A method for fabricating a bottom oxide layer in a trench (102) is disclosed. The method comprises forming the trench (102) in a semiconductor substrate (100), depositing an oxide layer to partially fill a field area (104) and the trench (102), wherein said oxide layer has oxide overhang portions (106) and removing the oxide overhang portions (106) of the deposited oxide layer. Thereafter, the method comprises forming a bottom anti-reflective coating (BARC) layer (108) to cover the oxide layer in the field area (104) and the trench (102), removing the BARC layer (110) from the field area (104), while retaining a predetermined thickness of the BARC layer (112) in the trench (102), removing the oxide layer from the field area (104) and removing the BARC layer and oxide layer in the trench (102) to obtain a predetermined thickness of the bottom oxide layer (114).