Ultrathin Silicon Oxide Films Research Articles

Effects of nitric-oxide-plasma treatment on the electrical properties of tetraethylorthosilicate-deposited silicon dioxides on strained-Si1−xGex layers

Gate-quality ultrathin silicon dioxide films on strained-Si0.74Ge0.26 layers have been deposited by microwave plasma-enhanced chemical vapor deposition technique using tetraethylorthosilicate. Effect of nitric-oxide (NO)-plasma treatment on the electrical properties of the deposited oxides have been studied using a metal–insulator–semiconductor structure. A significant improvement in the interface trap level density (Dit) and charge trapping behavior under Fowler–Nordheim constant current stressing is observed for NO-plasma treated deposited oxide films.

Nanometer-scale Ge selective growth on Si(001) using ultrathin SiO 2 film

We performed nanometer-scale Ge selective growth using ultrathin silicon dioxide film on Si(001) surfaces. Growth was observed in real time by scanning tunneling microscopy (STM). Window areas with a size of 10–50 nm were fabricated using two different methods: void formation during thermal decomposition of the oxide and field-emission electron-beam irradiation from an STM tip. Selective epitaxial growth was achieved by introducing germane gas (GeH 4). With the first method, 3D nucleations occurred near the periphery of the voids and several Ge clusters of irregular shape grew. With the second method, 3D nucleations occurred at the center of the window, and several clusters coalesced forming one hut cluster. The second method was used to form a nanometer-scale Ge dot array.

Density difference related to humidity during dry oxidation for ultrathin silicon oxide films

The densities of 3.5–6.5-nm-thick silicon oxide films grown on p-type Si(100) at humidities during dry oxidation of 0.5–1.0, 10–100 ppb and 200–500 ppm were determined by charged-particle activation analysis. It was confirmed that the density increases with decreasing humidity and its level is separated into two groups: an ultradry oxidation group that includes the films oxidized at a humidity of less than 100 ppb and a conventional dry oxidation group at a humidity of more than 200 ppm. Since similar humidity dependence was confirmed for several fundamental structural and electrical evaluations, the oxide becomes a homogeneous stoichiometric SiO2 compound and its quality approaches an intrinsic level by dehydrating. These strong similarities also suggest that all the humidity dependence possibly originates from a common cause—the slight microscopic structural change in the oxide near the interfaces. By dehydrating, therefore, its atomic arrangement may be efficiently transferred to a more stable state, and then consequently, the earlier humidity dependence would be confirmed.

A quantitative analysis of stress-induced leakage currents and extraction of trap properties in 6.8 nm ultrathin silicon dioxide films

An analytical model for the quantitative analysis of stress-induced leakage currents (SILC) in ultrathin silicon dioxide films is described, which enables the extraction of trap parameters, e.g., trap site location. Assuming a two-step trap-assisted inelastic tunneling mechanism, the conduction of electrons through the silicon dioxide film proceeds as follows: First, electrons tunnel from the cathode into neutral trap sites followed by an energy relaxation into the lowest available energy state of these trap sites. Finally, the electrons reach the anode by a direct tunneling process. We applied this model to the SILC characteristics of a stressed 6.8 nm ultrathin silicon dioxide film. The following parameters could be deduced: The trap sites are located at 4.47 nm relative to the cathode interface with a trapped sheet charge density of |6.54×10−8| C/cm2, and a trap state energy of 2.3 eV relative to the conduction band edge of the silicon dioxide.

Control tribological and mechanical properties of MEMS surfaces. Part 2: nanomechanical behavior of self-lubricating ultrathin films

Results of nanomechanical studies of ultrathin silicon dioxide and silicon nitride films are discussed. Films applicable to MEMS technology were manufactured on single-crystal silicon wafer’s at atmospheric perssure by the glow discharge technique.

Isotopic substitution of Si during thermal growth of ultrathin silicon-oxide films on Si(111) inO2

The transport of Si atoms during thermal growth of silicon-oxide films on silicon in dry ${\mathrm{O}}_{2}$ was investigated by isotopic substitution of Si. The experiment consisted of depositing a 7.6-nm-thick epitaxial layer of ${}^{29}\mathrm{Si}$ on a Si(111) substrate and determining the ${}^{29}\mathrm{Si}$ profiles, with subnanometric depth resolution, before and after oxidation in 50 mbar of dry ${\mathrm{O}}_{2}$ at 1000 \ifmmode^\circ\else\textdegree\fi{}C for 60 min. The results constitute an experimental confirmation of a widely held belief that Si does not diffuse through the growing oxide to react with oxygen at the gas/oxide interface, leaving ${\mathrm{O}}_{2}$ as the only mobile species.

Ultrathin silicon oxide film on Si(100) fabricated by highly concentrated ozone at atmospheric pressure

We have investigated ultrathin silicon oxide film growth by highly concentrated ozone at atmospheric pressure. Oxide film >2 nm was grown on as-received Si(100) even at room temperature. The etching rate by dilute hydrofluoric acid solution of oxide fabricated on Si(100) at 350 °C by this method was almost the same as that of thermally grown oxide so that film density is equivalent to that of thermally grown oxide. The etching rate of this film also shows no dependence on the film depth. This is indicating that the transition layer due to the lattice mismatch of substrate and oxide is limited within a thinner region than that of thermally grown oxide. It also indicates that an oxide film with higher film density can be synthesized on the surface with preoxide film already formed to protect bare substrate surfaces.

