Measurement of interface states in the LDD region of a MOS transistor using a modified charge pumping technique

In this work, a set of LDD NMOS transistors are used as test structures for a modified charge pumping technique (LDD charge pumping) to directly measure the interface state density in the LDD region. The technique is validated by measurements on virgin samples and those subjected to hot carrier stress and Fowler-Nordheim stress, which are known to cause different amounts of degradation of the interface over the LDD region and that over the channel region. GIDL current measurements are shown to be in agreement with the charge pumping results. By combining the LDD charge pumping technique with gate to drain capacitance measurements, the lateral profile of the interface state density in the overlap region is obtained.