Chemical mechanical polishing of alumina
A CMP method uses a slurry including a first metal oxide or semiconductor oxide particles (first oxide particles) in water. At least one particle feature is selected from (i) first oxide particles having a polydispersity >30%, (ii) a coating on first oxide particles including Group I or Group II ions, transition metal oxide, or organic material, (iii) first oxide particles mixed with fumed oxide particles, (iv) first oxide particles with average primary size >50 nm mixed with fumed oxide particles having average primary size <25 nm, and (v) first oxide particles with a per surface area per unit mass <100 m 2 /gm mixed with another oxide particle type having an average area per unit mass >150 m 2 /gm. A substrate having an alumina surface is placed into a CMP apparatus, and CMP is performed with a rotating polishing pad and the slurry to polish the alumina surface.
1. A chemical mechanical polishing (CMP) slurry, comprising:
a plurality of colloidal metal oxide or colloidal semiconductor oxide particles (colloidal particles) in water,
(i) said plurality of colloidal particles having a particle size polydispersity >50% determined by a polydispersity formula for a distribution width (w) involving a first width (w 1 ) at a first particle size and a second width (w 2 ) at a second larger particle size, said polydispersity formula =(w 2 −w 1 ) ×100/d which includes 63% of a total of said plurality of colloidal particles by volume and said d av is an average particle size of said plurality of colloidal particles; and
(ii) mixed particle types comprising said plurality of colloidal particles with average primary particle size >50 nm mixed with fumed oxide particles having an average primary particle size <25 nm,
wherein a weight ratio of said fumed oxide particles to said colloidal particles is from 0.1% to 30% .
2. The slurry of claim 1 , wherein said colloidal particles comprise silica.
3. The slurry of claim 1 , wherein a pH of said slurry is >7.
4. The slurry of claim 1 , wherein said particle size polydispersity is >80%.
5. The slurry of claim 1 , further comprising alkali metal ions in a concentration from 500 ppm to 5 weight %.