DEFECT ELECTRICAL-CONDUCTION IN SIMOX BURIED OXIDES

The buried oxide (BOX) layers in SIMOX structures exhibit localized defect conduction superimposed on the background (bulk) conduction. The defect conduction is observable with relatively large-area (0.05-cm2) capacitors fabricated by patterned etching of the heavily doped top Si layer. Type I defects show a pre-breakdown quasi-linear I-V characteristic with 10(-7) < I < 10(-3) A in the voltage range of 0.01-10 V. Type II defects exhibit a superlinear I-V behavior above 5 V and breakdown usually occurs at 10-50 V. A large number of samples prepared in various manners has been studied with automatic test equipment by which the number of Type I defects has been determined from several hundreds of capacitors on a given wafer. The defect density was calculated using the Poisson distribution; for annealed samples the values range, by and large, from 0.1 to 10 defects/cm2, while for un-annealed samples the range is 40-120 defects/cm2. Type I defects are very probably Si pipes in the BOX which results from particulate contamination during implantation. Statistical analysis revealed that the sample preparation technique has improved significantly in 1992 as shown by the decrease in both Type I defect densities of individual samples and their sample-to-sample variations. The situation regarding the Type II defects is more complicated as these defects appear to be closely related to some fundamental aspects of bulk conduction of the BOX layer in which electron traps play an important role.