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Residual Stress Reduction in Sputter Deposited Thin Films by Density Modulation

Published online by Cambridge University Press:  31 January 2011

Arif Sinan Alagoz ,
Jan-Dirk Kamminga ,
Sergey Yu Grachev ,
Toh-Ming Lu  and
Tansel Karabacak
Arif Sinan Alagoz
Affiliation:
asalagoz@ualr.edu, University of Arkansas at Little Rock, Department of Applied Science, Little Rock, Arkansas, United States
Jan-Dirk Kamminga
Affiliation:
j.kamminga@m2i.nl, Materials Innovation Institute, Delft, Netherlands
Sergey Yu Grachev
Affiliation:
Sergey.Grachev@saint-gobain.com, Saint-Gobain Recherche, France, United States
Toh-Ming Lu
Affiliation:
lut@rpi.edu, Rensselaer Polytechnic Institute, Physics, Troy, New York, United States
Tansel Karabacak
Affiliation:
txkarabacak@ualr.edu, University of Arkansas at Little Rock, Department of Applied Science, Little Rock, Arkansas, United States
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Abstract

Control of residual stress in thin films is critical in obtaining high mechanical quality coatings without cracking, buckling, or delamination. In this work, we present a simple and effective method of residual stress reduction in sputter deposited thin films by stacking low and high material density layers of the same material. This multilayer density modulated film is formed by successively changing working gas pressure between high and low values, which results in columnar nanostructured and dense continuous layers, respectively. In order to investigate the evolution of residual stress in density modulated thin films, we deposited ruthenium (Ru) films using a DC magnetron sputtering system at alternating argon (Ar) pressures of 20 and 2 mTorr. Wafer’s radius of curvature was measured to calculate the intrinsic thin film stress of multilayer Ru coatings as a function of total film thickness by changing the number of high density and low density layers. By engineering the film density, we were able to reduce film stress more than one order of magnitude compared to the conventional dense films produced at low working gas pressures. Due to their low stress and enhanced mechanical stability, we were able to grow these density modulated films to much higher thicknesses without suffering from buckling. Morphology and crystal structure of the thin films were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). A previously proposed model for stress reduction by means of relatively rough and compliant sublayers was used to explain the unusually low stress in the specimens investigated.

Keywords

sputteringRumicrostructure
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1224: Symposia FF/GG – Mechanical Behavior at Small Scales — Experiments and Modeling , 2009 , 1224-FF05-22
Copyright
Copyright © Materials Research Society 2010

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