the parameters were determined. Results show that as the thickness of i-ZnO was increased, the average efficiency and the fill factor (FF) of the solar cells increase. Device parameters reveal that although the series resistance increased with thicker i-ZnO layer, the solar cells absorbed more photons resulting in higher short-circuit current density (J_sc) and, consequently, higher photo-generated current density (J_L). For solar cells with 303-454 nm-thick i-ZnO layer, the best devices achieved efficiency between 15.24% and 15.73% and the fill factor varied between 0.65 and 0.67.     

Fabrication of metal nano-structures using anodic alumina membranes grown in phosphoric acid solution: Tailoring template morphology

The influence of experimental parameters on the morphology of the porous structure and on the formation kinetics has been investigated for anodic alumina membranes (AAM) grown in aqueous H₃PO₄ at 160 V. It was found that pore aspect ratio and membrane porosity on the solution-side surface are influenced by tensiostatic charge, bath temperature and the presence of Al³⁺ ions in solution. Morphological and kinetic data, recorded in different conditions, give useful information on the growth mechanism of pore channels in phosphoric acid solution.Nickel nano-structures have been fabricated using AAM as template. Electroless deposition, performed by adding the reducing agent to a suitable bath in several steps, resulted in the formation of short metal nanotubes (about 5 μm long) in the upper part of the channels. Long Ni nanowires (up to 25 μm) with aspect ratio higher than 100 were obtained by pulsed unipolar electrodeposition from a Watt bath. In this case, both the influence of some experimental parameters on the nanowires growth and the fast current transients during the electrodeposition steps were analyzed.     

The influence of Mn content on luminescence properties in Mn-doped ZnO films deposited by ultrasonic spray assisted chemical vapor deposition

Mn-doped ZnO (Zn_1−xMn_xO, 0 ≤ x ≤ 0.1) films are prepared by an ultrasonic spray assisted chemical vapor deposition method. X-ray diffraction and Raman scattering show that all the Zn_1−xMn_xO films are good wurtzite structures without any impurity phases. Cathodoluminescence spectra show that ultraviolet emission and green luminescence can be observed. The intensity of ultraviolet emission decreases with the increment of x, while the intensity of green luminescence increases with the increment of x when x ≤ 0.02. However, when x (x > 0.02) is further increased, the intensity of green luminescence decreases gradually, and the green luminescence disappears when x is above 0.075. We consider that the change of the luminescence is related to the competition between the radiative recombination and the non-radiative recombination.     

Silicon-on-Nothing MOSFETs: An efficient solution for parasitic substrate coupling suppression in SOI devices

With today's technology downscaling, the coupling through the substrate becomes an important limiting factor for the performance of mixed-mode high-frequency integrated circuits, filters, convertors, transmission lines and even single MOSFETs. This paper presents original studies on the coupling through the substrate in SOI devices and on substrate engineering which allows to suppress this effect. Particular attention is paid to the Silicon-on-Nothing (SON) MOSFET architecture as one of the most promising solutions to suppress the effect of parasitic coupling through the substrate on the transistor behavior.     

The switch of the worst case on NBTI and hot-carrier reliability for 0.13 μm pMOSFETs

This investigation describes experiments on two sizes of p-channel metal-oxide-semiconductor field-effect-transistors (pMOSFETs), to study the negative bias temperature instability (NBTI) and hot-carrier (HC) induced degradation. This work demonstrates that the worst condition for pMOSFETs under HC tests occurs in CHC (channel HC, stressed at V_g = V_d) mode at high temperature. This study also shows that the worst degradation of pMOSFETs should occur in NBTI. This inference is based on a comparison of results for forward saturation current (I_ds,f) and reverse saturation current (I_ds,r) obtained in NBTI and HC tests.     

Self-limited growth of Si on B atomic-layer formed Ge(1 0 0) by ultraclean low-pressure CVD system

Utilizing BCl₃ reaction on Ge(1 0 0) and subsequent Si epitaxial growth by SiH₄ reaction at 300 °C, B atomic-layer doping in Si/Ge(1 0 0) heterostructure was investigated. Cl atoms on the B atomic-layer formed Ge(1 0 0) scarcely affect upon the SiH₄ reaction. It is also found that Si atom amount deposited by SiH₄ reaction on Ge(1 0 0) is effectively enhanced by the existence of B atomic layer and the deposition rate tends to decrease at around 2-3 atomic layers which is three times larger than that in the case without B. The results of angle-resolved X-ray photoelectron spectroscopy show that most B atoms are incorporated at the heterointerface between the Si and Ge.     

