Analysis of the structure and defects in heteroepitaxial Si/CoSi 2/Si layers produced by ion beam synthesis and rapid thermal annealing

Abstract

The effects of rapid thermal annealing (RTA) on the microstructure and electrical properties of ion-beam-synthesized silicide layers fabricated using cobalt doses of 7×10 17, 5×10 17 and 1.5×10 17 cm −2 at an energy of 200 KeV have been studied. For all three doses, increasing RTA temperature leads to the chemical segregation of the implanted cobalt—via the thermodynamically controlled dissolution of the small CoSi 2 precipitates in the wings of the distribution. Likewise, increasing the anneal temperature affects the removal of defects lying on Si{311} lattice planes, which are created by an excess of silicon self-interstitials. For the two highest doses, the phase transformation CoSi→ CoSi 2 is also facilitated by increasing anneal temperature. In all cases, it is found that the resistivity and crystallinity of the layers are critically dependent on the Co:Si ratio, with high quality low resistivity layers only being attained when this is close to 1:2, i.e. CoSi 2. After RTA at 1000 °C for 5 s, stoichiometric CoSi 2 layers were achieved for all doses, with layer thicknesses ranging from 600 to 18000 Å. The value of resistivity and crystallinity obtained for the medium dose specimen (5 × 10 17 cm −) were close to those achieved by conventional furnace annealing, with those for the higher and lower doses being slightly higher.