Influence of Si Surface Orientation on Screen-printed Ag/Al Contacts

In this study the influence of the crystallographic surface orientation of n-type Si wafers on the contact formation of Ag/Al thick film pastes to p+-type Si layers is investigated. Therefore, n-type Si wafers with two different crystallographic orientations, namely polished (111) and (100) FZ wafers, with BBr3 based emitter and 75 nm SiNx:H are screen-printed with Ag/Al paste. Then contacts are fired in either a slow firing process or a fast one with the same peak temperature. Afterwards, contacts are prepared for scanning electron microscopy (SEM) analysis. The Ag/Al contact spots show different shapes on the differently oriented surfaces. For the slow firing process, no significant difference in number and size of the contacts spots can be found for the two surfaces. For samples fired in the fast firing process, the density and size of the contact spots on (100)-oriented surfaces is strongly reduced, whereas for the (111) surfaces only a slight reduction in density is visible as compared to the slow firing process.