Paper PS-ThM3
Effect of SiH₄ Addition on the Sidewall Passivation Mechanism during the Anisotropic Etching of III-V Materials in Cl₂-based ICP Discharges

Thursday, October 21, 2010, 8:40 am, Room Aztec

III-V semiconductors remain unequalled materials to fabricate high efficient emitters. Anisotropic etching of III-V heterostructures is a key building-block for the processing of such photonic devices (e.g. low-optical loss waveguides or optical cavities with high quality factors, ...) and the ICP etching technique is now widely used for this purpose. Several Cl₂-containing chemistries have been proposed to date for the smooth and high-aspect-ratio etching of InP-based or GaAs-based heterostructures required to reach the NIR region. We have evidenced that in many cases anisotropic etching is due to a passivation mechanism involving SiOx deposition on the III-V sidewalls [JVSTB 26, 666 (2008)]. SiOx passivation simply occurs when a Si wafer is used as the sample tray; this configuration corresponds actually to most commercial ICP etch systems having an electrode diameter of 4-in or more, used to etch III-V samples of not more than 2-in size. However this will not be the case in future large surface processing of III-Vs, when the III-V wafer becomes of the same size of the electrode, or when III-V dies bonded onto a 200/300mm wafer have to be etched, with the wafer surface covered by protecting layer that is not silicon as it may be the case in III-V/Si photonic technologies. Other passivation mechanisms have therefore to be found. For example a Si-containing gas could be added in order to maintain SiOx passivation. In this work we have investigated the Cl₂-SiH₄ chemistry for this purpose. It is found that highly anisotropic etching (aspect ratio > 30 for micropillars) of III-V patterns with a high etch rate (> 0.6 µm/min) can be obtained by optimizing the SiH₄/Cl₂ ratio, independently from the nature of the sample tray. A high selectivity > 1:30 is also obtained with the process using a metallic/ dielectric mask. Ex-situ EDX-TEM analysis of the thin (10-50 nm thick for a 3-µm etch depth) passivation layer deposited on the sidewalls of etched sub-micrometer pillars shows that in optimized conditions this layer consists of micro-crystalline silicon We also confirm that the deposition of the passivation layer is enhanced by H addition, as previously proposed in Cl₂-H₂ chemistry [JVSTA 27, 262, 2009]. We will further discuss the possibility to use HBr/SiH₄ plasma for the anisotropic etching of InP-based or GaAs-based heterostructures, and the effect of oxygen or nitrogen addition in the gas phase on the composition of the passivation layer. We also will compare the respective effects of SiCl₄ and SiH₄ addition on the etched surface passivation process.