Study of the CF4 capacitive plasma chemistry through mass spectrometry technique and global model

Summary form only given. Carbon tetrafluoride (CF₄) is a common etchant in the microelectronics industry. It is commonly used to etch silicon-based materials such as Si, SiO₂, SiC, Si₃N₄, etc. The presence of carbon in CF₄ molecule structure allows, depending on the process parameters, to obtain highly anisotropic profiles due to polymerization of the walls of etched structures¹. Due to the complexity of CF₄ gas chemistry, few works that present studies of the chemistry of the generated plasma, particularly in capacitive type reactors, are presented. In this work the chemistry of CF₄ capacitive plasma is studied. For this, experimental measurements were made by mass spectrometry technique which allowed the analysis of neutral species generated during the fragmentation of the source gas by the electrical gas discharge. Additionally, we use simulations of global model in order to complement the experimental results, allowing discern the main reactions occurring during the CF₄ plasma. The global model developed here considers the main chemical reactions occurring in CF₄ plasma: momentum transfer, vibrational, ionization, dissociation, electron attachment and loss, recombination between charged and neutral species in the gas phase and the reactor walls. The experimental measurements of mass spectrometry were performed for different values of pressure and power in order to verify the behavior of CF4 radical species namely CF_x (x = 1-4), F and S. Through the global model was possible to verify, in addition to the neutral chemistry, the chemistry of charged species as positive ions (CF_x⁺, x = 1-3, F⁺, etc.) and negative ions (F^- and CF₃^-). It was observed a good agreement between experimental and theoretical results, confirming the validity of the chemical reaction set and respective cros- -sections/constants reactions used in the model. On the dissociation rate of CF₄ gas was found that the increase of discharge power causes its elevation, while the increase of CF₄ gas pressure (for a constant value of power) causes its decrease. This fact is directly related to the electron density behavior.