Study and optimization of room temperature inductively coupled plasma etching of InP using Cl2/CH4/H2 and CH4/H2

We report an optimized room-temperature etching recipe for Indium Phosphide (InP) based on the inductively coupled plasma (ICP) reactive-ion etch using Cl2/CH4/H2 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 CH4/H2 without chlorine. The Cl2-based recipe does not require substrate heating and thus can be more cost effective and widely applied. The Cl2/CH4/H2 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 CH4/H2 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 (SiO2) mask. The selectivity of InP against oxide mask (up to 35:1) for the Cl2/CH4/H2 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 °C).