A study of effect of precipitates and lattice defects on the electrical performance of P-N junctions

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Ryoo, Kunkul
Oregon Health & Science University
Ion implantation; Semiconductors -- Defects
thesis / dissertation description
Ion implantation when used as a doping technique introduces damage to the surface of a silicon wafer. This damage in turn may result in formation of dislocation loops or stacking faults, depending upon the subsequent heat treatment. These defects in turn may degrade electrical properties in a P-N junction. The importance of the location of defects on the P-N junction performance has not been studied in detail. In this work, P-N junctions have been fabricated, tested electrically and analysed with transmission electron microscopy (TEM). Two types of defects, dislocation loops and stacking faults were introduced into P-N junctions. Sometimes "dog-bone" shape stacking faults were produced. TEM analysis revealed that the "dog-bone" fault is a stacking fault decorated by precipitates. High magnification (200K) revealed two kinds of precipitates, individual plates and colony clusters. Colonies exhibited Moire fringes which were used to characterize their crystallographic structures. X-ray Energy Dispersive Spectroscopic data from these two precipitates showed that colonies consisted of Ni, Cu and Si, while the plate contained Ni and Si only. It was concluded that the plate type is pure NiSi2 and that the colonies are metastable (Ni [subscript x'] Cu [subscript 1-x]) Si2 due to Cu alloying. Diodes containing stacking faults or dislocation loops were fabricated by implanting boron into N-type silicon wafers. Cross section TEM analysis showed that the desired configurations, diodes containing stacking faults in the P-region or extended into the depletion region, or diodes containing dislocation loops in the P-region, the depletion region or the N-region, were obtained. Diodes containing stacking faults or dislocation loops in the P-region acted as diodes without defects except for increased resistance due to hole scattering. The scattering mechanism for stacking faults was found to be different from that for perfect dislocation loops in the P-region. Diodes containing stacking faults extending into the depletion region were degraded since partial dislocations surrounding stacking faults provided leakage paths. Diodes containing dislocation loops in the depletion region or N-region still acted as ideal diodes except for higher current levels. In reverse bias, N-region defects showed lower generation current than those in the depletion region. This proved that point defects introduced into the diode may or may not affect the electrical property of P-N junctions depending upon their locations.