A novel blanket tungsten etchback scheme

A novel W etchback scheme using a sacrificial nitride layer is presented. This scheme significantly reduces both loading effects and surface roughness. A comparison is made between the conventional and the present scheme. In the latter both SiO₂ surface roughness and etch loading effects, as observed in the conventional scheme, are virtually eliminated. In the case of the conventional scheme, the W etchrate in the contact hole dramatically increases during overetching, as a result of both global and local loading effects. The global component is absent in the case of the SiN sacrificial layer scheme since the F consumption rates of W and SiN are assumed to be comparable. Furthermore, no oxygen is liberated during overetching of SiN and the F concentration is not increased close to the W plug. Therefore, overetching is less critical and can be used to compensate for nonuniformities in W deposition and etching. Measurements and mechanisms of loading effects are discussed