Investigation of Laser Ablation of Different Dielectric Layers with Ultra Short Pulses

Abstract

Laser ablation of dielectric layers offers a low cost and contact free structuring method for producing highly efficient silicon solar cells in an industrial environment. In this work we investigate the ablation of SiNx and AlOx/SiNy layers on damage etched Cz silicon wafers. A Nd:YVO4 laser source is used with a fixed pulse length of ∼ 10 ps and a wavelength of 1064nm whereby the second (532nm) and third harmonics (355nm) are also applied. Laser ablated spots are characterized by light microscopy as well as SEM and EDX measurements. We produce symmetric test samples and conduct implied Voc measurements by means of QSSPC to detect laser induced damage. A strong influence of the wavelength and laser fluence on the results is found. To investigate whether the dielectric layers are properly opened, the test samples are metalized on both sides. Measurements of the series resistance from front to rear side through the samples show a clear influence of the laser parameters applied. By combining the results of both measurements we find a suitable process window for laser ablation with little damage to the substrate and a reasonable low series resistance.