High-aspect-ratio inductively coupled plasma etching of InP using SiH4/Cl2: Avoiding the effect of electrode coverplate material

A new SiH4/Cl2 chemistry is proposed for the high-aspect-ratio etching of InP-based heterostructures. Anisotropic etching is obtained through the deposition of a SiOx passivation layer on the etched sidewalls. SiH4 has been chosen as a single precursor for both Si and H species that are necessary to promote the passivation process. Previously developed Cl2/H2- or HBr-based chemistries for anisotropic etching of laser waveguides or vertical microcavities require a silicon wafer below the InP samples in order to assist the passivation mechanism. In contrast, the authors show that a SiOx passivation can be achieved and maintained almost independent of the nature of the wafer surface when SiH4 is added. This is of practical importance for the processing of III-V wafers having the same size as the electrode or for III-V heterogeneous integration when III-V dies bonded onto a 200/300 mm diameter wafer have to be etched. Smooth, notch-free, anisotropic etching of InGa(Al)As/InP heterostructures is demonstrated. Ex situ energy-dispersive x-ray spectroscopy coupled to a transmission electron microscope is used to analyze the composition of the thin passivation layer deposited on the sidewalls of etched features. The authors show that the passivation layer consists of a Si-rich silicon oxide (Si/O∼1) in Cl2/H2/SiH4 chemistry and is changed to nanocrystalline Si in SiH4/Cl2 chemistry depending on the SiH4 concentration in the feed gas. An aspect ratio as high as 28 is obtained in the latter case.