Optical diagnostics for plasma-surface interaction in CF₄/Ar radio-frequency inductively coupled plasma during Si and SiO₂ etching

Highly selective etching of SiO₂ over Si is central to the manufacture of ultralarge scale integration devices; the process is generally one of reactive ion etching using polymerizing fluorocarbon chemistry. A number of species including electrons, ions, and radicals are generated by reactions in the gas phase and on the surface in the plasma process. A large number of highly reactive fluorine atoms, fluorocarbon radicals, and ions interact with the substrate and produce etch products. These etch products, primarily SiF ₄ and SiF₂, diffuse back into the bulk plasma where they are dissociated and ionized by interactions with electrons, and the resultant products are transported and redeposited onto the substrate and/or wall surface. That is, the plasma structure may differ depending on whether the Si (or SiO₂) surface has been exposed to etching or not. Hence, it is essential to investigate the spatiotemporal characteristics of the plasma structure during etching. In this study, measurements of plasma structure during Si or SiO₂ etching in CF₄/Ar radio-frequency inductively coupled plasma (rf-ICP) were performed using computerized tomography of optical emission spectroscopy to investigate plasma-surface interactions. We focused on the characteristics of etch products, their daughter products, and the etchant in the gas phase during Si and SiO ₂ etching in CF4/Ar rf-ICP and the disturbance of the plasma structure at high amplitudes of LF bias.