SiCOH Dielectrics: From Low-k to Ultralow-k by PECVD

Carbon doped oxide low-dielectric constant (low-ê ) thin film insulating materials comprised of Si, C, O, and H (SiCOH) prepared by plasma enhanced chemical vapor deposition (PECVD) have been developed, initially with dielectric constants of about 2.7 - 2.8. These values are almost independent of the deposition system (tool and precursor) used for the deposition, although the precursor and process used here did lead to films with relatively superior mechanical properties for the same dielectric constant. These films have been integrated successfully in multilevel Cu and W Damascene BEOL structures. The adoption of PECVD deposited SiCOH as the on-chip interconnect dielectric is dependent on the extendibility of SiCOH to even lower dielectric constants. We have shown that the dielectric constant of such materials can be reduced further by depositing multiphase films containing at least one thermally-unstable phase, and annealing the films to remove the volatile fraction from the material. The dual phase materials in the present study have been prepared by PECVD from mixtures of the SiCOH precursor with organic precursors. It was found that the films stabilized after an initial anneal, which resulted in a significant loss of mainly CH fractions and was accompanied by a thickness loss. Depending on the deposition conditions, choice of the organic precursor, and its concentration in the feed gas, we are able to produce stabilized films with reproducible dielectric constants below 2.1. The electrical, mechanical, thermal, and chemical properties of these ultralow-ê films indicate the potential extendibility of the PECVD SiCOH system to future generations of ULSI chips.