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A novel evaluating method to determine fractal dimension of SEM images: a study of heat treated Au/Pd/GaAs contacts

M. SCHUSZTER1, L. DOBOS2, I. MOJZES1,*

Affiliation

  1. Dept. of Electronics Technology, Budapest University of Technology and Economics, Budapest H-1521, Hungary
  2. Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences, P.O.B. 49 Budapest H- 1525, Hungary

Abstract

The heat treatment is an essential step of making Ohmic contacts to compound semiconductors. During the heat treatment a remarkable volatile component (arsenic) loss takes place due to the thermal decomposition of GaAs and the interactions between Ga and the contact metals. Using scanning electron microscope combined with mass spectrometer (constructed at our institute) it was possible to perform ‘in situ’ studies on the contacts. We examined the changes of the surface pattern and measuring the arsenic evaporation during heating up the sample to 630 °C. The volatile component loss vs. temperature (EGA) curve shows two peaks before the rapid decomposition of GaAs substrate begins at around 600 °C. Examining the ‘in situ’ SEM images of the surface we proved, that from the first evaporating peak the contact structure can be described by its fractal characteristics. The SEM pictures show homogenous shape below 375 °C; above this temperature separate clusters emerged. We found between 375 °C and 400 °C and above 620 °C two, and between 420 °C and 600 °C three different clusters in the images, respectively. We introduced a new method (soft segmentation) to determine the fractal dimension (D) of multi-cluster images. The soft segmentation can be used for any number of clusters, and it is applicable to determine the 'joint fractal dimension' of any clusters treated as one..

Keywords

Compound semiconductors; Evaporation; Fractals; Metallization.

Submitted at: Feb. 7, 2007
Accepted at: Sept. 18, 2007

Citation

M. SCHUSZTER, L. DOBOS, I. MOJZES, A novel evaluating method to determine fractal dimension of SEM images: a study of heat treated Au/Pd/GaAs contacts, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 9, pp. 2853-2856 (2007)