Method for fabricating semiconductor device with vertical transistor having a second active pillar formed over a first active pillar

Abstract

A method for fabricating a semiconductor device includes forming a plurality of first active pillars by etching a substrate using a hard mask layer as an etching barrier, forming a gate conductive layer surrounding sidewalls of the first active pillars and the hard mask layer, forming a word line conductive layer filling gaps defined by the gate conductive layer, forming word lines and vertical gates by simultaneously removing portions of the word line conductive layer and the gate conductive layer on the sidewalls of the hard mask layer, forming an inter-layer dielectric layer filling gaps formed by removing the word line conductive layer and the gate conductive layer, exposing surfaces of the first active pillars by removing the hard mask layer, and growing second active pillars over the first active pillars.