Abstract
Ion implantation is an advanced technology developed to inject dopants for shallow junction formation. Due to the ion-induced sputtering effect at low implant energies where dopants tend to accumulate at the silicon surface, the excess ion doses can be easily removed via a surface chemical wet etching process. Modulating surface doses could enhance the collection of minority carriers through the substrate. By taking advantage of the dose limitation characteristic, this study proposed a novel method to form shallow emitters with various dopant densities. Each blanket and selective emitter structures with two process flows have been investigated: 1) Performing wet etch after implantation before junction anneal; 2) Performing wet etch after implantation and junction anneal. In the two process flows, we observed a difference in the density of doping impurities during the thermal process, which is related to the substrate recombination rates. Comparing the blanket emitter and selective emitter structures with two types of etching methods, the device with wet etch before annealing process achieved the best effective carrier lifetime of 53.05 μs, which led to a higher short circuit current density. Hence, this selective emitter cell demonstrated a better blue response and showed an improvement in the conversion efficiency.