MACROSCOPIC AND MICROSCOPIC STUDIES OF ELECTRICAL-PROPERTIES OF VERY THIN SILICON DIOXIDE SUBJECT TO ELECTRICAL STRESS

The electrical characteristics of various size tunnel switch diode dev ices, composed of Al/SiO2/n-Si/p(+)-Si layers, which operate with a ra nge of parameters (such as current densities in excess of 10(4) A/cm(2 )) that stress the oxide layer far beyond the levels used in typical t hin oxide metal-oxide semiconductor research have been examined. It is found that the first time a large current and electric field are appl ied to the device, a ''forming'' process enhances transport through th e oxide in the vicinity of the edges of the gate electrode, but the ox ide still retains its integrity as a tunnel barrier. The device operat ion is relatively stable to stresses of greater than 10(7) C/cm(2) are ally averaged, time-integrated charge injection. Duplication and chara cterization of these modified oxide tunneling properties was attempted using scanning tunneling microscopy (STM) to stress and probe the oxi de. Electrical stressing with the STM tip creates regions of reduced c onductivity, possibly resulting from trapped charge in the oxide. Late ral variations in the conductivity of the unstressed oxide over region s roughly 20-50 nm across were also found. (C) 1997 American Vacuum So ciety.