Measurement of stresses in MEMS structures by stress release

The paper presents a recently developed method of measuring frozen elastic stresses in micro components and devices. The approach bases on stress release at the component surface by focused ion beam (FIB) milling. Stresses are deduced from the experimentally determined deformation field around the FIB milling pattern, applying reasonable stress hypotheses and appropriate modeling of the stress release field. Because of the local nature of ion milling and the limited material volume affected by deformation, the method suites to very local stress measurement. Commonly, spatial resolution is achieved in a range from submicron to some tens of microns. Residual stresses in membrane type MEMS structures have been measured and results are reported. A broader group of potential applications is expected for non-membrane structures in micro-/nanosystems or their packaging. Possible approaches for those cases are discussed, considering comparison of measured deformation fields with either analytical solutions of the mechanical problem or with finite element simulations.

[1]  D. W. Burns,et al.  A simple technique for the determination of mechanical strain in thin films with applications to polysilicon , 1985 .

[2]  David B. Bogy,et al.  Edge-Bonded Dissimilar Orthogonal Elastic Wedges Under Normal and Shear Loading , 1968 .

[3]  Bernd Michel,et al.  Micro- and nanomaterials characterization by image correlation methods , 2002 .

[4]  Carles Cané,et al.  Measurement of residual stress by slot milling with focused ion-beam equipment , 2006 .

[5]  Ki-Ju Kang,et al.  Effect of Geometry and Materials on Residual Stress Measurement in Thin Films by Using the Focused Ion Beam , 2004 .

[6]  Hiroshi Tada,et al.  The stress analysis of cracks handbook , 2000 .

[7]  B. Michel,et al.  Measurement of thermally induced strains on flip chip and chip scale packages , 2000, ITHERM 2000. The Seventh Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (Cat. No.00CH37069).

[8]  Ingrid De Wolf,et al.  Strain determination in silicon microstructures by combined convergent beam electron diffraction, process simulation, and micro-Raman spectroscopy , 2003 .

[9]  Z. Suo,et al.  Mixed mode cracking in layered materials , 1991 .

[10]  Ingrid De Wolf,et al.  High-resolution stress and temperature measurements in semiconductor devices using micro-Raman spectroscopy , 1999, International Symposium on Photonics and Applications.

[11]  Freund.  Thin Film Materials , 2004 .

[12]  A. Wilkinson,et al.  High-resolution elastic strain measurement from electron backscatter diffraction patterns: new levels of sensitivity. , 2006, Ultramicroscopy.

[13]  J. Wortman,et al.  Young's Modulus, Shear Modulus, and Poisson's Ratio in Silicon and Germanium , 1965 .

[14]  Paul A. Totta.  Stress induced phenomena in metallizations: U. S. perspective , 2008 .