an apparatus for thermal treatment of dielectric films on substrates comprises : a microwave applicator cavity and microwave power source ; a workpiece to be heated in the cavity , comprising a porous coating on a selected substrate ; and , a means of introducing a controlled amount of a polar solvent into said porous coating immediately before heating by said microwave power . the interaction of the polar solvent with the microwaves enhances the efficiency of the process , to shorten process time and reduce thermal budget . a related method comprises the steps of : depositing a porous film on a substrate ; soft baking the film to a selected state of dryness ; introducing a controlled amount of a polar solvent into the soft baked film ; and , applying microwave energy to heat the film via interaction with the polar solvent .