Growth and characterization of ultrathin nitrided silicon oxide films

This paper reviews recent progress in understanding microstructural and growth-mechanistic aspects of ultrathin (<4 nm) oxynitride films for gate dielectric applications. Different techniques for characterizing these films are summarized. We discuss several nitridation methods, including thermal (oxy)nitridation in NO, N2O, and N2 as well as a variety of deposition methods. We show that a basic understanding of the gas-phase and thin-film oxygen and nitrogen incorporation chemistries facilitates the processing of layered oxynitride nanostructures with desirable electrical properties.

Hydrofluoric acid etching of ultra thin silicon oxide film fabricated by high purity ozone

Hydrofluoric acid etching indicates that ultra thin silicon dioxide film made by high purity ozone on Si(100) 2 × 1 between 300 and 700 °C has the same film density as that of thermally grown silicon dioxide for device use on Si(100) at 750 °C in a wet environment. Rate of oxide film growth > 6 Å on Si(100) 2 × 1 by ozone is, however, much lower at the substrate temperature between 300 and 500 °C than at 700 °C. This is indicating different kinetics and mechanism of oxide film growth > 6 Å by high purity ozone.

Correlation between reliability and oxidation temperature for ultra-dry ultrathin silicon oxide films

The correlation between time-dependent dielectric breakdown lifetime and oxidation temperature of 800–950°C for 3.5 and 5.0 nm thick silicon oxide films as gate insulators was investigated. To obtain ideal gate oxide films with few hydrogen-related defects and precise thickness distribution that extremely influence the lifetime, metal-oxide semiconductor diodes with the films used in the evaluation were produced by our continuous ultra-dry process. The films oxidized at 850°C showed the largest lifetimes irrespective of thickness. The enhancement, however, was confirmed only in the diodes selecting the oxidesilicon substrate interfaces as the anode-side, where the lifetime is mainly dominated. Interestingly, a similar relationship was observed in their density characteristics. This suggests that the condition near the oxide-silicon substrate interfaces is probably improved by the 850°C oxidation due to microscopic structural changes.

Non-Arrhenius temperature dependence of reliability in ultrathin silicon dioxide films

The non-Arrhenius temperature dependence observed in the charge-to-breakdown data in thin oxides is related to the temperature dependence of the defect buildup in the same films. For each temperature, this defect buildup is studied as a function of the defect generation probability and the total number of defects at breakdown. Each of these quantities is shown to have its own unique temperature dependence, which when combined gives the results observed for the charge-to-breakdown data. As the oxide layers are made thinner, the temperature dependence of the defect generation probability dominates these observations.

Thermal evolution of impurities in wet chemical silicon oxides

We have used infrared absorption spectroscopy and x-ray photoelectron spectroscopy to study the thermal evolution (under ultrahigh vacuum conditions) of ultrathin silicon oxide films grown in acid solutions (HCl, HNO3, and H2SO4). We find that adsorbed hydrocarbon contaminants dissociate and become chemically incorporated into the thin oxide as additional silicon oxide, carbide, hydride, and hydroxyl species. These species significantly influence the thermal evolution of the oxide films and persist up to the SiO desorption temperature (850–1000 °C) so that, once formed, these defects will be necessarily present in the final device structure.

Nanometer pores in ultrathin silica films prepared by self-assembly of organic spacers in an alkylsiloxane monolayer

Patterning of nanoscale pores in ultrathin silica films has been achieved via the self-organization of an organic spacer molecule in a monolayer of an alkyltrimethoxysilane. Langmuir–Blodgett films of monolayers of octadecyltrimethoxysilane (OTMS) doped with octadecylsulfonate sodium salt were deposited from a pure water subphase onto silicon substrates. The samples were heat treated at 80–101°C yielding highly condensed, molecularly flat films with good surface coverage. Removal of the organics and spacer molecules via calcination of the monolayers at 450°C for 8–10 h yielded thin (0.5–0.7 nm) silica films decorated with circular pores of uniform size, ranging from 0.8 to 400 nm dependent upon the ratio of spacer molecule to OTMS. Scanning force microscopy was used to image the nanoscale features generated in the films and also to provide some qualitative information on the mechanical properties of the films. The ability to create uniform pore sizes in metal oxide thin-films is attractive for selectively sorbent materials for sensors and separation membranes.

