STRESSES IN SIO2 FILMS OBTAINED FROM THERMAL DECOMPOSITION OF TETRAETHYLORTHOSILICATE - EFFECT OF HEAT TREATMENT AND HUMIDITY

The control of both the magnitude and sign (tensile or compressive) of stresses in thin film insulators deposited on semiconductors is of primary importance in the fabrication of semiconductor devices and circuits. On the basis of room temperature stress measurements in SiO//2 films deposited on silicon and germanium, it has been possible to estimate the intrinsic stress in vapor-deposited SiO//2 films by assuming for the values of the mechanical properties of the films deposited at high temperature those of the bulk properties of vitreous silica. The intrinsic stress derived is the same for both substrates. The heat-treatment effects of low- temperature films occur in two stagesfirst, an increase in tensile stress occurring with loss of moisture contained in the film, densification, and no variation in the Si-O stretching band, second, a decrease in tensile stress occurring gradually and resulting in a shift toward higher frequencies of the Si-O band. The room temperature stress in low-temperature films decreases sensibly on exposure to a humid ambient with no densification of the film. The intrinsic stress in these films is not explained.