Systems and methods for producing flat surfaces in interconnect structures
In interconnect fabrication (e.g. a damascene process), a barrier layer (possibly conductive) is formed over a substrate with holes, a conductor is formed over the barrier layer, and the conductor and the barrier layer are polished to expose the substrate around the holes and provide interconnect features in the holes. To prevent erosion/dishing of the conductor over the holes, the conductor is covered by another, “first” layer before polishing; then the first layer, the conductor, and the barrier layer are polished to expose the substrate. The first layer may or may not be conductive. The first layer protects the conductor to reduce or eliminate the conductor erosion/dishing over the holes.
1. A method of forming an interconnect structure, comprising:
forming a cavity in a substrate having a top surface;
depositing a barrier layer over the top surface of the substrate and the cavity;
depositing a seed layer over the barrier layer;
forming a copper conductor on the seed layer, an entire top surface of the formed copper conductor being higher than a top of the cavity;
depositing a layer of a sacrificial conductor on the entire top surface of the formed copper conductor;
applying an ECMP process to the layer of the sacrificial conductor and to the formed copper conductor to remove the layer of the sacrificial conductor and to partially remove the formed copper conductor from the top surface of the substrate; and
applying a CMP process to remove remaining formed copper conductor, the seed layer, and the barrier layer from the top surface of the substrate to provide a flat surface of the formed copper conductor over the cavity.
2. The method of claim 1 wherein the ECMP process exposes a flat top surface of the formed copper conductor over the cavity, the flat top surface comprising only the formed copper conductor.
3. The method of claim 1 wherein the ECMP process removes the entire layer of the sacrificial conductor.
4. The method of claim 1 wherein before the ECMP process, the top surface of the deposited copper conductor forms a recess over the cavity with respect to the deposited copper conductor on the top surface of the substrate.
5. The method of claim 1 wherein the substrate comprises a semiconductor.
6. The method of claim 1 , wherein the deposited copper conductor over the cavity has a decreasing corrosion rate during the ECMP in relation to the decreasing voltage and/or the decreasing current of the ECMP process as the deposited copper conductor is removed from the top surface of the substrate.
7. A method for producing flat damascene features, comprising:
depositing copper on a wafer, including depositing the copper on a top surface of the wafer;
overfilling cavities on the wafer with the copper, wherein the deposited copper follows contours of the cavities;
adding a sacrificial conductive layer over the deposited copper, the sacrificial conductive layer more resistive to ECMP than the copper;
removing at least a portion of the sacrificial conductive layer and at least a portion of the copper from the top surface of the wafer by applying the ECMP to the sacrificial conductive layer and the copper on the top surface of the wafer and over the cavities; and
removing any remaining sacrificial conductive layer and the deposited copper down to a flat surface.
8. The method of claim 7 , wherein the sacrificial conductive layer comprises a copper alloy more resistive to the ECMP than the copper.
9. The method of claim 8 , wherein the sacrificial conductive layer is selected from the group consisting of copper-tungsten, Cu-Ga, and Cu-In.
10. The method of claim 7 , further comprising
polishing the sacrificial conductive layer and the deposited copper to decrease an elevation of the copper over the cavities;
thermally treating the wafer and the deposited copper to stabilize a grain size of the copper in the cavities; and
polishing the deposited copper over the cavities with the ECMP to create the flat damascene features, wherein a thicker layer of the copper comprising the grain size in the cavities is more resistive to the ECMP than a thinner layer of the copper comprising the grain size on the top surface of the wafer.
11. A method, comprising:
depositing copper into cavities on a top surface of a wafer, wherein the copper follows contours of the cavities;
depositing a conductive material on the copper, wherein the conductive material has a lower corrosion rate during an ECMP process than the copper; and
applying the ECMP process to both the conductive material and the copper until the copper and the conductive material are flat, wherein a flat polished surface obtained from applying the ECMP process comprises both first areas of copper and second areas of the conductive material.
12. The method of claim 11 , wherein the conductive material fills recesses in the copper to provide the flat polished surface while preventing a dishing of the copper in the cavities during the ECMP process.
13. The method of claim 11 , wherein the conductive material comprises a copper alloy.
14. The method of claim 11 , wherein applying the ECMP process comprises decreasing at least one of a voltage or a current of the ECMP process as the copper is removed from the top surface of the wafer to obtain a finer flatness of the flat polished surface.