Effect of additional low temperature RTA on ultra-shallow p+ -n junction formation

The effect of Additional Low Temperature RTA process (ALTRTA) prior to furnace annealing (FA) on shallow junction formation has been investigated. In p⁺-n junction implanted by BF₂ at 20 keV with a dose of 3×10¹⁵ ions/cm², it was found that ALTRTA at 950°C for 5 sec before FA at 850°C for 60 min decreased the junction depth, sheet resistance and junction leakage current by 10%, 2%, and 83.7%, respectively compared to conventional FA process. As FA time increased, the retardation of boron diffusion by ALTRTA was more prominent. Cross-sectional TEM study showed that the density and size of dislocation in ALTRTA sample were reduced. Therefore, it is speculated that the density reduction of Si-interstitial due to point defect recombination (Interstitial+Vacancy=0) during ALTRTA retards the boron diffusion, and reduces junction leakage current. The effective ALTRTA condition was found to depend on ion implantation energy and/or dose, and the lower ion implantation energy and/or dose required the lower RTA temperature. From the results, the ALTRTA process prior to FA for BPSG flow is very effective for the formation of ultra-shallow junction with the improvement of junction characteristics