Effect of Residual Damage on Carrier Transport Properties in a 4H-SiC Double Implanted Bipolar Junction transistor

摘要

Nitrogen implantation into a boron implanted layer is a potential technology for the fabrication of double-implanted n-p-n bipolar transistor. The effect of various implant and anneal schedules on two key device parameters is studied: 1) residual implant damage close to the emitterbase junction and 2) ohmic contact resistance of the highly doped implanted emitter. The effects of post-implant anneal conditions on the level of residual damage under the nitrogen implant after different anneal processes are investigated using the PAS and RBS techniques. The PAS data show clearly that after implantation there is a substantial defect concentration as far as 400nm - significantly below the range of the nitrogen implant (in this case 150nm). The surface morphology of the nitrogen implanted emitter after a high temperature annealing is investigated by AFM. Surface roughness increases significantly at higher annealing temperatures, takin the form of a periodic undulation at 1700 deg C. Hall effect and contact resistivity measurements show that higher annealing temperatures result in decreased ohmic contact resistivity but poor surface mobility. Finally surface profiles show significant lattice swelling following highly doped nitrogen implant which can only lartially be removed after annealing.