Method of forming shallow trench isolation with rounded corners and divot-free by using in-situ formed spacers

Abstract

A method of fabricating an STI structure comprising the following steps. A silicon structure having a pad oxide layer formed thereover is provided. A hard mask layer is formed over the pad oxide layer. The hard mask layer and the pad oxide layer are patterned to form an opening exposing a portion of the silicon structure. The opening having exposed side walls. A spacer layer is formed over the patterned hard mask layer, the exposed side walls of the opening and lining the opening. The structure is subjected to an STI trench etching process to: (1) remove the spacer layer from over the patterned hard mask layer; form spacers over the side walls; (2) the spacers being formed in-situ from the spacer layer; and (3) etch an STI trench within the silicon structure wherein the spacers serve as masks during at least a portion of time in which the STI trench is formed. The STI trench having corners. Any remaining portion of the spacers are removed. A liner oxide is formed at least within the STI trench whereby the liner oxide has rounded corners proximate the STI trench corners. An STI fill layer is formed over the patterned hard mask layer and filling the liner oxide lined STI trench. The STI fill layer is planarized, stopping on the patterned hard mask layer. The patterned hard mask layer and the patterned pad oxide layer are removed to form a divot-free STI structure having rounded corners.