A Highly Selective Low Pressure Inductively Coupled Plasma Etching Process for GaAs Using Photoresist Mask

GaAs etch characteristics like etch rate, etch profile sidewall angle, etch surface morphology and selectivity are studied as a function of Inductively Coupled Plasma (ICP) power and Cl2/BCl3 flow rate ratio in ICP at low pressure (<15mTorr) and low RF bias power (<100W) regime to achieve moderate GaAs etch rate with an-isotropic profiles and smooth surface morphology. The low pressure regime etching at Cl2/BCl3 flow rate ratio of 4:1 has resulted in vertical etch profiles with controlled sidewall angle ~ 84o, smooth surface morphology and good mask selectivity ~15 without significant deposition of CClx polymer on the etched sidewalls but with limited etch depth ~ 100μm using photoresist mask. The mask selectivity is found to be a strong function of RF bias power and ICP power and a weaker function of process pressure. The resultant etch depth increases with an increase in pressure and flow rate ratio at the expense of etch surface morphology, as the desorption of chemical species limits the etching process at higher Cl2 flow rates and leaves some of the residue on the surface.