US Patent 7358144 Method for fabricating semiconductor device

A method for fabricating a semiconductor device includes forming first, second, and third device structures in a semiconductor substrate. Each device structure includes a first film, a second film over the first film, and a third film over the second film. The first and third device structures are device isolation structures. A portion of the second device structure is etched to define a bit line contact region, the bit line contact region extending from an upper surface of the second device structure to a lower surface of the second device structure. The second film of the second device structure is etched to define an under-cut space between the first and second films. A semiconductor layer is formed within the under-cut space and the bit line contact region. The third film of the second device structure is etched or removed to define a recess, the recess defining a gate region. A gate structure is formed at least partly within the recess.