AVS 56th International Symposium & Exhibition
    Applied Surface Science Wednesday Sessions
       Session AS-WeM

Paper AS-WeM9
Hot Electron Transport Properties of Thin Copper Films Using Ballistic Electron Emission Microscopy

Wednesday, November 11, 2009, 10:40 am, Room C2

Session: Electron Spectroscopies
Presenter: J.J. Garramone, University at Albany
Authors: J.J. Garramone, University at Albany
J.R. Abel, University at Albany
I.L. Sitnitsky, University at Albany
L. Zhao, University of Maryland
I. Appelbaum, University of Maryland
V.P. LaBella, University at Albany
Correspondent: Click to Email
Copper is widely used material for electrical interconnects within integrated circuits. In addition it has been recently utilized as a base layer for hot electron spin injection and readout into silicon[1]. Integral to both their application is the knowledge of the electron scattering length. Surprisingly little work exists that directly measures the scattering length of electrons in copper. One method for studying hot electron transport on the nanometer length scale is ballistic electron emission microscopy (BEEM). BEEM is a three terminal scanning tunneling microscopy (STM) based technique, where electrons tunnel from a STM tip into the grounded metal base of a Schottky diode[2]. The electrons that transverse the metal overlayer and surmount the Schottky barrier are measured as the BEEM current by a backside contact to the semiconductor.
In this study we used BEEM to measure the hot electron attenuation length of copper on Si. The samples consists of Au/Cu/Si(001) Schottky diodes and the measurements were taken at 77K under UHV conditions. The Au capping layer is used to inhibit the growth of copper’s native oxide. Analysis of BEEM current as a function of tip bias yield a Schottky barrier height of 0.64±0.02 eV. The barrier height is in good agreement with previous current-voltage measurements[3-5]. This, along with Rutherford backscattering spectrometry, indicates that we are measuring the Cu/Si Schottky height and have the ability to measure the attenuation length of copper by measuring the BEEM current as a function of Cu thickness. The measured hot electron attenuation length of Cu is 41.64±1.2 nm at a tip bias of 0.9 eV. The attenuation length decreases monotonically with increasing tip bias and is in good agreement with electron-electron scattering as derived from Fermi liquid theory with the addition of an elastic scattering term that is independent of tip bias. This provides insight into sources of both elastic and inelastic scattering of electrons in Cu.
References:
[1] Biqin Huang, et al., Phys. Rev. Lett. 99 177209 (2007)
[2] L. D. Bell and W. J. Kaiser, Phys. Rev. Lett. 61 2368 (1988)
[3]R. W. Soshea, et al., Phys. Rev. 138 A1182 (1965)
[4] J. M. Seiller, et al., Solid State Commun. 15 973 (1974)
[5]C. R. Crowell, et al., Phys. Rev. 127 2006 (1962)