CHARACTERIZATION OF LOW-k TO EXTREME LOW-k SiCOH DIELECTRICS

Carbon doped oxide dielectrics comprised of Si, C, O, and H (SiCOH) have been
prepared by plasma enhanced chemical vapor deposition from mixtures of
tetramethylcyclotetrasiloxane (TMCTS) and an organic precursor. The thermally unstable CHY fragments from the organic fraction incorporated in the SiCOH matrix are removed by thermally annealing the deposited films, thereby inducing nanoporosity in the films. SiCOH type of dielectric spanning a range of dielectric constants (k) from 2.8 to 2.05 have been prepared by this approach. The extreme low-k films have a porosity of about 30% with an average pore size below 2.5 nm. Rutherford backscattering (RBS) combined with forward recoil elastic scattering (FRES) has been used to determine the composition of the SiCOH films and have shown that the reduction of the dielectric constant is caused mainly by an increase in the porosity of the films, with very little changes in the composition of the film skeleton. The films have been characterized by FTIR and the deconvolution of the SiO absorption band has been used to evaluate the structure of the films of different dielectric constants. The results indicate that the organic fraction introduced in the films with ultralow and extreme low-k values is mainly incorporated through substitution at the Si-H bonds in TMCTS and that addition of the organic precursor to TMCTS in a plasma facilitates the enhancement or formation of a porous cage structure.