High Spatial-Resolution Analysis of Lateral Suicide Formation
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Department of* Materials and J.W. Mayer ; P.E. Batson J.C. Barbour IBM Thomas 14853; Science and Engineering, Cornell University, Ithaca, NY 10598. J. Watson Research Center, Yorktown Heights, NY ABSTRACT Thin-film Ni-Si lateral-diffusion couples were annealed at 450°C for 12 hours to cause formation of the silicide phases: Ni Si, Ni 5 Si2 , Ni 2 Si, and was used to NiSi. Scanning transmission electron microscopy (STEM) investigate the silicide growth. The mechanism of Ni transport to the growth front was shown to be bulk phase diffusion, as evidenced by a bulk phase concentration gradient of 0.03 atomic% Ni/nm in the NiSi phase. The transition from thin film kinetic behavior to bulk couple kinetic behavior was found to be greater than 200 nm. The absence of the Ni 3 Si 2 phase in the An excess lateral-diffusion couple was attributed to a nucleation barrier. amount of Ni in the Ni2 Si phase at the Ni2 Si-NiSi interface indicates the thereby limiting Ni interdiffusivity is lower in NiSi than in Ni 2Si, diffusion out of the Ni 2 Si phase. INTRODUCTION Thin layers of Ni deposited on Si react differently than bulk couples of Thin film reactions squentially form one new phase at a time, Ni and Si. such that at most two silicide phases are present, but many of the equilibrium phases appear simultaneously in a bulk-diffusion couple. Gosele and Tu [1] have modelled the diffusional-growth kinetics for planar diffusion couples in thin-film reactions (less than 10 pm) versus bulk reactions (greater than 10 pm) and they attribute the difference between thin-film to interfacial reaction barriers. and thick-film reactions reactions Application of their model relies heavily on a knowledge of the composition profile within a phase and in particular at the phase boundaries. over to study reactions Lateral-diffusion couples were developed [21
large
distances
Ni-Si
phase
(10-100
diagram
pm)
appear
inma thin film. in
the
thin-film
Nearly all the phases on the lateral-diffusion
couple.
Further, the silicide phases formed have a phase sequence and growth kinetics thin-film which relate bulk-couple silicide formation to conventional The extent of silicide growth in a lateral-diffusion silicide formation [3]. but a couple is empirically characterized by the reaction rate constants, detailed composition analysis of the sample yields further understanding of the This paper examines the mechanisms for the formation and growth.
reactions in self-supporting thin-film Ni-Si lateral-diffusion couples,
using
the high spatial resolution of a scanning transmission electron microscope The composition profile within the growing phases is measured, and (STEM). the profile across the Ni Si-NiSi boundary and throughout the NiSi region is Tge advantage of a self-supporting lateral diffusion measured in detail. couple, in comparison to a cross-sectional transmission electron microscope (TEM) sample, is that a self-supporting lateral-diffusion couple is thin over the entire area analyzed in an analytical electron mi
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