Defect formation in silicon during laser doping

Abstract

A main challenge in today's solar cell industry is to lower the production costs of solar cells. This can be achieved by applying laser technologies like the laser doping which is for example used to create a selective emitter, having a higher efficiency as a consequence. Due to the laser irradiation of the silicon, the irradiated area melts selectively and recrystallizes afterwards. This recrystallization process is supposed to behave epitaxially. However the parameters of the laser have a great impact on the development of dislocations and the tension of the solidified silicon. We denote that the shape of the laser focus influences the process of recrystalization. In the present contribution we analyze wafers processed with laser beams focused as a line and as a circle, varying the line thickness and the circle diameter. The differences that develop are analyzed. Using a transmission electron microscope no dislocations are found in the wafers irradiated with the line focus. Also a repetitive irradiation does not lead to the development of dislocations over the detection limit. If a laser beam with circular focus is used, cracks develop at the surface changing its structure.