Polishing slurry preventing agglomeration of charged colloids without loss of surface activity
A method for chemically stabilizing polishing slurries in aqueous suspension to prevent their agglomeration while maintaining their surface activity is disclosed. The method prevents the formation of irreversible particle agglomerates during drying and permits the subsequent re-suspension of dried particles with no impact on the particle size distribution. The stabilization method can be customized based on knowledge of the colloid surface charge at suspension pH conditions, addition of a charged species having like charge to the colloid at the suspension conditions, and control of the concentrations of the charged species and other ions in suspension.
1. A polishing slurry in suspension in a container, the polishing slurry comprising:
a solvent disposed in the container;
a plurality of ceria particles disposed in the container and supported in the solvent, wherein each of the plurality of ceria particles has a negative surface charge distributed over an outer surface of the ceria particle, wherein the solvent forms a positive charge layer around each ceria particle, the positive charge layer including ions that are more tightly bound to the ceria particle and diffuse ions that are more weakly bound to the ceria particle; and
a plurality of negatively charged species disposed in the container and comprising at least one of Ammonium Lauryl Sulfate (ALS), Sodium Dodecyl Benzene Sulfonate, or a phosphate ester, wherein at least some of the plurality of the negatively charged species are attached to the diffuse ions of the positive charge layer.
2. The polishing slurry in suspension of claim 1 wherein the plurality of negatively charged species comprises surfactants, particles, or molecules.
3. The polishing slurry in suspension of claim 1 wherein each of the plurality of negatively charged species comprises (i) a branched or linear alkyl or alkyl-ether tail and (ii) a charge-carrying head group comprising sulfate, sulfonate, phosphate, or carboxyl.
4. The polishing slurry in suspension of claim 1 wherein the plurality of negatively charged species comprises an anionic surfactant.
5. The polishing slurry in suspension of claim 4 wherein a molecular weight of the anionic surfactant is less than or equal to 384 g/mol.
6. The polishing slurry in suspension of claim 1 wherein the at least some of the plurality of the negatively charged species are separable from the diffuse ions by application of a shear force.
7. The polishing slurry in suspension of claim 6 wherein the at least some of the plurality of the negatively charged species reattach to the diffuse ions after removal of the shear force.
8. The polishing slurry in suspension of claim 1 wherein the polishing slurry consists of the solvent, the plurality of ceria particles, and the plurality of negatively charged species.
9. The polishing slurry in suspension of claim 1 wherein the plurality of negatively charged species consists of a single surfactant.
10. A polishing slurry in suspension in a container, the polishing slurry comprising:
a solvent including solvent ions, wherein the solvent is disposed in the container;
a plurality of ceria particles disposed in the container and supported in the solvent; and
a stabilizing agent disposed in the container, comprising at least one of Ammonium Lauryl Sulfate (ALS), Sodium Dodecyl Benzene Sulfonate, or a phosphate ester, and including stabilizing agent ions;
wherein:
each ceria particle has a negative surface charge distributed across an outer surface of the ceria particle;
the solvent ions are positively charged and form, around each ceria particle, a corresponding layer in which solvent ions closest to the ceria particle are more tightly bound to the ceria particle, and in which solvent ions farther from the ceria particle are diffuse and more weakly bound to the ceria particle; and
the stabilizing agent ions are negatively charged and attached to the more weakly bound solvent ions, away from the outer surfaces of the ceria particles.
11. The polishing slurry in suspension of claim 10 , wherein the stabilizing agent ions are separable from the more weakly bound solvent ions by application of a shear force.
12. The polishing slurry in suspension of claim 11 , wherein the stabilizing agent ions reattach to the more weakly bound solvent ions after removal of the shear force.
13. The polishing slurry in suspension of claim 10 wherein the polishing slurry consists of the solvent, the plurality of ceria particles, and the stabilizing agent.
14. The polishing slurry in suspension of claim 10 wherein the stabilizing agent consists of a single anionic surfactant.
15. The polishing slurry in suspension of claim 10 wherein a molecular weight of the stabilizing agent is less than or equal to 384 g/mol.