A method of forming a phosphosilicate glass, includes flowing a pre-deposition gas comprising an inert gas into a deposition chamber containing a substrate, where the temperature of the substrate is at a pre-deposition temperature of at least 400.degree. C; continuously increasing the temperature of gas in the chamber to a deposition temperature and simultaneously continuously increasing a flow rate of phosphine and silane until a phosphine:silane deposition ratio is achieved; and depositing the phosphosilicate glass on the substrate at the deposition temperature and at the phosphine:silane deposition ratio.