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 are 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 nitride and the ultrathin oxide on the silicon substrate. The photovoltages also greatly varied when the gas flow ratio of NH3 to SiH2Cl2 is changed from 5 to 50 while keeping the thickness constant. The ac photovoltaic measurement revealed a charge density inhomogeneity of 8-nm-thick silicon nitride films, which is attributed to local variations of the gas flow ratio.