Determination of the mechanical stress in plasma enhanced chemical vapor deposited SiO2 and SiN layers

Abstract

The mechanical stress in plasma enhanced chemical vapor deposited SiO2 and SiN layers is investigated. The dielectric films are deposited on Si and GaAs substrates, respectively. A first annealing of the samples yields irreversible structural changes of the films due to a loss of water and hydrogen. The elastic constant and the thermal expansion coefficient of the densified SiO2 layers are estimated by temperature dependent curvature measurements to be Ec/(1−γc)=(1.0±0.1)×1012 dyn/cm2 and αc=(0.6±0.2)×10−6 °C−1. IR absorbance measurements show a dependence of the center frequency of the Si–O bond-stretching vibration on the total film stress. Correlating the strain deduced from this measurement with the total film stress yields an elastic constant of about Ec/(1−γc)=(3±1)×1011 dyn/cm2. The physical fundamentals of this measuring method as well as the temperature dependent measurements are discussed in detail to explain the apparent discrepancies in the estimation of the elastic constant. These considerations show that the true elastic constant of the SiO2 film can only be estimated by the temperature dependent measuring method.