H. Baumann

Surface- and microanalytical characterization of silicon-carbonitride thin films prepared by means of radio-frequency magnetron co-sputtering

Abstract Thin Si-C-N films were produced by means of reactive radio-frequency (RF) magnetron co-sputtering using a special geometry for the sputter target consisting of silicon and carbon. The stoichiometry and the vertical and lateral homogeneity of these layers as well as the reproducibility have been investigated by means of X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), non-Rutherford backscattering spectroscopy (n-RBS) and nuclear reaction analysis (NRA). After calibration of the surface analytical techniques using absolute data derived from the nuclear methods, AES sensitivity factors for the ESCALAB-5 spectrometer (SSi=1.65, SC=0.57, SO=1.10, SN=0.50) as well as the sputtering yield for ternary Si-C-N compounds (YSi-C-N=1.00) have been estimated. The corresponding XPS binding energies were found for Si 2p=102.8 eV (Si-N-C), C 1s=285.9 eV (C(sp2)-N) and C 1s = 288.2 eV (Si-N-C), N 1s = 398.9 eV (Si-N-C) and N 1s = 400.6 eV (N-C(sp2)).

Field emission properties of self-assembled silicon nanostructures on n- and p-type silicon

This letter considers field emission from self-assembled silicon nanostructure arrays fabricated on n- and p-type silicon (100) substrates using electron beam rapid thermal annealing. Arrays of nanostructures with an average height of 8 nm were formed by substrate annealing at 1100 °C for 15 s. Following conditioning, the Si nanostructure field emission characteristics become stable and reproducible with Fowler–Nordheim tunneling occurring for fields as low as 2Vμm−1. At higher fields, current saturation effects are observed for both n-type and p-type samples. These studies suggest that the mechanism influencing current saturation at high fields acts independently of substrate conduction type.

Nanostructuring of silicon (100) using electron beam rapid thermal annealing

A technique for the rapid, uncomplicated and lithography free fabrication of silicon nanostructures on both n-type and p-type Si(100) substrates is presented. The nanofabrication method employs electron beam rapid thermal annealing of Si(100) substrates which have undergone no prior processing and thus still contain the native oxide. The resulting nanostructures are distributed across the entire Si surface and are square based and aligned to the [110] direction. Nanostructure growth was only observed in the temperature range 800–1200 °C and has been shown to occur following annealing durations as short as 3 s. Nanopillars over 20 nm high have been fabricated following annealing for 120 s. The initial stage of nanostructure growth involves thermal decomposition of the native oxide resulting in atomic scale disorder of the Si surface. Following complete oxide desorption, diffusive Si species migrate across the surface in response to diffusion barriers established on the strained potential-energy surface, nu...

Investigation of the Fluorine Microalloying Effect in the Oxidation of TiAl at 900°C in Air

High-temperature oxidation resistance of gamma titanium aluminides can be achieved by the formation of a continuous scale of slowly growing Al2O3. The formation of such a scale was favored by the addition of small amounts of fluorine. It is shown that fluorine can have a beneficial effect on oxidation resistance in a certain F-range which is quantified by thermodynamic calculations and by experimental investigations. It is assumed that the F-effect offers a significant potential for improvement of the oxidation resistance of technological TiAl alloys.

Comparison of 30Si diffusion in amorphous Si–C–N and Si–B–C–N precursor-derived ceramics

Abstract We carried out silicon self-diffusion studies in amorphous precursor-derived ceramics of composition Si3BC4.3N2 and Si2.6C4.1N2.3 to compare the atomic transport properties of a boron containing and of a boron free material in the system Si–(B)–C–N. Ion implanted stable 30 Si isotopes were used as tracers and secondary ion mass spectrometry (SIMS) was used for depth profiling. The experimentally determined diffusivities are lower by a factor of 10 for Si3BC4.3N2 than for Si2.6C4.1N3.3 in the whole temperature range investigated. This might be a hint that the mobility of the constituent elements plays an important role in the stabilization of the amorphous state of Si3BC4.3N2 at high temperatures. Both ceramics obey an Arrhenius behaviour with activation enthalpies and pre-exponential factors of ΔH=5.7 eV and D 0 =0.001 m 2 / s for Si3BC4.3N2, and ΔH=5.55 eV and D 0 =0.003 m 2 / s for Si2.6C4.1N3.3, respectively. These results are consistent with a diffusion mechanism mediated by vacancy like defects operating in these amorphous ceramics, which is analogous to the related crystalline silicon based non-oxide ceramics Si3N4 and SiC.

