Fast etching of sapphire by a visible range quasi-cw laser radiation

Experimental results are presented on laser-assisted etching of sapphire by a copper vapour laser radiation (wavelength 510 nm, pulse duration 10 ns, repetition rate 8 kHz, energy density ∼ 10 J/cm2). The etching is carried out under the laser irradiation through the sapphire substrate of the interface sapphire/absorbing liquid. The self-modulation of the groove depth is observed in a certain range of scanning velocities of laser beam. A qualitative model of the etching process is proposed where the maximal etching depth per pulse is limited by the thermal diffusion length of sapphire during the laser pulse. The corresponding etching rate of 0.3 μm/pulse (∼ 2 mm/s) is observed experimentally. The etched areas of sapphire show the ability to reduce Cu from the electroless plating solution. Area-selective Cu metallization of the etched grooves, via- and blind holes is reported with adherence up to 18 N/mm2.