Elimination of stress-induced curvature in thin-film structures

Thomas G. Bifano, Harley T. Johnson, Paul Bierden, Raji Krishnamoorthy Mali

Research output: Contribution to journalArticle

Abstract

Argon ion machining of released thin-film devices is shown to alter the contour shape of free-standing thin-film structures by affecting their through-thickness stress distributions. In experiments conducted on MEMS thin-film mirrors it is demonstrated that post-release out-of-plane deformation of such structures can be reduced using this ion beam machining method. In doing so optically flat surfaces (curvature < 0.001 mm-1) are achieved on a number of 3 μm-thick surface micromachined silicon structures, including mirrors with either initially positive curvature or initially negative curvature measuring up to 0.02 mm-1. An analytical model incorporating the relevant mechanics of the problem is formulated and used to provide an understanding of the mechanisms behind the planarization process based on ion machining. The principal mechanisms identified are 1) amorphization of a thin surface layer due to ion beam exposure and 2) gradual removal of stressed material by continued exposure to the ion beam. Curvature history predictions based on these mechanisms compare well with experimental observations.

Original languageEnglish (US)
Pages (from-to)592-597
Number of pages6
JournalJournal of Microelectromechanical Systems
Volume11
Issue number5
DOIs
StatePublished - Oct 1 2002

ASJC Scopus subject areas

  • Mechanical Engineering
  • Electrical and Electronic Engineering

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