Characterisation of laser scribes in thin film photovoltaics by coherence correlation interferometry

In this paper we present results measuring the precise shape of laser scribes in thin film photovoltaics using Coherence Correlation Interferometry (CCI). Laser ablation is used in interconnect processes in all types of thin film devices, including those based on CdTe, CIGS and amorphous silicon. The work presented in this paper was focused on the use of a laser ablation process in the interconnect of thin film CdTe modules. This process is known as monolithic integration. The laser scribe measurements presented here were obtained on a nanometre scale using Coherence Correlation Interferometry. The Coherence Scanning Interferometry (CSI) technique is able to provide three and two dimensional topographical images of the sample surface, with an ultimate vertical resolution of 0.01nm. It provides two dimensional profiles of the laser ablated trenches, from which it is possible to extract quantitative information of the detailed shape of the scribe including precise measurements of both depth and width. In addition, the CCI is able to provide detailed analysis of surface roughness within the bottom of the trench which is important for efficient electrical contact.