Patent ID: 6670275
Filing Date: 2003-12-30
Classification: H01L

Abstract:
A method of rounding a top corner of a trench in a shallow trench isolation process, comprising the steps of:preparing a substrate of Si and forming a SiO2 layer on the substrate; forming a Si3N4 layer on the SiO2 layer; partially etching the Si3N4 layer using plasma etching process to form a first-stage trench; etching the remaining Si3N4 layer and a portion of SiO2 layer under the first-stage trench with SF6/HBr gas to form a second-stage trench with depth gradient; etching the remaining SiO2 layer and a portion of the substrate under the second-stage trench to form a rounded platform for the second-stage trench; and etching the substrate under the rounded platform of the second-stage trench to form a completed shallow trench having a rounded top corner; wherein a gas used to etch the remaining SiO2 layer under the second-stage trench is selected from the group consisting of CH4/HBr, CF4/CH2F2, CF4/CHF3, CH2F2 and CHF3.