Factors influencing adhesion of fluorocarbon (FC) thin film on silicon substrate

Hydrophobic polymeric thin films (e.g., fluorocarbon) are used in micro-fluidic applications for drag reduction. However, one of the major issues hindering their usage is reliability. Previous work shows a degradation/delamination of fluorocarbon (FC) film over a period of time. This paper investigates various processing parameters influencing the adhesion of hydrophobic FC coating to a silicon substrate. The FC film is processed using the "Bosch" process (alternating etching and deposition steps) to perform deep anisotropic silicon etching. The Si(100) wafers are first etched to a depth of about 5-10 μm and then coated with CF_x film from the C₄F₈ monomer. The effect of pressure, inductively coupled plasma power, thickness of the film, and the gas ratio of mixing H₂ to C₄F₈ has been investigated using a fractional factorial experimental design. By better understanding the effect of each input variable, the reliability of the deposited film can be improved and this is discussed in detail in this paper.