Method for forming bottle trenches by liquid phase oxide deposition. The method includes the steps of providing a substrate having a pad layer formed thereon, and a trench formed in a predetermined position; forming a masking layer at the bottom part of the trench; using liquid phase deposition (LPD) to form an LPD oxide layer on the sidewalls of the trench; removing the masking layer to expose the bottom part of the trench; subjecting the LPD oxide layer to annealing; and etching the bottom part of the trench not covered by the LPD oxide layer to form a bottle trench.