Fraunhofer Institute for Solar Energy Systems ISE
Thermal processes are essential in solar cell production. The process quality is significantly determined by the temperature and its temporal course, and therefore, precise temperature regulation (or control) plays a decisive role in achieving high quality processing. For this reason, infrared (IR) emitters are often used as heat sources in industrial furnaces, in which large share of the required power is used to heat the chamber walls and the process atmosphere. The thermal mass of the process chamber and the IR emitters are the main factors that determine the achievable heating and cooling rates for a stationary substrate. Because the chamber typically has a high thermal mass, only slow temperature changes are possible. In solar cell production, full area laser irradiation of the target surface serves as an alternative energy (or heat) source to the IR emitters. In this case the target substrate is heated exclusively by laser absorption, which results in a selective heating of the substrate. The heating and cooling rates are essentially determined by the thermal mass and optical properties of the target substrate. This processing technique allows a silicon carbide (SiC) substrate to be heated to 1700 K with heating rates of 600 K/s under atmospheric pressure and room temperature, for example Additionally, the direct absorption of the radiative energy into the target substrate allows for a sophisticated temperature control.
