D. Bouchier

Local strains in Si1−x−yGexCy alloys as deduced from vibrational frequencies

Abstract Raman spectroscopy has been used to study the bond structure of Si 1− x − y Ge x C y alloys. An anharmonic model for the force constants is applied to interpret the results. It is well established that the Ge and C concentrations in these alloys can be chosen so that their average lattice constants may be equal to, or even smaller than that of the Si lattice. Our Raman results show that the C local mode vibrational energy increases rapidly with increasing C concentration, at a rate of 3.2 cm −1 /at%. Additional fine structure is observed near the Si–C main peak in samples grown by rapid thermal chemical vapor deposition (RTCVD). This fine structure is absent in samples grown by pulsed laser induced epitaxy (PLIE). In agreement with previous studies, the satellite structure of the Si–C peak is interpreted as an indication for short-range order. Our analysis shows that pronounced differences exist in the microscopic structures of SiGeC alloys grown by different growth techniques.

Argon incorporation effects on the conductivity of metal layers

Almost all plasma- and ion-beam-based deposition techniques involve energetic particle bombardment of the growing film and lead to a more or less significant incorporation of noble gas. This incorporation is considered by most researchers to have a negligible effect on the electron mobility in the films. It is clearly established that the conductivity of metals is limited by oxygen contamination and, for very thin films, by the reflection of electrons on the film interfaces and on the grain boundaries. We studied tungsten films deposited by ion beam sputter deposition, with Ar+ or Xe+ energies ranging from 0.3 keV to 20 keV. We also studied silver deposited by ion-beam-assisted deposition (IAD) with Ar+ over the energy range 0.25–1 keV. The incorporation of noble gas depends on the mass and on the energy of primary ions for sputtering and on the energy and the ion:neutral flux ratio for IAD: it is found to vary between 0% to 5% and may be modified by post-deposition implantation at 45 keV. For film thicknesses above 50-100 nm, the resistivities of argon-free layers are 2.5 μΩ cm and 9 μΩ cm for silver and tungsten respectively. The incorporation of argon results in an increase in the resistivity proportional to the concentration (2.9 μΩ cm and 11 μΩ cm per percentage unit for silver and tungsten respectively), whatever the energy of the incorporated particles. In the case of tungsten, we show that the linear relation ϱ([Ar]) we determined appears as a lower limit for a lot of previously published papers when oxygen contamination is avoided

In situ Auger electron spectroscopy investigation of the chemical bonding of ion-beam-deposited silicon nitride

Abstract The necessity of knowing the atomic ratio of nitrogen to silicon and the contamination of silicon nitride to obtain layers with reproducible physical, chemical and electrical properties is reviewed. Ion-beam-sputtered thin films of various nitrogen-to-silicon ratios with an oxygen content of less than 1% are analysed by in situ Auger electron spectroscopy. By deliberately allowing a pure silicon-rich nitride layer to become oxidized, the different signals contributing to the line shape of the derivative Si LVV peak are unambiguously identified. Assuming the peak-to-background ratio to be an intrinsic measurement, we propose a method to evaluate the composition of non-stoichiometric silicon nitride layers from the study of the Si LVV peak recorded in the EN ( E ) mode. This peak is reconstituted by using a linear combination of experimental Si LVV peaks from pure silicon and completely nitrided silicon. A realistic background is deduced from a step-by-step deposition of Si 3 N 4 onto carbon. The results are compared with Rutherford backscattering spectrometry measurements and discussed.

Structural particularities of carbon-incorporated Si–Ge heterostructures

Abstract The structural consequences of carbon incorporation into silicon and Si Ge layers deposited on silicon (100) by rapid thermal chemical vapor deposition have been studied. High resolution X-ray diffraction (HRXRD) analysis, channeling Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) have been used to discover the structural particuliarities of this material in relation to the temperature of deposition. Experimental elastic energy density measurements have been compared with theoretical predictions for germanium concentrations of 0%, 10% and 16% as a function of substitutional carbon content. Raman spectroscopy measurements compared with an original high resolution transmission electron microscopy treatment showed that local compressive and tensile zones can simultaneously coexist at the interface. These localized tensile zones could probably act as pinning centers, blocking the propagation of dislocations, and hence increasing the critical thicknesses. With unadapted growth conditions, carbon segregation can occur. This effect can enhance local strain variations.

