Characterisation of 13C implantations in silicon by NRA [13C(p,γ)14N] and RBS

SiC_X layers close to the surface have been produced by implanting 40 keV ¹³C ions into silicon with a fluence of 6×10¹⁷ at./cm² (j=12 μA/cm²) at room temperature (RT). Depth distributions and areal densities (doses) of the implanted carbon have been analysed by the nuclear reaction ¹³C(p,γ)¹⁴N (NRA) which shows a sharp resonance in the excitation function at a proton energy of 1748 keV (Γ=75 eV FWHM). The depth resolution at the surface amounts to 31 nm due to energy spread of the proton beam (1.2 keV FWHM) and resonance width. The surface resolution of the NRA can be increased up to 8 nm when tilting the sample (surface normal) to an angle of 75° with respect to the proton beam direction. Using a NaI detector the detection limit of ¹³C in silicon is approximately 1 at.%. Comparative elastic backscattering measurements with ⁴He⁺ projectiles were performed at 2 MeV (Rutherford backscattering spectroscopy, RBS) and 3.45 MeV (high energy backscattering, HEBS) at a backscattering angle of 171°. The measured ¹³C depth distributions have been compared with a distribution calculated by the Monte Carlo algorithm T-DYN.     

Characterisation of thin sputtered silicon nitride films by NRA, ERDA, RBS and SEM

Summary Thin, amorphous silicon nitride (a-SIN_x) films were deposited on n-type (100) silicon substrates using an argon ion beam for sputtering a HPSN block under high vacuum conditions. The substrates were kept at room temperature. Nitrogen depth distributions were determined by NRA using the resonance reaction ¹⁵N(p,)¹²C at 429 keV. Hydrogen profiles were analysed by NRA (¹H(¹⁵N,)¹²C at E_o=6.385 MeV) and by ERDA (²⁰Ne²⁺, E_o=10 MeV). The NRA was used to determine the depth distributions (concentration vs. areal density) of nitrogen and hydrogen taking calibration standards into consideration. The silicon depth distributions and the N/Si ratios of the deposited a-SiN_x films were determined by RBS (⁴He⁺, E_o=2.0 MeV). Film thicknesses were obtained by SEM. The density of the deposited a-SiN_x films was found to be =2.7 (±0.1) g/cm³ by correlating RBS data and real film thicknesses as obtained by SEM.     

Molecular ion implantation in silicon

¹⁵N₂ ⁺ molecular ions were implanted with 10keV (j=10 A/cm²) under high vacuum conditions close to room temperature in 100 silicon (c-Si) to study the¹³N depth distributions, particularly the dependence of peak concentration and dose on the ion fluence. The analysis were performed by the resonant nuclear reaction¹⁵N(p, )¹²C(NRA). A maximum peak concentration of 65 at.% was measured. Thin stoichiometric silicon nitride layers with a thickness of approx. 20 nm (15 at.% nitrogen at the specimen surface) were produced by this low-energy implantation of¹⁵N₂ ⁺ ions with an ion fluence of 1.5·10¹⁷ ions/cm². NRA analysis of 38 keV¹⁵N₂ ⁺ and 19keV¹⁵N⁺ ion implantations were performed to compare the¹⁵N depth distributions. No significant changes in the depth distributions are measured, that means, the molecular¹⁵N₂ ⁺ ions are already disintegrated passing the very first atomic layers of the sample during implantation. Non-Rutherford RBS with⁴He⁺ ions and 3.45 MeV was performed in order to confirm the results obtained by NRA.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Determination of boron in the thin surface layer of a silicon wafer by instrumental charged particle activation analysis

Instrumental charged particle activation analysis (CPAA) for determining boron in a thin surface layer of silicon was developed. The nuclear reaction and incident energy were selected in order to minimize any interference from surface or bulk impurities. Thin boron film was used as a standard sample and its boron content was determined by neutron induced prompt -ray analysis. As a result, we were able to determine¹¹B and¹⁰B at 10¹⁵ atoms/cm² with an accuracy of better than 3% by 4 MeV proton and 7 MeV -bombardment, respectively. Each boron isotope could be determined down to 10¹³ atoms/cm². Our CPAA was applied to determine boron in a boron implanted silicon wafer of a SIMS standard sample.     

