Fast etching and metallization of via-holes in sapphire with the help of radiation by a copper vapor laser

Abstract

Etching of sapphire is studied, induced by radiation from a copper vapor laser (wavelength of 510 nm, pulse duration of 10 ns and pulse repetition rate of 8 kHz) at the `sapphire–absorbing liquid' interface irradiated through the sapphire substrate. Various liquids absorbing in the laser wavelength range are used, such as aqueous solutions of CrO3, FeCl3, and KMnO4. The maximal etching rate is as high as 0.3 μm per laser pulse and is limited only by the heat diffusion length in sapphire during the pulse. This permits etching via holes with an aspect ratio of 15 in 500 μm thick sapphire substrates in a fraction of a second. The etching of sapphire is accompanied by the formation of a thin solid film at the interface for all investigated liquids. In the case of aqueous solution of CrO3 the solid film is Cr2O2 which is shown to grow epitaxially on the sapphire. Similarly, epitaxial growth of Fe2O3 and MnO2 on sapphire is observed upon its etching in FeCl3 and KMnO4, respectively. The processing of etched holes in the electroless copper plating solution results in filling the hole with copper providing thus the interconnection of both sides of the sapphire substrate.