The role of polysilicon film in the suppression of bird´s beak in poly-buffered LOCOS

The oxidation behavior of buffer polysilicon and its contribution to the suppression of bird´s beak in the polybuffered local oxidation of silicon (PBL) isolation have been studied. Shorter bird´s beak in PBL than that in conventional LOCOS can be mainly attributed to the role of the buffer polysilicon, the oxidation of polysilicon is pinned near the LOGOS edge due to large compressive stress during field oxidation. The polysilicon-oxidation triangles caused by the oxidation pinning consume a large amount of laterally diffusing oxidants, thus leading to shorter bird´s beak. The geometrical analysis of polysilicon-oxidation triangles enables us to reasonably explain the observed 2ΔW trends with PBL parameters