J. Siejka

Transport number measurements during plasma anodization of Si, GaAs, and ZrSi2

In contrast to the thermal oxidation of Si where molecular oxygen is the sole moving species, the plasma anodization involves the movements of anions (oxygen or its compounds) or cations (Si or its compounds) or both. A similar situation is observed during the plasma anodization of refractory metal silicides (ZrSi2) or even GaAs. To get some insights on the mechanisms of plasma anodization, the transport number of cations t+ in oxides grown by anodization in oxygen plasma has been investigated using Xe atom markers. Rutherford backscattering techniques were used to determine the change in Xe marker position related to the change in oxide thickness. Results showed that t+≂0 for SiO2 growth indicating oxide formation solely by oxygen ion movement while for GaAs oxide, the t+ value obtained (t+≠0) evidences cation and oxygen anion migration during the growth. For ZrSi2 anodization, the position of the Xe markers remains unchanged during oxide formation yielding t+≂0, while the analysis of the backscattering ...

Composition, structure, and ac conductivity of rf‐sputtered calcia‐stabilized zirconia thin films

Thin 12 mole% calcia‐stabilized zirconia CSZ films (500–17 000 A) were deposited by rf sputtering onto single‐crystal silicon substrates. When deposited in an oxygen‐containing plasma (more than 0.2% O2 in Kr), such films appeared to be stoichiometric, as verified by nuclear microanalysis; while their structure, analyzed by x rays, appeared to be of the fluorite type. The ac conductivity measured on Al/CSZ/Si structures between 200 and 400 °C suggests an activation energy and a preexponential factor close to that of bulk‐sintered material having the same composition. This result tends to prove that conductivity in sputtered CSZ thin films is due to anion‐oxygen movement. Preliminary emf measurements on Pt/O2/CSZ/Ni/Si thin‐film galvanic cells confirmed this interpretation.

A quantitative study of impurities in photoluminescent and nonphotoluminescent porous silicon layers

The visible photoluminescence of porous silicon layers has been attributed to energy confinement of carriers in the Si microcrystallites, but this hypothesis is currently challenged by models in which the photoluminescence originates in silicon based molecules, possibly formed during the etching process, such as siloxene, siloxene derivatives with fluorine substitution, hydride species. To study the possible relation between the photoluminescence phenomenon and such molecules we have performed quantitative analysis of hydrogen, oxygen, and fluorine and of carbon which is also present in porous silicon layers. Oxygen, fluorine, and carbon content have been measured by nuclear reaction analysis. To measure the hydrogen content we used elastic recoil proton detection analysis. We found similar impurity content in photoluminescent and in nonphotoluminescent layers, which seems to indicate that the photoluminescence does not originate in silicon based molecules present in porous silicon layers. In freshly prep...

Optical properties of Sb and SbOx films

The optical constants of Sb and SbOx films grown by d.c. sputtering are determined over a wide spectral (270–870 nm) and composition (x = 0.12−2.0) range. Spectroscopic ellipsometry is used to determine the film optical constants. The composition of the films is obtained by combining nuclear reaction analysis and Rutherford backscattering spectrometry. Optical properties of the films change drastically at a critical oxygen content (x = 0.19) which is related to the transition from a crystalline Sb-like film with optical properties similar to crystalline Sb to an amorphous Sb-like film. It will also be shown that amorphous SbOx films behave optically as a mixture of amorphous Sb-like material and a stoichiometric Sb oxide (Sb2O4, x = 2.0).

Kinetics of pulsed ultraviolet laser induced oxidation of c‐Ge: The role of optical coupling and material losses

Ultraviolet pulsed laser induced oxidation kinetics of crystalline germanium (c‐Ge) is determined from real‐time optical measurements in conjunction with absolute measurements of the oxygen incorporation performed by nuclear reaction analysis. Although the oxidation process can be triggered at laser fluences initially below the melting threshold of c‐Ge, it is strongly activated when surface melting occurs and therefore the fast oxidation process observed is mainly a thermally activated process. Because an optical coupling between the oxide layer and the c‐Ge underneath, the growth kinetics is complex and leads to nonconstant rates. The oxygen incorporation reaches a saturation value which depends both on the laser fluence and the oxygen pressure. The results show that the oxygen incorporation is limited by an overlapped laser‐induced material removal process rather than by the diffusion length of oxygen species.

