Electrical measurements of moisture penetration through passivation

The low-frequency (10 KHz) dissipation factor of metal comb/serpentine structures sandwiched between a phosphosilicate glass (PSG) substrate and passivation is a useful electrical indication of moisture penetration through the passivation. Wafer-level dissipation factor readouts after periods of highly accelerated temperature/humidity stress technique (HAST) testing at 159 degrees C and 85% relative humidity were used to monitor the rate of moisture ingression through passivations of various compositions and thicknesses. For plasma-deposited oxynitride films the dominant mechanism is uniform penetration (intrinsic) with a median-time-to-failure of 370 hours (at 159/85). For oxynitride films capped by nitride films, the dominant mechanism is penetration through defects in the nitride film. The defect density of nitride cap films increases with decreasing nitride film thickness.<>