Stressing and High Field Transport Studies on Device-Grade SiO(sub2) by Ballistic Electron Emission Spectroscopy

The tip of a scanning tunneling microscope was used to inject hot electrons across the gate and into the oxide of a metal-oxide-semiconductor (MOS) structure. This method, known as Ballistic Electron Emission Microscopy (BEEM) allows an arbitrary choice of the energy of the injected electrons, which may be further accelerated by the application of a gate bias. The high current densities and choice of energy make BEEM an attractive method to study hot electron transport and breakdown phenomena in dielectrics. The studies reported here were made on Pd/SiO(sub2)/Si(100) strucutres, with a SiO(sub2) layer thickness of 3.8 nm. Monte Carlo techniques were used to calculate the spreading of the electron beam as it traverse the oxide. A strong dependence of the spreading on the kinetic energy and oxide thickness were observed. Using the calculated beam spreads to determine current densities and injected charge densities, the charge-to-breakdown (Qbd) was measured for several breakdown sequences. The Qbd's consistently exceeded by several orders of magnitude the values obtained by conventional Fowler-Nordheim (F-N) tunnel injection under high field conditions. Most of the time breakdowns could not be achieved for 3.8 nm oxides. It is concluded that impurity/defects still control all observed breakdowns; an intrinsic limit, although claimed to have been reached, has not yet been established.