In-depth exploration of Si-SiO2 interface traps in MOS transistors using the charge pumping technique

It is shown that the charge pumping (CP) technique can be used for extraction of the depth concentration profile of traps situated in the oxide of metal-oxide-semiconductor (MOS) transistors, near and at the Si-SiO₂ interface. The trap density is obtained from the variation of the charge pumping current as a function of frequency, the other measurement parameters being kept constant. The concentration profiles are measured on n and p-channel transistors from several technologies, and on virgin and stressed devices. The results show that the trap concentration decreases rapidly from the Si-SiO₂ interface in the direction of the oxide depth and suggest that it becomes constant at a fraction of a nanometer from the silicon interface. The method easily demonstrates the trap creation due to Fowler-Nordheim stress. The profiles compare favorably with those measured using a new drain-current transient technique. In all cases, the integration of the depth concentration profiles leads to the interface trap densities measured using the conventional charge pumping method