1. Diffusion Effect of. Intermetallic Layers on
Diffusion Effect of Intermetallic Layers on Adhesion and Electrical Properties of Electrical Contacts
Golnaz Bassiri

2. Abstract Application of multilayer thin film
MEMS
Reasons for different layers
Ensure mechanical and electrical properties
Conduction layer
Au, Cu, Ag
Adhesion layer/diffusion barrier
Ti, Cr, Pt, Ta, Mo, Nb
Different factors in diffusion
Heat treatment, oxygen treatment
Diffusion changes properties of the film
Adhesion, contact resistance

3. 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

4. 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

5. 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]

6. 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.

7. 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]

8. 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]

9. 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

10. 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).

11. 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

12. 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

13. 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

14. Future Directions Grand challenge Significant technical 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

15. 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, 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,