Cu⁰, Cu⁺, and Cu₂ from excimer-ablated copper

Bulk copper is laser etched with 193- and 351-nm excimer radiation. The transition from the thermal to the plasma etch region is studied by measuring the densities and kinetic energies of three copper species (Cu0, Cu+, and Cu2) in the etch plume. A unique laser-induced fluorescence experiment allows these three species to be followed essentially simultaneously as a function of fluence. Three separate types of etching behavior are clearly evident (even within the small fluence range of ∼1-12.5 J/cm2); i.e., thermal vaporization of Cu, multiphoton ionization of the Cu vapor, and electron-atom collision-induced ionization (breakdown) and dissociation (of Cu2).