Terence M. Thomas

CMP surface characteristics of twinned copper subgrains

Copper wafers are polished with an experimental slurry prepared to contain strong oxidizing components for revealing grain structures. Two types of surface morphologies, twinned and equiaxed grains, are observed on two groups of wafers, following chemical mechanical planarization (CMP). An atomic force microscope surface analysis indicates that the equiaxed grain structure provides better overall surface quality than the twinned structure. A polishing model is proposed to explain the surface relief among the twinned subgrains. The results suggest that Cu electroplating and the subsequent annealing processes should be optimized to promote uniform equiaxed grains for better integration with CMP and other chip manufacturing processes.