EPI finish on sapphire has become to mean that the finish shall be 3 Angstroms Ra or less.
A common EPI polished sapphire substrate requirement is for manufacture of bright blue and green LEDs.
The tightest tolerance ultra-flat Blue and Green LED 2 in. (50.8 mm) polished Optical Grade Monocrystaline sapphire wafers:
Orientation | C-plane (0001) ±0.1 deg. |
Diameter | 50.8 ±0.05 mm (2 ±0.002 in.) |
Thickness | 330 ±10 microns or 430 ±10 microns |
Thickness variation – TTV | less than 10 microns |
Bow | less than 15 microns |
Surface finish | EPI polish – less than 3 Angstroms |
Flatness (restrained) | less than 5 microns |
Primary flat | 16 ±0.5 mm |
Primary flat orientation | A-plane (1120) ±0.5 deg. |