Semiconductor memory device and a method for producing the same

Abstract

A semiconductor memory device is provided which includes a semiconductor substrate of a first conductivity type, a plurality of trench capacitors formed in the substrate and a plurality of switching transistors formed on the respective trench capacitors. Each of the switching transistors is electrically connected to the corresponding trench capacitor. Each of the trench capacitors has a first electrode formed in the side portion of a trench provided in the substrate and a second electrode containing impurities of the first conductivity type and embedded in the trench. Each of the switching transistors has a source region formed from a first epitaxial layer of the first conductivity type grown on the trench so as to electrically contact the second electrode, a channel region formed from a second epitaxial layer of a second conductivity type grown on the first epitaxial layer, and a drain region formed from a third epitaxial layer of the first conductivity type grown on the second epitaxial layer. The first, second and third epitaxial layers are in contact with a polycrystalline silicon layer containing impurities of the second conductivity type. The first conductivity type is opposite to the second conductivity type.