Selective etching of AlGaInP laser structures in a BCl3/Cl2inductively coupled plasma

The etch rate of AlGaInP-based laser structures and selectivity, with respect to SiO2, are reported as a function of inductively coupled plasma (ICP) process parameters for a BCl3/Cl2 etch chemistry. At room temperature InCl3, a reaction product of In in this environment, is involatile, whereas the products of etching SiO2 are relatively volatile resulting in low selectivity (~4:1). Temperature is the most important variable for improving etch rate and selectivity. At 190 °C it is possible to obtain an etch rate up to 0.7 µm min−1 and a selectivity as high as 17:1. It is shown that increasing the ICP power increases the etch rate of AlGaInP but decreases the selectivity, whereas increased reactive ion etching (RIE) power results in improved etch rate and selectivity. The etch rate is also found to be higher at lower chamber pressures although again with little or no change in selectivity. These results are consistent with an AlGaInP etch rate that is dependent on both dc bias and ion flux, in contrast to a SiO2 etch mechanism that is relatively independent of dc bias but strongly dependent on ion flux. With total gas flow kept constant the etch rate and selectivity are found to increase with the fraction of Cl2 present. The addition of Ar to the gas mix does increase the etch rate, reaching a maximum at around 70% Ar, but without any significant effect on selectivity.