A device comprises a first metal structure, a dielectric structure, a dielectric residue, and a second metal structure. The dielectric structure is over the first metal structure. The dielectric structure has a stepped sidewall structure. The stepped sidewall structure comprises a lower sidewall and an upper sidewall laterally set back from the lower sidewall. The dielectric residue is embedded in a recessed region in the lower sidewall of the stepped sidewall structure of the dielectric structure. The second metal structure extends through the dielectric structure to the first metal structure.