Flow Characteristics of SiOF Films in Room Temperature Chemical Vapor Deposition Utilizing Fluoro-Trialkoxy-Silane Group and Pure Water as Gas Sources

The flow characteristics of SiOF films formed by room temperature chemical vapor deposition (CVD) for interlayer dielectrics of multilevel interconnections have been studied. The room temperature CVD technique utilizes fluoro–tri–alkoxy–silane group (FTAS, FSi(OR)³, R^: alkyl group) and pure water as gas sources. It has been revealed that the films deposited using fluoro–tri–normalpropoxy–silane (FTNPS, FSi(n~OC³H⁷)³) have better flow surface profiles on A1 wirings than others such as fluoro–trimethoxy–silane (FTMS), fluoro–triethoxy–silane (FTES), and fluoro–tri–isopropoxy–silane (FTIPS). From the speculated SiOF films deposition mechanism, it is considered that the flow surface profiles are due to the fluorosilanol oligomers flow. It is also speculated that the fluorosilanol oligomers flow occurs when the surface migration velocity of the oligomers with reaction by–products is larger than the polymerization velocity at the trenches between aluminum (Al) wirings. The reasons why the SiOF films deposited using FTNPS have better flow surface profiles are considered that normalpropyl alcohol, reaction by–product, has lower vapor pressure (20 Torr) than other reaction by–products such as methyl alcohol (125 Torr), ethyl alcohol (58 Torr), and isopropyl alcohol (44 Torr) at the deposition temperature (25°C), and that the polymerization velocity is smaller than those using FTMS, FTES, and FTIPS. The deposition rate, corresponding to the polymerization velocity, for the SiOF films deposited using FTNPS is about 16 nm/min, and is smaller than those using FTMS, FTES, and FTIPS. Similar flow surface profiles are obtained by adding normalpropyl alcohol to FTES during the films deposition. Although the deposition rate and etching rate for the SiOF films depend on the carbon number in the alkyl group of FTAS, the nature and quality of the Si–0 bonds in FTIR spectra, refractive index do not depend on the carbon number.