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/O-2 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 similar to 200 degrees 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-F-2) bonds. Since Si-F-2 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-F-2 bonds are formed should be avoided.