Diffusion Effect of
Intermetallic Layers on
Adhesion and Electrical
Properties of Electrical Contacts
Golnaz Bassiri
Abstract

Application of multilayer thin film


Reasons for different layers


Ti, Cr, Pt, Ta, Mo, Nb
Different factors in diffusion


Au, Cu, Ag
Adhesion layer/diffusion barrier


Ensure mechanical and electrical properties
Conduction layer


MEMS
Heat treatment, oxygen treatment
Diffusion changes properties of the film

Adhesion, contact resistance
Background and Introduction



Microelectromechanical systems (MEMS) are
vastly used as an intelligent integrated electrical
systems in contacts, relays, actuators, RF
circuits, hybrid switches [1].
To ensure some of the properties of the
electrical contacts and relays, multilayer thin
films are prepared to provide the reliability, long
term stability and the performance of these thin
films [2].
The selection of the sublayers of the sandwich
depends on the application of the films
Background and Introduction

Diffusion of intermetallic layers change the
properties of individual layers, and the over all
thin film

Diffusion effect of different intermetallic layers on
the mechanical (adhesion) and electrical (mostly
resistivity and contact resistance) to determine
the most efficient layers in the electrical contact
layer
Literature Review

Au, Ag and Cu are commonly used as a
conduction layer for the multilayer thin films[3,4]

Cr, Pt, Ti, Ta, Mo, and Nb are usually used for an
intermediate layer as an adhesion layer/diffusion
barrier[4,5]

Holloway et al.(1976) studied the effect of
oxygen treatment of the adhesion layer on the
properties of films[4]
Literature Review


Understanding of this subject is derived from
chemistry, physics, material science, electrical
and mechanical science, and manufacturing
process of these multilayer thin films.
Different fabrication methods has an impact on
the effect of diffusion on the properties of thin
films. Different methods such as electron beam
evaporation, laser pulsed deposition, chemical
vapor deposition, and Langmuir–Blodgett films
changes some of the properties of the film.
Theoretical Background



Diffusion is intermingling of one or more
substance into each other and diffusion is
present in multilayer films[6]
To have the high conductivity and low electrical
resistance and high corrosion resistance, Au, Ag
is used on the silicon wafer substrate.
To increase the adhesion of noble metals to the
silicon, few angstrom of adhesion layer is
deposited on the substrate[5]
Current Research and
Applications

Application of the
multilayer thin films
are in MEMS such as
in actuators, relays,
ohmic or electrical
contacts, RF
switches, hybrid
circuits[1]
Current Research and
Applications



Holloway et al. studied that oxidation decreases
the diffusion effect of some of the intermetallic
layers (Cr in Au) which can be used as a
diffusion barrier[4]
The Cr forms the Cr2O3 with oxygen (diffusion
barrier), and causes delamination of the surface
(poor adhesion)
The oxygen treated Au/Cr/Si does not change
the resistivity compare to the bulk gold
Current Research and
Applications



Ono et al. studied the diffusion
effect of Cu/Cr/Si vs. Cu/Ta/Si
as a function of heat treatment
of the specimen[3]
The top image RBS result of
Cu/Cr/Si and bottom is Cu/Ta/Si
before and after annealing at
600°C for 1 hr
The different peaks represent
different layers of deposited
metals, annealed peak shows
the diffusion of Cu,Cr and Si in
the top image and insignificant
change of Cu/Ta/Si after
annealing (bottom image).
Current Research and
Applications


He also compared the
different intermetallic
layers resistivity as a
function of annealing
temperature[3]
Ti and Cr abruptly
increase in resistivity
at about 500°C while
Mo, Nb at about
600°C and Ta and W
about 700°C
Current Research and
Applications
Diffusion effect on mechanical properties
such as hardness and elastic modulus
 Metals for different sublayers of the
sandwich with the maximum desired
properties
 The most efficient method of fabrication
and treatment to obtain the desired
adhesion

Future Directions
Determination of the diffusion effect can
resolve by:
 Selection
based on the appropriate layers
relative to the application (mechanical
properties i.e. hardness, elastic modulus or
electrical properties)
 Selection based on the fabrication method
 Selection based on the thickness of the layers
 Selection based on the different treatment of
layers
Future Directions

Grand challenge
 Determination
of the most efficient multilayer
thin films with respect to the metal
configuration, fabrication method, and
required treatments

Significant technical challenge
 Geometry
of the multilayer thin films changes
the properties
References
[1] D. C. Miller, C. F. Herrmann, H. J. Maier, S. M. George, C. R. Stoldt, and K.
Gall. Intrinsic stress development and microstructure evolution of Au/Cr/Si
multilayer thin films subject to annealing. Scripta Materialia, 52(9):873–879,
2005.
[2] M. Martyniuk, J. Antoszewski, B. A. Walmsley, C. A. Musca, J. M. Dell, Jung
Yeon- Gil, B. R. Lawn, Huang Han, and L. Faraone. Determination of
mechanical properties of silicon nitride thin films using nanoindentation.
volume 5798, pages 216–225, USA, 2005. SPIE-Int. Soc. Opt. Eng.
[3] H. Ono and T. Nakano. Diffusion barrier effects of transition metals for
Cu/M/Si multilayers (M=Cr, Ti, Nb, Mo, Ta, W). Applied Physics Letters,
64(12):1511, 1994.
[4] P. H. Holloway and C. C. Nelson. In situ formation of diffusion barriers in thin
film
metallization systems. Thin Solid Films, 35(1):L13–6, 1976.
[5] Milton Ohring. The Materials Science of Thin Films, volume 1. ACADEMIC
PRESS LIMITED, San Diego, united kingdom edition edition, 1992.
[6] Diffusion, 01Dec. 2006, 2004. www.dictionary.com