Aluminum
The original interconnect metal — easy to deposit and etch, still used for certain layers, bond pads, and robust designs.
In short
Aluminum was the standard interconnect metal for decades because it conducts well, adheres to silicon dioxide, and can be deposited and etched with straightforward processes. Copper has replaced it for dense high-performance wiring, but aluminum remains common for bond pads and some layers.
Why it matters
Aluminum's easy processing — it can be etched directly, unlike copper — made early integrated circuits practical, and its maturity and reliability keep it in use for specific roles even in modern chips.
Beginner intuition
Metals are needed to wire devices together and to form the contact and bond pads a package connects to; aluminum was the first good fit because it sticks to oxide and is easy to pattern by etching.
Copper conducts better, but aluminum's simplicity and reliability mean it never fully went away — for example, it is common for the top bond pads.
Material properties
- Electrical
- A good conductor (higher resistivity than copper), adequate for many wiring roles.
- Process (etchable)
- Can be deposited and etched with standard processes — simpler than copper's damascene.
- Reliability
- Mature and well understood, though more prone to electromigration than copper in thin lines.
A note on properties
Where it is used
- Bond pads that packages connect to
- Interconnect in mature/robust processes and some layers
- Where simple, reliable metallization is preferred
Manufacturing process connection
Aluminum is deposited (often by PVD) and patterned by etching — a simpler flow than copper damascene — which is part of its enduring appeal for certain layers.
Equipment connection
Common issues
What can go wrong:
- Electromigration in thin, high-current lines
- Hillocks or voids from stress
- Etch residue or corrosion if not controlled
Performance implications
Aluminum illustrates process-driven choice: an easily etched metal (property/process) forms wiring and pads (device structure) with mature reliability (performance) — chosen where simplicity beats copper's lower resistance.
Packaging connection
Aluminum bond pads are a common interface between the die and the package's wire bonds.
Packaging →Alternatives & material selection
Aluminum vs copper is a classic trade-off: copper for dense, fast wiring; aluminum for easy processing, pads, and robustness. Neither is universally better.
- Copper
- Lower resistance for dense, high-performance interconnect.
- Tungsten
- For contact and via plugs.
Advanced & research
Emerging and research directions, beyond today’s established practice.
- ESTABLISHEDAluminum for power and specialty devices
- ESTABLISHEDElectromigration mitigation by alloying
- ESTABLISHEDLegacy-node metallization