Electrical and physical characteristics of thin nitrided oxides prepared by rapid thermal nitridation

Abstract

Ultrathin oxides (5-12 nm) were nitrided by lamp-heated rapid thermal annealing in ammonia at temperatures of 900-1150°C for 5-300 s. Elemental depth profiles were measured by Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS). Both the nitrogen concentration measured by AES and the hydrogen one measured by SIMS for a nitrided oxide are found to increase monotonically as nitridation proceeds. The AES depth profiles of oxygen show that the Si-SiO 2 interface does not move during nitridation. Dependences of midgap interface state density ( D_{it}_{m} ) and fixed charge density (N f ) on nitridation temperature and on oxide thickness were studied. For a given temperature, both D_{it}_{m} and (N f ) are found to show turnarounds as nitridation time increases in a similar manner: at first both increase, reach respective maxima at a certain nitridation time t_{\max} , and then decrease gradually. The ( D_{it}_{m} ) and (N f ) increase more rapidly and the t_{\max} is shorter as the nitridation temperature is raised or the oxide film is thinner. The maximum of D_{it}_{m} increases as the oxide film is thinner. A two-step model is newly proposed to explain the turn-around behaviors of D_{it}_{m} and N f : the first step is defect formation as a result of nitrogen incorporation and the second step is reduction of the defects by an annealing-type process. The simulation reproduces the turnaround behaviors very well.