Method of vapor deposition

In a method of coating a substrate with a film by deposition from a vaporous reactant composition where a solid phase reactant is vaporized and the resulting vapors are conveyed into contact with the substrate to be coated, the improvement which comprises

• fluidizing a mass of particulate solid reactant with a gas at a first temperature substantially below the reaction or decomposition temperature and below the vaporization temperature of the reactant;
• drawing a volume of fluidizing gas and suspended particulate solid reactant from the fluidized mass as a particulate reactant-gas composition;
• mixing the withdrawn volume of fluidizing gas and suspended particulate reactant with an additional volume of gas which is at a second temperature, also below the reaction or decomposition temperature for the reactant to dilute the particulate reactant-gas composition;
• heating the diluted particulate reactant-gas composition to a temperature above the vaporization temperature of the reactant to vaporize the reactant in order to form a vaporous reactant-fluidizing gas composition mixture;
• and
• conveying the heated vaporous reactant-fluidizing gas composition mixture into contact with the substrate to be coated while maintaining the substrate at a temperature sufficient to cause the reactant in the composition to react, depositing a film thereon.