Hydrogen Segregation at the Al/Si Interface Studied Using a Nuclear Resonant Reaction
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HYDROGEN SEGREGATION AT THE Al/Si INTERFACE STUDIED USING A NUCLEAR RESONANT REACTION JOYCE C. LIU, A.D. MARWICK AND F.K. LEGOUES IBM, T.J. Watson Research Center, Yorktown Heights, NY 10598
ABSTRACT Hydrogen segregation at the interface between an epitaxial Al film and a Si (11) substrate is studied using the 'H(' 5N, ay)12C nuclear resonant reaction. Hydrogen depth profiles show that H atoms diffuse through the 1600/A thick Al layer during 500 eV H implantation and2 are trapped at the Al/Si interface. The total amount of interface H is about 2 x 101l/cm after a 1.4 x 1011 H/cm 2 implantation, and the H atoms are narrowly distributed in the direction normal to the interface. During an isothermal anneal at 360 K, the amount of interface H decreases exponentially with annealing time; and during ramp annealing from 110 to 500 K, an abrupt release of the interface H is observed at temperature around 380 K. The release rates in both cases are controlled by a first order thermally activated detrapping process with a binding energy of 0.86 eV/atom. INTRODUCTION Hydrogen segregation at grain boundaries and interfaces has a substantial effect on their mechanical and electrical properties. However, only a limited number of direct measurements of hydrogen at grain boundaries or interfaces have been made. For example, the segregation of deuterium at grain boundaries in Ni has been observed by using secondary ion mass spectroscopy (SIMS) [31 and the distribution of hydrogen in Al/SiO 2/Si (MOS) structures has been investigated by SIMS [4] and by using the IH(15 N, a-Y)'2 C resonant nu-
clear reaction [7]. In the present paper, we study the H distribution at an interface between an epitaxial Al layer and a Si (111 ) substrate by using the IH('5 N, ay)' 2 C resonant nuclear reaction, and determine the H-interface binding energy from de-trapping kinetics. EXPERIMENTAL PROCEDURE The samples were prepared by electron beam evaporation of 1600 A thick Al layers onto 10 Q.cm P-type Si (111) substrates at room temperature and a base pressure of 1 x 10-7 Torr. The as-deposited samples were annealed in forming gas at 673 K for 2 hours and then implanted with H at room temperature using a Kaufman ion source. The energy of the H ions was 500 eV and the current density was 0.068 mA/cm 2. During the implantation, the sample was held in contact with a water-cooled block. After 30 and 60-min implantations, which correspond to doses of approximately 7 x 1017 and 1.4 x 1018 /cm 2 , the samples were stored in liquid nitrogen to prevent hydrogen out-diffusion. The microstructure of the Al/Si interface was examined by high-resolution cross-section transmission electron microscopy (TEM) in a JEOL 4000 microscope. Auger depth profiling was used to check for possible contaminants at the interface. The hydrogen depth profile in the samples was measured using the 6.4 MeV IH('5 N, ay)12C nuclear resonant reaction. A hydrogen-implanted silicon standard was used for calibration of the amount of hydrogen detected. During the measurement the samples were m
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