Method for preparing a narrow angle defined trench in a substrate

Abstract

Polysilicon (20) in a trench (21) is etched at an angle to produce a conductor within the trench that has shape characteristics which approximate the shadow of the side wall (26) of the trench (21) closest the beam source. Specifically, when the first side wall (26) is closest the beam source and the second side wall (27) is furthest from the beam source, the polysilicon on the first side wall (26) is almost as high as the first side wall (26), while the polysilicon on the more exposed side wall (27) is considerably lower than the first side wall (26) and approximates the shadow of the first side wall (26) on the second side wall (27) relative to the beam. The polysilicon (20) in the trench (21) may be in the shape of a solid angled block approximating the shadow line from the top of side wall (26) to side wall (27); however, it is preferred that the polysilicon take the form of a conformal layer in trench (21) prior to etching such that the polysilicon ultimately has an angled 'U' shape which approximates the shadow line. Contact is made to the polysilicon (20) using strap (23) that electrically connects the side wall (26) with the polysilicon (20). Strap (23) is sized such that it does not extend to the opposite side wall (27) of trench (21), thereby avoiding short circuits. Having the polysilicon (20) approximate the shadow line of the etch permits narrowing the distance between adjacent straps (23) and (24) in an array without the risk of creating a short circuit.