Optimization of the CMP Process with Colloidal Silica Performance for Bulk AlN Single Crystal Substrate

Abstract

Chemical mechanical polishing (CMP) of bulk AlN was performed with colloidal silica slurry at pH 9 for different times. The result shows that colloidal silica slurry at pH 9, which has the relatively high surface charge of-50.7 mV is most stable. Thus, it was selected as chemically optimum condition in this study. The ultrasmooth surface was shown in CMP 90 min with the roughness average (Ra) value of 0.172 nm. It was demonstrated that the damaged layers including subsurface defects and micro scratches in the whole machining process were successfully removed and atomically flat surface can be shown. With increasing process time, the zeta potential and mean particle size of the colloidal silica decreased and increased to 35.07 mV and 143.4 nm, respectively. While the silica particles agglomerated and densely packed slurry particles were formed by mechanical shearing, these increased the Ra value to above 0.5 nm of AlN substrate and generated additional surface damages. In terms of the surface chemistry, the carbon compounds and organic impurities adsorbed on the substrate during mechanical polishing (MP) can be removed and aluminum oxide-hydroxide; AlOOH and Al(OH) 3 were observed during the CMP. It was determined that the chemically polished AlN substrate was continuously hydrated with generating the AlOOH and Al(OH) 3 on the surface.

Effect of Dry Thermal Oxidation on Bulk GaN Substrates Grown by HVPE during CMP

“…The MRR was calculated using Eq. 1: 16 MRR = m/ ρ × r 2 × t , [1] where m (g) is the removal mass of the material, ρ (g/cm 3 ) is the density of GaN, r (cm) is the radius of the substrate, and t (h) is the polishing time. Prior to the CMP process, the thermal treatment was conducted at 700-1000°C for 5 h in ambient air in a home-made furnace to anneal the nitride single crystal.…”