High Dose Oxygen Research Articles

Oxide formation during ion bombardment of small silicon structures

The kinetics of high dose oxygen implantation and of surface sputtering in silicon are investigated by atomic force microscopy, transmission electron microscopy, transmission electron holography, and electron energy-loss spectroscopy. The implantation was performed into accurately defined submicrometer areas. The behavior of the erosion rate as a function of the implantation dose proved to be nonmonotonic. After native oxide sputtering, a period dominated by (i) implantation of oxygen and (ii) induced oxide formation with volume increase takes place, causing a maximum surface step around the bombarded area of about 1.1 to 1.3 nm at bombardment doses below 2×1016 O+ cm−2. Subsequently, higher doses cause a sputtering of the surface with a sputter yield of about 0.32 Si atoms/O+. Electron holography revealed the double layer character of the implanted region, and electron energy-loss spectroscopy, especially near the relevant Si-L23 ionization edge, identified these two layers which are (i) amorphous silicon oxide and (ii) amorphized silicon. Electron energy-loss line scans show the oxygen distribution inside the implanted areas with a lateral resolution of about 1–2 nm. It was found that the interface between the oxidized layer and the amorphized silicon sharpens with increasing implantation dose.

Nanomechanical properties of energetically treated polyethylene surfaces

The effects of energetic treatments, crosslinking, and plasma modification on the surface mechanical properties and deformation behavior of ultrahigh molecular weight polyethylene (UHMWPE) were examined in light of nanoindentation experiments performed with a surface force microscope. Samples of UHMWPE were subjected to relatively high-dose gamma irradiation, oxygen ion implantation, and argon ion beam treatment. A range of crosslinking was achieved by varying the radiation dose. In addition, low-temperature plasma treatment with hexamethyldisiloxane/O2 and C3F6 was investigated for comparison. The surface mechanical properties of the treated UHMWPE samples are compared with those of untreated UHMWPE samples used as controls. Surface adhesion measurements obtained from the nanoindentation material responses are also discussed in terms of important treatment parameters. Results demonstrate that high-dose oxygen ion implantation, argon ion beam treatment, and low-temperature C3F6 plasma modification are effective treatments for enhancing the surface mechanical properties of UHMWPE.

Amorphous structures of buried oxide in SiC-on-insulator

A buried amorphous layer in high-dose oxygen ion-implanted silicon carbide (SiC) has been characterized by transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), and energy dispersive x-ray spectroscopy. Single crystalline (0001)-oriented 6H-SiC wafers were irradiated with 180 keV oxygen ions at 650°C to a fluence of 1.4 ×1018/cm2. A fully amorphous SiO2 layer was formed insido the irradiated crystal, while the surrounded 6H-SiC exhibited minimal damage. This SiO2 layer included self-bonded carbon atoms and showed a layered structure due to compositional variations of silicon, carbon, and oxygen.

Determination of sub‐2‐nm SiO2 interlayer thickness using secondary ion mass spectrometry

AbstractThe development of secondary ion mass spectrometry (SIMS) methodology for the determination of sub‐2‐nm SiO2 interlayer thickness is reported here. The SiO2 interlayer to be evaluated is within the structure of polycrystalline Si SiO2 Si substrate. The polycrystalline Si layer can be up to a few hundred nanometers thick. The sample is analyzed by SIMS and a concentration–depth profile of oxygen is acquired. High‐energy Cs+ primary ion bombardment is used, so that the thin SiO2 layer is diluted by ion beam mixing. A 14.5 keV net impact energy provides sufficient mixing to change the composition of the interface from that of stoichiometric SiO2 to Si with a high dose of oxygen. The areal density of the interfacial oxygen peak is calibrated against a SIMS oxygen ion implant standard with a precision of better than 3%. The SiO2 thickness then is calculated with equal precision using the formula derived. In the present work, the differentiation among interfacial oxide thicknesses of 5–10 Å with a step width of 1 Å is demonstrated by this SIMS method with good precision and accuracy. Copyright © 2001 John Wiley & Sons, Ltd.

Non Destructive Determination of the Threading Dislocation Density of Smooth Simox Substrates using Atomic Force Microscopy

Abstract Atomic force microscopy (AFM) has been used extensively in recent years to study the topographic nature of surfaces in the nanometer range. Its high resolution and ability to be automated have made it an indispensable tool in semiconductor fabrication. Traditionally, AFM has been used to monitor the surface roughness of substrates fabricated by separation by implanted oxygen (SIMOX) processes. It was during such monitoring that a novel use of AFM was uncovered. A SIMOX process requires two basic steps - a high dose oxygen ion implantation (1017 to 1018 cm-3) followed by a high temperature anneal (>1200°C). The result of these processes is to form a buried oxide layer which isolates a top single crystal silicon layer from the underlying substrate. Pairs of threading dislocations can form in the top silicon layer during the high temperature anneal as a result of damage caused during the high dose oxygen implant.

