| The controlled etching of micro/nano structures is essential for a variety of technological applications, including microelectromechanical systems (MEMS) fabrication. XeF2 is an isotropic and highly selective etching gas used to remove semiconductors and metals in the fabrication of MEMS and other devices. While the kinetics of XeF2 etching Si has been widely documented, XeF2 etching of metals is not widely understood. For better process control and device quality, it is important to understand the etching mechanism at the molecular level. In this work, we explore the surface and gas phase chemistry of XeF2 etching Mo films. Studies on the general characteristics of etching Mo blanket films were carried out on 1000AMo/475ASiO2/100ANi/glass samples at different sample temperatures and etchant pressures in a standalone etching chamber. They were analyzed ex-situ by atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) for investigating morphology and chemical composition of the surfaces after etchings, respectively. Rutherford back scattering (RBS) was used to measure the thickness of the films and the depth profile of near-surface species after etching. Downstream mass spectrometry was used to identify the volatile products of the etching process. The composition and chemical state of the etched surface (reaction layer) is further investigated by in-vacuo etching and XPS analysis experiments using 3750AMo/quartz samples in an integrated etching/analysis system. The XPS studies have clarified issues on: (i) the thickness and chemical composition of the reaction layer during etching, (ii) the effects of the surface native oxides and adventitious hydrocarbons on the initiation and progress of etching, (iii) the re-deposition of etched products. Post-etching thermal processing and XPS analysis studies were performed to investigate the chemical composition of residues left after etching. Kinetics of etching blanket Mo films was investigated using total pressure change and a quartz crystal micro balance (QCM). The rates of etching blanket films were determined to be 60-75 nm/sec at 25-90°C. The rate of undercut etching, measured on patterned samples, changes significantly (0.5-2.5 mu/min) under different conditions, depending on the etching method, temperature, and pattern size. Different gas delivery methods were tested and their efficiency is discussed. |