Formation of Pt-C films by ion beam assisted deposition for the application of suppression thermo-electron emission

Platinum and carbon were deposited onto the surface of molybdenum grids simultaneously by ion beam assisted deposition. The structure of the Pt-C films was studied by XRD and Raman spectroscopy. The XRD results showed that Pt exhibited mixed strong (1 1 1) and weak (2 0 0) orientations. The Raman spectra showed that the carbon existed in the form of graphite-like phase. Electron emission characteristics from the Mo grid with and without Pt-C films were measured using analogous diode method. The results showed that electron emission from the Mo grid coated with Pt-C films was much less than that from the Mo grid without Pt-C films. The obtained results demonstrated that the Pt-C films are effective grid-coating materials for the application of suppression thermo-electron emission.     

Spin-deposited nanocrystalline lithium ferrite thin films: Fabrication and characterization

Thin films of lithium ferrite (with general composition Li_0.5Fe_2.5O₄) were fabricated at low temperatures (up to 650 °C) by citrate-route using spin-deposition technique. Deposited films consisted of nanometer-sized grains as evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD patterns for annealed films showed broad peaks exhibiting a spinel phase. Size of nanocrystallites is estimated to be 3-7 nm using Scherrer's equation. Average grain size ∼8.5 nm is observed from TEM images of films annealed at 650 °C. Scanning electron micrographs show the formation of spherical aggregates of around 130 nm in diameter. The AFM analysis clearly evidenced the development of nanograins even at low (∼500 °C) annealing temperatures. Significant decrease in complex dielectric permittivity (∈′ − j∈″) with frequency is observed in the low frequency (100 Hz-1 MHz) as well as in X-band microwave frequency (8-12 GHz) region. ∈′ is found to be in the range of 15.7-33.9 in low frequency region, whereas in X-band microwave frequency region, it is found to lie between 3.9 and 4.9. Similarly, ∈″ is found to be 0.16-5.9 in the low frequency region, and 0.002-0.024 in the X-band microwave frequency region. Room temperature dc resistivity of these films is estimated to lie in the range of 10⁶-10⁸ Ω cm. These results strongly suggest that citrate-route processed nanocrystalline lithium ferrite thin films are promising candidates for monolithic microwave integrated circuits (MMICs).     

Synthesis and characterization of nanostructured bimetallic films on α-Al2O3 substrates using electroless deposition

The Pt-Pd and Pd-Ag nanostructured bimetallic films on porous α-Al₂O₃ substrates are successfully synthesized by chemical deposition using lyotropic liquid crystalline templating strategy. The co-reduction of two metallic species in the presence of liquid crystalline phase by hydrazine hydrate produces hexagonal nanostructured Pt-Pd and lamellar nanostructured Pd-Ag films. Low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies show the ordered nanostructure of both Pt-Pd and Pd-Ag films. The energy dispersive X-ray (EDX) and wide-angle XRD analyses of the bimetallic films have verified the coexistence and uniform distribution of constituent metallic species. By taking into account of catalytic activities, well-defined nanochannels and higher surface areas, the nanostructured bimetallic films might have application potential in microreactors.     

Heteroepitaxial growth of gallium nitride on muscovite mica plates by pulsed laser deposition

We have grown GaN films on mica substrates using pulsed laser deposition for the first time and investigated their structural properties using electron beam and X-ray diffraction. We found that GaN (000-1) grows on mica (001) with an in-plane alignment of [11-20] GaN//[010] mica. Despite the large lattice mismatch between GaN and mica, 6 and 43% along the [100] mica and [010] mica directions, respectively, cubic GaN phase or 30° rotated domains are scarcely observed in the film. This phenomenon can be attributed to the enhanced surface migration of film precursors due to the large atomically flat terraces and the weak Van der Waals bonding on the mica surface.     

Magnetic properties of CoFeP films prepared by electroless deposition

Structure and magnetization of CoFeP films prepared by the electroless deposition were systematically investigated by varying the bath composition and deposition parameters to optimize soft magnetic properties. The cobalt content in the CoFeP films varies from 40.4 to 94.9 wt% by controlling the bath composition. Increase of the metallic ratio FeSO₄·7H₂O/(CoSO₄·7H₂O+FeSO₄·7H₂O) affects the films’ microstructure, which switches from amorphous to crystalline structure. The magnetic properties of CoFeP films reveal that the coercivity (H_c) values range from 80 up to 185 A/m and the saturation magnetization (M_s) from 82 to 580 eum/g depending on the bath composition, deposition parameters and heat-treatment conditions. Increase of M_s and remanent magnetization (M_r) as well as decrease of H_c are observed for the CoFeP films with bath pH, temperature and the metallic molar ratio increasing. It is also found that the H_c is enhanced with the increase of NaH₂PO₂·H₂O concentration. CoFeP films showing good soft magnetic properties with coercivities less than 140 A/m and M_s close to 600 emu/g can be obtained in high pH bath and thereafter heat treatment. The deposit is found to be suitable as soft magnetic materials for core materials.