Effect of N₂ Plasma Annealing on Properties of Fluorine Doped Silicon Dioxide Films with Low Dielectric Constant for Ultra-Large-Scale Integrated Circuits

The influence of N₂ plasma annealing on the properties of fluorine doped silicon oxide (SiOF) films is investigated. The stability of dielectric constant of SiOF film is remarkably improved by the N₂ plasma annealing. After enduring moisture absorption test for six hours in a chamber with 60% humidity at 50°C, the dielectric constant variation of the annealed SiOF films is only 1.5%, while the variation for those SiOF films without annealing is 15.5%. Fourier transform infrared spectroscopic results show that the absorption peaks of Si-OH and H-OH of SiOF films are reduced after the N₂ plasma annealing because the annealing can wipe off some unstable Si-F₂ bonds in SiOF films. These unstable Si-F₂ bonds are suitable to react with water, resulting in the degradation of SiOF film properties. Therefore, the N₂ plasma annealing meliorates the properties of SiOF films with low dielectric constant.