AC PHOTOVOLTAIC MEASUREMENT OF CHARGE-DENSITY UNIFORMITY IN SILICON-NITRIDE FILM DEPOSITED ON SI WAFER

Charge density uniformities in an as-deposited silicon nitride film ar e evaluated using an ac photovoltaic method. The experimental results for photovoltages as a function of the thickness of a silicon nitride film showed that the net charge in silicon nitride is positive, and a negative charge is located near the interface between the silicon nitr ide and the ultrathin oxide on the silicon substrate. The photovoltage s also greatly varied when the gas flow ratio of NH3 to SiH2Cl2 is cha nged from 5 to 50 while keeping the thickness constant. The ac photovo ltaic measurement revealed a charge density inhomogeneity of 8-nm-thic k silicon nitride films, which is attributed to local variations of th e gas flow ratio.