etching patterns into the sapphire prior to growth. This can give a >98% improvement on light extraction from the finished device.
Sapphire is a very stable material, with a melting point of 2054°C that consequently makes it difficult to plasma etch. However Photoresist (PR) which is used to achieve the very specific pattern definition has an upper temperature limit before it degrades, typically 150oC.
PR is the mask of choice for this process as the ultimate ‘dome’ shape is reliant on all the mask being removed on completion, and the shape is closely linked to the relative etch rates of the sapphire and mask. PR is also preferred as it simplifies the manufacturing flow and reduces the overall Cost per Lumen. In order to etch the material, combinations of Cl2, BCl3 and Ar are commonly used with higher etch rates achieved at higher plasma source powers. However this increases