M. Dutoit

High quality Si1−x−yGexCy epitaxial layers grown on (100) Si by rapid thermal chemical vapor deposition using methylsilane

We have produced epitaxial Si1−x−yGexCy/Si heterostructures by rapid thermal chemical vapor deposition using methylsilane SiCH6). These layers were grown in the SiH4/GeH4/SiCH6/H2 system between 550 and 600 °C at 1.5 Torr. Suitable process conditions were found that allow very efficient substitutional carbon incorporation. No carbon cross contamination was observed. Crystal quality, chemical composition, and lattice strain were deduced from Nomarski microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, secondary ion mass spectrometry, and x‐ray diffraction. Defect‐free alloy layers with compositions of up to 20 at.% Ge and 2.2 at. % C were produced. The lattice parameter was tailored so that the strain in these layers gradually moved from compressive to tensile. A tensile strain of up to 0.35% was achieved.

Influence of nitrogen profile on electrical characteristics of furnace‐ or rapid thermally nitrided silicon dioxide films

Thin silicon dioxide films nitrided in N2O by rapid thermal processing (RTP) or in a classical furnace were investigated by x‐ray photoelectron spectroscopy, secondary ion mass spectroscopy, and electrical measurements on metal‐oxide‐semiconductor capacitors. Differences between the two nitridation processes were observed and explained. In lightly nitrided films, nitrogen occupies two configurations. Nitrogen is bound to three silicon atoms with at least one in the substrate or all three in the oxide. In RTP‐nitrided films, both of these species are confined to within 1.5 nm of the Si/SiO2 interface. In furnace‐nitrided films, the first species is also located close to the interface whereas the second one fills most of the regrown oxide thickness. In furnace‐grown films, which are more heavily nitrided, a third structure due to Si2=N–O is observed throughout the layer. The electrical characteristics are well correlated with the amount of nitrogen at the interface that is bound to Si atoms in the substrate.

Thermal stability of Si/Si1 − x − yGexCy/Si heterostructures grown by rapid thermal chemical vapor deposition

Abstract High quality pseudomorphic Si 1 − x − y Ge x C y alloy layers were grown on (100) silicon substrates by rapid thermal chemical vapor deposition with 0 or 11 at% Ge and 0.5 or 1 at% C. The relaxation behavior of these strained layers was investigated using rapid thermal annealing between 1000 and 1130°C. Substitutional C gradually precipitated out to form cubic silicon carbide (β-SiC). The in-plane lattice constant remained constant after annealing, indicating that there was no mechanical strain relaxation by misfit dislocations. The perpendicular lattice constant increased due to the decreasing substitutional C concentration. The same behavior was observed for both SiC and SiGeC samples, showing that Ge did not influence C precipitation. C atoms diffused over very short distances before they precipitated. It appears that, once formed, the β-SiC particles stayed put. Germanium out-diffusion was found to be somewhat higher than calculated with published diffusion coefficients.

Characterization of hot-electron-stressed MOSFET's by low-temperature measurements of the drain tunnel current

It is shown that measurements of the forward and reverse current in the gated drain-substrate diode of a MOSFET in accumulation, before and after stress, provide a sensitive means of characterizing hot-electron-induced degradation. Measurements on this diode under forward and reverse bias at temperatures between 300 and 77 K reveal an anomalous current that is weakly temperature-dependent. Computer simulations suggest that under reverse bias this excess current is due to band-to-band tunneling, while under forward bias it is due to tunneling through interface states. Both currents are modified after hot-electron (HE) injection in the gate-drain overlap region. Under reverse bias, the current is most sensitive to oxide trapped charges, while under forward bias, it is also sensitive to the generated interface states. The measurements confirm the high concentration of trapped electrons and acceptor interface states above the drain in NMOSFETs, after an HE stress. Characteristic peaks in the I-V curves are related to the energetic and spatial distribution of these interface states. In PMOSFETs, no degradation is detected above the drain after a HE stress. >

Optimization of Thin Si Oxynitride Films Produced by Rapid Thermal Processing for Applications in EEPROMs

