Method of making a vertical mos transistor

Abstract

A transistor structure is disclosed which has a vertical channel which has its length controllable by currently-used diffusion processes, and which occupies a minimum of silicon surface area. The transistor is constructed by using a triple-level implant and diffusion process. The drain region is diffused into the silicon area by way of ion implantation and subsequent diffusion. The channel region, of opposite conductivity-type from the drain region, is implanted and diffused into the drain region. The source region is similarly implanted, and diffused into the channel region. A trench is etched into the silicon, extending through the source, channel and drain regions; gate oxide is grown in the trench and a polysilicon gate is deposited in the trench, conformal with the gate oxide. Transistor action takes place in the channel region along the walls of the trench, dependent upon the voltage applied to the gate electrode. Series drain resistance, and gate-to-drain capacitance, is minimized by a deeper implant of the drain region away from the trench and under the electrical interconnection to the drain diffusion.