US Patent 7910438 Method for fabricating semiconductor device including recess gate

A method for fabricating a semiconductor device includes etching a substrate to form a first trench pattern, forming spacers over sidewalls of the first trench pattern, etching a bottom portion of the first trench pattern using the spacers as a barrier to form a second trench pattern, performing an isotropic etching on the second trench pattern to round sidewalls of the second trench pattern and form a bulb pattern, and forming a gate over a recess pattern including the first trench pattern, the rounded second trench pattern and the bulb pattern.