Physico-chemical and electrical properties of rapid thermal oxides on Ge-rich SiGe heterolayers

Rapid thermal oxidation of high-Ge content (Ge-rich) Si_1−xGe_x (x = 0.85) layers in dry O₂ ambient has been investigated. High-resolution X-ray diffraction (HRXRD) and strain-sensitive two-dimensional reciprocal space mapping X-ray diffractometry (2D-RSM) are employed to investigate strain relaxation and composition of as-grown SiGe alloy layers. Characterizations of ultra thin oxides (∼6-8 nm) have been performed using Fourier transform infrared spectroscopy (FTIR) and high-resolution X-ray photoelectron spectroscopy (HRXPS). Formation of mixed oxide i.e., (SiO₂ + GeO₂) and pile-up of Ge at the oxide/Si_1−xGe_x interface have been observed. Enhancement in Ge segregation and reduction of oxide thickness with increasing oxidation temperature are reported. Interface properties and leakage current behavior of the rapid thermal oxides have been studied by capacitance-voltage (C-V) and current-voltage (J-V) techniques using metal-oxide-semiconductor capacitor (MOSCAP) structures and the results are reported.     

Relaxed SiGe-on-insulator with high Ge fraction obtained by oxidation of SiGe/Si-on-insulator with hydrogen ions implantation

The SiGe-on-insulator (SGOI) materials were obtained by thermal oxidation of SiGe layers on SOI wafers. As a comparison, H ions were implanted into SiGe layer of some samples before oxidation. The high degree relaxed SGOI materials with high Ge fraction were fabricated by two kinds of samples, including the samples without and with H ions implantation, and relaxation degree of SiGe layers is above 93%. The different result is that implantation of H ions decreased the oxidation rate of SiGe layer and decreased the loss of Ge in SiGe layer during oxidation. The effect of implantation of H ions is discussed in the paper.     

Effects of high-concentration phosphorus doping on crystal quality and lattice strain in SiGe HBTs

A high-concentration in-situ phosphorus-doping technique for silicon low-temperature epitaxial growth with Si₂H₆ has been developed. Growth temperature has an impact on the crystal quality and on lattice strain of phosphorus-doped silicon layers. Resistivity, micro-Raman spectroscopy, and high-resolution X-ray diffraction indicated that good crystal quality was achieved at a growth temperature of 525 °C. On the other hand, growth pressure has little influence on crystal quality or on lattice strain except for surface morphology. By optimizing epitaxial growth conditions, an extremely high concentration of phosphorous doping was achieved without a high-temperature activation annealing, and the resultant good crystal quality of the phosphorus-doped silicon layer gave a very low resistivity. Accordingly, the high-concentration in-situ phosphorus doping is a powerful technique to fabricate future ultra-high-speed SiGe HBTs.     

A Novel Super-Junction Lateral Double-Diffused Metal--Oxide--Semiconductor Field Effect Transistor with n-Type Step Doping Buffer Layer

A novel super-junction lateral double-diffused metal-oxide--semiconductor field effect transistor （SJ-LDMOSFET） with n-type step doping buffer layer is proposed. The step doping buffer layer almost completely eliminates the substrate-assisted depletion effect, modulates lateral electric field and achieves nearly uniform surface field. On the other hand, the buffer layer also provides another conductive path and reduces on-state resistance. In short, the proposed LDMOSFET improves trade-off performance between breakdown voltage （B V） and specific on-state resistance Ron,sp. Compared with the conventional SJ-LDMOSFET, the simulation results indicate that the BV of the SSJ-LDMOSFET is increased from saturation voltage 121.7V to 644.9 V; at the same time, the specific on-state resistance is decreased from 0.314 Ω.cm^2 to 0.14 Ω.cm^2 by virtue of 3D numerical simulations using ISE when the drift region length and the step number are taken as 48μm and 3, respectively.     

New Power Lateral Double Diffused Metal-Oxide-Semiconductor Transistor with a Folded Accumulation Layer

A new lateral double diffused metal oxide semiconductor field effect transistor with a double-charge accumulation layer using a folded silicon substrate is proposed to improve the performance of the breakdown voltage and specific on-resistance. Three kinds of technologies, which are the additional electric field modulation effect, majority carrier accumulation and increasing the effective conduction area, are applied simultaneously by a semi- insulating polycrystalline silicon layer deposited over the top of thin oxide covering the drift region. It is indicated that by the simulator, the ideal silicon limits of the breakdown voltage and specific on-resistance have been broken due to the complete three-dimensional reduced surface field effect and the doubled majority carrier accumulation layer.     

