DISCONTINUITY OF B-DIFFUSION PROFILES AT THE INTERFACE OF POLYCRYSTALLINE SI AND SINGLE-CRYSTAL SI

Boron diffusion in polycrystalline Si-on-single crystal Si systems has been studied by secondary ion mass spectrometry, The extrapolated B-d iffusion profiles in polycrystalline Si and in the single crystal Si s ubstrate reveal a discontinuity at the polycrystalline Si-single cryst al Si interface. The discontinuity in the B profiles is believed to oc cur due to the blockage of B-defect complexes by the interfacial oxide between polycrystalline Si and the single-crystal Si substrate, as we ll as the immobility of these defect complexes in single crystal Si. T he B in the implant peak region above the B solid solubility limit is found to be immobile in single crystal Si during annealing due to the formation of electrically inactive B-defect complexes. In polycrystall ine Si, however, our results show that the B in the peak region spread s out more rapidly than in single crystal Si possibly due to the diffu sion of B-defect complexes along grain boundaries. The B-defect comple xes are electrically inactive as determined by spreading resistance an alysis. If the B concentration is lowered below the solid solubility l imit, either by decreasing the dose or by raising the anneal temperatu re, no discontinuity is observed in the B profile across the polycryst alline Si-single crystal Si interface.