Accelerator Surface Phase Associated with Superconformal Cu Electrodeposition
Thomas P. Moffat, Liang Yueh Ou Yang
Superconformal film growth is a key process in state-of-the-art Cu metallization of electronic devices. Superfilling of recessed surface features results from competition between electrolyte additives that accelerate or inhibit Cu electroplating. In situ STM is used to image the accelerating SPS-Cl- surfactant phase that is responsible for displacing and preventing formation of the inhibiting PEG-Cl- layer. Various aspects of competitive and/or co-adsorption of Cl- and SPS on Cu(100) were examined for industrially relevant additive concentrations. At potentials associated with superfilling, a saturated, c(2x2) Cl- ordered adlayer forms on the surface. When SPS is added individual molecules are imaged as a mobile 2-D gas diffusing on the Cl- adlattice. The SPS-Cl- surfactant accounts for many aspects of additive function previously observed and stipulated by the curvature enhanced accelerator model of superconformal film growth. Several SPS derived species of differing mobility and tunneling contrast appear with exposure time. The lattice gas species are sensitive to the imaging conditions with tip-molecule interactions particularly evident at higher tunneling currents. At negative potentials the c(2x2) Cl- adlayer is disrupted by an order-disorder transition, while desorption occurs at more negative potentials. This allows SPS direct access to the Cu metal whereupon irreversible sulfide formation occurs.
Journal of the Electrochemical Society
Cu, Damascene Processing, In Situ STM, Superconformal Film Growth, SPS, TSV