Microstructural Modification of Thick Copper Films to Optimize Chemical-Mechanical Planarization of Through-Wafer Interconnects

Patrick Andersen, Boise State University
Mariela Bentancur, Boise State University
Megan Frary, Boise State University

Abstract

Large through-wafer interconnects may be required for high current applications or novel devices like backside connected solar cells. The electroplated copper film required to fill large vias is typically much thicker than conventional films and has a much different microstructure. Previous work has shown films with smaller, more equiaxed grains tend to have lower removal rates and different topography after chemical mechanical planarization (CMP). Here we alter the plating parameters (bath chemistry and current density) and thermal treatments in order to create different microstructures and measure their effects on CMP outputs. Electron backscatter diffraction is used to quantify microstructural parameters such as grain size and crystallographic texture. We find that annealing thick copper films after complete room-temperature relaxation has a significant impact on CMP outputs such as removal rate and surface roughness. The results of this work could be applied to optimize CMP of thick copper films and through-wafer interconnects.