Single-crystal Silicon Surface Research Articles

Kinetics of TiSi 2 thin film formation at a single-crystal silicon surface by Ti ion irradiation

In the present study a general growth sequences is noted in which thin amorphous Ti films are formed at initial stages (the growth kinetic is described by a straight-line dependence). Complicated phases of silicides grow subsequently in accordance with Avrami's equation. The process of subsequent dissolution leads to the nucleation and growth of a Ti-Si 2 film (thermodynamically stable compound). The growth kinetics at this stage are described by a parabolic law. A phenomenological model has been proposed allowing us to estimate some characteristics and parameters of the process.

Spectroscopy and reactions of hydrazoic acid on silicon single crystal surfaces: III. HN 3 and DN 3 on Si(111)(7 × 7)

We have studied the thermal stability and spectroscopy of HN 3 on Si(111)(7 × 7) in the temperature range from 120 to 1350 K. The results are similar to those observed on other two low-index Si surfaces. HN 3 was found to molecularly adsorb on Si(111)(7 × 7) at 120 K, with the formation of dimers at higher dosages (≥ 2.0 L). At 270 K, HN 3 began to decompose into HN and N 2 species as indicated by the changes in the NH vibration mode in HREELS and the chemical shift of the N 1s XPS peak. Between 300 and 800 K, the NH species further decomposed into H and N on the surface, while N 2 desorbed molecularly. In this temperature range, the steady increase of the SiN x and SiH peaks were noted and LEED exhibited a weak (1 × 1) pattern. When the surface was annealed at T s > 800 K, H (a) recombined to desorb, with N remaining as the only species on the surface. Further annealing at higher temperatures caused the gradual transformation of the SiN x species into Si 3N 4, as confirmed by all the spectroscopic results, including LEED which showed an (8 × 8) pattern.

Spectroscopy and reactions of hydrazoic acid on silicon single crystal surfaces III. HN3 and DN3 on Si(111)(7 × 7)

Spectroscopy and reactions of hydrazoic acid on silicon single crystal surfaces III. HN3 and DN3 on Si(111)(7 × 7)

Biologically Derived Nanometer-Scale Patterning on Chemically Modified Silicon Surfaces

ABSTRACTIn recent experiments we have patterned smooth HOPG surfaces with periodic arrays of nanometer dimension holes on a 20nm lattice using two-dimensional (2-D) protein crystals as templates. The bacterial cell wall crystals were deposited on HOPG substrate and overcoated at oblique incidence with an ultrathin (3.5 nmn) TiO2 film. Fast atom beam (FAB) milling patterns the TiO2 film into a screen having the protein lattice periodicity and the screen then acts as a mask for the pattern transfer to the HOPG substrate. This method provides an inexpensive, “benchtop,” intrinsically parallel technique for the periodic nanostructuring of surfaces. Here we extend it to the patterning of silicon single crystal surfaces. We will describe the use of silane coupling agents to enable protein adhesion with the cytoplasmic side up, as is preferable for the patterning. We will show AFM images of the T1O2 -protein-silicon composite surface at various stages of the fabrication process.

Granulation of silicon surface through reactive ion etching

A spherelike granular structure has been observed to appear on the surface of single crystal silicon as a result of a two step reactive ion etching (RIE). Fluorocarbon plasma in RIE mode has been found to create a micromasking of bare silicon. Subsequent application of silicon etch recipe produces a texture with submicron spherical granules. Energy dispersion of x ray and Auger spectra analysis reveal that the suspected deposition or adsorption of etchant and effluent species onto the final surface is insignificant. The technique has a potential for controlling the reflectivity of silicon in specific regions of the spectrum and providing a large throughput.

Influence of silicon X-ray photoelectron diffraction on quantitative surface analysis

The problem of XPS quantitative measurements on silicon single crystal surfaces is discussed in relation to the X-ray photoelectron diffraction (XPD). This effect consists in electron emission enhancements in some particular space directions with reference to the polar angle θ and the azimuth φ and originates in the preferential electron scattering in the directions of the interatomic axes (forward scattering). The polar scans I∞Si(θ) of the Si 2p core level intensities of Si(001) and Si(111) surfaces are given in azimuthal high symmetry directions. The relevant spectra display intensity fluctuations in the emission space up to 40% for angular variations of only 10° around the surface normal. They may induce corresponding inaccuracies in quantitative surface analyses when, by approximate sample positioning, this effect is not taken into account.

In situ spectroscopic ellipsometric investigation of argon ion bombardment of single-crystal silicon and silicon dioxide films

Ion-bombarded single-crystal silicon surfaces, maintained in ultrahigh vacuum, are characterized by in situ spectroscopic ellipsometry over the photon energy range 2.0–5.5 eV. The incident energies of argon ions from a Kaufman ion source are 100 to 1500 eV. Spectroscopic ellipsometry, SE, was found to be a very sensitive tool for characterization of these samples. The computer modeling analysis of this data demonstrated the ability of SE to determine the crucial parameters describing the damage to these samples. It is shown that SE with effective models can yield information on the depth profile of multilayer structures, quantitative information on the thicknesses of each layer, and the microstructure (crystalline, amorphous, or oxide). Argon ion beam etching (IBE) of silicon dioxide on crystalline silicon substrates at incident energies of 300 and 1200 eV and the substrate damage induced by IBE was investigated by means of in situ SE.

A study of hydrogen adsorption on the silicon single crystal surfaces by electron stimulated desorption (TOF-ESD)

A study of hydrogen adsorption on the silicon single crystal surfaces by electron stimulated desorption (TOF-ESD)

A study of hydrogen adsorption on the silicon single crystal surfaces by electron stimulated desorption (TOF-ESD)

The adsorption of hydrogen on a silicon surface plays an important role in the reconstruction of the surface structure and terminations of the dangling bonds of the surface atoms. Hydrogen adsorption experiments on Si(100) and Si(111) surfaces were perfomed using the electron stimulated desorption spectroscopy (TOF-ESD) combined with the thermal desorption spectroscopy (TDS). The H + signal intensity of TOF-ESD was observed on Si(100) but not Si(111) after hydrogen exposure in spite of observing hydrogen desorptions from both surfaces in TDS.

Fluorine-containing species on the hydrofluoric acid etched silicon single-crystal surface

The chemical structure and property of fluorine-containing species on the hydrofluoric acid (HF) etched Si surface was examined by use of x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The fluorine content on the surface was found to increase with increase of HF concentration. A silicon surface etched by 50% HF has fluorine of 2.6×1014 atoms/cm2 as Si–F. Most of the Si–F bondings are rapidly hydrolyzed to Si–OH by rinsing the wafer in water. Thus prepared Si–OH groups are found to be useful as active sites for chemical modification of the bare silicon single-crystal surface. The Si–F was observed not to influence the oxidation rate of HF etched silicon surface.

The Effect of Argon Addition on the Microstructure, Texture and Phases of Silicon Carbide Prepared by Chemical Vapor Deposition

Silicon carbide was chemically deposited on the (111) surface of silicon single crystal and isotropic pyrolytic graphite by using methyltrichlorosilane as source gas. The deposits were examined by X-ray diffractometry and electron scanning microscopy (SEM) and found to be composed of β-SiC, free Si and a trace of 2H-SiC. The coatings yielded the less free silicon in it using graphite as substrate and at a higher argon flow rate. X-ray analysis indicated that the degree of preferred orientation varied with the kinds of substrate materials and the amount of argon added.

The adsorption and thermal decomposition of trimethylamine alane on aluminum and silicon single crystal surfaces: kinetic and mechanistic studies

The mechanism and kinetics of the thermal decomposition of trimethylamine alane (TMAA) on aluminum and silicon single crystal surfaces in ultrahigh vacuum are reported. The products obtained are elementally pure aluminum thin films and gas phase hydrogen and trimethylamine. On single crystal aluminum substrates, epitaxial growth is observed. On Si(111), polycrystalline growth is noted although LEED studies suggest that the initial growth is heavily (111) textured. The reactive sticking probability on aluminum surfaces in the temperature range 80–280 K is low and we present evidence for the importance of TMAA decomposition at defects. At higher temperatures ( t ≳ 320 K.) the reactive sticking probabilities are high and steady-state film growth is observed. Under these growth conditions, the rate of deposition is described by a single first-order rate law. The decomposition of TMAA on clean silicon and oxidized aluminum is kinetically complex and more highly activated than the steady-state growth process.

Control of the chemical reactivity of a silicon single-crystal surface using the chemical modification technique

A technique is developed to control the chemical reactivity of a silicon single-crystal surface through chemical modification with atomic hydrogen. The reactivity of the reconstructed single-crystal surface prepared by high-temperature treatment in an ultrahigh vacuum is significantly decreased by capping the dangling bonds of top-layer silicon atoms with hydrogen atoms. The Si—H bonds on the hydrogenated surface are found to be much more stable against oxidation than the Si—Si back bonds. The hydrogen-passivated silicon surface is reactivated by electron beam irradiation. An ultrathin oxide layer pattern can be prepared using preferential oxidation of the area reactivated by a focused electron beam.

An S/XPS study of hydrogen terminated, ordered silicon (100) and (111) surfaces prepared by chemical etching

There is considerable current interest in the passivation of single crystal silicon surfaces, particularly with reference to the fabrication of epitaxially grown solid state device structures.In this paper, we discuss ordered Si(100) and (111) surfaces prepared by chemical etching in solutions of hydrofluoric acid and studied by use of Soft XPS, XPS and LEED. Despite transfer through the atmosphere before being loaded into the UHV of our analysis instruments, the hydrogen terminated surfaces observed are shown to be among the most perfect yet produced by such chemical means. Under optimum conditions, the etch can yield levels of carbon and oxygen impurities of less than 2% of a monolayer and lead to surfaces where the Fermi level is not pinned.The etched surfaces are modified by the hydrogen termination such that they are electrically passivated and ordered into a (1 × 1) periodicity. Upon annealing at (520 ± 10)°C in UHV, the hydrogen is removed, the surface changes to a (2 × 1) reconstruction and also exhibits band bending due to Fermi level pinning by surface strates.The relationship between residual contamination and etching parameters such as time and etchant concentration has been examined, together with the stability of the passivated surface under exposure to wet and dry environments. This has shown that the surface condition is sensitive to etching procedure and that the optimum surface may be obtained by using a 5% non-aqueous solution, or by pre-cleaning a surface using a UV generated ozone exposure prior to an aqueous etch. It has also been shown that a controlled reoxidation of an etched surface using UV-ozone can produce a non-abrupt Si-SiO2 interface. This may form a useful part of a reduced temperature surface preparation, compatible with any subsequent epitaxial overlayer growth.

Decomposition of silane on Si(111)-(7×7) and Si(100)-(2×1) surfaces below 500 °C

Using static secondary ion mass spectrometry (SIMS) to observe the silicon hydride species formed by silane adsorption on atomically clean single crystal silicon surfaces, two distinct adsorption mechanisms are identified. Dissociation to SiH3 plus H occurs on the Si(100)-(2×1) surface, which contains pairs of dangling bonds located on Si dimers (with Si–Si distance ≊2.4 Å). In contrast, SiH2 formation in the adsorption step is indicated on the Si(111)-(7×7) surface, where adjacent dangling bonds are separated by more than 7 Å. Lower limits on the silane reactive sticking coefficient (SR) are evaluated using hydrogen coverage (ΘH) measurements after calibrated SiH4 exposures, and this limit is ≊10−5 for 25 °C gas and 100–500 °C surface temperatures. Within experimental error, SR is the same for both mechanisms on the two clean surfaces (ΘH near zero). Dependence of SR on ΘH is reported at 400 °C for both surfaces, and differences appear as ΘH exceeds 0.1 H/Si. Silane adsorption is weakly activated on Si(111)-(7×7), as evidenced by enhanced adsorption as TS is increased between 50 and 400 °C.

Oxides grown on textured single-crystal silicon-dependence on process and application of EEPROMs

The electrical properties of oxides grown on textured single-crystal silicon (TSC oxides) are dependent on the process used to roughen or texture the single-crystal silicon surface. The effects of different processing steps on the I-V, C-V, charge trapping, interface trap generation, and breakdown characteristics of TSC oxides are examined. By choosing a particular set of processing steps, a TSC oxide can exhibit enhanced conduction and very good charge trapping and breakdown characteristics, which make it an interesting dielectric for EEPROM applications. Floating-gate EEPROMs fabricated using this TSC oxide demonstrate the feasibility of this new technology. Programming, cycling, and retention characteristics of this EEPROM are presented. In particular, the retention data of the TSC EEPROM show an improvement over those of EEPROMs using oxides grown on untextured single-crystal silicon.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of a damaged layer thickness with reflection acoustic microscope

An acoustic microscope was used for determining the frequency dependence of surface acoustic wave (SAW) velocity on a specimen whose silicon single-crystal surface was machined under various conditions. Consequently, thickness of the damaged layers could be estimated from the curvature points of frequency dispersion curves of the SAW velocity. It was revealed that thicknesses of the damaged layers can be estimated through rough approximation by about one-half the wavelength determined by the frequency at curvature points. From specimens possessing two damaged layers, frequency dispersion curves with two curvature lines can be obtained. From the curvature point at high frequencies the thickness of the top damaged layer can be determined. On the other hand, from the curvature point at low frequencies, the thickness of the inner damaged layer can also be determined. By choosing an acoustic lens as the condition for exciting SAWs, images can be observed while varying the frequency. From observation results obtained with this method, the distribution in the depth direction can be clarified.

Preparation and characterization of ZnS thin films produced by metalorganic chemical vapor deposition

Thin, polycrystalline films of ZnS are grown on single-crystal silicon(100) surfaces by metalorganic chemical vapor deposition. Exposure of the Si substrate to hydrogen sulfide and dimethylzinc at low temperature and low pressure produces films which grow uniformly across a 100-mm diameter. The reactant gases used in this work are not diluted in carrier gases. Reactions are carried out for the temperature range 25–125 °C. ZnS film growth rates for this temperature regime vary from 125 to 2700 Å/min. The ZnS thin films were characterized using scanning electron microscopy, x-ray diffraction, Rutherford backscattering, and x-ray photoelectron spectroscopy.

The formation of hydrogen passivated silicon single-crystal surfaces using ultraviolet cleaning and HF etching

We have tried to develop a new procedure to prepare the clean surface of a silicon single crystal. We successfully prepared the contamination free bare silicon surface with ultraviolet cleaning followed by HF dipping with low concentration HF obtained by dilution by organic free ultrapure water, at room temperature under the atmospheric condition. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet photoelectron spectroscopy measurements proved thus prepared surface has a hydrogen monoatomic layer terminating the dangling bonds of silicon. The hydrogen termination was found to have remarkable passivation effect against surface oxidation reaction. A silicon thin-film epitaxially grown on the prepared surface was confirmed to have perfect crystal structure and high-purity level by scanning electron microscopy, reflection high-energy electron diffraction, Raman spectroscopy and secondary ion mass spectroscopy.

Chemisorption of HF on Silicon Surfaces

ABSTRACTWe have investigated the interaction of gaseous hydrofluoric acid (HF) with single crystal silicon surfaces using soft x-ray photoemission spectroscopy and Electron Stimulated Desorption Ion Angular Distributions (ESDIAD). Examination of the Si(2p) core level for surfaces saturated with HF shows the formation of silicon-fluoride bonds indicating the dissociative chemisorption of HF on both Si(111) and Si(100) surfaces. Inspection of the F(2s) and F(2p) valence levels at saturation coverage indicate that only one-half monolayer of fluorine bonds to the silicon. The primary ion desorbed by electron bombardment of these surfaces is F+ with only a minor contribution from H+. ESDIAD images from a saturation coverage of HF on stepped Si(100) surfaces reveal F+ desorption primarily along the direction of the terrace dimers. The ESDIAD patterns from HF adsorbed on Si(111) are characterized by strong normal F+ emission with a weak background component of off-normal emission. These results are consistent with the dissociative chemisorption of HF where the ion emission direction is determined by the Si-F bond directions.