Strain relaxation in SiGe layer during wet oxidation process

The strain relaxation in SiGe layer on silicon substrate during wet oxidation at 1000 °C was investigated. It was proposed that the competition between Ge accumulation and diffusion led to different strain-relaxation behaviors. At the very beginning, Ge atoms at the oxidizing interface were quickly accumulated due to the high oxidation rate resulting in the additional nucleation of misfit dislocations (therefore a lot of threading dislocations) to relieve stress after the thickness of the Ge condensed layer was larger than the critical value. And then, when the Ge accumulation rate was less than the diffusion rate, Ge content started to decrease from a maximum value and the strain in the SiGe layer was mainly relieved through surface roughing and the degree of strain relaxation reached a maximum. When the samples were further oxidized, Ge accumulation could be neglected because of the self-limiting oxidation and the Ge diffusion dominated the consequent processes. As a result, Ge content at the interface was reduced, with the contribution of the strain relaxation in SiO₂ viscously, leading to the decrease of degree of strain relaxation in the SiGe layers slowly.     

Violet luminescence in Ge nanocrystals/Ge oxide structures formed by dry oxidation of polycrystalline SiGe

Nanocrystals of Ge surrounded by a germanium oxide matrix have been formed by dry thermal oxidation of polycrystalline SiGe layers. Violet (3.16 eV) luminescence emission is observed when Ge nanocrystals, formed by the oxidation of the Ge segregated during the oxidation of the SiGe layer, are present, and vanishes when all the Ge has been oxidized forming GeO₂. Based on the evolution of the luminescence intensity and the structure of the oxidized layer with the oxidation time, the recombination of excitons inside the nanocrystals and the presence of defects in the bulk oxide matrix are ruled out as sources of the luminescence. The luminescence is attributed to recombination in defects at the Ge sub-oxide interface between the Ge nanocrystals and the surrounding oxide matrix, which is GeO₂.     

Phase evolution of an aluminized steel by oxidation treatment

Effects of temperature and time on the microstructure and phase evolution for different thermal treatments were investigated with respect to the measurement of intermetallic layer thickness, phase identification and microhardness distribution in the aluminized zone of a steel substrate. The intermetallic phases present in the aluminized region after hot dip aluminizing is mainly Fe₂Al₅. The thickness of the intermetallic layers increases with increasing oxidation temperature and time. In the oxidation treatments of the aluminized steel in air, the initial Fe₂Al₅ phase remains at the temperature below 950 °C in 2-h, and the Fe₂Al₅ phase is completely transformed into low iron content Fe-Al intermetallics due to oxidation at 950 °C for 4 h. However, the Fe₂Al₅ phase remains in the outer layer of the aluminized samples diffusion-treated in vacuum regardless of diffusion time. The microhardness values of the Al₂O₃ and the intermetallic Fe₂Al₅, FeAl₂, FeAl and Fe₃Al phases are HV1150, HV1010, HV810, HV650 and HV320, respectively. The oxide layer formed on the steel substrate has an extremely fast adherence to the steel substrate and excellent properties of thermal shock resistance, high temperature oxidation resistance and anti-liquid aluminum corrosion.     

The effect of cerium and lanthanum surface treatments on early stages of oxidation of A361 aluminium alloy at high temperature

X-ray photoelectron spectroscopy analysis has been used to study the surface of A361 aluminium alloy after electrodeposition of cerium and lanthanum compounds followed by oxidation tests in air at 100-500 °C for 2 h. Cerium and lanthanum oxide deposits are found on the β-AlFeSi second phase particles and to a lesser extent on the eutectic Al-Si areas, while the α-Al phase is covered with a thin aluminium oxide film. This uneven deposition may be related either to a preferential nucleation and growth process on active interfaces or to the differing electrical conductivity of the phases and intermetallic compounds of the alloy. Initial stages of oxidation of A361 alloy disclosed thickening of the aluminium oxide layer and Mg enrichment at the surface, especially above 400 °C. Rare earth deposits revealed two different effects: reduced Mg diffusion and enhanced thickening of the aluminium oxide film. A distinctive behaviour of Ce oxide appears at 300-500 °C related with Ce(III) to Ce(IV) transition.     

