Etching of silicon in alkaline solutions: A critical look at the {111} minimum

A.J. Nijdam, J. van Suchtelen, J.W. Berenschot, J.G.E. Gardeniers, M. Elwenspoek

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Anisotropic wet-chemical etching of silicon in alkaline solutions is a key technology in the fabrication of sensors and actuators. In this technology, etching through masks is used for fast and reproducible shaping of micromechanical structures. The etch rates R{hkl} depend mainly on composition and temperature of the etchant. In a plot of etch rate versus orientation, there is always a deep, cusped minimum for the {111} orientations. We have investigated the height of the {111} etch-rate minimum, as well as the etching mechanisms that determine it. We found that in situations where masks are involved, the height of the {111} minimum can be influenced by nucleation at a silicon/mask-junction. A junction which influences etch or growth rates in this way can be recognized as a velocity source, a mathematical concept developed by us that is also applicable to dislocations and grain boundaries. The activity of a velocity source depends on the angle between the relevant {111} plane and the mask, and can thus have different values at opposite {111} sides of a thin wall etched in a micromechanical structure. This observation explains the little understood spread in published data on etch rate of {111} and the anisotropy factor (often defined as R100/R111).
Original languageEnglish
Pages (from-to)430-434
Number of pages5
JournalJournal of crystal growth
Issue number1
Publication statusPublished - 2 Mar 1999
Event12th International Conference on Crystal Growth, ICCG 1998 - Jerusalem, Israel
Duration: 26 Jul 199831 Jul 1998
Conference number: 12


  • METIS-111697
  • IR-14610
  • Anisotropic etching
  • Anisotropy factor
  • EWI-13209
  • Surface morphology
  • Kinematic wave theory
  • Silicon
  • METIS-111683


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