Method of making a sloped sidewall via for integrated circuit structure to suppress via poisoning

Abstract

Via poisoning of vias formed in low k carbon-containing silicon oxide dielectric material is suppressed by forming the via in a layer of such dielectric material with a smooth inwardly sloped sidewall. Such a sloped sidewall via can be etched in a low k dielectric layer by first forming a via resist mask over the upper surface of such a dielectric layer, then heat treating the mask sufficiently to deform the sidewall geometry of the resist mask to form a sloped sidewall on the opening or openings in the heat treated resist mask. The resulting erosion of such a resist mask, during a subsequent etch step to form the via in the low k dielectric material through such a sloped sidewall resist mask, imparts a tapered or sloped sidewall geometry to the via which is then formed in the underlying layer of low k dielectric material. In a preferred embodiment, when the via is cut through several layers of different types of dielectric material, the smoothness of the sloped sidewall of the resulting via is enhanced by adjusting the selectivity of the via etch to uniformly etch each of the layers of dielectric material at approximately the same rate.