Study and optimization of room temperature inductively coupled plasma etching of InP using Cl_2/CH_4/H_2 and CH_4/H_2

摘要

We report an optimized room-temperature etching recipe for Indium Phosphide (InP) based on the inductively coupled plasma (ICP) reactive-ion etch using Cl_2/CH_4/H_2 gasses. The process was optimized using design of experiment (DOE) (Taguchi method). The results, in terms of etch rate, surface roughness and etched profile, are compared with the more conventional CH_4/H_2 without chlorine. The Cl_2-based recipe does not require substrate heating and thus can be more cost effective and widely applied. The Cl_2/CH_4/H_2 process generally gives a reasonable higher etch rate (as high as 848 nm/min) and cleaner surface with no polymer formation, but it requires a high ICP power. The CH_4/H_2 process produces lower etch rate (with possibly polymer contamination), but smoother surface and better structural verticality at a lower ICP power. Both processes give very good selectivity against the silicon dioxide (SiO_2) mask. The selectivity of InP against oxide mask (up to 35:1) for the Cl_2/CH_4/H_2 process is one of the highest reported so far. The etched structure possesses good verticality and good surface quality comparable to that obtained under elevated temperature condition (> 200℃).