We have studied both the etching Of SiO2 film and the growth of an amorphous fluorinated carbon (a-C:F) film by mass-analyzed fluorocarbon ion irradiation. This experiment was done in, an ultrahigh vacuum with a pressure of 10(-7) Pa Eden during irradiation. When using a carbon monoflouride (CF1+) ion with an energy of 300 eV to irradiate, it was found that SiO2 film a few nm thick was initially etched away. Then, an a-C:F film was continuously deposited on the SiO2 surface as the ion dose exceeded about 5 X 10(16) cm(-2). Using in situ x-ray photoelectron spectroscopy analysis, it was determined that carbon accumulates on the surface at this early stage as the ion dose increases, so that this transition is resulted by the surface modification on which the CF1+ ion itself irradiates the SiO2 surface. Especially in highly ionized fluorocarbon plasmas, surface conditions such as the carbon concentration affect possibly etching performance. (C) 2003 American Vacuum Society.