Trench semiconductor device manufacture with a thicker upper insulating layer

Abstract

In the manufacture of semiconductor devices that have an electrode (11,41) in an insulated trench (20), for example a trench-gate MOSFET, process steps are performed to line the trench walls with a lower insulating layer (21) in a lower part of the trench and with a thicker upper insulating layer (22) in an upper part of the trench. The steps include: (a) etching the trench (20); (b) providing the lower insulating layer (21) on the trench walls; (c) depositing on the lower insulating layer (21) a further layer (51) of a different material; (d) depositing on the further layer (51) a filler material (52) that is of a different material from the further layer (51); (e) etching away the further layer (51) from the upper part of the trench walls while using the filler material (52) as an etchant mask, so as to form a space (50) adjacent to the upper part of the trench walls while leaving the further layer (51) in the lower part of the trench; and (f) providing the thicker upper insulating layer (22) in the space (50) adjacent to the upper part of the trench walls.

Dependencies are inferred from the claim text.