Metallization

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

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

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)

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

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.

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

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

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%.

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

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

Metallization Copper interconnections and Damascene processes

Process Integration

Major Fabrication Steps in MOS Process Flow