Solid Phase Epitaxy of Implanted Si-Ge-C Alloys
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ABSTRACT Sil-x-yGexCy/Si heterostuctures were formed on Si (100) surface by Ge and C implantation with a high dose rate MEtal - Vapor Vacuum Arc (MEVVA) ion source and subsequent Solid Phase Epitaxy (SPE). After thermal annealing in the temperature range from 600 °C to 1200 °C, the implanted layer was studied using Rutherford Back-scattering Spectrometry (RBS), cross-sectional High Resolution Transmission Electron Microscopy (HRTEM) and fourbounce X-ray Diffraction (XRD) measurement. Due to the small lattice constant and wide bandgap of SiC, the incorporation of C into Si-Ge can provide a complementary material to SiGe for bandgap engineering of Si-based heterojunction structure. Polycrystals are formed at temperature at and below 1000 °C thermal growth, while single crystal epitaxial layer is formed at 1100 'C and beyond. XRD measurements near Si (004) peak confirm the compensation of the Silx Gex lattice mismatch strain by substitutional C. C implantation is also found to suppress the End Of Range (EOR) defect growth.
INTRODUCTION The Si-Ge system has been extensively synthesized by researchers using various synthesis techniques, such as Molecular Beam Epitaxy (MBE), Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD), and ion implantation with subsequent Solid Phase Epitaxy (SPE) [13]. The high-dose Ge implantation process is advantageous over the other two direct epitaxial methods because it is compatible with conventional Si processing technology, and can readily be integrated into standard IC process sequence. However, crystal defects introduced by the implantation process, such as the End Of Range (EOR) dislocation loops formed near the amorphous/crystalline (a/c) interface after SPE, have to be eliminated for any device applications. Recently, interest in the group IV Si-Ge system has extended to the Si-Ge-C ternary system [4, 5]. One of the fundamental difficulty to form defect-free Silx Ge x/Si heterojunction is due to the over 4% lattice constant mismatch between Si (asi = 0.543 nm) and Ge (as, = 0.566 nm). C is the only element in group IV with a single crystal (diamond) lattice constant less than Si, and has the potential to compensate the built-in strain in the Si-Ge system. Recent work by Im et al. [5] has demonstrated that Sil.x.yGe.Cy shows less strain induced dislocation formation than Si1 xGex alloy. Being isoelectronmc with Si and Ge, C is not expected to be a dopant. Nevertheless, it is also known that C inhibits the kinetics of Si SPE such that a low growth rate is expected. This paper presents the material synthesis results of Sil.xyGexCy alloy formed by high-dose, implantation using a MEtal-Vapor Vacuum Arc (MEVVA) source [6, 7]. Different from conventional implanters, the MEVVA source provides a high current density implantation using solid Ge and C (graphite) sources. A relatively low voltage ( i.e. 20 kV) is needed in our work to synthesis surface layer of Si-Ge and Si-Ge-C alloys. Issues on the solid phase epitaxy crystalline quality of the SilxyGexCy layer, as well as the recovery of
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