Pores in ultra-low-k carbon-doped silicon oxide (SiOCH) film have been a serious problem because they produce fragile film strength, with the film incurring damage from integration and diffusion of Cu atoms in thermal annealing. To address this problem, we developed a practical large-radius neutral beam enhanced CVD process to precisely control the film structure so as to eliminate any pores in the film. We used the process with dimethoxy-tetramethyl-disiloxane (DMOTMDS) as a precursor to form a SiOCH film on an 8-inch Si wafer and obtained a non-porous film having an ultra-low k-value of 2.2 with sufficient modulus (>10 GPa). Analyzing the film structure by experimental and theoretical techniques showed that symmetric polymethylsilaxane (PMS) chains were grown and cross-linked to each other in the film. This particular film did not incur any damage from acid or alkali solution or oxygen plasma. Furthermore, the dense film almost completely resisted Cu diffusion into it during thermal annealing.