Laser scribing of polycrystalline thin films

We have investigated the use of several different types of lasers for scribing of the polycrystalline materials used for thin-film solar cells: CdTe, CuInGaSe2 (CIGS), ZnO, SnO2, Mo, Al, and Au. The lasers included four different neodymium-yttrium-aluminum garnet (Nd:YAG) (both 1064 and 532nm wavelengths), a Cu vapor (511/578nm), an XeCl excimer (308nm), and a KrF excimer (248nm). Pulse durations ranged from ~0.1 to ~250ns. We found that the fundamental and frequency-doubled wavelengths of the Nd:YAG systems work well for almost all of the above materials except for the transparent conductor ZnO. The diode-laser-pumped Nd:YAG was particularly convenient to use. For ZnO the uv wavelengths of the two excimer lasers produced good results. Pulse duration was found generally not to be critical except for the case of CIGS on Mo where longer pulse durations (>250 ns) are advantageous. The frequently observed problem of ridge formation along the edges of scribe lines in the semiconductor films can be eliminated by control of intensity gradients at the film through adjustment of the focus conditions.