The effect of hydrogen addition on the fluorine doping level of SiOF films prepared by remote plasma-enhanced chemical vapor deposition using SiF4-based plasmas

Fluorinated silicon dioxide films (SiOF) have been prepared by high-density remote plasma-enhanced chemical vapor deposition from silicon tetrafluoride (SiF4), oxygen and helium feedstock gas mixture at substrate temperature as low as 175 degrees C. Addition of hydrogen has been found to control the fluorine doping level of the SiOF films over a wide range of fluorine concentrations while the SiF4-to-O-2 flow rate ratio is kept constant. It has been confirmed that hydrogen addition does not lead to the incorporation of hydrogen in detectable quantities into the grown film with Si-F-x bond concentrations in the range of 0.5-4.9 at.% because of effective mutual scavenging behavior of fluorine and hydrogen in the entire range of hydrogen flow rates used. The decrease in the refractive index of the SiOF films from 1.463 to 1.410 and the increase in Si-O-Si bonding angles from about 137 degrees to about 148 degrees were found to be approximately linear with the increase in fluorine concentration. The hydrogen added to the process gas mixture has been found to play an active role in the film formation process affecting both the surface reactions and properties of the obtained SiOF films.