Tunable selectivity slurries in CMP applications

1. A method of chemically-mechanically polishing a substrate, which method comprises:

(a) providing a substrate with at least a first layer and a second layer, wherein the first layer and the second layer have not been contacted with a chemical-mechanical polishing composition,

(b) preparing a final chemical-mechanical polishing composition comprising the steps of:

(i) providing a first chemical-mechanical polishing composition comprising an abrasive with a first selectivity for a first layer as compared to a second layer,

(ii) providing a second chemical-mechanical polishing composition comprising an abrasive with a second selectivity for the first layer as compared to the second layer, wherein the second chemical-mechanical polishing composition is stable in the presence of the first chemical-mechanical polishing composition, and wherein the first and second selectivities are different, and

(iii) mixing the first and second chemical-mechanical polishing compositions in a ratio to achieve a final chemical-mechanical polishing composition with a final selectivity for the first layer as compared to the second layer,

(c) contacting the substrate with the final chemical-mechanical polishing composition,

(d) moving the polishing pad relative to the substrate with the final chemical-mechanical polishing composition therebetween, and

(e) abrading at least a portion of the first and second layers of the substrate to polish the substrate.

2. The method of claim 1 , wherein the first layer is a metal layer, and the second layer is a dielectric layer.

3. The method of claim 2 , wherein the first layer comprises tungsten.

4. The method of claim 2 , wherein the second layer comprises silicon oxide.

5. The method of claim 1 , wherein the first selectivity for the first layer as compared to the second layer is about 25:1 to about 1:1.

6. The method of claim 1 , wherein the second selectivity for the first layer as compared to the second layer is about 0.04:1 to about 1:1.

7. The method of claim 1 , wherein the first chemical-mechanical polishing composition further comprises:

(a) an iron catalyst selected from the group consisting of inorganic iron compounds and organic iron compounds having multiple oxidation states,

(b) at least one stabilizer selected from the group consisting of phosphoric acid, phthalic acid, citric acid, adipic acid, oxalic acid, malonic acid, benzonitrile, and mixtures thereof,

(c) an inhibitor of metal etching selected from the group consisting of tetraalkylammonium hydroxides and amino acids, and

(d) a liquid carrier.

8. The method of claim 7 , wherein the iron catalyst is ferric nitrate, the stabilizer is malonic acid, the inhibitor is tetrabutylammonium hydroxide, and the abrasive is silica.

9. The method of claim 1 , wherein the second chemical-mechanical polishing composition further comprises a tetraalkylammonium hydroxide and a liquid carrier.

10. The method of claim 9 , wherein the tetraalkylammonium hydroxide is tetrabutylammonium hydroxide.

11. The method of claim 9 , wherein the abrasive is silica.

12. The method of claim 1 , further comprising (b)(iv) adding an oxidizing agent to the mixture of the first and second chemical-mechanical polishing compositions.

13. The method of claim 12 , wherein the oxidizing agent is hydrogen peroxide.