Deposition characteristics of low dielectric constant siof films prepared by ECR PECVD

Abstract

SiOF film has attracted significant attention as a new interlayer dielectric material since it exhibits a lower dielectric constant than SiO2. In this study, we prepared SiOF films by using the electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) method and observed the dependence of the film properties on such various deposition parameters as the SiF4/O2 flow rate ratio, substrate temperature, microwave power and pressure. The increase in the film’s fluorine content led to a decrease in the dielectric constants. This was due to a decrease in ionic polarization rather than to a decrease in electronic polarization. The film properties have not exhibited a large dependence on the substrate temperature, in the range of 25~200°C. When the plasma was not activated, i. e. when the microwave power was as low as 300 W or the pressure was higher than 5 mTorr, the dielectric constants of the films were lower than 3.0 because of the high fluorine content, but the films contained silicon difluoride (Si-F2) bonds. Since Si-F2 bonds play a critical role in the absorption of water molecules which causes an increase in the dielectric constants of the films, the deposition conditions where the Si-F2 bonds are formed should be avoided.