What are the performance characteristics of the oxide film?

　The metal passivation theory suggests that passivation occurs due to the formation of a dense, well-protective passivation film on the surface. Most passivation films are composed of metal oxides, which is why they are called oxide films. For example, the iron passivation film is γ-Fe2O3 or Fe3O4, while the aluminum passivation film is pore-free γ-Al2O3, etc. The thickness of the oxide film is generally 10-9 to 10-10 m. Some reducing anions, such as Cl-, have a significant destructive effect on the oxide film. To obtain a thick and dense oxide film, chemical or electrochemical treatments are commonly used. 　　In the manufacturing of semiconductor devices, oxide films play an extremely important role. It is used as the gate oxide film for MOS transistors, a protective film for PN junctions, and a mask for impurity diffusion. Representative methods for manufacturing oxide films include thermal oxidation and vapor growth (CVD) methods. 　　Thermal oxidation method: This is a process in which the surface of a silicon wafer is oxidized using high-temperature oxygen or steam. Due to its ability to form a fine oxide film, it is used as the gate oxide layer and passivation film in MOS transistors. The thickness of the film formed by oxidation can be controlled by temperature, time, or the flow rate of water vapor. 　　Chemical Vapor Deposition (CVD): This is a method in which silicon oxide is deposited on the surface of wafers through chemical reactions using gases such as silane (SiH4) and oxygen, within a high-temperature reaction chamber. It includes methods like normal-pressure CVD (1 atmosphere) and low-pressure CVD. Its main purpose is to form insulating films between wiring layers and to serve as a passivation film to protect the surface of the chip. This gas can also be used in the processes related to polycrystalline silicon shed electrodes and similar applications.