Formation of CoSi 2 in SIMOX wafers by high dose cobalt implantation

Abstract

SIMOX (separation by implanted oxygen) wafers were implanted with high doses of cobalt and annealed at high temperature in order to study the formation of buried single-crystal CoSi 2 layers in this material. For this study SIMOX wafers of (100) oriented silicon were implanted at 100–200 KeV with doses of 1.2–2.0×10 17 Co + cmsu−2, and annealed in a rapid thermal processor or tube furnace. As-implanted and annealed samples were analyzed by Rutherford backscattering with channeling spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM), secondary ion mass spectroscopy, and the van der Pauw technique. The best buried CoSi 2 layers were obtained at an implantation energy of 100 KeV and by subsequent rapid thermal annealing. RBS minimum yields of approximately 6% were obtained for the buried layer, which is the same as that reported for bulk (100) silicon. The measured resistivity of 15 μω cm and XTEM confirmed the continuity of the layer. Buried CoSi 2 layers were successfully produced up to an implantation energy of 180 keV. However, as the energy was increased the quality of the CoSi 2 layer degraded, with minimum yields increasing to 24% at 180 keV, and with a corresponding degradation in the minimum yields in the top silicon layer. At 200 keV a buried epitaxial layer was not produced. The degradation of crystal quality with ion implantation energy and the failure to produce a buried layer at 200 keV are discussed.