Daniel Bensahel

Selective epitaxial silicon growth in the 650–1100 °C range in a reduced pressure chemical vapor deposition reactor using dichlorosilane

Selective epitaxial silicon layers have been grown in a reduced pressure (<2 Torr) reactor in the 650–1100 °C temperature range using only dichlorosilane (DCS) gas diluted in hydrogen. The growth rate plotted in Arrhenius coordinates (log G vs 1/T) shows an activation energy of 59 kcal/mol in the 650–800 °C range. A comparison is made between the DCS system and our previous results concerning the SiH4/HCl/H2 system.

Optical characterisation of porous silicon layers by spectrometric ellipsometry in the 1.5–5 eV range

Spectroscopic ellipsometry study in the 1.5–5 eV range have been performed in 3 μm thick porous silicon layers, made on p and p+ substrates and with porosities varying from 10% up to 86%. Above 2.5 eV, spectroscopic data are shown to depend on material morphology. Below 2.5 eV and for very high porosities, the PS films reveal an uniaxial optical anisotropy. A quantitative determination of this anisotropy, i.e., the bifregingence, in both p and p+ porous films can be achieved.

Covering and filling of porous silicon pores with Ge and Si using chemical vapor deposition

Filling of the pore network of porous silicon layers with Ge and Si has been demonstrated using a chemical vapor deposition (CVD) technique. It is shown that at low growth rate the species are deposited throughout the whole layer which can be completely filled. At high growth rate, the deposition takes place mainly on the top surface leading to pore mouth bridging. Investigation of the experimental data through a model shows that pore filling is a powerful tool for the study of the mechanisms involved in CVD processes at low temperature.

Characterization of Porous Silicon: Structural, Optical and Electrical Properties

The aim of this paper is to provide a better understanding of photoluminescent porous silicon (PS) microstructure in relation to their electronic properties: absorption band edge shift 1 and quantum confinement hypothesis 1,2 , dielectric constant evolution and electroluminescence characteristics. Results concerning the p type PS microstructure characterization by X ray diffraction and electron microscopy are presented showing a noticeable decrease in crystallite size and surface area with decreasing substrate doping and increasing porosity. The optical transmission of homogeneous free-standing PS layers of different porosities and substrate dopings is studied, showing no evidence of a direct energy gap in PS. On the contrary, a large blue shift of the optical absorption edge, taking into account the total Si mass content in the PS film, is demonstrated. This shift is well correlated with the crystallite size variations with porosity and substrate doping and is attributed to a quantum confinement of electronic wavefunctions in the nanocrystallites. On the other hand, ellipsometry measurements show the PS absorption to be little affected by the microcrystalline structure of the material in the 3.5–5 eV range, i.e. above the direct band gap of bulk Si. This indicates that, if confirmed, the quantum confinement strongly affects the PS joint density of states in the vicinity of the Si band edge and, as could be expected, to a much lesser degree near the edge of the confining potential. Capacitance voltage measurements of thin PS layers allow the determination of the dielectric constant which is shown to decrease with increasing porosity. This behavior is in reasonable agreement with thee values deduced from the transmission experiments in the near infrared. Furthermore, it is shown that this dependence on porosity is well accounted for by the Bruggeman effective medium approximation. Finally, recent results concerning visible light emission from solidstate porous silicon devices will be presented: I-V characteristics, electroluminescence intensity and dynamic, quantum efficiency and device ageing.

Formation kinetics of MoSi2 induced by cw scanned laser beam

Scanned cw laser beams at different scan velocities from 10 to 400 cm/s have been used to study the interaction of thin metal films of molybdenum deposited by electron beam evaporation with single‐crystal silicon substrate. Backscattering technique has been used to investigate the growth mechanism of hexagonal silicide MoSi2 as a function of the number of repetitive laser scans. Silicide layers are found to grow at a rate proportional to the square root of the effective annealing time in the whole range of scan velocities. Effective annealing temperatures are calculated for each laser annealing condition, and from an Arrhenius plot a mean value of activation energy for MoSi2 growth is estimated.

In situ spectroscopic ellipsometry of porous silicon layers annealed under ultrahigh vacuum

In situ spectroscopic ellipsometry measurements in the 1.8–2.8 eV spectral range were performed on porous silicon (PS) layers annealed in an ultrahigh vacuum chamber up to 600 °C. It is shown that both the refractive index and the absorption coefficient increase after the thermal anneal and the effect is reversible when samples are returned to atmosphere and HF dipped. These changes in the optical properties of the material can be attributed to an intrinsic strain modification in the PS cellular structure induced by hydrogen desorption upon annealing.

Kinetics aspects of TiSi2 deposition without silicon consumption

Selectively deposited layers of TiSi2 have been obtained without Si substrate consumption using the TiCl4/SiH4 system diluted in H2 at 800 °C. For a given set of parameters, we show that TiSi2 formation uses Si coming from the substrate or from the gas phase, the principal parameters being the TiCl4/SiH4 ratio, the carrier gas, and gas mass transfer as the limiting mechanism of the reactions.

Growth and in situ ellipsometric analysis of Si 1−x Ge x alloys deposited by chemical beam epitaxy

Growth of strained Si1-xGex alloys on Si (100) by chemical beam epitaxy using silane and germane as gas precursors is reported. Selectivity on SiO2 patterned substrates, superlattices with sharp interfaces are easily achieved for x values varying between 0 and 25%. The incorporation rate of germanium and the growth kinetics are analyzed as a function of the germane gas flow and substrate temperature. The growth process is controlledin situ using a multi-wavelength ellipsometer. An accurate monitoring of the germanium content and thickness of multi-quantum well along with bulk structures can be obtained by this method. We show that a three-dimensional growth analysis is also worth consideration for structural characterization of the layer.

Kinetic aspects of epitaxial silicon growth using disilane in a rapid thermal processing system

We have measured the epitaxial growth rate of Si in the disilane/hydrogen system for different experimental conditions in a rapid thermal processing–low‐pressure chemical vapor deposition reactor. The measured activation energy is about 43 kcal/mol for temperatures below 700 °C. The growth rate dependence on disilane or hydrogen partial pressures is measured in order to verify the reliability of a proposed model for the decomposition of the disilane molecule in the torr pressure regime. The obtained crystal quality is comparable to that obtained with silane gas except for higher growth rate in the disilane system.

In situ ellipsometric control of Si1−xGexSi heterostructures grown by chemical beam epitaxy

Abstract In situ ellipsometric characterizations of Si 1− x Ge x alloys are presented. The samples are grown by chemical beam epitaxy using silane and germane. The growth process (kinetics, composition etc.) is in situ controlled using a rotating-polarizer multiwavelength ellipsometer. Several examples of heteroepitaxy followed by ellipsometry are shown: desorption of the native oxide and the initial growth stages are analysed at different photon energies. The sequential heteroepitaxy of Si 0.85 Ge 0.15 on Si and Si on Si 0.85 Ge 0.15 is investigated.