Dynamic Thermal Thin Film Processing of Large Areas With High Power Laser Sources

High power laser sources are used in various production tools for cutting, welding and hardening of metal parts and patterning, annealing and lithography of flat panel displays, solar cells and microelectronic devices. Beside the right choice of the laser source suitable high performance optical beam delivery and shaping systems are needed for generating the appropriate beam profile and intensity distribution are of high importance for the right processing speed, quality and yield. In addition to the typical laser processes with circular beam shapes LIMO has developed laser sources with line shaped beams for large area processing for e.g. crystallization and tempering of conducting and semi-conducting films on glass for FPD, PV and thermal processing of semiconductor wafer, coated float glass and sheet metal. Due to the high power density of several 100kW/cm² and line length up to several hundred millimetres a treatment capacity of several m² per minute and processing speeds up to 1 m/s can be achieved per laser head with typical scan & repeat processes. The use of multiple laser heads in one machine scales the productivity to the individual needs. The high scanning speed together with line widths of 0,01mm to 0,1mm is the basis for heating only a few microns of the surfaces layers and no costly cooling time is needed like with regular heating technologies. With this controlled surface heating even more sensitive materials can be processes like inks on polymers and paper for RFIDs, printed solar absorbers and coatings. For industrial applications equally important is an adequate understanding of the physics of the light-matter interaction behind the process. In advance simulations of the tool performance can minimize technical and financial risk as well as lead times for prototyping and introduction into series production. Based on this knowledge together with a unique free-form micro-lens array production technology and patented micro-optics beam shaping designs a number of novel production tool sub-systems have been built by LIMO: 1. a multi-kilowatt direct diode illumination modules for solar cell annealing, and crystallization; 2. a novel green laser beam line for the annealing of silicon thin films on glass; 3. a novel wavefront shaping optics that generates a top hat beam profile from a TEM00 high-power laser source for accurate thin film structuring. For each of these sub-system basic functionalities, design principles and performance results are presented with a special emphasis on resilience, cost reduction and process reliability.