DOSE-RATE AND THERMAL BUDGET OPTIMIZATION FOR ULTRASHALLOW JUNCTIONS FORMED BY LOW-ENERGY (2-5 KEV) ION-IMPLANTATION

High implant dose rates and two-step anneals have been used to optimiz e ultrashallow junctions (similar to 60 nm) formed by low-energy (2-5 keV) BF2 ion implantation. Variation in junction depth and dopant prof ile as a function of beam current density (dose rate) and damage/activ ation anneal is studied. Junction depths and transient enhanced boron diffusion, as seen from secondary ion mass spectroscopy, are reduced f or increasing implant dose rate. In addition, transmission electron mi croscopy images indicate that implantation at a higher dose rate yield s lower residual defect levels following anneal. Dependence of sheet r esistance on dose rate seems to be a function of the amorphizing natur e of the implant. At a dose of 1x10(14) cm(-2), use of a low-temperatu re, 600 degrees C furnace preanneal, prior to a high-temperature rapid thermal anneal, serves to reduce transient enhanced diffusion. At a d ose of 1x10(15) cm(-2), subtle changes in residual damage are observed while no apparent changes in transient enhanced diffusion or sheet re sistance are seen. (C) 1996 American Vacuum Society.