Development of High Purity One Atm Ozone Source - Its Application to Ultrathin SiO2 Film Formation on Si Substrate

ABSTRACTA high-concentration ozone generator operating at atmospheric pressure has been developed for fabrication of ultra thin silicon oxide films. The generator can supply atmospheric pressure of ozone jet with ozone concentration up to 80 vol%. The ozone jet is generated by desorbing ozone at nearbyn room temperature, which has been condensed on silica-gel by passing ozone/oxygen mixture gas from a commercial ozonizer at a low temperature (&lt;-50°C); at the temperature ozone is more selectively adsorbed on silica-gel than oxygen. The high purity ozone jet with a concentration of 25 vol% at a pressure of 1 × 105 Pa had so large oxidation power that SiO2 film as thick as 3.3 nm grew on a Si surface after 60 min exposure at 375°C. The density of the film was equivalent to that of the film formed by a conventional thermal oxidation process, judging from etching rate with dilute HF solution.

Ultra-thin silicon-oxide films by sputter-deposition and their application to high-quality poly-Si TFTS

This paper describes ultra-thin high-quality silicon oxide (SiO 2) films deposited at low temperature by sputtering from a SiO 2 target in an oxygen–argon mixture. SiO 2 films up to a thickness of 6.5 nm are successfully formed on polycrystalline silicon (poly-Si) films which have a surface roughness of several nanometers. The SiO 2 films show electrical properties with a sufficiently high breakdown voltage and low leakage current which are comparable with the electrical properties of the thermally grown SiO 2 film on single-crystalline Si at high temperature. Moreover, both n- and p-channel polycrystalline silicon thin film transistors (poly-Si TFTs) with ultra-thin sputtered SiO 2 films show excellent characteristics.

Interfacial Layer in Thermally-grown Ultra thin Silicon Dioxides Measured by Grazing Incidence X-Ray Reflection

The effects of oxidation temperature and post-oxidation annealing (POA) on density variation within ultra-thin (3 nm) silicon dioxide films were investigated via grazing incidence X-ray reflection (GIXR). At the SiO2/Si interface, it was found that the oxide films without POA have slightly denser layers than those of the bulk. These interfacial layers were found to be thicker for the oxide grown at a lower temperature and to become indistinguishable from the bulk of the film after POA.

Observation and creation of current leakage sites in ultrathin silicon dioxide films using scanning tunneling microscopy

We used scanning tunneling microscopy (STM) to investigate the local leakage current through ultrathin silicon dioxide (SiO2) films grown on Si substrates. Individual leakage sites, which were created by hot-electron injection from the STM tip under a high sample bias of +10 V, were identified from the local change in surface conductivity due to defect creation in the oxide films. When we reversed the stressing polarity (using a negative sample bias) no leakage sites were created in the oxide film.

Pyrolysis of Tetraethoxysilane on Mo(100) at Low Temperatures

Deposition of ultrathin silicon dioxide films on Mo(100) substrates by pyrolysis of tetraethoxysilane (TEOS) vapor has been investigated at temperatures between 300 and 860 K with X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), and infrared reflection−absorption spectroscopy (IRRAS). Up to temperatures of ∼600 K, TEOS adsorbs on the Mo surface forming an ethoxysilyl intermediate, whereas at higher temperatures SiO2 is formed during the initial exposure, as evidenced by both XPS and IRRAS data. Deposition of silicon dioxide is reaction-limited in the temperature range studied with roughly a monolayer forming on the surface at 860 K. Heating the TEOS-exposed Mo(100) surfaces to ∼1000 K yields ethylene as the predominant gas-phase decomposition product and improves both the stoichiometry and order of the films as indicated by an increase in the stretching frequency of the Si−O IRRAS peaks. A decrease in the amount of desorbed ethylene is observed as the deposition temperature increases from 300 to ∼600 K, and no significant desorption of any other decomposition products was detected at higher deposition temperatures. Carbon contamination is minimal in these SiO2 films.

Nanometer-scale germanium islands on Si(111) surface windows formed in an ultrathin silicon dioxide film

Three-dimensional Ge islands between 15 and 200 nm in size were found to grow only on Si(111) surface windows in ultrathin SiO2 film after Ge deposition and subsequent SiO2 decomposition. The size of Ge islands gradually decreased as the Ge thickness decreased. Pseudomorphic two-dimensional Ge layers with the 5×5 structure formed in surrounding areas of the windows. The windows were produced by selective thermal SiO2 decomposition induced by focused electron beam irradiation. These results suggest a new technique for nanometer-scale Ge island fabrication at given points on Si surfaces.

Cathodoluminescence Studies of Si-Sio2 Interfaces Prepared by Plasma-Assisted Oxidation and Subjected to Post-Oxidation Rapid Thermal Annealing

ABSTRACTWe have used low energy cathodolumrdinescence spectroscopy (CLS) to characterize defects at ultrathin (50 Å) silicon dioxide films, prepared on Si substrates by low-temperature plasma deposition. Variable-depth excitation with different electron injection energies provided a clear distinction between deep levels localized within the films versus at their interfaces. Defect bands are evident at 0.8 eV and 1.9 eV, characteristic of an amorphous, silicon-rich local bonding environment. Closer to the film surface, CLS reveals a defect at 2.7 eV indicative of oxygen vacancies in stoichiometric SiO2. The effect of hydrogenation at 400°C, rapid thermal annealing at 900°C, and especially the combination of both processing steps is shown to reduce the density of these defects dramatically.