Precipitate Formation and Effects on Electrical and Mechanical Properties of Fluorinated Silicon Oxide

Precipitates appear on fluorine-doped silicon oxide (SiOF) film when the film surface is exposed to atmospheric air. They are flake-type and hexagonal-shaped and show up rapidly after initiation, and then densely clustered. Energy-dispersive X-ray (EDX) analysis results of the precipitates show that mainly Si & O are detected. From the analysis of Raman spectra, the decreased intensities at about 600 cm-1 and 500 cm-1 post precipitation indicates the reduction of strained low-order ring structure in SiOF film. It is found that the dielectric constant of SiOF films initially increases at exposure to air and is attributable to the absorption of water, and then on the contrary a declining trend of the dielectric constant was observed after precipitation. From the Current-Voltage (I-V) characteristics, there is an apparent shift of the breakdown distribution to lower values of electric field for the SiOF films post-precipitation. Slight but appreciable reduction in hardness could be observed along exposure to air and precipitation. Precipitation on SiOF film at exposure to humid air is accompanied by reconstruction in structure, leading to further increase in film porosity and reduction in film rigidity.

Formation of SiOF Films by APCVD Using TEOS-O3-HF Gas Mixture

Fluorinated silicon oxide (SiOF) films have been prepared in a conventional atmospheric pressure chemical vapor deposition (APCVD) reactor. APCVD technique utilizes tetraethoxysilane, ozone and hydrofluoric anhydride as gas sources. SiOF films are deposited by changing the temperature of deposit. Substrate holder was maintained in the temperature range of 200 to 275°C. Films were characterized based on the deposition temperature. Chemical bonding structure of the films was evaluated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and ellipsometry techniques. FTIR spectra revealed Si-F bond at about 935 cm-1. Incorporation of fluorine has a minimal contribution in the reduction of refractive index of SiOF films from 1.46 to 1.35.Therefore, the main mechanism responsible for this reduction of refractive index is the porosity generated by incorporation of fluorine atom in the SiOF films. Dielectric constant was reduced from 4.2 corresponding to that of SiO2 films, to the values in the range of 3.18 to 3.6 for SiOF films deposited by APCVD technique.