The Effect of Plasma Chemistry on the Damage Induced to Porous SiCOH Dielectrics.

We have investigated the effects of plasmas of He+H₂, N₂+H₂ and NH₃ on the properties of three porous SiCOH dielectrics (pSiCOH) with ultralow dielectric constants of about 2.4. All plasma treatments have been performed in the same plasma tool under identical RF power and pressure in the plasma. Exposure of the films to the plasmas resulted in structural modifications of the bonding structure of the films, loss of film thickness, and an increase in index of refraction and dielectric constant. The degrees of these modifications varied among the studied films and changed from plasma to plasma.

It was found that Fourier transform infrared spectroscopy (FTIR) analysis can indicate the type of structural modification caused by a certain plasma treatment, but cannot be used to predict the level of damage to the dielectric constant. No correlation was observed between the shrinkage of the film after a plasma treatment and the corresponding increase of the dielectric constant. The increases of the dielectric constant correlated only to increases of the index of refraction caused by the plasma treatments.

The largest damages to the dielectric constants were caused by plasma treatments at room temperature. Among the investigated plasmas, the most damaging one to the porous SiCOH films, at RT or 180 ^oC, was the He+H₂ plasma, while the least damaging one was the NH₃ plasma at 180 ^oC.