Plasma-enhanced chemical vapor deposition of low dielectric constant materials
Lahlouh, Bashar Ibrahim
Plasma-enhanced chemical vapor deposition (PECVD) and supercritical carbon dioxide (SCCO2) were used to create nanoporous low dielectric constant (low-k) films. A material with low dielectric constant (~2) is needed to reduce the crosstalk noise and the dissipated power in these circuits. Amorphous SiC:H/SiO/C:H films were deposited using PECVD. Aimealing treatments and supercritical carbon dioxide (SCCO2) freatments were used to selectively remove or reduce the concentration of one phase. The removal of the methyl (CHn) group associated with the C:H phase introduced nanoporosity in these films and low-k values of 2.1 were obtained. The effects of different deposition and treatment parameters on the structural and electrical properties of the films were studied. In another project, a new source, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS), was used as a precursor for depositing organosilicate low-k films. This source has a ring structure, if preserved, introduces free volume that helps to lower the k value of the film. An organosilicate/fluorocarbon composite film was also deposited, and SCCO2 was used to selectively remove the fluorocarbon phase in an attempt to introduce porosity to these films. Dielectric constant values as low as 2.48 were obtained for these films. Finally, SCCO2 was used to cure plasma damaged nanoporoiu-s low-k film. Plasma ashing of low-k films removes the methyl group and replace it with the silanol group. This increases the dielectric constant of the material. SCCO2 was used as a carrier for hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDS) to reverse the plasma-damage; SCCO2 carries HMDSO or HMDS to every point in the film and HMDSO or HMDS reacts with the silanol group and replaces it with the methyl group. The dielectric constant reduced from 3.71 for the plasma-damaged films to 2.3 for the treated films. This k value is similar to the undamaged film. Annealing the treated films at 400°C indicates that the SCCO2/HMDSO treatment is thermally unstable. The SCCO2/HMDSO treated film lost almost all the added methyl groups after the high temperature annealing. The SCCO2/HMDS treatment was thermally stable with 400°C annealing and there was no methyl group loss.