A Cahn Hilliard Modeling of Metal Oxide Thin Films for Advanced CMP Applications

Abstract

Chemical mechanical planarization (CMP) process enables topographic selectivity through formation of a protective oxide thin film on the recessed locations of the deposited metal layer while a continuous chemical oxidation reaction is followed by mechanical abrasion takes place on the protruding locations [1]. This paper demonstrates a new approach to CMP process optimization in terms of slurry formulations by analyzing the nature of the protective metal oxide nano films and modeling their growth through a Cahn Hilliard Equation (CHE) approach [2]. The commonly utilized models on the material removal rate calculations are also revisited to address the differences from the typical approaches to the dynamic removal models at the elevated layers.In previous work we have demonstrated the formation and mechanical properties of the chemically modified metal oxide thin films in CMP and discussed the stresses develop at the interfaces delineating the stability and protective nature of the chemically altered films [3]. The preliminary model is developed on the very well established tungsten films by assuming a constant temperature and metal oxide thin film volume to apply the CHE approach. As the CMP nano metal oxide films of tungsten have been shown to be self-protective, these assumptions are valid. Thin film analyses were conducted through XRD, XRR and FTIR characterization and compared to the theoretical calculations for the modeling simulations. The atomic force microscopy surface structures observed on the tungsten wafers are shown to be predicted by the CHE approach as spinodal decomposition structures. This new modeling approach is going to help in formulating optimal slurries for the new generation CMP materials by considering not only the active material removal concept but also the very critical planarization requirement through enabling protective oxide layers for planarization.