Method to define a transistor gate of a dram and the transistor gate using same

Abstract

A method to determine the predetermined location of a transistor gate of a dynamic random access memory (DRAM). A trench capacitor is respectively provided in a silicon substrate at the two sides of the gate, along the direction of a bit line. The method is to first form a patterned layer of silicon nitride over the substrate so that at the location where the two trench capacitors are desired to be built, the substrate is exposed; then to build the two trench capacitors at the location of the exposed substrate. Form a layer of silicon oxide to cover the capacitors and make the layer of silicon oxide and the layer of silicon nitride at the same level. Layer of silicon nitride is removed afterwards, and a polysilicon layer is conformably formed on the substrate. A BF2 ion implantation is performed twice at different tilt angles on the polysilicon layer in order to define an undoped area between the two trench capacitors. Then remove the undoped area of the polysilicon layer so that part of the silicon substrate is exposed to serve as the predetermined location of transistor gate.