Sandrine Juillaguet

Investigation of 2 inch SiC layers grown in a resistively-heated LP-CVD reactor with horizontal “hot-walls”

With respect to more standard and more widely used inductive-heating, the resistivelyheated reactors offer the strong advantage of low cost, easy installation and low running constraints. Combined with an easy adaptation to the increasing size of wafers, this results in very strong advantages. This simple technique was mainly restricted to the growth of small size samples for academic purpose [1]. In this work we report an investigation of 2 inch SiC layers deposited in a new, horizontal and resistively-heated, “hot-wall” LP-CVD reactor specially designed for large flexibility. Introduction Due to superior physical properties, SiC appears as a most promising material for high power, high frequency and high temperature electronic devices or sensors. In this case, whatever is the targeted application, one needs to deposit a low doped, electronic grade material, on a large diameter single crystalline wafer. A promising technique is the use of hot-wall CVD, coupled with resistive heaters. With respect to the more standard and widely used inductive-heating technology, a resistivelyheated reactor offers advantages in terms of (low) cost, (easy) installation and (low) running constraints. Combined with a very easy adaptation to the increasing size of wafers, this seems very appealing. Unfortunately, up to now, this simple technique has been restricted to the growth of small size samples for academic purpose [1] and was not seriously considered for industrial applications. In order to establish more the potentiality of this system, we report a detailed investigation of the thickness uniformity, surface morphology and low temperature photoluminescence properties of a series of epitaxial layers deposited on silicon. We show that, on 2” Si substrates, state of the art material can be easily obtained. Experimental The reactor has been specially designed to allow, both, usual SiC growth by LP-CVD [1] as well as full Si-wafer conversion by LPE [2]. In this case, the control of the vertical temperature gradient is essential to insure an optimised liquid phase diffusion. This technical constraint dictated the choice of two independent heaters (upper and lower resistive) forming then a standard“hot-walls” configuration. The walls are thin (0.5mm) and made of high purity graphite sheets. The thermal inertia is then very low, which allows RTP (Rapid Thermal Processing) to be done up to 1800°C. In order to Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 273-276 doi:10.4028/www.scientific.net/MSF.457-460.273

Hexamethyldisilane/propane versus silane/propane precursors: application to the growth of high-quality 3C–SiC on Si

From a comparative evaluation of hexamethyldisilane (HMDS) and silane–propane (SP) precursor systems, it is shown that HMDS needs a small addition of propane to deposit heteroepitaxial layers of 3C–SiC on Si with superior crystalline properties. In this case, propane compensates for the secondary reactions induced by hydrogen reacting with carbon. Using atmospheric pressure chemical vapour deposition conditions, the new system (HMDS–propane) demonstrates several advantages. It is safer to handle than SP and allows a higher growth rate (up to 7 µm h−1 at 1350 °C) without any degradation of the layer morphology. However, when lowering the deposition temperature, HMDS is revealed to be more stable than silane. This is in contrast to most standard beliefs but explains why a high temperature (~1350 °C) is always necessary to grow high-quality material using HMDS.

Specific Aspects of Type II Heteropolytype Stacking Faults in SiC

Focussing on the fine structure of excitons bound to large 2-dimensional stacking faults in a 4H-SiC matrix, we show that the intrinsic type-II nature of the band alignment, combined with the effect of the spontaneous polarization, should result in a double bound-exciton signature per well. Then, we present the first observation of a 3C-QW sandwiched between two higher energy bandgap polytypes in a 3C-SiC matrix.

Optical investigation methods for SiC device development: application to stacking faults diagnostic in active epitaxial layers

We present a review of the different optical techniques that can be used to investigate the presence of as- grown and/ or process- induced stacking faults ( SFs) in 4H - SiC epitaxial layers. A SF is always a finite admixture of different polytypes, and we begin with a brief review of the systematic of SiC polytype structure and electronic properties. Next, we discuss the optical signature and compare with the results of several model calculations, taking successively into account the effect of valence band offset, internal polarization and non-homogeneity of the potential well. Finally, we consider cathodo-luminescence and micro- photoluminescence techniques and show that, in both cases, some screening of the built- in electric field can be achieved.

Investigation of porous silicon as a new compliant substrate for 3C-SiC deposition

Investigation of porous silicon as a new compliant substrate for hetero-epitaxial deposition of 3C-SiC on silicon has been performed. The resulting layer has been analyzed in terms of X-ray diffraction, infrared reflectivity, micro-Raman scattering and low temperature photoluminescence experiments. From the results, intermediate properties between 3C-SiC deposited on bulk silicon and 3C-SiC deposited on SIMOX have been found.

Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)

Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn.

Characterization of Bulk 3C-SiC Single Crystals Grown on 4H-SiC by the CF-PVT Method

Because of the formation of DPB (Double Positioning Boundary) when starting from a hexagonal <0001> seed, DPB-free 3C-SiC single crystals have never been reported up to now. In a recent work we showed that, using adapted nucleation conditions, one could grow thick 3C-SiC single crystal almost free of DPB [1]. In this work we present the results of a multi-scale investigation of such crystals. Using birefringence microscopy, EBSD and HR-TEM, we find evidence of a continuous improvement of the crystal quality with increasing thickness in the most defected area, at the sample periphery. On the contrary, in the large DPB-free area, the SF density remains rather constant from the interface to the surface. The LTPL spectra collected at 5K on the upper part of samples present a nice resolution of multiple bound exciton features (up to m=5) which clearly shows the high (electronic) quality of our 3C-SiC material.

Intensity Ratio of the Doublet Signature of Excitons Bound to 3C-SiC Stacking Faults in a 4H-SiC Matrix

In 4H-SiC, 3C stacking fault (SF) behaves like a finite thickness type II quantum well. As a consequence, it can bind two excitons per well. We show in this work that, as the SF thickness increases, the relative intensity of the two transitions changes. This comes from a change in the wave functions overlap between the electron trapped in the well and the holes trapped neighbouring parts of the 4H-SiC matrix.

Screening the built-in electric field in 4H silicon carbide stacking faults

The authors report a detailed comparison of low temperature photoluminescence (LTPL) and cathodo luminescence (LTCL) spectra collected in the same stacking faults rich area of a 4H silicon carbide epitaxial layer. In both cases, they find that the maximum wavelength of the defect-related emission lines shifts when the excitation spot position moves across the defect zone. The shift is excitation-intensity dependent. It is very small for LTPL (4meV) but reach 20meV for LTCL. This constitutes the first experimental evidence that a screening of the quantum confined Stark effect can be achieved in 4H-SiC SF quantum wells.

Optical investigation of residual doping species in 6H and 4H-SIC layers grown by chemical vapor deposition

Abstract We report the results of a series of optical investigations performed on both 6H and 4H epitaxial layers grown at low rate (≈1 μm h −1 ) in a home-made cold-wall chemical vapor deposition (CVD) reactor. To keep the level of contamination as low as possible, attempts have been made to investigate the origin of residual dopants. In this way, we have found that aluminum comes only from the use of uncoated graphite susceptors. When using a SiC coated susceptor, we have found that the protection is only effective for about ten runs.