• PDF / 2,144,002 Bytes
• 12 Pages / 414.72 x 648 pts Page_size
• 42 Downloads / 234 Views

DOWNLOAD

REPORT

---

D.A.Smith*, P.V.Evans** and S.R.Koppikar* Stevens Institute of Technology, Hoboken NJ 07030 ** Alcan Research Center, Banbury, Oxon, UK

ABSTRACT

Extensive in situ investigations of the crystallization of amorphous cobalt disilicide have been conducted using a transmission electron microscope with a hot stage. Thermodynamic and kinetic parameters describing the heterogeneous transformation have been evaluated. The angle of contact betwen crystalline and amorphous material was determined from tilting experiments to be 760 . Nucleation rates in samples 40 nrn thick were evaluated at various temperatures and compared with thermodynamic models to 2 deduce an interfacial energy between amorphous and crystalline CoSi2 (oca) of 121 mJ/m and an activation energy for crystallization of 1.27 eV. Johnson-Mehl-Avrami analysis of the observed continuous nucleation and steady state isotropic growth in 100 nm thick samples points to a gradual transition of the crystallization mode from 3-dimensional (n=4) to 2-dimensional (n=3) growth as might be expected. Comparison of the nucleation and growth rates in 40 nm and 100 nm thick samples demonstrated the influence of surfaces on crystallization phenomena in thin films.

INTRODUCTION Silicides for application as contacts in integrated circuits can be formed by chemical

reactions between a deposited metal film and a silicon substrate. This method requires interdiffusion which requires time at temperatures undesirably high for semiconductor device fabrication; a further difficulty is that precursors may crystallize before the formation of the desired phase, e.g., Co 2 Si and CoSi before CoSi 2 .1 Another method is the crystallization of a co-deposited amorphous film. This requires no long range diffusion; since the stoichiometry is easily controlled by the co-deposition process the formation of precursors is also precluded. Of all the "self-aligned" silicides available TiSi2 and CoSi 2 seem the most suitable choices. Although CoSi 2 is not as susceptible to impurity and dopant interactions as TiSi2 , exposure to high temperatures induces grain

coarsening. The interface between silicon and silicide subsequently roughens, leading to penetration of underlying shallow junctions. It is therefore important to elucidate the kinetics and thermodynamics of CoSi2 formation and crystallization. Crystallization of amorphous CoSi2 was previously studied by resistometry 1 . This approach provides a measure of the total fraction transformed but does not permit the

271 Mat. Res. Soc. Symp. Proc. Vol. 321. ©1994 Materials Research Society

nucleation and growth kinetics to be evaluated separately. In situ studies of crystallization allow the determination of the fraction of crystallized material, the nucleation rate, the growth rate and the influences of temperature, time or irradiation (ion or electron). 1,2,3

EXPERIMENTAL PROCEDURE Amorphous films of CoSi 2, 40 and 100 nm in thickness, were prepared by dual e-gun codeposition at room temperature onto amorphous silicon nitride window substrates.