Microstructural analyses of Ag thick-film contacts on n-type silicon emitters

The microstructural properties of Ag thick-film contacts on P diffused [100] Si wafers are investigated. By transmission electron microscopy, the contact interface is found to be composed of mostly 100-500 nm sized Ag crystallites penetrating into the Si on average up to 100 nm. The crystallites are mostly in epitaxial relation with Si, indicating their growth from the glass frit melt. A quasi continuous glassy layer is present between the crystallites and the Ag grains forming the contact bulk. Conductive atomic force microscopy on cross sections shows that the interface crystallites form a low contact resistivity with the Si emitter below 2/spl times/10/sup -7/ /spl Omega/cm/sup 2/. The measurements indicate selective current paths across the interface via few isolated Ag crystallites. In-plane atomic force microscopy on Si after contact removal confirms the statistical nature of the interface and an improved contact uniformity in case of firing through processes.