Roland Madar

Thermodynamic Heat Transfer and Mass Transport Modeling of the Sublimation Growth of Silicon Carbide Crystals

The deposition of single SiC crystals has been processed inside a sealed enclosure at temperatures above 2300 K and pressures lower than 5.10 3 Pa by the modified Lely method. The purpose of this work is to examine the potentialities of different macroscopic models, thermodynamics, heat, and mass transfers on the simulation of the growth of such crystals with a special emphasis on their coupling mechanism. Thermodynamic modeling has been used to determine the most important reactive species involved in equilibrium conditions. Induction heating modeling has allowed the calculation of the actual temperatures inside the reactor which are not well known because of the difficulty associated with their measurements. Finally, mass transport modeling provided the calculated deposition rate. It was found that the calculated growth rates were close to the experimental ones which may indicate a good representation of the actual phenomena involved in the crucible. As a matter of fact each of the proposed models has contributed to a better knowledge of the process.

Structure antiferroma gnetique de Fe1. 125Te accompagnee d'une deformation monoclinique

Abstract The antiferromagnetic structure of the tetragonal phase Fe 1. 125 Te has been determined. Below the magnetic-order temperature x-ray and neutron diffraction show a monoclinic deformation.

Temperature gradient controlled SiC crystal growth

Abstract 6H-SiC ingots, 1 in, in diameter have been grown by the modified Lely method with ‘in situ’ sublimation etching. Nucleation was controlled by the temperature gradient. Pinholes density was in the range of 100–200 cm−2. It is proposed that the developed method allows to realise step flow growth to decrease pinhole density.

Continuous Feed Physical Vapor Transport Toward High Purity and Long Boule Growth of SiC

A new reactor concept for the growth of silicon carbide bulk crystals and/or thick epitaxial layers is presented. A coupled approach involving process modeling and numerical simulation and experimental results and characterization was used. This new process combines both high-temperature chemical vapor deposition (HTCVD) for continuous feeding of the polycrystalline source and physical vapor transport (PVT) for single-crystal growth. A special crucible design was built to perform both steps simultaneously. For the feeding step (HTCVD), tetramethylsilane diluted in argon was used. The typical growth rate obtained by the continuous feed PVT process is 100 μm/h at 1900°C. The growth of thick epitaxial layers is demonstrated with a pure two-dimensional growth regime.

Resistivity and magnetoresistance of high-purity monocrystalline MoSi2

The authors report resistivity and magnetoresistance measurements (4.2<T<300K; H<or=7.6 T) of extremely pure monocrystalline MoSi2 (RRR approximately=1800). This metallic compound behaves like a compensated metal (n(h+)=n(e-)) with a very large magnetoresistivity at 4.2K which varies like H2 up to 7 T. The anisotropy of the electronic structure accounts well for the anisotropy of the results. Deviations from Matthiessens rule are also reported.

Millitorr range PECVD of a-SiO2 films using TEOS and oxygen

Abstract SiO 2 films have been deposited using TEOS and oxygen in a microwave excited plasma reactor at a pressure of 3 mTorr. Layers have been characterized using FTIR, refractive index, chemical etch rate, electron spin resonance, Rutherford backscattering spectroscopy, nuclear reaction analysis and electrical measurements. The influence of substrate temperature and impinging ion energy has been studied. Layers having satisfactory physical properties were obtained for deposition at 400°C with a substrate polarization of the order of −120 V.

LPCVD WSi2 Films Using Tungsten Chlorides and Silane

This paper makes a systematic study of blanket and selective low pressure chemical vapor deposition (LPCVD) WSi 2 films from tungsten chlorides, silane, hydrogen, and argon on silicon as well as on patterned oxidized silicon substrates. Experiments were performed by varying the initial gaseous WCl 4 to SiH 4 ratio (Rx) or the deposition temperature (T d ). Initially, yield and CVD-phase diagrams of the W-Si-Cl-H-Ar chemical system were drawn, based on thermodynamic simulations. The deposition of pure WSi 2 phase and mixed solid phases involving W, W 5 Si 3 , WSi 2 , and Si was predicted to occur in relation to process parameters

Large Area DPB Free (111) β-SiC Thick Layer Grown on (0001) α-SiC Nominal Surfaces by the CF-PVT Method

Thick (111) oriented β-SiC layers have been grown by hetero-epitaxy on a (0001) a-SiC substrate with the Continuous Feed-Physical Vapour Transport (CF-PVT) method. The growth rate was 68 µm/h at a pressure of 2 torr and a temperature of 1950°C. The nucleation step of the β-SiC layer during the heating up of the process was studied in order to manage first the a to b heteropolytypic transition and second the selection of the b-SiC orientation. With a adapted seeding stage, we grew a 0.4mm thick layer almost free of Double Positioning Boundaries on a 30mm diameter sample. First observations of the layer by cross-polarised optical Microscopy are presented both in planar view and in cross section geometry.

Different macroscopic approaches to the modelling of the sublimation growth of Sic single crystals

Abstract Different macroscopic models such as thermodynamics, heat transfer and mass transport have been applied to the simulation of the growth of single SiC crystals prepared according to the so-called ‘modified Lely method’. Thermodynamic modelling has been used to determine the most important reactive gaseous and solid species present under equilibrium conditions. Heat transfer modelling (including induction heating, radiation with multireflection, convection and conduction) has been performed to calculate the actual temperatures inside the reactor. Different temperature fields have been obtained depending on the level of complexity of the thermal modelling. Finally, mass transport modelling provided the chemical fields of the process and calculated deposition rates which were found to be close to the experimental ones. It appears that the solid SiC surface shape after growth depends on the temperature gradient existing along the seed.

Preparation and crystal structure of a new family of transition metal phospho-silicides

Single crystals of new high phosphorus-silicon content compounds of transition metal FeSi4P4, RuSi4P4 and OsSi4P4 have been obtained from tin flux. Powders of the same composition have been prepared by reaction of the elemental components in evacuated silica tubes. These compounds are isomorphic. Crystal structure of FeSi4P4 and RuSi4P4 have been determined from four-circle diffractometer data of single crystals.