High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas

Sapphire wafers which are generally used for the fabrication of GaN-based optoelectronic devices are found to be very difficult in lapping, polishing, and cutting for packaging due to the chemical stability and hardness of sapphire. To study possibilities of replacing some of these processes by dry etching, (0001) sapphire wafers were etched using inductively coupled plasmas as a function of gas combination of Cl2/BCl3 and Ar/Cl2/BCl3. The increase of BCl3 in Cl2/BCl3 increased the etch rates. Also, the increase of BCl3 in Cl2 improved the etch selectivity over photoresist. With the mixture of 50% Cl2/50% BCl3, sapphire etch rates of 362.7 nm min−1 could be obtained and, by the addition of 20% Ar in this mixture, the etch rates increased further to 377.5 nm min−1. When the sapphire etching with 50% Cl2/50% BCl3 was applied to lapped wafers for polishing, the surface roughness was decreased from 12.95 to 1.43 nm and the smoothness was better than mechanically polished sapphire surface (5.3 8 nm).