Fraunhofer ISE develops faster laser system for wafer processing

From pv magazine Germany

With a new type of laser, wafers can be processed 10 to 20 times faster than before. This is the result of a research project at the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany.

The researchers developed a prototype that can engrave the finest structures in silicon wafers using UV waves. The new system concept enables solar cell manufacturers to carry out laser processing at the highest speed without having to compromise on the size of the structure or processing field.

In order to produce photovoltaic cells from wafers, the wafers must, among other things, be metalized. During this step, fine channels are furrowed on the top of the cells. The silver paste goes into the channels and then serves as a conductor track. The speed at which the channels come onto the wafer is very important for the production of cells to further reduce production costs.

The laser presented by Fraunhofer ISE can draw 1800 lines per second. This is 10 to 20 times as fast as a so-called galvanometer scanner, which is often used for this purpose. The laser has a high repetition rate of 10 megahertz and a maximum pulse energy of 5.6 microjoules.

The laser can also process wafers in M12 format with a side length of 210 millimeters. The channels engraved by the laser are just 15 micrometers wide. This is 30 percent finer than current UV wave lasers that are already used commercially. Compared to the very widespread infrared lasers, the channels of the new laser are three times as fine. Finer channels allow for reduced use of silver paste and can thus help further reduce production costs.

“The special thing about the design of the demonstrator is that large workpieces can be processed very quickly and with a small structure size,” said Jale Schneider, project manager at Fraunhofer ISE. “A large image field, fast processing, fine structures – the idea that you can only have two of these three properties at the same time is firmly anchored in the laser material processing industry. With this system, we have fulfilled all three wishes at the same time.”

German laser specialist Edgewave GmbH developed the prototype. Moewe Optical Solutions built a polygon scanner for the project. At Fraunhofer ISE, the team put together the polygon scanner, the laser and an axis for beam guidance into a system. The group now wants to look at new processes to increase throughput.