Paper PS1-TuA8
Low-Damage Low-k Etching by CF₃I Plasma with Low Global Warming Potential

Tuesday, October 16, 2007, 4:00 pm, Room 606

The CF₃I gas has been developed to reduce the recent global warming¹ because it has a low global warming potential (GWP) of 1.0 while most of conventional etching gases have considerably higher potentials of more than 1000 (CF₄: 6500, C₄F₈: 8700). The feasibility of CF₃I plasma etching and its damage to the porous low-k film (SiOC, k=2.6) were studied in this work. When an SiOC film was exposed to the CF₃I plasma, increase in the k-value and decrease in CH₃ group of the film (FTIR) were found to be suppressed compared with those caused by conventional CF₄ plasma because intensity of the ultra violet (UV) light in CF₃I plasma was lower than that of CF₄ plasma. To investigate etching property of CF₃I gas, we used a photolithography patterned wafer with the resist mask of 200-nm pitch size. As a result, the etching profile of CF₃I plasma was comparable with that of CF₄ plasma. Since the etching selectivity (SiOC/ArF) of CF₃I plasma was higher than that of CF₄ plasma, the remaining resist thickness after etching increased, thereby line edge roughness (LER) was suppressed. Moreover, the pulse operation in CF₃I plasma drastically increased etching rate and minimized UV damage to the low-k film because injection of negative ions in pulsed plasma enhanced the low-k film etching. Accordingly, we found that CF₃I plasma is one of the promising candidates for low-damage and highly selective low-k etching. This work is supported by the New Energy and Industrial Technology Development Organization (NEDO).

¹N. Nagasaki et al., "The Development of a Novel Catalytic Technology for CF₃I Manufacture", Halon Options Technical Working Conference, May 2000.