Method for forming trench isolation

Abstract

A trench isolation method is disclosed. A substrate having thereon a pad layer and a hard mask is provided. An opening is formed in the hard mask. The substrate is etched through the opening to thereby form a first trench. A spacer is formed on a sidewall of the first trench. A second trench is then etched into the substrate through the first trench by using the spacer as an etching hard mask. The substrate within the second trench is then oxidized by using the spacer as an oxidation protection layer, thereby forming an oxide layer that fills the second trench. The spacer is then removed to reveal the sidewall of the first trench. A liner layer is then formed on the revealed sidewall of the first trench. A chemical vapor deposition process is then performed to deposit a dielectric layer that fills the first trench.

What is claimed is: 
     
         1 . A method for forming trench isolation, comprising:
 providing a substrate having thereon a pad layer and a hard mask layer;   forming at least one opening in the hard mask layer;   forming a spacer on a sidewall of the opening;   after forming the spacer, etching the substrate through the opening to thereby form a trench; and   performing a thermal oxidation process, using the spacer as a protection layer, to oxidize the substrate within the trench until the trench is completely filled up with an oxide layer.   
     
     
         2 . The method for forming trench isolation according to  claim 1  wherein the pad layer is a silicon oxide pad layer. 
     
     
         3 . The method for forming trench isolation according to  claim 1  wherein the spacer is a silicon nitride spacer. 
     
     
         4 . The method for forming trench isolation according to  claim 1  wherein the thermal oxidation process is performed at a temperature between 800-1200° C., using steam, oxygen, or steam or oxygen containing hydrogen chloride or nitrogen, under process pressure ranging 600-760 torr. 
     
     
         5 . The method for forming trench isolation according to  claim 1  wherein the spacer has a thickness that is smaller than a quarter of a width of the opening. 
     
     
         6 . The method for forming trench isolation according to  claim 1  wherein the oxide layer has a wedge-shaped recess structure on its surface. 
     
     
         7 . The method for forming trench isolation according to  claim 1  wherein a recess region is formed in the substrate through the opening after forming the opening in the hard mask and before forming the spacer.