The Effect of Impurities on Diffusion and Activation of ion Implanted Boron in Silicon

AbstractThe interaction between boron and silicon interstitials caused by ion implant damage is a physical process which hinders the formation of ultra-shallow, low resistivity junctions. The possibility of mitigating the effective interstitial point defect population via introduction of nonmetallic impurities in ion implanted silicon has been investigated. Amorphization of a n-type Czochralski wafer was achieved using a series of Si+ implants of 40 keV and 150 keV, each at a dose of 1×1015/cm2. The Si+ implants produced a 2800Å deep amorphous layer, which was then implanted with 8 keV 1×1014/cm2 B+. The samples were then implanted with high doses of either carbon, oxygen, sulfur, chlorine, selenium, or bromine. The implant energies of the impurities were chosen such that the damage and ion profiles of the impurity were contained within the amorphous layer. This allowed for the chemical species effect to be studied independent of the implant damage caused by the impurity implant. Post-implantation anneals were performed in a tube furnace at 750° C. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Hall effect measurements were used to study the dopant activation. Transmission electron microscopy (TEM) was used to study the end-of-range defect evolution. The addition of carbon and chlorine appear to reduce the boron diffusion enhancement compared to the boron control. Carbon and chlorine also appear to prevent boron out-diffusion during annealing compared to the control, which exhibited 20% dose loss following annealing.

High-dose oxygen ion implantation into 6H-SiC

Microstructures of oxygen ion implanted SiC have been examined using transmission electron microscopy (TEM) and scanning transmission electron microscopy equipped with an energy-dispersive x-ray spectrometer. 6H-SiC (0001) substrates were implanted with 180 keV oxygen ions at 650 °C to fluences of 0.7×1018 and 1.4×1018/cm2. A continuous buried oxide layer was formed in both samples, while the surrounding 6H-SiC contained minimal damage. These results suggest that oxygen implantation into SiC is a useful technique to establish SiC-on-insulator structures. In bright-field TEM images, the amorphous layer possessed uniform contrast in the low-dose sample, while it consisted of three distinct layers in the high-dose sample: (1) a bubbled or mottled layer; (2) a dark contrast layer; and (3) a light contrast layer. Chemical measurements revealed that the bubbled and light contrast regions have low silicon and oxygen contents, while carbon enrichment was found in these layers.

XRD, ESCA and C– V investigations of Al 2O 3 SiO 2 composite thin films synthesized by high dose oxygen ion implantation

High purity aluminium (99.999%) films were deposited onto cleaned silicon substrates. 30 keV 16O 2 + ions were implanted in Al–Si system with dose levels varying from 1 × 10 17 to 7 × 10 17 O 2 + cm −2. X-ray diffraction (XRD) studies reveal the formation of α-Al 2O 3 phase at all doses and γ-Al 2O 3 and SiO 2 phases only for high dose implants. ESCA studies for Al 2p 3/2 and Si 2p lines at various depths confirm the formation of Al 2O 3 at all doses and the gradual chemical transformation of the SiO x towards the stoichiometric composition of SiO 2 with implanted oxygen dose. The interface-state density of Al 2O 3·SiO 2–Si MOS device shows approximately U shape distribution with a discrete peak at <0.4 eV above the valence band edge.

High dose MeV oxygen ion implantation into SiC

By high-dose MeV oxygen implantation into 6H–SiC bulk crystals at temperatures between 650 ∘C and 700 ∘C buried SiC–SiO x layers were produced. In the infrared and visible region these layers exhibit a refractive index which is significantly reduced with respect to the virgin SiC making them useable as cladding layers for SiC waveguides. For the first time waveguiding at λ=633 nm was demonstrated after annealing such an ion implanted SiC–SiO x layer system.

Raman microstructural analysis of silicon-on-insulator formed by high dose oxygen ion implantation: As-implanted structures

A microstructural analysis of silicon-on-insulator samples obtained by high dose oxygen ion implantation was performed by Raman scattering. The samples analyzed were obtained under different conditions thus leading to different concentrations of defects in the top Si layer. The samples were implanted with the surface covered with SiO2 capping layers of different thicknesses. The spectra measured from the as-implanted samples were fitted to a correlation length model taking into account the possible presence of stress effects in the spectra. This allowed quantification of both disorder effects, which are determined by structural defects, and residual stress in the top Si layer before annealing. These data were correlated to the density of dislocations remaining in the layer after annealing. The analysis performed corroborates the existence of two mechanisms that generate defects in the top Si layer that are related to surface conditions during implantation and the proximity of the top Si/buried oxide layer interface to the surface before annealing.

