The restoration of porous methylsilsesquioxane (p-MSQ) films using trimethylhalosilanes dissolved in supercritical carbon dioxide

Repair and capping of porous methylsilsesquioxane (JSR LKD 5109) low-k films using a series of trimethylhalosilanes (trimethylchlorosilane-TMCS, trimethylbromosilane-TMBS, and trimethyliodosilane-TMIS) dissolved in supercritical CO2 (scCO2) was studied using Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, goniometry, and electrical measurements. FTIR results showed that all trimethylhalosilanes reacted with silanol (SiO-H) groups in the fluid and on the surface of oxygen ashed porous methylsilsesquioxane (p-MSQ) films depositing trimethylsilyl -O-Si-(CH3)3 moieties. XPS results showed that no Br and I were detected after processing. Spectroscopic ellipsometry and goniometry showed that the total film thickness and contact angle increased in the series TMCS < TMBS < TMIS. These results indicate that the reactivity increased in the order TMCS < TMBS < TMIS, yet the dielectric constant was in the range of 2.56-2.60 within the limits of experimental error. One interpretation is that the increased thickness and contact angle were the result of self-condensation between trimethylsilanols in the fluid phase, which were formed by reaction of trimethylhalosilanes and water molecules. The dimers produced were strongly physisorbed to the p-MSQ film after processing.