Plasma Assisted Remediation of SiC Surfaces

Due to advances in chemical mechanical polishing (CMP), SiC surface quality has improved remarkably over the years. Despite this progress, there is extensive literature reporting the limitations of the CMP process. Wafers purported to have CMP surfaces can range from high-quality, optically perfect surfaces, exhibiting well-defined step and terrace structure to low-quality surfaces with highly scratched regions. Thus, methods are required to remediate these surfaces if they are to be used effectively as substrates for device fabrication. The novel surface remediation approach explored in this presentation utilizes a three-step scalable method referred to here as plasma assisted remediation. In this process, a CF₄-based inductively coupled plasma with reactive ion etch was used to remove material to a depth which was unaffected by surface and sub-surface polishing damage. This produced a planarized but carbon-rich fluorinated surface. This surface was exposed to a rapid thermal oxidation in air to oxidize and volatilize the excess carbon and fluorinated species. The resulting surface oxide was stripped using a dilute hydrofluoric acid in water solution. This process reproducibly yielded planarized, stoichiometric surfaces with low levels of carbon and oxygen contamination for both 4H- and 6H-SiC(0001) surfaces. This presentation describes x-ray photoelectron spectroscopy and atomic force microscopy studies used to characterize each step of the process and provide an understanding of the process mechanism. In addition, experimental studies under ion-rich and radical-dominant plasma conditions are reported which provide greater insight into the underlying chemistry and physics of the process.