This paper studies the nanomechanical properties, including hardness and Young's modulus (both in a dry condition and in deionized water), fracture toughness, cohesive strength and scratch resistance of eight commonly used SiO2-based dielectric films, Boron Phosphosilicate Glass (BPSG), BPSG with Rapid Thermal Processing (RTP), Phosphosilicate Glass (PSG), Spin-On Dielectric (SOD), Plasma Enhanced Chemical Vapor Deposition (PECVD) Tetraethyl Orthosilicate (TEOS), high aspect ratio oxide (O3-TEOS), High Density Plasma Oxide (HDP), and Silane Oxide. Significant differences were found among these films. The effects of the nanomechanical properties on dielectric film reliability and CMP process are discussed.