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Author Norga, G. J. ♦ Platero, M. ♦ Reddy, A. J. ♦ Michel, J. ♦ Kimerling, L. C. ♦ Black, K. A.
Sponsorship National Renewable Energy Lab., Golden, CO (United States)
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ ENGINEERING NOT INCLUDED IN OTHER CATEGORIES ♦ COPPER ♦ DEPOSITION ♦ INTEGRATED CIRCUITS ♦ SILICON ♦ HYDROFLUORIC ACID ♦ CHEMICAL REACTION KINETICS ♦ CRYSTAL GROWTH ♦ CLEANING
Abstract Metal deposition on silicon from HF-based solutions is initiated by electrochemical reduction of metal ions, a process which is driven by the difference between the electron quasi Fermi energy in the silicon, E{sub Fn}, and the redox energy level of the ions in solution, eE{sub M{sup z+}/M{sup o}}. Mechanisms for metal ion reduction are elucidated by aligning the silicon bands with the redox levels of ions in solution. For copper, the reduction reaction occurs by capture of conduction band electrons, a process which requires nucleation of nanometer-sized precipitates on the silicon surface. As the concentration of electrons at the surface is increased (e.g., by n-type doping, illumination, or cathodic biasing), the nucleation rate of precipitates, N, increases steeply. N is further dependent on the activity of the metal ion in solution and the amount of surface charge at the Si/HF interface. The growth rate, v, of copper nuclei is determined by the surface concentration of holes and is increased by illumination and p-type doping. The predicted effects on N and v of illumination level, doping level, and substrate bias were verified by immersion tests on Czochralski wafers in 1:100 HF. Total reflection x-ray fluorescence was used to measure copper coverage; atomic force microscopy and surface-sensitive minority carrier lifetime measurements were used to determine the areal density of copper precipitates. Application of these findings to reduce copper deposition from HF in industrial wafer cleaning practice are discussed.
ISSN 00134651
Educational Use Research
Learning Resource Type Article
Publisher Date 1997-08-01
Publisher Place United States
Journal Journal of the Electrochemical Society
Volume Number 144
Issue Number 8


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