The Influence of Oxygen on the Contact Barrier and the Tungsten Plug Process Post Rapid Thermal Anneal Step

摘要

The Ti/TiN film is commonly used as the barrier layer in contacts followed by the Rapid Thermal Anneal of the Ti/TiN film and then a blanket CVD tungsten (WCVD) film as the contact plugs. The blanket WCVD process is used to fill contacts in multilevel metallization devices due to its excellent step coverage. The TiN layer acts as diffusion barrier to prevent the interaction between the reacting species of WCVD (mainly WF_6) while the Ti layer is used for improving the contact resistance. For contacts, the deposited Ti/TiN film is typically annealed in N_2 at 600 to 700℃ to form Ti silicide. TiN film, on the other hand, undergoes a structural change upon exposure to N_2 ambience during the Rapid Thermal Anneal step. A yield loss signature was seen on product wafers in the form of a concentric circle either on the entire or half the wafer. An intermittent problem was found to be originating from the tungsten CVD toolset. Failure analysis of the affected wafers revealed that the yield loss was mainly due to the poor fill in the contacts. Further studies revealed that the intermittency of the issue was due to an integration aspect with a particular RTA toolset. Different Rapid Thermal Anneal (RTA) tools were was used to anneal the barrier layer put on the wafers before tungsten deposition. An Auger analysis revealed an increased concentration of the oxygen species on the surface of the wafers processed through this particular RTA toolset. This paper will describe the elimination of the yield loss by modifying the WCVD process and to accommodate the impact from the excess oxygen observed after the contact barrier anneal step