Patent ID: 8178418

Claim:
A method for fabricating intra-device isolation structures, comprising: providing a semiconductor substrate with a mask layer formed thereover; forming a plurality of first trenches in the semiconductor substrate and the mask layer; forming a first insulating layer in the first trenches; partially remove the mask layer and exposing a portion of the first insulating layer in the first trenches; forming a protection spacer on a sidewall surface of the portion of the first insulating layer exposed by the mask layer, partially exposing a portion of the mask layer between the first insulating layer; performing an etching process to the mask layer exposed by the protection spacer and the semiconductor substrate thereunder, forming a plurality of second trenches in the semiconductor substrate and the mask layer; forming a second insulating layer in the second trenches; and removing the protection spacer, the mask layer, the first insulating layer and the second insulating layer over a top surface of the semiconductor substrate.