Method for forming shallow trenches of the dual active regions

Abstract

The invention disclosed a method for forming shallow trenches of the dual active regions. Firstly, forming an etch stop layer on a semiconductor substrate; secondly, using a first accurate photomask to expose and develop the semiconductor substrate, until the etch stop layer has been exposed on the top of the first shallow trench regions and the second shallow trench regions; thirdly, etching the etch stop layer entirely in the exposed regions; fourthly, using a second photomask to expose and develop the first shallow trench regions which require a deeper etch depth of the trench than that of the second shallow trench regions; fifthly, etching and forming preliminary entirely depth in the first shallow trench regions, and then removing the second photomask; at last, taking the etch stop layer as a mask, and simultaneously etching the first shallow trench regions and the second shallow trench regions to form the first hallow trenches and the second shallow trenches having different depths. The invention has realized a low-cost photomask application and an optimization of the etching process by optimizing the photomask design.