Observations of Silicon Surfaces Exposed to Inductively Coupled CHF3 and C4F8/H2 Plasmas Using Fourier Transform Infrared Ellipsometry

In situ Fourier transform infrared ellipsometry has been used to investigate the characteristics of fluorocarbon films deposited in inductively coupled CHF3 and C4F8/H2 plasmas. Chemical composition and thickness of the films have been studied as a function of process parameters. For the CHF3 plasma, the mode strength of CF2 bond group increases monotonically with pressure varying from 3 to 20 mTorr. The mode strength ratio of hydrogen-containing fluorocarbon bond groups (CHFx) to CF2 bond group increases with decreasing pressure. If He gas is admixed to CHF3, the CHFx/CF2 ratio also increases. Changes in the film structure have been discussed in terms of the relationship between electron temperature and CHF3 dissociation. As the discharge power is increased, the deposition rate increases linearly without considerable changes in the chemical composition of the film. For the C4F8/H2 plasma, relative concentration of CHFx species increases linearly with H2 mixing ratio.