Low temperature wet etching to reveal sub-surface damage in sapphire substrates

► Low temperature wet etching was studied to reveal sub-surface damage in sapphire. ► Etching in H2SO4 at temperatures ≥125 °C and 3:1 H2SO4-H3PO4 at temperatures ≥75 °C was found to reveal sub-surface damage as scratches. ► This technique can be used to observe very low density of sub-surface damage. ► The depth of surface and sub-surface damaged layer was 1.6 and 2.2 μm respectively for wafers lapped with 1 μm diamond particles.