One-Step Fabrication of Si Coupons for Micro-Transfer Printing by MacEtch

Abstract Integration of electronic and optoelectronic devices via micro-transfer printing (µTP) enables efficient use of growth substrates by maximizing source wafer use, expanding the integrated device heterogeneity on a target over standard homogeneous flip-chip processes. The fabrication of device structures or “coupons” for µTP is associated with additional process complexity, however, and conventionally requires reactive-ion etching (RIE) for lateral isolation of coupons from the source wafer. As an alternative, metal-assisted chemical etching (MacEtch) is a simple, solution-based, and room-temperature catalytic etching method that employs a metallic catalyst to locally and anisotropically accelerate the vertical wet-etch rate of semiconductors. In this work, we used a MacEtch process to define, etch, and release Si µTP coupons using a one-step fabrication approach prior to heterogeneous integration with various print targets. Polysilicon-on-silicon oxide wafers were grown and used as a comparison to process standard, monocrystalline silicon-on-insulator (SOI) wafers for this study. The poly- and single-crystal SOI samples were patterned and catalytically etched to define the planar coupon dimensions, expose the buried oxide (BOX) layers, and laterally etch them to release the coupons in a single, benchtop processing step. The Au catalyst thickness, oxidant concentration, and release layer thickness were varied to evaluate their influence on the process. Using this approach, successful coupon fabrication by MacEtch and subsequent µTP of both poly-Si-on-SiO x and SOI were realized. It was determined that 90 nm Au film thickness and MacEtch solution of 12.5 M HF and 1.1 M H 2 O 2 were optimal etch conditions. This one-step approach to heterogeneous integration is energy-efficient and will streamline µTP by reducing process complexity from six process steps to three, alleviating equipment requirements and decreasing total fabrication time.