Characterization of gadolinium oxide film by pulse laser deposition

In this work, Gd-oxide dielectric films were deposited on Si by pulse laser deposition method (PLD), moreover, the micro-structures and electrical properties were reported. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) indicated that Gd-oxide was polycrystalline Gd₂O₃ structure, and no Gd metal phase was detected. In addition, both interface at Si and Ni fully silicide (FUSI) gate were smooth without the formation of Si-oxide. X-ray photoelectron spectroscopy (XPS) confirmed the formation of Gd₂O₃ and gave an atom ratio of 1:1 for Gd:O, indicating O vacancies existed in Gd₂O₃ polycrystal matrix even at O₂ partial pressure of 20 mTorr. Electrical measurements indicated that the dielectric constant of Gd-oxide film was 6 and the leakage current was 0.1 A/cm² at gate bias of 1 V.     

Thermal annealing effects on a compositionally graded SiGe layer fabricated by oxidizing a strained SiGe layer

Thermal annealing effects on a thin compositionally graded SiGe buffer layer on silicon substrate fabricated by oxidizing a strained SiGe layer are investigated with X-ray diffraction, ultraviolet Raman spectra and atomic force microscopy. Interestingly, we found that the surface roughness and the threading dislocation densities are kept low during the whole annealing processes, while the Ge concentration at the oxidizing interface decreases exponentially with annealing time and the strain in the layer is only relaxed about 66% even at 1000 °C for 180 min. We realized that the strain relaxation of such a compositionally graded SiGe buffer layer is dominated by Si-Ge intermixing, rather than generation and propagation of misfit dislocations or surface undulation.     

C-V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

Electrical properties of Schottky- and metal-insulator-semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance-voltage (C-V) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance (g_m) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f_T compared with that of the Schottky-gate device. In this study, C-V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel.     

A High Performance Silicon-on-Insulator LDMOSTT Using Linearly Increasing Thickness Techniques

We present a new technique to achieve uniform lateral electric field and maximum breakdown voltage in lateral double-diffused metal-oxide-semiconductor transistors fabricated on silicon-on-insulator substrates. A linearly increasing drift-region thickness from the source to the drain is employed to improve the electric field distribution in the devices. Compared to the lateral linear doping technique and the reduced surface field technique, twodimensional numerical simulations show that the new device exhibits reduced specific on-resistance, maximum off- and on-state breakdown voltages, superior quasi-saturation characteristics and improved safe operating area.     

AC plasma electrolytic oxidation of magnesium with zirconia nanoparticles

The incorporation of monoclinic zirconia nanoparticles and their subsequent transformation is examined for coatings formed on magnesium by plasma electrolytic oxidation under AC conditions in silicate electrolyte. The coatings are shown to comprise two main layers, with nanoparticles entering the coating at the coating surface and through short-circuit paths to the region of the interface between the inner and outer coating layers. Under local heating of microdischarges, the zirconia reacts with magnesium species to form Mg₂Zr₅O₁₂ in the outer coating layer. Relatively little zirconium is present in the inner coating layer. In contrast, silicon species are present in both coating layers, with reduced amounts in the inner layer.     

Coating formation by plasma electrolytic oxidation on ZC71/SiC/12p-T6 magnesium metal matrix composite

Plasma electrolytic oxidation (PEO) of a ZC71/SiC/12p-T6 magnesium metal matrix composite (MMC) is investigated in relation to coating growth and corrosion behaviour. PEO treatment was undertaken at 350 mA cm⁻² (rms) and 50 Hz with a square waveform in stirred 0.05 M Na₂SiO₃.5H₂O/0.1 M KOH electrolyte. The findings revealed thick, dense oxide coatings, with an average hardness of 3.4 GPa, formed at an average rate of ∼1 μm min⁻¹ for treatment times up to 100 min and ∼0.2 μm min⁻¹ for later times. The coatings are composed mainly of MgO and Mg₂SiO₄, with an increased silicon content in the outer regions, constituting <10% of the coating thickness. SiC particles are incorporated into the coating, with formation of a silicon-rich layer at the particle/coating interface due to exposure to high temperatures during coating formation. The distribution of the particles in the coating indicated growth of new oxide at the metal/coating interface. The corrosion rate of the MMC in 3.5% NaCl is reduced by approximately two orders of magnitude by the PEO treatment.     

F2 laser induced oxidation of inorganic material

Transparent SiO₂ thin films were selectively fabricated on Si wafer by 157 nm F₂ laser in N₂/O₂ gas atmosphere. The F₂ laser photochemically produced active O(¹D) atoms from O₂ molecules in the gas atmosphere; strong oxidation reaction could be induced to fabricate SiO₂ thin films only on the irradiated areas of Si wafer. The oxidation reaction was sensitive to the single pulse fluence of F₂ laser. The irradiated areas were swelled and the height was approximately 500-1000 nm at the 205-mJ/cm² single pulse fluence for 60 min laser irradiation. The fabricated thin films were analytically identified to be SiO₂ by the Fourier-transform IR spectroscopy. The SiO₂ thin films could be also removed by subsequent chemical etching to fabricate micro-holes 50 nm in depth on Si wafer for microfabrication.     