A photoemission and XAS study of oxygen coadsorbed with a (2 × 2) layer of K on graphite

We have studied the coadsorption of oxygen with a (2 × 2) monolayer of K on graphite. At least three different adsorption phases for oxygen have been found. Different spectroscopic techniques have been used in order to identify the different oxygen species adsorbed on the surface. For low oxygen coverage, the molecules dissociate and form a K 2O species. At higher oxygen doses, K 2O 2 and KO 2 are present on the surface up to saturation coverage. XAS yields an O 2 bond length of about 1.39 Å for the KO 2 in this phase. This species is found to form an ionic complex which is weakly bound to the graphite.

Pneumocystis carinii pneumonia in Malawian children

Sixty children aged between 1 and 23 months admitted to Queen Elizabeth Central Hospital in Blantyre, Malawi for diagnosis of acute lower respiratory tract infections (ALRI) were investigated for laboratory diagnosis of Pneumocystis carinii pneumonia (PCP) by indirect immunofluorescence assay on nasopharyngeal secretions. P. carinii was found in five of the 60 children. Three PCP cases had AIDS. The clinical presentation of children with PCP was of little diagnostic value and all the children were infants. Arterial oxygen saturation was significantly lower in PCP cases. Of the five PCP cases, four died, indicating that the marked hypoxaemia was associated with poor prognosis. These results indicate that an immunofluorescence assay on nasopharyngeal secretions could be used for first-line diagnosis of PCP in Africa.

The effects of fluorine ion implantation on the formation of SIMOX structure

The effects of fluorine ion implantation on the formation and characteristics of SOI/SIMOX structure have been investigated by the combined implantation of high dose oxygen and lower dose fluorine into silicon. After high temperature annealing, fluorine atoms migrated to the Si surface, showing an anomalous out-diffusion behavior. The SOI structure is very different from that of non-fluorinated samples. A polycrystalline silicon layer was formed between the silicon overlayer and the buried oxide. Furthermore, the lower energy F + implantation affected the SOI structure more significantly and a Si-rich layer was formed in the buried oxide. The electrical properties of the silicon overlayer were analyzed by spreading resistance probe and Hall measurements. © 1997 Elsevier Science S.A. All rights reserved.

Influence of high dose and high energy oxygen implantation on the mechanical surface properties of aluminium

The increase in hardness and wear of aluminium was studied as a function of the oxygen ion implantation dose and energy. The ion energy was varied from 100 keV to 2 MeV. The maximum oxygen concentration within the implanted layer was varied in the range 20–55 at.%. The relative hardness increase due to implantation as a function of depth was studied using dynamic microhardness measurements. The maximum hardness increase varied between 1.8 and 3.5 depending on the implantation energy and fluence. The wear behaviour was investigated using a steel ball sliding on an implanted aluminium disc with ethanol as lubricant. By implantation at 100 keV, it was possible to avoid adhesive wear and cladding using a load of 200 mN. At higher implantation energies, a clear wear track was observed for this load, as for the non-implanted sample. However, the cross-sectional area of the wear track was remarkably reduced, e.g. by a factor of ten after 20 min sliding for 1 × 10 18 O + cm −2 implanted at 200 keV. The optimum wear improvement was obtained by a three-step implantation process using energies of 100 keV, 1 MeV and 2 MeV.

Improvement of the mechanical surface properties of aluminium by high dose oxygen implantation

In commercial semi-hard aluminium substrates layers with a high concentration of very small Al 2O 3 precipitates were formed by oxygen implantation in the energy range from 100 keV to 2 MeV. The depth distribution of the implanted oxygen has been determined by computer simulation and Auger depth profiling. The maximum oxygen concentration within the implanted layer covers the range from about 20 to 55 at.%. Auger electron spectroscopy is also used in order to prove the oxide formation. The depth dependence of the relative hardness increase due to the implantation has been studied using depth resolving measurements of the dynamic microhardness. The observed maximum hardness increase varies between 1.8 and 3.5 depending on implantation energy and fluence. The wear behaviour has been investigated using a steel ball sliding on the implanted aluminium disc with ethanol as lubricant. By an implantation at 100 keV it was possible to avoid adhesive wear and cladding for a load of 200 mN. Only for a load of 1.6 N the wear becomes comparable to the non-implanted state. At higher implantation energies a clear wear track is observed like for the non-implanted sample. However, the cross-section area of the wear track is remarkably reduced, e.g. by a factor 10 after 20 min sliding with a load of 200 mN for 1 × 10 18O +/cm 2 implanted at 200 keV. The optimum wear improvement has been obtained by a three step implantation using the energies 100 keV, 1 MeV and 2 MeV.

