Laser-induced deposition of silicon films

Abstract

Recent advances in the laser-induced deposition of thin films are briefly reviewed in connection with the present experiment conducted for silicon films. Either gases or solids are used as starting materials. In the so-called laser chemical vapour deposition process, gases are decomposed by laser-induced photolysis or pyrolysis. Amorphous silicon films were deposited from silane using a CO 2 laser which was used to heat a quartz substrate and to excite gas molecules vibrationally; deposition rates are several micrometers per minute at about 10 W cm -2. Ultrafast deposition of amorphous silicon films with instantaneous speeds as high as 10 μm s -1 is made possible by laser sputtering, where a Q-switched laser irradiates solid silicon targets to generate atomic beams mixed with ions. The dynamics of laser sputtering have been studied through emissions from neutral silicon and silicon ions which show acceleration of ions by local electric fields followed by electronic recombination near the target. When gas molecules are introduced, they are decomposed by collisions with these energetic particles. This decomposition is responsible at least partly for the incorporation of atoms into films and for the modification of their physical properties.