a diffusion step following pre-deposition. Drive-in increases the diffusion depth of a pre-deposition, pre-depositions are commonly masked by silicon dioxide, if a long diffusion took place during pre-deposition the pre-deposition dopant could penetrate the masking oxide and enter the silicon where it isn't wanted. Following pre-deposition a dip is used to clean off the oxide surface so that it is dopant free prior to drive-in.
