UHV Interface Studies of Palladium Silicide Formation on Hydrogenated Amorphous Silicon Films

Abstract

ABSTRACTSilicide formation by reaction of palladium metal (Pd0) 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 low-temperature (200° C) annealing, RBS and TEM show a single-phase Pd2Si. 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 Pd2 Si on a-Si:H is identical to that of Pd2 Si formed on cr stalline silicon. Binding energy and peak shape analysis show the Pd2Si/Pd0 interface to be composed of one additional phase, Pd4Si, 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 Pd4 Si interface phase may be important in understanding palladium silicide growth.