Methods of curing a polymer layer on a substrate using variable microwave frequency are provided herein. In some embodiments, methods of curing a polymer layer on a substrate using variable microwave frequency include (a) forming a first thin-film polymer layer on a substrate, the first thin-film polymer layer including at least one first base dielectric material and at least one microwave tunable material, (b) applying a variable frequency microwave energy to the substrate and the first thin-film polymer layer to heat the substrate and the first thin-film polymer layer to a first temperature, and (c) adjusting the variable frequency microwave energy applied to the substrate and the first thin-film polymer layer to tune at least one material property of the first thin-film polymer layer.