The formation of optically-transparent films of fusible materials like zinc, lead, bismuth on glass substrates to obtain single-mode optical diffusive waveguides is considered. The quality of films for waveguides depends on the amount of oxygen in residual environment, the gas exchange rate in the working chamber, the rate of oxygen desorption from the heated elements in vacuum chamber, the evaporator and the substrate. The regularities of variations of local layer thickness and the procedure phase diagram from the local gas exchange rate are determined.