Using an in situ technique, stress was measured as a function of annealing temperature to investigate the effect of phosphorous and boron doping of silicon dioxide glass films deposited by low-pressure chemical vapor deposition (LPCVD). It was found that the initial stress of phosphosilicate glass is independent of the amount of phosphorus present, while the boron content influences the initial stress in borophosphosilicate glass. The stress increases to a maximum, sigma(m), corresponding to a temperature T(m), above which the onset of viscous flow reduces the stress to zero at a temperature T0. All these.parameters are dependant on dopant concentrations. The observed mechanical behavior is discussed in terms of film viscosity.