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Fracture Mechanisms of SiNx Thin-films on Compliant Substrates

Published online by Cambridge University Press:  01 February 2011

Alex Z Kattamis ,
Kunigunde H Cherenack ,
I-Chun Cheng ,
Ke Long ,
James C Sturm  and
Sigurd Wagner
Alex Z Kattamis
Affiliation:
akattamis@exponent.com, Exponent Inc., Electrical and Semiconductor, 420 Lexington Ave #1740, New York, NY, 10170, United States
Kunigunde H Cherenack
Affiliation:
kcherena@princeton.edu, Princeton University, Electrical Engineering and Princeton Insitute for the Science and Technology of Materials, Princeton, NJ, 08544, United States
I-Chun Cheng
Affiliation:
ichuncheng@cc.ee.ntu.edu.tw, National Taiwan University, Department of Electrical Engineering, Taipei, N/A, Taiwan
Ke Long
Affiliation:
ke.long@asu.edu, Arizona State University, Flexible Display Center, Tempe, AZ, 85284, United States
James C Sturm
Affiliation:
sturm@princeton.edu, Princeton University, Electrical Engineering and Princeton Insitute for the Science and Technology of Materials, Princeton, NJ, 08544, United States
Sigurd Wagner
Affiliation:
wagner@princeton.edu, Princeton University, Electrical Engineering and Princeton Insitute for the Science and Technology of Materials, Princeton, NJ, 08544, United States
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Abstract

The prospect of large-area electronics on polymers, for flexible applications requires a study of thin film fracture mechanisms. To fabricate thin-film transistor (TFT) backplanes on polymer foils the substrate must first be passivated to protect the polymer substrate from chemicals used during processing and to protect the TFTs from substrate out gassing. Silicon nitride (SiNx) is commonly used for this purpose since it tends to adhere well to polymers and is easily deposited by PE-CVD. When rigid thin films such as SiNx are deposited onto compliant substrates, such as polymer foils, stresses caused by built-in strains and the mismatch in coefficients of thermal expansion can cause fracture. The deposited thin films may fracture, and also the polymer substrate below. Using focused-ion beam milling and scanning electron microscopy we analyzed two distinct thin film fracture morphologies for SiNx films on two different types of polymer substrate. One had a relatively low, the other a relatively high coefficient of thermal expansion. For both SiNx/substrate systems the SiNx was under residual compressive stress and the substrate under tension. In one case the compressive stress in the thin films cause them to debond, buckle, and crack. In the other case the tensile stress in the substrate causes it to tear, followed by the fracture of the SiNx film above.

Keywords

thin filmplasma-enhanced CVD (PECVD) (chemical reaction)scanning electron microscopy (SEM)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1078: Symposium M – Materials and Technology for Flexible, Conformable and Stretchable Sensors and Transistors , 2008 , 1078-M14-02
Copyright
Copyright © Materials Research Society 2008

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