Mechanical Properties of SiO<sub><i>x</i></sub>N<sub><i>y</i></sub> Films Deposited by RF Plasma-Enhanced CVD

Abstract

Silicon oxynitride (SiOxNy) films were deposited by plasma-enhanced chemical vapor deposition (PCVD), using silane (SiH4), nitrious oxide (N2O) and nitrogen (N2) as reactive gases. Studies on the mechanical properties and composition of the SiOxNy films indicated that an increase in N2O flow rate leads to an increased SiO2 molar fraction in SiOxNy films, a decrease in microhardness, and change from a compressive stress for Si-N rich films to a tensile stress for Si-O rich films. It was found that there was a good relationship between the SiO2 molar fraction and the stress and the microhardness of the SiOxNy films formed under the various conditions of N2O flow rate or pressure. Experimental results showed no significant dependence of the microhardness and the composition of the films on the N2 flow rate, but the residual stress depended on the N2 flow rate. The residual stress changed from compressive to tensile with increasing N2 flow rate, indicating that the residual stress in SiOxNy film was controlled by N2 flow rate, while the microhardness and the composition of the films were kept constant. This has been explained in terms of the bombardment effects of N2 ions against the growing layers, which was confirmed by measuring the optical emission spectrum from a PCVD plasma of an SiH4-N2-N2O gas mixture. A good correlation between the microhardness and the refractive index of the films deposited at constant substrate temperature was found, leading to the conclusion that fairly accurate estimation of microhardness of SiOxNy films with thicknesses of 1μm or less was possible through measuring the refractive index.