Dual-beam laser thermal processing of silicon photovoltaic materials
Brian J. Simonds, Anthony Teal, Tian Zhang, Joshua A. Hadler, Zibo Zhou, Sergey Varlamov, Ivan Perez-Wurfl
Laser processing for photovoltaics (PV) has traditionally been used for very small dimension features where focused beams are rastered to create lines for edge isolation, scribing, and selective emitter formation and for drilling holes for drilling in wrap-through style cells. Larger area laser applications are under investigation, for instance in liquid-phase crystallization of thin film Si on glass, however these rely on additional isothermal heat input. We have developed an all-laser processing technique using two industrially-relevant continuous-wave fiber lasers operating at 1070 nm that is capable of both substrate heating with a large defocused beam and material processing with second scanned beam, suitable for a variety of PV applications. We have demonstrated this technique for rapid crystallization of thin film (~10 μm) silicon on glass, which is a low cost alternative to wafer-based PV. We have also applied this technique to wafer silicon to control dopant diffusion at the surface region where the focused line beam rapidly melts the substrate that then regrows epitaxially. Finite element simulations have been used to model the melt depth as a function of preheat temperature and line beam power. This readily scalable process is carried out in a matter of tens of seconds for an area around 10 cm2 using only about 1 kW of total power. In this paper, we will discuss our results with both c-Si wafers and thin film silicon.
Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXI