Mechanism of anisotropy during inductively coupled plasma (ICP) etching of inp-based heterostructures for the fabrication of photonic devices

Using energy dispersive X-ray (EDX) spectroscopy coupled to transmission electron microscopy (TEM), we have identified the anisotropy mechanism allowing for the smooth and vertical etching of InP-based heterostructures of interest in the fabrication of photonic devices. We show that the anisotropic profiles reported with Cl₂/H₂- or HBr-containing gas mixtures are due to the formation of a thin silicon oxide passivation layer resulting from the reaction of Cl₂ or HBr with the silicon wafer used as the sample tray. The experimental results give useful guidelines to define anisotropic etching processes scalable to large-diameter InP wafers in future industrial applications.