Severe loss of dopant activity due to CHF3+CO2 reactive ion etch damage

Abstract

We report direct evidence from spreading resistance carrier profiling that an effective reduction of up to 5×1019 carriers cm−3 is caused by etching 10–150 nm of doped silicon with a CHF3+CO2 plasma in a commercial hexode reactor. During an 80-nm etch of bulk p+- and n+-Si, over 99 and 90% respectively of the carriers are trapped or complexed to a depth extending 200 nm from the etched surface. Thermal annealing at 450 °C restores all of the electrical activity, a behavior which is similar to the recovery of phydrogen-passivated acceptor impurities. More complicated behavior was observed for carrier deactivation of both p+ and n+ implanted junctions, where only partial recovery occurs after a 450 °C anneal. Further annealing at 850 °C does not reactivate any further p-type dopant, but a 950 °C anneal does increase the n-type dopant activity.