Carrier transport properties of thin gate oxides after soft and hard breakdown

This paper presents the experimental results of the carrier conduction mech anism in thin gate oxides after soft and hard breakdowns, obtained from the carrier separation technique. This technique allows the identification of the dominant carrier type on the gate leakage current, which is shown to be an important factor for clarifying the physical picture of breakdown spots . The carrier conduction after hard breakdown is shown to be dominated by t he majority carrier in the poly Si gate, meaning that the poly Si gate is d irectly contacting a Si substrate after hard breakdown. It is found, on the other hand, that hole current becomes dominant on the leakage path after s oft breakdown. This difference in dominant carrier type between soft and ha rd breakdown suggests that the ultrathin oxide region still remains in the leakage path after soft breakdown. The dominance of hole current is attribu table to larger tunneling probability of holes than that of electrons throu gh the extremely-thin oxide region remaining after soft breakdown. (C) 2001 Elsevier Science BY. All rights reserved.