The effect of abrasive hardness on the chemical-assisted polishing of (0001) plane sapphire

Abstract

A series of abrasives with various hardness values including monocrystalline and polycrystalline diamond, α- and γ-alumina, zirconia, ceria, and silica were used to examine the concept of chemical-assisted polishing for finishing the (0001), c-plane (basal plane), of sapphire. Diaspore, a monohydrate of alumina, was also evaluated. Atomic force microscopy suggested that the hydrated layer of the c-plane surface was about 1 nm thick. Polishing experiments were designed to determine whether the chemically modified surface hydration layer forms on the basal plane in water. The results indicate that harder abrasives do not necessarily cause faster material removal and better surface finish for similar abrasive particle size. Abrasives with hardness equal to or less than sapphire such as α-Al2O3 and γ-Al2O3 achieved the best surface finish and greatest efficiency of material removal. It is proposed that the (0001) c-plane sapphire surface was modified by water to form a thin hydration layer with structure and hardness close to diaspore. This reaction layer can be removed by an abrasive that is softer than sapphire but harder than the reaction layer. α-Al2O3 was particularly effective. This result is attributed to adhesion between identical reaction layers on the basal planes of the alumina abrasive and the sapphire. This demonstrates that high removal rates and good surface finish can be achieved without costly diamond polishing.

Preparation of γ‐alumina/silica core–shell abrasives and their chemical mechanical polishing performances on sapphire substrates

“…During the CMP process, the pure γ-alumina tends to hydrate to soft boehmite which may lead to the lower MRR. The hydration effect of γ-alumina becomes weaker [13] and the hardness of core-shell abrasives is harder than the pure silica when coated with a layer of silica. Thus, the MRR of core-shell abrasives is higher than that of pure silica.…”

“…with various characteristics were used to study the sapphire CMP performances. Zhu et al [13] have studied the CMP performances of sapphire substrates with γ-alumina and silica. The results indicate that the roughness values of polished sapphire substrates using pure γ-alumina need to be improved.…”

Machining processes for sapphire wafers: a literature review

“…The wafer surface being polishing is pressed against a resilient polishing pad attached to a rotating table [63]. For CMP of sapphire, various slurries (like SiO 2 and Al 2 O 3 ) have been used [62,[64][65][66][67][68][69][70][71]. There have been many published papers on CMP of sapphire since 2000 [62,[64][65][66][67][68][69][70][71].…”

Atomic force microscopy study of sapphire surfaces annealed with a H2O flux from a baffled molecular-beam epitaxy effusion cell loaded with Al(OH)3

“…The aspurchased sapphire substrates typically contain surface defects and impurities, such as scratches 8 and hydrocarbons, 9 that need to be removed prior to use. Various combinations of techniques can range from chemical cleans 8,10 involving trichloroethylene or a combination of H 2 SO 4 :H 3 PO 4 , to chemical-assisted polishing, 11 as well as plasma-based cleans. Various combinations of techniques can range from chemical cleans 8,10 involving trichloroethylene or a combination of H 2 SO 4 :H 3 PO 4 , to chemical-assisted polishing, 11 as well as plasma-based cleans.…”