Electrical conductivity of sidewall-deposited fluorocarbon polymer in SiO2 etching processes

Abstract

High-aspect-ratio SiO2 contact hole etching is one of the key processes in the fabrication of ultralarge scale integration devices. However, there are many serious problems, such as charge-build-up damage, etching-stop, and microloading effects. Charge accumulation in high-aspect-ratio contact holes during etching is one of the main causes of these problems. In SiO2 etching using fluorocarbon gases, it is well known that a fluorocarbon film is deposited on the underlayer surface and sidewall of contact holes. It is also predicted that an increase in the conductivity of the fluorocarbon film deposited on the SiO2 sidewall markedly reduces the charging potential in the high-aspect-ratio contact holes because of the high conductivity of the deposited polymer. To clarify these phenomena, it is necessary to obtain quantitative measurements of the conductivity of the sidewall surfaces in contact holes. Therefore, we fabricated the sensing device using semiconductor production technology, and monitored sidewall current of SiO2 contact holes on the silicon wafer. The relationship between the chemical structure and sidewall current of the fluorocarbon films deposited in contact holes is investigated. We have found that highly cross-linked and unsaturated fluorocarbon polymer causes high sidewall conductivity in SiO2 contact holes. It is suggested that the deposited fluorocarbon film reduces the charging potential during the SiO2 etching process.