Failure Analysis of Evaporated Metal Interconnections at Contact Windows

An analysis of the open metallization problem at oxide steps at the surface of planar devices is described. This failure mechanism is essentially based upon the presence of a film discontinuity which grows during the evaporation process at the interface of coarse and dense crystal structures of the evaporated film. The growth rate of the coarse surface is somewhat larger than that of the normal surface. This mismatch in growth rates gives rise to the film discontinuity due to the self-shadowing effect by the former surface. The film discontinuity is apt to occur at the sharp step of phosphosilicate glass because of the following two reasons: a) a large vapor-incidence angle to the perpendicular side wall; b) a spontaneous growth of the coarse surface at the sharp edge of the step. Techniques investigated to improve the interconnection reliability include: a) evaporation at elevated substrate temperature (~ 300°C), b) reduction of the thickness of phosphosilicate glass, c) perpendicular vapor incidence to the substrate and d) protection of thle discontinuity against corrosive agents.