Optical properties of bulk and multi-quantum well SiGe:C heterostructures

Abstract We have investigated optical properties of SiGe: C layers deposited on Si(100). Bulk and multi-quantum well heterostructures were grown by rapid thermal chemical vapor deposition using methylsilane as carbon precursor. The optical properties are analyzed as a function of the structural properties of the alloys. The photoluminescence of these structures exhibits two features: deep level photoluminescence associated with localized states and band-edge recombination which gives an indication of the band gap variation due to carbon incorporation in substitutional sites. In the case of multi-quantum well heterostructures, we report on an enhancement of the radiative recombination associated with silicon at room temperature in presence of Si 1 − x C x layers. The strain compensation induced by carbon in SiGe, which is evidenced by X-ray diffraction, is compared to the Raman spectroscopy of the vibration modes of the alloy.

Reactive‐ion‐beam‐sputtered WNx films on silicon: Growth mode and electrical properties

WN films were deposited on clean Si(100) substrates via reactive‐ion‐beam sputtering a W target by a nitrogen ion beam in an UHV system. The energy of the incident ions varied in the range of 0.250 to 3 keV. The growth mode dependence of the films on the nitrogen ion energy was studied by in situ Auger electron spectroscopy measured as a function of coverage. Nitridation of the Si at the first stage of deposition has been found. This nitridation was more pronounced for the lower N beam energies, and minimal for the 2 keV beam. A similar trend was observed for the bulk film composition. In a complementary way, the dependence of electrical properties of the WN/Si junctions on the nitrogen energy has been studied. A higher barrier height on p‐type Si than on n‐type Si was found, unlike the expectation for regular metallization of W and its compounds on Si. The electrical characteristics can be attributed to the deposition technique. For the low‐energy beams, the formation of the interfacial layer was probabl...

Effects of impurities on the interface of ion beam sputtered tungsten with silicon

Abstract In this study, we have investigated the properties of the interface of ion-beam-sputter-deposited-W (IBSD-W) with silicon modified by the presence of an interfacial contamination (oxygen, nitrogen or boron). Auger electron spectroscopy combined with depth profiling was used to investigate the growth mode of IBSD-W onto Si as well as the redistribution of elements during in-situ thermal annealing. The growth mode is strongly affected by the incident ion energy and the presence of an interfacial oxide. We found that a thin oxide layer (≈ 2 ML) is not an efficient barrier to prevent silicon diffusion toward the metal surface. A thicker oxide (≈ 6 ML) greatly limits the silicon diffusion and inhibits silicide formation up to 700°C. Finally, the deposition of WN films by reactive ion beam sputtering leads to the nitridation of the silicon substrate and a stable contact up to 700°C.

Structural and Optical Properties of Sigec Alloys and Multi-Quantum Wells Grown by Rapid Thermal Chemical Vapor Deposition

We have investigated structural and optical properties of SiGeC layers. Bulk and multiquantum wells heterostructures were grown by rapid thermal chemical vapor deposition. The photoluminescence of these structures exhibits two distinct features : deep level photoluminescence associated with localized states and bandedge photoluminescence which gives an indication of the band gap variation due to carbon incorporation in substitutional sites. In the case of multiquantum wells heterostructures, a strong segregation is reported as the growth temperature is decreased. An alternate technique to incorporate carbon in SiGe layers, the pulsed laser induced epitaxy with an excimer laser, is presented. The incorporation of carbon in substitutional sites is evidenced by Raman spectroscopy. As the laser flux is increased, new Raman lines associated to carbon-induced disorder are observed in the spectra.