Molecular Interlayers and the Mechanism of Abrasive Wear of Ultrathin Metal Films

F.T. Xu+, M. Curry#, F. Huang+, P.P. Ye#,J. A. Barnard+, and S. C. Street#

The MINT Center and#Department of Chemistry and

+Metallurgical and Materials EngineeringThe University of Alabama

This project was funded by grants from NSF MRSEC DMR-9809423

MINT Fall Review, November 2001Center For Materials For Information Technology

An NSF Materials Research Science and Engineering Center

Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering Center

BackgroundHybrid Organic(dendrimer)/Inorganic nanoscales

Superior flatness (Appl. Surf. Sci. 175-176, 134-139, 2001)

Better nanomechanical hardness and adhesion (Chem. Mat., April, 2001; Anal. Chem. 71, 4403-4406,1999 )

No nanoscratch tests yet

ExperimentalSamples: Dendrimer generation 8 (D8) mediated metal layer

15nm Cu/D8/Si and 15nm Cu/Si

Tests: five 4mN constant load nanoscratch by NanoindenterII

Scratch observed by AFM & SEM, Structure by XPS & XRR, TEM

Results submitted to Tribo. Lett.

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The residual impression left by the scratch tip in a thick sputtered Cu film after a simple indentation. The direction of motion of the tip during the scratch is illustrated by the arrow.

AFM image of the scratch tip

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(a) (b)

(a) 15nm Cu/Si (b) 15nm Cu/D8/Si

results show that there is strong dendrimer, while in Cu samples,

nt scratching mode is not due to the

SEM images of five 4mN constant load scratches

Scratch direction

Clear difference in scratching mechanism observed, same phenomena happened in 12nm Cr samples. XPS chemical interaction between Cr andthere isn’t, indicating that the differechemical interaction (See poster besides for XPS results)

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AFM plane (up) and line (down) view of initial scratch in film without (left) and with(right) dendrimer underlayer

Different nanoscratchingmode observed.

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AFM plane (up) and line (down) view of ending scratch in film without (left) and with(right) dendrimer underlayer

Ridge formed along trench, Plowing mode Cutting mode

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0 1 2 3 4 5

Line --- SimulatedCircle --- Experimental

15nm Cu/D8/Si

15nm Cu/Si

2θ (degree)

X-ray reflectivity resultsTabulated XRR data

layer thickness roughness density(nm) (nm) (g/cm3)

15nm Cu/SiCu 12.6 ± 0.1 0.8 ± 0.1 8.92 -0.1CuO 2.0 ± 0.1 0.6 ± 0.1 4.84 ±0.1

15nm Cu/D8/SiD8 2.4 ± 0.1 0.4 ± 0.1 1.58 ±0.02mixed layer 1.1 ± 0.1 0.4 ± 0.1 7.04 ±0.02Cu 11.1 ± 0.1 0.9 ± 0.1 8.84 ±0.1 CuO 2.1 ± 0.1 0.9 ± 0.1 4.98 ±0.1

SiOx 2.7 ± 0.6 0.2 ±0.05 2.42 ±0.07

Si 0 2.33

Mixed layer between Cu and Dendrimer found by simulation

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CPS

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(a) (b)

(a) 15nm Cu/Si (b) 15nm Cu/D8/Si

It can been seen clearly that the grain size of the film with D8mediated layer is more homogeneous and smaller

TEM plain view of the films

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Conclusions:

♣ Different nanoscratching mechanism applied in Cu/D8/Si and Cu/Si films.

♣ The different scratching mechanism is not due to the strong chemical interaction between metals and the organic layers. While it may be due to the microstructure of Cu films.

♣ XRR results show the dendrimer mediated layer has a mixed layer of Cu and dendrimer.

Future work:

Cross-sectional TEM of the film, Auger scan of scratch trench

Acknowledgement: Thanks Min Chen for the help of TEM