Impurities-related memory traps in silicon nitride thin films

Abstract

Internal photoelectric-effect technique in combination with Auger electron spectroscopy and argon-ion sputtering has been developed for quantitative measurements of impurity and defect-related memory traps in the Si3N4 thin film of a metal–Si3N4–SiO2–Si (MNOS) device. Electrons generated by internal photoemission at the metal electrode under an applied gate bias of −80.0 V and light of energy 4.14 eV were captured by memory traps in the Si3N4 insulator. The resulting trapped electron density of the order of 1.5×1018/cm3 was determined by capacitance-voltage measurements. The chemical depth profiles of nitrogen, silicon, and oxygen throughout the stoichiometric Si3N4 films grown at various NH3 to SiH2Cl2 gas ratios were measured. The amount of oxygen impurity in the film was correlated with variations in the gas ratios and in the trapped electron density. The data suggests an association of trapped electronic charge with some structural defects in addition to oxygen impurity incorporated in the Si3N4 film during the chemical deposition process.