Patent ID: 7407886

Claim:
A method for preparing a contact plug structure, comprising the steps of: forming a first mask having a plurality of first openings on a substrate including a silicon substrate having a shallow trench isolation structure surrounding a plurality of doped regions, a first dielectric layer positioned on the silicon substrate and a second dielectric layer positioned on the first dielectric layer; removing a portion of the first dielectric layer and the second dielectric layer under the first openings to form a plurality of first depressions in the first dielectric layer, wherein the first depression exposes the doped region in the silicon substrate; forming a second mask having a plurality of second openings on the substrate, each second opening connecting a plurality of the first openings; removing a portion of the second dielectric layer under the second openings to form a plurality of second depressions in the second dielectric layer; and depositing a conductive layer in the first depressions and the second depressions to form the contact plug structure.