As-grown SiO Research Articles

Influence of nitrogen incorporation in ultrathin SiO 2 on the structure and electronic states of the SiO 2/Si(100) interface

The vibrational and electronic structures of N 2O-annealed SiO 2 layers on Si(100) have been studied by infrared absorption and photoemission measurements in comparison with those of as-grown SiO 2/Si(100) without N 2O annealing. The analysis of N1s core spectrum as a function of the distance from the SiO 2/Si interface shows that nitrogen atoms pile up in the SiO 2 network within ∼2 nm from the interface. The frequency change in the LO-phonon mode for N 2O-annealed SiO 2 indicates that three-coordinate nitrogen atoms, whose concentration is a few atomic percent in the interfacial region, relax built-in compressive stress in the oxide network near the interface. The energy loss spectra of O1s photoelectrons and the valence band spectra exhibit no changes in the oxide bandgap and the valence band offset, respectively, being consistent with a theoretical prediction for compressed SiO 2 glass. On the other hand, the gap state density above midgap in Si bandgap is significantly decreased by nitrogen incorporation with such a low level, which might be involved with the structural relaxation near the interface.

Electron trapping probabilities in hydrogen ion implanted silicon dioxide films thermally grown on polycrystalline silicon

Fowler–Nordheim tunneling currents in hydrogen ion implanted and as-grown SiO2 films, thermally grown on polycrystalline silicon(polysilicon), have been investigated. The ion implantation is performed through the SiO2 films for hydrogenation of the grain boundary states in the polysilicon layer on which the SiO2 is grown. A model of Groeseneken and Maes is used to include in the calculations the field enhancement caused by asperities at the SiO2–polysilicon interface. The oxide field reduction, caused by electron capture in initially neutral electron traps into the SiO2, is also modeled. Electron trapping probabilities, defined as the product of the bulk electron trap density in SiO2 and the electron capture cross section of the traps are determined in both as-grown and hydrogen ion implanted oxides. In the hydrogen ion implanted oxides electron trapping probabilities higher than three orders of magnitude are obtained. Native electron traps in the as-grown oxides with capture cross section of the order of 10−20cm2, as well as ion implantation generated electron traps with capture cross section of the order of 10−18cm2 are deduced from the calculated trapping probabilities.

XRR and XPS studies of SiO2 thin films formed by r.f. magnetron sputtering

Grazing-incidence x-ray reflectivity has been exploited to study as-grown SiO 2 thin films deposited on Si(100) substrates by radio-frequency (r.f.) magnetron sputtering under various substrate temperatures and gas flow conditions. Results indicate that an increase of substrate temperature from room temperature to 763 K only slightly decreases the surface roughness. Comparatively, the surface morphology is strongly controlled by the gas flow conditions during deposition. The surface roughness increases almost linearly from 0.51 to 2.38 nm as the argon gas flow is increased from 8 to 50 sccm. The chemical state and composition of the films were analysed by XPS.

Temperature dependence of SiO2/Si interfacial structure formed by radio-frequency magnetron sputter deposited SiO2 thin films on Si(111)

X-ray reflectivity has been used to characterize the interfacial structure of as-grown SiO2 layers deposited on Si(111) substrates by rf magnetron sputtering under different substrate temperatures. Results indicate that there exists a higher-density interfacial layer between crystalline Si and the amorphous SiO2 overlayer. As the substrate temperature was increased from 200 to 620 °C, the density of the interfacial layer increased from 2.37 to 2.67 g/cm3, and the thickness of the interfacial layer also increased slightly.

