A metal layer (24) is formed on an isolation layer (22) to act as interconnections. Subsequently, a thin liner layer (26) is optionally formed along the surface of the metal layer (24) to serve as a buffer layer. An undoped silicate glass (USG) layer (28) is deposited on the liner layer (26). The USG layer (28) is formed using ozone and tetraethylorthosilicate (TEOS) as a source at a temperature of approximately 380 to 420.degree. C. Oxygen gas is used as a carrier for the ozone. The flow rate of the oxygen gas is approximately 4000 to 6000 sccm. Helium gas is used as a carrier for the TEOS. The flow rate of the helium is approximately 3000 to 5000 sccm. A silicon nitride layer (30) is deposited on the USG layer (28) using plasma enhanced chemical vapor deposition (PECVD). The silicon nitride layer (30) serves as a main passivation layer. The thickness of the silicon nitride layer (30) is approximately 3000 to 7000 angstroms.