Microstructure evolution during electroless copper deposition
by J. Kim, S. H. Wen, D. Y. Jung, R. W. Johnson
A study using transmission and scanning electron microscopy was made of the evolution of the microstructure of electroless plated Cu on activated amorphous substrates and on single-crystal Cu grains. On amorphous substrates activated in a PdCl2SnCl2 colloidal solution, Sn atoms dissolved into the plating solution concurrently with Cu deposition on the substrate during the initial stage of deposition. The very small face-centered-cubic grains of Cu-Pd solid solution agglomerated into much larger particles and later coalesced into spherical grains. As the grains grew, they developed crystallographic facets, impinged upon one another, and finally covered the entire substrate. Grains of energetically favorable crystallographic orientation selectively developed into the columnar structure. These columnar grains contained subgrains, dislocations, and twins. Remarkably different structures were observed for the Cu grown on large single-crystal grains. In this case epitaxial growth dominated the plating process. Low-surface-energy (111) Cu planes were frequently observed on plated Cu surfaces. Growth rates were a function of substrate orientation.