Chemical mechanical polishing pad and polishing method
The present invention concerns a chemical mechanical polishing pad having a polishing layer that possesses a consistent positive zeta potential across the entire surface. Also disclosed is a chemical mechanical polishing method using the polishing pad together with a positively charged slurry.
1. A method of chemical mechanical polishing a substrate,
comprising:
providing the substrate;
providing a polishing slurry comprising water and a silica abrasive;
providing a chemical mechanical polishing pad having a positive zeta potential, the polishing pad comprising a polishing layer having a composition, and a polishing surface, wherein the composition is a reaction product of ingredients, comprising:
(a) a polyfunctional isocyanate having an average of at least two unreacted isocyanate (NCO) groups per molecule;
(b) a first curative consisting of a hydroxyl substituted quaternary ammonium;
(c) a second curative, wherein said second curative is free of quaternary ammonium; and,
(d) optionally, a plurality of microelements;
wherein said first curative is present at equal to or greater than 50 mol % based on the total molar amount of the first curative and the second curative, and wherein the stoichiometric ratio of the combined reactive hydrogen groups in the curatives of (b) and (c) to the at least two unreacted isocyanate (NCO) groups in the polyfunctional isocyanate of (a) is 0.8 to 1.1; and
wherein said positive zeta potential is consistent across the surface of the entire polishing pad and is independent of pH over a pH range of 2 to 12 using nitric acid or potassium hydroxide to adjust pH of deionized water;
creating a dynamic motion between the polishing surface and the substrate to polish a surface of the substrate; and
dispensing the polishing slurry onto the chemical mechanical polishing pad at or near the interface between the polishing surface and the substrate.
2. The method of claim 1 , wherein the first curative contains at least two hydroxyl groups per molecule.
3. The method of claim 1 , wherein the first curative contains at least three hydroxyl groups per molecule.
4. The method of claim 3 , wherein the second curative contains less than 0.1 wt % of tertiary amine.
5. The method of claim 1 , wherein the second curative comprises an amine.
6. The method of claim 5 , wherein the amine is an aromatic amine.
7. The method of claim 6 , wherein the aromatic amine is 4,4′-methylenebis(2-chloroaniline) (MBOCA).
8. The method of claim 1 , wherein the quaternary ammonium is tris(2-hydroxyethyl)methyl ammonium methyl sulfate.
9. The method of claim 1 , wherein the silica abrasive has a positive surface charge measured at a polishing pH of 1 to 6.
10. The method of claim 1 , wherein the polishing slurry has a pH of 3-5.