Characterization of TiN/TiSi₂ bilayer for application to ULSI

The properties of TiN/TiSi₂ bilayer formed by rapid thermal annealing (RTA) in an NH₃ ambient after the titanium film is deposited on the silicon substrate is investigated. It is found that the formation of TiN/TiSi₂ bilayer depends on the RTA temperature and a competitive reaction for the TiN/TiSi₂ bilayer occurs at 600°C. Both the TiN and TiSi₂ layers represent titanium-rich films at 600°C anneal. The TiN layer has a stable structure at 700°C anneal while the TiSi₂ layer has C₄₉ and C₅₄ phase. Both the TiN and TiSi₂ layers have stable structures and stoichiometries at 800°C anneal. When the TiN/TiSi₂ bilayer is formed, the redistribution of boron atoms within the TiSi₂ layer gets active as the anneal temperature is increased. According to secondary ion mass spectroscopy analysis, boron atoms pile up within the TiN layer and at the TiSi₂-Si interface. The electrical properties for n⁺ and p⁺ contacts are investigated. The n⁺ contact resistance increases slightly with increasing annealing temperature but the p⁺ contact resistance decreases. The leakage current indicates degradation of the contact at high annealing temperature for both n⁺ and p⁺ junctions.