Laser scribing of polycrystalline thin films

We have investigated the use of several different types of lasers for scrib ing of the polycrystalline materials used for thin-film solar cells: CdTe, CuInGaSe2 (CIGS), ZnO, SnO2, Mo, Al, and Au. The lasers included four diffe rent neodymium-yttrium-aluminum garnet (Nd:YAG) (both 1064 and 532 nm wavel engths), a Cu vapor (511/578 nm), an XeCl excimer (308 nm), and a KrF excim er (248 nm). Pulse durations ranged from similar to 0.1 to similar to 250 n s. We found that the fundamental and frequency-doubled wavelengths of the N d:YAG systems work well for almost all of the above materials except for th e transparent conductor ZnO. The diode-laser-pumped Nd:YAG was particularly convenient to use. For ZnO the uv wavelengths of the two excimer lasers pr oduced good results. Pulse duration was found generally not to be critical except for the case of CIGS on Mo where longer pulse durations (greater tha n or equal to 250ns) are advantageous. The frequently observed problem of r idge formation along the edges of scribe lines in the semiconductor films c an be eliminated by control of intensity gradients at the film through adju stment of the focus conditions. (C) 2000 Elsevier Science Ltd. All rights r eserved.