Deposition temperature effect on thermal stability of fluorinated amorphous carbon films utilized as low-K dielectrics

Fluorinated amorphous carbon films (alpha -F:C) were deposited by high-dens ity plasma-chemical vapor deposition (HDP-CVD) using C4F8 and CH4 as precur sors. The deposition process was performed at two temperatures: similar to 200 and similar to 350 degreesC. In order to study the thermal stability of the films, the samples were annealed at 400 or 500 degreesC for 30 min in an NZ ambience. We have found that the films deposited at similar to 350 de greesC were more thermally stable than those deposited at similar to 200 de greesC. Both deposition conditions produced a-F:C films with a C:F ratio of 1.7 and a very low content of H; The bonding types identified by XPS were C-C/C-H, C-CF, CF-CF and C-F in all the alpha -F:C films and in addition CF 2 bond was found in the as-deposited films deposited at similar to 200 degr eesC,. The films' composition was maintained after annealing at 400 degrees C. However, after 500 degreesC annealing, in the low-temperature deposited films, F out-diffusion was observed in large amounts compared to the very s mall changes observed in the high-temperature films. The alpha -F:C films r emained amorphous at least up to 500 degreesC. The dielectric constant of t he low-temperature deposited films was similar to2.7 after 400 degreesC ann ealing, and increased after 500 degreesC anneal to similar to9.3. The high- temperature deposited films had a higher dielectric constant of similar to2 .7-3, remaining stable after the various thermal treatments employed. These results indicate a trade-off between thermal stability and lowering the di electric constant. (C) 2001 Elsevier Science Ltd. All rights reserved.