Method of selectively exposing the sidewalls of a trench and its use to

Abstract

Deep trenches (14,15) are formed according to the desired pattern through the N epitaxial layer (13) and N.sup.+ subcollector region (12) into the P.sup.- substrate (11) of a silicon structure (10). Where a substrate contact is needed, the trenches delineate a central stud (16) or mesa of silicon material. Channel stop regions (18) are formed e.g. by ion implantation of boron atoms at the bottom of trenches, SiO.sub.2 and Si.sub.3 N.sub.4 layers (17,19) are then deposited on the whole structure. A substrate contact mask is applied and patterned to selectively expose one side of the trench sidewalls, the bottom of the trenches adjacent thereto and others areas if desired such as the top surface of the stud. The composite SiO.sub.2 /Si.sub.3 N.sub.4 layer is then etched to leave exposed only the sidewalls of the stud, at least partially the bottom of the trenches adjacent thereto and the top surface of the stud. Platinum is deposited preferably via sputter deposition, conformally coating all regions of the structure. After sintering, the unreacted platinum is removed using wet chemical etch (aqua regia). Platinum silicide is left in all opened contacts and on the stud sidewalls where its defines a metal silicide lining (25) or cap, covering the stud. This lining connects the top surface (25a) of the stud, with the channel stop implanted regions (18) and then forms the desired substrate contact.