Structural defects in SIMOX

The sources of the defects in the Si-overlayer and the SiO 2 buried layer which are produced during high dose oxygen implantation and annealing treatment are discussed. These defects are related with the significant differences in the formation of thermally grown oxide and the buried oxide (BOX) in SIMOX. Trapping of Si in the BOX results in the formation of Si-islands and strained SiSi bonds. Stacking fault (SF) complexes are formed during the high temperature annealing at the back side of the Si-overlayer due to the dissolution of the SiO 2 precipitates.

Hemodynamic effects of supplemental oxygen administration in congestive heart failure

Objectives. This study sought to determine the hemodynamic effects of oxygen therapy in heart failure.Background. High dose oxygen has detrimental hemodynamic effects in normal subjects, yet oxygen is a common therapy for heart failure. Whether oxygen alters hemodynamic variables in heart failure is unknown.Methods. We studied 10 patients with New York Heart Association functional class III and IV congestive heart failure who inhaled room air and 100% oxygen for 20 min. Variables measured included cardiac output, stroke volume, pulmonary capillary wedge pressure, systemic and pulmonary vascular resistance, mean arterial pressure and heart rate. Graded oxygen concentrations were also studied (room air, 24%, 40% and 100% oxygen, respectively; n = 7). In five separate patients, muscle sympathetic nerve activity and ventilation were measured during 100% oxygen.Results. The 100% oxygen reduced cardiac output (from 3.7 ± 0.3 to 3.1 ± 0.4 liters/min [mean ± SE], p < 0.01) and stroke volume (from 46 ± 4 to 38 ± 5 ml/beat per min, p < 0.01) and increased pulmonary capillary wedge pressure (from 25 ± 2 to 29 ± 3 mm Hg, p < 0.05) and systemic vascular resistance (from 1,628 ± 154 to 2,203 ± 199 dynes's/cm5, p < 0.01). Graded oxygen led to a progressive decline in cardiac output (one-way analysis of variance, p < 0.0001) and stroke volume (p < 0.017) and an increase in systemic vascular resistance (p < 0.005). The 100% oxygen did not alter sympathetic activity or ventilation.Conclusions. In heart failure, oxygen has a detrimental effect on cardiac output, stroke volume, pulmonary capillary wedge pressure and systemic vascular resistance. These changes are independent of sympathetic activity and ventilation.

High-dose oxygen ion implanted heterointerfaces in silicon

Emitter-base band gap differentials realized with alloys such as Si x Ge 1− x , SiC x and μc-Si:H have been widely investigated for stretching the performance of Si bipolar transistors. We report on the properties of wide-gap surface regions generated in crystalline Si (c-Si) by high-dose oxygen ion implantation. The electrical and physical property changes of crystalline Si after substoichiometric O ion implantation have been investigated using current-voltage, capacitance-voltage, spreading resistance, secondary ion mass spectroscopy, spectroscopic ellipsometry and Fourier transform infrared spectroscopy. A key finding is the presence of donors in the vicinity of the implanted region, resulting in extensive counterdoping of p-type c-Si. Redistribution of the oxygen atoms during the high-temperature (1200°C) anneal results in sharp interfaces aiding the formation of the heterojunction. Mesa-type diodes on the implanted sample exhibit excellent rectification with diode ideality factor of 1.2, and a room temperature reverse saturation current density of 1 × 10 −8 A/cm 2 with a thermal activation energy of 0.92 eV.

Sharp 1.54 µm luminescence from porouserbium implanted silicon

Sharp luminescence at 1.54 µm from erbium doped porous silicon has been observed. The silicon was made porous after implantation of high doses of erbium and oxygen into p-type Czochralski silicon. The erbium related luminescence from porous silicon is an order of magnitude more intense than that from erbium doped single crystal silicon.

Defect formation in oxygen-multiply implanted silicon-on-insulator material

High dose oxygen implantation (SIMOX) has been a successful fabrication technology of silicon-on-insulator (SOI) material for CMOS circuits with reduced power consumption and higher operating speed. However, high density (~108 cm-2) of the through-thickness defects (TTD) in the top Si layer of SIMOX is one of the most serious problems. Hill et al. reported multiple implant/anneal method to remarkably reduce defect densities to &lt;104 cm-2. In the multiple implant/anneal material, however, ~106 cm2 of the final dominant defects, including stacking fault pyramids (SFP) and the precipitate-dislocation complexes (PDC), still remained after high temperature annealing. In this work, the microstructures and formation mechanism of the final defects were studied by various TEM techniques.Silicon (100) wafers were sequentially triple implanted to doses of 6/6/6×l017 at 200kev and 620°C. After each implantation the wafers were held at 1000°C for 2 hours and annealed at 1325°C for 4 hours in argon ambient plus 5% oxygen. Cross-section (XTEM) and plan-view (PTEM) transmission electron microscopy specimens were examined by using a weak beam dark field (WBDF) and high resolution electron microscopy (HREM) techniques in JEM 2000FX and Topcon 002B operating at 200kev.