SEMI MS4 - Test Method for Young's Modulus Measurements of Thin, Reflecting Films Based on the Frequency of Beams in Resonance
This Standard was technically approved by the MEMS/NEMS Global Technical Committee. This edition was approved for publication by the global Audits and Reviews Subcommittee on December 4, 2015. Available at www.semiviews.org and www.semi.org in April 2016; originally published November 2007; previously published November 2013.
The absence of a generally accepted method to determine Young’s modulus has provided a challenge to the microelectromechanical systems (MEMS) community for many years. Without a standard measurement technique, measurements between different laboratories cannot be meaningfully compared. This Standard provides a test method to determine Young’s modulus for thin, reflecting films, based on the average resonance frequency of a single-layered cantilever. It also provides a test method to determine Young’s modulus based on the average resonance frequency of a single-layered fixed-fixed beam, but this method is only to be used if a cantilever is not available for measurement.
Young’s modulus measurements are an aid in the design and fabrication of MEMS devices and integrated circuits (ICs). For example, high values of residual stress can lead to failure mechanisms in ICs such as electro migration, stress migration, and delamination. So, methods for its characterization are of interest for IC process development and monitoring in order to improve the yield in complementary metal oxide semiconductor (CMOS) fabrication processes. The residual stress of a thin film layer is calculated in this Test Method based on the Young’s modulus value also obtained in this Test Method.
This Test Method covers a procedure for measuring Young’s modulus in thin films. It applies only to films, such as found in MEMS materials that can be imaged using a noncontact optical vibrometer, stroboscopic interferometer or comparable instrument that is capable of obtaining the resonance frequency of a beam oscillating out-of-plane. (Measurements from beams that are touching or touch the underlying layer are not acceptable.) The average resonance frequency of a single-layered cantilever is used in Young’s modulus calculations. (If a cantilever is not available for measurement, the average resonance frequency of a single-layered fixed-fixed beam can be used, but this approach is not recommended due to a higher combined standard uncertainty value.) The Young’s modulus value can then be used in calculations of residual stress and stress gradient.
The fabrication, including the etching steps required to release the beams, is considered outside the scope of this Test Method. The determination of the beam’s length, width, thickness, and density, as well as whether the beam is exhibiting stiction is also considered outside the scope of this Test Method.
If the test instrument incorporates a laser, this Test Method only applies if the laser is Class 1 or Class 2.
Referenced SEMI Standards
SEMI MS2 — Test Method for Step Height Measurements of Thin Films