Abstract
The demands for manufacturing integrated circuit devices with high circuit speed and high packing density have driven the development of multilevel interconnection system. However, miniaturization of the circuits severely restricts the performance of the interconnects. For instance, layered interconnect architecture is constructed in order to obtain increased packing density. Nevertheless, as the metallization levels are increased, some serious process concerns arise, such as planarization, lighographic pattern transfer, and process yield. Shrinking device feature size requires higher resolution steppers. That, in turn, demands a more planar surface. Besides, as the number of metal layers increases, planarity has become a critical issue. When non-planarity is imprinted or amplified onto the next layers in the case of stacked patterns, the cumulative non-planarity may become so severe after just a few layers that lithographic process becomes a limiting factor in the device fabrication. Planarization of each layer can reduce the topographic variations on the surface and meet the requirement of the lithographic tools, thus allowing for fabrication with tighter design rules and additional interconnection levels. Among the planarization techniques utilized, Chemical Mechanical Polishing (CMP) has been recognized as a necessary step for achieving global planarization in multilevel metallization process. Besides, the adoption of Al plug and Al damascene process in the 0.25 μm regime has necessitated the development of chemical mechanical polishing of Al alloy thin film. During metal CMP, the metal film surface reacts with the slurry chemicals, resulting in corrosion or dissolution reactions. In this study, Al-CMP characteristics are evaluated on Al alloy thin films of different compositions including, pure Al, Al-1.0%Si-0.5%Cu, Al-1%Cu, Al-0.5% Cu and Al-1%Si. Characteristics of the films such as native oxide, alloy content and grain size and their effects on the CMP removal rates will be assessed. Corrosion potentials of each film will also be measured to investigate the corrosion susceptibilities of these films and their correlation with Al CMP results will be discussed. Slurry chemistry is also a critical issue in the Al CMP process. In this study, Al2O3-based slurry is formulated for the polish experiment, hydrogen peroxide is added as the main oxidizer. The slurry pH valus and the concentrations of hydrogen peroxide are varied to investigate their influences on Al CMP removal ate. Static etching experiment is designed to simulate the chemical environment that the films are subjected to during the CMP process. These results are consistent with those obtained fromt he CMP experiments, suggesting that alloying compositions influence the polishing behavior to a great extent, and chemical reactions play a dominant role in the Al CMP process.