We optimized thin reoxidized nitrided SiO 2 (ROXNOX) films produced by RTP on the basis of a careful analysis of the requirements of EEPROMs. The influence of oxidation, nitridation, and reoxidation parameters on charge-trapping and breakdown during a constant current stress was studied in detail. We show that a very light nitridation gives a maximum nitrogen concentration at the Si/SiO 2 interface and the largest increase in the endurance of the films under a high-field stress. The physical basis of these results is discussed

Comparison of gate-induced drain leakage and charge pumping measurements for determining lateral interface trap profiles in electrically stressed MOSFETs

Improved methods for extracting lateral spatial profiles of interface traps in electrically stressed MOSFETs from gate-induced drain leakage and charge pumping measurements are proposed. Simplified theoretical models are developed. The formal similarity of the two methods is shown. The results obtained on submicron MOSFET after uniform (Fowler-Nordheim) and nonuniform (hot carrier) stress are compared and found to be in good agreement. The relative merits of these techniques are discussed.

Epitaxial growth of Si1-x-yGexCy alloy layers on (100)Si by rapid thermal chemical vapor deposition using methylsilane

High quality pseudomorphic Si1−yCy and Si1−x−yGexCy layers were grown on (100) Si between 530 and 650 °C by rapid thermal chemical vapor deposition in the SiH4/GeH4/SiH3CH3/H2 system. These layers contained up to 30 at. % Ge and up to 2.2 at. % C. Strain engineering was achieved. The strain could be tailored continuously from compressive (up to 2.2% in Si1−xGex) to tensile (up to −0.8% in Si1−yCy and −0.35% in Si1−x−yGexCy). The relationship between the process parameters and the physical properties of the layers was investigated. A process window for growing high quality layers was defined in terms of the partial pressures of SiH4 and SiH3CH3. It was found to be independent of Ge content, growth temperature, and growth rate. No carbon contamination was observed. No interference between Ge and C incorporation was observed. A model for the incorporation of substitutional C in the films which is based on the chemical reaction of SiH4 and SiH3CH3 on the surface is proposed.

Dielectric breakdown in thin Si oxynitride films produced by rapid thermal processing

Thin films of silicon oxide and oxynitride were prepared by rapid thermal processing. Under optimum conditions (e.g., nitridation at 1100 °C for 4 s followed by reoxidation at 1150 °C for 60 s), their electrical properties (charge trapping, low‐field leakage, and charge to breakdown) were significantly improved over those of the starting oxide. Values of Qbd as high as 260 C/cm2 for a positive current density of 200 mA/cm2 were obtained. Yet, the improvement was much smaller for negative than positive stress. This difference is ascribed to the asymmetrical role of nitridation on the prevention of interface trap generation at high fields and is consistent with models of the generation of interface traps described in the literature.

Thin SiO2 films nitrided by rapid thermal processing in NH3 or N2O for applications in EEPROMs

Abstract Thin silicon dioxide (SiO2) films nitrided by rapid thermal processing (RTP) in ammonia and nitrous oxide are compared. Their electrical characteristics (oxide and interface trapped charge densities, resistance to high-field stress, breakdown charge) are correlated with the concentration of nitrogen at the Si/SiO2 interface. An optimum in several parameters is found for very light nitridations (0·5-1 at.% N). In this case, a significant improvement in the reliability of non-volatile memories (EEPROMs) is anticipated.

Fabrication and photoluminescence investigation of silicon nanowires on silicon-on-insulator material

A process compatible with very large scale integrated technology for preparing high densities (up to 500 μm−2) of well-passivated sub-5 nm diam silicon nanowires is presented. The nanowire formation consists of the deposition of a fine-grained natural mask and the subsequent transfer of the pattern into the silicon substrate by reactive ion etching. To isolate the nanowires from the bulk and from each other, this process was applied on silicon-on-insulator material, where the buried oxide layer acts as an etch stop. The nanowire diameter distribution was then shifted below 5 nm by self-limiting oxidation. Finally, hydrogen-rich amorphous silicon nitride (a-SiNx:H), prepared by plasma enhanced chemical vapor deposition, was deposited onto the structures to act as a source of hydrogen. After annealing in forming gas, visible photoluminescence (PL) is detected under 325 nm excitation. The a-SiNx:H was found to emit broad PL, where peak position and intensity depend on the layer composition. Buried silicon ox...