Dry etching and residue removal of functional polymer mixed with TiO₂ microparticles: Via inductively coupled CF₄/O₂ plasma and ultrasonic-treated acetone for humidity sensor application

In this study, the etching characteristics of a functional polymer mixed with TiO₂ microparticles are investigated using an inductively coupled CF₄/O₂ plasma (ICP) dry-etching method for humidity sensor application. The etching rate and surface morphology associated with different etching conditions (e.g., ICP power, chamber pressure, and different percentages of CF₄ in O₂) are investigated, and a maximum etching rate of 795 nm min^-1 is obtained. Furthermore, the surface reactions of the polymer with a gas mixture containing CF₄/O₂ are studied with X-ray photoelectron spectroscopy (XPS), by which the surface binding states and elemental changes are measured during the ICP dry-etching process. We find that the CF₄/O₂ plasma treatment leads to the presence of TiO₂ residue on the surface of the pattern. Therefore, methods for removing the TiO₂ residue are tested, and an ultrasonic-treated acetone is chosen to totally remove the residue without damage.