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Research Papers

Quantitative Interfacial Energy Measurements of Adhesion-Promoted Thin Copper Films by Supercritical Fluid Deposition on Barrier Layers

[+] Author and Article Information
Christos F. Karanikas

Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, MA 01003

Han Li, Joost J. Vlassak

School of Engineering and Applied Science, Harvard University, Cambridge, MA 02138

James J. Watkins

Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003

J. Eng. Mater. Technol 132(2), 021014 (Feb 22, 2010) (7 pages) doi:10.1115/1.4000283 History: Received November 20, 2008; Revised July 19, 2009; Published February 22, 2010; Online February 22, 2010

A fivefold increase in adhesion energy is observed for poly(acrylic acid) (PAA) modified Cu/TaN interfaces in which the thin copper films are deposited by the hydrogen assisted reduction of bis(2,2,7-trimethyloctane-3,5-dionato) copper in supercritical carbon dioxide. The PAA adhesion layer is sacrificial at the reaction conditions used, and X-ray photoelectron spectroscopy has shown that the Cu/TaN interface is free of contamination following deposition. The resulting average interfacial adhesion energy is just above 5J/m2, which meets adhesion requirements for integration in Cu interconnects. The adhesion measurements are performed with a custom built four-point bend fracture mechanics testing system. Comparison of the copper film thickness to the measured adhesion energy indicated that there is no effect on the adhesion energy as the film thickness changes.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Chemical structure of bis(2,2,7-trimethyloctane-3,5-dionato) copper, Cu(tmod)2

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Figure 2

Custom built 316 stainless steel cold wall reactor with resistive heated aluminum sample stage

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Figure 3

Experimental sample stack for mechanical adhesion testing of copper deposited film on unmodified TaN capped substrates. Si, SiO2, epoxy, and TaN thicknesses are approximately 700–750 μm, 500 nm, 5 μm, and 30 nm, respectively. Cu thickness varies according to Table 1.

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Figure 4

Experimental sample stack for mechanical adhesion testing of copper deposited film on poly(acrylic acid) modified TaN capped substrates. PAA thickness is approximately 15 nm.

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Figure 5

Schematic and force diagram for four-point bend technique

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Figure 6

Load-versus-displacement plot for sample A-5, unmodified surface

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Figure 7

Load-versus-displacement plot for sample B-3, poly(acrylic acid) modified surface

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Figure 8

Statistical data for adhesion energy versus thickness of the deposited copper film for both treated and untreated substrates

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Figure 9

Representation of the postmechanical tested sample stack with directionality indication of XPS for sputter depth profiling

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Figure 10

XPS sputter depth profile (top) and survey scan (bottom) of sample A-5, deposition side. No Cu layer is detected prior to the TaN region, which confirms that the crack propagated at the desired interface.

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Figure 11

XPS sputter depth profile (top) and survey scan (bottom) of sample B-5, support side. The lack of presence by the TaN layer prior to the copper rich region confirms propagation of the crack at the desired interface.

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