Glass made of SiO2 is attacked by HF with the formation of SiF62- anion The analogous CF62- dose not exist.
Silicon has 3d-orbitals and can use octahedral sp3d2-hybrid orbitals to bond to six F– ions. Carbon lacks 2d-orbital (2d does not exist) and with just 2s and 2p valence orbitals, carbon can form maximum of only four bonds.
