Electronic and Atomic Properties of a-C:H/Semiconductor Interfaces
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ELECTRONIC AND ATOMIC PROPERTIES OF a-C:H/SEMICONDUCTOR INTERFACES M. WITTMER', D. UGOLINI" AND P. OELHAFEN" "IBM T. J. Watson Research Center, Yorktown Heights, N.Y. 10598 "*Instituteof Physics, University of Basel, CH-4056 Basel, Switzerland ABSTRACT We have investigated the electronic and atomic properties of the interface between amorphous hydrogenated carbon (a-C:H) films and the semiconductor materials Si, Ge and GaAs with photoelectron spectroscopy, high resolution transmission electron microscopy and ion channeling technique. The different properties of the interfacial layers are summarized and compared to the adhesion quality of a-C:H films on these semiconductor materials. 1. THE IMPORTANCE OF a-C:H FILMS Amorphous hydrogenated carbon (a-C:H) films find many applications in magnetic recording media [1,2], microelectronics [3-5] and optical components [6,71. This is due to a large extent to their outstanding properties which gave them the attribute of 'diamond like carbon films'. Unfortunately, the adhesion of a-C:H films on many materials is poor. Since the adhesion is directly related to the electronic and atomic properties of the interface between film and substrate, a thorough knowledge of these properties is crucial for the improvement of the adhesion quality of the films. Towards this goal we have performed a detailed study of the interface properties of a-C:H films on three different semiconductor substrate materials, silicon, germanium and gallium arsenide. A detailed account of our investigation is presented in the literature [8-101. The purpose of this paper is to summarize our results on Si and GaAs substrates and to compare them with the interface properties of a-C:H films on Ge substrates. 2. SAMPLE PREPARATION All substrates were cleaned in UHV environment by sputtering with Ar+ ions. The a-C:H films were deposited with either a Penning ion or Kaufman source operated with methane gas. The ion energy ranged between 100 and 500eV and the deposition rates were in the order of 6 x 10-4 to 5 x 10- 2nm/s. The electronic properties of the interface were investigated with XPS and UPS photoelectron spectroscopy (Leybold EA 10/100 and EA 11/ 100 spectrometers) and the atomic properties of the interface were studied with ion channeling and transmission electron microscopy. The details of the experimental procedures can be found in the literature [8-10]. 3. INTERFACE PROPERTIES OF a-C:H FILMS ON Si, GaAs AND Ge The electronic properties of the a-C:H/semiconductor interfaces are summarized in Table I which lists the bulk and interface core level energies measured with XPS. For comparison purposes we have added the results of the a-C:H/Au interface. It can be seen that the Au 4f7,/ core level does not shift at all whereas the C ls core level shows a Mat. Res. Soc. Symp. Proc. Vol. 159. ©1990 Materials Research Society
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TABLE I. Bulk and interface core level energies
Substrate
Core level
Binding energy (eV) bulk
interface
Shift (eV)
Si
C Is Si 2p
284.6 99.4
283.4 100.7
-1.2 1.3
GaAs
C Is A
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