Nitrogen depth distribution, interface and structure analysis of SiNx layers produced by low-energy ion implantation

Thin silicon nitride (SiN _x ) layers with the stoichiometric N/Si ratio of 1.33 in the maximum of the concentration depth distributions of nitrogen were produced by implanting 10 keV¹⁵N ₂ ⁺ in 100 silicon at room temperature under high vacuum conditions. The depth distribution of the implanted isotope was measured by resonance nuclear reaction analysis (NRA), whereas the layer structure of the implanted region and the geometrical thickness of the layers were characterised by high resolution transmission electron microscopy (TEM). SiN _x layers with a thickness of about 30 nm were determined by NRA. Channeling Rutherford backscattering spectrometry was used to determine the disorder in the silicon substrate. Sharp interfaces of a few nanometers between the highly disordered implanted region and the crystalline structure of the substrate thickness were observed by TEM. The high thermal stability of SiN _x layers with N/Si ratios from under to over stoichiometric could be shown by electron beam rapid thermal annealing (1100 °C for 15 s, ramping up and down 5 °C/s) and NRA.     

Depth profiling Cr in surface layers by 52Cr(p,γ)53Mn nuclear resonance reaction analysis

A method for depth profiling chromium in the surface and near surface regions of materials using the resonance at 1,005 keV in ⁵²Cr(p,γ)⁵³Mn nuclear reaction is presented. The detection sensitivity, depth resolution and probing depth of the resonance in Si are determined to be about 3 at.%, 25 nm and 2.5 µm respectively from the excitation function of the reaction constructed in 0.90–1.2 MeV proton energy region by measuring 378 keV prompt γ-rays from ⁵³Mn nuclei. The reaction is interference free. These features make the approach attractive for profiling chromium in mid as well as high Z matrices.     

High energy proton beam bombardment of polyaniline

Irradiation effects of 35 MeV proton beam bombardment on polyaniline (PAn) have been studied. PAn was made by standard MacDiarmid method, and the irradiation was performed at ambient temperature lower than 20°C. A 511 keV γ photon was detected by γ spectrum analysis, and a nuclear reaction ¹⁴N(p,α)¹¹C in collaboration of ¹²C(p,pn)¹¹C took place. By means of chemical ionization, mass spectra of samples before and after ion bombardment were recorded. Experimental results showed that products such as

Full-size image (1K)

and cyclic compounds like

Full-size image (1K)

and

Full-size image (1K)

were produced. IR spectra and SEM micrographs gave results of vibrational frequency shifts and morphology consistent with mass spectrometry. Finally we conclude that high energy proton beam bombardment resulted in main-chain scission and carbonization of PAn. Although the electrical conductivity reduced from 0.72 to 0.62 S cm^-1, it retained at the same level. This implies that PAn might be used under the influence of high energy radiation.     

Silicon nitride homogeneity and compositional analysis by nuclear track counting and 14 MeV NAA

The distribution of nitrogen in plasma deposited silicon nitride films and in commercially produced, hot-pressed bulk material has been determined by the nuclear (proton) track image analysis technique. The nuclear track technique is shown to have the unique capability of sampling large areas (cm²) while providing distribution information on the micro scale (100 m²). Nitrogen over the range of 2 to 40% is determined quantitatively. Spatial distribution and topographical maps are plotted. The overall composition of the material is established by 14 MeV NAA through the determinations of silicon, nitrogen, and oxygen. An application in the micro electronic industry is described.     

Surface-near analyses of ultra thin silicon nitride layers by NRA, channeling RBS, FT IR ellipsometry and AFM

Homogeneous ultra thin silicon nitride layers (SiN_x layers) close to the surface have been produced by 10 keV ¹⁵N ₂ ⁺ molecular ion implantation and an ion current density of 10 A/cm², into single crystal silicon at room temperature. Stoichiometric SiN_x layers with thicknesses of about 28 nm (analyzed by NRA) were obtained at fluences of 1.5×10¹⁷ at/cm². NRA analyses of samples annealed by EB-RTA at T=1150° C for 15 s indicated that the N/Si ratio and the layer thickness did not change drastically. FT IR ellipsometry analyses indicated the existence of Si₃N₄ bonds in as-implanted specimens. A disordered Si layer (d-Si, typically 15 nm thick) underneath the implantation region caused by the ion implantation was found by channeling RBS analyses. The d-Si layer partly recrystallized during EB-RTA showing a thickness of 6 nm afterwards. The SiN_x layers showed no decomposition and detachment after EB-RTA. Due to EB-RTA, however, the smooth surface of the as-implanted specimens changed into a surface with remaining whisker-like structures surrounded by circular recesses as shown by AFM analyses. A model for the growth of these whisker-liker structures caused by low energy ion implantation and EB-RTA is presented on the basis of the thickness of the SiN_x layer, the existence of the d-Si layer and the special annealing process.