W. F. van der Weg

Energy spectra of 6–32 keV neutral and ionized Ar and He scattered from Au targets; ionized fractions as functions of energy

Abstract The neutralization of ions is an important aspect of low energy ion scattering for surface analysis. Electrostatic energy analyzers (ESA) have been used almost exclusively in such work, and information on charge neutralization efficiencies is needed for quantitative interpretation of ESA data. In the past, the occurrence in low energy ion spectra of surface peaks and low backgrounds due to scattering from inside the solid has been attributed to preferential neutralization of ions which penetrate beyond the surface. In the work to be described, a time-of-flight technique was used to measure energy spectra of both neutral and ionized Ar and He scattered at 90° from a polycrystalline gold target. Incident energies of 6–32 keV were used. The energy spectra of neutral Ar scattered from polycrystalline gold exhibit sharp surface peaks, and double scattering shoulders, over this entire energy range. For He there is a gradual downward slope toward lower energy rather than a sharp surface peak. The behavior in both cases is attributed to large scattering cross-sections which cause a loss of beam particles during penetration. A calculation using a 1 r 2 potential illustrates this effect as a function of energy for helium. In the present experiments we find that the ion fraction of scattered argon does indeed depend on depth of penetration. This is in contrast to the behavior of He and H at higher energies, e.g. 100 keV, in which cases the charge state depends on emergent velocity but not on depth of penetration. The characteristic shapes of ion scattering spectra in this energy range appear to result from both neutralization and beam attenuation inside the target.

Plasma‐enhanced growth and composition of silicon oxynitride films

Silicon oxynitride films with varying oxygen/nitrogen ratio were grown from SiH4, N2O, and NH3 by means of a plasma‐enchanced chemical vapor deposition process. The elemental composition of the deposited films was measured by a variety of high‐energy ion beam techniques. To determine the chemical structure we used Fourier transform infrared absorption spectroscopy and electron‐spin resonance. Ellipsometric data and values for mechanical stress are also reported. We show that the entire range of compositions from silicon oxide to silicon nitride can be covered by applying two different processes and by adjusting the N2O/NH3 gas flow ratio of the respective processes. It is suggested that the N2O/SiH4 gas flow ratio is the major deposition characterization parameter, which also controls the chemical structure as far as the hydrogen bonding configuration is concerned. We found that the films contain significant amounts of excess silicon and that the mechanical stress in the oxynitrides is lower than in plasm...

Interactions in the Co/Si thin‐film system. II. Diffusion‐marker experiments

The Kirkendall effect in thin‐film Co/Si couples is investigated by He backscattering using diffusion markers. The couples contain the compounds Co2Si and CoSi. The markers used are Xe implanted into Si, C, or Co2Si and a discontinuous W film between Si and Co. In the case of Xe implantation into Co, the experiments can be explained by dragging of Xe bubbles by the moving Co/Co2Si phase boundary. Xe implanted into Si is located at the Si/CoSi interface after the reaction and W is found at the Co/Co2Si interface after the reaction. The same applies to Xe implanted through Co into Co2Si. The results are evidence for predominant Co diffusion in Co2Si growth and Si diffusion in CoSi growth. Grain‐size measurements suggest that grain‐boundary diffusion plays a role in the growth of the silicide layers. The results of a Xe implantation into Co2Si without Co suggests that at the Co2Si/CoSi interface both Si and Co diffusion currents flow.

Concentration dependence of UV and electron‐excited Tb3+ luminescence in Y3Al5O12

The emission spectrum of Tb3+ substituted in YAG to various concentrations (x in Y3−xTbxAl5O12 ranges from 3×10−5 to 3×10−1) has been measured on samples prepared by two different methods. These methods are powder preparation by coprecipitation and growth of crystalline layers by liquid‐phase epitaxy. The spectrum consists of two groups of lines, one group around 550 nm originating from the 5D4 level and one group around 450 nm from the 5D3 level. The intensity of the two groups of lines depends on the method of excitation. In the case of UV excitation (λ=254 nm) the emission intensity for low Tb concentrations is mainly governed by the absorption of the incident radiation. With electron excitation, the energy loss of incoming electrons to ‘‘killer sites’’ in the lattice is found to influence the emission. The ratio, however, of 5D4 to 5D3 intensity is independent of the excitation mode. This ratio tends to a constant value at low concentrations and increases strongly with increasing concentration. These ...

