Effect of Ion Bombardment on the Dopant Diffusion During Reactive Ion Etching (RIE) of Dielectric Films Deposited on Silicon

ABSTRACTWe report on the results obtained from a study conducted to understand the effect of reactive ion etching (RIE) of oxide films on the dopant diffusion in ion-implanted silicon. Thermally grown oxide films on silicon were plasma etched in a CHF3/CO2 plasma. The residual silicon surface damage created during plasma etching was removed by employing a low ion-bombardment, two-step surface plasma cleaning process. The samples with oxide films etched in a wet chemical etchant provided the control for evaluating the effect of the RIE process. The samples were implanted with boron and boron was activated under various conditions to form p-n junctions to obtain a range of boron doping profiles and junction depths. Some boron doped samples were implanted with arsenic to form a heavily doped n+ region at the silicon surface. The resulting doping profiles were analysed using spreading resistance profiling (SRP), four-point probe measurements, and secondary ion-mass spectrometry (SIMS) to understand the activation, diffusion, and precipitation of various dopants. Detailed transmission electron microscopy (TEM) analysis was used to study the microstructural effects. It was observed that plasma etching of the oxide films prior to the formation of boron diffused surface regions in silicon resulted in significant changes in boron diffusion. For low boron implant doses, plasma etched silicon surfaces resulted in retarded boron diffusion. For high boron implant doses, plasma etched silicon surfaces lead to enhanced boron diffusion.