Process for 4f2 stc cell having vertical mosfet and buried-bitline conductor structure

Abstract

A method of forming a vertical transistor. A pad layer is formed over a semiconductor substrate. A trough is formed through the pad layer and in the semiconductor substrate. A bit line is formed buried in the trough. The bit line is enclosed by a dielectric material. A strap is formed extending through the dielectric material to connect the bit line to the semiconductor substrate. The trough is filled above the bit line with a conductor. The conductor is cut along its longitudinal axis such that the conductor remains on one side of the trough. Wordline troughs are formed, substantially orthogonal to the bit line, above the semiconductor substrate. A portion of the conductor is removed under the wordline trough to separate the conductor into separate gate conductors. Wordlines are formed in the wordline trough connected to the separate gate conductors.