Petia Weih

Stress Control in 3C-SiC Films Grown on Si(111)

In this study we report on the effect of Ge coverage prior to carbonization, on the stress state in 3C-SiC thin films grown by solid source MBE on Si (111). Plan view μ-Raman technique was used to extract the residual stress in the 3C-SiC films. The obtained results showed that the stress depends strongly on the Ge amount and decreases linearly with increasing the Ge amount. The linear dependence of the residual stress allows to adjust the stress to a given value. For the obtained correlation between the predeposited amount of Ge and the residual stress a model will be proposed to explain the obtained results within the framework of the S-correlated theory of 3C-SiC on Si.

Etching of SiC with Fluorine ECR Plasma

Electron cyclotron resonance (ECR) dry etching of 3C-SiC with different fluorinated gases, namely, sulfurhexafluoride (SF6) and tetrafluoromethane (CF4), was carried out. The influence of the gas flow, the etch gases and the applied bias voltages on the etch rate was studied. The maximum etch rates in the case of SF6 achieved were 1570 Å/min and 260 Å/min for Si and 3CSiC, respectively. In the case of CF4 the 260 Å/min (Si) and 160 Å/min (3C-SiC) were obtained. Furthermore, we investigate the selectivity of this dry etching process of SiC against Si. The residue free surface conditions were determined with Auger electron spectroscopy.

High-Resolution XRD Investigations of the Strain Reduction in 3C-SiC Thin Films Grown on Si (111) Substrates

In this work the biaxial stress of 3C-SiC thin films epitaxia lly grown on Si(111) substrates has been investigated by using x-ray diffraction methods. The influence of the resulting strain on the electrical properties of SiC/Si heterojunctions was an lyzed. Different methods to prepare the surface prior to the SiC deposition were compared: (i) ex situ carbonization, (ii) interface modification by deposition of Ge prior to epitaxial growth and (iii) annealing of the silicon surface. The x-ray measurements revealed the lowest strain in ex situ carbonized samples, showing a transition from tensile to compressive strain when off-axis substrates were used. The highest strain appeared in SiC layers grown on a thin Ge intermediate layer whi ch was deposited prior to SiC growth without an additional annealing step of the substrate. The strai n in the SiC layer is directly correlated with the reverse current through the heterojunction. Introduction Epitaxially grown mismatched semiconductor heterostructures are of increasing importance for microand optoelectronic devices or circuits. Lattice mismatched layers can be elastically strained by pseudomorphic growth on the substrate. Alternatively the strain can be relieved by relaxation of the epilayer due to formation of misfit dislocations resulting in a n in-plane lattice parameter of the epitaxial film close to that of the bulk material. If epitaxia l l yers of 3C-SiC are grown on Si substrates the large mismatch in the lattice constants and the thermal expansion coefficients lead to a substantial residual tensile strain. A significant part of the 20% mismatch in lattice constants can be released by the formation of a dislocation network. However, the mis match in thermal expansion coefficients of SiC and Si introduces an additional strain into the s yst m during the cooling down process after growth. This strain results in a strong degradation of the layer properties and a wafer warpage, limiting the use of SiC/Si hetrostructures for device a pplications and as pseudo substrate for the deposition of group III-nitrides. In this work we analyze the e ffect of different techniques to minimize the residual strain of the SiC layers and to improve the structural and electrical properties of the grown heterostructures. Experimental The 3C-SiC thin films (thickness ~120 nm) were grown by solid-source mol cular-beam epitaxy (MBE) on (111)-oriented onand off-axis Si crystal wafers at a substrate temperature of 1000°C with a growth rate around 1 nm/min. Prior to epitaxial growth the Si( 111) substrates were prepared by different methods. The first method uses an ex vacuo carbonization process at 1280°C in a propane-hydrogen atmosphere inside a rapid thermal processing (RTP) sy stem [1]. The MBE Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 233-236 doi:10.4028/www.scientific.net/MSF.433-436.233

Influence of the Ge Coverage Prior to Carbonization on the Structure of SiC Grown on Si(111)

A structural study of SiC layers grown by molecular beam epitaxy on carbonized Si(111) substrates with Ge modified interfaces is reported. Different quantities of Ge were predeposited prior to the SiC growth for comparison. X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy in both conventional (CTEM) and high-resolution modes (HREM) and selected-area electron diffraction (SAED) have been used to evaluate the structural quality of the SiC layers. SIMS measurements show that, after the epitaxial growth, the predeposited Ge remains at the interface and in the region of the silicon substrate closest to the interface. This observation was confirmed by HREM investigations. The 300 nm-thick SiC layers are subject to a residual in-plane tensile strain of 0.70.8 %. The defect structure indicates an enhanced lattice relaxation caused by Ge incorporation into the SiC/Si interface. The grain size tends to decrease as Ge coverage increases. Furthermore, the presence of Ge suppresses the formation of voids at the interface thanks to the formation of a Si/Ge/C alloy interlayer acting as a barrier for the outdiffusion of Si.

High dose high temperature ion implantation of Ge into 4H-SiC

A box like Ge distribution was formed by ion implantation at 600°C. The Ge concentration was varied from 1 to 20 %. The TEM investigations revealed an increasing damage formation with increasing implantation dose. No polytype inclusions were observed in the implanted regions. A detailed analysis showed different types of lattice distortion identified as insertion stacking faults. The lattice site location analysis by “atomic location by channelling enhanced microanalysis” revealed that the implanted Ge is mainly located at interstitial positions.

Growth of 3C-(Si1-xC1-y)Gex+y Layers on 4H-SiC by Molecular Beam Epitaxy

In the present work cubic 3C-(Si1-xC1-y)Gex+y solid solutions were grown at different^temperatures by molecular beam epitaxy on on-axis 4H-SiC (0001) substrates. Two different growth methods are compared in order to explore the optimal growth conditions for the incorporation of Ge into the SiC lattice during the low temperature epitaxy. For this reason simultaneous growth and migration enhanced epitaxy were used. The chemical composition of the grown layers were analyzed by energy dispersive x-ray methods during transmission electron microscopy investigations. It was found that the migration enhanced epitaxy is a more suitable technique for the formation of high quality (Si1-xC1-y)Gex+y solid solutions. Additionally, polytypes transition from 4H-SiC to 3C-SiC occurs during the growth independent of the applied growth technique.

Atomic Layer Epitaxy of (Si1-xC1-y)Gex+y Layers on 4H-SiC

3C-(Si1-xC1-y)Gex+y ternary alloys were grown on 8.5° off axis 4H-SiC substrates by solid source molecular beam epitaxy in a temperature range between 750°C and 950°C. Energy dispersive X-ray (EDX) analysis revealed a decrease of the Ge incorporation versus substrate temperature. This effect is due to the fixed Si/Ge ratio during the epitaxial growth. The Ge distribution within the grown epitaxial layers was found to be nearly homogeneous. The investigations by atomic location by channeling enhanced microanalysis allowed the conclusion that Ge is located mainly at Si lattice sites.

Strain relaxation and void reduction in SiC on Si by Ge predeposition

In this work, 120 nm cubic SiC layers have been grown on Si (111) by SSMBE, depositing 1ML of Ge at different temperatures before carbonization. In every case, SiC was epitaxially grown on Si (111) showing characteristic defects and more relaxation than a reference sample where Ge was not employed. Depending on the temperature of Ge predeposition, a reduction of voids or stacking faults was achieved. The residual strain depended on this temperature, as was confirmed by electron diffraction and infrared ellipsometry measurements.