Theoretical analyses of chemical reactions for forming hydrocarbon-bridged SiOCH low-k Films in PECVD processes

The advantages of the SiOCH low-k films with hydrocarbon cross-links (hydrocarbon bridges) Si-C_n-Si have been reported recently. However, hydrocarbon cross-links are not produced so selectively by the PECVD method, since the hydrocarbon components tend to form terminal atom groups such as Si-CH₃. For producing hydrocarbon cross-links effectively by the PECVD method, the polymerization reactions of SiOCH precursors in the PECVD process should be understood well. We have theoretically examined the bonding reactions of the atom groups of SiOCH compounds. By examining the reactions involving radicals and ions, it has been found that the radical species Simiddot, Cmiddot, and Omiddot produce Si-O, C-Si, and O-Si bonds, respectively, while the ionic species produce Si-O bonds. These results suggest that the precursors should produce Si-C_nmiddot radicals preferably for the effective production of the hydrocarbon cross-links.