Mo/Ti Double Layer Contact for VLSI

Abstract

A dual layer metallization system, consisting of a thin contacting layer of titanium covered by a thick layer of molybdenum, has been developed for VLSI applications. At 400°C the thin titanium layer is shown to dissolve thin oxide layers on the silicon surface to make good ohmic contact. Thick molybdenum over the titanium layer has high conductivity, good step coverage, low electromigration, and very smooth surface morphology. This system is both electrically and mechanically stable. Both layers were sequentially sputtered without breaking the vacuum and patterned with a single‐step RIE process. Contact resistance to n+ silicon is about 10 Ω·μm2, and that to p+ silicon is about 19 Ω·μm2, which is lower than that of a W or contact. Leakage current and contact resistance were measured as a function of annealing temperature. The n+ contact does not degrade up to 650°C, whereas the p+ contact is reliable up to 600°C. The overall contact system is stable up to 550°C, maintaining the physical and electrical integrity of the film. SIMS analyses were used to help explain the variations observed in these parameters at high temperatures.