Hydrogen profiles of thin PVD silicon nitride films using elastic recoil detection analysis

Abstract Thin silicon nitride films (e.g. D = 100 nm) produced by the ion beam sputtering technique show different depth profiles of hydrogen concentration depending on process parameters. The hydrogen profiles of these thin films can be varied within certain limits by annealing. Films prepared on a silicon substrate have been analysed with respect to the hydrogen content by the elastic recoil detection analysis method (ERDA) using a 10 MeV 20 Ne beam impinging on the target at an incident angle of φ = 10° relative to the ion beam axis. Comparison of the results of the ERDA with the results from analyses using the nuclear reaction 1 H( 15 N, αγ) 12 C shows good agreement. The experimental results illustrate the advantage of the PVD sputtering deposition technique in controlling the hydrogen concentration of thin silicon nitride films.

Change of surface structure of thin silicon nitride layers during electron beam rapid thermal annealing

The surface of 〈100〉 Si specimens implanted at room temperature (RT) with 15N+2 ions at 10 keV with fluences of 5×1016 at./cm2 was subsequently annealed by electron beam rapid thermal annealing (EB‐RTA) at temperatures between 900 and 1150 °C forming SiNx layers 25–20 nm thick. The modification in surface structure of these layers by EB‐RTA was investigated by atomic force microscopy (AFM) and nuclear reaction analysis (NRA). The 15N depth profile measurement [15N(p,αγ)12C] at target tilt angles from 30° to 7° indicates a shift of the low energy edge which represents the SiNx sample surface. This shift is attributed to the shadowing effect of the SiNx sample surface. Detailed AFM analysis shows that the surfaces are covered with irregularly distributed vertical structures, being whiskers of ∼16 nm height. These structures become more pronounced with increasing annealing temperatures.

Formation of SiC-surface nanocrystals by ion implantation and electron beam rapid thermal annealing

SiC-surface nanostructures on silicon were produced by 10keV carbon ion implantation into silicon followed by annealing to 1000°C for 15s under high-vacuum conditions using a raster-scanned electron beam. Following implantation, an amorphous layer is produced which starts at the surface and extends 65nm into the substrate. Following annealing, the implanted surface layer remains amorphous but becomes covered with semi-spherical crystalline features up to 300nm in diameter. The nanocrystals have been confirmed to be SiC which, following nucleation, grow as a result of C and Si diffusion across the oxide free substrate surface during annealing.

Thin hydroxyapatite surface layers on titanium produced by ion implantation

In medicine metallic implants are widely used as hip replacement protheses or artificial teeth. The biocompatibility is in all cases the most important requirement. Hydroxyapatite (HAp) is frequently used as coating on metallic implants because of its high acceptance by the human body. In this paper a process is described by which a HAp surface layer is produced by ion implantation with a continuous transition to the bulk material. Calcium and phosphorus ions are successively implanted into titanium under different vacuum conditions by backfilling oxygen into the implantation chamber. Afterwards the implanted samples are thermally treated. The elemental composition inside the implanted region was determined by nuclear analysis methods as (α,α) backscattering and the resonant nuclear reaction 1H(15N,αγ)12C. The results of X-ray photoelectron spectroscopy indicate the formation of HAp. In addition a first biocompatibility test was performed to compare the growing of marrow bone cells on the implanted sample surface with that of titanium.

Chemical bonding and interface analysis of ultrathin silicon-nitride layers produced by ion implantation and Electron Beam Rapid Thermal Annealing (EB-RTA)

Abstract15N2+ions were implanted into c-Si with an energy of 5 keV/atom and fluences ranging from 5×1016 to 2×1017 atoms/cm2 at RT to form ultrathin silicon-nitride layers (SiNx) with different N/Si ratios depending on the fluences (up to an overstoichiometric N/Si ratio of 1.65). The 15N depth distributions were analysed by the resonant nuclear reaction 15N(p, αγ)12C(Eres=429 keV). The implanted samples were processed by Electron Beam Rapid Thermal Annealing (EB-RTA) at 1150° C for 15 s (ramping up and down 5° C/s). The chemical structure of the 15N implantation into Si was investigated by EXAFS and NEXAFS. Channeling-RBS (4He+, E0=1.5 MeV) measurements were performed to observe the transition region (disordered-Si layer, d-Si) being underneath of the SiNx layer (typical values of layer thicknesses:SiNx 24 nm, d-Si 6 nm).