Thickness determination of thin and ultra-thin SiO2 films by C-AFM IV-spectroscopy

Conductive atomic force microscopy was used to determine the electrical oxide thickness for five different silicon dioxide layers with thickness in the order of 1.6-5.04 nm. The electrical thickness results were compared with values determined by ellipsometry. A semi-analytical tunnelling current model with one single parameter set was used to superpose current/voltage curves in both the direct tunnelling and the Fowler-Nordheim tunnelling regime regions. The overall electrical oxide thickness was determined by statistical means from results of nearly 3000 IV-curves recorded for different conductive CoCr-coated tips. Good agreement between the shape of model and experimental data was achieved, widely independent of the oxide thickness. Compared with the ellipsometry value, the electrical thickness was larger by a value of 0.36 nm (22%) for the thinnest oxide and smaller by a value of 0.31 nm (6%) for the thickest oxide, while intermediate values yielded differences better than 0.15 nm (<6%). The physical differences between the measurement techniques were shown to contribute to this observation. In addition, statistical deviations between single and multiple measurements using a single tip and using a number of different tips were analysed. The causes, for example, natural oxide thickness variations, tip wear, air humidity induced effects and contaminations, are evaluated and discussed. The method proposed was able to determine the electrical oxide thickness with a standard deviation in the order of ±6-9%. The results suggest that for optimal results it is necessary to perform several repetitions of IV-measurements for one sample and, in addition, to employ more than one tip.     

C-AFM-based thickness determination of thin and ultra-thin SiO2 films by use of different conductive-coated probe tips

The influence of the probe tip type on the electrical oxide thickness result was researched for four differently coated conductive tip types using SiO₂ (oxide) films with optical thickness of 1.7-8.3 nm. For this purpose, conductive atomic force microscopy (C-AFM) was used to measure more than 7200 current-voltage (IV) curves. The electrical oxide thickness was determined on a statistical basis from the IV-curves using a recently published tunnelling model for C-AFM application. The model includes parameters associated with the probe tip types used. The evolution of the tip parameters is described in detail. For the theoretical tip parameters, measured and calculated IV-curves showed excellent agreement and the electrical oxide thickness versus the optical oxide thickness showed congruent behaviour, independent of the tip type. However, differences in the electrical oxide thickness were observed for the different tip types. The theoretical parameters were modified experimentally in order to reduce these differences. Theoretical and experimental tip parameters were compared and their effect on the differences in the electrical oxide thickness is discussed for the different tip types. Overall, it is shown that the proposed model provides a comprehensive framework for determining the electrical oxide thickness using C-AFM, for a wide range of oxide thicknesses and for differently coated conductive tips.     

The influence of oxidation with nitric acid on the preparation and properties of active carbon enriched in nitrogen

The effect of oxidation by 20% nitric acid on the properties and performance of active carbons enriched with nitrogen by means of the reaction with urea in the presence of air has been studied. The study has been made on demineralised orthocoking coal and the carbonisates obtained from it at 600 or 700 °C, subjected to the processes of nitrogenation, oxidation and activation with KOH in different sequences. The amount of nitrogen introduced into the carbon with the aid of urea has been found to depend on the stage at which the process of nitrogenation was performed. The process of oxidation of the demineralised coal and the active carbon obtained from the former has been found to favour nitrogen introduction into the carbon structure. In the process of nitrogenation of the carbonisates the amount of nitrogen introduced has inversely depended on the temperature of carbonisation. The modifications of the processes permitted obtaining materials of different textural parameters, different acid-base character of the surface and different iodine sorption capacity.     

Formation of As enriched layer by steam oxidation of As-implanted Si

Segregation of implanted As during steam oxidation of Si wafers is shown to result in a highly enriched, thin layer of As at the interface between the oxide and the underlying Si. Also, the oxidation rate was found to increase by as much as a factor of ∼2 depending on the depth distribution and fluence of the implanted As impurity. The thin As layer collected at the interface can be used in the design of very shallow junctions. This mechanism enables the formation of a narrow, degenerately doped layer of Si, which can be tailored to have a thickness of only few monolayers depending on the fluence of the implantation used.