Gate current suppression in buried lightly doped drain (BLDD) MOSFETs

Hot electron degradation creates serious long term reliability problems for short channel MOSFETs. Consequently, a variety of device designs have been employed to minimize the degradation. Amongst these, the lightly doped drain (LDD) structure, which is aimed at reducing the peak electric field near the drain, has proved to be very successful. One problem with this technique, however, is that the peak electric field remains close to the gate oxide. A new structure, the buried LDD (BLDD), has been devised to overcome this difficulty and early results suggest improved reliability. One technique for predicting the long term reliability of the various structures is to measure the hot electron gate current present under stress. The authors have measured the gate current using the `floating gate´ method. The results suggest that the BLDD device is successful in limiting electron injection into the gate and, therefore, shows promise for improved reliability