FILM STACK AND METHOD FOR FABRICATING THE SAME

摘要

A film stack (50) and a method for fabricating the same. In one embodiment, a film stack (50) comprises a semiconductor substrate (52) with the following layers: a first layer of oxide (54) over the substrate (52) ; a first layer of polycrystalline silicon (56) over the first layer of oxide (54) ; a second layer of oxide (58) over the first layer of polycrystalline silicon (56) ; a second layer of polycrystalline silicon (60) over the second layer of oxide (58) ; a third layer of oxide (62) over the second layer of polycrystalline silicon (60) ; and a layer of nitride (64) over the third layer of oxide (62) . The second layer of polycrystalline silicon (60) and the third layer of oxide (62) reduce the formation of bird's beaks after liner oxidation of a trench (66) formed in the film stack (60) . The reduced bird's beaks prevent unwanted residual strings of the first layer of polycrystalline silicon (56) remaining after subsequent processing of the film stack (50) .