Process and mechanistic studies of the patterning of aluminum and copper thin films for multi-level metallization structures by chemical-mechanical planarization

In this thesis, chemical-mechanical planarization (CMP) of aluminum, copper and silicon dioxide is investigated. Chemical-mechanical planarization is a polishing process that is used in the semiconductor industry to delineate the metal interconnections on a silicon chip and to provide the planarity necessary to build multi-level interconnect schemes with sub-microscopic lines. It uses a combination of mechanical forces from a polishing pad and abrasive slurry mixture, and chemical forces from chemical reagents in the slurry to remove and planarize material. The main goal of this thesis is to examine the effects that changes in the pad and slurry properties have on the polishing of Al, Cu, and SiO₂ and from these results, to gain insights into the fundamental mechanisms involved in the removal of these materials.; Presented in this thesis are detailed studies of the chemical-mechanical planarization of Al and Cu thin films with various alumina-based slurry mixtures. Etching and polishing of aluminum showed that the oxidizer (H₂O ₂) concentration in the slurry has no effect on the Al removal rate. However, further analysis established that the incorporation of H₂O ₂ in the slurry is critical when polishing patterned aluminum samples to remove the TiN adhesion/diffusion barrier liner.; In both etching and CMP of copper, the H₂O₂ concentration in the slurry has a substantial effect on the copper removal rate. For the etching experiments, a thick cuprous oxide (Cu₂O) forms on the surface of the etched metal at high %H₂O₂ concentration which limits the etching. For copper CMP, the removal rate behavior at high (H₂O₂) is attributed to a CuO film that forms on the copper. The polishing of copper is described as a combination of two processes, mechanically enhanced oxidation of the metal and dissolution of the oxidation reaction products.; In an effort to improve the performance of existing SiO₂ slurries, oxide polishing studies were done with two novel slurries containing a spherically shaped silica abrasive. The results of this study revealed a substantial decrease in the amount of abrasive particles that adhere to oxide surface when polishing with these unique slurries.