| Aluminum nitride is a high thermal conductivity electrical insulator with a band gap of 6.2 eV. For microelectronics applications, it is necessary to be able to drill and metallize small holes in aluminum nitride substrates to form electrical connections. In this work, samples of polycrystalline aluminum nitride were exposed to two excimer laser wavelengths at various laser energy densities. The photon energies of ArF and KrF lasers represent energies above and below the band gap corresponding to shallow and deep penetration depths. The samples were processed in air and in a vacuum cell under nitrogen, helium, hydrogen, argon and in vacuum.; Excimer laser ablation of aluminum nitride occurred by laser heating a small volume of material near the surface. The short pulse length and high energy density produced a layer of highly energetic species evaporating from the solid. The dense ionized plasma layer absorbed some of the ablating laser pulse, thus decreasing the energy reaching the surface. As laser energy density increased, the ablation rate increased due to increased heating in the sample. The longer wavelength had a greater penetration depth and, therefore removed more material per pulse. At reduced pressures, the ablation rate increased as the ablated material expanded more rapidly reducing the density and absorption factor of the plasma.; Emission spectra collected during ablation and Auger electron spectroscopy of the redeposited debris indicated Al, Al{dollar}sp+,{dollar} Al-O, Al-N, N{dollar}sb2,{dollar} O{dollar}sb2{dollar} and NO{dollar}sb{lcub}rm x{rcub}{dollar} species. These products were expected from the decomposition of aluminum nitride into aluminum and nitrogen and subsequent reaction with air.; Rapid expansion of the ablation products created shock waves in the solid sample and in the ambient gas. Supersonic shock waves propagating in the gas were observed by photothermal beam deflection. The shock wave traveling in the solid reflected off of the back surface interface producing a tensile wave traveling toward the front surface. Damage was prevented by applying a backing material to reduce the reflection coefficient at the back surface interface. By choosing a metal backing, the craters were eliminated and the ablated metal produced a metallized through hole. |
