Abstract: A method and apparatus are disclosed for forming thin polymer layers on semiconductor substrates. In one embodiment, the method and apparatus include the vaporization of stable di-pxylylene, the pyrolytic conversion of such gaseous dimer material into reactive monomers, and the optional blending of the resulting gaseous p-xylylene monomers with one or more polymerizable materials in gaseous form capable of copolymerizing with the p-xylylene monomers to form a low dielectric constant polymerized parylene material. An apparatus is also disclosed which provides for the distribution of the polymerizable gases into the deposition chamber, for cooling the substrate down to a temperature at which the gases will condense to form a polymerized dielectric material, for heating the walls of the deposition chamber to inhibit formation and accumulation of polymerized residues thereon, and for recapturing unreacted monomeric vapors exiting the deposition chamber.