Method of forming shallow trench isolation with rounded corner and divot-free by using disposable spacer

Abstract

A method of fabricating an STI, comprising the following steps. A silicon structure having a pad oxide layer formed thereover is provided. An undoped poly buffer layer is formed over the pad oxide layer. A hard mask layer is formed over the undoped poly buffer layer. The hard mask layer, the undoped poly buffer layer and the pad oxide layer are patterned to form an opening exposing a portion of the silicon structure within an active area. The opening having exposed side walls. Inorganic spacers are formed over the exposed side walls. Using the patterned hard mask layer and the spacers as hard masks, the silicon structure is etched to form an STI opening within the active area. The inorganic spacers are removed exposing the upper corners of the STI opening. Using an oxidation process, a liner oxide layer is formed within the STI opening, over the upper corners of the STI opening and at least the patterned undoped poly buffer layer exposed by the removal of the inorganic spacers. An STI oxide layer is formed over the patterned hard mask layer, filling the liner oxide layer lined STI opening. The STI oxide layer is planarized and the patterned hard mask, the patterned undoped poly buffer layer and the patterned pad oxide layer are removed to fabricate the STI having rounded corners and without substantial divots.