Investigation of inductively coupled SF6 plasma etching of Si and SiO2 throught a global model coupled with langmuir adsorption kinetics

Summary form only given. Sulfur hexafluoride (SF₆) plasmas are commonly used in the deep etching of silicon (Si), silicon oxide (SiO₂) and more recently silica glass [1]. Due to the complexity of fluorinated plasma environment during Si-based material etching, there are few works presenting experimental and/or theoretical studies about the chemistry established. However, the chemical behavior of the plasma has a direct influence on the etching characteristics such as etch rate, profile and their microscopic uniformity [2]. Thus, it is interesting to understand the dependence of the plasma chemistry with macroscopic process parameters in order to better understand the process tool as well as to optimize it. In this work, a global model coupled with Langmuir adsorption kinetics has been developed to study the plasma chemistry of reactants and products during SF₆ ICP etching of Si and SiO₂. A complete set of gas phase reactions with respective reaction rates was mounted for SF₆ plasma considering the last database presented in literature. Moreover, through the Langmuir adsorption kinetics model the products of interaction plasma - Si-based substrate surface (for example, SiF_x species, x = 0-4) are calculated and considered as a second gas source in the balance particle formulation of global model. We investigated the dependence of the neutral and charged species density as a function of gas pressure, mass flow rate, discharge power, substrate-holder bias and substrate material (Si or SiO₂). The results indicate that the density of the main product of Si etching, SiF₄, can reach the order of the density of SF₆ specie, confirming the high etch rates observed experimentally for the Si in this type of reactor [3]. Contrary fact is observed for the SiO₂ etching, where the strong link between the Si and oxygen atoms limits the desorption process of Si gas phase species. Some results were compared with experimental results from literature.