On the excited state of sputtered particles

Abstract The possible electronic transitions of ionized and excited atoms at small distances from metal surfaces are investigated and the results are applied to sputtered copper atoms. It is assumed that sputtered ions and excited atoms are converted into atoms in the ground state by resonance processes. The large abundance of excited sputtered particles in the case of oxides is ascribed to the occurrence of forbidden energy gaps in the oxide, which make resonance transitions less probable.

Hydrogen in low‐pressure chemical‐vapor‐deposited silicon (oxy)nitride films

Silicon (oxy)nitride films (SiOxNy) have been deposited onto silicon by low‐pressure chemical vapor deposition using SiH2Cl2, N2O and NH3 or ND3. Nuclear reaction analysis, elastic recoil detection, and Rutherford backscattering spectrometry have been used to determine the elemental composition of the films with emphasis on the hydrogen and deuterium content. In the as‐deposited, NH3‐grown films the bulk hydrogen concentration is about 3 at. % for an oxygen/nitrogen atomic ratio (O/N) smaller than 0.4, for O/N>0.4 it is lower. In 900 and 1000 °C vacuum annealed films the bulk hydrogen concentration as a function of O/N goes through a maximum at O/N≊0.4. By comparing this observation with the D content in ND3‐grown films as a function of O/N, a model is deduced which explains this behavior. This model involves an oxygen induced increase of the electronegativity of the atoms to which hydrogen/deuterium is bound. Annealing at 1000 °C in a H2/N2 gas mixture of NH3‐grown films results in bulk hydrogen concentr...

Fitting the Stillinger–Weber potential to amorphous silicon

Abstract Modifications are proposed to the Stillinger–Weber (SW) potential, an empirical interaction potential for silicon. The modifications are specifically intended to improve the description of the amorphous phase and are obtained by a direct fit to the amorphous structure. The potential is adjusted to reproduce the location of the transverse optic (TO) and transverse acoustic (TA) peaks of the vibrational density of states (VDOS), properties insensitive to the details of experimental preparation. These modifications also lead to excellent agreement with structural properties. Comparison with other empirical potentials shows that amorphous silicon configurations generated with the modified potential have overall better vibrational and structural properties.

Annealing of plasma silicon oxynitride films

The anneal behavior of plasma‐enhanced chemical vapor deposited silicon oxynitride films has been studied using Fourier transform infrared absorption spectroscopy, nuclear reaction analysis, and electron‐spin resonance. The anneal temperature range was 500–1000 °C. It is observed that the oxynitrides which contain only N–H bonds are thermally stable in the temperature range under study. The layers which also contain Si–H bonds are considerably less thermally stable. Abundant hydrogen effusion from these layers is observed at temperatures as low as 600 °C, accompanied by cracking and shrinkage of the films. It is suggested that the coexistence of both Si–H and N–H bonds offers the possibility for cross linking and that consequently the decomposition temperature of both types of bonds is lowered. Evidence for the occurrence of cross linking is found in the infrared difference spectra. Consistently, the silicon unpaired electron density does not increase upon annealing. The Si–H and N–H bands effectively shi...

Deposition of amorphous silicon films by hot-wire chemical vapor deposition

Device-quality a-Si:H films have been deposited by hot-wire chemical vapor deposition (HWCVD). We have investigated the influence of deposition parameters on the film growth and properties. The most important deposition and growth processes that influence the optoelectronic material properties of a-Si:H deposited by HWCVD are clarified. During the deposition process attention must be paid to accurately control the substrate temperature, which is a key parameter to obtain device-quality films. A heat transport model is presented to be able to correct for the heating of the substrate by the filaments. It is found that films deposited at high deposition temperatures are under a high compressive stress. We show how the hydrogen incorporation in the layer is influenced by hydrogenation of subsurface layers by the atomic hydrogen flux that is inherent to the HWCVD process. We further identify the fundamental differences between plasma enhanced CVD and HWCVD material.

The sputtering of PtSi and NiSi

Abstract Absolute sputtering yields have been obtained, by Rutherford scattering, for the consttuents of the thin film compounds PtSi and NiSi on bombardment with 900 eV and 20 keV Ar; sputtering yields have also been determined for thin film samples of Si (poly and single crystal), Ni and Pt. The partial sputtering yields of the compounds are not related in any simple fashion to the corresponding elemental sputtering yields (e.g. the partial sputtering yields of Si in PtSi, S Pt Sl and NiSi, S Ni Si are considerably larger than that of elemental Si, SSi). No deviations from stoichiometric sputtering are observed. However 20 keV Ar sputtering of PtSi produces a 200 A surface layer substantially enriched with Pt.