Defect electrical conduction in SIMOX buried oxides

It is pointed out that the buried oxide (BOX) layers in SIMOX structures exhibit localized defect conduction superimposed on the background (bulk) conduction. 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. For annealed samples the calculated defect density values range from 0.01 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 result from particulate contamination during implantation. Statistical analysis revealed that the sample preparation technique has improved significantly in 1992. 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