Properties of Nonvolatile Semiconductor Memories by Using Silicon Clusters in the Gate Insulator
Shumpei Yamazaki, Koichi Hatakeyama, Ichiro Kagawa and Yoshinari Yamashita
Nonvolatile memories are now focused by many people. One of the most popular structure of the memories is an MNOS (metal-silicon nitride-silicon oxide-semiconductor) structure. However the structure has poor memory retention when B-T (80℃, -10V) stress is applied to the sample. The developed structures are MNCOS and MNCNOS (metal-over silicon nitride-silicon clusters-under silicon nitride-semiconductor), in which the silicon clusters are the small polycrystalline silicon particles having a compressed hemisphere. As the clusters act as trap centers of both holes and electrons, the trapping efficiency of centers increases, and the thicker silicon oxide film (tox=50-60A) is able to use for the better memory retention. The memories can operate more than ten years under the BT (-10V, 80℃) stress condition.