AVS 53rd International Symposium
    MEMS and NEMS Monday Sessions
       Session MN+BI-MoA

Paper MN+BI-MoA5
Role of Metal Impurities in Anisotropic Wet Chemical Etching

Monday, November 13, 2006, 3:20 pm, Room 2007

Session: Surface and Interface Science of MEMS and NEMS
Presenter: T. Hynninen, Helsinki University of Technology, Finland
Authors: T. Hynninen, Helsinki University of Technology, Finland
A.S. Foster, Helsinki University of Technology, Finland
M. Gosálvez, Nagoya University, Japan
H. Tanaka, Nagoya University, Japan
R.M. Nieminen, Helsinki University of Technology, Finland
K. Sato, Nagoya University, Japan
Correspondent: Click to Email
Previous studies@footnote 1@ have shown that great progress in understanding anisotropic wet chemical etching of silicon can be achieved by linking Monte Carlo (MC) atomistic simulations to experimental results. A key part of this effort was parameterizing the MC model according to first principles calculations. This provided a fundamental basis of high accuracy. However, that model focused exclusively on removing silicon atoms from an effectively clean surface. In reality, metal impurities are an unavoidable element in standard etchants, and their effects should be included in any comprehensive model of the etching process. In this work we use a combination of experimental and theoretical approaches to study the influence of metal impurities on the etching rates and surface morphologies, and provide an atomic scale understanding of their role. For the etching of the (110) surface, we experimentally find that copper has the most prominent effect on both surface roughness and etch rate. Lead also lowers the etch rate to some degree, but the other impurities have no effect. On the (100) surface, copper exclusively affects the surface roughness, with little influence on the etch rate. Again the introduction of lead lowers the etch rate. These results can be understood by assuming that the metal impurities act as micromasks pinning certain sites. This is supported by first principles calculations of adsorption energetics of the different metal atoms on a H or OH terminated silicon surface, which provide significant differences between the different metals and explain their influence in etching. The calculated energetics are used as basis for a full Monte Carlo model including the influence of metal impurities. @FootnoteText@ @footnote 1@ M. A. Gosálvez, A. S. Foster and R. M. Nieminen Appl. Surf. Sci. 202 (2002).