Patent ID: 7125784

Claim:
A method for forming a trench for an isolation film, comprising the steps of: forming an etching mask on a semiconductor substrate; etching the semiconductor substrate to form a trench having a sidewall by an etch process using the etching mask; performing a strip process for removing the etching mask; performing a first cleaning process for removing byproducts generated during the etch process on a sidewall of the trench to improve the roughness of the sidewall by using BFN (B(Piranha(H 2 SO 4 +H 2 O 2 ))+F(50:1 Dilute HF)+N(SC-1(NH 4 OH/H 2 O 2 /H 2 O))) after the step process for removing the etching mask; performing a second cleaning process to uniformly form a sidewall oxide film through subsequent processes by using CLN (N(SC-1(NH 4 OH/H 2 O 2 /H 2 O)); and performing a sidewall oxidation process to form a sidewall oxide film in the trench.