Investigation of macroscopic uniformity during CH4/H2 reactive ion etching of InP and improvement using a guard ring

The reactive ion etching (RIE) with CH₄/H₂-based plasmas is a widely used fabrication tool for devices in the InP material system. Its microscopic characteristics like etch profile, surface roughness and material damage have been extensively studied. Now also the macroscopic properties become important since the large-volume production of InP-based devices and the development of complex OEICs require the introduction of a full-wafer technology. Therefore we have investigated the wafer uniformity of the etch attack. We found that CH₄/H₂-RIE inherently tends to form a rather nonuniform distribution of etch rates across an InP wafer with fastest etching occurring at the wafer edge. Nonuniformities of up to 35% are observed. This effect can be counteracted by an appropriate choice of the process pressure or by the introduction of a guard ring