IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Tuesday Sessions
       Session PS1-TuM

Paper PS1-TuM2
CF@sub x@ Kinetics, Gas Temperatures and Instabilities in a CF@sub 4@ Inductively-coupled Discharge

Tuesday, October 30, 2001, 8:40 am, Room 103

Session: Diagnostics II
Presenter: J.P. Booth, Ecole Polytechnique, France
Authors: J.P. Booth, Ecole Polytechnique, France
H. Abada, Ecole Polytechnique, France
P. Chabert, Ecole Polytechnique, France
G. Cunge, CNRS/LETI, France
Correspondent: Click to Email
The use of inductive discharges in fluorocarbon gases for SiO@sub 2@ etch applications has been hampered by narrow process windows and severe process drift problems, despite promising etch rate, selectivity and anisotropy results. We have extended our study of free radical kinetics in capacitively-coupled plasmas to these systems in order to investigate the origin of these problems. Laser-induced fluorescence was used to probe the axial concentration and temperature profiles and the kinetics of CF and CF@sub 2@ radicals in a pure CF@sub 4@ ICP. Rotationally-resolved LIF of CF shows that very high gas temperatures can occur (up to 1000K). Therefore, large gas temperature and density gradients exist within the reactor. The CF and CF@sub 2@ axial concentration profiles are hollow, showing that these species are produced at the reactor surfaces due to C@sub x@F@sub y@@super +@ ion bombardment, and are destroyed in the gas phase. The nature of the gas-phase destruction processes will be discussed, in relation to the formation of heavier C@sub x@F@sub y@ species. We also observed the occurrence of plasma instabilities over a wide range of gas pressure and injected RF power. This phenomena can mostly be explained in terms of relaxation oscillations between capacitive and inductive plasma modes as observed by previous workers in SF@sub 6@ plasmas, but with the added mechanism of the formation of heavy C@sub x@F@sub y@ oligomers, which are much more electronegative than the parent gas, CF@sub 4@.