Plasma-enhanced chemical vapor deposition of low dielectric constant materials

Low dielectric constant materials (low k) are an essential component of ultra large-scale integrated circuits. A material with low dielectric constant (∼2) is needed to reduce the crosstalk noise and the dissipated power in these circuits. Plasma-enhanced chemical vapor deposition (PECVD) was used to deposit a triple phase low k amorphous SiC:H/SiO/C:H films. Annealing treatments and supercritical carbon dioxide (SCCO2) treatments were used to remove or reduce the concentration of one phase selectively. The removal of the methyl (CH_n) group associated with the C:H phase introduced nanoporosity to these films and low k values of 2.1 were possible for these films. The effects of different parameters on the structure of these films were studied, and it was found that annealing is dominant factor in removing the CH _n from these films. A new source, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS), was used as a precursor for depositing low k film. This source has a ring structure that, if preserved, introduces free volume that helps to lower k. A fluorinated version of this film was also deposited, and SCCO2 was used to remove the fluorocarbon phase in an attempt to introduce more free volume. A dielectric constant values as low as 2.4 were possible for these films. Finally, SCCO2 was used to cure plasma damaged nanoporous low k film. Plasma ashing of low k films removes the methyl group and replaces it with the silanol group. This increases the dielectric constant of the material. SCCO2 was used to carry hexamethyldisioxane (HMDSO) or hexamethyldisilazane (HMDS) to reverse this damage; SCCO2 carries HMDSO or HMDS to every point on the film and HMDSO or HMDS reacts with the silanol group and replaces it with the methyl group. The dielectric constant was brought from 3.71 for the damaged films to 2.3 for the treated film. This value is similar to the undamaged film. Annealing the film at 400°C indicates that the SCCO2/HMDS treatment is thermally stable, while the SCCO2/HMDSO treatment is thermally unstable.