The superior water blocking ability of electron cyclotron resonance (ECR)-plasma SiO2 film has been investigated. We compared this film to normally used dielectric films in the field of multilevel interconnection technology, such as a SiH4-plasma SiO2 film and a tetraethoxysilane (TEOS)-plasma SiO2 film by the pressure cooker test. The structural difference between these films was investigated by Fourier transform infrared spectroscopy and Raman spectroscopy. We found that the improved performance was due to structural differences and the content of hydrogen in the ECR-plasma SiO2 film.