Abstract: A method of forming a ?-shaped trench is disclosed. The method includes: providing a silicon substrate; and sequentially performing a plasma etching process and a wet etching process on the silicon substrate to form a ?-shaped trench therein. The plasma etching process includes: horizontally etching the silicon substrate using a first plasma etching gas including a nitrogen-containing fluoride; and vertically etching the silicon substrate using a second plasma etching gas including a polymer gas. A method of forming a semiconductor device is also disclosed.