Selective Emitter Using APCVD PSG Layer as Doping Source

Using atmospheric pressure chemical vapour deposition (APCVD) of phosphosilicate glass (PSG) allows the separation of the PSG deposition and the thermal drive-in, adding another degree of freedom and control to the emitter formation. A large survey is carried out varying the process parameters such as phosphorus concentration and layer thickness of the PSG layer and the temperature and duration of the thermal drive-in in a tube furnace. We show that the data of the survey can train a metamodel, which can predict the emitter sheet resistances Rsh based on the process parameters. An emitter with Rsh = 120 /sq and an emitter dark saturation current density j0e = 40 fA/cm² after firing (textured surface, SiNX passivation) is demonstrated using this approach. For the formation of a selective emitter, laser diffusion is carried out. The laser process takes place between the PSG layer deposition and the drive-in process. A 1.4 mm deep profile with a peak concentration of 7×1019 cm-3 at the surface is fabricated using a longpulse infrared laser. This process leads to a specific contact resistivity C = 4.2 mcm² using a commercially available screen-printed and fired silver paste. Specific contact resistivity down to C = 1 mcm² is reached using a short-pulse green laser process.