Chemical Bonding Structure of Low Dielectric Constant Si:O:C:H Films Characterized by Solid-State NMR

Organosilicon films (Si:O:C:H) have the potential to replace SiO2 as a lower dielectric constant microelectronic interconnection layer. The structure of Si:O:C:H films was characterized by 1H, 13C, and 29Si solid-state nuclear magnetic resonance (NMR) and also by X-ray photoelectron and Fourier transform infrared spectroscopies. Spin-coated hydrogen silsesquioxane, methyl silsesquioxane, and surface-modified nanoporous silica films were observed to be more homogeneous in structure than films grown by chemical vapor deposition (CVD). The CVD films were deposited from N20 mixed with either tetramethylsilane, a mixture of tetramethylsilane and silane, trimethylsilane, or methylsilane. The various gas mixtures altered the degree of oxidation and hydrogenation in the resulting films, confirming that the composition of Si:O:C:H can be readily adjusted by CVD. Of all the characterization methods, the 29Si NMR was most readily able to distinguish differences between the Si:O:C:H films, resolving up to twelve distinct bonding environments. These same bonding configurations are also found in bulk organosilicate glasses. In all films studied, 13C NMR reveals that methyl is the primary bonding configuration for carbon and no sp2-bonded carbon was detected.