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

• Published in: 2013 Abstracts IEEE International Conference on Plasma Science (ICOPS) p. 1
• Main Authors: Toneli, David, Pessoa, Rodrigo S., Roberto, Marisa, Petraconi, Gilberto, Maciel, Homero Santiago
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.06.2013
• Subjects: Carbon; Chemistry; Discharges (electric); Inductors; Mass spectroscopy; Plasma measurements; Plasmas
• ISSN: 0730-9244; 2576-7208
• DOI: 10.1109/PLASMA.2013.6634930

Summary form only given. Carbon tetrafluoride (CF 4 ) is a common etchant in the microelectronics industry. It is commonly used to etch silicon-based materials such as Si, SiO 2 , SiC, Si 3 N 4 , etc. The presence of carbon in CF 4 molecule structure allows, depending on the process parameters, to obtain highly anisotropic profiles due to polymerization of the walls of etched structures 1 . Due to the complexity of CF 4 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 CF 4 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 CF 4 plasma. The global model developed here considers the main chemical reactions occurring in CF 4 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 CF 3 - ). It was observed a good agreement between experimental and theoretical results, confirming the validity of the chemical reaction set and respective cross-sections/constants reactions used in the model. On the dissociation rate of CF 4 gas was found that the increase of discharge power causes its elevation, while the increase of CF 4 gas pressure (for a constant value of power) causes its decrease. This fact is directly related to the electron density behavior.