INVESTIGATION OF CHARGE-TRAPPING CENTERS IN LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION SI3N4 THIN-FILMS

Defects in Si3N4 films formed by low-pressure chemical vapor depositio n(LPCVD) were investigated by electron spin resonance measurement. At room temperature, no electron spin resonance signal was observed in as -deposited films. When the films were illuminated by ultraviolet ray ( UV), signals of dangling bonds of Si (Si-DB, N-3 = Si .) are detected, where the g-values were 2.0028 and the half-value width was 14 G. Thi s means there are N vacancies of weak Si: Si bonds (N-3 = Si:Si = N-3) and/or dipolar-type defects (N-3 = Si:(-), Si-+ = N-3) caused by redi stribution of electrons in N vacancies which cause pairs of defects (N -3 = Si ., . Si = N-3) by UV illumination. It is proposed that these v acancies can become dipolar-amphoteric charge-trapping centers of elec trons and holes. The trap density and the charge-trapping behaviors we re investigated by evaluating the characteristics of MNOS nonvolatile memory devices with Si3N4 gate dielectrics.