Etching of Silicon Dioxide with Gas Phase HF and Water: Initiation, Bulk Etching, and Termination

摘要

University of Arizona. 1133 James E Rogers Way. Tucson, Arizona USA 85721 The semiconductor industry requires robust cleaning and surface preparation steps in order to enable device fabrication and sustain yield. Amongst the variety of chemicals required to eliminate metals, organic residues, and other contaminants, liquid phase HF solutions are used to remove SiO_2 during front end operations and can be tailored to obtain a specific surface passivation[1]. However, the need to incorporate new materials and device geometries in future process flows will require new approaches to SiO_2 removal. Gas phase HF/H_2O chemistries have shown advantages over liquid phase cleans, including better selectivity[2,3], process integration[3], lower resource utilization[4], and access to smaller geometries given the absence of surface tension in gases[5]. In spite of previous gas phase etching studies[6-9], questions still persist regarding the reaction initiating species (RIS), the induction time, the dynamics of the reaction, and the post etch surface termination. Several authors concluded in previous studies that gas phase removal requires the formation of a condensed water layer before HF contact to initiate and sustain the reaction[7,10]. In this scenario, the initiating species are produced when HF dissolves in the liquid layer, resulting in a reactive system akin to liquid phase etching. Other authors have shown that etching can also occur without the formation of a condensed layer[11]. Although quantum chemistry calculations indicate that gas/solid removal of silicon dioxide is possible[12], no previous experimental results had corroborated the feasibility of this reaction pathway. In this study, the SiO_2 etching process was investigated using in situ Fourier transformed infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) in an attempt to explain the initiation mechanism and reaction kinetics of the SiO_2 etching process and the surface termination on the resulting Si surface.