Paper PS2-ThM6
Chlorine-based Etching of InP Laser : Effect of Plasma Chemistry on Sidewall Roughness and Damages

Thursday, November 10, 2016, 9:40 am, Room 104B

Development of photonic devices on silicon could open the path to the design of new components, mixing optoelectronics and microelectronics. However, indirect band of silicon makes an all-silicon photonic device impossible. An alternative is the hybrid integration which consists in building active laser emitters with III-V materials, and other components (waveguides, filters, photodetectors) with silicon-based materials. In this study, we will focus on the dry etching of Indium-Phosphide (InP) for laser emitter fabrication reported on 200mm silicon-on-insulator wafer by molecular bonding. The major challenges related to this integration are (i) high InP etch rates necessary for micrometric high lasers, (ii) high selectivity toward silicon oxide to preserve the underneath passive components, (iii) anisotropy and (iv) smooth and undamaged surfaces. Plasma etching experiments are carried out in an inductively coupled plasma reactor from applied materials equipped with a hot cathode. In order to achieve these objectives, two plasma chemistries were developed: Cl₂/CH₄/Ar and Cl₂/N₂. They will be compared in terms of profile, roughness, surface chemical composition, and a particular attention will be paid on the chemical and physical damages induced on the pattern sidewalls. The pattern profiles are characterized by electron microscopies. The sidewalls roughness is measured by AFM using a homemade setup where the sample is tilted to allow the tip to scan the sidewalls. The sidewalls chemical composition and stoichiometry after etching is analyzed by EDX. In Cl₂/CH₄/Ar, the process performance is mainly driven by the CH₄ flow. The anisotropy is ensured by the redeposition of SiO_xC_y byproducts, coming from the SiO₂ wafer, on the InP sidewalls. A compromise has been found to ensure anisotropy and sufficient selectivity of InP over the SOI substrate. Sidewall roughness on InP patterns is very close to the one measured on the mask sidewalls before etching, thus proving that this etching process does not produce supplementary roughness. Concerning Cl₂/N₂ plasma, etching selectivity is high and leads to highly anisotropic profile. In that case, the sidewall passivation layer is formed by the preferential etching of indium by chlorine, leading to a phosphorus-rich layer. The counterpart is that this P-rich layer also forms on the open-area and is responsible for roughness formation. Afterwards, we will also consider different strategies to remove these passivation layers so as to obtain clean InP ribbons sidewalls suitable for laser emitter fabrication.