Structural Studies of High-Performance Low-k Dielectric Materials Improved by Electron-Beam Curing

With the use of a newly developed electron beam (EB) curing process, an advanced methylsilsesquioxane (MSQ) low- k dielectric (LKD) film of k =2.9 was developed. It is noteworthy that the EB curing process can drastically improve the mechanical strength of LKD film and reduces the thermal budget without increasing the k value. The X-ray absorption fine structure (XAFS) study on the LKD was conducted to clarify the structural change upon EB curing. The structure of the film was compared with those of two different types of other MSQ films, the ladder-network structure and the random-network structure, and a chemical vapor deposition (CVD) film. The Si–O–Si bond angle and Si–O (Si–C) bond length were determined by fitting the Fourier transformed extended X-ray absorption fine structure (EXAFS) spectra. Si–O–Si bond angle of LKD film was found to be between those of the ladder and the random structure, which are 135° and 147°, respectively. The X-ray absorption near-edge structure (XANES) spectra of LKD film revealed two broad features corresponding to a mixture of the two structures. In contrast, Si–O–Si angles of the EB-cured LKD film and the CVD film were similar, and the XANES features of both films were almost identical with those of the random structure. The electronic structure as determined from XANES spectra was also discussed by comparing three-dimensional-linkage models obtained by ab initio calculations. We confirmed that the EB curing process of LKD film causes a drastic structural change. The change from the mixture of ladder and random structures to the completely random structure was caused by C–H bond breaking followed by the formation of new polymer-like clusters with C–C bonds.