Study of non-radiative silicon deexcitation in an oxygen atmosphere using the differential measurement of the excited state lifetimes

Having developed a new method of differential lifetime measurement using atomic ionoluminescence as an excitation process, we applied this method to a monocrystaline silicon sample in an oxygen atmosphere of variable pressure. We found decreased values of the experimental lifetimes concerning levels 4s ³ P ⁰ and 4s ¹ P ⁰, which are more marked when the oxygen pressure increases. This tends then towards a saturation of the observed phenomenon. We propose, in agreement with other authors, an explanation which is based on the existence of non-radiative deexcitations. We present also a mathematical model for calculating this transition effect on the lifetime measurements. We consider that it is possible to take advantage of this experimental lifetime variation to determine a parameter of the model which characterises the non-radiative deexcitations. This measuring method appears to be a simple and original procedure for the study of certain nonradiative transitions.     

A simple formula for low-energy sputtering yields

A simple formula for low-energy sputtering yields of elemental targets is presented. The formula follows directly from Sigmund's theory but includes a modified form of the function(M _t /M _p ) and an accurate expression for the nuclear stopping cross section. Good agreement with experimental results is obtained for the projectiles Ne, Ar, Kr sputtering not too reactive surfaces at energies 1 keV. Further experiments are suggested as well as theoretical work concerning the meaning of the surface binding energy and the effect of the surface on the sputtering process in general.     

An RBS technique for measurement of the erosion rate of ion implanted films

The glancing incidence Rutherford backscattering method is used to study the erosion of aluminium films during bombardment by 10 keV Ar⁺ ions. It is found that the erosion rate of the firm is about one third the value expected and also that the depth profile of previously implanted 80 ke VPb⁺ ions changes during the erosion.     

Focused ion beam gallium implantation into silicon

Samples formed of a thin metal film deposited on silicon single crystal were annealed with electron and laser (ruby and excimer) pulses over a wide range of fluences. From a comparison of the experimental results with the temperature profiles of the irradiated samples, it turns out that suicide formation starts when the metal/silicon interface reaches the lowest eutectic temperature of the binary metal/silicon system. The growth rate of reacted layers is of the order of 1 m/s.     

Amorphous-polycrystal transition induced by laser pulse in self-ion implanted silicon

Reflection high energy electron diffraction has been used to investigate the amorphous to polycrystalline structure transition in silicon induced by laser pulse. The power density of the ruby laser pulse, in the free generation mode, has been maintained below the threshold to induce surface damage. Depth analysis has been carried out in 〈100〉 silicon crystal using the channeling effect technique.     

Orientation dependence of the survival fraction of molecular ions reflected from a single crystal

The experiment aimed at studying the 30 keV molecular nitrogen ion reflection from the (110)Cu single-crystal face has shown that the reflected molecular ion survival fraction is a strong and non-monotonic function of target orientation relative to the primary beam incidence plane.     

On the fluence dependence of the sputtering yield for low-energy noble gas ions

The fluence dependence of the sputtering yield has been studied on amorphous silicon under uhv conditions with 0.5 to 5keV Ar⁺ using the KARMA technique (Kombinierte Auger/Röntgen Mikro-Analyse). It allows to measure simultaneously the surface composition, the differential sputtering yield, and the total amount of implanted gas. For all energies, the yield increases initially and reaches saturation after the removal of a layer the thickness of which is closely correlated to the ion range. Gas implantation as a cause for these fluence effects can be ruled out by quantitative analysis. The relative yield increase is found to be larger for low energies than for higher ones. Both these findings can be qualitatively explained by a simple damage collection model.     

Laser photochemical etching of silicon

Argon laser induced chemical etching of single crystal silicon with chlorine is studied. Etch rates are determined as a function of gas pressure, crystal orientation, laser power and wavelength. Analysis of gas phase and surface products by Fourier transform IR and X-ray photoelectron spectroscopy are used to probe the reaction mechanism. Contrary to previous reports, no thermally enhanced etch rate is observed for Si (111) and the presence of oxide on the surface is found to inhibit etching even at high laser power.     

Lattice disorder in silicon induced by 2.0 MeV Cu+ irradiation

The effect of 2.0 MeV Cu⁺ irradiation on Si(100) crystal has been studied by the Rutherford backscattering/channeling technique. Analysis of the lattice disorder distribution has been performed under 100 direction of tilting off from the target normal: 7°, 30°, and 45° as well as different doses. The lattice disorder distributions in Si(100) have been compared with TRIM'89 simulation. The results show that the lattice disorder distributions in Si(100) under different irradiation angles seem to be in good agreement with TRIM'89 simulation. When the dose increases up to 8.7×10¹⁴ ions/cm², the defect concentration increases leading to the formation of an amorphous layer.     

FIB processing of silicon in the nanoscale regime

We have investigated the impact of shrinking feature sizes on the sputter efficiency of focused ion beams on crystalline silicon. On the basis of this analysis, we have demonstrated the main competitive mechanisms determining the complex response of silicon. Low-dose irradiation with a 50-keV Ga⁺ beam in the range from 10¹³ ions/cm² to 10¹⁵ ions/cm² produced pronounced swelling of the silicon due to amorphization. Higher doses led to material removal with an efficiency of about 2.5 atoms/ion. A sputter yield promoting the self-focusing effect combined with the sputter rate increase at oblique angles, and an opposing dose-deficiency effect, determined the complex characteristics of nanoscale trench milling. Shrinking critical dimensions led to higher sputter yields, attributable to self-focusing effects of incident ions becoming dominant at aspect ratios in the region of unity. At aspect ratios beyond unity, re-deposition was the dominant effect. Received: 17 June 2002 / Accepted: 26 July 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +43-1/588-0136-291, E-mail: alois.lugstein@tuwien.ac.at     

Hydrogen implantation and diffusion in silicon and silicon dioxide

Depth profiles of hydrogen implanted into crystalline silicon in random direction at different fluences have been measured by the¹⁵N technique and by SIMS. Whereas hydrogen implanted at a fluence of 10¹⁵ ions/cm² shows some limited mobility, no such mobility is observed for higher implantation fluences. In these cases, ballistic computer codes describe the depth distributions well, within the ranges of both experimental and theoretical accuracy. Annealing up to 510 K does not change the hydrogen distributions.Furthermore, high-fluence hydrogen implantation into silicon dioxide has been examined. There is some indication for radiation-enhanced diffusion during the implantation process. Upon subsequent thermal annealing, the hydrogen is found to diffuse, probably via a trapping/detrapping mechanism associated with an OH/H₂ transformation of the hydrogen bonding.     

Depth distributions of Au recoil atoms in silicon

The depth distributions of Au recoil atoms in Si have been investigated for Ar, Kr, and Xe ions implantation in 25–30 nm of an Au-Si system. The profiles were measured by means of RBS and radioactive techniques. The experimental results were compared with theoretical Gras-Marti analytical expressions and Monte-Carlo simulated depth distributions.     

Depth of origin of sputtered atoms

Estimates are given for the distribution of the depth of origin of sputtered atoms in the low-fluence limit, as well as the corresponding distribution of atoms sputtered into a given energy interval. The former distribution is well described by an exponential profile, with the characteristic depth being consistent with previous results. The latter distribution is characterized by an energy-dependent depth scale and a shape that varies from exponential at low sputtered-atom energies to inverse-power form at higher energies.     

Au gettering by Ne and Ar implantation in silicon

The gettering efficiency for Au induced by Ne⁺ and Ar⁺ implantation has been studied. The depth distribution of gettered Au as a function of annealing temperature and dose of implanted Ne⁺ and Ar⁺ ions are presented. The experiment shows that the maximum efficiency of gettering occurs when the implantation doses are comparable with amorphization dose.     

Temperature evolution during scanning electron beam processing of silicon

Temperature profile evolutions produced by a scanning electron beam in crystalline silicon have been numerically calculated using a two-dimensional finite-element scheme. The temperature dependence of the different silicon properties as well as the electron penetration effects have been taken into account. Numerical calculations carried out at different conditions have been compared with experimental melting-threshold measurements using an electron beam with a Gaussian power density distribution. The good agreement between numerical calculations and experimental results proves the validity of the two-dimensional approach.     

Analytical formula describing the non-saturating linear magnetoresistance in inhomogeneous conductors

The effective-medium theory (EMT) has proved successful in modeling the non-saturating linear magnetoresistance induced by inhomogeneity. However, calculating magnetoresistance using the EMT usually involves solving coupled integral equations which have no analytical solutions, and therefore, it is still difficult to directly compare the predictions of EMT with experimental data. Here we demonstrate that the linear magnetoresistance predicted by the EMT can be either exactly formulated or well approximated by a simple analytical equation $\Delta\rho/\rho_0=\sqrt{k^2B^2+a^2}-a$ in a number of known situations. The relations between the EMT parameters and the phenomenological parameters $k$ and $a$ are evaluated. Our results provide a convenient and effective method for extracting the EMT parameters from experimental data.     

Nd: YAG laser annealing of gallium-implanted silicon

A Q-switched Nd: YAG laser with a pulse duration of 20 ns was used to investigate effects of laser annealing in gallium implanted silicon. Rutherford backscattering and Hall-effect measurements were performed to evaluate the annealed layer. Differential Hall-effect measurements were carried out to obtain carrier concentration profiles after annealing. It was found that a maximum sheet carrier concentration of 8×10¹⁵ cm⁻² can be obtained for a gallium implantation of 10¹⁶ cm⁻² by laser annealing with an energy density of more than 1.0 J cm⁻². Although the peak carrier concentration was found to be 8.0×10²⁰ cm⁻³, the annealed layer showed polycrystalline structures even after annealing with an energy density up to 4J cm⁻². The annealing took place in the solid phase in this energy density range.     

Femtosecond pulsed laser ablation of diamond-like carbon films on silicon

Femtosecond pulsed laser ablation (τ = 120 fs, λ = 800 nm, repetition rate = 1 kHz) of thin diamond-like carbon (DLC) films on silicon was conducted in air using a direct focusing technique for estimating ablation threshold and investigating the influence of ablation parameter on the morphological features of ablated regions. The single-pulse ablation threshold estimated by two different methods were ?_th(1) = 2.43 and 2.51 J/cm². The morphological changes were evaluated by means of scanning electron microscopy. A comparison with picosecond pulsed laser ablation shows lower threshold and reduced collateral thermal damage.     

A contribution to the investigation of ion impact desorption by ion scattering

Sputtering or ion impact desorption of adsorbed layers can be directly investigated by low-energy ion scattering. Because of its specific sensitivity to surface atoms, this method provides the possibility of monitoring the decrease of the signal from the adsorbate or the increase of the signal from the substrate. Both signals were studied with He⁺ backscattering from the system O on Ni (110). The measured desorption cross-sections and the principal implications for both ways of observation are discussed. The use of the substrate signal for the desorption study can be of major advantage, particularly in the case of light adsorbates.