K. Bethge

Infrared absorption study of nitrogen in N-implanted GaAs and epitaxially grown GaAs1−xNx layers

Fourier-transform infrared absorption measurements have been carried out in the two-phonon region of GaAs. Implantation of the nitrogen isotopes 14N and 15N, respectively, into bulk GaAs shows that a local vibrational mode at 471 cm−1 (14N) is due to isolated nitrogen. The band is also found in GaAs1−xNx(0<x<0.03) layers grown by solid-source molecular beam epitaxy. The strength of the band correlates quantitatively with the decrease of the lattice parameter determined by x-ray diffraction for x<0.01 and can be used for the assessment of the nitrogen fraction incorporated substitutionally on anion lattice sites.

Ion beam analysis of nitrogen

Nitrogen plays an important role in almost all materials. In metals its presence influences the tribology. In semiconductors nitrogen compounds act as insulating. The less abundant isotope 15N can be used as tracer element to investigate biological processes. Thus the analysis of materials concerning the nitrogen content needs adequate methods. Nuclear reactions on both isotopes reveal an appropriate tool, if the cross sections are known to a high degree of accuracy.

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.

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).

In situ detection of rearrangement processes during electron beam annealing of ion implanted InP

Abstract Ion implantation and short-time electron beam annealing can be used as precise and reproducible tool for introducing controlled quantities of impurities into semiconductors. Measurement of the thermal radiation of ion implanted samples during the electron beam tempering process allows the in situ detection of changes in the surface structure and charge carrier density. In contrast to temperature controlled annealing methods, it is therefore possible to precisely control the annealing by the detection of rearrangement processes. We exemplify the method by the activation and diffusion of P during the temperature treatment for the well-known system of P implanted Si[2]. Furthermore, tempering of semi-insulating as well as of Mg+ implanted InP by means of electron beam irradiation is presented.

Nitrogen profiles of thin sputtered PVD silicon nitride films

Abstract Thin amorphous silicon nitride films (D= 100 nm ) were deposited on silicon substrates by means of argon ion beam sputtering under high vacuum conditions (residual gas pressure below 10 −5 Pa). The nitrogen depth profiles were measured by using the nuclear resonance reaction 15 N(p,αγ) 12 C at E res =429 keV ( Γ =120 eV ). The hydrogen concentration was determined by ERDA using a 10 MeV 20 Ne ion beam. Results show that the nitrogen concentration of thin films is inversely proportional to the hydrogen concentration . The nitrogen profiles obtained by NRA and by comparative RBS meaurements ( 4 He + , E 0 = 2.0MeV) showed good agreement. Annealing of the sample in nitrogen atmosphere at 600°C for 1 h did not influence the nitrogen concentration.

Investigations of ultrathin silicon nitride layers produced by low-energy ion implantation and EB-RTA

Abstract Ultrathin silicon nitride layers were produced by implanting 10 keV 15 N + 2 ions into 〈100〉 silicon at RT with fluences from 5.0 × 10 16 at/cm 2 to 5.0 × 10 17 at/cm 2 . The 15 N depth distributions were analysed by the resonant nuclear reaction 15 N(p, αγ) 12 C. The NRA of the silicon nitride layers show understoichiometric, stoichiometric, and overstoichiometric N/Si ratios depending on the fluences. The implanted samples were processed by electron beam rapid thermal annealing (EB-RTA) between 900 and 1130°C under high vacuum conditions. The layer thicknesses and the 15 N peak concentrations of EB-RTA samples varied with reference to non-annealed 15 N layers. The alteration of the chemical bonds of SiN x layers by EB-RTA was investigated by XPS. NRA analyses of the EB-RTA samples at tilt angles from 65 to 83° indicated a shift of the low-energy edge which represents the sample surface. This shift is attributed to a shadowing effect of the SiN x surface. AFM analyses confirmed that the surfaces of EB-RTA samples were covered with irregularly distributed vertical very elastic, needlelike structures. Their average height was 16 nm ( F = 5.0 × 10 16 at / cm 2 , EB-RTA at 900° C for 15 s).

Boron detection using the nuclear reaction 11B(p, α)2α

Abstract The nuclear reaction 11 B(p, α)2α has been used for the determination of boron impurities in silicon. α-particles with a continuous energy spectrum are produced by the three-body-dynamics of this reaction. Therefore, the differential cross section of this reaction has specifically been defined for materials analysis and measured at the three different laboratory angles θ = 108°, 138°, 158°, for incident proton energies between 150 keV and 800 keV. The formalism for concentration measurements has been developed for a thin boron layer and for a homogeneous boron distribution in the target. The concentration has been compared with results of charged particle activation analysis (CPAA) using the nuclear reaction 10 B(d,n) 11 C.