Formation of self-aligned TiSi₂ p⁺-n junctions by implanting BF₂⁺ ions through thin Ti or SiO₂ film on Si substrate rapid thermal annealing

High-quality Ti silicided p⁺-n junctions have been fabricated by implanting BF₂⁺ ions through α-Si/Ti films on an Si substrate (ITM), with subsequent rapid thermal processing. A leakage current density of about 4 nA cm^-2, a forward ideality factor greater than 1.02 and a reverse breakdown voltage above 80 V were achieved for the specimens annealed at 800°C for 30 s. For comparison, junctions were also formed by directly implanting BF₂⁺ ions into Si substrates, with the following depositions of α-Si/Ti films and silicidation/activation (ISA). Various implant and anneal conditions were studied to clarify their effects on fabricating junctions by the ISA and ITM schemes. Adequate anneal conditions must be used to vary the dopant activation, damage annihilation and Ti penetration into the junction regions so as to optimize the junctions formed by the respective schemes. In particular, ITM yielded a much higher breakdown voltage than ISA, due to a smoother TiSi₂/Si interface. It is shown, for the first time, that the silicide/Si interface is mainly responsible for the diode characteristics at high reverse bias.