ETCH-STOP BEHAVIOR OF BURIED LAYERS FORMED BY SUBSTOICHIOMETRIC NITROGEN ION-IMPLANTATION INTO SILICON

In this work the etch-stop behavior of buried layers formed by substoi chiometric nitrogen ion implantation into silicon is studied as a func tion of the processing parameters, the implantation dose and temperatu re, and the presence of capping layers during implantation. Etching ch aracteristics have been probed using tetramethylammonium hydroxide or KOH solutions for different times up to 6 h. Results show that, after annealing, the minimum dose required for the formation of an efficient etch-stop layer is about 4 x 10(17) cm(-2), for an implantation energ y of 75 keV. This is defined as a layer with an efficient etch selecti vity in relation to Si of s greater than or equal to 100. For larger i mplantation doses efficient etch selectivities larger than 100 are obt ained. However, for these doses a considerable density of pits is obse rved in the etch-stop layer. These are related to the presence of nitr ogen poor Si regions in the buried layer after annealing, due to a par tial separation of silicon and silicon nitride phases during the annea ling process. The influence of this separation of phases as well as ni trogen gettering in the buried layer on the etch-stop behavior is disc ussed as a function of the processing parameters.