A first low dielectric constant (low-k) dielectric material layer is lithographically patterned to form a recessed region having expose substantially vertical sidewalls, which are subsequently damaged to de-carbonize a surface portion at the sidewalls having a sublithographic width. A second low-k dielectric material layer is deposited to fill the recessed region and planarized to exposed top surfaces of the damaged low-k dielectric material portion. The damaged low-k dielectric material portion is removed selective to the first and second low-k dielectric material layers to form a trench with a sublithographic width. A portion of the pattern of the sublithographic-width trench is transferred into a metallic layer and optionally to an underlying dielectric masking material layer to define a trench with a sublithographic width, which can be employed as a template to confine the widths of via holes and line trenches to be subsequently formed in an interconnect-level dielectric material layer.