UHV Interface Studies of Palladium Silicide Formation on Hydrogenated Amorphous Silicon Films
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UHV INTERFACE STUDIES OF PALLADIUM SILICIDE FORMATION ON HYDROGENATED AMORPHOUS SILICON FILMS 1
2 1 AND L. RIVAUD G. APAI, H. E. RHODES, iElectronics Research Laboratories, Photographic Products Group and 2 Corporate Research Laboratories, Eastman Kodak Company, Rochester, New York 14650
L.S. HUNG AND J. W. MAYER Department of Materials Science and Engineering, Cornell University, NY 14853
Ithaca,
ABSTRACT 0
Silicide formation by reaction of palladium metal (Pd ) with hydrogenated amorphous silicon (a-Si:H) substrates was studied with Rutherford backscattering spectrometry (RBS), forward recoil spectrometry, x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Upon 0 low-temperature (200 C) annealing, RBS and TEM show a single-phase Pd 2 Si. This phase grows with the square root of time, and the activation energy is identical to that of the corresponding metal on single-crystal silicon substrates. The growth is slightly faster for hydrogenated amorphous silicon, which is attributed to its amorphous structure. During silicide formation, the hydrogen is released from silicides and presumably outdiffuses into a vacuum without interfacial accumulation. Thus, barrier formation does not occur, and the presence of hydrogen in the substrates has no effect on silicide growth. The silicide electronic structure (core level binding energies, lineshapes, and d-band filling) of Pd 2 Si on a-Si:H is identical to that of Pd 2 Si formed on cr stalline silicon. Binding energy and peak shape analysis show the Pd 2 Si/Pd interface to be composed of one additional phase, Pd 4 Si, which has a well-defined binding energy (335.8 eV) and a narrow (FWHM = 1.1 eV), symmetric line shape. It has long been postulated that interface phases may be important in determining the phase sequence in silicide growth and the dominant diffusing species. This Pd 4 Si interface phase may be important in understanding palladium silicide growth.
INTRODUCTION Metal/crystalline silicon interfaces have been extensively studied due to their important device applications and their role as models for obtaining a basic understanding of metal-semiconductor interfaces. UHV formation of silicides is important if characterization is to be undertaken without the serious complications of impurity effects. To our knowledge, there has been no reported study of UHV formation and in-situ analysis of metal/a-Si:H interfaces. These interfaces are important for their own set of device applications. Metal/a-Si:H interfaces have been used in a-Si:H solar cells and high density CCD's using a-Si:H photoconductors. To fill this gap, we have extensively studied Pd 2 Si formation on a-Si:H by standard non-UHV device processing and by total UHV formation with in-situ analysis. In all cases, we find identical results independent of the preparation method [1]. Because of space limitations, XPS figures will report only our UHV results. However, we will refer to our non-UHV results where appropriate.
EXPERIMENTAL One micron of undoped a-Si:H was deposit
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