Ultrapure colloidal silica for use in chemical mechanical polishing applications

1. A method of chemical mechanical polishing a surface of a substrate comprising the step of:

contacting said substrate with a composition, said composition comprising:

(i) a plurality of colloidal silica particles; and

(ii) a medium for suspending said particles;

wherein said composition has less than 200 ppb of each trace metal impurity, excluding potassium and sodium, less than 2 ppm residual alcohol, and wherein the cumulative trace metal concentration, excluding potassium and sodium, is in the range from about 0.5 to about 5 ppm;

wherein said composition is an ultrapure colloidal silica dispersion; and wherein said contacting is carried out at a temperature and for a period of time sufficient to planarize said substrate;

wherein said colloidal silica particles have a surface area from about 20 m 2 /g to about 300 m 2 /g, and

wherein said colloidal silica particles are prepared by a process comprising the steps of:

dissolving a fumed silica in an aqueous solvent comprising an alkali metal hydroxide to produce a alkaline silicate solution;

removing said alkali metal via ion exchange to convert said alkaline silicate solution to a silicic acid solution;

adjusting temperature, concentration and pH of said silicic acid solution to values sufficient to initiate nucleation and particle growth;

cooling said silicic acid solution at a rate sufficient to produce a colloidal silica dispersion; and

isolating said colloidal silica particles from said colloidal silica dispersion to produce colloidal silica particles having a mean or aggregate particle size about 10 nm to about 200 nm.

2. The method of claim 1 , wherein said colloidal silica particles are from about 0.2 wt % to about 45 wt % of the total weight of said composition.

3. The method of claim 1 , wherein said colloidal silica particles are from about 2 wt % to about 24 wt % of the total weight of said composition.

4. The method of claim 1 , wherein said composition further comprises a surfactant selected from the group consisting of:

an anionic surfactant, a cationic surfactant, a non-ionic surfactant, an amphoteric surfactant, and a mixture thereof.

5. The method of claim 4 , wherein said surfactant is an alkoxylated non-ionic surfactant.

6. The method of claim 1 , wherein said composition further comprises:

(iii) carboxylic acid, at a concentration of about 0.01 wt % to about 0.9 wt %;

(iv) oxidizer, at a concentration of about 0.001 wt % to about 2.5 wt %; and

(v) corrosion inhibitor, at a concentration of about 0.001 wt % to about 0.1 wt %.

7. The method of claim 1 , wherein said composition is in a form selected from the group consisting of:

an emulsion, colloidal suspension, solution, and slurry.

8. The method of claim 1 , wherein said medium is selected from the group consisting of:

water, an organic solvent and a mixture thereof.

9. The method of claim 1 , wherein said medium is from about 1 wt % to about 86 wt % of the total weight of said composition.

10. The method of claim 1 , wherein said medium has a pH of about 2.0 to about 11.

11. The method of claim 1 , wherein said composition has a pH of between 9 and 11.

12. The method of claim 1 , wherein said composition has a pH of between 2 and 4.

13. The method of claim 1 , wherein each said trace metal is present in said dispersion in a range from about 5 to about 200 ppb, excluding potassium and sodium.

14. The method of claim 13 , wherein the composition further comprises a stabilizer selected from the group consisting of alkaline compounds including K, ammonia compounds, and a combination thereof.

15. The method of claim 1 , wherein the cumulative trace metal concentration of said dispersion, excluding potassium and sodium, is in the range from about 0.5 to about 3 ppm.

16. The method of claim 1 , wherein said cumulative trace metal concentration, excluding potassium and sodium, is in the range from about 1 ppm to about 3 ppm.