US Patent 7615451 Method for forming semiconductor device

A method for forming a semiconductor device is provided. More specifically, a method for forming a bulb-shaped portion of a bulb-shaped recess gate is provided to overcome an etching process margin reduction caused by a spacer oxide film formed on sidewalls of a recess and thickly laminated to a lower part of a recess. In one aspect, a buffer dielectric film pattern is formed additionally by a plasma enhanced chemical vapor deposition (PECVD) process over a hard mask pattern, so that a sufficient process margin used for forming the bulb-shaped portion is ensured and a process margin for forming a semiconductor device is increased.