Microtech2010 2010

fibDAC Stress Relief – a Novel Stress Measurement Approach for Semiconductor BEoL Structures

D. Vogel, A. Gollhardt, J. Keller, B. Michel
Fraunhofer ENAS, DE

Keywords: stress measurement, semiconductor, BEoL


Residual stresses in BEoL structures of semiconductor devices are one of the crucial reliability issues. Mostly used wafer bow or x-ray diffraction measurements for residual stresses in thin films suffer from the fact that they average over larger lateral wafer or die areas and cannot be applied very locally, i.e. within structure areas of some microns or of even substantially smaller size. The new approach developed by the authors intends to overcome the mentioned drawbacks. The authors present a new stress measurement method basing on the specific treatment feasibilities provided by focused ion beam (FIB) equipment. Ion milling is utilized to release very locally residual stresses on stack layers of interest. Deformations around the milled surface area generated this way are measured precisely by fibDAC digital image correlation algorithms. The latter are applied to SEM micrographs captured before and after ion milling. As a result originally existing residual stresses are computed from measured stress relief displacement fields. Finite element analysis (FEA) is used to simulate the expected stress relief deformation for particular stress relief patterns. Fitting of experimental and numerical FEA data allows to quantify stresses. This method has been applied very locally on semiconductor structures.
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