Silicon Layers Grown on Patterned Substrates by Liquid Phase Epitaxy
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ABSTRACT Single-crystal silicon layers and dcping multilayers have been grown by liquid phase epitaxy on silicon substrates. The substrates were either partially masked by Si02, with via holes of various shapes and sizes, or patterned with SiO 2 stripes, or profiled with grooves and ridges. The via holes and grooves were just refilled, or they acted as seeding areas for lateral overgrowth of the oxidized wafer up to 100um. The silicon layers, interfaces and heterointerfaces were free of defects. With apprcpriate growth conditions the surfaces and interfaces of the epitaxial Si were cutstandingly planar. INTRODUCTION Liquid phase Epitaxy (LPE) of Si offers specific advantages for selective growth, growth on patterned substrates and growth of high quality silicon on insulators (SOI). The tenperatures of the LPE process are generally low /1-3/. The teaperature is always uniform across the whole sample. Tenperature gradients, which are necessary in other techniques to drive the growth fronts /4/, are not required. Device structures which are already fabricated in substrates will therefore remain unaffected by subsequent LPE growths. Mechanical stresses between Si and Si02 due to the different thermal expansion coefficients are kept small due to low Epitaxial growth tenperatures. Hence, structural defects are not formed at the Si/SiO2 heterointerfaces. The low supersaturation required for LPE growth prevents heterogeneous nucleation on the Si02 masks. Lateral overgrowth, therefore, can be achieved by one single deposition step, without any etching or liftoff of polysilicon nuclei during or after Epitaxial growth. This makes an epitaxial lateral overgrowth (ELO) process with LPE very easy compared to CVID- or MBE processes /5,6/. The high growth anisotrcpy at low temperature and low super saturation is favorable for substrate seeded, single-crystalline lateral overgrowth with high aspect ratios. Several experiments were carried cut to demonstrate (test) these vievpoints and will be described in the following. EXPERIMENTAL The growth eperiments were made either in a tipping boat Epitaxial system for single layers or in a centrifugal system for multilayers. Both growth systems wye descrý8ed e2rlier /7-9/. Electron and hole concentrations between 10 and 10 cm- in the Epitaxial silicon were adjusted by apprcpriately composing the solvents. The main constituent of the solvents was indium (or bismuth for a few experiments) with small amounts of Ga, P or As added as dcpant materials. The layers were grown on (111) orientated Si
Mat. Res. Soc. Symp. Proc. Vol. 54. ' 1986 Materials Research Society
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wafers. For the studies of selective growth and seeded lateral overgrowth, patterns of via holes and parallel stripes in various orientations, and in widths of 1 to 100 Pm were etched into the thermal oxide. Growth tenperatures of the Epitaxial layers were chosen between 950 and 750*C. RESULTS AND DISCUSSION Selective growth on partially Si02 -masked substrates occurs without any competing nucleation or undesired growth on the ma
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