O 2 18 isotope labeling studies of stress effect on oxidation kinetics

It is observed that in sequential two-step thermal oxidation in dry O2 at 800 °C with Ar annealing at 1100 °C following the first oxidation, the oxidation rate increases by nearly four times at the early stage in the second oxidation. Because an intrinsic stress of about 1.4×109 dyne/cm2 induced during the thermal oxidation in the as-grown SiO2 films was sufficiently relaxed following the annealing, the increase in the oxidation rate is supposed to be due to relaxation of the intrinsic oxide stress. For the purpose of investigating this stress effect in terms of the oxygen transport mechanism during thermal oxidation of silicon, O218 isotope oxidation is performed and the isotope profiles in oxides are measured by secondary ion mass spectroscopy. It is found that the bulk O18 concentration in the annealed oxide is much higher than that in the unannealed oxide and increases with the annealing temperature. This strongly suggests that the increase in oxygen concentration is due to the stress relaxation. Since the bulk O18 concentration in the oxide annealed at 1100 °C is over three times higher than that in the unannealed oxide, the increase in oxygen concentration is most likely the cause for the enhanced oxidation. The mechanism of the stress effect is discussed. Furthermore, it is found that the oxygen concentration in oxide on the (111) Si substrate is higher than that on the (100) Si substrate. This could also be explained by the stress effect.

MBE growth and characterization of buried silicon oxide films on Si(100)

Silicon molecular beam epitaxy (Si-MBE) has been used to produce silicon oxide (SiO x ) films by evaporating Si on a heated Si(100) substrate in an ultra high vacuum system with an O 2 pressure of 10 −6 to 10 −4 mbar. Then the SiO x films were overgrown with pure Si. The influence of the substrate temperature, the O 2 pressure and the Si deposition rate on the oxygen content in the SiO x films and on the crystalline quality of the Si top-layer was investigated by Rutherford backscattering spectrometry and ion channeling. Epitaxial growth of the Si top-layer was observed up to a maximum concentration of ≈20 at.% oxygen content in the SiO x film. Cross-sectional transmission electron microscopy shows that the structure of the SiO x film changes duringa subsequent annealing procedure. Electron energy loss spectrometry proves that amorphous SiO 2 is formed and the development of holes indicates that the density of the as-grown SiO x film is much lower than that of SiO 2. The specific for the as-grown SiO x films was determined by I– V measurements.

Degradation of silicon dioxide during selective silicon epitaxy in a dichlorosilane environment

The electrical degradation of dry thermal SiO2 upon exposure to selective silicon epitaxy using dichlorosilane has been investigated. Capacitors were fabricated with thermal gate oxides (120 to 440A thick) grown on p-type silicon (100) substrates. Prior to the gate electrode formation, the oxides were exposed to hydrogen and dichlorosilane + hydrogen anneals. Leakage current and electric field breakdowns were measured to evaluate the effects of these anneals on the SiO2 degradation. The SiO2 degradation occurring because of dichlorosilane exposure was studied as a function of the temperature and time. While dichlorosilane exposure at temperatures above 850°C was found to cause high leakage current and breakdowns at low electric fields for silicon dioxide films thinner than 440A, little effect was observed as a result of hydrogen and chlorine exposures. The degradation mechanism was attributed to pinhole etching via volatile SiO formation along defects present in the as-grown SiO2.

Self-Assembling Formation of Silicon Quantum Dots by Low Pressure Chemical Vapor Deposition

AbstractThe growth of Si dots on thermally-grown SiO2/c-Si from a thermal decomposition of pure silane has been systematically studied in the temperature range from 500 to 650°C. It has been suggested mat the Si dot height and dot diameter on as-grown SiO2 are rate-limited by the cohesive action of adsorbed precursors and the thermal decomposition of silane on Si nucleation sites, respectively. The nucleation site on as-grown SiO2 is likely to be generated by the thermal dissociation of surface Si-O bonds. It has been also found that in Si dot formation on OH-terminated SiO2 surface the nucleation density is dramatically enhanced and consequently the dot size and its distribution become small. This implies that surface OH bonds can provide the nucleation sites.

Chemical States of Bromine Atoms on SiO2 Surface after HBr Reactive Ion Etching: Analysis of Thin Oxide

Low-energy ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS) have been used to determine the nature of Br atoms on very thin thermal silicon dioxide (approximately 5 nm) after HBr reactive ion etching (RIE). The result of ISS clarified that the etched surface was covered with 1 monolayer Br. The Br atoms on the etched SiO2 surface were found, from the result of XPS analysis, to have two chemical adsorption states. The experiment of atomic Br exposure showed that one adsorption state was on the as-grown SiO2 surface and the other state was at the damaged sites induced by ion bombardment.