A vapor phase deposition method and apparatus for the application of thin layers and coatings on substrates. The method and apparatus are useful in the fabrication of electronic devices, micro-electromechanical systems (MEMS), Bio-MEMS devices, micro and nano imprinting lithography, and microfluidic devices. The apparatus used to carry out the method provides for the addition of a precise amount of each of the reactants to be consumed in a single reaction step of the coating formation process. The apparatus provides for precise addition of quantities of different combinations of reactants during a single step or when there are a number of different individual steps in the coating formation process. The precise addition of each of the reactants in vapor form is metered into a predetermined set volume at a specified temperature to a specified pressure, to provide a highly accurate amount of reactant.