Patent ID: 8685830

Claim:
A method of filling shallow trenches, the method comprising the steps of: providing a silicon substrate, the silicon substrate having a mask layer formed thereon; etching the silicon substrate to form one or more shallow trenches therein; depositing a first oxide layer, which serves as a first pad oxide layer, over surface of the silicon substrate; depositing a second oxide layer over surface of the silicon substrate; etching the second oxide layer by using a dry etch-back process to form inner sidewalls in the one or more trenches, wherein the dry etch-back process has a high etching selectivity ratio of the second oxide layer to the first oxide layer, such that the first oxide layer is remained after the dry etch-back process; removing the inner sidewalls by using a wet etching process, wherein the first pad oxide layer is simultaneously removed by the wet etching process so that the underlying silicon is exposed in each of the one or more trenches; growing a silicon dioxide layer, which serves as a second pad oxide layer, over a surface of each of the one or more trenches by thermal oxidation of the exposed underlying silicon; and filling the one or more trenches with an isolation dielectric material.