US Patent 7754561 Method for fabricating isolation film in semiconductor device

A method for forming an isolation layer in a semiconductor device comprises forming a trench inside a semiconductor substrate, forming a first high density plasma (HDP) oxide layer such that the first HDP oxide layer partially fills the trench, etching overhangs on sides of the trench by first cleaning with a hydrofluoric acid (HF) solution, subjecting a upper portion of the first HDP oxide layer to densification by second cleaning with an ozone (O3) solution, forming a liner HDP oxide layer having a high content of silicon (Si) over the first HDP oxide layer, and forming a second HDP oxide layer such that the second HDP oxide layer entirely fills the trench.