Relation between surface morphology, facet selection, and crystal orientation in electroless copper deposits on polycrystalline copper substrates

The relationship between surface morphology and crystal orientation in polycrystalline films is investigated using a quantitative experimental approach that analyzes hundreds of crystals and identifies thousands of facets. Four industry-relevant electroless copper deposits used for microvia filling in high-density interconnect printed circuit boards are examined. The reliability of copper–copper interlayer connections depends critically on the surface characteristics of the electroless copper layer prior to subsequent electrodeposition. Electroless copper films deposited from baths stabilized with sodium cyanide or 2,2′-bipyridine, each prepared with and without nickel additives, are characterized. Surface topography measured by atomic force microscopy is correlated with crystal orientation data obtained by electron backscatter diffraction to identify the crystallographic facet types present at the surface. Deposits from cyanide-stabilized baths exhibit angular surface morphologies with smooth low-index {100} and {111} facets oriented parallel to the surface. Grains with a [110] orientation display increased roughness due to alternating {110} and {100} facets. In contrast, deposits from 2,2′-bipyridine-stabilized baths show more gradual facet transitions and a broader distribution of facet types. Statistical analysis reveals distinct correlations between crystal orientation and surface facet combinations.