Low‐temperature plasma anodization of tantalum silicides

The low‐temperature plasma anodization of cosputtered Ta silicide has been studied. The anodization parameters, oxide growth rate, electric field, and faradic efficiency showed a strong dependence on the silicide formation (with or without annealing). Rutherford backscattering techniques were employed to characterize the oxide films and it was found that the plasma oxides grown on as‐deposited silicide are of uniform composition in the oxide bulk, but the near‐surface region shows a slight Si oxide enrichment, and, thus, a Ta oxide depletion. On the contrary, for annealed (950 °C) silicides, when the hexagonal Si‐enriched TaSi2 phase is formed, a high‐surface enrichment in Ta oxide is observed in the plasma grown oxides. The insulating properties of the oxide films as determined by capacitance, electrical conductivity, and dielectric strength measurements also depend on the silicide formation, and these properties were correlated to the cation depth distributions in the oxide mixtures. A spectacular diffe...

Study of ytterbium implanted calcia stabilized zirconia thin films and yttria stabilized zirconia single crystals

Abstract Calcia stabilized zirconia thin films and yttria stabilized zirconia single crystals were Yb implanted at 150 and 210 keV, and at various doses up to 1.3 × 1017 ions/cm2 in order to modify locally the oxygen transport properties. Rutherford back-scattering and nuclear microanalysis on the implanted thin films give information about the implantation profiles and sputtering yields. The results show that the ratio of the sputtering rates of two elements of the film is equal to their concentration ratio. At high implantation doses the Yb profile is nearly flat in the surface region with [Yb]/[Zr] = 1.1. 18O tracing experiments demonstrate that a significant oxidation of the implanted samples occurs in air at room temperature. Further oxidation takes place during a 500 °C annealing in air which does not modify the Yb profile and leads to a final mean composition (ZrO2)x(Yb2O3)y (CaO)z. For the YSZ single crystals, channelling measurements demonstrate that the implanted region is highly damaged. As YSZ...

Silicon loss during TiSi2 formation

When Ti‐Si diffusion couples are annealed in vacuum to form TiSi2, most of the oxygen contamination in the as‐deposited metal film is lost. An experiment demonstrating that a Si loss also takes place is presented, thus confirming that the oxygen loss occurs by SiO sublimation.

Recent Progress In Epitaxial Growth Of Semiconducting Materials On Stabilized Zirconia Single Crystals.

The present understanding of the properties of heteroepitaxial Si films grown on yttria stabilized zirconia single crystals (YSZ) is reviewed with particular emphasis on the properties of Si films resulting from high temperature post oxidation treatment. The crystalline, physic() chemical and electrical properties of Si films obtained by pyrolysis of SiH4 have been characterized by various analytical techniques. The results indicate that under carefully controlled deposition conditions, the crystalline quality (density of defects, of grain boundaries ....) is better for Si deposited on YSZ (SOZ structure), than for Si deposited on sapphire (SOS structure). The Si films, as deposited on YSZ, are highly resistive (cil -,_, 105 Q cm) ; a high temperature annealing in neutral atmosphere improves the quality of the films. In contrast to SOS, self doping is absent in SOZ structures (p lir O. cm). Further

Ion implantation of silicon in gallium arsenide: Damage and annealing characterizations

Abstract The purpose of this work is twofold: (i) to study the damage induced by ion implantation, with special attention to low implanted doses; (ii) to study the efficiency of annealing techniques — particularly incoherent light annealing — in order to relate the electrical activity of implanted atoms to damage annealing. We have used three methods to study the damage induced by ion implantation: (1) RBS (or nuclear reactions) in random or in channeling geometry (2) RX double crystal diffractometry and (3) electrical measurements (free carrier profiling). Damage induced by silicon implantation at doses >1014at/cm2 can be monitored by all three techniques. However, the sensitivity of RBS is poor and hence this technique is not useful for low implantation doses. As device technology requires dopant levels in the range of 5 × 1012 atoms/cm2, we are particularly interested to the development of analytical techniques able to detect the damage at this implantation level. The sensitivity of such techniques was checked by studying homogeneously doped (5 × 1016 e−/cm3) and semi-insulating GaAs samples implanted with 3 × 1012 silicon atoms/cm2 at 150 keV. The substrate temperature during implantation was 200°C. The damage produced in these samples and its subsequent annealing are evidenced by strong changes in X-ray double crystal diffraction spectra. This method hence appears as a good monitoring technique. Annealing of the implanted layers has been performed using incoherent light sources (xenon lamps) either in flash or continuous conditions. Reference samples have also been thermally annealed (850°C, 20 min in capless conditions). The results are compared, and the electrical carrier profiles obtained after continuous incoherent light irradiation indicate that the implanted silicon atoms are almost dully activated. The advantages and disadvantages of incoherent light irradiation are discussed (surface oxidation, surface damage) in comparison with standard thermal treatment.