1. Metallization

2. Metallization Front End Of the Line or FEOL
The active and passive parts are fabricated in and on the wafer surface.
Back End Of the Line or BEOL
The interconnection layers, contacts, vias and dielectric layers that wire the active devices into specific circuit configurations
Schematic cross section of back-end structure
Back-End Technology
SEM micrography of an IBM circuit

3. Metallization Contact Technology Ohmic Contact Formation
rectifying contact
Practical nonlinear ohmic contact
Ideal ohmic contact

4. Metallization Al-Si Contact Melting point : Si=1412 C, Al = 660 C
Al-Si eutectic behavior
- The minimum melting point, or eutectic temperature, is 577 C and
corresponds to an 88.7%Al, 11.3%Si composition.
Problem : Al spiking and Junction Penetration
Use of Al-Si alloys (1.0∼1.5 wt% Si)

5. Metallization Diffusion Barrier Layer
- Intermediate layer of metal that prevents silicon diffusion.
- Ti-W metal

6. Metallization Silicide Process
Silicides : Si- noble and refractory metal compounds
Silicide films are used in two ways in integrated devices :
(a) as part of the contact that joins an interconnecting line to the substrate, and
(b) for interconnectings.

7. Metallization Interconnect Al low resistivity Hillock growth
Hillock formation due to compressive stress in an Al film. Al diffusion along grain boundaries is indicated.

8. Metallization Electromigration
Electromigration with resulting hillock and void formation. Diffusion of Al through grain boundaries is indicated.

9. Metallization Al-Si(1wt%)-Cu(0.5-1wt%)
to prevent the failure of circuits due to electromigration and hillock and void formation.
Adding these elements to the Al increases the sheet resistivity of the interconnect by as much as 35%.

10. Metallization Multilevel Interconnect
Basic two-level metallization process.
(b) Planarized metallization

11. Metallization Multilevel aluminum metallization with tungsten plugs.
SEM image of W plug after blanket CVD deposition and Chemical-Mechanical Polishing(CMP).

12. Metallization
Copper interconnections and Damascene processes

13. Process Integration

14. Major Fabrication Steps in MOS Process Flow