Effect of ramp rates during rapid thermal annealing of ion implanted boronfor formation of ultra-shallow junctions

Over the last couple of years, manufacturers of rapid thermal annealing (RT A) equipment have been aggressively developing lamp-based furnaces capable of achieving ramp-up rates of the order of hundreds of degrees per second. One of the driving forces for such a strategy was the experimental demonstr ation of 30 nm p-type junctions using a approximate to 400 degrees C/s ramp -up rate during a spike-anneal (zero soak-time at temperature). It was prop osed that the ultra-fast ramp-up was suppressing transient enhanced diffusi on (TED) of boron caused by implantation damage. Ultra-fast ramp rate capab ility was thus embraced as an essential requirement for the next generation of RTA equipment. In this paper, we review more recent experimental data e xamining the effect of the ramp-up rate during spike- and soak-anneals on e nhanced diffusion and ultra-shallow junction formation. The advantage of in creasing the ramp-up rate (above approximate to 50 degrees C/s) is found to be appreciable only during spike-anneals of the shallowest implants. Since TED naturally decreases with decreasing implantation depth, it follows tha t the observed advantage of a fast ramp-up does not arise from a so-called suppression of TED but from a straightforward reduction of the thermal budg et. Since the temperature ramp-down is in practice limited to a rate much s maller than the achievable ramp-up rates (approximate to 75 degrees C/s vs. approximate to 400 degrees C/s, respectively), a point of diminishing retu rn is quickly reached when attempting to decrease dopant diffusion by incre asing the ramp-up rate only. The advantage of a fast ramp-up is similarly m itigated by the finite minimum soak-time achievable in practice, as well as by decreased process control at faster ramp-up rates. While it is apparent that spike-anneals can minimize dopant diffusion while maximizing dopant a ctivation we find that some of the advantages offered by fast ramp-up rates can be duplicated via modification of the implantation parameters. A surve y of spike-anneal data from different sources supports this point.