A method for fabricating a 
semiconductor device and forming an insulating film used therein, includes forming an isolation insulating film on a 
semiconductor wafer and forming gates, separated by gaps having a predetermined distance, on an active region. Next, a first interlayer 
dielectric film is deposited to a predetermined thickness on the 
semiconductor wafer having the gates, so that the gaps between the gates are not completely filled. Then, a 
sputtering etch is performed entirely on a surface of the first interlayer 
dielectric film. Thereafter, the first interlayer 
dielectric film is partially removed through 
isotropic etching. Next, a second interlayer dielectric film is deposited on the first interlayer dielectric film so that the gaps between the gates are completely filled. According to the above method, a gap between gate patterns can be completely filled without a void by performing 
sputtering etch on interlayer dielectric films formed on gate patterns, thereby enhancing the reliability of a 
semiconductor device.