Highly efficient transistor for fast programming of flash memories

摘要

In a semiconductor fabrication method for forming a transistor structure upon a semiconductor substrate, a nitride layer is also formed over the semiconductor substrate. A gate oxide layer is formed over a region of the semiconductor substrate. The gate oxide layer has a relatively thinner oxide region over the nitride layer and a relatively thicker oxide region over the substrate adjacent the nitride layer. A transistor gate is formed extending over the relatively thinner oxide region and over the relatively thicker oxide region. The transistor thus formed is therefore asymmetric. A first transistor active region is formed in the vicinity of the relatively thicker oxide region and a second transistor active region is formed in the vicinity of the relatively thinner oxide region. The nitride layer can be formed by rapid thermal nitridization of the semiconductor substrate. The relatively thinner oxide region can be one-half as thick as the relatively thinner oxide region. The surface of the semiconductor substrate can be curved in the vicinity of the drain of the asymmetric transistor in order to permit the momentum of the charge carriers to facilitate penetration of the charge carriers into the gate.