Compact Laser Source for Metal Deposition

For the past few years, there has been considerable interest in using lasers for the directed deposition of metal [1,2,3,4]. Part of this interest is driven by technological applications in microelectronics. In particular, this includes the rapid interconnection of gate arrays [5] and the repair of defects in photomasks [6]. The techniques used for the laser patterning of metal include Laser Chemical Vapor Deposition (LCVD) [7], and the decomposition of spin-coated organometallic inks [8]. In the first process, LCVD, a laser with a power of several hundred milliwatts or more is used to irradiate a substrate in the presence of an organometallic vapor. The substrate is chosen so that it absorbs the the incident laser radiation while, in general, the organometallic vapor is transparent at the laser wavelength. The absorption of the laser energy by the substrate results in a temperature rise which depends on the thermal properties of the substrate. If the temperature rise is sufficient, organometallic molecules impinging on the irradiated area decompose. Non-volatile components (such as metal fragments) remain on the surface and form a deposit. In the second process, decomposition of organometallic films, a substrate which was previously spin coated with an organometallic ink is irradiated wherever metal patterns are desired. The ink decomposes in these areas leaving a film of metal. The unirradiated areas of the ink are then washed away with a suitable solvent. Such processes have been extensively studied and developed using primarily argon, krypton, and CO2 lasers [1,2,3,4]. In general these lasers are large, expensive, require maintenance, and raise reliability concerns. These characteristics add to the challenge of introducing laser deposition processes into the manufacturing environment.