Integrated Processinyg of Silicided Shallow Junctions using Rapid Thermal Annealing Prior to Dopant Activation

Abstract

ABSTRACTA method for producing shallow silicided diodes for MOS devices (with junction depths of about 0.1 µm), by implanting after forming the silicide layer was investigated. The key to this integrated process is the use of rapid thermal annealing (RTA) to activate the dopants in the silicon, so that there is very little thermal broadening of the implant distribution. Self-aligned titanium silicide (TiSi2) films with thicknesses ranging from 40 to 80 nm were grown by RTA of sputter deposited titanium films on silicon substrates. After forming the TiSi2, arsenic and boron were implanted. A second RTA step was used after implantation to activate these dopants. It was found that implanting either dopant caused a sharp increase in the sheet resistivity of the TiSi2. The resistivity can be easily restored to its original value (about 18 µΩ-cm) by a post implant RTA anneal. RBS analysis showed that arsenic diffuses rapidly in the TiSi2 during RTA at temperatures as low as 600°C. SIMS data indicated that boron was not mobile up to temperatures of 900°C, possibly because it forms a compound with the titanium which precipitates in the TiSi 2. Coalescence of TiSi2 occurs during post implant furnace annealing, leading to an increase in the sheet resistivity. The amount of coalescence depends on the film thickness, but not on whether or not the film had been subject to implantation. Spreading resistance profiling data showed that both arsenic and boron diffused into the TiSi2 during furnace annealing, reducing the surface concentrations of dopant at the TiSi2/Si interface. Both N+/P and P+/N diodes formed by this technique exhibited low leakage currents after the second RTA anneal. This is attributed to removal of the implant damage by the RTA. In summary, the second RTA serves the dual purpose of removing implant damage in the TiSi2 and creating the shallow junction by dopant activation.